What exactly are the functions of an aviation headset? All I know from Google searching is that they provide hearing protection and ATC communication maybe? Do pilots have to attach them or are they wireless? Who can the pilot reach using them?  How much hearing protection does a pilot need? For instance, how does a pilot figure out how many decibels of protection is needed say for a Cessna 172? Must headsets always be worn? I'm interested in knowing all aspects of the uses of an aviation headset.

Aviation headsets are just like gaming headsets on a computer or console gaming system, except they are sturdier and much more expensive.

At the basic end of the spectrum, an aviation headset is just a big clamp style pair of around the ear headphones with a microphone.  The cable from the headset has 2 plugs (for airplanes) or one plug (for helicopters).  These two plug styles are equivalent electronically, with the helicopter cable having an extra conductor in order to include the microphone and headphones in the same plug. The two-plug variant has one plug for the headphones and one of the microphone.  These differ from gaming headsets in that the headphone plug is 0.25" (the kind a nice stereo receiver uses) and the microphone plug is 0.206".  This difference in sizes is to avoid mixing up which plug goes in which jack.

Aviation headsets fall into two broad categories: passive noise reduction and active noise reduction (ANR).  The passive noise reduction headsets rely on a good seal around the ear and a strong clamping force (e.g. David Clarks).  Active noise reduction are somewhat less "clampy" and provide less passive protection but make up for this with the active protection.  An ANR headset is money well spent, but these do top out at around \$850-\$1000 for the top models from Lightspeed and Bose respectively.  ANR headsets must be powered to work properly but all ANR headsets still function without power as passive noise reducing headsets.  Power for an ANR headset can come from a battery box or from aircraft power but not interchangeably.  Aircraft power requires panel installation of a plug specific to the headset brand (a single connector provides power, headphone and microphone connections).  In general, unless you happen to own an airplane and install the power plug, you should get the battery version of a headset.

The primary purpose of these headsets is to reduce the noise in the cockpit (they can be very loud) in order to avoid hearing loss (yes, it is that loud) and to facilitate clearer communication with ATC.

For quieter airplanes there are in-ear headsets that have more in common with earbuds than the bigger headsets.  Some of these are just earplugs wired for sound and some use molds of your ear to provide the seal.

The headset is connected to the airplanes audio panel.  Audio panels vary in complexity but their basic job is to provide an intercom for communication between occupants of the airplane and access to the com radio for communication with ATC.  The audio panel is also able to monitor (listen) the navigation radios certain types of beacons.  In transport aircraft the audio panel is also tied into the passenger address system and the flight attendant's phones in the cabin.

The headsets can be operated in a hot mic setup or the mic can be explicitly turned on and off.  The hot mic is the usual method and the audio panel provides a squelch control so you aren't broadcasting the cockpit noise when not talking.  The ATC transmissions are via a push-to-talk (PTT) switch.

Aviation headsets for the most part do not need to be approved to use in airplanes, but in some situations for US registered aircraft, the requirement of an approved headset can be mandated (some (all?) 121 carriers).  The FAA standards for approval are specified in TSO C-57a and C-58a.  You'll find many, but certainly not all, aviation headsets conform to these orders.  They define minimum performance characteristics of the electronics, speakers, microphones, etc that make up the headset.

How much hearing protection is needed depends greatly on the specific airplane in question.  Jets can be on the very loud end of the spectrum (EMB-145) or they can be quiet enough that even passive noise reduction is largely unnecessary.  For the noisy end of the spectrum peak wavelengths can be well in excess of 100 dB.  I can find reports of 130 db in some smaller airplanes and reports of 84 db in a 737 during cruise, but these numbers are all anecdotal in nature.  What is important to take from these is not the specific numbers but that they are high enough to cause hearing loss during prolonged exposure.  The National Institute on Deafness and Other Communication Disorders defines 85 dB as the threshold for hearing damage from long or repeated exposure.

Passive headsets generally advertise noise reduction around 20 dB (23 dB for the venerable David Clarks) and some people will wear earplugs under a headset to further increase the passive noise reduction. A cursory look at ANR headsets reveal that they tend not to advertise their performance and instead specify maximum ambient noise levels for ANR to properly function (around 120-125 dB for Bose and Lightspeed headsets).  I can personally add an anecdote that both the Lightspeed Zulu and Bose X make dramatic changes in noise level (both of these headsets are now outdated and replaced by newer versions).

For most smaller airplanes you will wear the headset from startup to shutdown.  As you get into the large jets I have observed crews that wear minimal headsets during takeoff and landing, but not always during cruise.  These airplanes were quiet enough that they were not needed.  On turboprops and smaller jets that I have been in, headsets were worn throughout the flight.

On newer ANR headsets in particular you will find some extra features beyond just being a pair of headphones and a microphone.  These extras include a 3.5 mm auxiliary jack to connect external music and bluetooth to connect your phone or other device to the headset.  These typically come with circuitry to automatically mute or greatly decrease the volume of these inputs when ATC is transmitting.


What are the steep ramps often erected at large airports? For example, the following white and orange striped ramp:

I've seen these at a couple large airports but I've never seen them actually used for anything.

Here in the United States these are called blast fences.  They protect whatever may be behind them from the direct effects of jet blast by directing the blast upwards.


How does static port measures the static pressure? I have always thought that there is a probe or sensor kind of thing inside the static port so that it "measures" the static pressure and compare to other pressure sources for airspeed, altitude, and VSI reading.

But my other pilot friend recently told me that the way static port works is because of the air actually flows in and out of it.

For example, when you climb, the ambient pressure decreases so the air will flow out of the static port until it reaches equilibrium, which causes the static pressure inside the casing of altimeter to decrease and the altimeter shows an increase in altitude.

Tried to find answers about how static port work online but did not find a satisfying explanation...

If anyone knows more on this topic please share your opinion.

Your friend is correct. It's situated in a spot where the dynamic pressure is non-existent or minimal such as on the rear side of the fuselage on a Cessna 172 where it's able to measure the ambient pressure. This pressure is then either fed by tubes to their respective instruments (ASI, Altimeter, and VSI), or on modern aircraft, it is read by a transducer (or analog to to digital interface units - A/DIFU) which converts the reading to electronic data which is then fed to the air data computer.


Was there ever a fuel-injected Spitfire? I couldn't find one but did it ever exist? Would adding fuel injection have improved combat effectiveness or fuel efficiency?

Yes there was. A Spitfire which was converted by Daimler Benz engineers to use a DB 605 engine. See the following links:

https://www.klassiker-der-luftfahrt.de/geschichte/flugzeuge/daimler-benz-versuch-die-daimler-spitfire-die-db-spitfire-zeigt-gute-flugeigenschaften/615458?seite=2

https://defenceoftherealm.wordpress.com/2014/11/17/the-franken-spitfire/


How much aluminum was used in the Boeing 727? What is the weight of aluminum used in the Boeing 727 fuselage? Do you know where I can find it? Any manual or site or something like that?

It may not be possible to provide a precise number for a question with so many variables. Likely, the amount differed between variants. Without speaking to a materials acquisitions director from Boeing in the 70s and 80s, the precise number is probably not available.
That said, this airplane scrapyard website mentions that aluminum accounts for approximately 20% of the weight in a Boeing 747. Going by that same rubric, one might estimate that a 727 would contain approximately 41,900 pounds of aluminum.


May I fly with passengers on a homebuilt experimental airplane with only a simple PPL? So I’m in the market for a small two-seater. I see a lot of homebuilts and experimentals listed that are perfectly priced. I have my private pilot certificate but that’s it.

Would I be able to fly an experimental with a passenger?

Do I need something special if I wanted to buy one of these planes?

Currently I live in Ohio, United States.

Yes, you can, you don't need anything other than the words EXPERIMENTAL to be visible by the passenger. Your PPL is fine for flying experimentals, although like any other aircraft change, I would get instruction from an experienced instructor in that type/model before going solo. Experimental aircraft can have some pretty different handling characteristics.

So, from a regulations standpoint, you are looking for CFR 91.319: Aircraft having experimental certificates: Operating limitations.. According to (j) of that:

  No person may operate an aircraft that has an experimental certificate under § 61.113(i) of this chapter unless the aircraft is carrying not more than 6 occupants.

So you can have up to 6 occupants (including the pilot).

  Do I need something special if I wanted to buy one of these planes?

No, your PPL allows you to fly experimentals, but as I said above, please get training from an instructor familiar with the aircraft and its handling characteristics. Many dear departed pilots probably wished in the last moments that they had some formal training in the experimentals they bought. You should also get somebody to go over the aircraft mechanically that is familiar with that model. Also look into your insurance costs, the airplane may be cheaper, but your insurance will probably be more expensive.


How does the position of the center of pressure change with the use of different high lift devices? How is the position of the center of pressure affected by different high lift device deployments?

My guesses are:

When I use a high lift device that just increases the chord length, it moves backwards so that it stays at the same percentage of the length of the chord - correct?
When I use a high lift device that moves downwards, it has the same affect as increasing the AoA (or in fact: it does increase the AoA), so the center of pressure moves forward

Are those two guesses correct? Which other influences are there from high lift devices on the position of the center of pressure?

When I use a high lift device that just increases the chord length, it moves backwards so that it stays at the same percentage of the length of the chord

Only when the Fowler flap does not change the airfoil's camber, which is rarely the case. Normally, the flap will not only move backwards, but also rotate trailing edge down. A bit only for the take-off setting, but a lot for the landing position. This camber change will move the center of pressure back even if there were no surface increase, and the extension of the wing at the trailing edge will move the center of pressure further back again.

  When I use a high lift device that moves downwards, it has the same affect as increasing the AoA, so the center of pressure moves forward

Again, no. The camber change dominates the position of the center of pressure, and it will move back since the wing now sports more rear loading (more lift is created at the rear end of the airfoil due to local camber increase).


What is this runway marking on Kirkwall Airport's runway? What are these markings on Kirkwall Airport's runway? From where they are on the runway, they seem like the touchdown markers, is that what they are?

That's the aiming point mark, UK style. The UK AIP GEN 1.7 (2018-8) notes the following reasons for the different marking:

  The shape of the marking means that 1/3rd of it is outside the centre 3rd of the runway and is therefore less prone to rubber contamination.
  The marking is more easily identifiable as it differs from the TDZ markings.
  It provides enhanced visual cues for the angle of approach.

(Source: CAP 637: Visual Aids Handbook, May 2007)


Does the AC-130 have de-ice or anti-ice protection for wings and surfaces? Does the AC-130 have de-ice or anti-ice protection for wings and surfaces? Can it fly in icing conditions? Looking at many pictures I see no sign of a shiny "hot wing" leading edge nor any boots. Does anyone have more information on this?

The C-130 uses pressurized bleed air for leading-edge and window anti-ice. The props are deiced with electric heaters in the prop.

Source

The C-130 is very often used in places that experience icing. For example, the US Air Force flies the C-130 as a cargo/transport aircraft for Antarctic and Greenland operations:

(Source: Popular Science)


What is the rod attached to the top of the Bell UH-1N's rotors? So, I was looking at an image of a Bell UH-1N, and noticed that the top if the rotor has a little stick or rod
What is this rod for? I also see this rod on a RC helicopter.

It is a stabilizer bar used on some two blade helicopters. The spinning weights want to stay in one plane and are used in conjunction with the cyclic to control changes in pitch and roll. Depending on how it is designed, it counters these changes making the helicopter more stable (less maneuverable).


Single vs Twin motor for an electric RC airplane I'm designing a fixed wing UAV for a project. I need an airplane that can fly for at least 200 minutes. Obviously, it means a big battery and thus a lot of added weight. I've been debating whether or not I need a twin motor configuration. The idea came after I saw a video of a modified "My twin dream" airplane that has a range of 269 km and can fly for more than 5 hours. The extra thrust might be the reason it can fly for that long but I can not find any research for electric twin motors whatsoever.
Let's say the cruise speed would be 15 m/s. If it only has one motor, maybe it would need to run at 90% of its power vs if it has two motors they would need to be at 45% of their power to match the required thrust for that cruise speed. This could mean, two motors are more efficient than one, even though the extra weight of the added motor.
I'm not sure how to solve this problem.

You should keep in mind that adding an engine adds wiring, extra propeller (a larger single prop might to be lighter in RC than an equal setup of two), overall complexity etc.
As I understand it, electric motors have a "sweet spot", or rather an area of (iirc) certain load and rpm. You should desing your configuration so, that the motor(s) would operate in this rpm/load range in cruise. This sweet spot is (again, iirc) much higher than half load. So it is likely you are better of with a single engine than two that are only utilizing about half their rated pwr.
This sweet spot is very motor specific, so you need to dig deep into spec sheets.


Who has final say over an aircraft flight path? This question got me thinking... if there was an emergency situation on a commercial airliner (let's say both engines have flamed out or something) and the pilot wants to do one thing (land in the sea), while ATC insists they try to turn around and land at  the airport... who has the final say?

Obviously the pilot is the one physically in control of the aircraft, but if he ignores ATC, believing his approach is the only safe approach and ends up killing half of the passengers in the process, would he be liable for 100% responsibility since he didn't listen to ATC?

The pilot has 100% responsibility for how, where and when to fly/land. The movies make it seem like pilots are just mindless drones, under the control of ATC.

In actual fact ATC are there as an aid to the pilot, helping stop big metal tubes from colliding with one another.

This was borne out (to some extent) on US Airways 1549 where ATC were advising the pilot he could aim for his nearest airfield. His skill and experience (and of course having a front-row seat!) told him he would not make it, and he took the action to ditch on the Hudson river - saving all on board. We will never know what the outcome would have been if he had followed ATC advice, but multiple trips in a simulator have told us it might not have ended so well.

Final say is ALWAYS, 100% of the time, with the PIC.


Why are the minimums between these two ILS instrument approaches to the same runway so different? The minimums for the Van Nuys ILS Z Rwy 16R are 1095/40.  The minimums for the Van Nuys ILS Y Rwy 16R are 1461-1 1/2.

Question: Why are the minimums for the ILS Z so much lower than the minimums for the ILS Y?

Van Nuys ILS Z Rwy 16R

Van Nuys ILS Y Rwy 16R

The equipment requirement (in the aircraft) are different for each of these approaches.  In the upper-left box of the Z approach, you can see that DME is required to make this approach.  This requirement is not listed in the Y approach.

If your aircraft has the right equipment, you can reduce your minimums by selecting the appropriate approach plate.

In this particular case, the missed approach procedure from the lower minimums is more precise. The procedure includes DME distances that must be used while executing the missed approach procedure.  Without DME onboard the aircraft, you would have to use the less-precise missed approach procedure requirements of intersecting VOR radials. This lack of DME, and thus a less-precise procedure, results in higher minimums.

In Section 4, para. 140 of the TERPS, the reason for multiple approaches to the same runway, using the same navigation system (ILS in this case) allows better-equipped aircraft to gain an "operational advantage".


Can X-Plane be used as a professional simulator? Can X-Plane be used as an actual Flight and Navigation Procedures Trainer (FNPT) level 1 flight simulator with Out The Window (OTW) visuals, separate Instructor Operation Station (IOS) and replica hardware?

Maybe.

From the page linked by falstro above:

  These include the ability to use cylindrical and spherical projection (as found in large simulators), and the ability to drive real Garmin 1000, Garmin 430, Garmin 430 WAAS, Garmin 530, and Garmin 530 WAAS units.

Pictures are included of a particular setup. The large projection format allows all-around visuals. The simulator can drive real Garmin devices, not just replicas. They recommend this vendor for FAA approved hardware (and for $2,100 I would hope a yoke could be FAA certified).

You can use an IOS even with the personal license for the simulator, on the same computer or a separate one.

X-Plane also explains that only the complete hardware+software combination can be certified for use as an FAA approved flight simulator. So it may be easier to just buy a package from a company like PFC, which has the combination already certified. They offer BATD and AATD simulator setups that use X-Plane.

If you need more information, you can contact X-Plane via the link on the same site linked above. They do not keep track of what people use their professional licenses for, but they may be able to comment on what level of certification is achievable.


Do you need FAA approval to land a helicopter on Miami Beach? Do you need FAA approval to land a helicopter on Miami Beach, Florida?

No; you may need permission from the local authority.  FAA doesn't regulate where you can land or take off.


Why was the production of the Lockheed SR-71 Blackbird halted? Why was production of Lockheed's SR-71 Blackbird halted, given that it was an advanced supersonic jet that was ahead of its time?

Why did they stop building it?

Because they built 32, and that was as many as was needed at the time. 32 spy planes was plenty for the USAF/CIA to use, so building more would have been a waste. By the time those airframes may have needed to be replaced after 30 years or so, the SR-71 had been withdrawn from service and there was no need to build any more.

I think the question you're really trying to ask, though, is:

Why was it withdrawn from service?

And why wasn't it replaced when it was withdrawn?

The answer to those questions is a bit more complex, but essentially comes down to "Because it wasn't really needed any more."

The SR-71 was designed and built in the 50's and 60's. That means it was designed shortly before the first space flight, and built shortly afterward.

When designed, there was a huge need for a fast, "impossible to shoot down" reconnaissance aircraft. The SR-71 suited that - it could dodge missiles just by outrunning them, and by the time any adversary scrambled a fighter and got to the SR-71's altitude, the SR-71 would be a couple of hundred miles away and possibly even over a different country.

So what happened?

Satellites happened.

Why maintain a fleet of very high maintenance planes and keep them on high alert, then fly them over your rival's airspace? That's expensive, time consuming, difficult, risky, and (quite understandably) tends to upset your rival. It was, in short, an expensive way to annoy Russia and China. Okay sure, it got some reconnaissance too, and did its job (as an aircraft) beautifully, but when times are tense the last thing you need is to antagonise each other.

As an aircraft, then, it was a huge success... but as a geopolitical pawn, and as a military asset? It's a little more questionable. It certainly performed a vital role, but it had negative downsides from doing that.

Fast forward a few years, and we developed reconnaissance satellites with a whole bunch of advantages

With a few of them in the right orbit, you can have a satellite over an interesting part of the world pretty much 24/7. Even without that many, you can pass over an area pretty regularly.
Less obvious. Okay, your rival does not like you launching them - but once in space they're just "there", there's no antagonising "Oh look, an SR-71 flying over us"
They're "fire and forget" for the most part. Once in space, you just use it: you don't need to keep a bunch of pilots and aircraft on the ground ready to fly
It's less obvious what you're looking at, and when... if an SR-71 flies over the base that contains your new secret weapon, you're gonna notice. But when a satellite flies over for the 18th time today? Not so much
No planning and preparation time (which, for an SR-71, was a huge undertaking).  You just start taking pictures, or wait for a satellite to get to the right place, then start taking pictures.

They have disadvantages, too

For 24/7 coverage, you need quite a lot of them, and they aren't cheap
You have to replace them occasionally (and/or boost them into higher orbits)
If you upgrade your camera, it's a lot harder to replace the one on a satellite than an SR-71

But overall, a satellite is a more reliable, less antagonistic way to spy on your rivals. They're not perfect, but you know you've got permanent spying capability with no need to plan your reconnaissance ahead of time.

In short: It wasn't needed anymore.


Is "lower pressurization" the correct term for the 787 Dreamliner? In this blog, the FA refers to the 787 Dreamliner as having "lower pressurization":

http://theflightattendantlife.com/the-boeing-787-8-a-flight-attendant-takes-you-on-an-inside-tour-of-the-dreamliner/

The Dreamliner has higher air-pressure in the cabin due to its fuselage construction -- but this higher air-pressure makes the perceived 'altitude' lower.

Is the correct (air transport) term for this "lower pressurization" or "higher pressurization" or is there a better third alternative??

The terminology is confusing. When you say lower or higher, it is better to clarify the reference.

Boeing 787 has a higher cabin pressure compared to the legacy airliners.

The best way to say it is that it is pressurized to (or has) a lower cabin altitude compared to other airliners.


How does a pilot maintain stability for an unbalance loaded airplane? Consider Cessna 172 which has 4 seats, including the pilot, with the seat configuration as the picture below. Say the airplane has no passenger, only the pilot him/her self. I am not sure where it center gravity (CG). For longitudinal (roll), probably we can consider it separate between left and right seats. But for pitch, I don't have any idea.

My question is, if a pilot want to fly his/her airplane, how he/she assign stability control so the airplane will not has tendencies, either regarding the longitudinal (roll) or the pitch. What else control he/she needs to apply to make the airplane safely fly due to the unbalance load?

Use the available trim (elevator, and rudder if installed), and then manage the left/right fuel tanks if they are not feeding evenly.  Use the autopilot if so equipped, even if it's just a single axis wing leveler.

With just 1 passenger, it is hardly out of balance tho. The POH has a Weight & Balance chart as seen here  How are the limits of the center of gravity chart established?, plotting front seat weight and fuel will show the plane to be well within limits.


Is there a standard format for pre-departure clearances? I am curious to know, from current airline pilots, if the formatting - and therefore reliability and ease of use - of pre-departure clearances (PDC's) has improved since they were first introduced?

Back then we would see differing formats, incorrect flight numbers and routings, and the like.  ATC would send them to the company and then the company would give them to the flight crew together with other relevant documents.

I'm sure that the process has greatly improved since those days, but I'd like to know if PDCs have now been standardized?

I know nothing about PDCs, but it does seem that they are now standardized. One aircrew training site said in April 2014:

  For those of you capable of receiving a Predeparture Clearance (PDC),
  have you noticed a change since the first week of April? The FAA
  changed the way it issues PDCs. Gone are the days of trying to decide
  if you got a reroute in the PDC. The FAA recognized there was a
  problem with standardization with regards to reroutes

The article points to JO 7110.113, Procedures for Issuing Automated Clearances, which says:

  5. Explanation of Policy Changes. This order is revised to provide standardization of PDC clearances across the FAA.

I guess you can read the rest of the JO for more information, it means nothing to me :-)


In the modern aviation context, is the word "supercharger" generally assumed to mean a gear-driven system rather than an exhaust-driven system? In the modern aviation context, is the word "supercharger" generally assumed to mean a gear-driven system rather than an exhaust-driven system?

At one time the word "supercharger" often was used to encompass both turbosuperchargers (aka turbochargers) which were exhaust-driven, and gear-driven superchargers.  But I have seen the word "supercharger" used to specifically mean a gear-driven system as distinct from an exhaust-driven system.  Would this usage be generally considered unambigous and good practice in the modern aviation context?  Or at least, very common practice in the modern aviation context?

(Include belt-driven along with gear-driven, if such a thing even exists in aviation engines.  The question is about exhaust-driven versus mechanically-driven devices, and how these two different sorts of devices map out against the various terminology in current aviation use.)

A supplemental question might be: "Has the word 'turbosupercharger' completely disappeared from modern aviation terminology?"

"Turbosupercharger" was General Electric's official term for their system, probably the first mass produced turbocharging system and was used on a range of US fighters and bombers (the system was very sensitive to back pressure in the turbine outlet which could promote stalling, and so they either had the turbine exposed like on the P-38, or if there was an exhaust duct it was very very short).

Anything that compresses the intake charge is a supercharger. Prior to the GE system, they were all mechanically driven and the mechanical drive naturally had horsepower losses associated with that type of drive.  GE added the word turbo to differentiate between the common gear driven or direct driven supercharger and their new and novel system that eliminated most of the energy losses from compressing air.

Move forward into the post war era and the adoption of systems to cars and light aircraft and people get annoyed having to say this pain in the butt 6 syllable word and start to cut out the "super" part, because it doesn't really detract from the meaning, and there you are with "turbocharger" for both cars and airplanes.

Meanwhile, "supercharger" stays as it always was and remains associated with mechanical systems, because the terms, although incomplete technically, don't contradict each other on common usage they continue.


How does the bypass air provide thrust? To my knowledge, bypass air produces 80% of total thrust. But I don't understand to how it does that. By accelerating the air, by increasing the speed or increasing the pressure of the air? Is it doing this by Bernoulli's principle or something like that?

The bypass air is accelerated by the fan at the front of the turbofan engine. This changes its velocity and therefore its momentum, which is the definition of a force (in this case: thrust):

$$ F = \frac{\text{d}}{\text{d}t} p = m \frac{\text{d}}{\text{d}t} v = m \cdot a $$

This thrust contributes to the total thrust of the engine. How much will depend on the bypass ratio of the engine and other parameters, but 80% is plausible for a high bypass turbofan. Bernoulli's principle has nothing to do with this.

You can see the accelerated airflow in the following animation:

(source: Wikimedia)

The air coming from the engine core will move even faster, but there is less of it in a high bypass turbofan resulting in less total thrust coming from the core:

  The fan airflow, referred to as the cold air stream, is accelerated by the fan and passes through the engine remaining outside of the engine core. The cold air stream moves much slower than the hot stream gas flow passing through the engine core.

(skybrary.aero)


Why is the 60-year-old NK-12 more fuel efficient than Europrop TP400? If Wikipedia is correct the 60 years old NK-12 is more fuel efficient than the Europrop TP400, the engine for the Airbus A400M transport aircraft.

For the NK-12MV a specific fuel consumption of 0.219 kg/kW-hr is given.

The TP400 has a specific fuel consumption of 0.238 kg/kW-hr according to Wikipedia.

Am I interpreting these specifications wrongly?

The source of the Specific Fuel Consumption in Wikipedia is unclear. I have found a paper (PDF) that discusses the efficiency of shaft power off-take (that is using engine power to drive systems such a electric and hydraulic generators instead of delivering propulsion).

It mentions the TP400-D6 (which is installed on the Airbus A400M) has a SFC of 0.167 kg/(kW.h) for shaft power off-take and a SFC of 0.213 kg/(kW.h) for delivering propulsive power. This means that the TP400 is more efficient than the Wikipedia article presents and more efficient than the SFC of the NK-12 presented by Wikipedia.

It also shows that the TP400-D6 is more efficient in delivering shaft power than in delivering propulsive power.


Should an emergency field landing be performed with landing gear down or up? Suppose you are flying an aircraft with retractable gear and have to make an emergency landing on that big "flat" stretch of grass up ahead and have only one shot at it, what's better, do it with wheels down or up.

Obviously, if the ground is flat enough, wheels down may be great and may even let you recover your aircraft basically undamaged. However, hitting a rut or other obstacle with the gear could have some rather unfortunate consequences.

That left me wondering which is better, dropping the gear and hoping for the best, or a controlled belly landing. (Also hoping for the best!)

I also wonder what, if any, instruction is given on this situation during flight training.

There are various factors here:

Gear acts as a speed brake, in some emergency situations if you need the added drag as you approach the field (to make the field) a gear down situation may be called for regardless of ground condition. On the flip side if the field is on the edge of gliding distance you may want to keep the gear up to improve glide. This is a judgement call during the emergency.
Gear will provide you limited steering on the ground which for what ever reason you may need. In a gear up situation you are sliding to a stop.
Gear will provide you brakes, if the field is short you are going to want this option.
If something is critically wrong with the plane and you need to do an emergency gear deploy there may be no time during the emergency.

Like anything, it depends and it will be a situational decision with merits to both aspects. You should consult the POH for your air frame as they will most likely have check lists for both scenarios.

For example in a Piper Arrow they offer a checklist of a gear up emergency specifically:

  Gear up emergency landing:

  In the event a gear up landing is required,
  proceed as follows:

  (a) On aircraft equipped with the backup gear
  extender, lock emergency gear lever in "Override Engaged" position
  before airspeed drops to 115 mph to prevent landing gear from
  inadvertently free falling.

  (b) Flaps as desired.

  (c) Close throttle
  and shut off the master and ignition switches.

  (d) Turn the fuel
  selector valve to OFF"

  (e) Contact surface at minimum possible airspeed.

Here is what happens in a small plane when the gear collapses on a grass field. A gear up landing is not an automatic hull loss, in many cases they can be repaired. Considering the age and use level of most of the countries GA fleet you may be surprised to find out just how many planes have actually been through a gear up landing.

I was always instructed during my training that ditching gear down (or with a fixed gear) in water was not really viable. There seems to be some info indicating that there is little data to support this. Of course you will find endless debate on the internet about it and some answers that fail to provide sources. Some of the misconceptions may be fueled by what happens when a float-plane digs in on landing.


Is the airspeed different between above and under the wings? I heard that when an airplane is flying, air speed or air pressure is higher under the wings. Is it true?

In case of a subsonic attached flow over the cambered airfoil (or a symmetric one at an angle of attack), the airflow speed is higher over the wing and pressure is lower. It is the other way around on the lower surface.

Source: virtualskies.arc.nasa.gov

Note that this is just the mechanics of the flow over the wing. This is not an explanation of lift.


Is it dangerous for a supersonic aircraft to fly at exactly Mach 1? If a plane that is designed for supersonic flight, say the Concorde, kept flying at exactly the speed of sound, would there be any danger in that? If so, what could get dangerous at constant Mach 1 flight and how long can a plane survive in flying at Mach 1?

Make sure to read this answer to understand what is special about Mach 1.
Pilots regularly report that, approaching Mach 1, the airplane is shaken by oscillating shocks (they don't use that term, though, they speak of buffeting) and once the Mach meter needle crosses the 1, the airplane becomes calm and flight smooth again. Since the flow speed around the airplane is normally a bit higher than flight speed due to the displacement effect and the need to produce lift, supersonic pockets start to occur as early as at Mach 0.6 (depending on the particular design) and expand the closer flight speed comes to Mach 1.
Swept wings delay those Mach effects and the peak of the drag coefficient of supersonic-capable designs is also delayed to somewhere between Mach 1 and 1.2. While the drag coefficient normally drops a bit past this peak, drag itself normally rises with speed. Flight at Mach 1 is particularly inefficient but, apart from that, drag is not an issue.
What is more important is the shift in the center of pressure when changing from sub- to supersonic flight. It will move aft and requires the pilot to re-trim the airplane. Supersonic-capable designs normally use full-flying tails for that and delta airplanes raise their trailing edge flaps. Concorde added pumping fuel aft and the XB-70 reduced the rear part of the wing by folding its wing tips down. When flying at Mach 1, the airplane is smack in the middle of the largest pitch moment change over speed range, so any change in speed means also a strong change in pitch moment. When no trim change accompanies that change in speed, the airplane will be unstable in pitch: Flying faster will move the center of pressure aft and make the airplane dive (Mach tuck), speeding up more, and vice versa. Reducing speed might even lead to structural failure from the sudden pitch-up and increase in load factor if not corrected by control deflections.
That is what makes flight at Mach 1 unadvisable. If the pilot or the FCS keep pitch under control, flight at Mach 1 can continue until the fuel runs out and the airplane hits the ground, causing speed to drop dramatically.


Can only victor way be used for route in cross country? In IFR low-en route chart, there are many ways related to victor ways. Do I have to select the route for cross county? Or, Can I choose the ways between victor ways?

You just use (starting waypoint)  DCT  (ending waypoint) in your flight plan (DCT = Direct) and submit that.  It's up to ATC to approve that routing and you'll find out when you are issued your clearance.

Especially at lower altitudes it's likely you'll be cleared as filed, but there's always a chance they'll shift your route a bit to improve traffic flow for whatever reason, adding waypoints or moving you to an adjacent V airway, doing their best to minimize any increase in your distance.


Does a "take-off" assist make sense for electric aircraft? There is already a good answer that talks about how a catapult provides virtually no benefit for fuel-based aircraft.

However, I'm wondering if the same answer is true for electric planes?  For example, I see here:

  The high-lift [leading edge] propellers are all used during takeoff….
  Once you get to a comfortable margin, say 30 percent above stall
  speed, then it will just run off the cruise [wingtip] props and you
  can fold the [blades on the] lift propellers.

This suggests to me that the aerodynamics, complexity, and weight of (at least that design of) electric aircraft could be improved if there were some other means of getting planes up to speed.

While a catapult is a pleasingly high tech solution, there are a number of reasons (some mentioned in that other answer) that make it impractical.

But what about some lower-tech options?  A truck with a tow rope?  A specially designed cart that the plane sits in that accelerates it up to take off velocity?

I know, that's not going to be practical for jumbo-jet sized craft.  But for planes that seat (say) a dozen passengers, could this be a part of the solution?  Or does the math work out essentially the same?

EDIT in response to GdD's question What problem are you trying to solve?

The biggest obstacles to adopting electric aircraft are the limitations imposed by today's battery technology.  My question is intended to determine whether take off assist could address that limitation both by alleviating the high demand for power at take off, and by reducing the weight, complexity, etc of equipment that is only needed at take off.

So, the first part of the question is: Would any type of "take off assist" make useful contributions to the operation of electric airplanes?

Peter Kämpf's answer is "no" for existing aircraft.  But does electric make things different?  Especially given that electric airplanes are currently being designed from scratch?

The second part of the question is: Would any useful "take off assist" for electric planes be viable?

While a steam-powered, extended-length catapult might be both possible and beneficial (and cool), it's hard to believe it's ever going to be practical.  But if a truck with a tow rope allows you to extend the plane's range by 25% while also reducing cost and maintenance, that seems interesting.

To address jamesqf's other comment, my target family of aircraft is something along the lines of Eviation's Alice.

I guess I'm just wondering if electric airplane designers are failing to consider it just because that's how existing planes work?  Or have they done the math?

Yes it would, for fuel based aircraft and for electrical ones. The higher the MTOW, the larger the benefit.
This article makes a case for installing catapults on runways for commercial aircraft: the engines are dimensioned for the take-off, and an assisted takeoff means lighter engines with the associated fuel burn savings. Take-off is particularly demanding on the power installation because it needs to acquire a lifting velocity from standstill.
Other power-hungry flight stages:

TOGA for go-arounds is applied when the aircraft is at approach speed. The more the better of course - but why should GA power be max TO power for the highest payload ever, on the hottest day ever, on the shortest runway ever. This is what the engines are dimensioned for. From the wikipedia article:

..the engines then increase to their computed take off power. Modern aircraft flight management computers will determine the power needed by the engines to take off, based on a number of factors such as runway length, wind speed, temperature, and most importantly the weight of the aircraft.

Climb power is set after TO: a lower thrust/power setting is selected after the TO. When reaching cruise altitude the thrust/power setting is reduced further. So the engines would be dimensioned for the climb stage.

Aeroplanes certified under 14CFR part 25 must be able to climb after a single engine failure after $V_1$: twin engined aircraft will be dimensioned for this case, if the launching device accelerates the aircraft to a high velocity such as $V_4$ there will still be an engine size saving.
A steam catapult will do the trick, or any of the options that OP states. Of course, the take-off run should not be the couple of metres that an aircraft carrier allows, but should be longer to limit the accelerations that the structure is subjected to.


Are there any airports whose budgets are in the public domain? Most airports - at least in India - are privately owned. AFAIK, even the ones which are owned and operated by the government (i.e. managed by the Airports Authority of India) do not make any financial numbers known.

Are there any airports whose records are in the public domain (even if they are small island airports)? I'd like to have some idea how things work, even if it's only about a small airport.

This varies heavily by country but I can answer this for the United States operating under the FAA/General US legislation (which varies by city).

Here in the US some airports are owned by the local government (there are also privately owned/publicly used and fully privately owned airports). Publicly owned airports (owned by cities/towns/localities etc.) generally either publish their budgets or you can obtain them if you request it. For example if you want to see the information for KPNE or KPHL (owned by the city of Philadelphia) you can submit a form to the city and request the information. Every city is a bit different and there may be small processing fees/long wait times but generally the records can be obtained.

The FAA also published a lengthy brief on the cost-benifit analysis of having an airport in your area. It sheds light on some common costs and such.

Keep in mind that the airport while owned by the city and operated by the city, often has many private companies on its premises that simply lease a building or plot of land. The budgets to operate these FBO's, service centers and the such are more than likely private information.


Can IAF and IF be in the same spot? While looking over an ILS approach chart,
I found that there is a fix where says : (IF/IAF) ACZUP ...

And I was consfused whether the two IF and IAF can be in the same place, or the spot is used as IAF or IF in a certain occasion.

Could anyone tell me which is the right thing?

(IF = Intermediate Fix; IAF = Initial Approach Fix)

An IF is any fix between the IAF and FAF, so as a matter of logic, the same fix cannot be both an IAF and an IF at the same time. Therefore the label IAF/IF must mean it can be either one or, in some cases, both at different times.

If you are cleared to ACZUP for the straight-in approach, then ACZUP is the IAF only. You never pass it a second time, so it doesn't get a chance to be an IF.

If you are cleared to HABJE for the approach, then HABJE is the IAF and you do not pass over ACZUP, so it is neither IAF nor IF.

Otherwise, ACZUP is the IAF when you pass over it outbound, then you do the Hold in lieu of Procedure Turn (HiloPT), and then ACZUP is an IF when you pass over it again the second time inbound. The same would be true if it were charted as a PT instead of HiloPT.

In all three cases, MRVIN is the FAF due to the lightning bolt symbol.


Did Pacific Southwest Airlines ever operate flights under VFR? Does anyone know if Pacific Southwest Airlines (PSA) ever flew certain routes under VFR?

I've read this question and I understand that Part 121 does allow for VFR flight, but my question is specific to PSA. I've heard they routinely flew low altitude VFR flights on shorter routes throughout California.

I was a controller at L.A. Center around that time, and it was extremely common for airlines on the short-haul routes to go VFR-on-top, which is VFR but on an IFR flight plan. There would have been a lot of downsides to flying VFR but every advantage to them to fly VFR on top: with on-top they didn't need clearance into class B (back then the TCA) or get refused or delayed because the controller was "too busy"; didn't have to fly airport patterns (basically guaranteed a straight-in since they would be on an instrument approach); and for flying into the metered airports like LAX or SFO they would have a guaranteed slot, unlike trying to call up as a VFR where they would go to the back of the line and might have to hold for an hour. Plus of course on-top has the benefits of not needing IFR separation, so ATC would almost always give them a direct routing and they could climb all the way up to 16500/17500 instead of being step-climbed under everyone else and capped at maybe 10,000.

So while I don't remember specific routine flights from 25+ years ago, I do remember working a LOT of airlines flying VFR on top on the short routes like LAX to Bakersfield, Burbank to Fresno, etc.


How do the engines of a multi-engine airplane shut down after fuel starvation? If a multi-engine aircraft runs out of fuel, can the engines flame out at different times due to fuel inequality between the tanks, or do they both die at the same time because fuel is constantly balanced?

On multi-engine aircraft the engine on one side is normally fed by the respective tank, so the left engine(s) is fed by the left tank etc... it is possible to cross-feed to allow access to all the fuel in the event of an engine failure.

In order for a simultaneous run down to occur - both tanks would have to have precisely the same amount of fuel loaded and both engines would have to burn fuel at exactly the same rate, which is unlikely.


What are the BUGS and RST buttons on the A320's ISIS for? What is the BUGS and the RST function for the A320's ISIS for?

The RST button is the attitude reset (note the ATT next to the button) function. The ISIS contains an attitude gyro that has to be re-aligned periodically.

Credit: Smartcockpit.com

The BUGS button enables the BUGS function, which allows the crew to enter speed and altitude bugs on the display. The bugs are a visual identifier to aid the crew in maintaining a speed or altitude.

Credit: Smartcockpit.com


What is this odd aircraft? What is this aircraft? It was parked at transient parking at the Southern California Logistics Airport.  It is a pusher prop driven plane with a conventional tail.  High aspect ratio un-swept wings.  Odd shaped fuselage.  Any ideas?

It appears to be a Celera 500L, owned by Otto Aviation Group.

This article has more information: "Unmasking The Bullet-Shaped Mystery Aircraft After It Reemerges At Victorville"

  The registration also provides us with a designation for this mystery
  plane—the Celera 500L. It is the only aircraft registered by the
  company with the FAA. The War Zone contacted the Otto Aviation Group
  by phone and they said they could not comment on the aircraft in any
  way.

  This new high resolution image shows the rear of the airframe, which
  is the perfect companion photo to the lower resolution, front aspect
  image that we posted last April. We can now clearly see the five
  bladed, variable pitch, "pusher" propeller that will provide thrust.
  The airframe also features what appears to be all-moving vertical and
  horizontal stabilizers, and long, slender wings that are likely
  optimized for laminar flow.

  The Bell X-1 like teardrop fuselage design, which includes a cockpit
  windscreen seamlessly blended into the fuselage, gives the aircraft a
  large internal volume and high aerodynamic efficiency. It's safe to
  say that efficiency is what this aircraft is primarily about. Even the
  prop size looks small in relation to the overall aircraft, which would
  point to the possibility that it makes very good use out of the thrust
  it has on hand.


Can we eliminate the center tank of large passenger planes? This is a safety question about fuel and fires. This all regards commercial aviation for large passenger planes.

Most fuel is stored in the wings, but in the largest planes, there's also a center tank for the longest flights. It's this center tank I'm concerned with. In the event of a fire, this seems to be the most dangerous tank.

I'm obviously concerned with fires in the fuselage, or very close to it. Obviously this is where all the people are and we don't want smoke or flame there, but remember also there are overhead oxygen canisters that if heated or fueled, will explode.

Jet fuel is flammable by its nature. This cannot be changed because its purpose is to combust in an internal combustion engine. So it seems the best we can do is to keep the fuel as far from the fuselage as possible, to make it unlikely that fuel will cause a fire there (initially).

Isn't there someplace we can move this center tank? Some ideas I thought of: store fuel in anti-shock bodies on the wings (or they could be just small sears-haack bodies on the wings); store fuel in the empannage; store fuel in nacelles that have a larger diameter than the engine itself, to make room for fuel.

Another exotic idea: Is it possible to engineer the wing such that the most likely structural failure will happen first near the wingtip rather than the wingroot? This would spill the fuel farther from the fuselage. (I got this idea from a really wierd Boeing 747 crash in Netherlands where one engine jumped off then fell back into the other engine, causing 2 engine losses. They said some pins were designed to fail first for a more "benign" failure, but apparently those pylon pins were engineered wrong.)

There's one more tricky caveat, though: the cross feed line to balance fuel loads in the wings. If we eliminate this line, we increase the dangerous consequences of a fuel imbalance. But, it's interesting to think of what might cause a major fuel imbalance other than a leak, in which case the cross feed valve should not be opened. I can't think of anything so I'm leaning toward the opinion that this line can be eliminated too.

EDIT: Thanks to bodargpd for pointing this out. Losing an engine in flight means the consumption rates will be hugely different. Without a cross-feed line, all that fuel in the other wing is unavailable and we may have to ditch early. So the cross-feed line is still necessary. I still say this is much less dangerous than a center fuel tank, however. It would also be nice if we engineered the cross-feed line to be weakest at the sides, so any leak will most likely be as far to the outside of the fuselage as possible.

To sum up, the basic question is, can we viably move the center tank volume of fuel somewhere outside the fuselage?

EDIT: I'm not primarily worried about fuel explosions. I'm concerned mostly about fuel leaks during hard emergency landings. I'd rather have a fuel leak out on the wing than in the fuselage.

I'm assuming you're talking passenger safety in the event of a ground impact - if anything happened midair, it wouldn't really matter if it were in the fuselage or one of the wings.

Moving the fuel somewhere else is going to have center of gravity implications. Moving it to wing pods or lager nacelles in particular would increase drag, which would require the plane to have even more fuel on board, which seems counterproductive to decreasing the fuel risk to passengers (and, of course, would substantially increase the cost of operating the flight).

Some military aircraft do carry fuel in removable underwing fuel pods (particularly fighters being ferried somewhere, where increased endurance/time between refuelings is more important than performance for that particular mission). However, that's less a safety design and more the lack of anywhere else to put the extra fuel on a small aircraft.

If an engine fails, the rate of fuel consumption is going to be different on each side of the plane. Although both are rare, you likely have far more situations where different wings use fuel at different rates than situations where having fuel feed under the body would be dangerous. If that's true, then removing the cross-feed line would be more dangerous than leaving it in.


What does this formulation mean? Just was reading this manual => DLE-120 engine User Manual
On this page (pg 4), I saw this formulation:

What does it mean? How is the 30:1 ratio calculated? What does "fl oz" mean? What does "2-cycle oil" mean? Where are these number coming from?

What does mean "fl oz"?

"fl oz" means fluid ounce (1 fl oz ≈ 30 ml), which is a unit of volume, as opposed to dry ounce, which is a unit of mass.

How are they calculated the 30:1 ratio?

By ratioing 128:4.26, it is 30.05:1, so 30:1 is a good approximation

What does mean "2-cycle oil"?

It is oil for 2-cycle/stroke piston engines

from where these numbers have came?

Probably some design specs/limitations. You have to ask them if you want the details.

What does it mean?

That when you refuel, for every 30 parts of fuel you put in the tank, you need 1 part of oil for correct lubrication of the engine.


How is the speed of a helicopter controlled? How is the speed of a helicopter controlled? Does the pitch of the blade vary for speed while rotor blade moves at a constant speed as with turboprops? Or is there a throttle mechanism for varying the rotational speed of the rotor for forward airspeed?

There are many fine articles existing that discuss how the throttle is used to input power into the rotor disc system to lift the helicopter, and how the rotor disc system is tilted to change the direction the helicopter flies. Putting more tilt into the forward direction makes the helicopter fly faster in that direction.

Optimum cruise speed is discussed in this paper, where knots of airspeed vs fuel needed is derived/plotted.  I wouldn't consider fuel wasted if one wanted to go faster, any more than driving 75 mph vs 55 mph on the highway is wasting fuel.  You just get to your destination faster. "Time is Money", yes? So what is worth more - an extra gallon or two of fuel/hour, maybe outrunning a storm in the process, or climbing above turbulent air, vs your time being spent travelling and doing productive work (or vacationing) at your destination?
http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm


How to check if (small) aircraft's radio is working properly? Is there a standard way to test/check aircraft's radio without calling anybody (Ground/Tower) to see if it is receiving and transmitting?

Is there a way to check aircraft radio with your own handheld radio on the ground before takeoff? I am referring to small aircraft type like Cessna 172.

Here are some things you can do, there are probably more. I'm assuming you're mainly interested in checking COM, not NAV.

Controlled airport

Check if you can hear the ATIS, Ground or Tower; if you can, then at least you know you can receive. But you might as well just call Ground immediately and ask for a radio check. The correct phraseology in the US (see the Pilot/Controller Glossary) is "how do you hear me?":

  Bowman Ground, N12345, radio check please. How do you hear me?

Uncontrolled airport

Listen to the AWOS, if there is one, to determine if you can receive. Ask UNICOM or another aircraft to give you a radio check. If none of those options are available then you can use a handheld airband transceiver to test. Tune it to the frequency you're listening on and click transmit a few times, as if you're turning on pilot-controlled lights (PCL). If you hear the clicks in your headset, you can receive. To test transmission, do the opposite: click the transmit button on the yoke and listen on the handheld.

Airborne

You could call Approach, Center or FSS; try activating the nearest PCL (works best at night); tune and identify a navaid (that doesn't verify COM works, but at least you know something's working); listen to 121.5 (in the US, you should be doing that anyway) because there's usually some bored pilot asking for sports scores on it and some other equally bored pilot yelling at him to "stop talking on guard!".

Troubleshooting

As always, if you have any problems with transmitting or receiving do some basic troubleshooting first: check you have the correct radio selected; check you have the correct frequency; check the volume controls on your headset and/or panel; turn the squelch up/down/off; check your headset is plugged in correctly; if you have a right-seat passenger, see if they can hear/transmit; and anything else you can think of.


Does the pressure change inside a plane when it is opened for paratroopers? Does the pressure change inside a plane when it is opened for paratroopers?

For low deployment the cabin pressure is already equal to the outside pressure.

For High altitude jumps the pressure is reduced to the outside pressure before opening the door (and everyone puts on oxygen masks).


Is it possible to fly a large aircraft inverted? I am curious if the inverted plane in the movie Flight 2012 has anything to do with reality / emergency practices. And if it does, can you please explain the concept/ aerodynamics behind of it , or why someone would ever do that even as last resort?

In the movie Flight (2012), Captain Whittaker (Denzel Washington) does not explain why he deliberately inverted his aircraft, but the obvious inference is: since the horizontal stabilizer has slipped off its jackscrew and become jammed into a descent angle beyond the authority of the elevators to correct, in inverted flight this would push the nose far above the horizon and result in either a climb or a stall.

In this attitude, Whittaker would have been pulling back on the yoke to prevent the stall.  In the movie, this worked.  The aircraft was still not under control, but was no longer diving and overspeeding.  Suddenly rolling the aircraft upright in the last seconds before contact with terrain is the unrealistic part.  A hot fighter jet might accomplish this but the roll rate of a passenger jet is too slow.

The movie's flight emergency is based mostly on the crash of Alaska Airlines flight 261 on January 31, 2000.  In that incident, the pilots experienced a jammed horizontal stabilizer with uncontrollable dive, and inverted their MD-80 to arrest their descent.  Unfortunately in real life neither flying officer was stuffed to the gills with booze and coke: the maneouver failed and the aircraft crashed with no survivors.


Where can I find an ATM simulation software to investigate traffic flow capacities? Does anyone know what software is suitable to investigate air traffic flow capacities in various FIR's / routes. I need to see the effect of temporary reserved ares due to military activities, weather, changes of routing due to LOAs. Taking into account meteorological data would be advantage but it is not necessary.

It would be great if it will be possible to emphesize (colours, histogram, ...). usage of FIR areas.

What kind of software tools are used by EUROCONTROL or ATM consultancy firms providing this service. What standard tools commercially available (or for free)?

I have already found answer for my problem. ACES and FACET from NASA Aviation System Division solve my problem. It should handle all statistical data, it has statistical output as well and it could also handle meteorological data. Currently this SW use FAA and some airline companies to modelate ATM concepts (aviationsystemsdivision.arc.nasa.gov).
Thanks for all your help!


What would have happened when the Concorde's low-pressure emergency system brought it lower mid-flight? My understanding is that the Concorde was equipped with a system that automatically lowered the aircraft to a safe altitude if cabin pressure was lost. I know such emergency never occurred in its history but did the Concorde have the range to make it to the closest airport if say this happened in the middle of the Atlantic. With a range figure of approximately $6500$ km at Mach $2.0$ and $50000$+ feet cruise, it is not clear that this bird would make it to land in such an emergency given it was terribly inefficient at low speeds and altitudes. What happen if this emergency had ever happened?

I'm answering a point in a comment by the OP, rather than answering the question itself directly - but I do think it's totally relevant.  Feel free to vote accordingly :)

This list provides a list of Concorde destinations.  I am assuming that it is complete.  I have not gone through every route but looking down the list suggests that GOOY-SBGL (Dakar to Rio) is the route with the longest ocean crossing.  This list seems to confirm this.

Concorde did not fly the southerly Pacific routes, I guess because it would not be capable of diverting in exactly the situation you ask about.

Suitable diversions on that route would be FHAW (Wideawake on Ascension Island), SBNT (Natal), SBRF (Recife) and SBSV (Salvador).

Using this tool, we can see that GOOY-SBNT is 1870nm and it's all ocean between them.

Using this tool, we can calculate that the mid-point of GOOY-SBNT is at 10° 26′ 47″ N, 026° 29′ 44″ W.  We can also calculate that the midpoint to FHAW is 732nm and the midpoint to SBNT is 587nm.

So a reasonable guess (without access to the original flight plans) is that the maximum distance from a diversion is to SBNT from the midpoint which is 587nm.  Easily done, even at 10,000 feet.

Before the midpoint, I guess they would have returned to GOOY since it is closer than FHAW.  Therefore, I also guess that FHAW would only have been considered if SBNT and GOOY were not available - most unlikely.

I have now found a longer one!  KLAX (Los Angeles) to PHNL (Honolulu).  This one's easy.  The Great Circle mapper shows us it's 2220nm.  There is nowhere to divert between those two so the new greatest distance is 1110nm.

Concordes' max range was about 3900nm so as long as it was about 60% efficient at 10,000 feet compared to cruise (1110 / ( 3900/2) plus a bit for go-around time), the diversion was no problem.  Although inefficient at lower levels, I doubt it was less than 60%.


Measurement discrepancy on vfrmap dot com sectional -- is the grid wrong? At Nome Alaska-- KOME-- the E2 airspace (dashed magenta line) is listed as extending 13.2 (nautical) miles east of the airport-- according to this source page E-9 -- https://www.faa.gov/documentLibrary/media/Order/JO_7400.11C.pdf  --

"Within a 4.1-mile radius of the Nome Airport and within 3.4 miles each side of the Nome
Airport 106° bearing extending from the 4.1-mile radius to 13.2 miles east of the airport..."  'AMENDMENTS 07/07/05 70 FR 22590 (Revised) Corr: 70 FR 33349""

But when I measure on the online sectional chart http://vfrmap.com/?type=vfrc&lat=64.513&lon=-165.444&zoom=10, using the tic marks on the lines of longitude (the lines running north and south) as a scale equal to nautical miles,  the far edge seems to measure more like 15.5 nautical miles from the middle of the airport symbol (as shown by the little blue square) -- now why would that be?  That's about 20% further -- about 2.3 miles different -- not insignificant.

What is going on here?

Is the scale wrong, or is the dashed magenta line shown in the wrong place, or is the airport shown in the wrong place?

I assume "east" in the above usage means "generally east, measuring along the 106-degree radial".

It's not a one-time thing, I'm getting a similar discrepancy with some other similar measurements of other similar regions of Class-E-to-surface airspace, always biased in the same direction.

All the clues were there; another member figured it out (see comments).  My computer screen was stretching out the image in the left-right sense, so when I took my nautical miles scale off the tick marks on the north-south line of longitude, and then made an east-west measurement, the measurement ran significantly high.  The question noted I had seen this elsewhere and the fact that that was also on an east-west measurement, but at much lower latitude than Alaska (neither of which were noted in the question), should have been a clue to me as to what was going on.  Nothing to do with high latitudes and nothing to do with errors in the way the airspace or the map grid were charted.

I looked at the same url on a different computer screen and the measurement came out fine.


What do Air Traffic Controllers (tower supervisors) say to pilots before takeoff and landing? I would like to know exactly what Air Traffic Controllers say to pilots pre departure and pre arrival. (In terms of exact information rather than specific example) For example what dialect they use and what info they give.

ICAO document 4444 contains phraseology and pronounciation in chapter 12. It might however be a little bit difficult (but not impossible) to find online, as ICAO documents are rarely officially published online.

CAP 413: Radiotelephony Manual is published by the Civil Aviation Authority (CAA) in Britain, but is considered reference material for pilot training throughout Europe. CAP 413 is largely built on ICAO doc 4444.

Phraseology in the US differs somewhat from ICAO standard (but is getting more and more harmonized). The Pilot/Controller Glossary published by the FAA may be of some help.


Can you identify this antenna on a Cessna 172N? Does anybody know what this antenna is used for?  I suspect a glideslope antenna but I am not totally sure.

Glideslope antennas are those U shaped stubby 3 prong fork things that look like heating elements for a water heater.  That's a 75 Mhz Marker Beacon antenna.  I have revised this post.  I thought it was just a VHF antenna, mainly because almost all Marker Beacon antennas you see out there these days are faired-in blade antennas, but the comment by @Gerry got me to do a bit more rummaging around, and found a couple examples of the same antenna as on that 172 and judging from the apparent length it's likely for Marker Beacon.  That antenna is probably quite old and I'm not even sure you can buy one today, as all the news ones seem to be blade style.


Do gyroscopic forces (from rotating engines) significantly affect yaw or pitch? It occurs to me that jet engines are very heavy objects operating at high RPMs. This must have a very high angular moment and thus a high gyroscopic force.

This would restrict rotation when trying to yaw or pitch. Rolling, however, would not be effected.

How big of a problem is this? I imagine it is a concern to military aircraft as they want to be as maneuverable as possible. But I'm very interested in commericial efficiency too. I wonder if the giant A380, for example, had to be given greater elevator and rudder authority to help it pitch up at takeoff.

Note: all engines rotate but I'm assuming the jet engine will have by far the highest angular moment due to the weight of their turbines and compressors. Turbofans with high bypass ratio probably have the greatest gyro forces due to their huge fan in addition to heavy spinning spools.

(Presumably, contra-rotating engines would have zero gyroscopic forces.)

Yes. The more so the higher the inertia and speed of the rotating masses and the lower the control authority. While the gyro forces of a jet are negligible in regular flight due to the high damping provided by the wings and tail, in hover they can become dominant. The Bristol-Siddeley Pegasus engine of the Kestrel, Harrier and AV-8B jump jets needs to have the low pressure spool run in opposite direction of the high pressure spool to balance its gyro effects. If that would not be the case, a yawing motion would produce a pitching motion, and vice versa. When you sit on a jet, the thrust of which is equivalent to your weight, tilting this jet fore or aft only slightly will produce a quick shift of your location, so any maneuvering in hover will become extremely hard.

USMC AV-8B Harrier in hover (picture source, © Richard Seaman 2001)

Generally, contra-rotation of engine parts has been used to reduce gyro effects. They first became an issue with rotary engines in WW I. A rotary engine has its crankshaft fixed to the airplane, and both the cylinder block and the propeller rotate. This gives better cooling at low speed and produces a flywheel effect, so the engine runs more smoothly. But when you yaw, the gyro effect pitches the aircraft up or down, so any precise maneuvering becomes very hard.

With the increasing engine power in 1916 and 1917, this effect became so severe that geared engines were developed where the cylinders rotate in one direction and the propeller in the opposite direction. As a consequence, the propeller had only half the RPM in air as it had with the cylinder block. This resulted in great propeller efficiency, but also big propeller diameters, so airplanes with those engines needed a high landing gear. Below is a picture of a Roland D XVI with a Siemens & Halske III contra-rotating rotary engine from 1918. This was an excellent fighter aircraft for its time with almost no gyro coupling.

Roland D XVI (picture source)

Generally, jet engines are sensitive to maneuvering: Changing load factors will bend the spools between their bearings such that the tip clearance of both the turbine and the compressor need to be big enough to avoid contact under g forces, or when rolling with a wing-mounted engine. Every engine manufacturer will publish a load factor envelope within which the engine is safe to operate. Widening this envelope will reduce engine efficiency because the gaps between the rotating parts and the engine housing need to grow with the maximum load factor.


Are the fastest moving pieces of a jet engine supersonic? A jet engine is composed of fast moving pieces. Those pieces are moving into an airmass different form the ambient airmass the aircraft is flying into.

The turbine pieces are spinning quite fast, thus its blade tips may be moving at a supersonic speed. But, the airmass may also be spinning modifying the speed of the blades into the airmass. Moreover, the temperature of the air at this stage may modify the speed of sound.

The first stage of compressor is spinning at a much familiar air temperature and pressure, thus it may be easier to find if those compressor's blades' tips are moving faster than the speed of sound. But pressure (and thus temperature) is not the same before and after each compressor stage. It may be hard to define the speed of sound for this airmass going through the compressor.

Given the airmass inside a jet-engine is different from the ambient airmass, are there any moving piece inside a jet-engine whose velocity (frame of reference: the airmass in which it is moving) is greater than the speed of sound?

Yes, the tips of the fan blades.

Let's look at an example: The GE-90 has a fan diameter of 3124 mm and a maximum rotational speed of 2475 RPM. Their circumferential velocity is d·π·41.25 = 405 m/s or Mach 1.19 at sea level and ISO atmosphere. Now you need to add the flow speed of the air, but this calculation alone should be sufficient to prove the point.

The inner part of the fan and all the compressor stages belonging to the core engine experience flow at subsonic speed, even if the whole engine is flying at supersonic speed (see picture below). To make ignition as complete as possible, the flow speed is continuously reduced the closer you move to the fuel injectors. Since the air is heated in the combustion chamber, the hotter gas has a higher speed of sound, and all the flow through the turbine is subsonic, too. This includes the low-pressure turbine. Even the 1,600 ft/s shown below at the turbine is subsonic, because at 1100°C the speed of sound in air is 720 m/s or 2,362 ft/s.

Overview of parameters in a typical jet engine.

Only in the rear part of a convergent-divergent nozzle with reheat switched on will supersonic flow again be attained. This is exactly aft of the narrowest section, called the throat, where airspeed is equal to the speed of sound, and the petals of the nozzle are the only moving parts here. And they move rather slowly.


Under VFR, can a pilot fly above a layer of clouds? Image source

I often see charts like the one above showing VFR cloud clearance minima. Since the regs list a minimum distance above clouds obviously VFR flights are allowed to fly over clouds. However, it's not clear what kind of clouds one can fly over: only individual smaller clouds, a broken layer or a solid layer. In the US does a pilot under VFR have to maintain a visual reference to the surface?

Yes, it's legal to operate under VFR without any visual reference to the surface. It's called operating VFR over-the-top, not to be confused with VFR-on-top which is an IFR clearance. Over-the-top is defined in 14 CFR 1.1:

  Over-the-top means above the layer of clouds or other obscuring phenomena forming the ceiling.

There are some exceptions and restrictions, though (this list may not be complete):

Recreational pilots must have visual reference to the surface (14 CFR 61.101)
So must sport pilots (14 CFR 61.315)
So must student pilots (14 CFR 61.89)
If the pilot has a foreign-based private license then all restrictions on the foreign license apply, which could prevent VFR over-the-top (14 CFR 61.75)
Large, turbine or fractionally owned aircraft must be equipped as for IFR (14 CFR 91.507)
If flying for an airline or other operator, their OpSpecs must allow it


What is an autogyro, and why would I ever want to fly one? Autogyros seem to be one of those mythical creatures: we know there are actually a few of them out there and they're supposed to be fun to fly.

What are they really; how do they work? And how do you fly one?

What is an autogyro?

Autogyros have been around for decades. They are also known as gyrocopters, gyroplanes, and autogiros. Gyroplane is the official FAA designation. It is basically a rotary wing aircraft just like a helicopter because the rotor  provides lift instead of wings like conventional airplanes.Since the rotor is not powered, an Autogyro uses a separate source for propulsion, just like an airplane. In other words, an Autogyro uses a propeller for forward motion and a freely rotating, un motorized rotor for lift.

http://www.jefflewis.net/autogyros.html

  How do you fly one?

There are only three flight controls: a control stick, rudder pedals and a throttle.

Autogyros do not stall, so it is a lot safer to fly an Autogyro than say a helicopter.You can expect control responses to be faster in a Autogyro than an airplane because you are moving the whole wing  instead of just a  tiny control element attached to a wing. Generally speaking, the control response will not be as quick as a helicopter because of the lower operating rpm of the Autogyro’s rotor system.The critical task in flying a Autogyro is managing the energy of the rotor. If you fail to maintain air flowing through it, the speed drops drastically, and so does the rotor's ability to provide lift.


Will reducing the electricity power in an aircraft save fuel? I was wondering if I reduce the power consumed by the aircraft, would the generator produce less power and if that would save some fuel.

Yes, in theory, but you would have to do a total energy analysis to decide if it's worth it.  On the surface of it, generators consume fuel not being made into thrust. Watts being made to power things is watts not going out the tailpipe.

A good example of the potential benefit is the switch to LED cabin lighting. A 40w incandescent light is more or less a 35w heater that makes a bit of light.  LED lights drop the power consumption by 80-90%, although if you need heat in the same space, you have to replace the heat being made by the lights, so if you did an overall energy balance analysis in that case, you might find the actual saving is negligible for the period when you need to heat the cabin in cruise at altitude (because the reduction in heat from the lights has to be replaced by more bleed air demand).

If you need cooling, it's the opposite because the heat from incandescent lights is working against you, and it's a huge benefit to get rid of the heat produced by the lights, which reduces cooling demand.

So overall, there is probably some fuel burn improvement over time switching to LEDs, very small, but something (say, 200 30w lights consuming 6kW, replaced by 200 5w LEDs consuming 1kW, a 6hp saving, maybe 4lbs/hr - not nothing, but, but as I said you'd have to take more bleed when heating, offsetting a lot of that improvement, and you'd probably have to spread it out over quite a while to get serious money out of it).

Most airlines that switch to LEDs do it mostly for reliability reasons, where labor hours savings and parts costs make a stronger financial business case than just a few pounds of fuel spread out over time, although the fuel-saving does add to the total.

Another area would be advances in avionics that reduce power consumption (you can just imagine the drop in energy demands when avionics went from vacuum tubes to solid-state in the 50s).  Even there though, it's the same issue with heat that is not really wasted when the cabin requires more heating than cooling, that steals some of the benefits you thought you were getting.

Reducing electrical demand with efficiency improvements also helps with weight savings (smaller, lighter generators).

On the other hand.... the 787 blows all that out of the water by going to the other extreme, making all sorts of services electrical, requiring really massive generators. I'm not sure that there is a net energy benefit to using electricity to replace bleed for anti-icing for example, and I think the main benefit is reliability (bleed air systems are a massive maintenance and reliability hassle).


How do jet fighters get to war? Currently Australia is deploying F/A-18E/F Super Hornets to the UAE to fight in Iraq. Obviously the UAE (and Iraq) is a very long way from Australia and well beyond the typical range of one of these aircraft.

On TV they literally showed the Australian Prime Minister waving goodbye while the jets took off and flew into the distance, which for some reason seemed odd and made me wonder about how fighter jets are typically ferried to a distant war.

I kind of assumed they were loaded onto an aircraft carrier and shipped there, but Australia doesn't have an aircraft carrier so obviously this isn't the case.

I assume they must therefore fly, but:

Do they fly hop to hop within their usual range refuelling at each stop? Where would these stops be? I assume they can't just refuel at a civilian airport in an arbitrary country and would have to be an air force base belonging to a close ally.
Do they fly continuously with aerial refuelling? Does the tanker need to make hops to refuel?
Do they swap their weapons for extended fuel tanks which provide enough range to fly continuously to the UAE?
Are they actually shipped via regular military cargo ship and the "departure" on TV just for show?
If they do fly continuously, it seems like flying non-stop for ~13 hours in a cramped fighter pilot cockpit would be unreasonable (even commercial pilots take shifts), or would they fly supersonic and perhaps reduce this to 5 or 6 hours?

Answers don't necessarily have to be Australia -> UAE specific, I'd also be interested to know how the US deployed to Iraq and Afghanistan for example and if the process is consistent or depends on the aircraft and location.

To answer the list in order:

Do they fly hop to hop?

An F-18 can go 3,000km unloaded (ordnance adds a lot of drag) and that's plenty from Australia. You can get to the Middle East in 4 hops, no air-to-air refuelling required. Although if you do an in-flight top-up you can add more than the regular range because you don't need to burn any fuel getting back up to cruise altitude.

Where would these stops be? Surely not at civilian airports?

Military aircraft often use civilian airports - they run on Jet-A just like everything else. Fighters were not an uncommon sight at the general-aviation terminal where I'm from. Loaded warplanes are a political issue, unloaded ones are a good day's business for the airport's fuel merchants. (note that fighters are almost never completely unloaded - the ammunition for the gun has a significant effect on the airplane's trim. But you can't see it.)

An external fuel tank can be added in place of weapons.

Are they actually shipped via regular military cargo ship?

Fixed-wing aircraft are typically not boxed for surface shipping. Helicopters are - no wings to remove and rotors can be folded up very easily.
Carrier-based aircraft will depart from land - the only way you get a Hornet off of a docked carrier is with a crane, so they typically launch everything when still offshore, and load the aircraft the same way on departure.

The USA has enough carriers that they would not deploy a carrier-based fleet like this. If they are adding / replacing aircraft there are probably enough already in Europe - send those where needed and replace them in the normal course of events.

Would they fly supersonic to reduce travel time?

No, they won't go supersonic to reduce the flight time. > Mach 1 consumes so much fuel you'd never get there. Fighters have supersonic capability so they can get there or run away as needed, but it's never used for very long. The Concorde was designed from the beginning for Mach 2 cruise, so it didn't use afterburners once at Mach 2. Subsonic flight suffered as a result, fighters would not accept the subsonic flight handling issues as that's rather important to them :-)

Bombers are often deployed directly from home bases. All modern strategic bombers have global range with in-flight refuelling. You don't leave North Dakota, blow up something in Longwayfromherestan and get home for dinner, but you don't land anywhere else either. Yes, it's many hours in the same seat but the military crews are used to it.


What hardware standards should the flight control computer pass? There are some standards for each part of the aircraft like actuators, sensors,...
I could not find one for the flight control computer hardware. For example what are the environmental tests, or any standards for its connectors and ports,...?

In the US for commercial aircraft, SAE-ITC provides recommended design standards in ARINC Characteristic 701-1 Flight Control Computer System (FCCS).

The recommended environmental standards are in Attachment 6 of ARINC 701. This references environmental categories defined in RTCA DO-160. The issue is that ARINC 701 references an earlier version of DO-160 than the current DO-160G.

The main reason ARINC 701 has not been kept current (701-1 was the last update in 1983) is that the aircraft manufacturers consider the FCC an integral part of the aircraft and they provide the detail design specifications to their FCC supplier. The specifications typically reference DO-160 (whatever version is current when designing the aircraft). The actual categories and test levels are specified based on their analysis of the environment where the equipment is installed in the aircraft.

To summarize; the FCC hardware will have to meet the customer's specification which is usually in terms of RTCA DO-160 tests and categories. The actual levels are unique to each aircraft.


What do I need to know to design contra rotating propellers for a powered paraglider? I wonder if anyone has any technical information that would assist in using the correct Size & Pitch Contra rotating Propellers (CRP) on this Foot launched Powered Paraglider engine ?

We are using CRP to Eliminate the dangers of Torque Twist associated when using a single propeller.

I am looking to use standard 100~125cm (40~49") Propellers that have approx. 28~22 pitch.  Noting the Forward prop would need to be a Puzzle type prop, or we would have to increase the forward Hub size, so that it would slip over the Aft prop hub, thus adding more weight & complexities.

This pre-production engine maximum operating speed is planed not to exceed  3'500rpm, so if the Prop output shafts are geared 1:1 with the piston speed or less, the props will also be rotating at 3'500rpm or less.

This is the current CAD design work, the 4stroke, 150cc engine, current weigh approx. 12kg, so it is a very small engine.

So, I hope someone can understand the unique workings of this engine design and move past that and recommend best size & pitch of after-market propellers that would Fit these hubs, preferably also with bolt pattern measurements ?

Using two counter-rotating props does indeed eliminate torque issues. The co-axial configuration has been around for a while, like the successful Breguet Dorand of 1936. The thrust, power and propeller disk issues are a bit complicated, let's start with a qualitative discussion.

Two 2-blade co-axial rotors compared with a single 4-blade rotor of the same size.
To generate a given thrust, two counter-rotating 2-bladed propellers use less power than a single 4-bladed propeller of the same size - if they are mounted far enough away from each other. Separating the two propellers helps in reducing power: the closer together they are, the less the power advantage. Separate them 20% of the rotor radius, and you still have a 7% power advantage over a single 4-blade propeller, as computed by Kamov (reference). Further away results in less power required. Note that the 7% power advantage may not account for losses from the dual gearing trains required.

Co-axial 2-bladed propeller compared with two 2-bladed separate propellers of the same size.
Momentum theory predicts a power penalty of $\sqrt{2}$ = 41% when two rotors are placed co-axially without separation, compared with the two identical rotors being operated in isolation. Test results have indicated that that is an overestimation: 20% is more realistic.

We're limited to commercially available sizes and pitches and are using fixed pitch. That means that we cannot optimise for the exact circumstances. My recommendations for the design process would be as follows:

From your link I see that there are 40" and 49" blades available. Go for the 40" props.
Your link gives an output RPM of 3500. With a 40" prop, the tip speed becomes (3500 RPM * $2\pi$ rad * 0.5 m / 60 sec) = 183.3 m/s, about Mach 0.55. Forward velocity is around 20 m/s. The velocity triangle at the tip has an angle of tan$^{-1}$ 20/183 = 6.2°
A typical symmetrical profile such as NACA 0012 has a maximum L/D at angle of attack = 4° at M=0.6 (reference).

Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
Naturally, one propeller must be clockwise and one must be counter-clockwise.
Both propellers should be 2-bladed. That will result in four blades in total, more than enough for this application. Adding more blades will cost horsepower and not result in any useful thrust increase.

For the thrust per propeller, if I compute that from a $C_L$ of 0.55 and integrate that over the blade radius from 5 cm to 48 cm (to account for tip losses), I get:
$$ T = C_L \cdot \rho \cdot A \cdot \int_{0.05}^{0.48} \omega \cdot r \cdot dr$$
$$ = C_L \cdot \rho \cdot A \cdot \frac{\omega^2}{2} \cdot (0.48^2 - 0.05^2) $$
$$ = 0.55 \cdot 1.225 \cdot 0.05 \cdot \frac{366^2}{2} \cdot (0.2304 - 0.0025)$$
With

$C_L$ = 0.55
$\rho$ = 1.225 kg/m$^3$ at sea level
A = blade area is about 0.05 m$^2$
$\omega$ = 3500*2$\pi$/60 = 366 rad/sec

= 514 N per propeller. Note that there are assumptions on propeller profile and blade area in there. $\alpha$ may not be exactly 4° so lets take a 10% lower value of 450N per propeller = 900 N total.
Power required to generate this thrust is the blade profile power plus the induced power from thrust generation. When I look up the $C_T$ and $C_P$ factors of the propeller disks, I get a $C_P$ of 0.001, resulting in a power P of
$$ P = C_P \cdot \rho \cdot A_{disk} \cdot {V_{tip}}^3 = 0.001 \cdot 1.225 \cdot 0.785 \cdot 183^3 = 5.9 kW $$
So for two propellers with a penalty of 20%, that would be 14.4 kW = about 20 hp. There are some estimates in here and all depends on the pitch size and if my assumptions of blade profile and blade area are correct, but it seems to be in the ballpark. The product would need to be tested for actual thrust and power consumption of course.
If your counter-rotating setup and gearing works, the main selling points would be absence of torque and a low tip speed resulting in low noise.

Update
Some of the comments are on using larger propellers and one 3-bladed and a 2-bladed, and there is a question on using a spreadsheet for single propellers.

The single propeller spreadsheet may be a compilation of experience on using one single propeller. However, you will be driving two propellers.
A main selling point for your set-up is elimination of torque. Use one 3-bladed and one 2-bladed propeller, and the difference in drag will re-introduce torque. You have 4 blades in total already, no need to add a 5th or more for any purpose.
A larger propeller uses more horsepower than a smaller propeller, and you're driving two propellers. If your engine can drive 2 larger diameter propellers, by all means go ahead.
Your vehicle travels at a maximum of 70 km/h, the propellers won't have an issue with attracting enough air.
Increasing output RPM would be a good way to increase thrust!


Does useful load increase with more horsepower? If an engine's horsepower is increased will max gross weight be increased?

For example what is the effect on max gross weight of changing the engine on a small GA airplane from 65hp to 100hp.

First, you ask one thing in the title and another in the text of your question. Useful load is the sum of fuel and payload, whereas the gross weight is the force produced by the mass of the whole aircraft in the gravitational field of Earth.

First: Gross Weight

If you change engine power during airplane design, gross weight will go up. At that point, you will have relative parameters like wing loading (kg/m²) and power loading (kW/kg) defined and will size the aircraft accordingly.

If you switch the engine of an existing aircraft to a more powerful one, you will need to modify the airframe and systems if the aircraft had not been designed for the more powerful engine initially. Now your gross weight is already defined and cannot simply be changed. Let's first see what happens if a more powerful and heavier engine is fitted:

The higher engine mass will affect the location of the center of gravity and reduce the possible payload. Note that the mass increase will include a stronger engine mount and firewall, and possibly a balancing weight in the tail to put the center of gravity back into the legal range.
If you want to maintain the same power loading, you will need to increase gross weight, which in turn will increase structural loads. Now you need a heavier structure.

For now, let's assume that you stick with the old gross weight and reduce payload accordingly, because you do not want to rivet doublers all over the structure. Fine, but we are not done yet.

You might want to fit a larger propeller, which might require changes to the landing gear to keep a minimum ground clearance.
Your minimum flight speed will go up. If the aircraft is certified according to FAR part 23, the minimum speed should stay below 61 knots (see §23.49(d)). Maybe you will need to fit more effective flaps to keep the minimum speed constant.
Your maximum flight speed will go up. Technically, you can keep the limit speeds of the less powerful aircraft, but dive speed is calculated in one case by assuming 75% engine power (see §23.335(b)4i), so you will most likely be required to adjust limit speeds.
Once you raise limit speeds, structural loads go up. Now you need again to start riveting doubles all over the place.

You see, you cannot legally escape. Fitting a more powerful engine will require adaptions in the structure, and once you need to reinforce wings, landing gear and fuselage, you can as well choose a higher gross weight. But now you need to re-size the structure and re-certify the modified aircraft.

And we have not even started to look at the systems:

The bigger engine will have a higher fuel flow. Are the fuel pumps adequate, or will you need to switch them for more powerful pumps?
The higher design speeds might increase control forces, so now you need to modify the control system to avoid exceeding maximum stick forces (§23.143, §23.175)
Will the new engine excite new harmonics somewhere in the aircraft? Maybe now a part will vibrate and shake itself to pieces which had stayed calm and in one before?

The list goes on, but this shall suffice.

Now to your specific case: If you want to keep the power loading constant (which will give you the same performance as before), the airplane gross mass goes up by 54%, and so does the wing area.

If you want more performance, you will need to reinforce the structure (or start all over with a new design of the same size), and now it is up to you which gross weight to pick. The heavier engine and structure will eat into your payload and fuel, but if you accept that limitation, you can fly with the same gross weight as before.

Second: Useful load

As you can see from the first part of the answer, useful load is reduced by fitting a heavier and more powerful engine. Only when you re-work the structure to cope with the higher loads can you raise wing loading and regain the loss in useful load. Whether you can increase it by more than what you have lost so far depends on the maximum wing loading.

Let's assume for the rest of the answer that the outside shape (wing area, airfoil etc.) will stay identical to the original aircraft, except for maybe a bigger cowling, propeller and radiator.

The mass increase of the power plant plus its supporting structure is linear to the increase in performance. To beef up the structure, you could use the same percentage rule to stay on the safe side, but the real increase will be smaller. There are books which list parametric formulas for airplane masses, and those will show you the influence of the main parameters. They show that wing mass goes up with the square root of dive speed. Since speed is proportional to the third root of engine power, you will see that 54% more power means 15.5% more speed and 7.5% more structural mass.

Now let's assume that the propulsion system is 15% of the aircraft mass, and structural mass is another 40%. Your empty mass will go up by 8% (engine) and 3% (structure), and if your useful load was 30% of gross weight before, it will now be down to 19% of the same mass. Now we need to bump up the gross mass, and go for half of what you would gain if you keep power loading constant. This means your gross mass is going up to 127% of the original gross mass.

Before you rejoice that now your useful load has gone up to 46%, we need to account for the additional structural reinforcement that this gross mass increase produces. The parametric formulas give a structural mass increase proportional to m$_{gross}^{0.3}$ for the fuselage and m$_{gross}^{0.7}$ for the wing, and a higher wing loading will again result in a dive speed increase, so your total structure will now maybe weigh 15% more than before, for a total of 47% or 48% of the initial gross mass. Yes, your structural mass fraction will go up when you  increase wing loading! But still a sizable increase in useful mass should remain - you will now have 39% or 40% of the original gross mass available for fuel and payload, for a relative increase of 30% over the original useful load.

Now I never tried to keep minimum speed constant, but that would had complicated this answer even more. If the original plane had no or very simple flaps, this would be quite feasible, but result in almost a new wing design.