What and when was the first gyroscopic flight instrument introduced? One of things which consistently amazes me about flight is the exceptional progress in the early decades of flight - especially in terms of avionics. Wikipedia tells me that the first ILS landing was in 1938.

I'd like to understand more about the early development of gyroscopic flight instruments - in particular, what the first instruments like? When were they first put to use?

It appears that the first gyroscopic flight instrument in aviation was a gyroscopic stabilizer, with the purpose of maintaining stability and control in a Curtiss C-2 biplane; it was first used (publicly) in 1914.

For this, the inventors, Elmer A and Lawrence B Sperry were awarded the Collier Trophy in 1914. Apparently they did this by,

  ...linking the control surfaces with three gyroscopes, allowing flight corrections to be introduced based on the angle of deviation between the flight direction and the original gyroscopic settings.

Lawrence Sperry and gyroscopic stabilizer, Image from wright-brothers.org

The device (with the gyroscopes spinning at 7000 rpm) was first tested by Lawrence Sperry and Berringer on a Curtiss F aircraft in 1913, with the first public flight in 1914.

Sperry’s second flyby in Paris in the 1914 competition, with Emil on the wing. Image from historicwings.com

Elmer went on to develop the turn and bank indicator and an optical drift indicator, for which he was awarded the Collier trophy again in 1916.


Can a seaplane make a long distance sea voyage on the sea? In general, if a seaplane can fly X distance, can it travel that distance on the surface of the water as if it was a boat or ship? In other words, this would be equivalent to taxiing all the way to a destination. E.g. if a seaplane has the range to fly from New York to Amsterdam, could a pilot simply choose to taxi all the way across the Atlantic Ocean and casually slip into the harbor?

If this is not generally possible, what rules define what sort of sea journeys a seaplane could undertake? Is there a coefficient of inefficiency (e.g. if a seaplane can fly X miles, it can taxi X/2 miles due to increased drag from the water)? Are the vast majority of seaplanes not set up to handle the stresses of a long-distance sea trip, making them likely to result in a shipwreck (er, seaplanewreck)?

This is not the same question as Is it possible to sail a seaplane? . That question is asking about sailing a seaplane using sails without any engines. I am asking about "sailing" a seaplane using the engines and whatever other tools are available for taxiing.

This question is about the physics and engineering issues - not about licensing. I am fully aware that taxiing a seaplane across a body of water might make the trip fall under boat regulations and require a sea captain's license, but I'm not asking about that.

Not very well. If we look back to the 1930's, the age of the large flying boat airliners, they were designed to take off and land in minimal sea states - no more than 3 foot swells. Typical usage would be in large rivers or protected bays, and the flying boat was used because long runways weren't available. Nor did those airliners tend to stay on the water for long, usually they were brought onto land with beaching gear if they weren't in service.

The problem is - an aircraft on water is highly susceptible to changes in wind - it is, after all designed specifically to use flowing wind to remain airborne, so gusts of wind while on the water will have a stronger effect on an aircraft than they would on a ship. As well, the aircraft's hull in the water tends to anchor it, subjecting the airframe to stresses from wind in varying directions, that it wouldn't encounter while flying.

Amphibious aircraft and the pure flying boats, left on the open ocean, tend to become damaged to the point of becoming non-airworthy.

Couple of examples:

While on lifeguard duty off of Truk during WW2 and landing to pick up a shot down pilot, Lt John Dowdle's OSU-2 Kingfisher had overturned due to a gust of wind. Lt John Burns also lost his Kingfisher due to the hull springing leaks from being pounded by waves, while he rescued Dowdle and the downed pilots. Both Kingfishers were lost, but their crews plus the airmen they had rescued were saved by submarine USS Tang, in an epic lifeguard mission that saw Tang pick up 22 aircrew.

The Bermuda Sky Queen, a Boeing 314 formerly known as the Pan American Capetown Clipper, ran short of fuel while flying from Foynes, Ireland to the US. It did survive for over 24 hours on the ocean before the 62 passengers and crew could be rescued, but after that much time on the open ocean, the plane was coming apart from the pounding of the waves (the tail section was starting to come loose) plus damage from colliding with the Coast Guard cutter picking up the people. As a result, the Bermuda Sky Queen, the last airworthy 314, had to be scuttled.


What should a pilot do upon reaching a Missed Approach Fix when holding instructions are not given? Typically, Missed Approach Procedures end with a hold at the Missed Approach Fix. This is written in the textual procedures as something like "direct ABC VOR and hold." The graphical section also depicts the Missed Approach Fix, and the holding pattern relative to that fix, including the inbound course, inbound radial, and outbound course.

However, the ILS 20R approach at John Wayne Airport (KSNA) has only a fix as the last element of the Missed Approach Procedures. The textual procedures say:

  Climb to 3000 on I-SNA LOC south course (196°) to MINOE INT/I-SNA 10.9 DME

The graphical representation of the Missed Approach Fix only shows the radials and DME used to identify the fix. It does not have a depicted holding pattern.

What should a pilot do upon reaching MINOE, in absence of other ATC instructions?

The clip doesn't show it, but you must be looking at an RNAV approach chart for 20R. The ILS charts for 20R show the holding pattern in the plates. Since RNAV states "Radar Required" if the pilot doesn't get further instructions he/she should immediately ask for them.


If unexpectedly in IMC, does it help to climb into clouds to get on radar? I gather that in the flatlands, probably not. But here is a tragic accident where a VFR-only pilot attempted to navigate steep mountain passes in Utah (Evanston, Wyoming west to Coalville, Utah, and south on to Heber City).  The clouds were reported to be closing in, but he wanted to go see for himself, and  promised ATC he would quit and go back "if" (when) visibility got too bad.  He was too successful following the freeways, and got cocky. Made his turnaround decision too late, turned around successfully, and headed back out the way he came - but collided with terrain nonetheless.  Reports compared with maps make it sound like he got turned around alright using the sky over a reservoir, and my guess is he lost contact with his "concrete compass".  It was terrible judgment all around.  Shouldn't have been there.

He did have a squawk, and was periodically picked up on radar.  He was too low for radio without relays.

Would it have been a viable strategy, instead of staying low in known mountains hoping for a sliver of navigable air between clouds and rocks... to boldly climb into the clouds, get seen by ATC, get enough altitude for radio, apologize and ask to be vectored back to usable VFR territory?

Absolutely not! If a pilot is not trained for instrument flight it would be near suicide to attempt flight in cloud due to spatial disorientation. In clouds you have to trust your instruments solely and be able to interpret them, which requires special training, retraining and practice. Without these pilots do not last long in cloud, see this related question for lots more details on inadvertent flight into IMC, which is applicable to your question.

What the pilot should have done is made a precautionary landing on one of his concrete compass lines or a field while he still had the option to do so. Instead, he had get-there-itis and got himself perished as a result.


If I were to scratch build a helicopter, as the manufacturer, would I need a pilot's license to fly it? If I were to scratch build a helicopter, as the manufacturer, would I need a pilot's license to fly it while its in the experimental stage?  This is in the USA, but I'd be interested in how it plays out in other countries which are different

Depends on what you build. It is possible to build a helicopter that qualifies as an ultralight, and thus no license needed.

If it exceeds the weight and power restrictions for an ultralight, then it is an experimental aircraft, that requires at least a solo ticket.

I would strongly suggest that rather than scratch build your own, an experience you might not survive, you take a look at what I'm currently lusting after:

Mosquito Helicopter

In kit form (which technically makes you the builder), it can be had in ultralight form, with limited range.

Or in experimental form with a more powerful 2 stroke engine and larger fuel capacity.

And finally, the (sigh) gas turbine powered version.

One advantage of building the experimental kit is: as the builder, you can perform all maintenance and the annual inspection yourself.

Another advantage of going the more capable experimental route is: you can log the hours.


Why does the SR-71 Blackbird sometimes have dents in the nose? On many pictures (maybe on most of the pictures) part of nose looks hammered or slightly smashed, or bent.
Please note these 2 symmetric dents just behind nose spike:

source

source

On other pictures these dents are missing:

source

Why? Is this a feature or damage?

The SR-71 had a detachable nose (photo #2), and could change between three different nose cones depending on the mission. I haven't found a lot of information on the three, other than what this site and this site mentions:

Training nose with dead weights
Radar nose containing a Side Looking Radar. This is probably the bulge you saw on the photos.
Photo nose containing the optical bar camera, taking very wide photos of the ground.


What are the most common uses of radio communication when flying? What are the most common uses of radio communication in aviation? I know that many aviators communicate with the people in towers with radio, but what do pilots say to the people in the towers and vice versa? What do pilots and ATCers communicate about.

It will be hard to list everything that is said, but I can try to start with some of the basic examples:

Pilot is ready to taxi to the Runway
P: Tower, N12345, has information Tango, at South Parking, ready to taxi.
T: N12345, taxi to runway 13 via Alpha, Delta.

Pilot is ready to take off
P: Tower, N12345, is ready to go at runway 13. Request SouthEast Departure
T: N12345, cleared for takeoff, SouthEast Departure approved.

Pilot wants to cross another airspace
P: Tower, N12345, is 10 miles to the East, 1,500, request transition east-to-west
T: N12345, transition approved as requested.

Pilot wants to approach an airport to land
P: Tower, N12345, is 10 miles to the South, 1,500. To Land
T: N12345, make Left-traffic for runway 17; report a 2 mile final


Do pilots need a clearance to go around? I have read about the missed-SFO-accident and watched the 2:22 movie. I want to ask about going-around (or canceling takeoff) when the pilot is fully aware of an emergency that the tower is not (or is late at acting).

According to the reconstruction of the real missed-accident done by the news:

Air Canada pilot was on final cleared to land, but instead heading to taxiway for reason that will be explained after FAA & TSB investigations
Tower did not notice and did not complain, clearance was still ok
Pilot double-checked with tower because he saw lights on the ground
Tower double-confirmed clear to land
Other pilot on queue said "where is this guy going?"
Tower requested go around
Air Canada flight crew initiated go around.

The order of the last two events is currently not clear and subject to investigation.

In the movie both ingoing and outgoing pilots are scared by the sight of each other but ATC Dylan doesn't command action until the last moment, while clearance to land and take off is still granted for both.

It is clear that in the movie ATC has failed and pilot(s) are aware of a real danger that affects the safety of flight operation.

Like a driver sighting an animal on the road and braking (or worse moosing) without calling the police first. I am no pilot, I understand that flight is definitely different from driving. And I also enjoyed my time on MSFS virtual flight school. I said the above because I know it could be disappointing for experienced pilots.

I want to ask for my culture/curiosity: when a pilot is cleared to takeoff/land but sees a legitimate reason to cancel the maneuver (e.g. stop/go around), can he simply advise the tower that he is doing that or must continue as earlier instructed? AFAIK when an indicator indicates failiure at < 80kt speed the pilot can immediately cancel takeoff, otherwise is required to continue.

My idea is that the Air Canada pilot could have told the tower something like "we are now fully thrusting and going around because I am not sure about the safety of this landing, please give me further instructions for looping" by his initiative.

This is allowed in the MSFS simulation (you can open virtual ATC radio and announce missed approach even a few feet above ground, they will tell you how to loop over the circuit asap). Is it allowed in reality, or do pilots need a clearance to go around?

No, and this applies to any pilot, not just an airliner pilot. After the pilot has been cleared to land (or even if you're landing at your own discretion at an untowered airport), he can decide to go around instead of landing if he's dissatisfied with the approach for any reason.

The pilot might need to abort the landing for reasons the tower can't possibly know about, such as a gear unsafe indication, failing to achieve a stabilised approach, not making visual contact with the runway, or some distraction within the cockpit. And even in the case of a reason the tower should be able to tell - such as another aircraft infringing the runway, lining up on the wrong runway by accident, or birds on short final - the pilot must still go around if he thinks it's not safe to land, without waiting to be told.

The same applies to taking off. Even after being cleared to take off, the pilot must not take off if he thinks it is not safe to do so, even if it's for a reason the tower should know about, such as a runway obstruction or a take-off clearance on a crossing runway.


How to estimate runway length for airport master planning? I use the manufacturer aiport planning manuals. But they are incomplete (unless for Boeing). Airbus and Embraer for example, only present range X weight charts for MTOW.
Is there a free (or affordable) software or good charts for this estimation?
I'm interested in airport planning.

The airport planning manuals from Airbus do include take-off field length charts for various weights, temperature and airport elevation.
Those of Embraer contain similar charts.


What is a straight wing on an airplane? What is a straight wing? I need this for my science project. I have looked for other answers on this website, but I cannot find any. Please help!

What is a straight wing on an airplane?

A straight wing is a wing that is not swept (see the images).

Straight and swept wings

Unswept, straight wings

Swept wings


What would happen if the entire blade on a turbojet engine went supersonic? I have seen that when a blade tip goes supersonic, there are vibrations and lower efficiency. If the entirety of the blade was to go supersonic, would it be more efficient?

Not much if designed for it, but efficiency will suffer. Also, if the blade is not designed for the loads, the all-supersonic flow could overload it.

How would you achieve the desired all-supersonic flow? By cooling the intake temperature or increasing the rotation speed, of course. Cooling is less practical, so lets assume you run the compressor faster. This would mean higher centrifugal loads, and the increased dynamic pressure would drive up aerodynamic blade loads with the square of the speed increase.

Also note that compressor blades for subsonic flow are highly cambered. Supersonic blades would better be uncambered. Thus, the blade would only function well if both its aerodynamics and its strength are designed for the full supersonic speed. A regular blade would perform poorly and probably fail. However, even an optimized blade would show lower efficiency due to the inherently higher aerodynamic losses in supersonic flow.


What is the available range for DME, and why do we need EFC? How far from the station can a DME signal be picked up, and why do we need EFC?

How can DME signal go from the station?

Your aircraft's DME sends a signal (when tuned to an appropriate frequency) to the ground station (suitably equipped with DME, e.g. Vortac, ILS/DME, etc.) and the station sends back an electronic reply. The aircraft's DME will measure how much time it took for the signal to travel to/from the station and translate that into a distance (in slant range).  Here is a good article explaining DME:

If you are asking what the maximum distance between the station (e.g. Vortac/VOR/DME, etc.) and the DME equipped airplane can be for a reliable DME signal, it's 199 NM (slant range).  Of course this depends on aircraft altitude and a few other variables.

See this excerpt from the Aeronautical Information Manual for more information:

DME Article from AVWeb

  why do we need EFC?

This answer pertains to EFC, meaning "Expect Further Clearance" time, route, altitude: (U.S)

If you are flying IFR and are given holding instructions (for example) you will be given an EFC time by ATC.  This is given to you in case of lost communications.  If you loose communications with ATC you are expected to continue with your originally planned, revised, or route/approach you were told to expect by ATC at your EFC  time.

There are other occasions that you may receive an EFC from ATC.  For example, you may be taken off of a previously assigned route, and ATC might say (for example) "N12345 turn right heading 230, vector for traffic, expect direct to Omaha in five miles."  If you lost communications with ATC, then five miles from the point of the vector you should go direct to Omaha.

Or, another example might be if you are told by ATC to "maintain Flight Level 270, expect Flight Level 350 in four minutes."  If you lost communications you would be expected to have maintained Flight Level 270 and, 4 minutes after receiving this instruction, begin your climb to Flight Level 350.

Since your question was not entirely clear regarding EFC, I included 3 different occasions that your might receive an "Expect Further Clearance" from ATC.

As a note, the actual ATC phraseology (generally speaking) where the 3 words "Expect Further Clearance" would be spoken would apply to a routing, or holding clearance (or a short term clearance to a fix/clearance limit other than an airport, with or without holding instructions). But the word "Expect," when used with regard to a route or altitude (such as "Expect Flight Level 350 in four minutes" or "Expect" direct to Omaha in five miles" is implied to be an "Expect Further Clearance." (EFC)

Finally, as noted above, EFC is directly associated with lost communication with ATC.  If you read the Federal Aviation Regulations, (FAR 91.185) you will have a better understanding of how the "Expect Further Clearance" procedures apply.


Is the Airbus Beluga's safety record comparable with the record of other Airbuses? Upon first sight, to the uneducated eye, the Airbus Beluga looks incredibly 'un-aerodynamic'. Is the Beluga just as safe as other Airbus models?

There's a history of oversize airplanes for transport. One of the earliest was the Pregnant Guppy and its successor the Super Guppy

By NASA/Tom Tschida - http://www.nasa.gov/centers/dryden/multimedia/imagegallery/Guppy/EC00-0212-2.html (image link), Public Domain, https://commons.wikimedia.org/w/index.php?curid=32895741

Boeing operates its own variant, the Dreamlifter

By scott wright (originally posted to Flickr as n780ba) [CC BY 2.0 ( http://creativecommons.org/licenses/by/2.0 )], via Wikimedia Commons

To my knowledge, none of these (including the Beluga) have had any safety incidents (although the Dreamlifter did once land at the wrong airport). I'm not sure if there's any conclusions on safety to draw from, however, as there aren't a lot of these around, as they primarily transport large materials (like aircraft parts).


How does flight control surface authority change with AOA? I am working on semi-realistic (let's just call it "believable") flight simulation component set for a game engine. One of the topics that I tried to research but could not find reliable information on is the authority or effectiveness of flight control surfaces over AOA. I would prefer to see some graphs or some approximate math expression. I've found more or less enough information on other topics (e.g. lift coefficient over AOA) but I cannot really come up with reliable information (even just theory) regarding flight control surfaces. Gut feeling tells me that they would probably behave similar to wing, but on the other hand elevators should really not lose much authority even past stall AOA.

Control authority is a function of the local dynamic pressure (the product of air density and speed squared), geometry (the product of control surface area and lever arm), local angle of attack $\alpha$, the angle of deflection $\eta$ and the relative flap chord. Generally, the control surface works fairly linearly in a range between $-15° < \eta < 15°$ for a relative flap chord of 25% rsp. $-25° < \eta < 25°$ for a relative flap chord of 15%. Interpolate for values in between. Note that flap effectiveness is proportional to the square root of the relative flap chord, such that a flap of 15% needs twice the deflection angle to effect the same control authority than a flap of 60% relative chord.

Bigger deflection angles reduce flap authority, and here it becomes complicated, because local flow phenomena can make a big difference, up to control reversal. For a simple model you may just assume that control authority is cut in half for all deflections exceeding the limits mentioned above.

This all is only valid for moderate angles of attack, when forces change linearly with angle of attack changes. Once you approach the lift force limits of the particular control surface, authority suffers. Now it is important to know the local flow field: Elevators fly in the wake of the wing, which in effect reduces the angle of attack changes at the elevator compared to those at the wing. This means that most elevators still have a healthy lift margin when the wing starts to stall. But stall they will, eventually. To give you an idea how a wing performs over the first 180° of angle of attack, see the plot below. A plot for a control surface should look similarly. It is taken from a book which should exhaustively answer all your questions about control surface authority, be it subsonic or supersonic, for all conceivable configurations. It has been written by Sighard Hörner half a century ago and is still the best you will be able to find on this topic.

For an example of an airfoil's flap effectiveness over AoA, see the plot below of the XFOIL calculation for a Wortmann FX71-L-120 symmetric airfoil with a 25% flap at a Reynolds number of 1 Million and with a fixed boundary layer transition at 60% of chord. Note especially the hysteresis close to the maximum and minimum lift angles of attack at higher deflection angles (own work; c$_a$ is the lift coefficient).


Why would a jet engine use cannular combustors if the annular design is superior? Why are cannular type burners used in aircraft engines if annular type have more advantages over it?

Single combustor cans are simpler to develop. To get the ignition and combustion process right in an annular combustor is quite a challenge. When the first jet engines were developed, Junkers decided for separate cans while BMW wanted to design a theoretically superior annular combustor. In the end, the troubles with the combustor meant that Junkers got their engine fielded much earlier, even though BMW had started their jet engine development before Junkers.

With today's CFD tools the annular design is not quite such a challenge any more.


Why do the A320’s primary flight controls have hydromechanical backups only for the rudder? The A320 is primarily a fly-by-wire aircraft, with the pilots’ joystick and rudder-pedal inputs not going directly to the flight-control surfaces, but, rather, to the aircraft’s flight-control computers, which then decide what, if any, control-surface deflection is necessary, and send the requisite commands to the hydraulic actuators which move the control surfaces:1

However, in the event of a complete failure of the aircraft’s flight-control-computer system, the A320 can switch to a backup mode known as mechanical law, which bypasses the FCCs completely.2  In this mode, the only one of the primary flight controls to remain active is the rudder, using an emergency cable mechanism which sends the pilots’ control inputs directly to the rudder actuators; with the elevators, ailerons, and spoilerons all inactive, pitch control is maintained using manual horizontal-stabiliser trim (which uses a similar cable mechanism to send trim commands to the hydraulic motors  powering the stabiliser jackscrew) and varying engine power, and the ability to control roll separately from yaw is lost completely (to roll the aircraft in one direction or the other, it has to be yawed in the desired direction using rudder inputs and differential engine thrust; the resulting sideslip then causes the aircraft to roll towards the trailing wing, due to the positive slip-roll coupling generated by the A320’s rearward wing sweep):

The reason the elevators, ailerons, and spoilerons are unuseable in mechanical law is that, unlike the rudder, they have no direct hydromechanical connections to the cockpit controls at all, being connected only via the flight-control computers (thus leaving them cut off from the pilots’ control inputs in the event of a total failure of those computers).  If the A320 did have hydromechanical backup controls for the elevators, ailerons, and spoilerons, the pilots would be able to control the aircraft in each of its three axes separately (rather than with roll dependent on yaw, which provides very sloppy roll control with a significant time delay between the initiation of the yaw and the resulting sideslip-induced roll, and with a small but significant initial rudder-induced rolling moment in the wrong direction), and would be able to do so using the same types of control inputs as would be used in normal, fly-by-wire flight (albeit likely with considerably-increased control forces and a markedly-different force gradient), rather than having to switch to a completely different input style in mechanical law:

So why is the rudder the only one of the A320’s primary flight controls to have hydromechanical backups allowing its use in mechanical law?

1: The A320’s flight-control system, and that of all later Airbus aircraft, has several different fly-by-wire flight-control modes.  In some of these (direct law, alternate 1/2A/2B law), the pilots’ flight-control inputs in some or all control axes are simply passed straight through the computers unfiltered, with the computers parroting whatever the pilots ask of the aircraft without any of the translation present in the usual operational mode (known as normal law); however, the pilots’ inputs are still passed to the computers first, and only then to the control-surface actuators, rather than going directly aft.

2: The pitch and roll/yaw axes can each also revert to mechanical law separately in the event of a major fault in one of the primary flight controls (for instance, a double elevator jam would cause the aircraft to revert to mechanical pitch control), while still leaving the other in fly-by-wire mode.

The mechanical backup is only meant to maintain basic controllability during a temporary failure of the whole fly-by-wire system. As the OP mentioned, the rudder is deemed sufficient for basic roll control, while the horizontal stabilizer is deemed sufficient for basic pitch control even without any stability augmentation. That being said, the mechanical backup is not meant to achieve continued safe flight and landing (I would be really surprised if the mechanical backup meets all of the ARAC minimum controllability guidance); it's expected that at least one flight control computer can be rebooted to take over control after the initial failure (Ref. Airbus A320 Crew Manual).

The reason for relegating the mechanical backup to rudder and trimmable stabilizer, instead of to elevator and ailerons, pretty much has to do with the choice of the passive sidestick as the pitch and roll inceptor. It lacks mechanical linkages to translate its motion to external assemblies, nor does it have a feel unit to provide feedback for the airloads. This leads to significant weight savings and simplicity in design, and is the primary advantage of the passive sidestick.

I suspect that the reason for even having a mechanical backup scheme is due to mistrust in FBW systems for civil aviation when they first came to use. As trust in redundancy and dissimilarity grew, newer generations of Airbus aircraft (e.g. A380, A350, A220) did away with it completely, and instead have an electrical backup servo control loop on each of the axis.


Does a tandem ultralight need flaps on the rear wing if the front wing has flaps? Does a tandem ultralight need flaps on the rear wing if the front wing has flaps?

I understand that most Rutan canards don't have flaps as I was told if the main wing has flaps, the canards need one too.

Rutan did make one with flaps on both the canard and the main wing.  I think it was called the Grizzly.

So... what about a tandem aircraft (with positive lift on the horizontal tail) with flaps on the front wing ? Does the rear wing need flaps too?

Can't you just use the horizontal trim tab as a flap if you need more rear lift to offset extra lift of the main wing with flaps extended?

After all, wouldn't most conventional aircraft with rear cg and slow flight ( low Cm) in a dive with a symmetrical horizontal tail, with elevator down, be generating positive tail lift anyways, so they are acting like a tandem aircraft, no?

As the love of tandems continues I will answer.  Because you are balancing lifting duties between two wings and (hopefully) still have the one in front stalling before the one in the rear, any configuration change in the front should be proportionately matched in the back so that the stall characteristics remain safe when flaps are deployed.

Deploying flaps increases the Angle of Attack of the wing and may cause a shift in the center of pressure.  So the design needs to be approached with care.

You could also put slats and flaps on both wings of a biplane too, but the whole point is to have one (smaller/less drag) wing for faster cruising flight and a larger, higher lifting wing for low speed flight (take off/landing).

For a GA personal use recreational aircraft, you may not need flaps at all.


Is seating distribution planned in airliners or is it left to casuality? One thing I have always wondered when taking intercontinental flights is the way passengers are distributed in an aircraft. It seems to me that in some way people of different ethnicities are purposely mixed. I have the strange idea that this is preset and done mostly for security reasons.

Seeking for clarification on this matter. Please do not get me wrong as I am not trying to classify different types of people!

People tend to travel by themselves or in small groups. They sit all over the airplane, either selecting their own seats or having them assigned by the airline's ticketing system. When you go to select your seats, the system shows you what seats are available, but it does not show you other passenger's ethnicities. Airlines also don't necessarily know passengers' ethnicities when assigning seats in advance, except to the extent that they could conceivably guess based on names (they may know what country's passport someone is traveling on, which is not the same as their ethnicity, but even so, they may not know this information until well after a seat assignment is in place).

So lots of people check-in and have their seats assigned basically randomly. The expected result is that small groups of people of different ethnicities would be mixed throughout the plane fairly randomly. I'm not understanding why you think this is something an airline would deliberately need to do, as it would already happen naturally.

Using ethnicity for seating purposes could also violate anti-discrimination laws in many countries, if this was something an airline even wanted to do.

It is sometimes the case that a large group of passengers largely of the same ethnicity will book a block of seats together as part of a group booking, such as a Japanese school trip or German musicians. Such groups may, if space permits, be seated together, and if the group is relatively ethnically homogeneous, you may find a number of travelers of one ethnicity seated together for this reason.


Why do jet engines get better fuel efficiency at high altitudes? I'm told that this is true, but I can't imagine why.  It seems like the fact that there is less air would make the engines less efficient...  But that probably just shows how little I know about jet engines.

For a quick explanation, you need to know that

Thrust is the difference between the entry impulse of the air entering the engine and the exit impulse of the heated fuel-air mixture leaving the engine. Impulse is mass times velocity, and expressed with a mass flow $\dot m$, thrust T is $$T = \dot m \cdot (v_{exit} - v_{entry})$$
The exit impulse is increased by accelerating the airflow through the engine, and the acceleration is achieved by heating the air.
Each gram of fuel heats up a given mass of air by a certain number of centigrades. The definition of the energy content of fuels is given as the capacity to heat one pound of water by one degree Fahrenheit. The definition of one Calorie is similar but in metric units. Since the heat capacity of both water and air are almost constant at moderate temperatures, the starting temperature makes little difference to the absolute temperature increase when a given amount of energy is added.

Thermal efficiency

Thermal efficiency is the ratio between the mechanical work extracted as thrust and the heat energy spent on heating the air, and it is affected indirectly by the flight altitude. Please see the Wikipedia article on the Carnot cycle. This and similar cycles describe the workings of all combustion engines in thermodynamic terms. Basically, it says that the efficiency of a combustion engine cannot be greater than the temperature ratio between the temperature increase from ambient ($t_{amb}$) to the maximum temperature $t_{max}$ of the process, divided by the maximum temperature. All temperatures must be expressed as total temperatures, where 0° means 0 K or -273.15°C. Operating in colder air makes the ratio bigger and improves efficiency.
$$\eta_t = \frac{t_{max} - t_{amb}}{t_{max}} $$

If $t_{amb}$ is 290 K (16.85°C or 62°F) and the fuel heats up the air to 1400 K (2060°F), the thermal efficiency according to the formula above is 79.3%.

At cruise altitude $t_{amb}$ is only 220 K (-53.15°C or -63.7°F), and the same fuel flow relative to air flow will lift the maximum temperature only to 1320 K (in reality even less; for more precise reasoning see below). Now the thermal efficiency is 83.33%! If the maximum temperature is maintained, both thrust and thermal efficiency will go up; the latter to 84.3%.

In reality, the total efficiency will be lower because we have not included propulsive efficiency, friction effects or power offtake by bleed air, pumps and generators. Propulsive efficiency describes how well the acceleration of air is performed.

Heating the fuel-air mixture

Burning a fuel-air mixture will add thermal energy to it, about 43 MJ for every kilogram of kerosene (if we assume complete combustion). The isobaric heat capacity or specific heat of air (close enough, the mixture has very little fuel but lots of air in it) is 29 J per mol and per K, so those 43 MJ will heat 1000 mol of air by 1483 K. The heat capacity changes slightly with humidity and temperature, but little enough that we can consider it constant for this purpose. If the air starts at 220 K, precompression in the intake will heat it to approx. 232 K, further compression in the engine will heat it up to approx. 600 K if we assume a compression ratio of 25, and this is the temperature at the entry of the combustion chamber.

Those 1000 mol of air weigh about 29 kg, and adding a full kilo of fuel and burning the mixture will heat it to 2083 K. If you want more details about the parameters in a typical jet engine, please see the diagram in this answer. Since the mixture picks up speed as it burns, the fuel mass is also heated and combustion is never complete, the maximum temperature given here will not be reached in reality.

If we start on the ground with an air temperature of 290 K, the temperature in the intake would drop slightly because we will not be flying fast enough for any precompression to happen in the intake. Now the compressor will heat the air to 730 K, and again adding and burning that kilo of kerosene will heat 1000 mol of air to 2213 K. Ideally.

In reality, the engine control will see that the limit temperatures are not exceeded, but here we can play with the numbers as we like. The exact values will certainly be slightly different (more frictional heating in the compressor, heat loss to the outside, slight drift in specific heat with temperature), but the gist of the explanation is correct.

Explanation in layman's terms

Burning the fuel-air mixture heats it and makes the gas expand. This happens at nearly constant pressure and in a restricted volume, so the only way to make room for this expansion is for the gas to flow faster. Nearly constant pressure means that the density of the gas must decrease. The density ratio between the heated and the unburnt gas is proportional to its temperature ratio, measured in absolute temperature.

However, the amount of fuel burnt determines the absolute temperature increase, the difference in degrees between the burnt gas inside the combustion chamber and the unburnt gas at the intake. For a given amount of fuel, the temperature ratio which can be achieved with an absolute temperature increase becomes smaller the higher the temperature of the unburnt gas is. Thus, efficiency decreases with a higher temperature of the intake air.


Design lift coefficient of an airfoil I have the design lift coefficient of the plane during the cruise condition. Now, I want to calculate the lift coefficient required by the airfoil which makes up the wing, taking into account the Aspect Ratio, Sweep, etc. Is there a formula for that? I have seen formulas that give the slope of the lift curve for a wing using the slope of the lift curve of an airfoil.

I need the design lift coefficient of the airfoil for choosing an appropriate airfoil.

As far as your question on sectional lift given a wing geometry and total lift coefficient is concerned, there is no one single formula that estimates this. The sectional lift is affected by downwash and spanwise flow, which are in turn dictated by the wing geometry and airfoil themselves.

For straight tapered wing, you can use the lifting-line, which computes the downwash angle at the discrete spanwise locations, which you can use to easily back-out local $C_l$. For swept wing, your easiest solution is to use a vortex-lattice method, such as AVL. AVL directly outputs the section lift coefficient at the corresponding control points.

As far as selecting/designing an airfoil is concerned, it's much more involved than just looking at the cruise lift coefficient. You should consider:

Takeoff and landing requirements. What kind of performance do you need? What kind of trailing-edge and/or leading-edge devices can you fit with the airfoil?
Operating conditions. Is it a point-design? Or does it need to cater for large range of operating conditions?
Structural concerns. Can you actually manufacture a super thin trailing-edge, even if it gives the best stall characteristics? Can you actually fit a spar tall enough (and at the right location), even if it gives the best drag characteristics?
Space concerns. Can you actually fit fuel tanks in the wing if it's super thin?


Why didn’t Boeing ramp 737NG production back up in response to the 737 MAX groundings? The predecessor of the currently-grounded 737 MAX is the 737 Next Generation (737NG), produced from 1997 through 2019.  The NG family (comprising the 737-600, -700, -800, and -900) is extremely similar to the MAX, with the main differences between the two families being the engines and mountings thereof (the 737NG uses the GE/SNECMA / GE/SAFRAN / CFM International CFM56 engine, housed in distinctive hamster-pouch nacelles, while the 737 MAX uses the Franco-American consortium’s newer, larger LEAP engine and mounts it in bog-standard round nacelles which are located further forward and higher above the ground than those of the NG1), the landing gear (the NG uses the same short-legged landing gear dating all the way back to the 737-100 in 1967,2 while the MAX’s landing gear is longer than that of all prior 737s3), and parts of the flight-control system (the MAX’s larger, more-forwardly engines cause it to handle slightly differently than the NG at very high angles of attack, so its pitch trim system was modified to introduce additional nose-down trim at high attack angles in order to make the MAX handle more like the NG and thereby ease cross-training of pilots; unfortunately, the modified trim system proved susceptible to inducing an uncontrollable nose-down trim runaway in the presence of certain sensor failures, which is why the MAX is currently grounded).

When the MAX was grounded in mid-March 2019, the NG was still in large-scale production, although the assembly lines were ramping down in preparation for a switch to producing the MAX and only the MAX; it would not have been particularly difficult to ramp production back up to full scale, enabling Boeing to continue producing, selling,4 and delivering airworthy 737s for the duration of the MAX’s grounding.  Boeing, however, did not do this, and instead continued to taper off NG production (finally ending it entirely at the end of 2019), while continuing to build and accumulate undeliverable MAXes until being forced to put production on hold in January 2020 for want of space to put them (thus marking the first time in the half-century-plus history of the 737 that production has ever stopped completely).

Why didn’t Boeing reincrease 737NG production in response to the MAX’s woes, rather than shutting it down completely and leaving the company with no deliverable 737s?

1: Which is part of the reason why the MAX, despite its larger engines, does not require hamster-pouch nacelles.

2: Which is the reason why the NG does require hamster-pouch nacelles (as did the 737 Classic before it), as the ground clearance beneath the wings (designed for the 737 Original and its slim Pratt & Whitney JT8Ds) would be too small to safely mount the CFM56 otherwise.  Even with the hamster-pouch nacelles (the pouches of which contain the engine accessories, moved from the bottom of the engine to the sides), SNECMA still had to shrink the diameter of the engine’s fan in order to get an acceptable amount of ground clearance, which is why the CFM56s used on the 737 Classic and NG are slightly smaller and less efficient (due to the decrease in bypass ratio resulting from the shrunken fan) than those used on the KC-135R/T, DC-8-70, and A319/20/21ceo.

3: Which is the other part of the reason why the MAX, despite its larger engines, does not require hamster-pouch nacelles.

4: Possibly, although not necessarily, involving offering MAX customers the opportunity to switch their orders to NGs, potentially along with other incentives to sweeten the deal (such as refunding them the difference between the prices of an NG and a MAX, or slightly more [thus turning an undeliverable MAX order into a discounted, but deliverable, NG order], and/or giving them a discount on future purchases of Boeing aircraft).

There are several reasons why.

First, it takes an awfully long time to make that kind of switch. While one can switch an assembly line for a product, that works rather differently for (say) transistor radios and Boeing 737s. The assembly line for an airliner winds back very, very far, and nothing happens or can happen immediately, or even very fast.

That would have made it very difficult, even if Boeing wanted to do that.

And here's a second reason: they didn't want to. They had orders for the MAX. If they were late in delivering those aircraft, they could be subject to financial penalties. Boeing agreed to deliver the aircraft, so had to build them. At the same time, they weren't facing overwhelming demand for other 737s that could possibly have made it worthwhile to do it in the circumstances.

A third reason: Boeing had every expectation that the aircraft would soon be allowed to fly again, and continued to operate under that expectation (for much longer than many observers shared the same expectations, it has to be said).

A fourth reason: it would have been bad for business to do that. Doing what you suggest would have sent out the most appalling signals, i.e. that the company had lost faith in one of its most important products. In a way, they simply had to hope that things would turn their way sooner rather than later, and the option of turning away from that would have had tremendous costs. (You might argue that it was a gamble that didn't pay off; I think that would be fair enough to say.)

And finally, I think that Boeing's slow responses at many points in this story look like the behaviour of a company in shock. On multiple occasions, the company has found itself struggling to keep up with and make sense of events, even if they been events of their own making. Quite possibly the company's decision not to do as you suggest, or at least not to have done it much sooner, will turn out to have been a very bad one, but unfortunately, it will also have been only one in a long chain of them.

By the time I make several bad decisions in a row in a crisis, it's pretty much guaranteed that the next one I make will make everything even worse. Organisations also fall victim to that pattern.


What are the factors required to estimate the minimum required power for an experimental aircraft of a specific mass? I have already viewed these questions:

Basic aircraft performance: how can you calculate the required power?
How can I estimate the required T/O power for propeller aircraft?

But is there a comprehensive list of factors, and a single formula for estimating the minimum required power, including the take-off power, for an aircraft of a certain mass?

EDIT: I'd like to be a bit more specific - I'm looking to estimate the minimum required power for an experimental micro-light (not ultra-light), for which I have a 3D model, and estimated MTOW in kg. The primary objective is to fly at a 'safe' speed (above stall speed - probably around 80 - 100 knots). So I have the following with me:

3D Model of Airframe: Composite + Foam (Burt Rutan style), closely resembles a Cirrus SR22
MTOW estimate: approx. 340 kg
Speed range: 60 - 100 knots

Can I calculate the minimum required engine power from these factors? Do I need more? How do I calculate the minimum required power (or is it thrust)?

A good engineer will first check existing designs: How much power is installed in comparable designs? Use airplanes of similar speed and built quality, such as the Super Diamond Mk 1 which needs 50 to 60 hp. Cruise speed is 90 knots and the MTOW is 450 kg.

Next, try to estimate the minimum wing area. Starting from the minimum speed requirement of 35 kts ( = 18 m/s), and assuming a maximum lift coefficient with flaps down of 1.6, the area to support 340 kg at sea level is $$S = \frac{2\cdot m\cdot g}{\rho\cdot c_L\cdot v^2} = \frac{2\cdot 340\cdot 9.81}{1.225\cdot 1.6\cdot 18^2} = 10.5 m^2$$

Now calculate the drag coefficient in cruise, using the parabolic drag equation. First, establish the lift coefficient at which drag is minimized: $$c_{L_{opt}} = \sqrt{c_{D0}\cdot\pi\cdot\epsilon\cdot AR}$$
The total drag coefficient at this point is simply twice the zero-lift drag coefficient $c_{D0}$, so a low drag design is important. Still, with a fixed gear your zero-lift drag coefficient will hardly be lower than 0.035, so your cruise lift coefficient is 0.938 (assuming an aspect ratio $AR$ of 10 and an Oswald factor $\epsilon$ of 0.8), resulting in a flight speed of just 23.51 m/s = 45.7 kts. Total drag at this point is $$D_{min} = 2\cdot c_{D0}\cdot S\cdot\rho\cdot\frac{v^2}{2} = 249 N$$

To sustain flight at this point only requires $P = v\cdot D$ = 5.85 kW, and assuming a prop efficiency of 0.75, the installed power should be 7.8 kW. But you want to fly faster, so we need the drag at 100 kts ( = 51.4 m/s):
$$D = \left(c_{D0} + \frac{c_L^2}{\pi\cdot\epsilon\cdot AR}\right)\cdot S\cdot\rho\cdot\frac{v^2}{2}$$
There, your lift coefficient is only 0.196 but the dynamic pressure rises to 1,621 N/mm². Since the Reynolds number is higher, your zero-lift drag could drop to 0.031, resulting in a drag force of 550 N. At that speed, the required power is 28.3 kW. Under the heroic assumption that your prop will still be 75% efficient at that speed, the installed power needs to be 37.8 kW or 50.65 hp.

If you "only" want to achieve a TAS of 100 kt at altitude, here is what you need to do in the case of cruise at 10,000 ft ( = 3048 m). First you need the density at that altitude, which is 0.9 kg/m³ or 74% of the value at sea level. This means that the dynamic pressure is 1,191 N/mm² and the lift coefficient 0.267, resulting in a drag force of 419 N. This needs a continuous power of 21.56 kW to overcome. Now I assume the 75% efficient propeller again and that you run the engine at 75% of max. power, so the installed power in 10,000 ft should be at least 38.3 kW or 51.4 hp. Assuming a normally aspirated engine, this would translate to a rated power of 70 hp at sea level.

Considering that similar designs require similar power, this looks about right. Normally, you now need to compute the climb speed with the excess power of 35.15 kW to check how usable this design is, but at 10.5 m/s I doubt this will be not enough.

If you manage to include a retractable gear with your limited mass budget, the zero-lift drag might be as low as 0.024. Now the drag force in cruise at 10,000 ft will be only 324.4 N and the installed rated power at sea level only 40.4 kw or 54 hp.

With piston aircraft, your power needs increase with the cube of airspeed. I leave it as an exercise to you to calculate how much more power the last 10 knots require: Repeat the calculation with only 90 kt cruise and your rated engine power can be as low as 51 hp with a fixed gear.


Do turbo prop airliners generate thrust using the propeller and compressed air or just the propeller? I looked at a picture of a q400 engine and it showed air being compressed so I was wondering if it has two systems to generate thrust.

Turboprop engines transfer almost all of the turbine's rotational energy to the propeller, though there is some waste in heat and exhaust gas as in all engines. The exhaust does not form any major amount of thrust unlike in other turbine engines ("jet engines", like a turbofan or turbojet). Turboprops are more efficient than other "jet engines" at lower altitudes due to the thickness of the air at lower altitudes whereas jets are more efficient at higher altitudes, though turboprop pilots will tell you they fly a jet, being that a turboprop is still a turbine engine, aka a jet. :-)


Should the weight of the lifting surfaces be deducted from the weight used to calculate the C of G of the aircraft? If the aerofoils are creating lift they are doing the work to lift the helicopter.  When the helicopter is hovering, the blades are carrying the weight of the entire ship. The forces on the aerofoils are acting in the opposite direction to gravity which is pulling the ship down. These opposing forces create a situation where the ship is now hanging from the aerofoils.

So would this mean that the weight and balance calculation for the pilot should not include the weight of the aerofoils as this weight difference would affect the C of G?

A fixed wing aircraft would suffer the same results?

My question is, should the weight of the section of the aerofoils of an aircraft  that provide lift be deducted from the weight used to calculate the C of G of the aircraft?

The center of gravity is relevant for all inertial forces. For example, if you turn, the centrifugal force would be calculated with the mass of all aircraft parts, including wings and rotor blades.

If you want to calculate the loads on the aircraft structure, things depend on the location. If, for example, you want to know the load on the wing root or the helicopter rotor shaft, you use the total mass minus wing / rotor mass times the acceleration to calculate the force.

While there are cases where the wing mass needs to be subtracted, center of gravity calculations must include it.


Why does the US not have AIREPs? After looking into aircraft report data at Aviation Weather Center, I realized that PIREP is usually reported inside of US; on the other hand, AIREP is typically reported outside of US. I was wondering if there is any specific/particular reason why AIREP is not available at US territory?

Apples and oranges. A PIREP is a report of current weather conditions at a specific location. An AIREP is primarily a position report, required of some aircraft that are not under radar control. Whereas the primary purpose of a PIREP is to report unusual weather conditions or things like turbulence and are not mandatory, AIREP's are in many cases mandatory and weather information in Section 3 is optional.


Is potentially dangerous to select the take-off power on airliner lower that temperature at the moment on the airport? Is potentially dangerous to select the take-off power on airliner at lower settings  value due to the temperature that could be increased by the time the aircraft will go up?

No it's not dangerous.  Flex thrust simply exploits all of the runway available, taking advantage of any length that is surplus to the minimum required at max thrust, to allow takeoff with less than maximum thrust to save wear and tear and fuel (wear and tear is a big deal taking off in a sandy/dusty environment and use of flex has a significant effect on engine life).

The fact that you are using "just enough power" for a flex takeoff does not change the technical risks.  The balanced field length requirements (accelerate/stop and accelerate/go safely) are still met, so the extra length available in a non-flex takeoff does not technically speaking, reduce the risks of something going wrong following an engine failure on takeoff or following a reject.


Is the Mil Mi-2 still in production? I have read conflicting reports that this Russian helicopter is out of production, yet others say otherwise. Could anyone confirm?

Mi-2 was almost entirely produced in Poland, on PZL-Świdnik. That production officially ended in 1992.

Since then, a few new modifications/prototypes may have been produced, according to various sources, but they were almost certainly retrofits of the existing airframes.

In 2012, it was announced that production of a modernised Mi-2A would start in China, but I could not find any confirmation that it actually happened. Frankly, I see no good reason why it would. Generally, any announcement of plans from Russia in the last 30 years should be treated with extreme caution and not considered valid without confirmation.


Do you need a commercial certificate to fly unpaid for a non-pilot owner? Let's say that an aircraft owner is not a pilot and needs someone to fly an airplane for him. If the owner pays 100% of the costs for the flights but does not pay the pilot, does the pilot require a commercial certificate?

This situation would be Illegal as the law stands. What it boils down to is that flight time is considered compensation. This answer covers it well and in your case, since you are not paying your pro-rata share and the owner is paying the full expenses you are in a way getting compensated in flight time.

This answer is somewhat related as well and its seems there needs to be some "common purpose" for everyone on board as well.


What are the considerations for coding the GPS before engine start without external power? Suppose I would need 10-15 minutes to fully configure my G1000 on a C172 ahead of a flight, with the flight plan, my personal view settings, etc., and prefer to do that before starting the engine. My goal is to save fuel, save hobbs/tach time, and reduce deposits accumulating on the spark plugs.

What would be the considerations against doing that on battery power alone? And what can I do to reduce the impact of any downsides?

15 minutes is a long time to be draining the battery, it's not just the G1000 that will be running but the electronic gyros, beacon, etc. If the airplane hasn't been recently flown and it's cold outside 15 minutes may be long enough that you can't crank your engine.

There's also problems with running the G1000 while starting the engine:

It's not good for the electronics: you get all sorts of electronic noise and surges when running the starter. I don't think it's that much of a problem with modern electronics, but the G1000 is a painfully expensive piece of equipment and you want to preserve it in any way you possibly can!
You get a power sag: the starter drains a lot of power, there may not be enough to keep the G1000 going and it may restart. It it restarts you lose all that configuration you did! You could mitigate that by saving your flight plan to an SD card, shutting down the avionics for start, then re-loading it

The last issue is that 15 minutes is time you could be flying, or someone else could be flying. It's also time you might be paying for depending on the school or group you rent from (if you rent)

There's no reason to do this anyway to be honest, you can use SkyVector, Foreflight, SkyDemon, Garmin Pilot and other flight planning software to plan your flight on a tablet or other computer, load onto an SD card, then load it on to the G1000. Some of the software costs money but it's worth every penny as it gives you the opportunity to take your time planning flights rather than rushing to get waypoints in. The interfaces are also much nicer to use than the G1000.


Why would a passenger airliner be missing windows in the fuselage? On many airplanes (you can take the A330 to make an example), the fuselage is not completely covered by windows. In some cases it is due to the presence of the lateral emergency exit, in some other cases I am not sure about the reason. Usually it's above the wings, so I made my idea but I want to know for sure the real reason!

In the linked video, for example, one windows is missing under the "R" of the "Garuda" logo in the fuselage.

Most of them are where there is a divider between sections or there is a lavatory there.

Here are the layouts for the Garuda A330-200 and -300. As you can see the divider between the classes (Between Blue row 11 and green row 21) and the lavatories (Between rows 31 and 32) are located where the missing windows are in the video.

-300:

-200:

Images by Garuda Airlines


Calculate pitch balance of RC glider? Today, I played with styrofoam gliders with my kids; I made an asymmetric  wing, asymmetric horizontal tail, symmetric vertical tail, and attached these to one stick for the fuselage.  I've had big problems with pitch stability, so I played with adding mass to the nose, hoping to solve the problem.
Every time I throw a glider with my hand, the nose lifts up or falls down (which one depends on where I set the glider's center of gravity), and the glider crashes.  I set the tail to produce downforce, but I can't find the right pitch balance to make the glider fly well.
I know that, for level flight, the CG has to be in the same place as the glider's overall center of lift (both wing lift + tail lift).
Should the horizontal tail have a symmetric or asymmetric profile, and what should the angles of incidence for the wing and tail be?
Maybe the best way is to put the CG at the wing's center of lift (at the 25% chord line) and set the tail to a neutral position (producing no positive or negative lift)?
What is the easiest way to calculate where to place the CG if I don't know how much lift is produced by the wings and tail?

Joe Ayoob's world record throw of the John Collins designed paper airplane is worth watching over and over again.

Every time I throw the glider with my hand ...

This caused me to split my free flight hobby into throwing gliders and launching from a hill.
A thrown glider experiences a wide range of speeds in flight, therefor it cannot be set with a staticly stable "tail downforce/weight forward" arrangement.  This type of glider will loop if thrown hard, but will be fine if thrown off a hill.  Try to gently release it at its trim speed.  Moving the weight/changing tail decalage will produce the best glide.
But for throwing on flat ground for distance the glider must be slightly staticly unstable to keep flying as it slows down.  You want it to gradually pitch up (increasing AOA) as it loses speed to generate adequate lift for level flight.
The plane flies straight out until it stalls.  Notice on Joe's throw the glider went around 150 feet, from 40 mph to maybe 5 mph, stalled, then recovered from the dive, flying on to the world record.

Glider has asymmetric tail, which produce downforce, then glider is "tail heavy"

An asymmetric tail will produce pitching force aerodynamicly, not by weight.  This is why "classic" aircraft design has an "upright" vertical stabilizer (many glider designers also benefit by putting the horizontal stabilizer on top in "T" fashion, increasing pitch torque without adding drag).  The tail must produce a down pitching force to "set" wing AOA if CG is forward.
For "throwing" gliders, you need tail upforce, weight aft (while maintaining directional stability), and some luck to go 226 feet. If one can control the elevator (by R/C) in flight, then discus launched gliders (DLGs) are worth a look!


What are the Autopilot Minimums for a C-172 G1000? (GA Pilot)

On a C-172 (G1000 Avionics), what would be the AutoPilot minimums OR at what altitude would one need to disengage the auto-pilot and take controls for:

1) Precision Approaches

2) Non-Precision Approaches

3) Visual Approaches ..?

Typically, the aircraft flight manual will identify this. In your particular case (Cessna 172 G1000), it is 200 feet AGL for all approach types.

The C-172 can be fitted with either a Garmin GFC 700, or a Bendix/King KAP 140.

For the GFC 700, it is listed in the aircraft operating limitations:

In the case of the KAP 140, it is listed in the autopilot supplement:


What is significance of N1 and N2 in Jet engine? Why N1 Low pressure compressor RPM and N2 High Pressure compressor RPM are monitored in jet engines ?
Why specifically compressor RPM rather than turbine RPM ?
What do N1 and N2 signify in terms of relation with any engine performance parameters?

Compressor and turbine are connected by the same shaft. You have LP compressor+turbine and HP compressor+turbine. For Rolls Royce engines you have N3 too because they use three rotors instead of two.

N1 or N2 show the percentage of rpm for the respective shaft. Each engine has a particular number of rpm corresponding to 100% N1 or N2 in order to make numbers easier to understand for pilots between different engines.


What does an absolute novice need to learn to make a successful emergency landing? Suppose I am a passenger in a small, non-commercial plane (e.g. at most 8 seats), and the pilot suddenly dies or is otherwise incapacitated mid-flight. Suppose further that nobody else on the plane knows the first thing about flying, or that I were the only other person on the plane. I understand the basic physics of flying, and have been in airplane cockpits before for a ride, but never piloted one. Cockpits are an intimidating bank of switches and dials, and I imagine I'd have very little time to acquaint myself with them experimentally in an emergency.

What minimalistic, general information should I know in an emergency situation to try to land a small plane?

I'm looking for perhaps 5–10 fast-and-simple rules-of-thumb that would be useful in a life-or-death situation, yet easy to remember.

A great answer might include 2–3 sentence answers for things such as:

Where might I expect to find certain, key controls?
How could I contact air traffic control?
What kind of terrain should I aim for, if possible?
What rate of descent is too dangerous?
How to deploy landing gear? (What might this button look like?!)
How to control the aircraft speed, and how slow is too slow?
How might I determine a good angle of attack?

ATC has successfully talked down folks with zero experience in GA planes, and if there's one thing you need to learn, it's how to call ATC so they can give you that help.  Any pilot would be happy to teach you this, and it should only take a few minutes while you're sitting in the plane before departure.  Anything you know beyond that will make ATC's help a lot easier to understand and get you safely on the ground that much faster, but that's the bare minimum.

My recommendation is a "discovery flight" at a nearby flight school; that will teach you far more of the basic skills you'd need to survive than days of looking for tips online.  Flight sim time would save money if you're interested in becoming a pilot, but otherwise I wouldn't bother; you need to actually sit in a real plane, touch real buttons and knobs and levers, and feel how a real plane reacts--with someone at your side explaining the key points along the way.  I learned every one of the things on your list and more, plus made my first landing, in that one hour lesson.

FWIW, it doesn't matter if that discovery flight is in a Cessna and your emergency happens in a Mooney, or whatever.  For light planes, most of the differences border on cosmetic for emergency purposes.  Once you know what to look for and why, it shouldn't take much to recognize the important controls and instruments in any other light plane.  Again, any pilot you're flying with should be happy to explain the differences if you don't pick them up on your own; an instructor is only needed when you're starting from zero.

If you'll be flying GA a lot, particularly in the same plane and/or with the same pilot, look into "Pinch Hitter" courses; they'll cost quite a bit more than a simple discovery flight, but they're worth every penny if you'll be flying often enough for real concerns about emergencies.


What determines the touchdown zone and aiming point markings on a runway? Large runways usually have a marked touchdown zone, and a marked aiming point (with two giant bars in the US). How is that location chosen? It seems like it is frequently further down the runway than I would have thought maximized available runway length.

How important is it for an airliner to land on that spot? Are there regulations about this?

There are actually several different indicators on the end of a runway. Here's a diagram of the most common ones during the day:

... and at night:

The first touchdown indicator, as shown, is usually placed a set distance (here 500') from the threshold of the usable runway. Then, there are additional markers at 500' increments. Which one the pilot will aim for on approach depends on the plane he's flying, its weight, and instructions from the tower such as to land "deep" or "shallow" (light craft, and sometimes even commercial airliners, are often given these instructions to help manage air and ground traffic more efficiently at peak times).

As you can also see from the night shot, the glide slope lights (here using a system called PAPI which is a more precise indicator of slope than the older and more well-known "white-over-red" VASI) are positioned smack in the middle of the touchdown zone; again, with an approach path aiming directly for that point from the pilot's perspective, the plane will touch down on full-strength runway pavement even if he's in a 747-800.

Of course, maintaining that glide slope all the way in is not the greatest idea, as a standard descent rate for an airliner on final approach is 400ft/min, which works out to more than 6 feet per second. Even the cushiest main gear struts are going to make that a pretty rough "smack" in the seats of the passengers and can cause very expensive damage to the airframe itself. To avoid that, pilots usually add a little throttle and/or pitch up a few more degrees in a maneuver called a "flare", which reduces the rate of descent, ideally zeroing the plane's descent rate just as the wheels touch. This means that during the last few seconds of approach, the glide slope decreases, moving the "aim point" further up the runway and causing the main gear to touch further down the runway.

You'll find that if you look at the touchdown marks on older, well-used runway surfaces, touchdown of the main gear (remember that's anywhere from 50 to 150' behind the pilot's perspective and up to 25' below it) actually ends up centered pretty close to the ideal spot, due to the leveling off of the flare maneuver:

You can see in this image the average touchdown point (the widest and blackest part of the runway) is right at the PAPI lights to the left.

You'll also notice a few significant tire marks just a little too close to the threshold for comfort. Clearly landing a plane is not an exact science, and this is why the touchdown zone and aiming point is further down the runway than you might think; a sudden downdraft or a thinning of the air due to surface heat at just the wrong time in these crucial final seconds, and if the pilot was aiming for the threshold, his main gear will touch down short of it, possibly doing millions of dollars of damage to his plane, the runway and approach lighting as well as likely closing the runway.


When Boeing designed the 737NG, what factors influenced the change in the flap system? The early Boeing 737 models had wings with triple-slotted flaps that appeared to be derived from the 727. When the 737 was redesigned as the Next Generation series (dash 600 through 900), these flaps were dropped in favor of a double-slotted design.

Why did Boeing choose to make this change, and what were the trade offs? Did it impact performance? I had always been under the impression that early 737s were reasonably capable on shorter and rougher runways.

One of the biggest differences that you will see between the flaps on the two is that the NG (photo on the right) has continuous span flaps while the classic has split inboard and outboard flaps.

Combined with the longer wing on the NG, this gives the new flaps more surface area, so they don't need to be quite as effective.  Overall, the NG actually has better performance than the classic, mainly because of the redesigned wing which is 25% larger and has winglets; both of which help out.

Even though the performance is better with comparable triple-slotted flaps, the double-slotted flaps are lighter (which helps with overall aircraft performance) and have fewer moving parts.  This makes them more reliable and they require less maintenance.  Most new aircraft designs are moving to either double or even single slotted flaps because of this simpler design and the fact that today's runways don't require the extra performance that would be gained by the more complicated flaps.

Photo Credits:
737 Classic Flaps
737NG Flaps


How to understand the requirements for IFR currency? So the requirement reads "six instrument approaches;
Holding procedures; and
Intercepting and tracking courses through the use of navigation systems."

I am still a little unclear on how to interpret that statement. I have been told you need to have a combination of the above that equal 6, but you could also read that as you need 6 approaches, 6 holds, 6 Intercepting and Tracking through Navigation Systems. Can someone help explain what I am missing from that rule?

The regulation here seems to be 14 CFR 61.57(c)(1). The way that the regulation is written, we can see that there are three separate requirements:

(1) Use of an airplane, powered-lift, helicopter, or airship for maintaining instrument experience. Within the 6 calendar months preceding the month of the flight, that person performed and logged at least the following tasks and iterations in an airplane, powered-lift, helicopter, or airship, as appropriate, for the instrument rating privileges to be maintained in actual weather conditions, or under simulated conditions using a view-limiting device that involves having performed the following -
(i) Six instrument approaches.
(ii) Holding procedures and tasks.
(iii) Intercepting and tracking courses through the use of navigational electronic systems.

So it's not "a combination of the above that total 6", and it's not 6 of each. It's 6 of the first one, and any amount of both of the other two.


The captain of an aircraft flying an international flight is required to have a Restricted Radiotelephone Operator Permit. How do you get one? 47 CFR 87.87 requires the captain of a US registered aircraft to have their Restricted Radiotelephone Operator Permit (RP) unless it is a domestic flight.

How do you go about getting one?  I used the FCC's website a long time ago and remember that it is terribly confusing.  A great answer would include step-by-step directions for those that haven't had to do it yet!

You have to use the remarkably obtuse FCC Universal Licensing System if you want to request a license online. You'll specifically need FCC Form 605, the apparently very-accurately-named "Quick-Form Application for Authorization in the Ship, Aircraft, Amateur, Restricted and Commercial Operator, and General Mobile Radio Services".

From there, you're on your own, I'm afraid. I applied for mine years ago and it looked identical.

Do note that this is essentially a fee on operators who fly internationally, as there's no exam to complete and no proof of eligibility to provide. You simply request the license and pay the application costs. It's a bit silly.


Can commercial aircraft dump luggage or cargo mid-air? In a situation where the pilot realizes that weight of the aircraft is too high, can they dump luggage / cargo mid air, similar to dumping fuel?

No they can't. The cargo doors are secured and will not open mid-flight.

Cargo holds are usually pressurized so opening the door anyway would cause depressurization.

Also if the weight was too high the pilot should never have lifted off in the first place.

Then after you theoretically throw the stuff off board think about what happens after to the stuff. It will drop down hard probably on someone's roof.

Only some military cargo planes with a back hatch are designed to jettison cargo.


What options are there to learning IFR flying on Garmin's G1000 (Cirrus Perspective)? I am about to begin my IFR training.  I can do this in a 5-year old 172 with the G1000 at a reasonable price.  I need a good tutorial or book for learning IFR with the avionics on which I plan to learn.  In particular, I do not first want to study avionics that I neither have seen nor operated, only so that I can then unlearn them and relearn how the G1000 has morphed their functionality.  Ideally, I would take a course that imagines that IFR was invented together with the G1000.  My particular situation is likely to become more common over the years, too, with wider spread of the G1000 and alike.

I have searched the net.

There is a book by Max Trescott, but it dates from 2012.  It is 2018 now.  Has the G1000 software since 2002 received some good or important updates ?!
There is an expensive course by King Schools.
There are the official Garmin manuals.

Are there any other options for training on the G1000? What are the advantages and disadvantages of these options?

Note: I am not affiliated with any of these vendors, nor do I have any information.  I am just looking for discussions of pluses and minuses of updated G1000 IFR books, courses, and tutorials.

You can get books on the subject, but one of the best ways to learn the G1000 is practice.  Fortunately, Garmin sells a G1000 simulator which can be installed on your computer and replicates all of the G1000’s capabilities.  Along with a joystick and throttle you can plan and execute flight, fly approaches, and practice anything else on your PC.  They are available in a variety of G1000 setups, including the Cirrus Perspective.  Cost is $25.

https://buy.garmin.com/en-US/US/p/35045


How does a higher temperature when programmed in the FMGC affect REC MAX FL? While I was reading the FCTM I came across this line mentioned below.

  An increase in the Outside Air Temperature (OAT), that results in a decrease of the REC MAX FL.

I wanted to know if we enter a higher than normal temperature for a particular FL or we even forget to put the minus sign in front of the temperature value (our older A320s with Honeywell FMS accepts the temperature without the minus sign) how does this cause the FMGC to compute a lower REC MAX FL?

FMS calculates REC MAX in cruise by calculating temperature from actual OAT and TROPO inserted in INIT A page. It assumes standard -2C/1000ft until inserted tropopause altitude which after it uses constant temperature.

During climb it calculates temperature profile from inserted tropo/temp. If your REC MAX seems to be off during climb check the inserted values. Also, when A/C reaches CRZ ALT entered to PROG page it starts to use measured OAT at once, so REC MAX can change suddenly if it was off in INIT A page.

Note that REC MAX is only function of A/C weight, TROPO and OAT. Cost Index does not affect REC MAX.


If the VVI, FPM, airspeed indicator somehow failed you can use fuel flow to help you with your attitude (climbing or descending)? If the VVI/attitude indicators , FPM, airspeed indicator somehow failed same time and now you could not get cross control check, can use fuel flow counter(because of the decrease consumption rate) to help you with your attitude(climbing or descending) if your aircraft is in the clouds at the moment ?

Without an Attitude Indicator, changes in altitude at a constant power setting gives you a fairly good indicator of pitch. If your Airspeed Indicator, Vertical Speed Indicator, and Attitude Indicator all failed at the same time, you would use your Directional Gyro and your Altimeter to stay straight and level. You would cross check that with your Magnetic Compass and your Turn Coordinator.
If your Altimeter fails you, you would keep wings level with your DG, TC, and Mag Comp while monitoring your Tachometer RPMs on a fixed prop or your Manifold Pressure on a constant-speed prop. This would give you a more immediate indication of pitch than your fuel flow counter. The DG, TC, and Mag Comp in most aircraft work off of separate systems from each other to avoid all three going inoperative at the same time. They are your instruments to indicate bank and turn.
The ASI, AI, VSI, and Altimeter are all pitot static instruments. And iced over pitot tube and static port can cause them to be inoperable. Using you alternate static port or breaking the glass face of your VSI will make your Altimeter work, making this scenario a non-issue.
Using a built-in GPS or an external AHRS like the Stratus will give you an unofficial altitude in a pinch.


What are the difference between FMC, FMS and MCDU and what do they do? +2 more questions What are the difference between FMC, FMS and MCDU and what do they do?

Do airliners have all of them or just 1 or 2 of them?

Do pilots learn how to program them/it?

FMC = Flight Management Computer

FMS = Flight Management System

MCDU = Multi-Function Control and Display Unit

With specifics depending on aircraft, generally the following applies:

FMC - Flight Management Computer

FMS - Flight Management System (consisting e.g. of two FMCs)

MCDU - Multi-Purpose Control and Display Unit (2 or 3 installed on the aircraft, the screen and keypad unit by which the crew interfaces with the FMS)

Airliners have all of the functions provided by the boxes above, although depending on setup sometimes some of the computers are called differently or are unified. E.g. on Boeings, it’s called a CDU not MCDU, and some retrofit older airliners have an FMCDU which is an MCDU with a built-in FMC.

Of course crew learn how to operate these systems.


C-152 carb heat on before landing in hot weather? I know the POH for the C-152 explicitly states carb heat should be applied before landing. I fly in a tropical country where temperature is at 30°C on average on the ground, twice the standard temp. Airports I frequent have an elevation at 300' the most. Cruising altitude on most days is between 2500-3500'.

Should I still treat the POH as the bible in this situation, or will the 30°C qualify as an exception?

You should always pull the carb heat when throttling back no matter the conditions for 3 reasons:

Ice forms from moisture (duh!), and there's much more moisture in hot tropical air than cold arctic air, so being in a tropical location does not lower the icing potential. The temperature drop is caused by the Venturi Effect which aerates the fuel in the carburetor, fuel is not frozen in the carb by the outside air temperature, you can get carb icing on a hot day
Habit: it's important to get into good carb heat habits, otherwise you may forget to pull the carb heat when you need it. Make it so automatic it just happens without conscious thought
Workload: Deciding when to use carb heat or not requires thought, you have to consider density altitude, temperature, relative humidity, the make of the carb, and other factors to make the right decision. Why add to your workload when 90% of the time you're probably going to conclude you do need it? Approach is a busy time, you should be spending time looking for traffic, maintaining airspeed and the other critical aspects of flight

It's worth reminding as well that icing can happen in cruise as well, so keep in the habit of applying carb heat regularly.


When do we use IATA codes and when do we use ICAO codes? I found on this website several questions speaking of IATA, ICAO and airports codes. The fact that two identification codes for the same airport exist means there are cases where you use one, and other cases where you use the other. I wonder what is the rule to know which code (IATA or ICAO) should be used.

It helps to know the objective of both ICAO and IATA to understand when which code is used.

ICAO (International Civil Aviation Organization) is a UN-body which focusses on international harmonization of civil aviation regulations.

ICAO codes are used for "official" purposes such as Air Traffic Control; E.g. flight plans use ICAO codes for airports and airline flight identification.

IATA (International Air Transport Association) is a trade association that focusses on making air traffic businesses safe, secure, reliable and efficient.

IATA codes are mainly used for ticketing. E.g. travel itineraries use IATA codes for airports and IATA flight numbers.


How would one calculate the thrust-to-weight ratio for a minimum turn radius? I'm looking to calculate the T/W from the minimum turn radius while level, as well as the load factor while banking, and the wing loading W/S

I plan to plot the thrust to weight ratio against wing loading given the inputs mentioned above.

You can't. Turn radius is a function of true airspeed & bank angle, and nothing else. A J-3 Cub flying at 40 knots will have a pretty tight turn radius compared to an F-16 with its 9-G turn at 100+ knots, just because the Viper can't approach the Cub's low speed. Or take a KC-135R -- better T/W than a T-38, but not really a low-speed performer nor a high-G machine.

Turn radius in isolation will favor low-speed aircraft over high-speed aircraft, even when the latter have better T:W ratios.


How long will one remain conscious in the event of a sudden cabin depressurization? I know the usual scenario is where an airliner suffers from an explosive decompression and the oxygen masks drop and the plane descends to a safer altitude but.....

This is a purely hypothetical situation but if a passenger plane was cruising at 39000ft+ and it suffered a cabin leak that somehow went unnoticed by the crew and passengers and the oxygen masks didn't drop, how long roughly would it be before the passengers were incapacitated, and how long before the lack of oxygen became fatal.

The question you're asking roughly translates to What is the time of useful consciousness at 39,000 feet?. The answer is "About 15-20 seconds, once the pressure bleeds off." The FAA has a handy table for this:

From Chapter 16 of the Pilot Handbook of Aeronautical Knowledge.
You can get a PDF of Chapter 16 here, or you can grab the whole thing from the FAA

The Time of Useful Consciousness will vary depending on personal physiological factors (e.g. if you're a smoker your blood doesn't oxygenate as well - you will probably have less time. If you're a mountain climber in excellent shape and used to breathing rarified air on your climbs you'll probably have a little more time).

In the case of a non-explosive decompression (say a pressurization system failure) you'll probably have more time than this from the start of the event to the point where everyone is unconscious: the cabin pressure will take time to bleed off. Whether that time is seconds or minutes depends on the nature of the leak.

Presumably while the pressure is bleeding off the aircraft's systems will complain about the loss of cabin pressure and give the pilots a chance to address the problem (fix the pressurization system or descend to a safe altitude). Unfortunately the effects of hypoxia can start setting in before the crew realizes what's going on (which is one of the contributing factors in the loss of Helios Flight 522, which suffered just this kind of gradual depressurization).


Is there a reason Germania aircraft cabins have blue lights? On my 2014-01-18 CET flight ST2114 from FKB to LPA on a Germania airplane, cabin lights were switched from white to blue for takeoff. I recorded this in a panoramic photo.

Granted, on sunset, the sun coming in through the windows made up for a beautiful play of light: Blue and yellow are complementary colors.

Is there a security or technical reason for the blue light, or is it just for
aesthetics?

Bergische Universität Wuppertal has done some research that chronobiologically-adapted LED lighting can enhance passengers well being and they can sleep better during a flight.

This article details about this research:

  Adaptive solid-state lighting (SSL) scenarios in which the color and
  brightness of lighting is varied during long-distance overnight
  flights results in passengers that sleep better and are more alert
  upon arrival.

  ... at the start of an overnight flight that warm-white light helps to
  stimulate melatonin production and increases passenger relaxation ...
  blue-rich cold light in the morning increased alertness

There have been studies showing benefits of biologically effective lighting for more relaxed flights.


Are NDBs and VORs dying as a navigational method? I am new to aviation, so bear with me on this question:

I have read in multiple places that the VOR/NDB navigational aids are dying out to GPS. Is this true? Are more modern aircraft being built with glass, digital instrument readouts that capitalize on GPS services instead of the traditional vacuum tube ADF and VOR Indicators?

Yes, without a shadow of a doubt. Many airports now publish GNSS (Generic term for all types of satellite navigation) approaches, completly negating the need for those aids even during complex, critical phases such as approach and landing and take off and departure.

Modern GNSS systems are capable of utilising synthetic VORs where even when doing something such as flying a particular radial, the aircraft actually uses it's GNSS data to do so.

And, if you needed outright evidence, how about this quote from the UK National Air Navigation provider (NATS):

  Commercial aviation – which has always funded the upkeep of the VOR beacons – now almost exclusively relies on the use of satellite navigation (read last week’s post on EGNOS for an example), making the majority of beacons an expensive and unnecessary financial burden. As such by 2020 we will be reducing their number from 44 down to 19.

Source: https://nats.aero/blog/2015/05/has-gps-killed-off-the-vor/


Under what conditions can the maximum angle of climb be achieved for jet and propeller aircraft? I know that the maximum angle of climb is reached at maximum specific excess thrust (S.E.T.) for jet airplanes, or minimum drag or maximum $\frac{L}{D}$.

Is this true, and if yes, is this valid also for propeller airplanes, or is $\gamma_{max}$ reached at another condition for props?

What you say is true only for turbojets and aircraft with fixed-pitch propellers. Generally, all optimum points for variable-pitch propeller driven aircraft are at lower speeds than those of jet aircraft. The reason is the variation of thrust with speed: For propellers, thrust is inverse to speed, while it is roughly constant over speed for turbojet aircraft in the subsonic speed range.

Specifically, the optimum angle of climb condition can be expressed as $$\frac{\delta \gamma}{\delta c_L} = 0$$
If we assume a quadratic polar, constant propeller efficiency over speed (which means a variable-pitch propeller) and an expression for thrust which lets us model an exponential variation of thrust over speed ($T = T_0·v^{n_v}$), we can write this condition as $$\frac{\delta \gamma}{\delta c_L} = -\frac{n_v}{2}·c_L^{-\frac{n_v}{2}-1}·\frac{T_0·(m·g)^{\frac{n_v}{2}-1}}{\left(\frac{\rho}{2}·S_{ref}\right)^{\frac{n_v}{2}}}+\frac{c_{D0}}{c_L^2}-\frac{1}{\pi·AR·\epsilon}$$
The general solution is $$c_{L_{{\gamma_{max}}}} = -\frac{n_v}{4}·\frac{T·\pi·AR·\epsilon}{m·g}+\sqrt{\frac{n_v^2}{16}·\left(\frac{T·\pi·AR·\epsilon}{m·g}\right)^2+c_{D0}·\pi·AR·\epsilon}$$
For jets and fixed-pitch propeller aircraft ($n_v = 0$) the solution is quite simple, because the thrust terms are proportional to the thrust coefficient $n_v$ and disappear: $$c_{L_{{\gamma_{max}}}} = \sqrt{c_{D0}·\pi·AR·\epsilon}$$
For turbofan and variable-pitch propeller aircraft, we have less luck and get a much longer formula. This is the one for propellers ($n_v = -1$):
$$c_{L_{{\gamma_{max}}}} = \frac{T·\pi·AR·\epsilon}{4·m·g}+\sqrt{\left(\frac{T·\pi·AR·\epsilon}{4·m·g}\right)^2+c_{D0}·\pi·AR·\epsilon}$$
To arrive from here at a flight speed, I recommend to look up the speed in a polar. Solving this analytically will get messy. Below I have plotted a generic climb speed over air speed chart for different thrust loadings of a typical turbofan. The blue lines show thrust (right Y-axis) and the green lines the resulting climb speed. The two black lines show how the optimum flight speed for best climb speed and best climb angle (steepest climb) vary over thrust loadings. They are easy to find graphically: Pick the tops of the green curves for best climb and the steepest tangent from the origin of the coordinate system to the green lines for best climb angle. Note that they cross when moving from positive to negative climb speeds. With a propeller, the results will look similar, however, the best climb speed line would be vertical. This will collect all optima at the low speed range of the plot - using a turbofan makes the effects easier to see because the optima are spread out more.

Climb optima for different thrust loadings (own work)

The optimum climb speed (which is proportional to $\frac{1}{c_L^2}$) varies inversely with the square of the thrust loading ($\frac{T_{ref}}{m·g}$)² of the aircraft. With lots of excess thrust, the optimum is limited by the stall speed (the black line bends into a vertical trend), while with no excess thrust both optimum speeds $v_x$ and $v_y$ converge. This makes sense: If thrust is just sufficient to keep the airplane from descending at one speed, this speed will both give the best flight path angle and the best vertical speed (unfortunately, both will be 0 at this point). It also helps to reduce induced drag, so aircraft with a high aspect ratio wing will climb steepest at a higher lift coefficient (= lower speed).

The steepest climb optimum looks a little more compact if we use the induced drag coefficient directly: $$c_{L_{\gamma_{max}}} = \frac{2·m·g·(c_{D0}-c_{Di})}{T}$$
but since the lift coefficient is hidden again in the induced drag term, and so sits on both sides of the equation, it is much harder to draw conclusions from this version.

Nomenclature:
    $c_L \:\:\:$ lift coefficient
    $n_v \:\:\:$  thrust exponent, as in $T \sim v^{n_v} $
    $T \:\:\:\:$  thrust
    $m \:\:\:\:$  mass
    $g \:\:\:\:\:$  gravitational acceleration
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor
    $c_{D0} \:$  zero-lift drag coefficient
    $c_{Di} \:\:$  induced drag coefficient


Can this aircraft be identified by the exposure pattern of its flashing lights? Can the aircraft on the attached photo be identified from the light pattern?  While photographing this globular cluster (M 13) in Hercules, an aircraft passed through the FOV.

The width between the outer lights is 3 arc minutes and the exposure time was 15 seconds.

The photo was taken on April 23, 2019, 10:28 PM at James River State Park, Gladstone, VA.

No, based on the exposure pattern I can't identify the aircraft. But based on the other information you gave, I can. It's an Embraer 175, registration N287SY.

After looking up the exact position of the M13 Globular cluster at the time the photograph was taken, I found that the telescope had to be facing to 64 degrees (East-Northeast), with an elevation angle of 28 degrees.

I used in-the-sky.org to find the position of the M13 cluster.

I then drew the geodesic from  James River State Park in a heading of 64 degrees
I used academo.org to draw the geodesic on the map

Then using Flight radar 24's history/replay function I found the aircraft

The aircraft is an Embraer 175, flight DL3693,  flying at 38000 feet.

If we assume:

the telescope is at 500ft MSL,
pointing up 28 degrees above the horizon,
the atmosphere is ISA, and
the earth is flat,

then we can calculate that the aircraft would be approximately 21.5 km horizontally away.

Measuring that out on Google maps gives the following:

That measurement is perfectly in line with the flight path of the Embraer 175.

The slant distance to the aircraft is approximately 24.5 kilometres. The track angle of the aircraft is 228 degrees, so we see the aircraft almost from straight ahead.

The span is 26 meter, I assume the lights are at the wingtips (they are not). The distance between the traces is thus expected to be 3.5 arc minutes.  Close enough!


Why do different aircraft have different maximum operating temperatures? I was reading this Wired article about the recent Phoenix heat grounding some jets. It's a great read on why heat is detrimental to lift, but it raises a point it never answers (emphasis mine)

Phoenix just provided another reason to hate flying: the heat. With temperatures there expected to hit 119 degrees Fahrenheit, airlines canceled more than 40 flights today.
Wait. What? Airplanes can't fly because it's too hot? That's crazy.
No, not really. According to news reports, the heat poses a particular problem for the Bombardier CRJ airliners, which have a maximum operating temperature of 118 degrees. Bigger planes from Airbus and Boeing can handle 126 degrees or so.

Is this solely due to the size of the aircraft, or is it a difference of manufacturer?

There are a few different things going on here. For the best answer, see this blog post.

To summarize his points, there's a combination of factors:

The Bombardiers simply aren't certified at those temperatures.
Their combination of small wings and small jet engines makes high temperatures particularly problematic for them. With the air density decreasing as the temperature rises the wings get less lift and the engines suck in less oxygen. The bigger jets have larger wings and bigger engines which make up for their larger weight so they can fly while the regional jets can't.

So to answer your question ("Is this solely due to the size of the aircraft, or is it a difference of manufacturer?"): Yes