<p>There's a simple formula for calculating to force due to moving air, usually called <a href="https://en.wikipedia.org/wiki/Lift_(force)#Lift_coefficient" rel="nofollow noreferrer">the lift equation</a>.</p>
<p>Wing (or in this case tail) area, * speed squared, * lift coefficient * air density  * 1/2 (for 'reasons')</p>
<p>If you work in metric, speed will be in meters/second, area in meters squared, and air density can be approximated to 1. The result will be in Newtons.</p>
<p>The lift coefficient changes with angle of attack and rudder deflection, and a bunch of other things, but the maximum occurs when the aerofoil stalls and is usually around 1 for models (highly developed airliner wings with flaps and slats can reach 1.6)</p>
<p>The problem with this approach is that you have to estimate the maximum speed of the model, and (because it's squared) a small error can change the result a lot. That's why full-scale planes have a &quot;Never Exceed&quot; speed.</p>

CC BY-SA 4.0
2024-12-10T13:10:00.880Z
2024-12-10T13:10:00.880Z
Robin Bennett
<p>Take the maximum dynamic pressure the tail surface is likely to experience. Multiply with area and the maximum lift coefficient (probably 1.6 - depends on the Reynolds number and flap deflection!). Use the result for stressing the structure.</p>
<p>Model airplanes can be made to survive all flight loads without much of a weight impact. The highest stresses are most likely from ground handling, anyway. Only when designing larger airplanes will overengineering the structure begin to have a weight impact. <a href="https://aviation.stackexchange.com/questions/32325/what-are-the-physical-laws-for-upscaling-an-rc-model-to-11/32335?r=SearchResults&amp;s=1%7C80.0283#32335">Scaling laws</a> will explain the reason.</p>

CC BY-SA 4.0
2024-11-05T16:17:23.633Z
2024-11-05T18:16:33.947Z
2024-11-05T18:16:33.947Z
Peter Kämpf
<p>I am designing the empennage of a large RC aircraft. How does one model or calculate the maximum force and moment experienced by the vertical stabilizer? Particularly when the aircraft rolls up to 90 degrees.</p>
<p>Thanks</p>

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How to model force experienced by vertical stabilizer
Gemma
# How to model force experienced by vertical stabilizer

(Asked by: username_0 on 2024-10-31)

I am designing the empennage of a large RC aircraft. How does one model or calculate the maximum force and moment experienced by the vertical stabilizer? Particularly when the aircraft rolls up to 90 degrees.

Thanks

**Tags:** untagged

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## 2 answers

### Answer by username_1 on 2024-12-10. Score: 0

There's a simple formula for calculating to force due to moving air, usually called [the lift equation](https://en.wikipedia.org/wiki/Lift_(force)#Lift_coefficient).

Wing (or in this case tail) area, \* speed squared, \* lift coefficient \* air density \* 1/2 (for 'reasons')

If you work in metric, speed will be in meters/second, area in meters squared, and air density can be approximated to 1. The result will be in Newtons.

The lift coefficient changes with angle of attack and rudder deflection, and a bunch of other things, but the maximum occurs when the aerofoil stalls and is usually around 1 for models (highly developed airliner wings with flaps and slats can reach 1.6)

The problem with this approach is that you have to estimate the maximum speed of the model, and (because it's squared) a small error can change the result a lot. That's why full-scale planes have a "Never Exceed" speed.


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### Answer by username_2 on 2024-11-05. Score: 0

Take the maximum dynamic pressure the tail surface is likely to experience. Multiply with area and the maximum lift coefficient (probably 1.6 - depends on the Reynolds number and flap deflection!). Use the result for stressing the structure.

Model airplanes can be made to survive all flight loads without much of a weight impact. The highest stresses are most likely from ground handling, anyway. Only when designing larger airplanes will overengineering the structure begin to have a weight impact. [Scaling laws](https://aviation.stackexchange.com/questions/32325/what-are-the-physical-laws-for-upscaling-an-rc-model-to-11/32335?r=SearchResults&s=1%7C80.0283#32335) will explain the reason.


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