RCU Forums - View Single Post - Base to final, cross wind stall
View Single Post
Old 10-27-2014, 06:37 AM
  #27  
JackD
My Feedback: (4)
 
JackD's Avatar
 
Join Date: Feb 2002
Location: Berkeley, CA
Posts: 759
Received 3 Likes on 2 Posts
Default

Originally Posted by Rob2160
Thanks Hoss,

The easiest way to understand stalling and recovery is to understand that your Elevator joystick is effectively an angle of attack control. The more back stick you apply, the greater the angle of attack will be on your wing.

Example below -

With neutral elevator stick assume your wing has 3 degrees angle of attack (normal for level flight) and full elevator deflection results in 23 degrees angle of attack.

Call neutral elevator position (0%) and full back elevator (100%)

Moving your elevator stick from neutral to full back results in a 20 degree angle of attack change. (so every 10% movement of the stick gives you 2 degrees angle of attack change)

If you move the stick 50% (half way) you have 10 degrees more angle of attack.

Assume our wing stalls at 18 degrees. (The stall angle of a wing is a fixed value and is independent of speed)

Now compare different Elevator stick positions (%) to the Angle of attack it generates (degrees)

0% = 3 degrees - unstalled
25% = 8 degrees - unstalled
50% = 13 degrees - unstalled
70% = 17 degrees - unstalled
75% =18 degrees - stall
80% = 19 degrees - stall
100% = 23 degrees -stall


Following this logic, you can see that every time you apply more than 75% elevator, your aircraft will stall. Relaxing the stick by just 5% will unstall the wing.

An aircraft will not stall by itself. The pilot is the one who makes the aircraft stall by using too much elevator.

These numbers are simplified for this example and will vary for your aircraft. The exact stick position to generate a stall in your aircraft depends on factors such as CG, mechanical throws of your servo / linkages and also the design of the aircraft, factors such as flap setting, prop wash / thrust setting etc will also change this position slightly.

But the basic concept is true for all aircraft. Your joystick controls the angle of attack. Pull too much elevator and you will stall.

To answer your original question Pete, your ARF Bandit may stall with the elevator stick at 90% deflection, but your balsa Bandit for reasons listed, may stall with only 60% stick deflection.

If you have been flying the ARF and using 65-70% elevator without stalling, then you fly the Balsa Bandit with the same inputs it will stall.

You develop short term muscle memory every time you fly due to feedback from the spring tension on your joystick

If you flew the ARF and acquired short term muscle memory, then flew the Balsa Bandit using the same (pressure) inputs it would stall where the ARF did not.

EDIT: after writing this I realised you can set up a basic stall warning horn in a radio like the Taranis. With a bit of fine tuning it could be very accurate.

https://www.youtube.com/watch?v=FAUTFjhYKTU
Rob,

it is not that simple. Power and Speed will affect the angle of attack for a specific stick position... Elevator effectiveness is a function of speed, so you cant assume same angle of attack for similar stick position across the whole flight envelope

Unfortunately, for us RC pilots, stall identification is an art. You feel your stick effectiveness, you see your plane, early behavior, etc etc... But hey!, that is part of what makes it fun!!!

Pete, Sorry to hear about your crash. One question: Did you build the plane, are you sure the wings are true? I really suspect a combination of increased wingloading (fuel almost full) and trying to maintain groundspeed (Yes groundspeed) coming out of a headwind direction to a cross wind one. Again, Groundspeed, we know the airspeed is a different story and it is not affected by changes in direction, other than the energy you lose turning...

BTW, thanks for spotting for me and Steve during our failed attempt at a Sabre formation

Later
Jack