Re: Ground AoA/ tailwheel angle


David J. Gall
 

Mike, why are you looking at the main wing here? It’s the canard that controls liftoff speed….

 

From: main@Q-List.groups.io <main@Q-List.groups.io> On Behalf Of Michael
Sent: Friday, January 7, 2022 6:28 PM
To: main@Q-List.groups.io
Subject: Re: [Q-List] Ground AoA/ tailwheel angle

 

Finally found the Wainfan references I was looking for; wanted to make sure I wasn't crazy before weighing in. The following is quick, back of the envelope engiNerding meant for illustrative purposes more than anything, so play along for funsies...

Aerodynamically, the best things to reduce takeoff roll are to reduce wing loading and get as close to maximum lift coefficient (Clmax) as possible. Our wings are pretty well fixed (pun intended) so that leaves us getting close to Clmax via mounting angle (angle of attack). Looking *just* at the main wing airfoil, at a close but not perfect takeoff condition since I'm lazy (Reynolds 1M vs ~800k), we see Clmax occurs ~15 degress AoA. We are a tandem wing airplane, so we can't get close to that.

So the next best thing we can do is get as much angle as possible before drag (Cd) goes straight through the roof. That appears to happen in the 10ish degree range:



A good bet here - where we can't achieve max lift - would be to maximize "lifting efficiency", or Cl/Cd for us engineer types. That appears to occur within a neat little plateau from around 10±2.5 degrees...SMACK where Jay has observed it on flying airplanes:



So basically...don't stress it too much. There's a fair bit of wiggle room, and Flying Airplanes don't lie 😉
--
-MD
#2827 (still thinking about planning on visualizing how to finish building)

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