RE: Re: 2015 Wright Stuff plane

From: Chuck Etherington <chuck.etherington_at_jeppesen.com>
Date: Mon, 17 Nov 2014 20:12:43 -0700

In reference to: “now that Chuck has tried to clarify Bill’s answer there is a little more to explain.” Actually there is a LOT more that could be explained but it is not useful for the purpose of this discussion.

- Chuck

From: Indoor_Construction_at_yahoogroups.com [mailto:Indoor_Construction_at_yahoogroups.com]
Sent: Monday, November 17, 2014 3:27 PM
To: Indoor_Construction_at_yahoogroups.com
Subject: RE: [Indoor_Construction] Re: 2015 Wright Stuff plane


Of course Bill is the best and I was happy to leave it at that but now that Chuck has tried to clarify Bill’s answer there is a little more to explain. If you assume the convenience of a Lift force at 25% of the chord then you also need to mention that there is usually a Pitching moment associated with the Lift. If the wing (or tailplane) section has positive camber then the pitching moment will be ‘nose down’. On typical Indoor models with large tailplanes and, usually, cambered surfaces the pitching moments can be significant.
John Barker - England

From: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com> [mailto:Indoor_Construction_at_yahoogroups.com]
Sent: 17 November 2014 16:16
To: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>
Subject: RE: [Indoor_Construction] Re: 2015 Wright Stuff plane


Bill; you’re the sharpest knife in the drawer as far as I’m concerned. You’re right about CG behind the wing having a lifting stab. The wing has a Center of Lift (CL) which is usually at about ¼ chord (25%) of the wing. If the CG is behind that point, the stab will be lifting.

Chuck Etherington



From: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com> [mailto:Indoor_Construction_at_yahoogroups.com]
Sent: Monday, November 17, 2014 8:50 AM
To: Indoor_Construction_at_yahoogroups.com<mailto:Indoor_Construction_at_yahoogroups.com>
Subject: Re: [Indoor_Construction] Re: 2015 Wright Stuff plane



I'm not the sharpest knife in the drawer on aerodynamics but I believe that any model with a CG behind the wing has a lifting stab. People not involved with indoor models might say this is a bad idea but it is very common and very successful on some models. Here's approximately where mine are (all with rubber):

WS - 1/2" in front of TE
LPP - 1 3/4" in front of TE
A6 - 2 1/8" behind TE
F1M - 1/8" behind TE
On 11/17/2014 9:41 AM, dweigt47_at_gmail.com<mailto:dweigt47_at_gmail.com> [Indoor_Construction] wrote:


Thanks, guys, for the quick answer. I'll have to look at the Chuck Marcos explanation and see if I understand it.



Lots of aviation people seem to think the horizontal stabilizer only pulls down to raise the nose to regulate speed and provide that pitch stability. That may be true, on planes with CGs in the 30% chord range and symmetrical stab airfoils. My casual analysis of free flight designs, their lifting stab airfoils, and their CGs well behind the trailing edge, showed me that simply isn't true. But, I've never gone their myself.



It seems to me, these rearward CGs you use put the planes somewhere between classic conventional aircraft and classical canards. More like true tandem wing designs. I have basic notions of how to do that, but am certain I have a great deal to learn.



I appreciate your putting up with my newbie ignorance. You do it with grace and polish.



Don


Received on Mon Nov 17 2014 - 19:12:50 CET