George
Registered Member
Joined: Feb/14/2008
Location: Golden, Colorado
Online Status: 
Posts: 16
 Skybolt
|
   Topic: tail - angle of incidence
Posted: Jul/17/2010 at 18:02 |
|
After powder-coating, we are getting our fuselage ready for covering. Does anybody flying (Skybolt with IO360) have any opinion on the angle of incidence for the horizontal stabilizer? The plans call for .5 to 1, but my friend and helper in this project (without whom I would be lost) who already build a Skybolt with an IO540 said he would love to have more. It would - of course - be not too easy to add washers once the fuselage is covered.
Anybody out there with an opinion on this? Should it depend on engine?
- George
|
|
|
|
|
|
Neil
Frequent Flyer
Tech' Advisor
Joined: Nov/10/2006
Location: Monroe, LA
Online Status:
Posts: 1288
Acro Sport II
 View My Gallery
|
Posted: Jul/18/2010 at 06:50 |
|
As long as the empty weight CG is in the right place the engine weight doesn't matter so much. Pilot weight may be more the cause for more incidence with a heavy pilot or less with a lighter pilot. About all you can do is make a "best guess" and then once the airplane is flying do what you have to do.
If I had to guess, a pilot weight over 200 would require 1.5 deg or more. Still just a SWAG. (Scientific wild @%* guess) My own thinking is that on an aerobatic aircraft the wing and tail incidence should match.
Perhaps some of the Skybolt guys that have fine tuned their airframe can be of more help.
Edited by Neil - Jul/18/2010 at 06:51
|
|
Born with nothing, still have most of it.
|
|
|
|
Skybolt540
Frequent Flyer
Joined: Aug/17/2006
Location: United States
Online Status:
Posts: 171
Steen Skybolt
View My Gallery
|
Posted: Jul/18/2010 at 08:25 |
I've asked this question for a long time of owners and large scale r/c biplane folks and here's what I know.
They all say you need more than the .5 to 1 range. One person told me (I can't recall who) that the .5 to 1 is relative to the wing angle of incidence, not the fuselage.
All that being said, I never got a really definitive answer, and I expect it's for two reasons. One is that every one of these things is different, so there is no correct angle, only correct starting points. Second is, if it's off, you tweak it by adding or removing washers until you get it right, and then who cares? No one bothers to take a final "corrected" measurement.
I'm not an aero engineer, but from what I understand, the downwash coming off the top wing causes the inflow angle at the stabilizer to be negative relative to what the wing sees, so it needs more positive incidence than the wing in order to fly straight. Makes sense to me. I confirmed this with the r/c guys who said all biplanes need more stabilizer incidence than their single wing counterparts. Don't know about high wing planes, which I would think should have the same issue.
I planned on an initial setup somewhere between 1.75 and 2 degrees relative to the fuselage. This is in the range the few people who actually knew what theirs was told me. I have heard of 2.25 and as much as 2.5 degrees (relative to the fuselage) so that makes sense with the .5 to 1 being relative to the wing, practically-speaking.
I have never heard of anyone having theirs setup .5 to 1 degree relative to the fuselage, but I do recall one guy saying his was setup to .5 on the initial flight and he almost lost it on takeoff due to the amount of down elevator required to keep it flying. I'd would think I'd err on the side of too much positive incidence, as that's more intuitive to correct (having to pull instead of push). I'd love to hear more people chime in on the matter. Anyone know what the Acrosport or Starduster plans call out?
Edited by Skybolt540 - Jul/18/2010 at 08:30
|
|
Scott In Ohio ...Spoot
|
|
|
|
George
Registered Member
Joined: Feb/14/2008
Location: Golden, Colorado
Online Status:
Posts: 16
Skybolt
|
Posted: Jul/20/2010 at 18:49 |
|
Thanks for the quick replies. Unless there will be more replies with different opinions, I will go with 2.25.
- George
|
|
|
|
