W&B, angle of incidence

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Postby Kevin Horton » Thu Jan 13, 2005 9:31 am

mr157ifhz wrote:Aha! no sooner had I posted that I realized what I think you were trying to say. With the lift moved back, and with no cg changes, the front end is effectivly 'heavier', requiring more downforce at the tail to counteract. Now I can sleep.
-Matt


The lift hasn't moved back at all. The wing is still in the same fore and aft location. At a given speed, the wing will be operating at the same angle of attack as before.

Given the info I now have at hand, my biggest concern with this change in the wing's incidence is structural. I.e. is the mod structurally sound? There will be some changes in handling qualities, but they probably won't kill anyone. Wing attachment failure is a different story. Matt is satisfied that the change is structurally sound, so I think our work here is done.

Matt - please let us know how the aircraft flys with this mod, once you have done some testing. What changes in performance and handling did you observe?
Kevin Horton - RV-8 - 80% done, 80% to go
Ottawa, Canada
http://www.kilohotel.com/rv8/
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Postby mr157ifhz » Thu Jan 13, 2005 2:49 pm

Ok. Will do. I thought I was missing something; that being the wing would be lifting back slightly, as well as up with the increased angle. I can see now it would not make much difference at all, my thinking was sound before. It is a balmy 17c here in Hamilton, too bad it is so windy (60km/h), otherwise I would go flying! Weekend looks good, but back to winter temps.
-Matt
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Postby mr157ifhz » Mon Apr 11, 2005 8:13 pm

It took a while, but finally got in first flight with the new wing angle. The biggest difference, seat of the pants, was that the plane now cruises at a nice level attitude. It has been over 4 months since I last flew this thing, so it is very hard to compare before and after. Very hard to tell if I was off the ground sooner or not. I have picked up 5mph in cruise, not as much as I was hoping for. The ailerons seem to be heavier than I remember. I would guess that is due to some slight changes in bellcrank angles as a result of adjusting for the lower trailing edge of the wing. I will make new pushrods to get the angles back to normal.
Overall, I think it was worth the effort.
-Matt
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Postby Kevin Horton » Mon Apr 11, 2005 8:30 pm

Glad to read that you have the aircraft flying again, and that the initial results are positive. You should do a careful flight test program to learn how your new aircraft flys. I say "new aircraft", because the change in wing incidence and change in aileron linkages will make it different from before. So don't assume that it will fly the same as before. Do the flight testing to feel it out, and learn how it behaves.

You can find lots of good info about suggested flight tests to perform in FAA Advisory Circular AC 90-89A. It is available on the FAA web site, or you can get it from my web site.

AC 90-89A on FAA web site:
http://www.faa.gov/avr/afs/acs/90-89a.pdf

AC 90-89A on my web site:
http://www.kilohotel.com/rv8/rvlinks/90-89a.pdf

Good luck. Fly safe.
Kevin Horton - RV-8 - 80% done, 80% to go
Ottawa, Canada
http://www.kilohotel.com/rv8/
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