Canard/Elevator Issue/Problem

Issue Statement

The problem is, I seem to have somehow cut the canard with the trailing edge (and the elevators) about 1/8" low, although I used the elevator mounting templates when attaching the elevator hinges. Here's a diagram of what I've got in relation to what it's supposed to look like:

As I said, the offset is about 1/8". The canard is smooth, the airfoil shape on the canard and the elevators match up with the templates (except for the last 1" of the canard where it slopes down too far).

So, I had the following questions: Do I need to completely remake my canard or the trailing edge? Do I need to remove the elevator hinges and raise the elevator 1/8"? Or can I just leave everything the way it is? Is there some other resolution?

Obviously, I have concern from an aerodynamic and safety standpoint, and want to make sure that I will be able to fly safely. If it's only a question of one or two knots in speed, I won't be concerned. If I need to perform some major rework, of course I'll do it, but if it's safe the way it is, I'll leave it.

Resolution Plan

After writing to Nat Puffer, Vance Atkinson, John Roncz, posting to the COZY mailing list and rec.aviation.homebuilt, I received a goodly number of reasonable responses, which I will summarize here. I'll list them in my completely subjective determination of quality, and summarize and paraphrase:

From Nigel Field and Nick Parkyn:
This is important - don't fly like this. Fix it by adding foam and/or glass to the top of the trailing edge of the canard to build it up to the correct shape. Sand away the bottom of the trailing edge of the canard, and then re-glass to join with the new glass from the top surface. Now, the canard is correct. Then rip out the hinges and re-install them 1/8" further up. Then, re-do the wingtips to match the new trailing edge and elevator.
From John Roncz (THE MAN):
(Incidentally, I got a response from him within 24 hours - I was VERY happy!). John said (after looking at the web page picture) that if it was HIS plane, he'd fly it, see if it exhibited any bizarre behavior, and then fix it if it did. He felt that it might raise the effective angle of attack slightly (the way it is) and that the hinge moments might increase slightly, affecting the stick forces. He didn't think it would be significant, however. (Some other respondents had the same basic comments).
From Nat Puffer:
Nat didn't want to commit to what the changes might be, but suggested building up the BOTTOM of the canard 1/8" with filler to blend into the bottom of the elevator.

Some people suggested (and offered) to perform computer analyses of the two different airfoils to try to predict what might happen. Given my experience with Finite Element Analysis and Fluid Dynamics codes, I don't think that the uncertainty involved here would tip the balance one way or the other as far as what I should do, and would involve as much work on the part of myself (and others) as just fixing the damn canard :-).

So, what am I going to do?

While I'd really like to ignore it, and follow John Roncz's suggestion, I've about run out of money for a while so I can't work on the landing gear (the next chapter in the ad-hoc schedule). This will give me a month or two over the winter to follow Nigel and Nick's recommendations (and many other people's suggestions) to fix it, and NOT fly as it is, and it'll cost less than $100 to do so.

What's an extra month over 4-5 years, when my safety's at stake, eh? :-).

Addendum to: what am I going to do?

After more thought, and a remeasuring of the canard, I've decided to follow John Roncz's advice and see what happens. I've had discussions with L.E. builders who've said that they've seen any old crap that people build get into the air, and I'm nowhere near what they described as "any old crap". The offset measures closer to 1/16" than 1/8", after a remeasurement. Anyway, that's the current plan.

Thanks again to everyone - I really appreciate it. I urge everyone to check their airfoils against the templates before and after hotwiring and sawing off the "fishtail" - had I done that, I'd have saved myself a lot of work.

[Prev][Next]