ES wing incidence discussion

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Dan OBrien
Posts: 46
Joined: Sun Feb 26, 2023 6:23 am
Location: Truckee, CA (KTRK)

A question was asked by Matt Candelaria on LancairTalk about whether right wing heaviness was common in ES's and whether he should consider lowing his right flap a bit more to get rid of it in his plane. I'll repost my answer here, as someone here is probably more knowledgeable than I am on this.
Hello all,

My ES pulls to the right. It has done this since I got it 5 years ago. I am wondering if this is normal. I seem to need a lot of aileron trim to keep it level. I have pictures showing how I adjusted the right flap down. It seems to have helped a little. Is there anything besides adjusting the flaps that I can do to get it to fly straight? Do I need to be more aggressive with adjusting the right flap? Here are some pictures:
Matt, my right wing was a bit heavy on the first couple flights, and aileron trim couldn't take it out given where that was set. We adjusted the right flap down nearly a degree to eliminate the issue. That straightened things out, though I realize I have a bit more drag than I would if that adjustment weren't necessary.

I wondered why my plane was right wing heavy. I used a smart level to check the washout in the left and right wings. Washout is the amount of twist that makes the angle of incidence lower at the tips than at the roots. The reason for washout is that we want the roots to stall before the tips. Our wings are supposed to have 2 degrees of washout. I measured a few tenths of a degree more washout on the left wing than on the right. This was "fixed" by lowering the right flap a bit.

There were something like 10-12 ES kits in some range kit # range that I don't have at my finger tips that had an even bigger difference in twist between the wings. Some of the builders of those planes used something called "eccentrics" to alter the relative incidence of the wings to eliminate the problem. I am not sure how they work, but there are Lancair ES folks out there that are familiar. (I have emails with posts on the old Yahoo ES list I could share, and perhaps some folks on this list also know.) Some builders went back to the factory and de-bonded then rebonded their wings to get the washouts equal and eliminate the eccentrics. I recall someone mentioning that that Tim Ong (he was at Lancair at the time) thought that was over-kill because the eccentrics largely eliminated the issue, maybe at the cost of a bit more drag, but some guys went back and re-bonded their wings anyway.

I am not an expert, but your right flap doensn't look any lower than mine, maybe less lower, though its hard to tell from the pics. However, it looks to me like you have more aileron trim in straight and level. You might want to consider lowering the right flap a bit more, though I suggest talking to the guys at Elite Pilot Services or some other knoweledgeable folks about this. Have you tried checking for a washout difference? If the difference is big enough, you might want to consider the eccentrics that others have used (maybe some still are using them, I dunno). I don't have more info, but JC (EPS) is on this list and might comment if he's aware of the issue, and like I said above, I could pass on relevant posts on the old Yahoo ES list, which discussed this issue at some length.
Happy & Safe Flying,
Dan
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Dan OBrien
Posts: 46
Joined: Sun Feb 26, 2023 6:23 am
Location: Truckee, CA (KTRK)

Here is an exchange about the incidence issue on the old ES Yahoo list, which was an incredible resource. (I've got almost all the emails, but the pics were mostly dropped.) This is just one small part of an extensive, open, highly informative discussion about the incidence issues. I wish the old ES list guys were all on this list. It was a great resource, with incredibly friendly and helpful participants. (The problem with trying to port the Yahooo ES List Emails over to LancairLive is that it would take significant software engineer time to make it happen).
[A Lancair employee] via returns.groups.yahoo.com
Aug 11, 2006, 6:38 PM
to Lancair_ES


......I spoke to Martin Hollmann, the ES designer, on the phone and he said that zero difference in washout was the tolerance. Based on some analysis of the ES wing tip airfoil, it's clear that the airfoil is used to maximize lift and cruise speed and never meant to ever be stalled.
1. Martin Hollman did not design the ES!?!?!?!?!?!
2. My discussions with Martin were significantly different, at no time did he say zero difference is washout was the tolerance! In fact he mentioned that 1 degree would be acceptable, more than that would be questionable. In fact his solution for the difference was to drop a flap slightly.
3. The only place that airfoil exists is absolutely at the tip .001 thick. Everywhere else is a blended airfoil and such has different characteristics. Probably not an optimal airfoil for stall characteristics, but these airplanes have fairly benign stall characteristics.

BTW, I flew [a lancair ES owner's] airplane. It is absolutely straight! He is working out some engine and avionics bugs, but has a great airplane.

I'm just finally getting to check through all my emails from OSH, I enjoyed seeing a lot of familiar faces.

Regards,

[A Lancair Employee]


----- Original Message -----
From: [A Lancair_ES@yahoogroups.com participant]
To: Lancair_ES@yahoogroups.com
Sent: Wednesday, August 09, 2006 5:48 AM
Subject: Re: [Lancair_ES] Wing Twist


Dave,

I would say .20 to .30 degrees difference and no less than 1.5 degrees total wing twist (washout) is acceptable.

*** Read on at your own risk! ***

The ES was designed with 2 degrees of twist (washout). If you build your wing cradles as described in the manual, the 2 degrees is built into the cradles. The washout is "locked in" when you close the wing.

I dealt with this issue when I had one wing with 1.7 degrees less washout than the factory setting. The other wing was right on the 2 degrees.

The solution proposed by the factory was tilt the entire left wing down and tilt the entire right wing up using eccentrics installed on the forward wing attach points. It definitely allows the plane to fly straight with no pronounced rolling tendencies. I flew that way for over a year. Some guys are still set up with eccentrics to correct asymmetrical wing washout.

First, we can all agree that two perfectly symmetrical wings is ideal. If you have asymmetrical twist a couple things happen. One, the amount of asymmetrical lift changes with airspeed so no set of eccentrics can make the plane fly straight at all speeds.

Second, and what I believe is the more critical issue, is how the wing performs at slow speeds and near the stall. The washout is there to cause the inboard section of the wing to stall first. That has the effect of giving the pilot warning of the stall before the entire wing stalls (the break). You also have aileron control at the onset of the stall. If a wing has little or no washout the whole wing will stall a the same time, not good. And having one wing stall before the other creates a dramatic wing drop in the stall, not a straight nose drop, again not good.

I did some significant research on certified aircraft on washout tolerance between wings. I read 3 Cessna repair manuals and all of them worked out to be between .10 and .20 degrees. I measured about a dozen aircraft on the ramp at my home airport. Although clearly not 100% accurate, even though I used my digital level, my sample group of old beat up Cessnas and Pipers measured out to be between .10 and .30 degrees for the most part. The worst plane was .50 degrees. I also spoke to a highly respected airframe rebuilding facility in Denver. The owner said nothing would leave his facility with more than .10 degrees from spec, often much less.

Throw into the mix that the ES airfoil has very benign stall characteristics at the root and comparatively violent stall characteristics at the tip (different airfoils). I spoke to Martin Hollmann, the ES designer, on the phone and he said that zero difference in washout was the tolerance. Based on some analysis of the ES wing tip airfoil, it's clear that the airfoil is used to maximize lift and cruise speed and never meant to ever be stalled.

So the 2 degrees of washout is there for a reason, and both wings should be very close to each other in washout to get optimum performance.

I warned you at the beginning!

[Lancair ES owner who had an incidence difference]
Happy & Safe Flying,
Dan
George Wehrung
Posts: 183
Joined: Tue Nov 22, 2022 3:56 pm
Location: KMRH

And to add the real cause was someone at the factory bent the wing jig with a fork lift and that’s what caused the issue. A builder discovered the error during his build and after much persuasion the factory investigated…


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