Unequal wing incidence - help needed

[Erfolg]

Ken,I have or that should be had a model which suffered a handling problem, related to an inaccurate wing.

The model is some 30 years old. How it was built etc is long forgotten.

I initially flew the model at my first club, without any real issues. It seemed fine for stooging about. However I wanted a "A" certificate, which necessitated me joining another club, as club No.1 does not use the BMFA system.

At club No.2, the model was put through its paces by one of the club instructors. Who was not happy with the model at all. The club also requires the user to undertake two loops, to be permitted to fly without supervision and a few other non BMFA manoeuvres, as the site requires a degree of skill in excess of the "A" test.

The point is that it became apparent that the model was speed sensitive, really showing up with the second loop, tending to screw out, correction being very dependant on the prevailing wind strength on the day.

Even simple manoeuvres like the figure of "8" required a lot more input than a true wing.

In the end i have rewinged the model, it looks identical, but is truly true. The model has become totally predictable, in all conditions.

In short, trimming out for one speed, works for that speed, at others, the modeller has to work much harder.

Incidentally, I cut the wing in halve, rejoined after setting up to guarantee success and perfection in my mind. I totally failed, it was if I had not bothered. But events have shown, it was just the wing. I had built a dog.

The new wing only took a week, cost about £5 in film.

Edited By Erfolg on 26/01/2014 16:49:28

[Colin Anderson]

Today I took the weights of the wing panels. Weighing the wing panels down with opposite twist spears to have done the trick. The wing is now true. Whether it will stay that way, now that the weights are off, will remain to be seen.

[john stones 1 - Moderator]

your on a roll Colin

hope it stays put for you

[Martin Harris - Moderator]

I used to have a share in a 1935 Rhonbussard glider which had been rebuilt (and modified) by a German university group with a 1 degree twist in one wing. The German airworthiness authority condemned it and said the wing would have to be completely rebuilt from scratch. The glider ended up at an international vintage meeting in Holland where, after some tentative enquiries with the British Gliding Association, it was bought for a very cheap price and brought back to England. The BGA's chief technical pilot test flew it and found a strong rolling tendency but recommended fitting some aluminium trim tabs to the trailing edges, whereupon it was issued with a Certificate of Airworthiness and a pretty high VNE (maximum speed allowed) of 95 knots.

Some years later, I bought my share in it and can honestly state that the tabs worked over the whole of the normal speed range with no noticeable change in trim - except on one very still air early morning flight where I was trying to establish some performance measurements and took it to close to VNE (this wasn't far off a vertical dive!) and I then found I had to hold off a little roll.

Many years later, I built a 1/5 scale model of the glider and agonised whether to to fit dummy trim tabs - but after covering and checking, I found I'd built in some twist - and on checking, it was even in the same direction! That made the decision to fit the scale trim tabs rather easier and, true to full size, the model trimmed out nicely and there were no adverse effects in flight.

...I've also trimmed out a very warped DH 71 model for a clubmate which also flew absolutely fine with massively deflected ailerons at neutral so even if a bit of twist creeps back in, I don't think you'll have any real problems, Colin.

Edited By Martin Harris on 29/01/2014 00:53:59

[Biggles' Elder Brother - Moderator]

Great story Martin! Funny old world isn't it?

BEB