The Seagull has landed

[Martin Harris - Moderator]

Those fears may still not be justified - my blue/yellow 120 FS powered (and later 180 FS) version needed the batteries (2 x 2S 18650 1100mAh LiFe) mounting on a piece of 1/4" balsa sheet to get them as far back as the construction would allow!

[Gary Manuel]

This next bit is what I've been putting off until the last minute as I'm dreading where it might lead.

Anyone following the thread may remember that I've not liked the way the model behaves in tight loops. I've found and fixed a problem with a warped tail, but I also suspected that the wings may also be warped because of the amount of aileron left trim it needed.

Here's how I checked the wings - starting with the right wing.

Aileron clamped in the neutral position and Clinometer zero'd using the canopy seat as a reference.

Root was measured at 0.1 degrees.

Tip was measured at -0.2 degrees and has a chord of 220mm. That's minus 0.2, so there is 0.3 degrees of (clockwise) twist in the wing (the trailing edge at the tip is higher than at the root).

This calculates at 220 Tan (0.3) = 1.15mm, which sounds reasonable to me.

Now on to the left wing.

Clinometer zero'd as before.

Root measured at 0.4 degrees.

Tip measured at -1.0 degrees.

That's a total of -1.4 degrees of clockwise twist.

This calculates at 220 Tan(1.4) = 5.37mm (The trailing edge at the tip is lower than the root).

So the right wing tip is 1.15mm high and the left tip is 5.37mm low - or 6.52mm total.

No wonder it needed so much left trim and it's not flying properly!

Now has anybody got any suggestions for straightening the wings up?

I've tried a bit of heat with twist pressure applied but it's made no difference. The whole wing is quite stiff, but apparently twisted!

[Bruce Collinson]

try to find the new wings which were at Elvington?

[Martin Harris - Moderator]

Ouch! You've got a nasty streak in you Bruce...

[Gary Manuel]

It's the best suggestion so far ....

[iqon]

you could always sell it !!! cheap

[Gary Manuel]

Posted by iqon on 22/08/2018 17:57:14:

you could always sell it !!! cheap

Oh yeah. Why didn't I think of that?

[Bruce Collinson]

Martin,

Nasty? It was serious! Brand new wings, almost certainly for the same variant (see above), probably take £20. Probably, when I post something nasty, you’ll know the difference.

Now to build a battery tray. Wonder if my wings are bent?

[MaL]

As the wings swivel on the main wing tube and are fixed by two (plastic) screws that fit through each fuz sides perhaps you can 'introduce' a corrective adjustment by filling and re-drilling the holes in the appropriate direction?......

[Bruce Collinson]

Ooh that reminds me. Last Sat when doing noisy tests the Best Flier in the Club, who kindly checked and maidened it prviously (it's the keyboard skipping strokes not me and I'm fd up going bak) brought his spirit level and concluded that it needed a tad of negative incidence.

A medium length debate ensued as to how to achieve this, the consensus being that elongating the bolt holes and installing further ply location tabs to move the bolt position was the best bet. If I got this right, and don't quote me, Terry believes that to fly properly it needs this adjustment. We agreed to defer it until the silencer, c of g and cowl are addressed.

Whether this would deal with Gary's bent wings is another matter, I suppose. Presumably trimming the ailerons is anathema?

Didn't finish the battery tray. Out tonight. Touch and go for Sat.

[Gary Manuel]

I'm thinking more along the lines of straightening the left wing up by soaking in water / Ammonia or whatever.

The incidence angle at the root looks OK, so there's no point adjusting that to my way of thinking. The problem is at the wing tip.

Edited By Gary Manuel on 23/08/2018 15:36:41

[Bruce Collinson]

Wondering whether steam would work.

Stickmakers bend and straighten walking sticks of many different hardwoods by putting them in a plastic soil stack tube, sealing both ends then connecting to a wallpaper steam stripper. That's how umbrellas and walking sticks get a 180 deg bend for a handle. I believe an hour renders them extremely ductile, and they set on cooling down.

Clearly, raw steam would be unhelpful for a wing, but if the temp could be regulated, maybe a big plastic storage chest would work with regulated exhaust too ... just thinking out loud. Balsa is a hardwood.

Lots of info on t'Interweb, as ever.

[john s]

Gone a bit quiet!!

Flew mine this morning with some trepidation, I'm not a very good flyer!, and was pleasantly surprised by its handling, I only got one flight in as I broke the wooden prop on a quickish landing running into long grass at the runway side, but it flew and landed well requiring only a couple of clicks trim on elev and ailerons.

I set the C of G very carefully at 135mm from the wing root leading edge, this is quite a bit fwd of Seagulls recommendation, I'm not saying this is perfect but it gave me a comfortable handling machine for its initial flight.

Right off to buy some props!

john.

[Gary Manuel]

Posted by john s on 04/09/2018 12:26:57:

Gone a bit quiet!!

I'm still pondering what to do with the warped wing. I've been putting it off to be honest.

[john stones 1 - Moderator]

I can't picture how much twist you're talking about, Mals idea of adjusting at the root sounds worth thinking about to me, gonna be very difficult to get a twist out of a covered wing, looks like it's get the covering off underneath and get stuck in, or settle for a compromise. Can we have a picy of the culprit ?

[MaL]

So...the starboard wing has 0.3 degrees of washout, so no problem there, but the port wing has 1.4 degrees of wash 'in'.. which is not good.

You seem to me to have 4 choices...

1. Remove the covering on the port wing and steam/ ammonia it straight(er), and recover it.

2, Redrill the mounting holes to give the port wing 1.7 degrees anti-clockwise rotation (increasing the tip washout and balancing the lift from both wings)

3. See if Seagull will send you a new pair of wings

4. Live with the port trim.... now you have straightened the tailplane has that cured the screwing out of tight loops?.. IIRC the one I had didn't take kindly to too much elevator, but was fine in big loops and inverted loops so I reduced the elevator travel. It still had plenty of authority when landing.

[Chris Walby]

Gary, Just being a bit dense here so bear with me. Is one wing warped with a twist in it or does the tip sit higher than the other side (like added dihedral)?

If its twist can't you set the middle of the wing straight (then the tip will be up and the root down by the same amount) by adjusting the wing bolt locations. Knowing Seagull you will need to re-glue every joint in the wing if you get it to move!

If its got a bit more "dihedral" than the other side then it will be a bit more tricky unless you off set the wing tube I the fuselage!

I know the above does not address the issue directly, but it might get it to fly in a reasonable way.

[john s]

Forgot to mention that I also reduced the low rate control throws from recommended by around 20-25% for its first flight, it still had plenty of elev authority but was not at all twitchy.

I agree with what the other guys are saying about adjusting the bolt holes on the offending wing and adjusting for the best compromise, worth a try and you may be pleasantly surprised.

john.

[Bruce Collinson]

John S,

Out of interest, do you have expo programmed in? I was trained/taught always to soften the initial movement on all 3 primary controls and was very surprised to read a thread here a few weeks back wherein the consensus was against expo, particularly for learners.

Battery tray just fitted. Vanessa is in the outside Mancave and it’s pitch dark.

BTC

[Gary Manuel]

I think I'll only be satisfied if I can remove the warp from the wing properly. It looks like the covering will be coming off. Maybe I can just peel it off from the leading edge and not touch the trailing edge.

The way I see it, the wings must have been made in a jig, so they will have been straight at one time. The warp must have happened later, probably as the sheeting dried out. If I give the sheeting a good soaking and then re-jig the wings as they dry out, hopefully the warp will be removed.

[Chris Walby]

Gary,

Do you have to set it straight or slightly more so it can relax back? Then go around the complete wing and make sure all the glue joints are okay.

Then get the covering back on, must say you do like a challenge

[Gary Manuel]

Good point Chris.

I guess it's inevitable that it will spring back a little when I liberate it.

[Bob Cotsford]

I had to rejig a pre-built fuselage, even though I removed and reglued the formers and wetted the balsa well then left it in the jig for several weeks it still took on a very slight twist after a few days out of the jig. Definely jig it a hair past straight and true! I am surprised that a good blast with the heat gun couldn't get rid of a few mm of twist, it must be the odd well glued artf wing!

[Bruce Collinson]

Reverting to my heat/steam analogy, is the issue with heat that it’s very difficult to get all of the “twisted” timbers to an adequate heat level at the same time, without which the unheated warped timbers will still be fighting against those which have been straightened?

Probably, that’s why the wings won’t straighten under heat with the covering on.

I’m starting to wonder whether there’s anything to lose by establishing the safe temp for the covering film then sealing the wings in just less heat for an hour before jigging them true/weighting down and waiting.

I recall retrieving a 100 yr old pine architrave from the dip and strippers (not that sort Cymaz) with a horrendous twist. I repeatedly soaked it whilst applying opposite torsion and after a week it went “boing” (think Zebedee) as soon as the clamps came off. I ended up dragging it back to true with twice as many screws and plugs. I’d try heat if I ever had to do it again.

BTC

[john s]

Hi Bruce,

yes I use around 30 expo initially then if the plane survives tune in expo and control throws to suit the way I fly. I have tried higher expo rates but found them to be too unresponsive around stick centres for me.