CO2 Bleriot - Rebuild

This is a model I built a while ago in 2009 and has been hanging in my workshop for the past few years. I think its probably time I gave it a bit of refit and got it flying again.



Its sort of scratch built though I think I had scaled plan to base it around. It has lots of carbon strip in the fuselage, I actually laminated flat carbon strip with the basswood to form the longerons so its surprising sturdy. Its powered by a Gasparin flat twin CO2 motor and is about 30" span so 1/12 scale. Its only 6oz so quite slow in flight

The model flew ok but really could do with bit more down thrust , though it has a lot already. It didn't get flown much as the trailing edge would warp very badly, I had to soak and then clamp the wing flat for a few days before flying it which made it a bit of a chore. Probably my over doping of the Jap tissue or just not accurate enough in the wing building ?? not sure??

Theres a couple of videos of it flying if you're interested on youtube

Bleriot flights

Bleriot maiden flight

My plan is to fit a carbon strip to the tailing edge , replace the damaged wing ribs and recover . I had thought I would convert it 2 channel RC using micro 2.4GHz RC gear. My logic being if I had elevator control I would not need to increase the down thrust as I could ride the nose up tendency with the stick. Also as it's controllable it may get flown more as there is less risk of damage ( or should that be more risk of damage due to..er pilot error ....not sure).

Anyway having watched the flying videos again I'm now thinking maybe I wasn't that far off with FF so maybe I should rebuild as it is as FF and add some down thrust to stop the nose up attitude into wind

Any thoughts out there ??

Chris

That looks a very nice and intricate model Mr Squirrel

Hi Eric
Yes I'm thinking it makes more sense to keep it FF.

Two different videos , grass is much longer in the first !!

Me too for F/F I see the wing warp you noted.Yes I would add carbon to it. Re the down thrust leave as is and put a bit of positive incidence on the tailplane .Or reduce wing incidence ??? Just my H'aporth

Thanks One Tenor.

As a Free fighter I get fixated on the glide which positive incidence would make steep ... but I think with a CO2 motor where it lands 'under power ' that may well work, Thanks

Hi Chris, fantastic model. I'm a massive CO2 fan although I don't 'do' much for lack of time. I have several motors but I dont recognise that twin - is it a Gasparin rather than a Gmot?
Looking at the good fligfht, I don't reckon there's much wrong with it as is. I'd only put radio in if you can't fly it often enough because of access to a suitable field.
I would laminate flat carbon strip vertically in the te, it should be stiifer than narrow rod. It needs to be prevented from twisting. Sorry if that's egg-sucking for you.
N

Thanks Nigel.

The motor according to the docs I got with it is a Model Technic GM-300T, this was stuck to the box when I got it (from eBay)
Vertical strip is what I was thinking too good to hear from another thanks
Chris

Interesting. My G300 has a nylon crankcase and my G120 twin has a single piece turned ally ccase. Nerd message out... Send us some pics, I'm sure they will cheer Gary up.
N

Yes I have a couple of GM300's and this has a very different crankcase but the cylinders and heads do look the same as GM 300's

Here's a GM300 for comparison

For what it's worth, here's my two-penn'rth:

You Tube - model looks good and flies well, but it's a little pitchy and has some spiral instability. Moving the C of G forward would help both.

Down thrust - increasing the incidence on the tail or reducing it on the wing will not cure the problem. If the model pitches up under power, it needs more down thrust.

TE - I have to say that I avoid using carbon on lightweight FF models like the plague. It's heavy, the adhesive you require is heavy and it's stiff. i.e it prevents bending which will lead to breakage at the point where the carbon stops. My fix would be to strip the wing, replace the TE, steam the wing before covering and pin it down until dry. Cover with Esaki tissue and water or steam shrink, pinning down until dry, then dope with non-shrinking dope, again, pinning it down until dry. The result should be light, warp free and the wing will keep it's flexibility.

The motor - the crankcase looks very much like the Gasparin twins I have in my CO2 box.

I hope that all helps.

.Yes Andy is right as he usually is I must read more slowly Re the TE maybe a harder grade of wood set in on edge spliced in or shorten the ribs and set it on the front face of TE.Say 1/32" Wont be as heavy as carbon. If not do as Andy suggested

Thanks for the advice Andy, much appreciated. I will try moving the CG forward first before I add more down thrust , I had not seen the spiral instability or identified it as instability.. but now you point it out !

With the TE I will try again with just a balsa strip, I built the original pretty much as you recommend BUT I used thinned shrinking dope, maybe this is the cause of the warps ? It was straight when I built it but over time its just keeps moving to the point where the ribs have distorted. I think accurate re-building of the wing will help as well the distorted ribs may have been a tad too long and under compression which wouldn't have helped.

I've also decided against any RC conversion, I'll keep it FF

Right time to strip some tissue

Chris

All good decisions Chris.

You can fix the spiral instability with dihedral - The Shuttleworth example has significant dihedral, which gave us some major handling issues, but that's another story!

I've added a link to a YouTube clip off the Shuttleworth machine, there's enough there to illustrate the rather excessive dihedral:



If you move the C of G forward, you'll need more down thrust as you'll increase the static stability. i.e. as the model speeds up (under power for example) it'll pitch up more with a forward C of G as you'll need more up elevator to balance the C of G change.

Looking closely at the wing, I would say that the ribs are very thin at the rear end. If you are fitting a new TE, it may be worth considering thickening the ribs a bit to give them more stability.