Slingsby firefly

[fly boy3]

Hi all, a fellow clubman has just completed building the above model from a plan. He is a very experienced flier and builder. Waiting for weeks for improved weather to maiden the model. Has anyone built this model, and should he be aware of anything untoward on his maiden. Thanks ps, model is Laser 120 powered.

[Gordon Whitehead 1]

That sounds like the model designed by one of the Gordon Whiteheads. I'm the GW that didn't do that one, but if it's a very old plan, Traplet sent it out with the CG marked in the wrong place.

Traplet used to forward letters of complaint to me from people who tried to fly it with the wrong balance point, despite the fact it wasn't my design. Eventually and after much cajoling from me via letter and phone, Traplet contacted the other GW and got the balance point corrected on the drawing - or at least they told me they had. Regrettably that was very many years ago and I was never informed where the balance point should be anyway. So if it's been built from a recent plan the CG should be OK. But I can't guarantee that. I'd be surprised if anyone at Traplet even remembers the saga, but it's etched on my mind all right!

Hopefully, either the "other" GW or someone who's flown the Traplet plan model successfully will be able to reply and be more helpful than I can.

Kind regards

Gordon Whitehead (not the Firefly designer)

[Martin Harris - Moderator]

Maybe worth running it through one of the on-line C of G calculators and see if the result makes sense with the plan position?

[fly boy3]

Thanks both for the heads up. Will see my clubmate re CoG position. This is the one thing that should be correct be on a maiden. LoL. Cheers

[Ted Oram]

Hi all…. I am about to maiden my GW firefly……I am sure the c of g shown on my plan is incorrect it is shown at about 55% back from the leading edge…..does anyone know the correct c of g position.

 

[Piers Bowlan]

I don’t know the correct c of g position Ted so i’m not much help but if no one comes forward with the info you require, you could start at 25% mac and incrementally move it further aft with subsequent flights. At least that is what the great Peter Miller does when he maidens one of his new designs apparently. To paraphrase him; ‘With a C of G too far forward the model flies badly, too far back and it only flies once!

?

Edited January 6, 2022 by Piers Bowlan

[kc]

I think this plane probably has a double tapered wing therefore you might need to find a book or website which explains calculating where the average chord is on tapered wings. 

You could try this site, or this one.   I would check several different websites and books to see how they compare before trusting the result!

 

Edited January 6, 2022 by kc

[Glynn Howson]

Hi has anyone now found the C G position for the Gorden Whitehead Slingsby Firefly I am just refurbing mine after almost 30 years but can't remember the C G position if anyone could please. Thanks in advance.