VMC Jodel D18 first flight issues

[Spiros]

Dear all,
VMC's Jodel D18 is now ready.

On Sunday, along with George Kandylakis, we tried the first flight in Thessaloniki.

Although the model is fairly well balanced and the "correct" thrust was given (I made an adjustable thrust),
I faced the flight as appears on the YouTube video.

Honestly I'm a bit puzzled so any ideas, advices are welcome.

What could be wrong? More down/right thrust? Change to a less powerful rubber (smaller width)?

Many thanks in advance

[Anyun]

My guess is that the left wingtip is stalling, which then causes the model to fall/dive towards the left side. Making the model fly less close to a stalled condition (moving CoG forward or using more downthrust) can help prevent this happening, but to get a nice slow flight pattern you really want to fly close to the stall...

I would check the wash-in of the left wingtip first. Wash-in of the left wingtip helps keeping the left wing up during a left circling pattern as yours, but also makes the left wingtip more prone to stall. Try removing any wash-in of the left wingtip (you could even have some wash-out), but use even more wash-out on the right wingtip to keep the differential tip-incidence setup that supports the left circling pattern.

Best of luck with the trimming! //Andrea

[OZPAF]

I suspect that it may be an issue with the tail setting -producing a bit too much " up" elevator together with not quite enough down thrust, which becomes more obvious as the power starts to run down. Checking the glide at the recommended CG would show if the tails setting is correct and then more down thrust could be added if the climb is still too steep.

I would check the wash-in of the left wingtip first. Wash-in of the left wingtip helps keeping the left wing up during a left circling pattern as yours, but also makes the left wingtip more prone to stall. Try removing any wash-in of the left wingtip (you could even have some wash-out), but use even more wash-out on the right wingtip to keep the differential tip-incidence setup that supports the left circling pattern.

Yes I feel this is much better than using wash in on the inside wing panel.

Good luck.

John

[OZPAF]

suspect that it may be an issue with the tail setting -producing a bit too much " up" elevator[/quote
More correctly I should have said "too much decalage" - ie too much difference between the wing and tail incidences - leading to a nose up attitude as I tried to simplify by saying more up elevator(as would be seen at the control stick).

Anyway good luck.

John

[Spiros]

Thank you very much for your replies.

To explain a bit more, the wing is neutral with no wash-in or -out.

Additionally, position of the stab is accoring to the plan.

This is my second VMC Jodel D-18 and I do remember that on the previous one, I had to put some weight on the right wingtip to manage a steady flight.

Still as I had no adjustable thrust back then, I though it would be the right thrust in this case.

Could it be possibly a "strong rubber" causing more torque than it should?

My initial idea (but we ran out of time), was to go for a narrower rubber. Would that help?

[Andrew D]

Hi All,

I replied to this on the Facebook page, but I thought it was worth repeating here too.

The prototype flew fine in nice wide circles, with the same dihedral and balance on the plan.  I have video of it doing just that but straightening up and the end and literally going to the wall (and me laughing like a drain at it!).  This means that the state of trim was probably that it had insufficient right thrust and left rudder.  I do remember having better flights with it later, and that the plan does call for a trim tab in the inboard wing (so it can't be penalised in your kit scale comp).  On these simpler scale models I do tend to err away from wash out, for a beginner getting a good flat warp free wing with an acetate tab trumps more advanced stuff like that.  I think things like the Hurri, Spit and ME109 call it up however.  I think that the Jodel dihedral is scale IIRC, and again probably decided that the trim tab was the lesser of two evils between that and extra dihedral, which already looks "extreme".  I do wish I had kept better notes, ok I admit I kept no notes!   

PS I still think it is stalling a bit though, i think  a bit more nose weight may be worth a go, also widening the turn a bit will  obviously help...

If I think of anything else I will let you know.

[Spiros]

Thanks for sharing experience and thoughts.

As described, I made a list of all changes/corrections might be needed.

However due to lack of a wide gym, I might find a decent high grassed flat surface to make some tests or directly to IIFI.

I sincerely hope I have it trimmed before this though.