OS Max 15LA Won't Run Upside Down

[EvilC57]

Posted by J D 8 on 07/09/2020 17:08:43:

What was the exhaust like?

If you mean exhaust deposits, there weren't any because the engine was out in the open on the test stand, so no model catch any deposits. If you mean was it clear or smoky, relatively clear, but most of the testing was done in drizzle, so wasn't the clearest of air to see what was really going on.

I'll have another go in some better weather sometime.

[Robin Colbourne]

EvilC57, I would just like to add that I hope your weather has improved, as I'm eagerly awaiting the next instalment! :-D

Robin

[EvilC57]

Posted by Robin Colbourne on 08/09/2020 12:05:48:

EvilC57, I would just like to add that I hope your weather has improved, as I'm eagerly awaiting the next instalment! :-D

Robin

No IC powered flying or engine running is allowed at our club on Tuesdays & Wednesdays, to give the neighbours some peace. However Thursday this week is looking good weather wise. So you’ll have to wait I’m afraid...!

I refitted the engine in the model this morning, and have shortened the feed pipe between the tank and the needle jet input, to remove the loop that was in it, and provide absolute minimum distance fuel has to travel between tank and carb. I also had the exhaust apart to check for any blockages or deposits which may have been causing problems.

[EvilC57]

First the good news:
Took the model to the field today, and the OS 15LA behaved itself at last!

It started first pull, and ran faultlesly the right way up (model upside down). I turned the model over, and the engine kept running this time.

So somewhere between a new Enya plug, a new carb, a newly resealed crankcase back plate, a shortened fuel feed pipe from the tank and fresh fuel, we got there.

Thanks for all the suggestions along the way fellow modellers.

Now the bad news:
The model was completely unflyable, despite following the plan and suggested CofG positioning to the letter. I suspect from the way it wallowed about and wouldn't respond to control inputs, that the CofG was all wrong. Unfortunately while trying to fight it, it ended up in a dangerous position behind the pits so I had to ditch it.

The model is no more - still, the newly sorted engine has survived!

In my experience, that's the thing with building from plans, you're never sure what your're going to get. Some of my plan-built models have been (and still are) excellent fliers, while others are duds.

[Jonathan M]

Well done for sorting out the engine and sorry about the demise of the Marquess itself.

From a quick gander at the design, originally for CL, it doesn't look like it was ever going to be the easiest small RC model to fly! Tailplane area too small with insufficient moment arm?

[EvilC57]

Posted by Jonathan M on 11/09/2020 08:01:24:

Well done for sorting out the engine and sorry about the demise of the Marquess itself.

From a quick gander at the design, originally for CL, it doesn't look like it was ever going to be the easiest small RC model to fly! Tailplane area too small with insufficient moment arm?

Interesting you should say that Jonathan. I can’t remember where now, but when I was researching the Marquess before I built it, I read a report or post from someone who‘d also built one and lost it in a crash. I’m used to flying small, fast EDFs etc., so I don’t think it was lack of skill on my part (he says, trying to deflect the blame!).

Looking for a new home for the 15LA now then - back to the Traplet (Sarik) plans catalogue I guess.

[J D 8]

If it is any consolation I once built the control line version and wreaked it on its first flight, tail feathers still survive on an o/d fun fly powered by guess what ? OS 15.

[EvilC57]

Yes. The general consensus on the flying field yesterday was ‘Yep, we’ve all been there.’ Scrape up the bits and carry on!

The most important thing is, I ditched it in a safe area and no one was hurt.

Edited By EvilC57 on 11/09/2020 09:08:32

[Keith Evans 3]

This is the twice size Marquis I built and flew a few years back .

The only difference I made to the original was to add 3degrees dihedral and 2 degrees of washout .It flew very well .

Later I modified the flap planform at the tips to give more area ,split the flaps to give flaps and aileron control .

I did read somewhere that the Marquess could be a bit twitchy .

I too originally had an inverted O.S.46 FX .but got fed up with it flooding on start up and I couldn't be bothered to invert the thing so I put the engine in the upright position .

The canopy I believe was for a Chipmonk from Vortex .The pilot was a sort of Barbie Doll .

[EvilC57]

Posted by EvilC57 on 11/09/2020 08:46:50:

Posted by Jonathan M on 11/09/2020 08:01:24:

Well done for sorting out the engine and sorry about the demise of the Marquess itself.

From a quick gander at the design, originally for CL, it doesn't look like it was ever going to be the easiest small RC model to fly! Tailplane area too small with insufficient moment arm?

Interesting you should say that Jonathan. I can’t remember where now, but when I was researching the Marquess before I built it, I read a report or post from someone who‘d also built one and lost it in a crash. I’m used to flying small, fast EDFs etc., so I don’t think it was lack of skill on my part (he says, trying to deflect the blame!).

Looking for a new home for the 15LA now then - back to the Traplet (Sarik) plans catalogue I guess.

Just established where I read about someone else who had also lost a Marquess on its maiden flight. It was an article in last April's RCME, reproduced below... seems small Marquesses aren't meant to fly!

[Martin Harris - Moderator]

Small tail, short moment suggests that the C of G would need to be further forward than the often quoted "on the main spar" or 25% chord guidance that you so often hear and might well have influenced the position shown on the plan. The planform also means that measuring such a position on the root rib would result in the true C of G being further back than expected so unless it's a tried and tested plan (always worth a Google for others' experiences) it's better to either do your own calculations as a check or opt for a slightly forward position for initial flights.

[EvilC57]

I guess I should have taken the demise of Connie Conradie’s model in the article as an omen!

[dave windymiller]

I know the problem has been "cured" but one thing ive learnt over the years if an engine is misbehaving is to reset the idle screw or air bleed to the recommended setting in the manual eg X no of turns from fully seated. If you play with the idle screws a lot trying to sort an engine out, a screw way off its setting can give very odd behavior.