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Multi Engine Plane

What happens if....

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cymaz22/10/2017 17:31:56
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Now that I have a 4 engine plane, I have been thinking, what if?

There must be some wizard at aerodynamics or someone good at plane design who could answer this question.....

" My plane has 4 x OS 40la 2t engines. They currently all use APC 10x6 props. What would be the effect of running 10x6 on the inner engines and 11x5 on the outer engines....or vice-versa for that matter. Would there be any advantages to do this and would it help in the event of an engine stopping".

Anyone come up with a good idea for this? Or otherwise for that matter.

PatMc22/10/2017 17:53:29
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They are matched engines so why would you want to run them at different rpm ? The ones on outer pair would need to run 20% faster or the inners run 16.6% slower for the props to have matched the "pitch speed".

Edited By PatMc on 22/10/2017 17:54:05

Jon - Laser Engines22/10/2017 18:00:58
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I agree with Pat, there is not really any advantage to this. If you need more thrust run them all on 11x5's, if not leave well alone!

cymaz22/10/2017 18:03:07
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I will see what the 10x6 props are like. Thanks for the advice. I will change all 4 should the need arise. Would it do any harm?

Jon - Laser Engines22/10/2017 18:04:12
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what model is it?

Stevo22/10/2017 18:18:16
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4 engines eh... c'mon, tell all!!

john stones 122/10/2017 18:24:20
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Blogs been on here a while. wink

Edited By john stones 1 on 22/10/2017 18:26:12

Stevo22/10/2017 18:35:00
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Thank you John.

Hmm a wierd one. He's from Cornwall, y'know...

Jon - Laser Engines22/10/2017 18:39:46
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ooo

10x6 will be fine

cymaz22/10/2017 19:29:14
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Just an thought . 10x6 gave 3200 idle, 10k @ WOT

Jon - Laser Engines22/10/2017 19:33:39
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thats a very fast idle. i would expect 3k at most, 2500 would be better.

cymaz22/10/2017 21:51:34
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Cheers Jon. I realise it's a quick one. There's still a bit a fine adjustment to do. Considering all four engines are working off 1 servo - I've got them within 200/250 rpm of each other...nearly there. I will do the final idle on end point, there is enough of that to complete the job.

They are also several years old, not that should make any difference!

Just a couple of minor bits of work to do. Finally fit the remote glows and get the cowls on. Range check and failsafe to do. Next Sunday looking good for the fly- off.

Jon - Laser Engines22/10/2017 22:04:17
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Dont forget that the air bleed carb slow run tuning works backwards

cymaz22/10/2017 22:34:10
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Posted by Jon Harper - Laser Engines on 22/10/2017 22:04:17:

Dont forget that the air bleed carb slow run tuning works backwards

No I hadn't...pick up from idle to WOT is good. Checked the price of remote needles for OS 40 la.....about £17. Daylight robberyface 17

Martin McIntosh22/10/2017 22:46:52
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Many years ago I guy by the name of Robin Lehman pioneered some multi engined models and set each one to give out thrust so that a single motor running would result in straight flight. Seemed to work.

Geoff Sleath22/10/2017 23:39:21
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Posted by cymaz on 22/10/2017 22:34:10:
Posted by Jon Harper - Laser Engines on 22/10/2017 22:04:17:

Dont forget that the air bleed carb slow run tuning works backwards

No I hadn't...pick up from idle to WOT is good. Checked the price of remote needles for OS 40 la.....about £17. Daylight robberyface 17

If the needles are remote then can't you use any needles and fit them in convenient places? I suppose they'd all have to be the same but not necessarily. I've use remote needles with 50mm long fuel lines to the carb which worked OK - to my surprise!

Geoff

Robert Berger24/11/2019 07:53:36
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17 forum posts
19 photos

Is there a thread on this site on how to plumb up a four engine IC fuel tank system. I am into a B17 Marutaka Kit and I have 4 OF FS26 engines that I have set up on a test board with 4 throttle servos on 4 channels running through 2 SBD-1 Futaba Decoders. Would I use 4 tanks, a pair of tanks or just one tank and how would I set up the tubing, vents and pressure tubes from the mufflers if multi engines were of one tank. Thanks if you can help.

Frank Skilbeck24/11/2019 08:33:11
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4515 forum posts
101 photos

4 tanks, keeps all the plumbing short, tanks should be in each nacelle, and adjusting each engine independent of the others.

cymaz24/11/2019 08:47:06
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8803 forum posts
1194 photos

The fewer the number of tanks the more complicated the plumbing, joins etc. With any multi engine, keep it simple, keep it easy to maintain and trouble shoot.

Great tips HERE

Edited By cymaz on 24/11/2019 08:50:00

Simon Chaddock24/11/2019 10:53:38
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cymaz

Reading through those tips highlighted in your last post "long tail moment" and "a thin wing" stand out.

I wonder how well your plane meets these criteria if you are worried about the effect of an "engine out" .wink 2

I certainly favour a long tail moment and a big fin on my multi engine jobs so if an engine dies things happen slowly enough for me to contain the situation.

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