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Old Jul 16, 2001, 03:51 AM
Mugi Pilot
Moogee's Avatar
United Kingdom, Scotland, Edinburgh
Joined May 2000
521 Posts
Multi engines - why are the engines angled outwards on full size?

I was looking for a subject for my next project - fancied a twin but then noticed in most of the three view drawings of planes, from above, the wing engines usually seem to be angled outwards - or point towards the wing tips.

It's very noticable on the Grumman Mohawk and to some extent the Sparviero and Junkers 52.

Why is this?

Is it perhaps because they've used contrarotating props - and therefore you'd have right sidethrust on one and left sidethrust on the other?

Cheers, Morgan
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Old Jul 16, 2001, 03:59 AM
Single-task at best...
tim hooper's Avatar
Telford, UK
Joined Feb 2000
7,498 Posts
Mugiman,

I think it's to do with stability in the event of single-engined flight being neccesary. A twin on one motor alone will try to turn (& maybe spin in), whereas angling both motors outwards wil tend to forestall this event, by lessening the turn-in tendency.

I think that's right......

tim
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Old Jul 16, 2001, 04:15 AM
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keven64's Avatar
United Kingdom, England, Burnley
Joined Apr 2001
5,499 Posts
Hello Morgan,

Yep - Tim is right.

The one engine running ( if the other fails )would pull the 'plane towards the dead-engine side.
You ask Tic ! Hehehe.
The out-thrust will help to alleviate this.

By the way, just what are you thinking of now ?

Not more multi's ?

Keven.
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Old Jul 16, 2001, 04:52 AM
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Bill Glover's Avatar
United Kingdom, Bracknell
Joined Nov 2000
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You will sometimes see more offset on one side than the other ... this is to take account of prop. torque. And on 4 engined aircraft the outers may be angled out more than the inners. Another trick is to use twin fins that are angled ... so if one engine stops the propwash on the other fin provides a correcting yaw action.
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Old Jul 16, 2001, 06:24 AM
Mugi Pilot
Moogee's Avatar
United Kingdom, Scotland, Edinburgh
Joined May 2000
521 Posts
Ah, the old engine failure chestnut.
I had forgotten they build aeroplanes with mishaps in mind. That does seem to make sense to me now.

Keven, just looking thru my Jane's big book of planes looking for something a bit easier than that Blohm & Voss p.170.
However, I'm settled on that as a project and it should roll off the line this week.

Incidentally then, if one were building a very scale multi - with 100% reliable electrics, thus not needing the offset, surely it would be better to mount them longitudinally and foresake this minor scale touch for the minutely increased thrust in the direction of flight?
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Old Jul 16, 2001, 06:40 AM
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Weilbach, Germany
Joined May 2001
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This is one subject that always fascinated me. The weird part, however, is that on the Short Sunderland they had strongly offset engines until the Mark V's when they straightened them back up.
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Old Jul 16, 2001, 06:50 AM
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Quote:
Originally posted by ChrisP:
This is one subject that always fascinated me. The weird part, however, is that on the Short Sunderland they had strongly offset engines until the Mark V's when they straightened them back up.

Perhaps the engines became more reliable?

I remember reading that Sunderland aircrew regularly used differential throttling when evading fighters ... much to the manufacturer's horror (the airframe had not been designed with such stresses in mind!).

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Old Jul 16, 2001, 06:53 AM
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Bill Glover's Avatar
United Kingdom, Bracknell
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Quote:
Originally posted by Moogee:
Incidentally then, if one were building a very scale multi - with 100% reliable electrics, thus not needing the offset, surely it would be better to mount them longitudinally and foresake this minor scale touch for the minutely increased thrust in the direction of flight?

Yes, apart from the normal requirement for a little right sidethrust somewhere in the setup.
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Old Jul 16, 2001, 06:57 AM
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ChrisP's Avatar
Weilbach, Germany
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Quote:
Originally posted by Bill Glover:

Perhaps the engines became more reliable?

Bill
The Mk V's had Wright Cyclones instead of Bristol Hercules sleeve valve engines, so you may be right on the reliability aspect. Actually if I had the choice I would be more inclined to favour the big Bristols.

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Old Jul 16, 2001, 08:01 AM
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Mark Haigh's Avatar
Barnsley, Great Britain (UK)
Joined Dec 2000
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Moogee. An unrelated topic, but as requested previously the OS grid ref. to my flying site: SE:36742 09076. If you stick this in Autoroute - entrance is via Far Field Lane.
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Old Jul 16, 2001, 08:13 AM
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Moogee's Avatar
United Kingdom, Scotland, Edinburgh
Joined May 2000
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thanks Mark, I read you were trying to test that new Star Jet - would love to see that go - when were you going to try it?
I'm ready to fly my new plane but for my Jeti ESC in other topic.
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Old Jul 16, 2001, 08:22 AM
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Quote:
Originally posted by ChrisP:
I would be more inclined to favour the big Bristols
er, yes, me too!
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