OT:Twin engine question

IIRC there have been experimental aircraft with odd number of prop blades on each engine, ie three blade on one side, four on the other.

The other day a pilot friend stated that this configuration was impossible.

Comments?

Tom

Reply to
maiesm72
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Can't think of any examples off the top of my head, apart from quads with different numbers of prop blades on the inboard and outboard engines; some of the GR Halifaxes had this I think. Not sure how wise it would be to mix props on a twin, but with careful throttle control to stop the aircraft from flying sideways due to asymmetric thrust more than could be handled by the rudders (and given a twin should be able to fly with one prop feathered, that shouldn't be too much of a problem) I can't think of a good reason why it couldn't be done, unless it resulted in unacceptable vibration.

Jon.

Reply to
Jonathan Stilwell

A friend of mine flew for Continental Motors many years ago & he flew some twin Cessna specifically for that purpose. They'd put different props on each side for testing. There's generally not a reason it couldn't be done. IIRC, the Consolidated (PB2Y ?) Coronado used 3 & 4 blade props.

Reply to
frank

The problem, I would think, would be that you would get some very odd passing frequency harmonics at some very unusual power/rpm settings. Such which might catastrophically impact operations with the throttles split, or rpm split...just ask any multi-engine prop jock that spends most of his time flying in aircraft without an auto-synch how much time he spends synching his props just to get rid of those annoying beats...

Not to mention the weight differential between the props that you'd have to trim out...

I'm sure someone has researched it, and found out it just better all the way around to keep things symmetrical. I'd think it's not really impossible...but seriously impractical.

Reply to
Rufus

At times, wasn't the XB-35 flown with a mixture of prop types?

Reply to
Greg Heilers

Any competent multi-engine pilot with properly functioning equipment doesn't spend that much time synching the props. It just ain't that hard to do.

Reply to
frank

most ww2 german pilots didn't synch. they weren't taught to and it wasn't considered important. guess it kept them awake.

Reply to
e

Not that it's hard to do, but the equipment doesn't seem to "properly function" on most of the light twins I've ever had to jump out of...or puddle-hopped on.

And I suppose it also depends on the mission - if you're just up and cruising, I suppose that's one thing. Most of the time I'm onboard there's a lot of power variation - climb, dive, speed up, slow down, cut...

Reply to
Rufus

Heh...and kept them mad enough to kill something...which was what they were up to in the first place...

Reply to
Rufus

sure would have bugged the shit out of me.

Reply to
e

Thanks, guys. Great replies.

I remember now that the Coronado had that odd configuration and I have seen Cessna/Continental experiments as mentoned.

just knew that y'all would know. :-)

Tom

Reply to
maiesm72

This was not uncommon when engine testing. The experimental engine was placed in place of one of the original engines in some cases, in others the test engine was placed in an entirely new place.

In fact, one of the interesting types is when a pure jet is used to test a turboprop engine, and one sees a "jet" aircraft with a prop. I have also seen a B-17 with a turboprop in NOSE!

There have also been rigs fitted by airlines in order to ferry engines to a maintenance site that does not have spare engines. A regular airliner of a type the airline uses is fitted with a rig to attach a non-operating engine, and used to ferry the engine to a needed site. I am assuming this is done with FAA approval.

Reply to
Don Stauffer

Jonathan,Jonathan!!!!............

You have forgotten Gelendzhik already !!!!!

There was a homebuilt amphibian - the LM-6 - with a three-bladed prop on the port engine and a two-blader on the starboard.

Check out my photo - near the bottom of :-

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Ken

Reply to
Ken Duffey

PS - Then there's the Ukrainian Antonov An-70 - it has a different number of blades ON THE SAME ENGINE !!!!!!

The D-27 propfan fitted to the An-70 has eight blades in front, six blades on the rear - making a 14-blade contraprop !!!

Ken

Reply to
Ken Duffey

Gelendzhik? The sunshine, the beer, the singing (only in Ruuuussian), the birthday cake and the lovely lady from Beriev trying to negotiate her way up various step ladders in a skirt? Yes, that rings a bell.

Ooo, look, a spam can. I guess my mind must have been on something interesting at the time.

Talking of odd props, have you got any on-line pictures of the An-26 at Vjasma in 1999 which had different props; same number of blades, but one with considerably shorter blades than the other (this is what it looked like after the ground power unit rolled into the prop arc). I wonder if it ever flew like that?

Jon.

Reply to
Jonathan Stilwell

This was almost a "standard feature" in the early days of the Boeing 707. There are numerous photos of an AC with a fifth engine slung under the wing.

Reply to
Greg Heilers

It also made it hard for listening posts to pinpoint exactly where they were. This was important in the pre-radar days.

Reply to
Jessie C

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