P-39 Airacobra and P-63 King Cobra

[Weaver]

It's not the dummy, he's the right size.  The J-21 in Weaves pic is on jacks! 

Nah, it's the carrier-version with beefed-up gear. You can see the twin arrestor hooks if you look veeeeeeeery closely.......

[Mossie]

Then they're on stilts too!  It's about a foot off the floor....



Sorry.

[Weaver]

LMFAO - okay, my turn to look dumb! 

Taking those stands away would put Mr. D.Ummi's head at almost exactly the same level as the guy with the blue shirt in sequoiaranger's pic.

[Mossie]

We're not having a good week are we, us two???

[Weaver]

We're not having a good week are we, us two???

Uh-huh. See that white line in the sky? That's an aeroplane, that is........

Weaver
Playing it safe

[JayBee]

No it is not.
The little shiny dot at the front of the white line is the aeroplane.
The white line is the cotton wool it trails behind it!!!!!

[sotoolslinger]

Sorry I have not visited this thread in a while ,I missed goodness. I love the concept of one engine driving two props. I am very enamored of apophenia's twin boom 63 .I won't have to worry about the undercarraige legs since I build everything wheels up

[Sauragnmon]

You know, if it's one engine driving two props, couldn't we go for broke and make it a doubled up engine too?  Fastback it, Saber it, give it an improved airflow cowling so you have air scoops over the wings and a pair of vents vertical over and under the tail prop, so you have the height adjusted without giving too much extra length to the curve for the tail prop.  You could also use that benefit, by the raised position of the crank shaft, to elevate the rear prop by a foot or two so you don't have to stretch the gears as much, though giving it a little bit of extra length could be good.  Not to mention, with the saber, you'd have bulked out engine output so you can get more thrust and power out of the design.

Question - are both props turning the same way, or do they couter-rotate?

[sotoolslinger]

Counter rotating should eliminate torque problems completely.

[sequoiaranger]

Now I'm ROFLMAO! Funny how the closer you look at a picture, the more you can discern!

I am in agreement that the twin-boom P-63 would need SOME extra clearance; I was just "arguing" about how much.

Could the solution be more but shorter blades on a lesser-diameter prop? I guess the prop in front would have to match, too. Put a 5-blade prop on? Or a six-blade like the Shinden?

[jcf]

You know, if it's one engine driving two props, couldn't we go for broke and make it a doubled up engine too?  Fastback it, Saber it, give it an improved airflow cowling so you have air scoops over the wings and a pair of vents vertical over and under the tail prop, so you have the height adjusted without giving too much extra length to the curve for the tail prop.  You could also use that benefit, by the raised position of the crank shaft, to elevate the rear prop by a foot or two so you don't have to stretch the gears as much, though giving it a little bit of extra length could be good.  Not to mention, with the saber, you'd have bulked out engine output so you can get more thrust and power out of the design.

Question - are both props turning the same way, or do they couter-rotate?

Two Sabres?? One would be a tough fit in the P-63 airframe, let alone the P-39.
The Sabre being ten inches wider and a thousand pounds heavier than a V-1710.

On the other hand if you are stating that the Sabre is a doubled engine, it aint'.
The Sabre is an H-shaped 24-cylinder engine, yes it has two crankshafts, however, that
does not make it a double engine. The Sabre was designed as a dual-crankshaft
24-cylinder engine, it is not two 12-cylinder engines sharing a common block. If you want
to think in multiples then consider it as being four 6-cylinder engines with a single crankcase,
this is closer to Frank Halford's philosophy. Halford's Rapier and Dagger engines were also
H-shaped with dual crankshafts. Halford liked the layout because the multiple, small-diameter,
short-stroke pistons meant lower reciprocating weight and thus higher RPM. At full power the
various Sabre marks ran at 700 to 1,000 RPM faster than comparable Merlins and up 1,250 RPM
faster than Griffons.

Also driving a second prop off the rear of the Sabre won't work without a major redesign,
that space is occupied by the supercharger.
The engine would probably have to be mounted front-to-back in a pusher set-up with the second prop
drive running beneath the engine, of course this would raise the height and weight of the engine installation.
Every change creates a new problem.

Perhaps a better engine choice would be derivation of the V-1710-E22 Turbo-compound;
http://www.enginehistory.org/v1710tc.htm



Jon

[kitnut617]

Could the solution be more but shorter blades on a lesser-diameter prop? I guess the prop in front would have to match, too. Put a 5-blade prop on? Or a six-blade like the Shinden?

IIRC, on the contra-props fitted to Spitfires, the rear prop has a smaller diameter to the front one, something to do with airflow off the front blades tips, if I understood it correctly. So having a smaller diameter prop at the rear wouldn't be a problem I would think.

[GTX]

A different (all be it crude) take on a pusher P-39:



Note it has a canard.

Regards,

Greg

[GTX]

and while we're at it, a 'conventional' P-39:



Regards,

Greg

[Sauragnmon]

I did mean one Saber, Jon, and my suggestion was to expand the back and give it ventilation ducts off the top and bottom of the engine mounting to allow it to have the height without needing a massive extension on the tail to get to the rear prop.  Alternate thought, perhaps aligning the engine with the supercharger in front might well work, and running a chain belt down to the nose prop's drive shaft that rides under the engine casing.  Yes, I will admit, my comment was off hand and simple in principle, I was simply meaning to think in terms like the Saber or other similar engines.  They would by far be potentially a better principle displacement for the engine mounting than a Radial, but we could get a beneficial design with a three or four bank radial mounted behind the cockpit.  That would certainly be a new thought, with a rear-mounted radial... or one at the least not looked at very often... and then you can have both sides of the crank open in some respects, and power the supercharger, or even a turbosuper, possibly by a chain link and mounting it low in the position.

I'm probably just rambling again...