Greg's view on the P-39s' unusual engine placement. Interesting new video.

[Draconis]

Here is the latest of Greg's Airplanes videos. This one takes another look on why the P-39 had a mid-mounted engine. And examines a few other features of the Airacobra as well. Are the aerodynamic advantages of placing the engine close as possible to the centre of gravity worth the added complications that location brings for piston engined airplanes?

 

[Canuck Wingnut]

The fact that, unlike Italy, America never built a radial mid-engine aircraft proves that all American aircraft designers of the Second World War were cowards.

 

[Carl Schwamberger]

Yugoslavia had a limited production of a mid engined interceptor A dozen (?) were built. Wrote a paper on mind engined aircraft designs of 1935-1945 for school. Unfortunately I don't recall threatening behind the mid fuselage placement. The aircraft was judged superior in maneuverability.

 

[Draconis]

The fact that, unlike Italy, America never built a radial mid-engine aircraft proves that all American aircraft designers of the Second World War were cowards.

An air-cooled radial engine wouldn't be an ideal choice for the mid-fuselage location. I think the various cooling problems through all flight regimes would be unsolvable. But any of the liquid cooled engines of WW2 would be more suitable for that location.

 

[Driftless]

Fascinating video - very informative! A couple of things come to mind in general:

• The paths of development for these aircraft weren't necessarily linear (going from a single brilliant idea carried through to production) Start/stop, try this original idea, but shift approach for various reasons. i.e. With the P-39, the biggest dilemma was the turbosupercharger vs the mechanical supercharger. With the the P-51, the Allison to Rolls Royce shift.
• Part of that non-linear development is always going to be constantly changing technology advancements. i.e. With the P-39(and others), the ongoing access to the big NACA report - even while it was being analyzed and written led to changes in design.
• With those two previous points in mind, the universal truth of "timing is everything" still was a major player.

 

[tomo pauk]

Are the aerodynamic advantages of placing the engine close as possible to the centre of gravity worth the added complications that location brings for piston engined airplanes?

The talk about the aerodynamic advantage of placing engine as close as possible to the centre of gravity is Bell's engineer trying to make a feature out of a necessity. I like it how he skips the talk about company's botched turbocharger installation, too.

The spec that led to the P-39 (and to the P-38, and to the Airacuda) mandated a 37mm cannon and was favoring tricycle. Easy to do on 2-engined A/C (but again, Bell managed to make the abomination there with Aircuda, and USAAC managed to squander the funds for it), harder to do on 1-engined A/C, especially if the engine is not conductive to the motor-cannon. So Bell 1st tried with the prop-cannon-engine-cockpit designs (Model 3, and then Model 4), and then swapped the places for engine and cockpit.

Yugoslavia had a limited production of a mid engined interceptor A dozen (?) were built. Wrote a paper on mind engined aircraft designs of 1935-1945 for school. Unfortunately I don't recall threatening behind the mid fuselage placement. The aircraft was judged superior in maneuverability.

Interesting. What were these Yugoslav mid-engined interceptors?

 

[Carl Schwamberger]

Interesting. What were these Yugoslav mid-engined interceptors?

Good question. I sourced it from a late 1960s book on WWII fighter types. It may have been na variant of the IK-3, which also had a very limited production run. The K-3 was a standard forward engined interceptor. I can find references to a IK5 design that never flew, but no details on its layout. I keep seeing remarks about the yugoslavian air force leaders ensuring everything possible was destroyed before the Germans seized it which does not help at all. The description in the book was fairly detailed. More than a token paragraph.

 

[tomo pauk]

Good question. I sourced it from a late 1960s book on WWII fighter types. It may have been na variant of the IK-3, which also had a very limited production run. The K-3 was a standard forward engined interceptor. I can find references to a IK5 design that never flew, but no details on its layout. I keep seeing remarks about the yugoslavian air force leaders ensuring everything possible was destroyed before the Germans seized it which does not help at all. The description in the book was fairly detailed. More than a token paragraph.

The IK-5 was to be a twin-engined fighter (and neat, too, at least by looking at the drawings).

 

[marathag]

The worst thing about a mid motor placement, is that it rules out place the variable load items there, like bombs of fuel tanks, weight that changes over the course if a mission.
So with a P-39, shoot off all your ammo with tanks near full of fuel, and you are then in a a tail heavy state of balance- Aerodynamically Unstable as CoG closes with CoP. The 10? Gallon Oil Tank was a almost two feet aft of the engine, so as that oil was gradually consumed during flight, you would get more nose heavy, increased stability.

If everything worked just right, your balance wouldn't get too screwed up.

But a P-39 Driver probably got really good with his trim-tabs, as nothing goes as expected.

 

[Dilvish]

The worst thing about a mid motor placement, is that it rules out place the variable load items there, like bombs of fuel tanks, weight that changes over the course if a mission.
So with a P-39, shoot off all your ammo with tanks near full of fuel, and you are then in a a tail heavy state of balance- Aerodynamically Unstable as CoG closes with CoP. The 10? Gallon Oil Tank was a almost two feet aft of the engine, so as that oil was gradually consumed during flight, you would get more nose heavy, increased stability.

If everything worked just right, your balance wouldn't get too screwed up.

But a P-39 Driver probably got really good with his trim-tabs, as nothing goes as expected.

Did experience with the P-39 and P-63 help with designing the P-59, P-80, and Meteor, since they were also mid-fusalage engine aircraft?

 

[Dilvish]

Good question. I sourced it from a late 1960s book on WWII fighter types. It may have been na variant of the IK-3, which also had a very limited production run. The K-3 was a standard forward engined interceptor. I can find references to a IK5 design that never flew, but no details on its layout. I keep seeing remarks about the yugoslavian air force leaders ensuring everything possible was destroyed before the Germans seized it which does not help at all. The description in the book was fairly detailed. More than a token paragraph.

I hadn't heard of the IK-5 till today. It is a neat looking bird. It is easy enough to not know about the IK-3.

I also don't think I had heard of the Douglas A-33 till this past Friday. It is the ultimate version of the Northrop A-17.

 

[Peg Leg Pom]

Did experience with the P-39 and P-63 help with designing the P-59, P-80, and Meteor, since they were also mid-fusalage engine aircraft?

Er not quite. The Meteors engines were in mid wing nacelles, and the P 59's engines were in the wing roots. The P 80's engine was in the rear fuselage.

 

[marathag]

Er not quite. The Meteors engines were in mid wing nacelles, and the P 59's engines were in the wing roots. The P 80's engine was in the rear fuselage.

But still is different from having the giant lump of Iron ahead of the Pilot.
Turbines were a bit lighter than a reciprocating V12, as not needing the Radiators, and th water inside them

 

[Peg Leg Pom]

But still is different from having the giant lump of Iron ahead of the Pilot.
Turbines were a bit lighter than a reciprocating V12, as not needing the Radiators, and th water inside them

It's not like mid engine aircraft were a new idea when Bell built the P39 either. Also note the lack of water cooling and that like a jet it's pushed through the air.

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