XP-39 Airplane in wind tunnel

[johnbr]

 

[Wurger]

 

[Gnomey]

Good one!

 

[spicmart]

Apart from the non-laminar profile wing the P-39 looks like the most streamlined fighter ever.

 

[tomo pauk]

Apart from the non-laminar profile wing the P-39 looks like the most streamlined fighter ever.

It have had many things that improved streamlining - fully covered U/C, well burried radiators, a ram air intake tucked behind cockpit, reasonably thin wing (nothing special, though) of modest size (smallest wing on ww2 US fighters). On same or even lower power it was faster than G.55 or Spitfire, let alone P-40.
We can recall that P-39 in racing trim (including extra radiator under belly) was very succesful in post-war air races.

Unfortunately, the XP-39 was a mess from aerodynamic point of wiev.

 

[Zipper730]

Apart from the non-laminar profile wing the P-39 looks like the most streamlined fighter ever.

It does have a streamlined quality that makes it look more like a jet than a propeller driven plane. From the streamlined nose, the raised canopy, to the overall elegant looks.

It have had many things that improved streamlining - fully covered U/C, well burried radiators, a ram air intake tucked behind cockpit, reasonably thin wing (nothing special, though) of modest size (smallest wing on ww2 US fighters).

I thought the intake produced fairly poor ram compression compared to other aircraft like the P-40? As for a buried-radiator: I would assume the idea is to avoid having anything protrude into the path of the airflow?

As for the wings: They don't seem unusually thin, though the wing-area probably is somewhat small (that said, I'm not sure how good a turning fighter it was).

On same or even lower power it was faster than G.55 or Spitfire, let alone P-40.

That I'm surprised about, especially with the Spitfire seeming even skinnier than the P-39 (from what I grasp, the thin fuselage was supposed to avoid changing the direction of the airflow excessively, which produces minimal turbulence, and that keeps the airflow over the horizontal and vertical stabs good, and makes the surfaces able to be smaller).

Unfortunately, the XP-39 was a mess from aerodynamic point of wiev.

And it all owed to the turbocharger arrangement. I do remember a proposal for a higher altitude V-1710, with different gearing. I'm not sure if it had two speeds, and what the gearing was.

 

[fubar57]

That I'm surprised about, especially with the Spitfire seeming even skinnier than the Spitfire

LOL....Wut?

 

[Zipper730]

Fubar57,

Good catch: I fixed it.

 

[tomo pauk]

I thought the intake produced fairly poor ram compression compared to other aircraft like the P-40?

Yes, ram air intake was not exactly a strong point on the P-39 with regard to engine-related ram effect, though it improved streamlining - the 'no free lunch' rule applies as ever.

That I'm surprised about, especially with the Spitfire seeming even skinnier than the P-39 (from what I grasp, the thin fuselage was supposed to avoid changing the direction of the airflow excessively, which produces minimal turbulence, and that keeps the airflow over the horizontal and vertical stabs good, and makes the surfaces able to be smaller).

No worries, P-39 was one skinny fighter.

And it all owed to the turbocharger arrangement. I do remember a proposal for a higher altitude V-1710, with different gearing. I'm not sure if it had two speeds, and what the gearing was.

I'm not sure where the statement ends, and the question starts here.

 

[Elmas]

By my personl point of view, P-39 was a mess not for aerodynamics, but for the distribution of the masses, expecially consumables.
That affected quite a lot Static balance (Moment of first order, expecially after ammunition expended) but even more the Moment of second order, namely the "Moment of inertia" of the airplane, making handling tricky, to say the least.

Moment of inertia - Wikipedia

 

[Zipper730]

No worries, P-39 was one skinny fighter.

True, I actually thought of a drawing project that involved "Spitfiring" a P-39. The idea was to put elliptical wings on it.

I'm not sure where the statement ends, and the question starts here.

What gear-ratios were proposed for the higher altitude V-1710? Was it single or twin-speed?

By my personl point of view, P-39 was a mess not for aerodynamics, but for the distribution of the masses, expecially consumables.

What changes could have been made? I had actually thought of creating a thread about theoretical ways WWII airplanes could have been made better with the knowledge of the time.

 

[tomo pauk]

True, I actually thought of a drawing project that involved "Spitfiring" a P-39. The idea was to put elliptical wings on it.

I've never heard about such a proposal. Any sources?

What gear-ratios were proposed for the higher altitude V-1710? Was it single or twin-speed?

Early altitude-rated V-1710s have had supercharger gear ratios of 8.77:1, that went to 8.80:1. Such engines were a bit better, for example, than DB 601A or M-105 in altitude power.
Gearing was changed to 9.60:1 to improve altitude performance, basically making it comparable with Merlin III on a test stand (the V-1710 having better carb and exhausts than early Merlins, so in everyday use such V-1710s might give a bit better altitude power, that was sorely needed for the heavy P-39/40/51).
Problem with such V-1710s was that initial prototypes have had one of the shafts involved being to weak for the horsepower needed to turn the S/C at greater rpm. Meaning that such V-1710s became available by some time of Autumn of 1942, or about 4 years after Merlin III entered service.
1-stage supercharged V-1710s were always with 1-speed S/C gearing in-service, there was a few prototypes with 2-speed S/C gearing.
2-stage supercharged V-1710s were with 1-speed gearing for engine-stage S/C, while the auxiliary S/C was driven via hydraulic coupling, thus it was variable speed within a specified range.

 

[Zipper730]

I've never heard about such a proposal. Any sources?

I said I thought of a drawing project. I was the person who was proposing to draw it up...

Early altitude-rated V-1710s have had supercharger gear ratios of 8.77:1, that went to 8.80:1. Such engines were a bit better, for example, than DB 601A or M-105 in altitude power.
Gearing was changed to 9.60:1 to improve altitude performance, basically making it comparable with Merlin III on a test stand (the V-1710 having better carb and exhausts than early Merlins

So that would have produced a critical altitude of around 16,250 to 18500 feet with ram compression?

Problem with such V-1710s was that initial prototypes have had one of the shafts involved being to weak for the horsepower needed to turn the S/C at greater rpm.

So that's why it was cancelled? The shaft that the supercharger was connected to was too weak?

Meaning that such V-1710s became available by some time of Autumn of 1942, or about 4 years after Merlin III entered service.

I thought the P-63 had a two-stage supercharger with a hydraulic clutch for the aux-blower?

1-stage supercharged V-1710s were always with 1-speed S/C gearing in-service, there was a few prototypes with 2-speed S/C gearing.

I guess they didn't pursue this due to shaft strength?

 

[pbehn]

The P-39 was years after the Spitfire, it should be better in every respect.

 

[Zipper730]

The P-39 was years after the Spitfire, it should be better in every respect.

True but there were ways the P-51 was beaten by the Spitfire and it flew later.

 

[pbehn]

True but there were ways the P-51 was beaten by the Spitfire and it flew later.

True but mainly because of the focus of the design. In terms of aerodynamics there were huge advances especially in USA between the first flight of the Spitfire and the other two.

 

[Shortround6]

I guess they didn't pursue this due to shaft strength?

I believe it was the strength of the gears themselves. The first engines with 9.60 gears were supposed to be delivered in Nov-Dec of 1941? However the solution to the problem was to make the area of the block holding the gears (or the gear case cover?) longer so wider gears which could spread the load/force over more tooth area could be fitted. Note that you cannot reffit and old engine with the new gears, although it might be possible to fit the old gears in a new engine (perhaps using spacers?) Anyhow, the changes to block castings took a while to implement and that is what caused the delay in service use.

I thought the P-63 had a two-stage supercharger with a hydraulic clutch for the aux-blower?

it was a hydraulic torque converter which is not quite the same thing. It was variable speed much like the torque converter used on the DB engines.

 

[Zipper730]

I believe it was the strength of the gears themselves.

What gear ratio did the early Merlins operate at?

the solution to the problem was to make the area of the block holding the gears (or the gear case cover?) longer so wider gears which could spread the load/force over more tooth area could be fitted.

Was that a normal practice?

it was a hydraulic torque converter which is not quite the same thing.

What is the difference?

 

[wuzak]

What gear ratio did the early Merlins operate at?

Which early Merlin?

Merlin

The ratio varied a bit. But it is not directly comparable to the V-1710 as the supercharger was larger (10.25" for most IIRC vs 9.5").

 

[wuzak]

What is the difference?

Pratt & Whitney 2 stage engines used a hydraulic clutch to change supercharger drive gears.

The torque converter/fluid coupling drove the supercharger directly.