P-40Q vs P-60A/D

wuzak · Jul 12, 2014

davparlr said:
I think that if you look at the main fuselage size, not including the aerodynamic flaring behind the cockpit, you will see that there is only a small taper from the engine area to the propeller, certainly not as much as on the 400 mph B-36 engine nacelles, which appears to be about 50% or more over a short distance. And since the XP-56 was cancelled before any wind tunnel testing, flow separation and turbulence concerns are hypothetical.

True, I overstated the taper.

Look at the relative size of the B-36 props to its nacelles and the XP-56's to its fuselage.

IIRC the B-36 did have some issues with prop vibrations. I certainly have read that the XB-35 did with its pusher props.

The taper of the B-36's nacelles were over a longer distance than the XP-56s.

wuzak · Jul 12, 2014

davparlr said:
I think that if you look at the main fuselage size, not including the aerodynamic flaring behind the cockpit, you will see that there is only a small taper from the engine area to the propeller, certainly not as much as on the 400 mph B-36 engine nacelles, which appears to be about 50% or more over a short distance. And since the XP-56 was cancelled before any wind tunnel testing, flow separation and turbulence concerns are hypothetical.

Yes, it is hypothetical. I found it in American Secret Pusher Fighters of World War II as a suggestion for the XP-56's poor performance.

davparlr said:
Again, looking at the B-36, it appears to have implemented a pusher prop in very similar manner as the XP-56 with both the exhaust and cooling air exiting right before the prop and I am sure that extensive wind tunnel testing went into making that an efficient design. Also, the Do 335, another fast pusher (and puller) type also put engine exhaust and cooling air right into the rear prop. I think the comment on the impact of dumping exhaust and cooling air into the prop was overstated.

The B-36 has turbos, so its exhaust has less (relatively speaking) energy. It is also confined to one area on the prop arc.

The Do 335 had somewhat more distance between its exhausts and rear prop. and, again, is confined to two areas of the prop arc.

The point, as I understood it, was that the exhaust in the XP-56 energised already unstable air flow.

davparlr said:
An unsupportable comment. Although larger, the XP-56 had a very similar configuration as the Me 163 and the German plane was aerodynamically capable of almost 700 mph. Of course the Me 163 was smaller and had a very small engine and fuel was pretty well centered, so stability would have been less a problem. The XP-56, with its heavy 2800 engine amid ship would have taken some work to get the CG correct, It would have always been sensitive in pitch. The airframe itself was very clean and, given it size, as clean as the Me 163 (I don't know about the airfoil of either, however).

Entirely unsupportable.

The big benefit the Me 163 had compared to teh XP-56 is that it was not dependent on a propeller for forward propulsion. Stick a rocket in the XP-56 and problems with airflow off the stubby fuselage may not have been as significant a problem as it was historically.

The theory is not that the turbulent flow off the fuselage caused excessive drag, but that it severely reduced the propeller efficiency.

GregP · Jul 12, 2014

Big difference in cross section between an Me 163 and the XP-56. We have an Me 163, well ... a 100% full scale replica, as well as a real Japanese rocket interceptor based on the Me 163, and you could never get an R-2800 in either of the rocket planes, even if there was nothing inside the fuselage at all.

davparlr · Jul 12, 2014

wuzak said:
True, I overstated the taper.

Look at the relative size of the B-36 props to its nacelles and the XP-56's to its fuselage.

B-36 engines were almost twice the power with twice the cooling and twice the exhaust.

IIRC the B-36 did have some issues with prop vibrations. I certainly have read that the XB-35 did with its pusher props.

The XP-56 engine was probably more closely coupled than the B-35 or 36. What I was surprised at was that there was no issues with the counter rotating prop gear box. It seems to have been a problem with almost all other applications. Perhaps both of these issues were undiscovered due to lack of flying time.

The taper of the B-36's nacelles were over a longer distance than the XP-56s.

No doubt but it looks like the taper was pretty severe.

davparlr · Jul 12, 2014

wuzak said:
The B-36 has turbos, so its exhaust has less (relatively speaking) energy. It is also confined to one area on the prop arc.

Can't argue here although it has two exhaust ports which would have expanded he impact area.

The Do 335 had somewhat more distance between its exhausts and rear prop. and, again, is confined to two areas of the prop arc.

Yes, but the expansion due to the forward placement of the exhaust would have impacted a larger area of the prop individually.

The point, as I understood it, was that the exhaust in the XP-56 energised already unstable air flow.

I have a hard time biting on the turbulent airflow. The fuselage appears too clean. Exhaust disruption is a possibility but could be addressed (route exhaust to the end of the vertical stabilizers?). Also, Consolidated, Dornier, and Northrop did not seem too concerned about locating the exhaust in front of the propeller. I would guess that the cause of the poor performance would be the exhaust disruption of the prop or, more likely, and based upon the flight test performance (the plane was nose heavy), the plane was out of trim due to messed up cg. Or, the wings were draggy.

davparlr · Jul 12, 2014

GregP said:
Big difference in cross section between an Me 163 and the XP-56. We have an Me 163, well ... a 100% full scale replica, as well as a real Japanese rocket interceptor based on the Me 163, and you could never get an R-2800 in either of the rocket planes, even if there was nothing inside the fuselage at all.

The design would have to be blown up to incorporate such a large engine, as the XP-56 was. However, Cd and aerodynamic performance should not change with the size of the design, otherwise wind tunnel models would always have to be full size. Area drag certainly would and power would have to be added accordingly. But, if a small version works aerodynamically, it is reasonable that the big version would also. Now, it is true the two aircraft are not identical but scope wise they are similar.

GregP · Jul 12, 2014

Similar configurations, yes, but the entire fuselage of the XP-56 was pretty fat while the Me 163 is pretty thin by coparison. To be sure, I'd have to take measurements and try scaling an Me 163. but the XP-56 just looks slow to me and it was. Some analysis might shed some light, but it's not that interesting. I've never seen a Cd0 for either aircraft and am not sure if there are already some analyses already out there to peruse.

So I'll agree the planforms are similar and say it might have been a different beast with a jet or rocket engine in it.

davparlr · Jul 12, 2014

Here's another short, stubby and blunt-nosed aircraft about the same size as the XP-56 and is known to be pretty fast.

Milosh · Jul 12, 2014

wuzak · Jul 12, 2014

davparlr said:
I have a hard time biting on the turbulent airflow. The fuselage appears too clean. Exhaust disruption is a possibility but could be addressed (route exhaust to the end of the vertical stabilizers?). Also, Consolidated, Dornier, and Northrop did not seem too concerned about locating the exhaust in front of the propeller. I would guess that the cause of the poor performance would be the exhaust disruption of the prop or, more likely, and based upon the flight test performance (the plane was nose heavy), the plane was out of trim due to messed up cg. Or, the wings were draggy.

Quickly reading back through the book American Secret Pusher Fighters of World War II by Gerald H Balzer, I've found that the fusealge alone wasn't thought to be the culprit for flow separation and the poor performance of the aircraft. The wing was thick (18%), which would not help, but it was the wing/fuselage interface which caused the flow disruption, due to the change in cross sectional area. The cooling intakes at the leading edge of teh wing were also thought to cause some flow disruption.

NACA's performance summary of the XP-56 estimated its top speed to be 340mph. Clearly there was more than an underperforming engine at play.

wuzak · Jul 12, 2014

wuzak said:
Look at the relative size of the B-36 props to its nacelles and the XP-56's to its fuselage.

davparlr said:
B-36 engines were almost twice the power with twice the cooling and twice the exhaust.

And the same diameter. The point I made about the size of teh B-36's props was that more of teh blade area would be in the free stream, and this the efficiency would be higher.

The F8F's prop was entirely in the free air stream, though the size of the radial and the blockage caused by the fuselage would have reduced the prop's efficiency - NACA did a study that showed that propellers were slightly less efficient ahead of radials than in-line engines due to the flow restriction behind them.

wuzak · Jul 12, 2014

We seem to have wandered off-topic and started talking about unconventional fighters. Which is unusual, since the XP-60 was far from unconventional.

XP-60

XP-60A

XP-40Q-1

XP-40Q-2

XP-60
Specifications
Crew: one
Length: 33.625 ft (10.25 m)
Wingspan: 45.44 ft (13.85 m)*
Wing area: 275 ft² (25.6 m²)
Empty weight: 7,008 lb (3,179 kg)
Loaded weight: 9,700 lb (4,400 kg)
Powerplant: 1 × Rolls-Royce Merlin 28 (eqivalent to Packad V-1650-1), 1,300 hp (969 kW)

Performance
Maximum speed: 387 mph (623 km/h) @ 22,000ft (6,706m)
Service ceiling: 29,000 ft (8,839 m)
Time to climb: 7.3min to 15,000 ft (4,572 m)

*Data is from Curtiss P-60 which differs in wingspan from Curtiss P-60 - Wikipedia, the free encyclopedia in wing span, though the area specified is the same.

XP-60A
Specifications
Crew: one
Length: 33.625 ft (10.25 m)
Wingspan: 41.33 ft (12.60 m)*
Wing area: 275 ft² (25.6 m²)
Empty weight: 7,008 lb (3,179 kg)
Loaded weight: 9,700 lb (4,400 kg)
Powerplant: 1 × Allison V-1710 with B-14 turbo, 1,300 hp (969 kW)

Performance
Maximum speed: 420 mph (623 km/h) @ 29,000 ft (8,839 m) estimated **
Service ceiling: 35,200 ft (8,839 m)
Time to climb: 6.5min to 15,000 ft (4,572 m) estimated
12.4min to 25,000 ft (7620 m) (Vees for Victory)

*data from Curtiss P-40Q, which now agrees with wiki on span
**Vees for Victory doesn't mention this performance as an estimation.

For comparison purposes (and since it used teh same engien as the XP-60)
P-40F
General characteristics
Crew: One
Length: 31 feet 2 in, from P-40F-5-CU 33 feet 4 in (10.16 m)
Wingspan: 37*ft 4 in (11.38*m)
Wing area: 235.94*ft² (21.92 m²)
Empty weight: 6,590*lb (2,990*kg)
Loaded weight: 8,500*lb (3,855*kg)
Maximum gross takeoff weight: 9,350*lb (4,238*kg)
Powerplant: 1 x*Packard V-1650-1, 1,300*hp

Performance
Maximum speed: 364*mph at 20,000*ft (585*km/h)
Service ceiling: 34,400*ft (10,500 m)
Climb rate: to 20,000 ft (6,100 m) in 11,6 min

Curtiss P-40 Warhawk variants - Wikipedia, the free encyclopedia

P-40Q
General characteristics
Crew: One
Length: 35 feet 4 in (10.77 m)
Wingspan: 35 feet 3 in (10.74 m)
Maximum gross takeoff weight: 9,350*lb (4,238*kg)
Powerplant: 1 x*Allison V-1710-121, 1,425*hp

Performance
Maximum speed: 422*mph at 20,500*ft (679*km/h)
Service ceiling: 39,000*ft (11,887 m)
Climb rate: to 20,000 ft (6,100 m) in 4.8 min

Curtiss P-40Q

wuzak · Jul 12, 2014

Oh, and the XP-60 first flew on September 18, 1941. The XP-60 was converted to XP-60D spec with the V-1650-3 in August 1942.

GregP · Jul 12, 2014

Give me the P-40Q any day. 4.8 minutes to 20,000 feet as opposed to 6.5 minutes to 15,000 feet for the XP-6A.

That 4.8 minutes beats a lot of 1944 - 1945 competition.

wuzak · Jul 13, 2014

GregP said:
Give me the P-40Q any day. 4.8 minutes to 20,000 feet as opposed to 6.5 minutes to 15,000 feet for the XP-6A.

That 4.8 minutes beats a lot of 1944 - 1945 competition.

I would imagine that the XP-60A could have climbed better had it the 1700hp the XP-40Q had available.

GregP · Jul 13, 2014

Maybe, but it didn't. I'm looking at the planes you wanted to compare, not something that might have been created from it by modification.

If you start doing that, you can't come up with an answer since everything has a "what if" attached to it.

Shortround6 · Jul 13, 2014

The trouble with comparing the P-60 and the P-40Q is that by the time the P-40Q comes along the P-60 is a done deal. And I mean well past 'stick a fork in it, it's done'

By the time the XP-40Q is flying with a 1700hp engine the P-60 has gone to the "E" model using the same engine as a Hellcat (tested Elgin Field Jan/Feb 1944). And the P-60 is far from a finished product. The Merlin powered XP-60D had crashed on May 6th 1943.
The XP-60E with the Hellcat engine was supposed to do "Maximum speed was 410 mph at 20,200, 391 mph at 24,200 feet," with an engine giving 1650hp at 22,500ft. Of course the radial engine tends to screw up a drag comparison with a P-40Q.

As I said back in post #3 the P-60s as built were saddled with a 275sq ft wing, which while showing a bit less drag than the P-40 wing didn't really allow a big performance jump with the available engines. The P-60 was supposed to have been refitted with a two stage Merlin but no performance figures seem to have shown up?

Armament was cut from the initial eight guns to six and then four in an attempt to get the performance up to what was wanted. Had the designers been given a four gun requirement to begin with the wing, while still laminar flow, might have been a lot closer to the size/area of the P-40 wing with some gain in performance.

The P-40Q performance is certainly competitive with a number of aircraft in service in the spring/summer/fall of 1944. The trouble is that the P-40Q is NOT using a production engine and production engines with that power rating don't show up until the winter of 1944/45 (if then).

The "what if" falls back to what engines were really available when and what the differences in the air frame (wing/s) were.

another picture:

BTW, for all those people who want to stick an R-2600 on a P-36.... It is just about the same diameter as an R-2800.

BiffF15 · Jul 13, 2014

wuzak said:
We seem to have wandered off-topic and started talking about unconventional fighters. Which is unusual, since the XP-60 was far from unconventional.

XP-60

XP-60A

XP-40Q-1

XP-40Q-2

Curtiss P-40Q

Gents,

Here is my question or questions:

The first XP-60 has inward retracting landing gear on what looks like an elongated P-40 type wing with 6 guns, while the XP-60A (fatter fuselage) has no gear doors and I'm unable to determine which way the gear went. On the P-40Q models it looks like the standard retract aft gear. Since drag and armament were both of serious importance, why didn't Curtis give the Q model inward swinging gear for less drag? This would open up room for more guns as it appears the Q used some space for the gear, and some for the coolers?

Cheers,
Biff

Shortround6 · Jul 13, 2014

A P-40 used a fairly narrow track landing gear (not as narrow as some but narrower than others) of 8ft 2.5 in ?

On most of the P-40s there were two fuel tanks inside the wing between the wheels, one behind the other on the centerline.

Also on the P-40, it used a 5 spar wing with the the #3 spar not quite being mid cord, it was right in front of of the wheel well with #4 being right behind the wheel well ( and having a slight curved section to clear the wheel).

On the P-40 the landing gear struts did NOT retract into the wing but laid on the bottom of the wing with fairings over them.

This left spars #1 2 un-notched. Redoing the P-40 landing gear for either inward or outward retraction and flush fitting basically calls for a new wing structure which rather negates the advantages of using the existing P-40 tooling.

BTW, thanks for the question as I had not really thought about and looked into before you asked.

BiffF15 · Jul 13, 2014

Shortround6,

Thanks for the explanation! I'm thinking another way of looking at is:

-The P-40Q had the fuselage cutdown for the bubble canopy (eventually) which I'm sure was a significant engineering task
-The Q also had to have more engineering work done to integrate the new "nose" / coolers / radiators into the K/N front section
-The standard P-40 wing had to be "clipped", plus tooled for more cooling ducts and possibly two more guns (total of 6)/ or cannons
-The P-60A wing had inward swinging gear (engineering work already done for the Warhawk fuselage integration)

It seems to me that most of the "lego" parts were at the Curtiss plant but not put together into one cohesive design (although the Q in my opine is the ultimate looking P-40 varient). Notice to all I said OPINE.

Why not combine all the above into the Q to lower drag / increase armament and speed?

I'm guessing that Curtiss had enough on it's plate that it couldn't focus enough talent into solving this. I've been a fan of the Q since I was a kid and always sort of thought of it as a serious "could have been".

Cheers,
Biff

P-40Q vs P-60A/D

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