P-40 vs. ME-109

[FLYBOYJ]

Maybe, but they still had the same HP. (with normal boost limitations of the Merlin) Top speed probably wouldn't change, but climb probably would. (like with the P-47's paddle prop, no change at high speed, but climb and initial acceleration did)

If you change a prop (pitch, blade count, etc.) you gain and loose. What you make up in climb, you're gonna loose in speed, what you make up in speed, you loose in fuel consumption and so on. Matching props to the airframe/ engine combo is an exact science and sometimes compromise is the end result.

 

[kool kitty89]

Hello
as it stands, 7sec for 180deg, especially mentioned that it went to turn clearly faster than Hawk 75A (P-36), so 360deg probably appr 13 sec.

Juha

Sorry missed the 180 degrees, but why 13 sec and not 14 for 360*?

The B-239 was certainly agile though, and could certainly out "dogfight" the Hurricane I. (though the Hurri had much better performance above 10,000 ft, the Finn's Brewsters' engines being rated for low altitude)

 

[Soren]

If you change a prop (pitch, blade count, etc.) you gain and loose. What you make up in climb, you're gonna loose in speed, what you make up in speed, you loose in fuel consumption and so on. Matching props to the airframe/ engine combo is an exact science and sometimes compromise is the end result.

100% true!

 

[Juha]

Hello Claidemore
because 1st half of full turn takes more time that the 2nd half, but because Finns reported that 239 went into turn clearly quicker than Curtiss Hawk 75 which was a good turner. maybe 13½ sec is nearer to truth.

HoHun
"I think that these figures are not directly comparable probably means that we have only some bits of the reports, not that the Finns didn't test systematically."

Probably Finnish test got more scientific as time passed. In 1942 it became clear that the new fighter, Myrsky, would be too slow to be used as first line fighter and Finns began to design a faster fighter, Pyörremyrsky, with DB605A engine. My guess is that Bf 109G-2 was seen as very interesting a/c for thorough testing to get basic data for modern high speed fighter. Finns went to roomier, bigger wing solution.

Finns were very pleased with Brewster Model 239 and planned to built 90 "copies" of it, called Humu (new, wooden wing, different fuel tank system, war booty M-63 engine etc), so they probably tested 239 thorougly.

MS 406 was also much tested, because Finns modified it for war booty M-105P engine, so called Mörkö-Morane. Main reason for this project was that MS 406 was underpowered and clearly too slow and too poor climber. So maybe the turning ability of MS 406 was not test as thorougly that 239 and 109G.

Juha

 

[kool kitty89]

Yeah, (on the prop issue) plus there's the fact that the Merlin P-51 would be operating with much higher powers at altitude as well.


THe Humu turned out to be a bust though, too heavy and much slower than the B-239. It also came even later than the Mirsky, which was considerably faster than the B-239.

 

[drgondog]

Yeah, (on the prop issue) plus there's the fact that the Merlin P-51 would be operating with much higher powers at altitude as well.


THe Humu turned out to be a bust though, too heavy and much slower than the B-239. It also came even later than the Mirsky, which was considerably faster than the B-239.

KK- As Joe said - it's more complicated...

Prop design is all about rotating 'wings'.. more props in the disk (usually) mean more thrust and more drag, ditto increasing pitch to take a bigger bite (higher local angle attack) but getting more drag and requiring more torgue, keeping the diameter to point below tip speed>high transonic, keeping the prop at smaller diameter but greater RPM so my airplane can take off and land w/o stubbing a prop, resonance issues based on natural frequency of the blades, etc, etc..

As you speculated "where do I want my best performances at (pick one - long range cruise?, high thrust at altitude where the density/drag is lower?, etc, etc)

 

[Hunter368]

Damn I need a note book to write this all down, good day guys. Lots of great information and facts today.

 

[FLYBOYJ]

KK- As Joe said - it's more complicated...

Prop design is all about rotating 'wings'.. more props in the disk (usually) mean more thrust and more drag, ditto increasing pitch to take a bigger bite (higher local angle attack) but getting more drag and requiring more torgue, keeping the diameter to point below tip speed>high transonic, keeping the prop at smaller diameter but greater RPM so my airplane can take off and land w/o stubbing a prop, resonance issues based on natural frequency of the blades, etc, etc..

As you speculated "where do I want my best performances at (pick one - long range cruise?, high thrust at altitude where the density/drag is lower?, etc, etc)

Just for the discussion - I had to choose a prop for our Supercubs - one that would pull at a high altitude (the academy is 6000' MSL) and at the same time limit noise and be efficient enough so we could fly our cubs cross country. After 3 weeks of research I had a headache for a week and didn't even want to see a propeller!

 

[kool kitty89]

Sorry, by yeah, I was agreeing with Joe that it's more compicated than I was initially thinking. I was just pointing out that, despite similar power up to ~10,000-12,000 ft there would also be more consideration of power at high altitude with the Merlin. (at 18,000 ft the V-1710-81 dropped to ~1,100 hp)


Also it may not have been the prop that resulted in the P-51B's better climb at low alt (obviously at high alt as well), but that it seems that it used the full 1,485 hp at 10,000 ft while the P-51A tests were limited to 1,320 hp at a similar altitude. (in the speed tests full hp was used) If pushed to full WEP the P-51A would probably climb at least as well as the P-51B from 3,000 ft to 11,000 ft. (below 3,000 ft power would limited by overboost)

P-51 Mustang Performance
Mustang (Allison Engine) Performance Trials

 

[drgondog]

Just for the discussion - I had to choose a prop for our Supercubs - one that would pull at a high altitude (the academy is 6000' MSL) and at the same time limit noise and be efficient enough so we could fly our cubs cross country. After 3 weeks of research I had a headache for a week and didn't even want to see a propeller!

ROFLMAO - just go fast forward and try to figure out what kind of rotor you need to put on a completely divergent system from your entire design experience - one in which you go from two blade semi articulate to four (or more) blade, rigid rotor for a new attack helicopter RFP - and we lost to the Apache.

There is art, and science. The good news is you can try a lot of differnt designs after you make your decision - to fine tune the analytics. A major benefit to test versus 'analyze' when involved in the Arcane.

I have never done any analysis on a conventional prop other than class work.

 

[drgondog]

Sorry, by yeah, I was agreeing with Joe that it's more compicated than I was initially thinking. I was just pointing out that, despite similar power up to ~10,000-12,000 ft there would also be more consideration of power at high altitude with the Merlin. (at 18,000 ft the V-1710-81 dropped to ~1,100 hp)

KK- it is complicated making design trade offs, because every 'positive' advantage usually has a negative somewhere else. For the Merlin at least one of the parameters was established - namely the best thrust RPM was 3000rpm. At least one 'given' was available before going to the rest of the considerations.

Also it may not have been the prop that resulted in the P-51B's better climb at low alt (obviously at high alt as well), but that it seems that it used the full 1,485 hp at 10,000 ft while the P-51A tests were limited to 1,320 hp at a similar altitude. (in the speed tests full hp was used) If pushed to full WEP the P-51A would probably climb at least as well as the P-51B from 3,000 ft to 11,000 ft. (below 3,000 ft power would limited by overboost)

If the P-51A had been tested with 150 octane fuel and tested at full boost it should have been close to the B and probably better than the D up to somewhere around 15,000 feet. I would have to look at flight test data to get a sense for best climb speed and angle for all of them. I remember that both the 109 and 190 climbed at a steeper angle, if not a steeper rate of climb - as an example - one of the reasons a 109 with a good pilot could initially escape from a Mustang with a tight spiral climb

P-51 Mustang Performance
Mustang (Allison Engine) Performance Trials

Remember 'time to climb to 20,000 feet is not possible to calculate simply by using rate of climb - it was different for different altitudes as the Merlin was exercising power available in low blower, kicking over to high blower and then climbing at a different rate (slower as the power/thrust available continued to fall off)

 

[kool kitty89]

Ok, but I didn't say anything about time to altitude. (there are figures there for that too though)

For some reason the climb power is different from the high speed test's power too.

For the V-1710-81 "normal" takeoff power was 1,200 hp. According to those tests throttle was limited up to 10,400 ft. (even in WEP, though 1,480 hp could be acheived above 3,000 ft at partial throttle) If the Boost limitations had been removed with 100/150 octane avgas,, max power output should have been increased significantly.

 

[Juha]

Hello kool kitty
you have very good knowledge on FAF a/c. Yes, Humu project was stopped after one prototype was flown, it has survived and can be seen at Keski-Suomen Ilmailumuseo. Main reason to its slowness was that M-63 gave less power than expected.

Myrsky was some 30kmh faster than Model 239, at least its Pilot's Notes gave max speed as 515kmh, IIRC. IIRC max speeds of protos were 530-535kmh. But it was slow for its day as first line fighter, even without serious flutter problem IMHO it would not have been ready for sqn service before the beginning of 44, and because of the flutter problem it began combat sorties as recon fighter in Aug 44 and IIRC flew only 66 combat sorties before armistice with SU in 4th Sept 44.

Juha

 

[kool kitty89]

One of the major problems with the Mirsky was the construction (wood+steel tubing), which had structural problems as well as maintence issues. (particularly in wet environments). It was a decent a/c but it came a bit late for it's performance. Considdering what the Finns had to work with otherwise it was pretty good, though not as high performing as their 109's, and probably not as agile as the B-239. (due to higher wing loading) It was a nice plane (good lokng IMO) with a concentrated armament of 4x 12.7 mm cowl guns. Visibility was also about as good as the Brewster with the clear rear decking.

But again were getting a little of topic.

 

[drgondog]

Ok, but I didn't say anything about time to altitude. (there are figures there for that too though)

For some reason the climb power is different from the high speed test's power too.

For the V-1710-81 "normal" takeoff power was 1,200 hp. According to those tests throttle was limited up to 10,400 ft. (even in WEP, though 1,480 hp could be acheived above 3,000 ft at partial throttle) If the Boost limitations had been removed with 100/150 octane avgas,, max power output should have been increased significantly.

The only reason I mention it is that virtually all engine/propeller designs were geared for the strike zone they wanted best thrust.

All of the best engines had one form or another of 'sawtooth' hp output as a function of altitude .. some aircraft climbed to altitude at a speed and climb angle different from another. So from a math standpoint, the calulations are step functions also.

Ditto turn performance... particularly in the case of an aircraft losing energy and speed. It ain't enough to apply static L/D/Gravity free body diagrams as the vectors change as a function of AoA and flight path and thrust available for the manuever.

All must be integrated as a function of rate of change (and time) of several variables..As you and several others have noted - a plan view of a high G turn would look like a like a curvelinear path (not a circle) in which both the rate of change of velocity and 'theta' would be integrated as a function of time. The radius of the turn would be lower on the back half of the circle than on the high energy side.

Some may perceive the analytical solution as simple.. but it never has been for serious students of the 'problem'.. and certainly not for me.

 

[kool kitty89]

I found some info on the P-40's (Hawk 75 actually) stall characteristics in a British comparison test.

They said that the stall was fairly mild but there was no warning until the stall hit and the wing drooped. The stall was easily and quickly corrected. This makes me think there was relatively little washout on the P-40's wing.

 

[FLYBOYJ]

They said that the stall was fairly mild but there was no warning until the stall hit and the wing drooped. The stall was easily and quickly corrected. This makes me think there was relatively little washout on the P-40's wing.

That's typical of of almost any stall, using right rudder to counter the wing drop (power on stall). If the P-40 is stalled at an extremely nose high attitude (power on) there is a possibility it could flip on its back and tumble - I read that in some pilot reports and that also might be mentioned in the -1.

 

[kool kitty89]

But there is no buffetting at the stall onset either, the RAF testers said it came on with less warning than the Spit, although the actuall stall was relatively mild and easy to correct.

In the case of the 109 the slats gave very mild stall characteristics on the F and later models. (the Emil and earlier models had slats that were sensitive to dirt and pron to jamming under high G conditions, they also opened very rapidly and caused the ailerons to snach and the a/c to shudder; the new slats were reliable and simply gave a "clunk" on full deployment)


And there's lot's on the P-40 performance and engines here: Perils P40 Archive Data

 

[claidemore]

From the Tomahawk 1 manual:

STALLING
15. The stalling characteristics of this aircraft are good. At minimum speed the stall is gentle and there is some buffeting and pitching before the wing, generally the right, drops gently, followed by the nose.

At high speed the machine can be stalled as a result of the coarse use of the elevators producing high acceleration loadings, but due warning is received, particularly on the high speed turn, by a shuddering of the aircraft, and loads of over 5g. can be applied to 180 to 200 m.p.h. without the aircraft stalling.

The stalling speeds of the aircraft at normal operational loads, were as follows:

Undercarriage up and flaps up - 80 I.A.S.

Undercarriage down, flaps up - 82 I.A.S.

Undercarriage up, flaps down - 73 I.A.S.

Undercarriage down, flaps down - 75 I.A.S.

Note that the P40 could pull 5 g at 180mph, while the 109 E was stalling at 3 g at that speed, according to RAE tests.

My understanding is that the LE slats in the F G 109s also caused aileron snatching, enought to disturb aiming. The difference between them and the ones on the Emil was that they didn't jam and were more reliable, opening simultaneously, rather than one at a time.

The problem with high lift devices, is that they are devices, and so the opportunity exists for them to malfunction. Willy M didn't use the KISS system when he chose that wing.

 

[kool kitty89]

According to Kfurst and Soren, the F's (at least the late F's) and all G and later models slats extended gradually and smoothly with a 'clunk' being heard and felt in the stick when fully extended, no directional changes occured.
These slats were of the same mechanism as on the Me 262 and F-86, and I don't remember any report of jostle/jolt etc occuring durring slat deployment on those a/c.


And on the stall; from R&M2379-curtiss H.75 Spitfire Gloster f5 aileron test.pdf (posted on the 109 v. Zero thread iirc):

There is good all-round control down to the stall, at which wing drops sharply without any pronounced stall warning.