Glider
Major
I've pulled approx. 6G in a glider at around 150 knots on a number of occasions when doing aerobatics and the most just above 8G when on a course. Speed has almost nothing to do with G forces. Where did you get that idea from?
Which is the better fighter, P-40F or Typhoon? (1 Viewer)
- Status
- Thread starter
- #782
I'm no aeronautical engineer but I'm gonna go out on a limb and say gliders have a much lower stall speed than a 7,000 lb fighter...
Glider
Major
The question is what has that got to do with the relationship between G forces and speed. By the way stalling speed also has nothing to do with it and I am confident that every fighter could pull over 4G. It's nothing special.
So just to repeat myself where did you get the idea that the following statement has anything to do with reality?
P-40s could sustain far more than 4Gs and the limit was basically what the pilot could endure. Of course any WW2 fighter will lose altitude in a turn though naturally. Usually you aren't pulling G's at all unless you are going pretty fast to begin with
I was about to post the same question.
- Thread starter
- #785
That's quite interesting and thanks for posting it because I hadn't seen it before.
But that is an overloaded P-40F, and much more importantly, flown at cruising power to max continuous power, not combat power settings.
The Merlin XX (the type used in the P-40F/L) is a pretty well known engine, and it's normal boost settings are also well established. 48" Hg (American) is just under 9 lbs boost under the British system (see here for a helpful conversion chart). My understanding is that the normal allowed boost was up to +14, with WEP at +16 lbs. That is considerably more horsepower.
These things can be confusing as comparisons between aircraft are often made showing HP of one under military power, another under normal WEP boost, and another using water injection or overboost settings. Similarly tests were done under different conditions and for different purposes, at various engine settings.
Here is another British test from Sept 42
http://www.wwiiaircraftperformance.org/P-40/Kittyhawk_II_performance_9sept42.jpg
I'll repeat the key passages:
"Following performance figures for Kittyhawk II have been obtained by B.A.C. pilot and agree well with U.S. Army results:
Level speeds
(a) Without air cleaner 370 mph at 20400 feet and 347 m.p.h. at 30,000 feet"
So obviously they are using different boost settings. US Army figures often quote 368 mph or 370.
Of course, in the field when frequently facing enemy fighters they typically stripped two of the four guns out, removed forward wing tanks and bomb shackles, and carried less fuel. Hence the P-40L at 8,000 lbs.
- Thread starter
- #786
This isn't something I particularly want to wade into since, as previously stated I'm no aeronautical engineer. I don't claim to know the physics of any of this particularly well. But Ok I'll bite.
Having read a lot of WW2 pilot accounts there is a close association with maneuvering at high speed and excessive G forces. Pilots routinely report blacking out during pull outs from high speed dives and while doing hard bank turns at high speed.
I know in my car if I turn 90 degrees around a city block corner at 10 mph I feel less G force than if I make that same turn at 60 mph. At the latter speed my tires squeal etc. and I feel pressure pulling me toward the outside of the turn. If I'm not careful I could flip the car.
From what little I understand about the physics, in an airplane a given turn will normally take longer in space at a higher speed. I think maybe you get G forces when you try to cut that turn tighter (like for example, when trying to pull lead on a target or trying not to let an enemy pull lead on you). I do know you can also pull G at lower speeds too if you turn very tight. In civilian flying you have 'normal' turn rates and everything is kind of standardized, but in stunt or combat flying you would push the limits much more, particularly the latter where your life is on the line. Sharp bank turns also increase stall speed and it was routine for combat pilots to snap roll and go into spins when trying to execute hard bank turns.
My only very limited piloting experience is in a Cessna 172 and that aircraft neither flies fast nor has acrobatic capabilities. I have experienced (light) G forces in a turn in a Cessna but it's nothing like a WW2 fighter. I think similarly while gliders or sailplanes can be acrobatic don't fly at 400-500 mph. I could be wrong though no expert and don't claim to be.
Maybe somebody else who does know the physics better can explain it.
- Thread starter
- #788
Ah, gotcha, so a tighter turn at higher speed will pull G quickly, but a very tight turn at lower speed will also pull G. Is that right?
The reason I had previously mentioned low stall speed on gliders / sailplanes is that I assume with their very low wing loading that they can pull lots of very tight turns for longer than a much heavier fighter plane can (because the latter will stall quicker). Therefore gliders can do more high G turns at lower speed.
It does not state that the P40-f is in overload state but it does have full fuel, ammo, radios, 6 x.50 mgs and armour ect. The merlin XX was, as you say, a pretty well known engine as it was first seen in action with Hurricane IIs in 1940. That being said I have not seen any engine rating for it higher than 9lbs that was not the 5 min WEP rating. Typical settings for the XX were just that 9lbs @ 3000rpm and 12 lbs at WEP using the emergency boost over ride cutout. 12 lbs was limited to the low speed supercharger gear. In late 42 the settings were inxcreased to 14 lbs WEP in low and then very shortly later to 14 in low and 16lbs in high, these were all WEP 5 minute ratings. Check here http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-18nov42.jpg and here http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-21nov42.jpg
After having read the whole report it is interesting to note that the limitations stated for the Merlin XX in the P-40F, for all out level were 3000 rpm and 9 lbs boost with a 5 minute limit. 12lbs boost was only allowed for take off. I wonder why that would be as 12lbs boost had been used by Hurricanes for years, were there problems with the proper operation of the merlin XX in the P-40F?
- Thread starter
- #790
Well, lets be precise, that guy wasn't just a test pilot he did the checkout flights for ~ 2,400 P-40s, in other words he put them through their paces to make sure they were capable of the normal combat performance expected of the aircraft and engine. P-40s were incidentally rated for 10Gs which is of course far more than a WW2 pilot could normally endure in the types of seats they had and without a G suit and so on. It's also why P-40s were so tough they were a little bit overbuilt.
I brought this up because it shows not merely that one or two guys dove the P-40 at 500+ mph, (or 600+ mph as was done in at least two other individual tests by Curtiss) but that a dive of 500+ mph was part of the normal routine checkout flight for the aircraft. Also Shortround had brought up the question of how many feet did you have to descend to reach high enough speed to intercept a Fw 190 and I thought that example gave us some insight into that question though it does not answer it definitively.
No, I answered it. I am basing that on the previously posted (not by me) turn radius chart and the NACA roll chart that everyone has seen. I also pointed out that per the memo you yourself reported the pilots said there was extreme vibration any time they tried to enter more than a 4G turn, which as you noted is not that much of a turn for a fighter, and that turning left at 4G caused the plane to go into a snap roll and stall. They did overall say favorable things about it though anyway I agree, and tended to say less than favorable things about the P-40N in some similar tests.
Finally, I also pointed out a couple of times the video in which one Typhoon pilot noted that "if the trim tab goes on a Typhoon your a finished". One of the other Typhoon pilots in another interview I posted upthread said "the Typhoon was not a good fighter" (but that it was an ideal rocket platform).
I didn't go cherry picking through Typhoon pilot interviews to find negative comments about the plane. I just googled "Typhoon Pilot interview" - for all I knew I was going to get pilot after pilot praising the Tiffy and describing how great it was at shooting down enemy fighters, but that is not what they said. You try it yourself and see what comes up.
See above for the answer. But that is just my opinion, I'm not claiming it's definitive. You said the NACA chart is an estimate? That is the only real hard data I know of. If it turns out that the Typhoon turned and rolled very well then I definitely agree it was a better fighter than a P-40. I don't think that was the case but I'm ready to be surprised. There must be some more concrete data somewhere that we can compare.
I know from previous discussions about the Hurricane roll can be tricky to test because sometimes they test with moderate stick force vs. heavy, there is a difference between maximum roll rate and roll acceleration and so on.
To summarize based on what I've seen so far, the Typhoon rolled slowly and had a limited turn rate. Maybe they only lost 20 or 30 to tails falling off but I suspect if you were a pilot that knew some were lost that way, and started a turn and felt "severe vibration of the airframe " he might hesitate to turn more. However that doesn't mean they were necessarily a bad fighter - that was a very fast plane especially down low and hit and run tactics do work very well. I think a good rate of roll is helpful but it isn't required.
- Thread starter
- #791
No it doesn't but it posts the weight at ~8,900 lbs which is 400 lbs more than the official "loaded weight" for a P-40F and about 850 lbs more than the "loaded weight" of a P-40L. 8900 lbs is closer to the gross weight. I've already posted sources for this and I believe other posters here acknowledged it but if you need me to I can do it again.
Well, as you noted - the ratings kept going up didn't they (partly due to improving fuel) long before the P-40F or L were even in action. From 12 to 14 to 16, and that is the official limit. By the time 16 lbs is the WEP setting do you think 14 is still just safe for 5 minutes? How about 12? Or 9 lbs?
By the time the Merlin XX / 28 was in action in the P-40 the engine was quite thoroughly tested and had been improved by Packard who introduced "indium" coatings to the crankshaft bearings, making them more resistant to corrosion and more importantly, wear.
No there was no problem. Those are just the old restrictions. I've already posted war diaries describing flying from 55-65 Hg (from +14 to +17 lb) for more than 20 minutes.
S
I found reference to +12 lb here. I haven't come across the Kittyhawk II pilot's notes but I'd put money on allowance for higher than +9 lb.
Shortround6
Lieutenant General
The revised June of 1943 manual for the P-40F says 61in of MAP in both low and high gear for WEP.
The chart also says 1300hp which is absurd.
The chart also says 1300hp which is absurd.
- Thread starter
- #794
Very interesting, thanks. Do you have a source for that? Is the manual online somewhere?
Shortround6
Lieutenant General
The manual is here, on this site.
P-40 Flight Manual
see. Other Mechanical Systems Tech.
for all kinds of manuals.
Schweik,
Just a few things that at are food for thought. First, your assessment of speed relative to G available is pretty close. The faster you go, the more G available you have, up unto either the Flight Manual limit, your limit, or the structural limits of the plane. The speed where you can full aft snatch the stick and not over G the plane is today called corner velocity. Above corner velocities any extra speed can be used to sustain max allowable G, or over-stress the AC if required. Conversely the slower you go the less G available all the way down to stall speed (wings level).
Second you have commented about the P40 dive speed allowing intercepting or catching Me109s or 190s. Realize the dive intercept is not easy as you have to realize whether a target is in range, then dive on it and do a good enough attack that you actually get a snap shot (quick squeeze of the trigger), and maintain enough energy / speed to safely get away. It's not easy is what I'm saying.
Third the comments by the Typhoon pilot regarding how the plane flew terrible, what was his perspective or comparison? The guys who went from the Spit to the Tbolt probably said the same thing. However each airplane has its strengths and weaknesses and it's up to the community to teach and the pilot to learn how to use them. If a Viper / Hornet guy jumped into an Eagle he would hate it at first since it flies nowhere near as nice however it's a much better war machine at heart. I have flown with these guys and they came around but it took a while. I flew it initially and had no reservations as it was what I knew. Earlier I mentioned the Spit, which has a wonderful reputation as a great, easy, responsive plane. If that's your first, you measure all others that follow by that yardstick if you will.
Lastly is Squadron versus Squadron comparisons. Two squadrons flying the same planes are not by any means to be assumed equal. The experience/ maturity of the pilots is one thing, the same for maintenance is another, and wing, theater, numbered Air Force is yet more of the same. Logistics, weather, and morale are variables as well. I've been in a wing with three squadrons of 24 A/C, and one squadron would always be stronger than the other two, and that changed every year to year and a half. Lots of variables. Comparing one squadron of German fighters in the MTO or Africa with a unit in Germany that's been in constant contact with Allied fighters / bombers in a different environment (high altitude at least initially), flying two or three times a Day is not a good comparo.
Once again just food for thought.
Cheers,
Biff
wuzak
Captain
So the Hornet is more responsive/agile, but the Eagle has greater all round capability?
The Hornet has higher AOA limits, lower max G limits and a lower thrust to weight. It's a tremendous slow speed fighter, bleeds energy like mad and is slower to accelerate. They are a fun fight!
The later model Vipers have gigantic motors, bleed energy slowly, and accelerate like a rocket. They are small, difficult to see and can sustain high G well, and can even accelerate at 9Gs in some regimes. Very difficult fight if flown well.
Cheers k
Biff
Heres the power curves for the merlin XX series
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-curve-c1.jpg
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-curve-c2.jpg
It looks like the merlin XX is already down to 10 lbs boost @ 17.5 k, at 20k its down to 7.5 lbs, therefore the increased boost allowances won't have any affect on the P-40 F max speed of 354 mph @ 20,200 ft.
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-curve-c1.jpg
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-curve-c2.jpg
It looks like the merlin XX is already down to 10 lbs boost @ 17.5 k, at 20k its down to 7.5 lbs, therefore the increased boost allowances won't have any affect on the P-40 F max speed of 354 mph @ 20,200 ft.
- Status
Users who are viewing this thread
Similar threads
