P40 Vs all other fighters in Europe

[BiffF15]

once you are dealing with high speeds you have more variables to come out and play with

Drag goes up with the cube of speed.
Your Lift goes up with the square of the speed.
The engine power (as opposed to propeller efficiency) is a combination of air density (not much change in speed) and the RAM effect of the intake and the pressure ratio of the supercharger on WW II airplanes.
Some of this is somewhat academic.

If your plane will only fly at 330mph true instead of 345mph true at 10,000ft due to hot temperatures you aren't going to know it. You are going to be looking at IAS for airspeed and the airspeed indicator is reading the existing air pressure (density). If the enemy airplane is also by 10-15mph from it's "book" figures it is going to take a long tail chase to to figure out the speed difference.

The speed/climb differences at 80-150mph when taking-off and landing are what can kill you every time you take-off and land.

View attachment 654450

I have no idea why they figured out the chart this way instead of using 59 Degrees (standard day) but the Army Charts are measured from O degrees C and 32 degrees F. (maybe they figure you know the difference between your boots sliding on ice or splashing through a puddle?). But at just about 92 degrees for the P-38 your take off distance will be 20% higher than the chart shows. North Africa can be worse.
Note that they are only figuring a 10% increase in time to climb compared to the 20% increase in take-off run.

Shortround6,

My guess on why the charts start at 0c for simplicity. Notice there are no corrections for below 0c (Assumption none needed. I fly the A319/320 and some of our charts bottom out at -5c). Makes for simpler math for your airmen.

Cheers,
Biff

 

[Thumpalumpacus]

I get that, my observation was, maybe aircraft with a little bit higher wing-loading and a shorter wingspan might have a bit more trouble in thinner air. Not saying that's it so, just speculating.

I think it's sound thinking. A smaller wing develops less lift anyway, and it stands to reason that in less-dense air a smaller wing carrying the same weight will have more trouble.

Mine wasn't a correction to you, simply an added thought.

 

[pbehn]

Spitfires were extensively tested by the RAE in regards to the who what and when and their effects speed, aerials, guns, blisters, ejection ports, rear view mirrors, exhaust types, panel fit and over paint condition and fit and finish where all tested and they had no trouble getting a 20-30mph increase in speed from Mk1's through to MkIX's by incorporating all the above.

I know, but a production machine was tested in the as produced condition (where this discussion started). Things like aerials cannon blisters etc would be noted.

 

[BiffF15]

It's one of those things that after near 40 years of reading about airplanes practically every day, I never really understood this until today. It's quite interesting and I suspect it does help explain why some types did better in tropical environments and some in cold.

When I first read that description of takeoff etc., I misread and thought you were describing the T-38 as a 'performance dud'.

Does the TOLD etc. have the same relevance once you are up high and it's colder ?

Schweik,

TOLD has relevance regardless of your altitude and temp. It's done to operate your airplane safely and efficiently. At my airline under normal conditions I pull up the data for the runway I think we will get, as well as a back up if I think there is a chance of a switch (it happens regularly). If my first runway is 15k long (think Denver) and the second is 12k, I should be able to use the same performance data (what my airline calls TOLD) but I can't. Our data is optimized around each runway (obstacles in the departure path not always visible), engine wear (we do reduced power take offs which is less stress / wear on the engines), take off speed (higher is better from a safety perspective should you lose an engine - you carry more energy airborne, getting to engine out acceleration altitude sooner + shorter distance from T/O = getting to clean maneuvering speed quicker / flaps up speed). As well as tire speed. All is balanced and done by the master computer at company HQ and accessed via a system called ACARS. Think limited texting with the ability to print out what we receive. Also runway 8 at Denver is downhill. Most airliners, and the F-15 operated with a 10 knot tailwind max (wouldn't mess with your TOLD enough to warrant a change). The A320 can go with a 15 kt tailwind. F-16s go with a 0 kt tailwind.

Prior to landing I pull up data that shows how long our landing roll should be for a given runway, and it covers various braking strengths, as well as runway slickness factors and how heavy we can be and still do a safe go around.

I fixed the above dud comment to include the Mighty Bronco.

In the Eagle, with a single centerline or no external tank, we could easily take off with one engine. While I haven't done that, I have heard of guys who did (by his wingman). TOLD is very important in airliners / big planes, and is of less relevance in a small afterburner equipped plane (you accelerate so fast it's almost "what's the point".

Cheers,
Biff

 

[BiffF15]

I think it's sound thinking. A smaller wing develops less lift anyway, and it stands to reason that in less-dense air a smaller wing carrying the same weight will have more trouble.

Mine wasn't a correction to you, simply an added thought.

Here is another way to thinking about it. The plane flies like it's at the altitude it thinks its at. If you take off from hot, it flies like it's higher than it is (it wheezes sooner). High altitude fields make this worse as your take off performance is even more affected. Take off from cold, the plane flies at the altitude it thinks its at, which is lower than it really is (has more get up and go). High altitude fields reduce this some.

If you didn't have an altimeter / airspeed indiciator but knew how your plane flies / what power it makes and speed that gives. Then you would set 50" of manifold pressure and would expect to see 300 mph at 10k (this is an example). In reality, using those power figures and altitude guesstimates you see less than 300 mph which would lead you to believe you are higher than you guessed. In reality you are at 10k and it's hotter than standard. The plane doesn't know, it makes the power and speed it can given the altitude and the temp.

Cheers,
Biff

 

[Thumpalumpacus]

Here is another way to thinking about it. The plane flies like it's at the altitude it thinks its at. If you take off from hot, it flies like it's higher than it is (it wheezes sooner). High altitude fields make this worse as your take off performance is even more affected. Take off from cold, the plane flies at the altitude it thinks its at, which is lower than it really is (has more get up and go). High altitude fields reduce this some.

If you didn't have an altimeter / airspeed indiciator but knew how your plane flies / what power it makes and speed that gives. Then you would set 50" of manifold pressure and would expect to see 300 mph at 10k (this is an example). In reality, using those power figures and altitude guesstimates you see less than 300 mph which would lead you to believe you are higher than you guessed. In reality you are at 10k and it's hotter than standard. The plane doesn't know, it makes the power and speed it can given the altitude and the temp.

Cheers,
Biff

Right, that's why we see more accidents in African highland airports, because while the plane knows what it needs to fly, the pilot still has ingrained patterns which can cause problems.

I guess that "listen to your airplane" is probably some good advice here.

 

[BiffF15]

Right, that's why we see more accidents in African highland airports, because while the plane knows what it needs to fly, the pilot still has ingrained patterns which can cause problems.

I guess that "listen to your airplane" is probably some good advice here.

My guess in third world countries you will see more accidents due to poor training / decision making.

Here is an example. I've been briefed but am unable to share details.


There is a reason we have the safety stats we do. Be very very careful the further you get away from North America or Europe.

 

[Simon Thomas]

Easy on. Australian & New Zealand are a long, long way from North America and Europe.

 

[BiffF15]

Easy on. Australian & New Zealand are a long, long way from North America and Europe.

Yes, I stand corrected! Sorry about that, no snub intended! I think Qantas has the hands down best safety record.

 

[pbehn]

I tried to avoid places where the pilot got a round of applause on landing, like Saudi Arabia internal flights.

 

[Thumpalumpacus]

My guess in third world countries you will see more accidents due to poor training / decision making.

Here is an example. I've been briefed but am unable to share details.


There is a reason we have the safety stats we do. Be very very careful the further you get away from North America or Europe.

No doubt lower training standards are a factor. I was just saying that planes don't like to fly so much when the air is hot and thin.

 

[wuzak]

Drag goes up with the cube of speed.
Your Lift goes up with the square of the speed.

Does not drag go up with the square of speed also?

Power required goes up with cube of speed.

 

[GrauGeist]

Then perhaps compare the accident rate for the P-38s of the 12AF that operated in the UK and then sent to North Africa in '42.

Two entirely different climates.

 

[Thumpalumpacus]

Then perhaps compare the accident rate for the P-38s of the 12AF that operated in the UK and then sent to North Africa in '42.

Two entirely different climates.

From what I've read, the -38 acclimated to the Med much better than it did in Northwestern Europe. Is this accurate? The reasons I've read refer to engine cooling and altitude flight. If you've got any insights I'd love to hear them.

 

[Shortround6]

Does not drag go up with the square of speed also?

Power required goes up with cube of speed.

you are correct.

But when you are accelerating down the runway at over 100mph and the wing is NOT lifting (less lift) and the engine/s are not supplying enough power and the embankment at the end of the runway is getting much closer are we talking about the required speed needed (power) to clear the runway or drag?

Drag does go up with square of the speed as an instantaneous force. As in "at 100mph the airframe will exbibit XXX lbs of drag."

 

[Greg Boeser]

I think it's sound thinking. A smaller wing develops less lift anyway, and it stands to reason that in less-dense air a smaller wing carrying the same weight will have more trouble.

Mine wasn't a correction to you, simply an added thought.

This severely hampered B-26 operations in the South Pacific. A Navy report from mid 1943 rated the early B-26B with the R 2800-5 engines as having a combat ceiling of 12000' and a max bomb load of 2000 lbs. Take off run was longer than a fully loaded B-17.

 

[Shortround6]

From what I've read, the -38 acclimated to the Med much better than it did in Northwestern Europe. Is this accurate? The reasons I've read refer to engine cooling and altitude flight. If you've got any insights I'd love to hear them.

The problem was that the P-38s used in the Med used different inter-coolers and quite possible different model superchargers (and possible different turbo controls ) over Europe in 1944 than they were using in early/ mid 1943.

 

[Thumpalumpacus]

The problem was that the P-38s used in the Med used different inter-coolers and quite possible different model superchargers (and possible different turbo controls ) over Europe in 1944 than they were using in early/ mid 1943.

Were the engines running too cold over ETO? That's the implication of what I've read. I know it's a big ask but it's something I'm curious about. If you or someone else could say a bit more about this I'd be grateful.

 

[nuuumannn]

I fixed the above dud comment to include the Mighty Bronco.

You flew the Bronco, Biff? Awesome! If ever I was in a position to operate an aircraft for that go-anywhere personal transport it'd be a Bronco.

 

[GrauGeist]

The problem was that the P-38s used in the Med used different inter-coolers and quite possible different model superchargers (and possible different turbo controls ) over Europe in 1944 than they were using in early/ mid 1943.

I suggested comparing the operational records of the 12AF P-38s groups that were first operating in the UK before being transferred to North Africa in 1942, because it would have the same aircraft piloted by the same guys.

If I remember right, some of the P-38s groups also operated in Iceland for a time before continuing on to the UK, too.

All my stuff is still in storage, so I'm not able to check any figures.