Author Topic: P38 Dive Flaps? (Read 1497 times)

BBGunn · « **on:** January 25, 2001, 05:18:00 PM »

In a small test I dove the AH P38 at 1/2 fuel, no bombs or rockets, trimmed level, IAS 225mph, 40" manifold and prop pitch at max from 15,000ft: three times with dive flaps and three times without and I could not tell any difference. Pilot comments from Martin Caidins book P38 Fork-tailed Devil indicate that the P38L should be safe to dive from 15,000ft especially with dive flaps deployed and was able to chase split S'ers. In AH the ship accelerates rapidly and when passed 450mph the elevator response quits and up trim may get you out of the dive if there is enough alt left. IMO the flaps in AH should have more of an effect on speed and turn. The 38 would also not likely experience any compressablilty at low altitudes like 15K and below.

jato757 · « **Reply #1 on:** January 25, 2001, 06:36:00 PM »

ive done some reserch of my own, or you could call it lookin for info, anyway as some of you may know Evergreen (that cargo company) has a musiem, one of the aircraft on dispay the P38-L sound familer, well on the info sheet it says its maxmum speed is 415 ias, and they also have a 109-g10, its max. speed is 428 ias and i dont think it gave a alt that the speeds would be acheved at.

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[This message has been edited by jato757 (edited 01-25-2001).]

jato757 · « **Reply #2 on:** January 25, 2001, 06:38:00 PM »

I've done some research of my own, or you could call it looking for info, anyway as some of you may know Evergreen (that cargo company) has a museum, one of the aircraft on display the P38-L sound familiar, well on the info sheet it says its maximum speed is 415 ias, and they also have a 109-g10, its max. speed is 428 ias and I don't think it gave a alt that the speeds would be achieved at.

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Widewing · « **Reply #3 on:** January 25, 2001, 07:00:00 PM »

The dive flaps installed a later P-38s did several things.

1) They prevented the scenter of lift from moving towards the trailing edge of the wing, thus inducing the dreaded 'tuck under'. This could cause the aircraft to do an outside loop, with G levels exceeding 8 gs. Like the wing flaps, the dive flaps induced some pitch-up.

2) The flaps added drag, which reduced both dive acceleration, and ultimately, peak velocity.

The P-38 would pull out of a high Mach dive at a steady 3 gs, hands-off. Having downloaded the AH software, I noticed that the maximum speed for the P-38 is limited to 450 mph. This is accurate for if at 25,000 feet. However, the P-38 is placarded for considerably higher at lower levels. I have duplicated the redline airspeed chart from the Pilot Training Manual and have posted it here for everyone to use.

Perhaps, the designers will consider this data the next time they look at thier P-38L modeling.

[img]http://home.att.net/~ww2aviation/RedLine.html [/img

My regards,

Widewing

Widewing · « **Reply #4 on:** January 25, 2001, 07:06:00 PM »

Let me try posting the chart again.

[img]http://home.att.net/~ww2aviation/RedLine.JPG [/img

My regards,

Widewing

Widewing · « **Reply #5 on:** January 25, 2001, 07:11:00 PM »

Maybe someone could explain what I'm doing incorrectly....

Or, perhaps someone would spare me further humiliation and post the &%$*#%&%@$!&% chart for me. :-(

My regards,

Widewing

Badboy · « **Reply #6 on:** January 25, 2001, 07:19:00 PM »

Quote

Originally posted by Widewing:
Maybe someone could explain what I'm doing incorrectly....

Or, perhaps someone would spare me further humiliation and post the &%$*#%&%@$!&% chart for me. :-(

My regards,

Widewing

My pleasure... The syntax has to be 100% and is case sensitive.

Leon "Badboy" Smith

[This message has been edited by Badboy (edited 01-25-2001).]

Karnak · « **Reply #7 on:** January 25, 2001, 07:23:00 PM »

Widewing,
Here you go.

BTW, you had a space between the "JPG" and the "[". Thats why it wasn't working.

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We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother

Sisu
-Karnak

[This message has been edited by Karnak (edited 01-25-2001).]

Widewing · « **Reply #8 on:** January 25, 2001, 07:33:00 PM »

Widewing · « **Reply #9 on:** January 25, 2001, 07:38:00 PM »

Posted by Karnak:
"Widewing, Here you go.

"

"BTW, you had a space between the "JPG" and the "[". Thats why it wasn't working."

Thank you, and thank's to BADBOY too. I figured it out while you guys were posting the chart. So, now we have three copies!

Again, thanks for your help.

Widewing

bolillo_loco · « **Reply #10 on:** January 25, 2001, 07:48:00 PM »

I see three charts above me, I find it hard not to post a 4th one. hehehe. ok wide wing. I have seen 3 different placard type dive charts from the usaaf. I am going to assume that the 1 that says 420 mph ias is an early chart, the one that says 440 was a chart around 1945 and the chart you posted is a post war dive chart. or are the three different due to errors in airspeed indicators and the usaaf or lockheed changing them or calibrating them differently? can somebody explain the 3 different charts? I have seen the above one in its official form.

bolillo_loco · « **Reply #11 on:** January 25, 2001, 07:52:00 PM »

sorry I mean the speed after the ias one for 10,000ft. some have 440, 460, and 480. what gives? the first number is always the same while the second changes.

Widewing · « **Reply #12 on:** January 25, 2001, 09:01:00 PM »

The early charts may not have been averaged for all climates.

The temperature aloft will vary according to the temperature as sea level. Using the basic calculation for a Standard Air Column, we find that under Standard conditions (Barametric pressure of 29.92 in/Hg @ 59 degrees F), the temperature of the air will decrease by 3.5 degrees per 1,000 ft. increase in altitude.

I do know that the Manual for the P-38L says of the redline chart:

Note: This chart has been designed for standard atmospheric temperature and pressure and the TAS has been corrected for average pitot location error.

I should also mention that early P-38s had the pitot located under the nose, with later models having it under the left wing. During the course of the war, the pitot tube changed slightly in length and the static system was revised several times. In all likelihood, this will account for the differences.

Other than the above, I cannot offer a better explanation.

My regards,

Widewing

bolillo_loco · « **Reply #13 on:** January 25, 2001, 09:36:00 PM »

ok and if I am reading the dive limit chart right for the P-38 in the pilots manual, the 420 mph ias is for a 3g pull out. cause it looks like it goes down to 390 mph ias for 6gs. and lastly how does the CAS and IAS differ here and throw off the speed?

Widewing · « **Reply #14 on:** January 25, 2001, 10:52:00 PM »

Quote

Originally posted by bolillo_loco:
ok and if I am reading the dive limit chart right for the P-38 in the pilots manual, the 420 mph ias is for a 3g pull out. cause it looks like it goes down to 390 mph ias for 6gs. and lastly how does the CAS and IAS differ here and throw off the speed?

Aircraft of that era did not have the most accurate technology, especially in measuring airspeed. Several things could distort the normal relationship between indicated airspeed and true airspeed. High angles of attack is one. An aeronautical engineer could answer your question better than I.

Another oddity occurs during high speed dives. The pressure change in the static system can lag well behind the airplane. In other words, in a high speed dive, possibly at rates above 35,000 ft/min, the pressure in the system cannot increase as fast as the aircraft descends. The altimeter may be at 25,000 ft, while the aircraft is passing 20,000 feet. This leads to the pilot believing that his speed is greater than it actually is. Lockheed began installing a simple machmeter in their test aircraft in mid 1944. This eventually worked into the production line with later run P-38Ls. Unlike a static pressure system, the machmeter was apparently not effected by rapid barametric pressure changes.

My regards,

Widewing