Author Topic: P-38 dive flaps and buffeting (Read 1100 times)

FLS · « **on:** February 15, 2002, 07:28:13 AM »

I have read that the P-38 dive flaps stopped buffeting as well as restoring pitch control. Any chance that this will be modeled in AH?

--)-FLS----
Musketeers

BigCrate · « **Reply #1 on:** February 16, 2002, 07:45:21 PM »

Hope so

Cw

Tac · « **Reply #2 on:** February 16, 2002, 10:28:52 PM »

the dive flap light bulb works.

Thats something

Vector · « **Reply #3 on:** February 17, 2002, 12:30:45 AM »

Should P-38's dive flaps really restore pitch control?
I tested P-47's dive flaps and they work as they should; dive until you compress then apply dive flaps and your nose starts to rise immediatly, but it will not restore pitch control. If P-38's dive flaps are similar to those in P-47 I doubt they just should rise its nose.

FLS · « **Reply #4 on:** February 17, 2002, 06:55:17 AM »

The Warbird Tech Series volume on the P-38 quotes a Lockheed publication as saying the dive flaps " did not lesson the overall speed of the Lightning in the manner of conventional braking flaps. They controlled boundary layer air flow under the wings, eliminated buffeting at extremely high speeds, and assured full pilot control."

Warren Bodie's book on the P-38 states that the compressibility tuck, which caused the nose to pitch down into an outside loop, never occured in dives starting at 25,000 ft or less, even without the dive flaps. It also quotes Lt Col Cass Hough who dove his P-38F, without dive flaps, from 40,000 ft, compressed with control loss noted at 35,000 ft and below 15,000 ft " the airplane began to recover by itself, and at 13,000 ft it was practically in level flight again with airspeed of about 400 mph."

This is in sharp contrast to the AH P-38L which compresses with control freeze at dives starting well under 25,000 ft. I realize that trim will bring the nose up but it seems that the controls shouldn't freeze in the first place. I also question the buffeting occurring with dive flaps extended.

Using trim to bring the nose up, which works in the AH P-38L with or without the dive flaps extended, is exactly the procedure recommended to pilots of P-38's without dive flaps.

Maybe we should have a P-38F with the current P-38L buffeting and perk the P-38L with buffeting eliminated by the dive flaps. It also seems likely that no AH aircraft should have controls freeze from compression at dives starting under 25,000 ft.

--)-FLS----
Musketeers

Tac · « **Reply #5 on:** February 17, 2002, 08:15:05 AM »

Dive flaps should

1) If deployed BEFORE the dive (aka, before the plane hits high speeds) they prevent the tuck under effect and allow the pilot to pull his nose up from the dive. This the AH dive flaps do sort of (they do this effect only in AH, and it doesnt matter if you deploy them at 200 mph or at 490 mph).

2) If deployed AFTER the dive (aka, at high speeds), the dive flaps would PULL the nose UP at 3 to 4'gs. The faster the plane was going, the faster the nose pull up effect. Pilots deploying the flaps in this situation had to put all their strength into KEEPING THE NOSE DOWN. Test pilots even said that if you deployed the flaps like this and let go off the wheel, the p-38 would execute a neat loop on its own. This effect is sorely missing in AH. Many P-38 pilots used this effect to escape away from better-diving planes like the 109 and 190.. they would dive to high speeds, near 500'ish (where 109 and 190 achieve faster and who'se controls become quite stiff), deploy the dive flaps and it would pull them off the dive at 3 to 4g's... which the 109 and 190 could never match.

Vector: Trim your jug when you dive. Then let go off the stick and push the dive flaps. It wont pull nose up. What the dive flaps in AH do is give the player about 10% pitch control back.

Anyway, the elevator trims will pull you out of the dive much, much faster than using the dive flaps.

Vector · « **Reply #6 on:** February 17, 2002, 12:08:27 PM »

Hi Tac

I agree that elevator trim will get you out of compress.
I'm not able to start AH now due my soundcard problems, but I recall doing the test as follows:
In testter -terrain I took off (D-30) from 34000ft and started to dive approx 70-80° angle. Auto trim on angle and full throttle. About 580mph IAS (can't recall accurate mph) plane shook all over and compressed. Trim off, moving stick back didn't do anything. Pulled out dive flaps, plane continued to shake, but immediatly started to rise its nose. Gotta try it again after I got some spare parts to my jug (soundblaster live)

BigCrate · « **Reply #7 on:** February 17, 2002, 07:29:30 PM »

Ok I have a ? about the real plane.. If you climbed to the critical alt in a 38 and tried to reach its top lvl speed. It would enter the early stages of compressibilty right?? And is he tried to dive it would just get worse nose would tuck badly and the plane would shake it self to death almost.
If that is not true than the 38 flight model would have to be changed and new dive speeds and compressibilty would have to be reworked. In AW and in AH the 38 has got the toejam end of the stick as well as real life to.
I would like to see the 38f and 38h models before i see a p40. I can't remember if the 38d or the f model had a 37mm cannon installed.

And it would be nice to have slow speed buffeting
and atleast a stall light that flickered when you are about to stall.

Cw

BigCrate · « **Reply #8 on:** February 17, 2002, 07:30:12 PM »

Ok I have a ? about the real plane.. If you climbed to the critical alt in a 38 and tried to reach its top lvl speed. It would enter the early stages of compressibilty right?? And if the pilot tried to dive it would just get worse nose would tuck badly and the plane would shake it self to death almost.
If that is not true than the 38 flight model would have to be changed and new dive speeds and compressibilty would have to be reworked. In AW and in AH the 38 has got the toejam end of the stick as well as real life to.
I would like to see the 38f and 38h models before i see a p40. I can't remember if the 38d or the f model had a 37mm cannon installed.

And it would be nice to have slow speed buffeting
and atleast a stall light that flickered when you are about to stall.

Cw

FLS · « **Reply #9 on:** February 18, 2002, 08:24:21 AM »

After taking another look at this I may be confusing power off dives with full power dives in the P-38 without dive flaps. Bodie doesn't specify when he states that there was no compressibility problem in combat at or below 25,000 ft but it is likely that compression was a problem in a full power vertical dive even under 25,000 ft. A power off dive from 25,000 ft will buffet but not compress to full control loss in AH. Still it seems that the dive flaps should eliminate power off buffeting and at least delay the onset of power on buffeting. Looking closer at the buffeting in AH it appears that only the cockpit graphics buffet while the gunsite and presumably the guns remain stable so it's not really a big issue.

Even with buffeting eliminated going from an eny value of 30 to perked would, on second thought, be silly. However, the P-38L doesn't seem less capable than say the P-47D-30. I would rate it closer to the P-47D-11 or P-51D at 18. If we get an earlier model P-38 that might be more suitable for a eny value of 30.

CW

The engines weren't powerful enough to cause compression problems in level flight. They'd have to dive and when they pulled level drag would slow them down. The amount of buffeting when compressed was proportional to the G load so they wouldn't break apart unless they tried to pull out too fast instead of easing out of the dive. When they dove with power and compressed the P-38, without dive flaps, they cut power and waited until the increased drag of the lower denser air slowed them enough to pull out. They could feel the increased buffet if they pulled back too much so they could tell where to hold the controls for "moderate to heavy buffeting" while slowly adding enough trim to pull out.

The slow speed stall buffet is different and I think you'd feel it in the stick more than see it. The audible stall warning works well to model this for those of us without force feedback sticks.

I believe the 37mm was only installed on one test aircraft.

--)-FLS----
Musketeers

BigCrate · « **Reply #10 on:** February 18, 2002, 09:11:54 AM »

Ok if no buffeting occuredtrying to reach the 38s top speed of 414mph then the 38 flight model should redone.. Cause once you get past 300ias in AH at it critical alt it starts to buffet. And 414mph is above 300mph ias.. And you said there was no buffeting. So the 38 has a bigger dive envelope that what AH has.
I'm gonna do some research on this some more and post what i find.

Cw

FLS · « **Reply #11 on:** February 18, 2002, 10:55:32 AM »

At 20,000 ft 414TAS is about equal to 300IAS. You can see this in AH by comparing the white needle on the airspeed indicator to the red one. There is no buffeting. The actual P-38 redline speed for compression was 360IAS/460TAS at 20,000 ft.

--)-FLS----
Musketeers

Vector · « **Reply #12 on:** February 18, 2002, 10:56:21 AM »

America's 100.000 states:

"With dive flaps extended before diving angles of dive up to 45° could be safely attained, whereas without flaps maximum dive angle was 15°. If the 45° dive angle was exceeded and speeds attained of more than 20 mph above placard (0.65 mach, 360 IAS @ 20000ft) a dangerous buffet of the airplane and tuck-under would occur even with dive flaps extended."
The elevator trim tab could be used to recover at lower altitudes but use resulted in a 5 G pullout.

AHT don't mention the altitude thought.

"Pilot survey ranked the P-38 last of all fighters tested in a category "best stability and control in a dive" ".

FLS · « **Reply #13 on:** February 21, 2002, 10:27:45 AM »

I wonder which P-38 that pilot survey referred to.

I've tried to find some specific information on how the dive flaps
changed the airflow but haven't found any. Since only the Lockheed
statement claims that buffeting was eliminated it's probably just
the company line rather than actual fact.

It does seem more likely that the dive flaps just moved the shock
wave location and didn't change the speed of the airflow to the point
where buffeting would be eliminated.

--)-FLS----
Musketeers

Tac · « **Reply #14 on:** February 21, 2002, 10:58:27 AM »

All 38's up to the P-38D model had the 37mm Oldsmobile cannon. The E model and up had the 20mm Hispano II.