Aces High Bulletin Board

General Forums => Aircraft and Vehicles => Topic started by: Regurge on April 27, 2001, 12:52:00 PM

Title: P38 compressibility
Post by: Regurge on April 27, 2001, 12:52:00 PM

When our p38 hits about 450mph tas all the control sufaces lock up. Should'nt the ailerons still be effective because of the hydraulic boost?

<edit> meant to say 450mph tas at 25k

[This message has been edited by Regurge (edited 04-27-2001).]

Title: P38 compressibility
Post by: wells on April 27, 2001, 04:30:00 PM

Sure, they'll move, but without anything resembling smooth airflow over them, what are they gonna do?

Title: P38 compressibility
Post by: Tac on April 27, 2001, 04:33:00 PM

what wells said.

Hint: dive flaps

Title: P38 compressibility
Post by: Citabria on April 27, 2001, 08:47:00 PM

wells how did dive flaps affect the real p38?

I've heard they created a large upwards pitching moment, added a large amount of drag, and created additional lift at the cost of said high drag.

what really happens when the flaps are deployed vs not deployed?

Title: P38 compressibility
Post by: Tac on April 27, 2001, 08:49:00 PM

Citabria, I got goodies for you. E-mail me tac@cfl.rr.com

Title: P38 compressibility
Post by: Citabria on April 27, 2001, 08:55:00 PM

hmm let me clarify my question:

aileron effectiveness in compressibility with and without dive flaps deployed.

elevator effectiveness in compressibility with and without dive flaps deployed.

effects of dive flaps at lower speeds: pitch up? lift? drag? braking action?

effects of dive flaps in compressibility: lift? drag? pitch? roll?

Title: P38 compressibility
Post by: Citabria on April 27, 2001, 08:56:00 PM

cool tac

Title: P38 compressibility
Post by: wells on April 27, 2001, 09:53:00 PM

Dive flaps change the pressure distribution over/under the stabilizer.  By deflecting the dive flap, the pressure is lowered under the stabilizer, causing a nose up moment.

Title: P38 compressibility
Post by: BBGunn on April 28, 2001, 02:55:00 PM

I suggest gleaning information from P38 pilot biographical stuff.  True air speeds approaching 550mph have been recorded and the plane was able to pull out of the dive when at lower altitude.  I believe that dive breaks were used in the above case. There has been confusion about flaps, even among book authors.  I think the best way to figure what happens is from pilots comments and maybe from Lockheed/AAC archives.  I've found that if one mentions flightmodel around here you usually get verbally fragged.

Title: P38 compressibility
Post by: rosco- on April 28, 2001, 04:34:00 PM

 seems to me the dive flaps on the P38 in Ah dont do didly.

Title: P38 compressibility
Post by: Tac on April 28, 2001, 07:57:00 PM

dive flaps in AH's 38 only give you like 30mph before you compress and when you do compress it allows you to PULL nose up at a very sluggish pace. Ironically, you can still trim elevators up to max and pull out.

Check out these pages: (btw cit, this is part of the 5 megs worth of goodies... you need to give me a non-hotmail account so I can send it)
 http://www.crosswinds.net/~twinengdevils/flaps.htm (http://www.crosswinds.net/~twinengdevils/flaps.htm)