Aces High Bulletin Board
Help and Support Forums => Help and Training => Topic started by: df54 on April 24, 2009, 05:28:03 PM
-
1- auto trim -
off
2- manual trim-set for straight and level flight
3- dive flaps extended.
No pitch up. Everything i have read states that with dive recovery flaps extended the nose would pitch up 10 to 15 degrees. Is this correct. If so why not in ah flight model
-
The dive flaps are modeled correctly for the P-38L in AH. Search for previous posts on this subject matter.
ack-ack
-
It's only like 8 posts down.
-Zap
-
1- auto trim -
off
2- manual trim-set for straight and level flight
3- dive flaps extended.
No pitch up. Everything i have read states that with dive recovery flaps extended the nose would pitch up 10 to 15 degrees. Is this correct. If so why not in ah flight model
Dive flaps on the P38 when extended or when retracted have no effect on pitch as far as I can tell. I there is a change in pitch when extending wing flaps, there is a noticeable change in pitch when wing flaps are extended or retracted.
-
Dive flaps on the P38 when extended or when retracted have no effect on pitch as far as I can tell. I there is a change in pitch when extending wing flaps, there is a noticeable change in pitch when wing flaps are extended or retracted.
There is also a nose up pitch when using the dive flaps.
ack-ack
-
Cartoon P38G pilots don't need dive flaps! :)
-
There is also a nose up pitch when using the dive flaps.
ack-ack
The problem, ack-ack, is that most guys deploy the recovery flaps after they are already too fast and too low or worse, in auto-trim. Assuming they are in manual trim, a 4g pull-out needs at least 4k altitude at 500 mph. So, they still auger.
What ack-ack says is true, the recovery flaps work as they should, but you need to be in manual trim and you need to get them deployed prior to the onset of buffeting so that you begin the pull-out before you go faster than 500 mph.
My regards,
Widewing
-
I thought the P38 Dive breaks were similar to those on gliders - that pop up and disrupt airflow over the wing - slowing it down. I know that the air-breaks finally allowed P38 pilots to chase after german planes who used to escape from 38s through steep dives. . .
-
I thought the P38 Dive breaks were similar to those on gliders - that pop up and disrupt airflow over the wing - slowing it down.
Those dive brakes were dive flaps, a completely different animal.
The dive flaps on the 38 were designed to maintain elevator control, without them, in a high speed dive the air would move away from the tail and limiting control surface authority.
-
LOL! df54 still doesn't believe they work, so he's posted on the Ubisoft/IL2 forums (http://forums.ubi.com/eve/forums/a/tpc/f/23110283/m/2651076257/p/1) instead. What is even funnier is that most on that thread have no clue about the P-38. One guy claims the L didn't have dive recovery flaps, another guy claims that they acted like speed breaks at low altitude. Even Crumpp throws in his two cents (and as usual is incorrect).
quote:
With all sue respect to the AH people they are inherently wrong, no need to check history books, just a logic check; if the plane does not pitch up or does not slow down then how does it recover?
It depends and IIRC this is covered in the P38 POH.
If you put the dive brake down first and then dive, there is no pitch up. You never reach compressibility and without a configuration change we have no pitching moment.
If you enter the dive and then put down the brake you will get a pitching moment.
All the best,
Crumpp
Only one person in that entire thread seems to have a clue and the rest just don't seem very bright.
-
The dive flaps are modeled correctly for the P-38L in AH. Search for previous posts on this subject matter.
if so, why do i still go into compressibility with the flaps down in the L? even diving with the throttle back
-
if so, why do i still go into compressibility with the flaps down in the L? even diving with the throttle back
Because you're not deploying them at the correct time. There is nothing wrong with the dive flaps, if anyone has issues with the dive flaps, it stems from operator error.
ack-ack
-
LOL! df54 still doesn't believe they work, so he's posted on the Ubisoft/IL2 forums (http://forums.ubi.com/eve/forums/a/tpc/f/23110283/m/2651076257/p/1) instead.
Why'd you have to post that, Ack-Ack? Being a link, I inherently had to click on it...now I feel such pity for the WWII world.
-
if so, why do i still go into compressibility with the flaps down in the L? even diving with the throttle back
The dive flaps aren't a guarantee against compression either, even without throttle nose low the 38 is going to pick up speed real fast. Try cross controlling/side slipping in addition to diving... if you find yourself compressing often, you need to re-examine how you are flying the 38.
-
I don't do much research, however I do know a little about the 38L's dive flaps. They were never designed to slow down the plane, only disrupt airflow where it was thought to be the most compressablility occuring so that airflow over the tail could be restored to a point that the plane could pull out of a high speed dive.
There is always the possiblility that I'm wrong, but they don't act any other way in the game either.
-
Cartoon P38G pilots don't need dive flaps! :)
Cartoon Pilots don't have scores.
-
Cartoon Pilots don't have scores.
What score?
-
http://www.kazoku.org/xp-38n/articles/p38info.htm
Pilots reported that when deployed in level flight, the nose would "pop up" very quickly, followed by a steady decrease in airspeed.
Is this statment fact or fiction.
-
Holy Thread Revival.
Dive Recovery flaps on the P38L were designed to move the center of lift back and help get out of compressability. There was an associated nose pitch up with it, but varied depending on how far you were into compressability.
" The P-38's dive problem was revealed to be the center of pressure moving back toward the tail when in high-speed airflow. The solution was to change the geometry of the wing's lower surface when diving in order to keep lift within bounds of the top of the wing. In February 1943, quick-acting dive flaps were tried and proven by Lockheed test pilots. The dive flaps were installed outboard of the engine nacelles, and in action they extended downward 35° in 1.5 seconds. The flaps did not act as a speed brake; they affected the pressure distribution in a way that retained the wing's lift.[40]"
From
PILOT'S FLIGHT OPERATING INSTRUCTIONS
FOR ARMY MODELS
P-38H Series, P-38J Series, P-38L-1 L-5 and F-5B AIRPLANES
"DIVE RECOVERY FLAPS.—P-38L and Later P38J
airplanes are provided with dive recovery flaps to improve
the dive recovery characteristics of the airplane.
As described above, the airplane without these flaps becomes
very nose heavy and starts to buffet above placard
dive speeds. This condition is caused by a high speed
stall and a consequent decrease in lift in the wing producing
the nose heavy condition. The dive recovery flaps
which are installed under the wings between the booms
and the ailerons, restore the lift to this portion of the
wing and thus cause the uncontrollable nose heaviness
to occur at a higher speed. The flaps also add some drag
to the airplane, which in conjunction with the higher
allowable dive speed, permits safe dives at a much steeper
diving angle. The dive recovery flaps should be extended
before starting the dive or immediately after the dive
has started before a buffeting speed has been reached. If
the airplane is buffeting before the dive recovery flaps
are extended, the buffeting will momentarily increase
and then diminish. With these flaps extended, the nose
heaviness is definitely reduced but the diving speed
should never be allowed to exceed the placard by more
than 15 or 20 mph. With the dive recovery flaps extended
before entering the dive, angles of dive up to 45° may
be safely accomplished. Without dive recovery flaps extended,
the maximum angle for extended dives is 15°.
Diving characteristics are better with power off than
with power on.
WARNING
Although the dive recovery flaps greatly improve
the diving characteristics of the. airplane,
dangerous buffeting and nose heaviness will
still be encountered at diving angles above 45°
if the diving speed is allowed to exceed the
placard limits by more than 15 to 20 mph."
-
An oldie but a goodie. A simple way to look at it is the dive flaps don't solve the flow problem across the upper wing surface they just make the bottom wing surface have the same problem as the upper wing surface.
-
...
Dive Recovery flaps on the P38L were designed to move the center of lift back and help get out of compressability. ...
The center of pressure moving back was the problem not the solution. You probably meant the center of lift moves forward.
-
An oldie but a goodie. A simple way to look at it is the dive flaps don't solve the flow problem across the upper wing surface they just make the bottom wing surface have the same problem as the upper wing surface.
No, the dive flaps didn't "make the bottom wing surface have the same problem as the upper wing surface". The problem with the P-38 in a high speed dive was that the center of pressure was moving back towards the tail (creating turbulence over the tail surfaces). The dive flap solution changed the geometry of the wing's lower surface when diving in order to keep lift within bounds of the top of the wing.
-
No, the dive flaps didn't "make the bottom wing surface have the same problem as the upper wing surface". The problem with the P-38 in a high speed dive was that the center of pressure was moving back towards the tail (creating turbulence over the tail surfaces). The dive flap solution changed the geometry of the wing's lower surface when diving in order to keep lift within bounds of the top of the wing.
Exactly, the formation of a high pressure region disrupts the flow of air over the top of the wing surface . The bottom wing gets its flow disrupted mechanically but the results are exactly the same. These compression issues were fist discovered by the propeller designers a few years before the P-38 problem and is limiting factor on fast you can go with a propeller driven plane. The original P-38 problem was nailed down after discussing the problem with a propeller designer. Can't remember his name.