Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Baloo on March 10, 2014, 10:11:43 AM
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(http://www.ausairpower.net/HISTORICAL/P-38-Compressibility-Chart.png)
Can we get the 38 to go a bit faster?? :noid
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That doesn't even stat which P38 variant :old:
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Sorry lol, but it's the P-38L-5/10-LO - albeit the J too was faster than it's German counterparts, especially after they came out with the modification kits for the dive flaps and hydraulics and what not.
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First you need to understand what you have posted. That chart shows the max dive speed before entering compressibility. It does not show P-38's max level speed. These are the "do not exceed" speeds when diving. All the dive flaps do is keep the speed under this "red line".
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All the dive flaps do is keep the speed under this "red line".
Is there ever gonna be a point in time when people understand that the dive recovery flap on the later 38s is not a "dive flap" as most people would percieve a dive flap to be? It doesn't slow you down one bit. Not a bit! That idea is a myth repeated by folks that didn't educate themselves about it. What it does do is change the airflow around the tail structure so that the pilot has some measure of control at these higher speeds where there was basically none in models prior. It attempts to pitch the nose up so you don't bore a hole in the earth--which had been a problem. That's all it does. There is no alternative use.
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Is there ever gonna be a point in time when people understand that the dive recovery flap on the later 38s is not a "dive flap" as most people would percieve a dive flap to be? It doesn't slow you down one bit. Not a bit! That idea is a myth repeated by folks that didn't educate themselves about it. What it does do is change the airflow around the tail structure so that the pilot has some measure of control at these higher speeds where there was basically none in models prior. It attempts to pitch the nose up so you don't bore a hole in the earth--which had been a problem. That's all it does. There is no alternative use.
And it is explained very well in Warren Bodie's book!
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What it does do is change the airflow around the tail structure
I think what the flap actually does is change the center of pressure of the wing, not change airflow around the tail.
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My bad homes, here is more info :ahand
Flight Tests on the Lockheed
P-38J Airplane, AAF NO. 43-28392
In level flight at 19800 ft., the critical altitude for 70" hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a maximum speed of 419 MPH was attained. At this altitude a high speed of 402.5 MPH was attained at 60" Hg. manifold pressure. At 24000 ft., the critical altitude for 60" Hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a high speed of 413 MPH was attained.
At sea level a maximum rate of climb of 4040 ft/min was attained at 70" Hg. manifold pressure and a rate of climb of 3570 ft/min at 60" Hg. manifold pressure and 3000 RPM. The service ceiling of the airplane was 39,000 ft., and the absolute ceiling was 39,700 ft.
====================================================
Flight tests were conducted on the P-38L airplane, AAF No. 44-25092, at Wright Field, Dayton Ohio and Miami Depot, Miami, Florida in order to obtain a performance and range check of the data given as tentative figures in Pilot's Flight Operating Instructions, AN 01-75-1.
Level Flight Performance
The following speed data was obtained with the airplane in the clean configuration. Data is corrected to weight at altitude as given in Figure 4, Appendix A and NACA standard day conditions.
a. True speed at sea level at war emergency power, 1530 BHP and 3000 RPM, was 342 MPH.
b. True speed at critical altitude, 26,000 feet, at war emergency power, 1495 BHP and 3000 RPM, was 416 MPH.
c. True speed at sea level at military power, 1395 BHP and 3000 RPM, was 331 MPH.
d. True speed at critical altitude, 26,200 feet, at military power, 1385 BHP and 3000 RPM, was 408 MPH.
e. True speed at sea level at normal rated power, 1110 BHP and 2600 RPM, was 302 MPH.
f. True speed at critical altitude, 32,200 feet, at normal rated power, 1138 BHP, was 400 MPH.
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And to placate the whole dive flap business, here is an excerpt from the manual itself:
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.
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Is there ever gonna be a point in time when people understand that the dive recovery flap on the later 38s is not a "dive flap" as most people would percieve a dive flap to be?
I long ago got it even though I don't fly 38s much.
Make sure to always call it a dive recovery flap. Never call it a dive flap or dive brake.
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Make sure to always call it a dive recovery flap. Never call it a dive flap or dive brake.
^ That. To appease our fastidious friends. :aok
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So lowering the "dive recovery flaps" into the airflow does not increase drag significantly?
(http://www.hq.nasa.gov/pao/History/SP-440/p28a.jpg)
My bad homes, here is more info :ahand
Flight Tests on the Lockheed
P-38J Airplane, AAF NO. 43-28392
In level flight at 19800 ft., the critical altitude for 70" hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a maximum speed of 419 MPH was attained. At this altitude a high speed of 402.5 MPH was attained at 60" Hg. manifold pressure. At 24000 ft., the critical altitude for 60" Hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a high speed of 413 MPH was attained.
At sea level a maximum rate of climb of 4040 ft/min was attained at 70" Hg. manifold pressure and a rate of climb of 3570 ft/min at 60" Hg. manifold pressure and 3000 RPM. The service ceiling of the airplane was 39,000 ft., and the absolute ceiling was 39,700 ft.
====================================================
Flight tests were conducted on the P-38L airplane, AAF No. 44-25092, at Wright Field, Dayton Ohio and Miami Depot, Miami, Florida in order to obtain a performance and range check of the data given as tentative figures in Pilot's Flight Operating Instructions, AN 01-75-1.
Level Flight Performance
The following speed data was obtained with the airplane in the clean configuration. Data is corrected to weight at altitude as given in Figure 4, Appendix A and NACA standard day conditions.
a. True speed at sea level at war emergency power, 1530 BHP and 3000 RPM, was 342 MPH.
b. True speed at critical altitude, 26,000 feet, at war emergency power, 1495 BHP and 3000 RPM, was 416 MPH.
c. True speed at sea level at military power, 1395 BHP and 3000 RPM, was 331 MPH.
d. True speed at critical altitude, 26,200 feet, at military power, 1385 BHP and 3000 RPM, was 408 MPH.
e. True speed at sea level at normal rated power, 1110 BHP and 2600 RPM, was 302 MPH.
f. True speed at critical altitude, 32,200 feet, at normal rated power, 1138 BHP, was 400 MPH.
So 416-419 mph at 26k... and 342 mph at SL...
Seems OK to me?
(http://www.hitechcreations.com/components/com_ahplaneperf/genchart.php?p1=122&p2=18&pw=1>ype=0&gui=localhost&itemsel=GameData)
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So lowering the "dive recovery flaps" into the airflow does not increase drag significantly
That's not really the idea so no. Whatever drag they might add is of a secondary nature. Besides, compared to other "dive flaps" do they look "significant" to you? Think Stuka, Val, SBD, hell even a Ju88! They all have what would be considered dive flaps. They ARE specifically designed to slow you down in a dive. They are large, sit almost perpendicular to the airflow and because of this, when deployed, they produce loads of drag.
To be clear they are not, repeat, not, designed to slow you down. They're designed to help you control the airplane by rerouting the airflow in the vicinity of the tailplane at high speed so you don't auger. That's why they pop out just a bit and at a shallow angle to the windstream. Just enough to do that job.
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From what Baloo posted above:
"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."
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No, not significantly, some is synonymous with little...where as significantly is synonymous with big
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On another note, this was all brought up with planes catching up to me or climbing up to me...and yes, I mean when we are at equal energy states. Try out running a Spit16. Maybe pilots are disguising their state well, but sometimes I know there's just no way.
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No, not significantly, some is synonymous with little...where as significantly is synonymous with big
Significant is also synonymous with measurable, noticeable, observable, perceivable, perceptible, pronounced, recognizable, substantial, tangible...
In other words: It makes a difference.
And if you're at equal energy state against a Spit16 you're in big trouble in a P-38 at anything less than top speed or very high altitude. The Spit16 can build energy like crazy and out-accelerates and out-climbs just about anything..
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On another note, this was all brought up with planes catching up to me or climbing up to me...and yes, I mean when we are at equal energy states. Try out running a Spit16. Maybe pilots are disguising their state well, but sometimes I know there's just no way.
Alot of this is easily explained but unless you have film of a specific incident it would just be guessing and assumptions in any explaination.
:salute
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Baloo have you actually checked the relative performance of the P-38L and Spit16?
(http://www.hitechcreations.com/components/com_ahplaneperf/genchart.php?p1=18&p2=86&pw=1>ype=2&gui=localhost&itemsel=GameData)(http://www.hitechcreations.com/components/com_ahplaneperf/genchart.php?p1=18&p2=86&pw=1>ype=0&gui=localhost&itemsel=GameData)
And on top of that it has much lower wing-loading so it turns better and bleeds less energy in turns.
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Alot of this is easily explained but unless you have film of a specific incident it would just be guessing and assumptions in any explaination.
:salute
I'll start running films, good advice.
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I'll start running films, good advice.
Do you see the post above,the performance figures alone show how it's quite possible!
With film you can see your speed and alt and the enemies,you can also see where any corners were cut to shorten the distance and any mistake you or the enemy might have made.
I will admit I dont film,I never have and likely never will,but then I blame myself when I get shot down not the other guy!
:salute
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Significant is also synonymous with measurable, noticeable, observable, perceivable, perceptible, pronounced, recognizable, substantial, tangible...
In other words: It makes a difference.
Now that's just backpedaling. ANY drag is measurable, etc.,--does that make it a significant ammount of force? Does that small ammount of drag make a difference? Certainly it does--just not in the sense that you think it does. That flap is not going to slow you down---at all. Don't believe me. Try it for yourself. Take a 38 up to say 10K and let the speed stabilize. Now hit the flap. You won't slow down at all---at ALL. Maverick isn't gonna hit that flap and make the bad guy fly right by. If that's the strategy he's dead. Now you can take any other plane in the game that has a dive flap on it and do that same flight and once you hit that flap it's gonna slow right down. Why? Because they're different flaps designed for different purposes. One is a brake the other is not. It's just not. Give it up.
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It is significant enough that they mentioned it in the text. If you think those flaps and the disrupted airflow they create won't produce significant drag then you're deluding yourself. Not my problem though...
"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."
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It is significant enough that they mentioned it in the text. If you think those flaps and the disrupted airflow they create won't produce significant drag then you're deluding yourself. Not my problem though...
I don't need to read that 30 times. I know what the flap is and what it does. That's what I meant when I said this:
"Does that small ammount of drag make a difference? Certainly it does--just not in the sense that you think it does. That flap is not going to slow you down---at all."
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That flap is not going to slow you down---at all."[/b][/size]
And that is where I call BS. Anything protruding into the airflow will slow you down, and certainly something as uncompromisingly flat and disruptive as that flap.
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Just because you don't know doesn't make it BS. I challenged you up the thread. Try it for yourself then come back. Hell post a film! That's how sure I'm right.
Hint: it won't slow you down in a dive either.
IT'S NOT A DIVE BRAKE
And That ain't no BS!
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IT'S NOT A DIVE BRAKE
And That ain't no BS!
Yea, that is true. I remember when I first started flying the 38 and thought just the opposite, grumbling about how the "dive brake" is a bunch of BS as I depended on it to get me out of a compression and ended up as a poor excuse for a tree...then after actually trying to learn the 38 is when i discovered that all it was meant to do was help you recover better. The following quote pretty much reiterates what Drano has been explaining to you, but maybe someone else's words may work better?
As noted in another reply, the only way you'll see the dive flaps deploy is if you're on the runway and hit F3 and look under the plane as you deploy them. You will not see them deploy sitting in the cockpit.
The dive flaps work as intended and will assist in recovering from a high speed dive. The problem with a lot of players is that they usually deploy and use the dive flaps incorrectly. A lot think that the flaps are intended to help you recover from a dive by acting as a brake and slowing your plane down enough that you can pull out of a dive. That is 100% incorrect. As you can see in the diagram below and in the photo with the dive flaps deployed, the dive flaps are a very inefficient design to act as a dive brake, why? Well, that's an easy answer because the dive flaps weren't designed to act as brakes but instead as someone else mentioned to change the airflow over the leading edge of the wings.
(http://www.kazoku.org/xp-38n/articles/p38diveflaps.gif)
(http://www.kazoku.org/xp-38n/articles/diveflap.jpg)
For the dive flaps to work properly, you need to be in a certain window where they are beneficial to get the most out of them. The dive flaps only work at high speeds, they are pretty much useless at speeds below 350mph IAS and you won't see any real effect if you deploy them at speeds lower than that. The best time to deploy the flaps is when you're about to enter the dive, though you can sometimes get away with deploying them shortly after you've started your dive. New or inexperienced P-38 drivers tend to deploy the flaps at the onset of a high speed buffet and by that time it's usually too late and the dive flaps aren't as effective and you'll need to manually trim to recover. As soon as you complete your dive recovery, retract the dive flaps.
A little trick you can do with the dive flaps that was used by real life P-38 drivers. The dive flaps can aid in high speed turns, just deploy them at the start of the turn and retract them as you finish the turn.
Now the brutal honest truth...if you have to deploy the dive flaps to recover you messed up. It's that simple. Properly flown, the P-38 (all models) can safely dive if you understand what compressability is and how it effects the P-38 without neediing to use dive flaps. Remember, compressability happens when the air over the leading edge of the wing reaches critical mach speeds, which means the higher you fly the P-38, the increased risk of entering compressability in a dive. The lower you fly the P-38, the risk decreases dramatically the lower in altitude you go. In other words, the P-38 will not enter into a compresability state below 20,000ft, the air is too thick for the air over the leading edge to reach critical mach. The P-38 will suffer from sluggish and hard controls below 20,000ft but that is due to regulary aerodynamic forces pushing on the control surfaces and not the phenomena that is compressability.
To safely dive the P-38, you need to control your speed and you can do that by decreasing throttle and using your rudders to "skid" the plane in the dive. Using this simple technique you can easily reach speeds up to 475mph IAS in a dive and still retain control (although sluggish) to pull up out of the dive without having to use dive flaps.
Why? They don't do anything at low speeds and even if they did wouldn't be smart to deploy them on landing. Besides, you don't need flaps to land a P-38.
ack-ack
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Just because you don't know doesn't make it BS. I challenged you up the thread. Try it for yourself then come back.
I just did and you're absolutely right! They produce no noticeable reduction in top level speed. I find that totally incredulous and have posted a bug report about it. http://bbs.hitechcreations.com/smf/index.php/topic,360029.0.html
This must produce drag!
(https://dl.dropboxusercontent.com/u/26232318/AH/p-38-dive-flaps-bug.jpg)
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You're right it does produce drag. I never said that it didn't! :D But it doesn't act as you think. The drag produced merely deflects the airflow in a way that helps to control the plane at high speeds. A low speeds it is totally ineffective. Slowing down isn't really the idea as it would be in a dive bomber where their flaps are applying a ton of drag by design. In those you want to slow down so you can aim a bomb accurately before you hit the target with your plane! Which would screw up your whole day! The P-38's a fighter so you want to go fast---but you need to be under control too. After augering a few lightnings they went to the wind tunnel and found the problem was with the action of the airflow on certain parts of the plane--the elevator in particular--at high mach numbers. At first they thought it was a balance problem with the elevator. They attempted to fix it with a counter balance--that's what that little thingy is on the center of the elevator. That didn't help but they kept it on there anyway thinking it wasn't a bad thing to have. But it was this deflection of the airflow by the recovery flap really helped solved that problem and it was added to later J models as a field mod and to the L's afterward as a factory installation.
Of course you can still get yourself going too fast! I screw up all the time. :D
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They don't produce any drag noticeable by the instruments in the game. They must produce a lot of drag. It must be a bug. There is no way you can place a flat "plank" that size almost at a right angle to the wing surface and not have it produce a lot of drag. :huh
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It isn't really at a right angle to the airflow. More like 40-45 degrees. Check this video at about 2:50:
http://www.youtube.com/watch?v=Y3nddCJbcdI&list=PL2hjKZefRkH82sWPVrLHcpeFt0lkYkCrU (http://www.youtube.com/watch?v=Y3nddCJbcdI&list=PL2hjKZefRkH82sWPVrLHcpeFt0lkYkCrU)
Jeff Ethell gives an explanation of it and you'll see it operate on the ground. Sadly he wrecked this bird and was killed not long after this was made.
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Another bug then. Take a look at them in the game. (Or just see the bottom picture I posted).
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Graphics thing. Doesn't bother me. I can't see it from the cockpit. If they wanted to fix it that's great but it's no biggy. It seems to work as it should tho and that's all I care.
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Another bug then. Take a look at them in the game. (Or just see the bottom picture I posted).
So the bug, then, is in the graphic, not the affect on the flight characteristics.
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You cannot have a flap protruding from the wing like that, at any angle, and not have it create drag. It is simply impossible. Hell, something as small and aerodynamic as a bomb rack or droptank pylon reduces top speed by several mph.
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Another bug then. Take a look at them in the game. (Or just see the bottom picture I posted).
It's a graphic bug with the P-38, not how the dive flaps looked in real life. Here is another shot of the dive flaps in AH.
(http://i547.photobucket.com/albums/hh473/cactuskooler/Untitled-1-29.jpg)
This is what the design of the dive flaps looked like.
(http://www.kazoku.org/xp-38n/articles/p38diveflaps.gif)
Dive flaps deployed.
(http://www.kazoku.org/xp-38n/articles/diveflap.jpg)
(http://farm3.staticflickr.com/2560/3969375710_1380c33a57_z.jpg)
(http://www.hq.nasa.gov/pao/History/SP-440/p28a.jpg)
(http://christophe.arribat.pagesperso-orange.fr/g1flap.jpg)
ack-ack
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Mach Tuck.
Here are some good articles.
http://en.wikipedia.org/wiki/Mach_tuck (http://en.wikipedia.org/wiki/Mach_tuck)
http://www.airspacemag.com/history-of-flight/mach-1-assaulting-the-barrier-22647052/ (http://www.airspacemag.com/history-of-flight/mach-1-assaulting-the-barrier-22647052/)
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You cannot have a flap protruding from the wing like that, at any angle, and not have it create drag. It is simply impossible. Hell, something as small and aerodynamic as a bomb rack or droptank pylon reduces top speed by several mph.
Believe me when I say I totally hear what you're saying about the drag but what I'm trying to get at is what you really want. Are you saying you want this flap to act like a standard dive flap, as in like a dive flap on a dive bomber would? Because it sure does sound like that. Again--these are not speed brakes. It's not a game glitch. They weren't designed as such in RL.
If they did slow the RL plane down I'd be interested in seeing some data to that effect. I'd imagine whatever effect on speed (and yes it makes sense to me that as it's protruding into the windstream and I'd think it should have SOME effect) would be minmal at best if only becasue of the size, angle and location of the flap. It was engineered to death and I'm sure that's the reason it's the size it is and is at the angle it is and it's where it is--to do a specific job. It's not very large and it protrudes at a shallow angle to the windstream quite unlike a standard dive brake which is larger and extends to almost perpendicular to the windstream.
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I don't want it to behave in any other what than what it did in real life. It is not a dive brake. It is a dive flap; A device that counteracts the Mach-tuck effect of a wing with different curvature on the upper and lower wing surface. However it counteracts this force by deflecting air downward. That must produce drag, and significant amounts of it. Not like an air brake that would almost stop the plane from flying in level flight, but it should significantly affect top level speed, like in the order of several tens of mph.
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I solved the whole issue by flying the G and J models :D
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:lol
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Any alteration of the skin effects the drag coefficient. The question is by how much. Without a test or calculation the argument is mute.
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Whether it was the intent out not, if it protrudes into the airstream it creates drag and slows down the plane.
Gscholz is correct about that.
Drano is correct about their intended purpose.
AH is incorrect in that the 38's speed is unaffected by them being deployed in level flight. It is physically impossible to throw something like that into the airstream and have it not affect speed at a static power setting. Physics is a B-atch like that.
~S~ Buck
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Like I wrote in the bug thread all the info needed is actually in that pilot's handbook that was quoted earlier in this thread.
Note that the flaps do not allow for an increase in dive speed of more than "15 or 20 mph" while allowing an increase in dive angle of 30 degrees (from 15 degrees without flaps to 45 degrees with flaps). That takes drag... and a lot of it.
Not 90 degree dive bomber speed brake drag of course, but 45 degree dive bomber speed brake drag...
With the dive flaps extended the P-38L should be able to safely dive at 45 degrees, but the top dive speed should only be 15 to 20 mph more than in a 15 degree dive without dive flaps.
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I don't want it to behave in any other what than what it did in real life.
In that, I am sure we all agree.
I am also sure nobody wants that more than HTC.
but it should significantly affect top level speed, like in the order of several tens of mph.
The problem is that intuitive estimates like that are meaningless without some form of data to support it. At best I think any data that could be found would be in the form of modified drag polars because I'm sure there would have at least been wind tunnel tests involved in that type of modification. It is very unlikely that anyone actually conducted tests for top speed with the dive recovery flaps deployed, so data for direct values probably does not exist. So even if data can be found it would probably require some analysis to interpret. I know that HTC can do the analysis, so if the data exists and can be found, I'm sure they would incorporate it if they haven't already done so.
Without any real data, all any of us can do is little more than speculation.
Badboy
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Yeah, that would be Pyro's department if I'm not mistaken. What surprises me is that it wasn't done when the flaps was added in the first place.
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Flight Tests of Dive Recovery Flaps on a Twin Engine Fighter Aircraft (Lightning). A.R.C.9251.
1945.
I tried to find this document.
There is one on the tempest and P47
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What do the Tempest and Thunderbolt tests say about drag?
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What do the Tempest and Thunderbolt tests say about drag?
I have not found the documents for any of the dive flap testing.
here is the document that references these test.
http://naca.central.cranfield.ac.uk/reports/arc/rm/2622.pdf (http://naca.central.cranfield.ac.uk/reports/arc/rm/2622.pdf)
I have been digging to try to find the technical reason for placing the flap where they do on the P38. The only conclusion I can reach at this time is the flap creates a shockwave of its own on the bottom of the wing and flow separation on the back-bottom of the wing to match the top wing more of less. I want argue with anyone who has this pinned down better than me.
All of this does create a lot of additional mach drag when in the transonic region but not in the laminar flow of level flight.
As a side note, the flap could have been considerably smaller if it could have been placed on the inside of the engine nacelles. I can only guess the attachment points prevented that.
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What boggles my mind is that anyone can rationally conclude that it is physically possible to have an airflow with an object in it that doesn't create drag. It must be magic... No wonder the Allies won the war! :aok
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The Borg cube had no drag either, so maybe its possible.
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The Borg cube had no drag either, so maybe its possible.
Space doesn't have an atmosphere.
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Actually even in space a moving object would generate some drag from the minute amounts of particles that are there. The solar wind must also be accounted for. So yes, a Borg cube does produce some drag when it moves on impulse power, but not at warp speed of course... Because then it isn't actually moving at all. :D
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Warp is an impossibility :old:
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Space doesn't have an atmosphere.
We are Borg. It was a joke, corrections are futile.
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:rofl :aok
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I have not found the documents for any of the dive flap testing.
here is the document that references these test.
http://naca.central.cranfield.ac.uk/reports/arc/rm/2622.pdf (http://naca.central.cranfield.ac.uk/reports/arc/rm/2622.pdf)
I have been digging to try to find the technical reason for placing the flap where they do on the P38. The only conclusion I can reach at this time is the flap creates a shockwave of its own on the bottom of the wing and flow separation on the back-bottom of the wing to match the top wing more of less. I want argue with anyone who has this pinned down better than me.
All of this does create a lot of additional mach drag when in the transonic region but not in the laminar flow of level flight.
As a side note, the flap could have been considerably smaller if it could have been placed on the inside of the engine nacelles. I can only guess the attachment points prevented that.
:airplane: Randy, I cannot place my finger on any document or tell you where to look, but Johnson and company of the skunk works at Lockeed tried the dive flaps both inboard of the engines and outboard. I recall reading that the problem with the dive flaps outboard of the engines created, under turning conditions, a aileron buffett and that is why they are place where they are. One thing I don't understand is why the DF's doesn't interfere with the air flow around and over the elevator. Our in game 38 doesn't seem to recognize where or not they are extended, and I think that is why all this discussion about them. I would think that the nose should pitch up some when you deploy them, but it doesn't and that is why I make that statement. (I know I am going to get an argument about pitch up or down, so have at it guys)
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Here's a document. It mentions drag and pitching up.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030066111.pdf
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One thing I don't understand is why the DF's doesn't interfere with the air flow around and over the elevator. Our in game 38 doesn't seem to recognize where or not they are extended, and I think that is why all this discussion about them. I would think that the nose should pitch up some when you deploy them, but it doesn't and that is why I make that statement. (I know I am going to get an argument about pitch up or down, so have at it guys)
You are incorrect, the dive flaps do work as intended in AH and do provide a positive pitch when deployed.
ack-ack
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I have been digging to try to find the technical reason for placing the flap where they do on the P38.
When compressibility hits, shockwaves are formed initially on the top surface of the wing, and there is flow separation after the shock wave, which is why the wing loses lift just as if it were stalled while not in compressibility. This is known at "mach stall" of the wing, and is like this:
(http://upload.wikimedia.org/wikipedia/commons/thumb/6/6d/Transonic_flow_patterns.svg/286px-Transonic_flow_patterns.svg.png)
There is no flow separation in front of the shock wave. So, if you want a flap to increase lift of the wing (to make up for the fact that everything behind the shock wave is producing no lift), you need to put it in the forward portion of the wing rather than the stalled-out rear of the wing.
Putting it outboard of the nacelles means it will generate less potential turbulence or other effects to airflow for the elevator.
With regard to whether or not the "dive recovery flap" increases lift or drag, it does both, because generally anything that adds lift is also going to create at least some (not zero) drag. The main purpose of the flap is to increase lift, though. It helps avoid or at least reduce "mach tuck," which is the nosing down of the aircraft as a result of the mach stall, and helps give the wing some lift instead of none. Adding drag is also helpful for obvious reasons, so even though it is a side effect, it is not a harmful one.
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There is no flow separation in front of the shock wave. So, if you want a flap to increase lift of the wing (to make up for the fact that everything behind the shock wave is producing no lift), you need to put it in the forward portion of the wing rather than the stalled-out rear of the wing.
Putting it outboard of the nacelles means it will generate less potential turbulence or other effects to airflow for the elevator.
The P38 dive flap, is a closer cousin to split flaps and therefore produces no significant lift as would a typical wing flap that alters the shape of the airfoil. What it does do, I believe is, create, or make larger the bottom wing shock wave to counter the top wing shock wave.
"Bridgland concludes that a flap area of about 0.01 of the wing area is generally required, if the flap is well inboard. If flap is so far outboard, as to have little effect on the downwash at the tailplane (or in the case of tailless aircraft), the flap areas will then need to besome three or four times this amount. "
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The P38 dive flap, is a closer cousin to split flaps and therefore produces no significant lift
Split flaps do produce lift. Here (graph on the left) is an example of C_L vs. alpha for a wing with and without split flaps deployed.
(http://forums.x-plane.org/uploads/monthly_05_2012/post-1379-0-03080900-1337808084.jpg)
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If you want to compare the dive flap to a split flap you have to consider it's position under the wing. It's not a trailing edge flap so it masks some of the wing behind it. This may offset some of the lift it creates.
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Here is a good quote Brooke and FLS. I think this pins it down. It is all about the downwash angle. It is so interesting that the people working on propellers new of the upcoming problem and Stark had written a paper foretelling of the upcoming compressibility issue on wings since he had encountered that problems on props.
http://history.nasa.gov/SP-4219/Chapter3.html (http://history.nasa.gov/SP-4219/Chapter3.html)
The flap was not a conventional dive flap intended to reduce the speed. Rather, Stack's idea was to use the flap to maintain lift in the face of the compressibility burble, hence eliminating the change in the downwash angle, and therefore allowing the horizontal tail to function properly. This is a graphic example of how, in the early days of high-speed flight, the NACA compressibility research was found to be vital as real airplanes began to sneak up on Mach one
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Randy did you read the study I linked? It's the wind tunnel test on dive flaps on what loooks like a P-38 wing.
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Randy did you read the study I linked? It's the wind tunnel test on dive flaps on what loooks like a P-38 wing.
It was the P-38 that was used in that wind tunnel test, there is another wartime NACA report from testing in the larger 16ft wind tunnel.
ack-ack
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And according to that document the drag of the wing increased by up to 59%.
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And according to that document the drag of the wing increased by up to 59%.
Was that increase related only to the dive flap? Could some of that drag increase be because of shock wave, etc?
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Randy did you read the study I linked? It's the wind tunnel test on dive flaps on what loooks like a P-38 wing.
FLS, yes I did. One of the best articles I have seen. And a great find.
I also have a quote from the test pilot doing the test that Megaloden sent me.
When I googled boundary layer in a reply to the other thread I found the same article and read it then as I remembered your reply post and link.
Having two threads is a bit confusing.
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If you want to compare the dive flap to a split flap you have to consider it's position under the wing. It's not a trailing edge flap so it masks some of the wing behind it. This may offset some of the lift it creates.
The portion of the wing behind it, once compressibility sets in, is stalled out, negating lift there.
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Was that increase related only to the dive flap? Could some of that drag increase be because of shock wave, etc?
Yes shock wave. This makes me wonder in all compression related planes if the acceleration is reduced when Mach drag comes into play. HTC is pretty sophisticated and may well include mach drag.
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Was that increase related only to the dive flap? Could some of that drag increase be because of shock wave, etc?
It was worded like this: "At a Mach number of 0.850 for an angle of attack of 4 degrees, the dive-recovery flap represents an increase of approximately 59% of the wing alone-drag."
It's on page 17.
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The portion of the wing behind it, once compressibility sets in, is stalled out, negating lift there.
There is a question about the effect of the dive flaps at subsonic speeds. I wonder if at certain speeds the added and reduced lift cancel out. That would explain anecdotes that the dive flaps don't have much effect unless compressing.
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There is a question about the effect of the dive flaps at subsonic speeds. I wonder if at certain speeds the added and reduced lift cancel out. That would explain anecdotes that the dive flaps don't have much effect unless compressing.
I suspect that deploying them increases lift for the forward portion of the wing. In compressibility, the lift of the after portion of the wing is zero, so that isn't reduced, so the net is an increase in lift. If the wing isn't in compressibility, deploying the dive-recovery flaps might reduce lift in the after portion of the wing (maybe because flow on underside after the recover flaps is disturbed) -- not sure -- but if so, then as you say increase in lift for forward portion could be cancelled out by decrease in lift for after portion.
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Stark is the designer of the flap.
"Stack's idea was to use the flap to maintain lift in the face of the compressibility burble, hence eliminating the change in the downwash angle, and therefore allowing the horizontal tail to function properly."
Note the problem in this case is separation on the top wing changes the down wash angle. The bottom flap counters that by producing its own separation.
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Note the problem in this case is separation on the top wing changes the down wash angle. The bottom flap counters that by producing its own separation.
Downwash is produced by lift. Compressibility results in stall of the wing, hence reduction in downwash. Add some lift by the dive-recovery flap, and you get downwash re-established.
So, there are three positive things the dive-recovery flaps do: add lift, add drag, add downwash.
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Stark is the designer of the flap.
"Stack's idea was to use the flap to maintain lift in the face of the compressibility burble, hence eliminating the change in the downwash angle, and therefore allowing the horizontal tail to function properly."
Note the problem in this case is separation on the top wing changes the down wash angle. The bottom flap counters that by producing its own separation.
The compression problem isn't the airflow over the tail. The problem is the center of pressure moving back on the wing and pitching the nose down.
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(http://i547.photobucket.com/albums/hh473/cactuskooler/BorgCheckPayment340.jpg)
(http://i547.photobucket.com/albums/hh473/cactuskooler/BorgCheckPayment341.jpg)
(http://i547.photobucket.com/albums/hh473/cactuskooler/BorgCheckPayment342.jpg)
(http://i547.photobucket.com/albums/hh473/cactuskooler/BorgCheckPayment343.jpg)
(http://i547.photobucket.com/albums/hh473/cactuskooler/BorgCheckPayment344.jpg)
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Thanks for posting that. One of my first posts here 12 years ago was about the P-38 dive flaps modeling. It's good to see more info available now. :D
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Awesome post! :aok
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Cactuskooler your reply should be a Sticky.
I am glad we all kept digging to get to the technical explanation of the dive flap's function. Between this and the document FLS found. It nails it down.
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Nails what down, exactly?
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nice post on the p38.
P38s still look funny trying to pull up at 580mph :cool:
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Nails what down, exactly?
The technical reason behind the design of the flap.
The only open question now is wither Mach Drag is included in the AH P-38 model or not when entering transonic speeds.
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We still don't know how much drag we should see in subsonic flight or if we should see a pitch change when deployed in subsonic flight. We don't know how much drag the flaps add at compression either. We have a wind tunnel test on a 3 ft model wing and advice to pilots that extending the dive flaps after compression causes a pitch up and leaving them down limits your speed.
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Yes, we don't know anything about the drag, except that there was some (obviously), and that it isn't modeled in the game right now. Unless the P-38 ran on magic and unicorn juice those flaps must produce drag at any airspeed.
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These calculations represent a stick-fixed trim change that, for a wing loading of 60 pounds per square foot at 25,000 feet at Mach numbers of 0.600 and 0.890, will correspond to approximately a 3.6g pullout; however, at lower altitudes the normal acceleration will be somewhat greater.
That's a lot stronger pitch moment that I expected.
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Just tested it again.
At 35k, 382 TAS, M .58 the flaps do nothing whatsoever.
I then took it to 40k and dived it past M .72 in a long shallow dive, but experienced no Mach tuck effect. Lots of shaking and controls stiffened up, but no increase in dive angle. Can anyone confirm that Mach tucking and compressibility effects are actually modeled in the game, or perhaps only superficially simulated as loss of control authority?
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I then took it to 40k and dived it past M .72 in a long shallow dive, but experienced no Mach tuck effect. Lots of shaking and controls stiffened up, but no increase in dive angle.
Were you hand flying or using auto-angle? Any chance you cancelled out any pitch down that was present? I don't expect that mach tuck is modeled, the shaking and loss of control is sufficient for AH needs.
Here's a question…why does the 38 roll left at high speed?
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I used auto pilot, which only controls trim IIRC.
So compressibility effects are not really modeled in AH?
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... the shaking and loss of control is sufficient for AH needs.
Whereas in real life the aircraft would "tuck under" and go into a vertical, sometimes even slightly inverted dive in the opposite direction.
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I used auto pilot, which only controls trim IIRC.
So compressibility effects are not really modeled in AH?
You used the auto pilot mode that maintains your dive angle and your dive angle didn't change. That sounds right. You might want to try a manual trim for level cruise.
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I used auto pilot, which only controls trim IIRC.
So compressibility effects are not really modeled in AH?
If you used auto pilot, Im assuming auto-angle, it would have cancelled any pitch down from mach tach. I suggest manually trimming for the dive then "freeze" the stick and watch for pitching.
No idea if they are or not, just "think" they probably aren't other than the shaking and control loss we see.
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No it wouldn't. Mach tucking was not correctable by using the controls. That's why it was a problem in the first place.
Mach tuck should start at M .68 in the P-38, but somehow it can stay perfectly controllable (though heavy on the controls) at M .72 or more, even without using the dive flaps. This gives the P-38 a capability it never had in real life, and I can only assume it's the same with the P-47. High altitude combat in AH scenarios then become anything but historically correct.
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No it wouldn't. Mach tucking was not correctable by using the controls. That's why it was a problem in the first place.
Mach tuck should start at M .68 in the P-38, but somehow it can stay perfectly controllable (though heavy on the controls) at M .72 or more, even without using the dive flaps. This gives the P-38 a capability it never had in real life, and I can only assume it's the same with the P-47. High altitude combat in AH scenarios then become anything but historically correct.
What you did show is that the auto angle mode isn't historically correct.
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The auto pilot in AH only controls trim input. It doesn't even have enough authority to prevent the 109K from drifting off course in a WEP climb.
Go test it yourself in you don't believe me. Take a P-38 above M .68 and test it. I bet if you turn off combat trim and trim neutral before diving it will even pull out of the dive by itself, rather than tuck under like it should.
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No it wouldn't. Mach tucking was not correctable by using the controls. That's why it was a problem in the first place.
Mach tuck should start at M .68 in the P-38, but somehow it can stay perfectly controllable (though heavy on the controls) at M .72 or more, even without using the dive flaps. This gives the P-38 a capability it never had in real life, and I can only assume it's the same with the P-47. High altitude combat in AH scenarios then become anything but historically correct.
Keep in mind at subsonic speeds there may be no boundary layer disturbance behind the open dive flap. When separation occurs the change down wash angle is unknown at least to us. HTC may have the information and it may be modeled.
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The auto pilot in AH only controls trim input. It doesn't even have enough authority to prevent the 109K from drifting off course in a WEP climb.
Go test it yourself in you don't believe me. Take a P-38 above M .68 and test it. I bet if you turn off combat trim and trim neutral before diving it will even pull out of the dive by itself, rather than tuck under like it should.
That sounds like the test you should have done. :D
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The auto pilot in AH only controls trim input. It doesn't even have enough authority to prevent the 109K from drifting off course in a WEP climb.
Go test it yourself in you don't believe me. Take a P-38 above M .68 and test it. I bet if you turn off combat trim and trim neutral before diving it will even pull out of the dive by itself, rather than tuck under like it should.
I was doing some dives this morning in the P-38. I established desired dive angle, hit auto angle to trim for that angle then turned auto OFF. It held the angle fine all the way up to loss of control authority. The dives I did started at 20K.
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If you load the TA terrain for offline you can spawn at 30k from one of the fields. Makes for easier testing. Diving from 20k you get into the denser air too soon.
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If you load the TA terrain for offline you can spawn at 30k from one of the fields. Makes for easier testing. Diving from 20k you get into the denser air too soon.
Yeah, I was using the TA terrain but only found a 20K field/air start.
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Keep in mind at subsonic speeds there may be no boundary layer disturbance behind the open dive flap. When separation occurs the change down wash angle is unknown at least to us. HTC may have the information and it may be modeled.
Localized supersonic airflow starts occurring at M .68 in the P-38. The real one that is. I was passing M .72 in the cartoon one and experienced no adverse effects beyond control stiffness and screen shaking.
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Yeah, I was using the TA terrain but only found a 20K field/air start.
It's field number A3, it's not Bishop by default. It's NW of A1 and the SE spawn is 30k over A1.