Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: YUCCA on February 23, 2006, 02:47:38 PM
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Well, i did a search and didn't come up with much information on how the dive brakes are modeled. Im fairly inexperienced here but i mean when you drop the dive flaps on a P47D-40 they seem rather large. With that in mind you would think it would provide more lift.
I notice no real difference in lift with the dive flaps being deployed unless in an actuall compression. A player told me once that it does provide lift but combat counteracts the effect? Well i've tried using manual trim in conjunction with the dive flap which produced little or no effect.
Another thing i've heard is, it was undermodeled because it would give allies too great an advantage in overshooting thenemy plane. Any truth to this?
Hopin ya can shine some light on subject. Im basically just curious as to how they're modeled. How many degrees lift do they provide ( if they do at all.) And if they do provide lift are they modeled so that at say 400-100mph they have no effect to eliminate too great an advantage for American planes?
Player input is appreciated too. (If you know what you're talking about.)
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Most dive flaps do not provide any lift.
Dive flaps have different purposes on different airplanes. Some are ment to provide lots of drag, some are ment to change air flow over a specific point.
Some are ment to change the center of pressure to assist in regaining elevator athortiy. But can't think of any whos purpose is to provide lift.
2nd we never change any model based on it's country of origen.
3rd we never base airplane modeling on anything other than our best interpitation of the data we have at hand at the time we model it.
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yeah, that's what i have found on the 38 and the 47, it doesnt seem to lift the plane up but it decreases the effect of compression, lets you move the elevators a little
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Ive quietly questioned this myself. P38 dive flaps were there to change the airflow over the wing, but by first hand accounts they tended to cause the nose to pitch up when deployed under compression speeds. Not that it bothers me, I just wondered why that effect isnt noticible to me in ah.
Yucca, elevator trim can help you recover from a dive. In the 38 at high speeds I am all over the elevator trim adjusting the amount of lift I want. Keeping that in mind, combat trim is generally trimming the elevator down as speed increases. So at high speed when you want to pull up, CT is trimming the opposite way, which is counteracting what you want the plane to do. You wouldnt see very much difference if you were on manual trim but didnt chage the trim settings. You should see a difference if you add elevator trim while in the dive though.
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It is noticable in the P-38 but I've found out that you've got to keep the elevator trim set to as close to neutral as you can get any benefits of the dive flaps.
Don't know about any other planes though but I would think that since the P-47 almost has the same dive flap system as the P-38 (the P-47 suffered from compressability like the P-38) that it would provide the same benefit as the dive flaps on the P-38 does.
ack-ack
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Dive recovery flaps on the P-38L and P-47D-40 will do nothing if you have combat trim on, as the combat trim will adjust your elevators to offset the pitch-up.
Dive reovery flaps were not designed to generate lift. They were designed to shift the center of lift aft along the wing chord, thus preventing Mach tuck (nose pitching down) and induce pitch-up. They also generate drag, thereby helping to control, or even limit peak airspeed.
My regards,
Widewing
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As far as drag goes, i did a test tonight. Military power in d40 on deck did 329 tas. Then i deploeyd dive flap... Still 329mph. hmmmmm
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I've read in Warren Bodie's book, "The Lockheed P-38 LIGHTNING " , that compressibilty was never encountered with dives starting below 25,000 ft .
In Chapter 7 "The Specters of War and Compressibility " PG:77 Pharagraph 2 SNIP: "For a number of reasons , it was virtually impossible to encounter compressibilty tuck in any P-38 types if the dive was entered at 25,000 feet or less . Numerous test flights confirm this " SNIP
Any comments ? 38Maw
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Originally posted by 38ruk
I've read in Warren Bodie's book, "The Lockheed P-38 LIGHTNING " , that compressibilty was never encountered with dives starting below 25,000 ft .
In Chapter 7 "The Specters of War and Compressibility " PG:77 Pharagraph 2 SNIP: "For a number of reasons , it was virtually impossible to encounter compressibilty tuck in any P-38 types if the dive was entered at 25,000 feet or less . Numerous test flights confirm this " SNIP
Any comments ? 38Maw
Compressability wasn't an issue with dives entered at 20,000ft.
A few years ago I posted a table that gave the approximate altitude and speeds were one would encounter compressability in the P-38.
ack-ack
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Dive flaps....bah! Fly a 38G. never have to worry bout em....no worries about WEP either. What a great bird :)
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Originally posted by Ack-Ack
Compressability wasn't an issue with dives entered at 20,000ft.
A few years ago I posted a table that gave the approximate altitude and speeds were one would encounter compressability in the P-38.
ack-ack
I havent tested it in AH , but im pretty sure you can get a 38 to compress easily diving from 20k and even lower in some cases .
EDIT: I just ran a few quick tests . @ 15k, start of dive is at 300mph /tas , the 38 is fully locked up at 8k . @10k 300mph tas , it fully locks @ 3k .
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Originally posted by YUCCA
As far as drag goes, i did a test tonight. Military power in d40 on deck did 329 tas. Then i deploeyd dive flap... Still 329mph. hmmmmm
Yep, same for P-38L.... Drag apparently isn't modeled, althought pitch-up effect is.
To add my comments on P-38 compressibility... Yes, you can get a P-38 into compression diving from 10k... That was one of my complaints going back four years ago. There should not be any compressibility effects until you exceed Mach .67, and even there it will only be buffeting. P-38s had tremendous elevator authority. So much so that many pilots found them too sensitive, but very powerful (see the joint fighter conference comments on elevators). The Aces High P-38 suffers from nearly immovable elevators when at 500 mph regardless of altitude. Buffet onset is at Mach .63, which is well below the speed defined in the P-38 pilot's manual.
My regards,
Widewing
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Originally posted by Widewing
Yep, same for P-38L.... Drag apparently isn't modeled, althought pitch-up effect is.
To add my comments on P-38 compressibility... Yes, you can get a P-38 into compression diving from 10k... That was one of my complaints going back four years ago. There should not be any compressibility effects until you exceed Mach .67, and even there it will only be buffeting. P-38s had tremendous elevator authority. So much so that many pilots found them too sensitive, but very powerful (see the joint fighter conference comments on elevators). The Aces High P-38 suffers from nearly immovable elevators when at 500 mph regardless of altitude. Buffet onset is at Mach .63, which is well below the speed defined in the P-38 pilot's manual.
My regards,
Widewing
Thx widewing , i am about to order the report of Joint fighter conference from amazon , im just wondering, am i going to need an engineering degree to understand the reports ? Thx
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vewwy interesting thread going on here!
:noid
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Originally posted by 38ruk
Thx widewing , i am about to order the report of Joint fighter conference from amazon , im just wondering, am i going to need an engineering degree to understand the reports ? Thx
No, much of the text is simply pilots discussing the aircraft in pilot vernacular. However, the discussions are frequently dull as is some of the subject matter.
One problem I have with the JFC is that it shows the abject subjective nature of pilots. For example, several pilots may rave about a particular quality, while others state that it was sub-par.
A majority of the pilots were Navy or test pilots from Navy contractors (Vought, Grumman, etc). Lockheed was under-represented. The ratio of combat vets was low as well. Interservice rivalry is rampant and this is evident in the surveys.
After someone reads through the book, they will better understand why it is a bad idea to rely on anecdotal evidence in developing flight models for games like AH2. Opinions tend to vary wildly. Also, most of the pilots were single-engine qualified and were not experienced in multi-engine fighters. Thus, they were confounded by the additional complexity and generally out of their element.
Despite the obvious flaws of the JFC, it's still a useful resource and interesting to read. You'll just need to have your BS detector calibrated in advance.
My regards,
Widewing
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Originally posted by Casper1
vewwy interesting thread going on here!
yeah, its a shame we dont see any intelligent discussions like this anymore
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Thx Widewing , im going to get the JFC Report ordered . Now about the compressibility issue , I have the chart thats printed in Bodies book . Basically it uses a .68 mach number from 30k to sea level .
Looking at the mach numbers in text on page 76-77 , it show a buffet developed at M= 0.675 with 1G of acceleration , at higher accelerations , buffet was encountered at a lower M= number. Shortly after buffet was encountered, the diving tendency (tuck) started . This tendency reached it's zeinth at M=0.74 .
My question is , what is the zeinth that is being referred to ? Is it complete lock of control surfaces , or is it the nose actually trying to tuck under ?
I know this has to be a hard thing to get modeled in a game , but has HTC ever stated what was used as data for the Mach numbers? I would like to find out what kind of test data would be needed to have them take a look at this issue again .
Thx for the replys , 38maw
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Originally posted by Pooface
yeah, its a shame we dont see any intelligent discussions like this anymore
actually surprised there isn't a 100 page dissertation by Kweassa with his usual rants about the P-38 flaps.
ack-ack
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Suggestion: Maybe different reports are talking about different things.
Maybe the reports of "No compressability below 25,000 feet" are talking about total, complete, lockout of elevator control no matter what.
Maybe the first-hand reports of ww2 p38 vets that talked to HiTech were not totally locked out, but were so steep and fast that they still could not pull up in time (or, "barely in time" for the pilot telling the tale, and "not in tie" for his wingmen that crashed).
So, while in AH we get stiffening of the controls, you can still pull up and get out of it, whereas perhaps the tests are talking about a situation where nothing can get you out.
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whereas perhaps the tests are talking about a situation where nothing can get you out
The test were done by humans , alot were done by Burcham and LeVier. Test showing that nothing could be done to get you out would effectively be committing suicide for the test pilots . IIRC full scale wind tunnels at the time couldnt produce the kind of speeds that would simulate
compressibilty .
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LeVier could dive a P-38 and recover while hitting speeds high enough to take panels off the plane.
What several pilots told me is that most of the compression losses were actually from guys trying to see what happened when you deliberately pushed past what the placard said. Meaning few accidentally compressed and couldn't recover. They also said that many times the failure to recover was evidently due to the fact that pilots panicked and didn't know what to do. The yoke would literally beat the crap out of you.
The compression losses during testing were most often due to failure of abused parts.
Kelly Johnson said he was certain a spring tab operating link failure is what actually killed Ralph Virden. It allowed the travel limit to be exceeded and snapped the tail off because the stress exceeded 9G, and Johnson said it may have exceeded 15G. The part that failed was designed to increase the leverage the pilot could apply to the elevator in order to effect a pullout. Virden was warned to be careful at low altitudes and high speeds, as he could easily exceed the design limits. At around 3000 feet and over 300MPH, Johnson said that the link broke, and allowed the elevator to go to full deflection. The plane Virden was in was the first YP-38, and the one with the most hours. It had for a while been the only one flying, and as such had logged a great number of hours. It was then committed to the dive and compressibility tests, after several more "Yippees" became available for other testing.
When Ben Kelsey lost a P-38 in dive testing it was because the flap lever failed. This plane was old and had suffered through a great deal of testing. Kelsey was able to get out, where as Virden could not, and Kelsey survived.
The truth about the wind tunnel was that NACA felt the speeds would wreck their wind tunnel. It could generate the speeds.
From Kelly Johnson's notes on the P-38 and compression:
At Mach .65, drag increases violently as a shock wave formed on the wing center section
At Mach .675 buffeting develops, and shortly after Mach tuck (diving tendency) begins. The tendnecy peaks at Mach .74.
For a number of reasons, it was virtually impossible to encounter compressibility tuck in any P-38 types if the dive was entered at 25,000 feet or less. Numerous flight tests by LeVier, Burcham, and Mattern confirmed that.
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I believe the 8 foot wind tunnel was capabile of the speeds , the full scale one wasnt. Ive read where the Naca was scared of damaging their tunnel , im not sure which one they were referring to .