Author Topic: Hitech- Explain Dive Flaps modeling (Read 1004 times)

YUCCA · « **on:** February 23, 2006, 02:47:38 PM »

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.)

hitech · « **Reply #1 on:** February 23, 2006, 03:45:09 PM »

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.

Pooface · « **Reply #2 on:** February 23, 2006, 03:59:28 PM »

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

Murdr · « **Reply #3 on:** February 23, 2006, 06:09:17 PM »

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.

Ack-Ack · « **Reply #4 on:** February 23, 2006, 06:52:24 PM »

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

Widewing · « **Reply #5 on:** February 23, 2006, 07:31:28 PM »

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

YUCCA · « **Reply #6 on:** February 23, 2006, 09:01:37 PM »

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

38ruk · « **Reply #7 on:** February 23, 2006, 09:06:19 PM »

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~~

Ack-Ack · « **Reply #8 on:** February 23, 2006, 09:14:47 PM »

Quote

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

Guppy35 · « **Reply #9 on:** February 23, 2006, 10:59:24 PM »

Dive flaps....bah! Fly a 38G. never have to worry bout em....no worries about WEP either. What a great bird

38ruk · « **Reply #10 on:** February 24, 2006, 12:38:09 AM »

Quote

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 .

Widewing · « **Reply #11 on:** February 24, 2006, 01:28:42 AM »

Quote

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

38ruk · « **Reply #12 on:** February 24, 2006, 06:17:31 AM »

Quote

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

Casper1 · « **Reply #13 on:** February 24, 2006, 07:24:56 AM »

vewwy interesting thread going on here!

Widewing · « **Reply #14 on:** February 24, 2006, 08:44:24 AM »

Quote

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