Flaps, flaps, & flaps.

[TimRas]

Found the following info from the net:

Stall speed at weight all P-38s pilots manual with engine power off:

94 mph tas at 15,000 lbs gear and flaps up
100 mph tas at 17,000 lbs gear and flaps up
105 mph tas at 19,000 lbs gear and flaps up

69 mph tas at 15,000 lbs gear and flaps down
74 mph tas at 17,000 lbs gear and flaps down
78 mph tas at 19,000 lbs gear and flaps down

using the lift coefficient calculator, the lift coefficient (flaps up) is around 2.1.

[niklas]

Originally posted by TimRas
Found the following info from the net:

using the lift coefficient calculator, the
lift coefficient (flaps up) is around 2.1.

And 2.1 with flaps and gear up is absoulty ridicolous and unrealistic, so donīt give anything on the speed values except you consider it as IAS comparison values for what the pilot reads from his instruments. But is has nothing to do with TAS and true Cl


niklas

[Schaden]

Originally posted by StarOfAfrica2
Thanks for posting that Schaden.  Just decided to read this thread today (Friday always seems so boring waiting for quitting time lol).

Apparently however LW did not have the greatest kit in terms of chutes - was reading JG26 and the number of chute failures is incredible.

[Crumpp]

dtango,

Prolonged usage had a detrimental effect on turn performance....Is absolutely true as with any flap.

You yourself showed the EM diagram!  Your airspeed bleeds to a point, you lose bank angle, and turn rate!  

Flying with flaps deployed in a sustained turn, you could leave your flaps out indefinitely with no degradation of sustained turn performance where excess power >= 0.

Yes but your power required shoots up considerably when you leave your flaps down. Therefore your power available is a lot less.

Lets examine the following diagram:



Pick any airspeed, reduce the bank angle and see what happens to turn performance?

All of the above statements are very true.

I have been arguing all along comparing the P 38 to other WWII fighters under the same conditions.  You seem to think I am comparing the P 38 in a flap up vs. flaps down turn rate.

Now the big thing is speed reduction.  Does the P38 have enough power to maintain an airspeed fast enough to achieve best turn performance with flaps down?  It certainly will be a shorter radius than when flaps are up.  

Lockheed says using flaps for more than a short period will leave the P 38 in a position that it does not have to power available to accelerate the aircraft.  

Don't be caught with your flaps down for any length of time in combat; the reason being that with maneuvering flaps down you can unknowingly get down to such low speeds that all the power in the world won't do you much good should you need sudden acceleration.

http://www.jamesreese.org/hangarflying/Issue6.htm

Question is how does it fair against fighters with equal lift, much better drag, and better Power to Weight using flaps?

All the best,

Crumpp

[dtango]

You yourself showed the EM diagram! Your airspeed bleeds to a point, you lose bank angle, and turn rate!

You don't know how to read EM diagrams then and what they tell you.  The EM diagram shows the envelope for the 3 dynamic energy states I've mentioned already.  Turn g-loading at or below the Ps=0 line you don't bleed airspeed even with flaps extended.  No bleed in airspeed --> no decrease in bank angle --> no change in turn performance.

Yes but your power required shoots up considerably when you leave your flaps down. Therefore your power available is a lot less.

You keep assuming this automatically means Drag > Thrust leading to energy bleed and there's where you're missing it.  I already did a few simple calcs for you using some whopping unrealistic parasitic drag values with flaps deployed to give you an idea the excess-power margin ([T-D]*V) is still positive.

Now the big thing is speed reduction. Does the P38 have enough power to maintain an airspeed fast enough to achieve best turn performance with flaps down? It certainly will be a shorter radius than when flaps are up.

 The only thing I can figure here is that you're confusing what "best turn performance" means and seem to be confusing instantaneous turn and sustained turn performance.

Lockheed says using flaps for more than a short period will leave the P 38 in a position that it does not have to power available to accelerate the aircraft.

Again only where Ps<0, excess-power<0.  Where Ps & excess-power >=0 this is not true.

Tango, XO
412th FS Braunco Mustangs

[dtango]

Maybe this will be helpful.  Here's Badboy's article on understanding EM charts.

http://www.simhq.com/_air/air_011a.html

Tango, XO
412th FS Braunco Mustangs

[Crumpp]

I do understand how to read a EM diagram dtango.

You are all over the map.  

First you misunderstand what particular conditions I am refering too and go into a nice but unecessary explaination.  You then ignore that part and move on to something else, equally misunderstanding me.

Then you claim to be educating and "glad I am finally getting it!"

You keep assuming this automatically means Drag > Thrust leading to energy bleed and there's where you're missing it. I already did a few simple calcs for you using some whopping unrealistic parasitic drag values with flaps deployed to give you an idea the excess-power margin ([T-D]*V) is still positive.

Please show me where I have said the excess power margin is negative??

You don't know how to read EM diagrams then and what they tell you. The EM diagram shows the envelope for the 3 dynamic energy states I've mentioned already. Turn g-loading at or below the Ps=0 line you don't bleed airspeed even with flaps extended. No bleed in airspeed --> no decrease in bank angle --> no change in turn performance.  

Your missing the point of what I am saying.  To add to the frustration, dtango you are insisting I do not understand the aerodynamics.  So you think we have access to aeronautical engineers when restoring an almost extinct aircraft?

We are not looking for a STEADY turn rate! We are looking for a BETTER turn rate than other WWII fighters using flaps!

1.  It is obvious from Lockheeds own instructions that the P38 moved quickly to a point Pa was very close too Pr with flaps down.  

2.  The P 38 had a rather unremarkable CL max.  It is interesting that the "calculator" you presented shows the same trend in the P38's CLmax as windtunnel investigations vs flight test's.  Windtunnel investigations put  the P38's Clmax much higher than actual flight testing.

http://naca.larc.nasa.gov/reports/1946/naca-tn-1044/index.cgi?page0038.gif

Which seems to be a reversal from other designs tested.

All the best,

Crumpp

[dtango]

Crumpp my friend,  I'm simply guffawed by your response.  I've been consistent with my responses which is dropping flaps does not mean you will bleed energy in a turn leading to turn performance degradation in a P-38 or any other plane for that matter.  This has been my statement all along and I've been trying to show that different ways.

Part of the problem is you never stated the particular conditions you were referring too which misleads people.  For instance you stated this...

The key was do the maneuver flaps drop the airspeed. According to Lockheed, YES they do. The flaps are to be used for short periods of time to complete a maneuver. Leave them down and your airspeed goes.

No conditions mentioned.  I and others can only assume this is a blanket statement meant to cover all cases.

Taken as a blanket statement this means that you believe for all cases with flaps deployed that D>T which means excess-power is negative.

1. It is obvious from Lockheeds own instructions that the P38 moved quickly to a point Pa was very close too Pr with flaps down.

I don't know how you can even make this leap.  Here again where are the conditions you are concerned with?  You're not stating them which means this is an inaccurate statement because having flaps deployed does not mean a P-38 moved quickly to Pa=Pr, nor does the phrase "prolonged usage" give you any idea what conditions you are concerned with which might lead to Pa>=Pr.

We are not looking for a STEADY turn rate! We are looking for a BETTER turn rate than other WWII fighters using flaps!

Two points here.  (1) The whole discussion started not on relative turn performance differences between different aircraft but if prolonged usage of flaps degraded turn performance or not for the P-38.  And my point all along is that ONLY in certain conditions they do.  (2) The reason I've brought up a steady turn rate is to demonstrate where it's inaccurate to say that "prolonged usage" of flaps in a turn for a P-38 = energy bleed as a blanket statement.

Tango, XO
412th FS Braunco Mustangs

[TimRas]

Originally posted by Crumpp
Windtunnel investigations put  the P38's Clmax much higher than actual flight testing.

http://naca.larc.nasa.gov/reports/1946/naca-tn-1044/index.cgi?page0038.gif

The report you linked states:
"Accordingly, initial-stall and maximum lift-coefficient points for the P-38 model, as obtained from figure 13, are plotted in figure 12. It may be seen that good agreement exists between the flight maximum lift coefficient and the initial-stall lift coefficient of the model."

[Crumpp]

Part of the problem is you never stated the particular conditions you were referring too which misleads people.

Certainly there is room for confusion when posting on a BBS.  I apologize if things were not clearer.  Perhaps in the future conditions should be defined well before the beginning of a lengthy discussion that leads nowhere.  Better communication from all parties.

I do enjoy discussing these aircraft and some members of this community are extremely knowledgeable.  I consider you one of them dtango.

The key was do the maneuver flaps drop the airspeed. According to Lockheed, YES they do. The flaps are to be used for short periods of time to complete a maneuver. Leave them down and your airspeed goes.

It was not meant as a blanket statement.  In fact Lockheed says:

For example, in an effort to stay on an enemy's tail, you might feel in a tight turn the buffeting which is characteristic of an accelerated stall. You can "reef" her in and tighten your turn by lowering the maneuvering flaps until you have completed the maneuver, then retract them. By doing so immediately, little air speed is lost, and the plane is set again for maximum operations.

http://www.jamesreese.org/hangarflying/Issue6.htm

Looks like the P38's turn ability from flaps came about as a result of using the stall, not the sustained turn ability of the flaps.

Lockheed most certainly warns not to leave them down for any length of time:

Don't be caught with your flaps down for any length of time in combat; the reason being that with maneuvering flaps down you can unknowingly get down to such low speeds that all the power in the world won't do you much good should you need sudden acceleration.

It must happen fairly quickly for a pilot to miss his speed bleeding down.

How do you explain Lockheeds instructions?

All the best,

Crumpp

[Widewing]

Originally posted by TimRas
The report you linked states:
"Accordingly, initial-stall and maximum lift-coefficient points for the P-38 model, as obtained from figure 13, are plotted in figure 12. It may be seen that good agreement exists between the flight maximum lift coefficient and the initial-stall lift coefficient of the model."

Yes, and I think that the below chart shows that the P-38 maintains more consistant lift coeffcient over a greater portion of AoA change than the others. Note that the CLmax numbers for the P-38 generally reflect higher speeds than the others as well.

 
My regards,

Widewing

[Crumpp]

Actually TimRas it says this about the CLmax in flight test vs Windtunnel:

http://naca.larc.nasa.gov/reports/1946/naca-tn-1044/index.cgi?page0006.gif

According to this Flight test CLmax will be lower than windtunnel test and is to be expected.

So yes figure 12:

http://naca.larc.nasa.gov/reports/1946/naca-tn-1044/index.cgi?page0036.gif

Does give good agreement given what they were expecting for this part of the test.  It still shows a below average CLmax for the P38.

The P38 and the P39 have the roughest finish of all the planes tested.  However the P 39 does quite well in it's CLmax.

http://naca.larc.nasa.gov/reports/1946/naca-tn-1044/index.cgi?page0038.gif

All the best,

Crumpp

[Murdr]

Originally posted by Widewing
Note that the CLmax numbers for the P-38 generally reflect higher speeds than the others as well.

 
My regards,

Widewing

Which reflects that report being a compilation of past tests.  My assumption when looking at this in the past has been that the higher speeds were resulting from studying its compressability problems.  Fig 12 show speeds >380 from the wind tunnel and >200 from flight test.

[Widewing]

From the same report:

"The actual maximum lift coefficient of the P-38 model then occurs at extremely high angles of attack."

That seems to me to be an important observation.

My regards,

Widewing

[Murdr]

Originally posted by Crumpp
It was not meant as a blanket statement.  In fact Lockheed says:

For example, in an effort to stay on an enemy's tail, you might feel in a tight turn the buffeting which is characteristic of an accelerated stall. You can "reef" her in and tighten your turn by lowering the maneuvering flaps until you have completed the maneuver, then retract them. By doing so immediately, little air speed is lost, and the plane is set again for maximum operations.

Looks like the P38's turn ability from flaps came about as a result of using the stall, not the sustained turn ability of the flaps.
[/B]

How so?  You deploy flaps which change the foil shape and add lift.  You just chaned the conditions needed for stall.  In the example given from Issue 6, you are at the threshold for accelerated stall conditions, by lowering the flaps, you change the threshold.  I dont see how that is "using the stall".

You also seem to strictly interprert "loss of speed" as a degenerative effect, and not a comparative effect.  If I were to fly level starting at 200mph for 30 seconds and achieve a speed of 275mph, then repeat under the same conditions with flaps down and only achieve 235mph, I lost speed with flaps down, when compaired with no flaps.  I did though still gain speed with flaps deployed.