Supercritical airfoil

drgondog · May 17, 2013

zjtins said:
I looked up the ME109 E airfoil and P51D airfoil. The P51 drops CL drops rapidly above 10 degree AoA, the ME109 continues with a greater CL until around 20 degrees AoA. What saves the P51 is as long as they kept speed up then 6-8 degrees AoA is all the plane can do in a continuous banking turn. Once below ~275 MPH the ME109 has the advantage.

The Stall CLmax is around .15. The 109 with LE slats is closer to .20 and does have an advantage - all other factors being equal. Factors that were not equal was tha a.) stick forces/aileron response above 300 mph favored the Mustang, with advantage increasing as speed increase, b.) the Mustang retained energy better, therefore lost velocity slower.

Last and hard to quantify. In a high G/high AoA envelope there is a pronounced increase in profile drag which again is a major factor in power requirements for the turn as well as increased energy bleed. The 109 CDo was about 60% higher than the 51. Presumably the Profile Drag contribution to the 109 was higher proportionately than the 51. Having said that, I don't know that.

A lot of 109s were shot down in turning fights. Presumably ditto for P-51 but pilot ability and feel for the airplane is a Major factor

zjtins · May 17, 2013

If you look at some of the discovery channels animated fights from actual WWII accounts you can find at least 2 examples of ME-109 pilots going into a circle and P51s chasing them. Eventually the P51s either catches up and shoots them down or the ME109s break realizing the P51s are closing the gap.
Looking up some numbers it looks like the P51 can hold a ~350MPH circle at 3Gs. The ME109 can do the same but has more drag and slows a bit.
I have never seen an account but in theory ME109 could slow then pull a tighter circle than the P51 below 275 MPH. Of course that means losing energy and I am sure there is a counter move the P51 could use without simply slowing down to try and force a tighter circle.

So the slower speed more capable maneuvers of ME109, at least from what I have read, never really made a difference once a fight began. Make sense as this would be roughly the same issue with the Zero vs US fighter once the pilots learned do not dogfight a Zero.

altsym · May 17, 2013

zjtins said:
If you look at some of the discovery channels animated fights from actual WWII accounts you can find at least 2 examples of ME-109 pilots going into a circle and P51s chasing them. Eventually the P51s either catches up and shoots them down or the ME109s break realizing the P51s are closing the gap.

Or it could be just young pilots without a lot of experience. Discovery channel fails to mention potentially relevant information.

zjtins said:
I have never seen an account but in theory ME109 could slow then pull a tighter circle than the P51 below 275 MPH.

For a good read: Operation Bodenplatte - The Luftwaffe's Last Hope. Various accounts (from both sides) of BF 109's doing just that, not only
against the P-51.. but P-47's also.

jim · May 17, 2013

: NACA 23018-630
Tip: NACA 23012-635
I read on LEMB that these are Do 335 airfoils . Do they relieve any information about aircrafts behavior?
Is it true that 5 digit series airfoils are for slower aircrafts in comparison with 6 digits airfoils?

OldSkeptic · May 19, 2013

nincomp said:
OldSkeptic,
I am glad that you brought up the vices of the Mustang's laminar-flow wing. I tend to tread lightly when discussing any of its potential shortcomings since, for some, the P-51 is a religion, not an airplane. I was certainly raised to believe this. You are a braver man than I, OldSkeptic.
Nothing to do with bravery, I love the Mustang (actually flew in one) one of the all time great fighters, But if anyone thinks it was perfect, then they are smoking something.

If I had wanted to give a simple, short, and not quite accurate answer to Jim's question of the ideal airfoil, I would have said a laminar flow type with gentler stall characteristics. The landing speed of such a wing, without additional high-lift devices would still be pretty high. I don't think that I would be comfortable landing at over 100 knots on a bumpy, soggy grass field.

Don't forget things like wing loading and wing twist. They can all have significant affects on stall speeds and characteristics.

I recently saw a documentary (on Youtube) about the Tempest. One pilot commented on the higher landing speed caused by the "low-lift high-speed wing." This supports zjtin's comment about the lower maximum lift of laminar flow designs.
Bit it was heavy with a high wing loading as well.

Did the laminar-flow-winged Tempests have the same kind of unpleasant stall characteristics as the Mustang?
No idea, that's an interesting question. Wonder if anyone knows. I'll have a look around to see what I can find.

Thanks
No worries.

Jim (but not the same Jim as the OP - unless I have developed some type of split personality)

Found something here on US trials of it (http://www.wwiiaircraftperformance.org/tempest/Tempest-V_Eng-47-1658-C.pdf).

90mph clean 74mph gear and flaps down. Said "not much stall warning ... slight aileron snatch".
"A good accelerated stall (about 140 in a tight turn) of the "shudder:" variety manifests itself". Whatever that means....

But as I said, it was different from a Mustang wing. Semi elliptical. Slightly lower wing loading on its loaded weight (37.7 lbs/ft^2 vs 39.1lbs/ft^2 for the P-51D).
The Mustang had a 2 degree wing twist, relatively linearly from about the mid point of the wing (from memory), don't know what the Tempest had or what way it did it.

So they were not really comparable wings, since they had quite different characteristics. Not even comparable planes either, the Tempest was about 2,000lbs heavier for a start.

tomo pauk · May 19, 2013

nincomp said:
OldSkeptic,
I am glad that you brought up the vices of the Mustang's laminar-flow wing. I tend to tread lightly when discussing any of its potential shortcomings since, for some, the P-51 is a religion, not an airplane. I was certainly raised to believe this. You are a braver man than I, OldSkeptic.

If I had wanted to give a simple, short, and not quite accurate answer to Jim's question of the ideal airfoil, I would have said a laminar flow type with gentler stall characteristics. The landing speed of such a wing, without additional high-lift devices would still be pretty high. I don't think that I would be comfortable landing at over 100 knots on a bumpy, soggy grass field.

I recently saw a documentary (on Youtube) about the Tempest. One pilot commented on the higher landing speed caused by the "low-lift high-speed wing." This supports zjtin's comment about the lower maximum lift of laminar flow designs.

Did the laminar-flow-winged Tempests have the same kind of unpleasant stall characteristics as the Mustang?
...

Since the Sea Fury employed the wing of similar design, and of smaller wing area, it could be safely assumed that it's low-speed characteristic were benign enough for a carrier-borne plane?

nincomp · May 19, 2013

OldSkeptic, I agree with your comments that numerous things, including wingloading and twist, need to be added into the equation for an effective wing, that is why I prefaced my comment post #18 with: "If I had wanted to give a simple, short, and not quite accurate answer ..." I thought that my earlier post, #16 may have been a bit too nebulous.

I have seen some comments about "the laminar flow wing," which implied that there was only one design rather than a multitude of designs. I wondered if, during the war, any of the designers had managed to produce a variant that had more benign stall characteristics. This led to my question about the Tempest.

Tomo pauk, I had not thought about the Sea Fury. Good point.

My joking comments about the P-51 were just a way to try to avoid yet another heated debate about which fighter was the best.

Supercritical airfoil

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