Corsair vs. BF 109G,K or FW 190's

[Crumpp]

Thanks Henning!

I downloaded it and will play with it. I like some of the features it has especially the error range plots. You could show the normal performance variation of a design.

All the best,

Crumpp

[HoHun]

Hi Crumpp,

>I downloaded it and will play with it. I like some of the features it has especially the error range plots. You could show the normal performance variation of a design.

Glad you like it

Be warned that there is an error in my sample script: I left an extra "," behind the second line that will mislead Gnuplot to expect more graph specifications that I actually provided.

I'll edit that out, but only after I have mentioned it here so you know about the changes. It could be terribly confusing if you had already copied the flawed script and I'd make the edit without telling you!

Regarsd,

Henning (HoHun)

[Crumpp]

Thank You!

[Soren]

Another great fighter to add is the Ta-152 H-1, with its highly efficient high AR wing it was a formidable turnfighter. The high AR made sure that the L/D ratio was very high, and coupled with the high CLmax of the NACA 23000 series airfoil this made for a lot of lift for a minimum amount of drag.

Ta-152H-1 wing AR: 8.94.

L/D ratio = Lift to drag ratio.

The more lift you have pr amount of drag the better, and the less your energy loss is going to be in maneuvers, and the higher the AR the higher the L/D ratio.

Higher AR wings also have the advantage of producing a higher amount of lift pr. area in the first place - forgetting about the L/D ratio.

L/D ratio at an AR of 4:


L/D ratio at an AR of 9:


As you can see the wing with an AR of 9 has over twice as high a L/Dmax and optimum CL.

[Glider]

One question about the TA152H as a high altitude fighter. Those wings could I think have been a significant problem as very high altitudes.

I have only flown a glider a couple of times at high altitude and I was briefed about the absolute requirement of being careful about the airspeed I flew at. The difference in airspeed between encountering a stall and a shock stall was very small, around 10 knots and the VNE was also impacted. For obvious reasons any form of manoevering had to be very smooth and slow.
I know that this isn't specific issue with gliders, the Lockheed U2 had similar problems and I would have thought the 152 must have followed as there isn't a magic cure for this, even today.

I have no access to any tests undertaken by the 152 and was wondering if this problem had ever some up.

[Soren]

Glider, a glider ( ) is a different beast than a powered a/c. Also I'm wondering why you would ever be warned about a shock stall in a glider as they don't often reach their critical mach number I can see why the U2 jet had this problem though, but the Ta-152H wouldn't be susceptible to this unless in a very high speed dive.

High AR wings are necessary for high altitude fighters as a very efficient and high lift wing is needed at high altitudes in order to preserve a good degree of maneuverability.

PS: The AR of a glider's wing is usually around 12-14.

[FLYBOYJ]

It's not a matter of the glider (or powered aircraft) hitting its critical mach number, its a matter of exceeding Vne based on TAS at altitude. The Ta-152H like any other aircraft could be affected by this. One would have to look at the aircraft's Vne, service ceiling, maximum speed and calculate that in a hypothetical setting at altitude.

[Glider]

Originally Posted by Soren

Glider, a glider ( ) is a different beast than a powered a/c. Also I'm wondering why you would ever be warned about a shock stall in a glider as they don't often reach their critical mach number I can see why the U2 jet had this problem though, but the Ta-152H wouldn't be susceptible to this unless in a very high speed dive.

High AR wings are necessary for high altitude fighters as a very efficient and high lift wing is needed at high altitudes in order to preserve a good degree of maneuverability.

PS: The AR of a glider's wing is usually around 12-14.

We were carefully briefed because people didn't want us to die, and I was willing to listen, as I didn't want to die. Simple really.

I am very aware of a gliders wing and how to fly them. I am interested as to your assumption that the 152 wouldn't be susceptible to shock stall and VNE problems, when ALL other aircraft that I know of with this wing configeration, both then and now are.
There is no magic formula and if you flew on that basis then you would be in serious trouble very quickly.

[Soren]

I know FLYBOYJ, however a glider has a much much lower Vne than any respectable WW2 piston engined fighter, so comparing the two is pretty ridiculous.

Glider,

As to why I think the Ta-152 wasn't susceptible to shock stall unless in a high speed dive: Simple, look at the top speed of the aircraft, 760 + km/h in straight flight, and the Vne is 850 km/h. - Hence why no such problems were ever registered or noted by any Ta-152 pilot.

That the U2 experienced problems with shock stall is understandable, its a jet aircraft with long slender straight wings - not a good combination in all situations. The U2 mind you also had a higher wing AR of 10.6, and gliders usually have a wing AR of 12-14.

[Crumpp]

Hi guys,

Soren you are correct in that the high aspect ratio of the Ta-152H series is the key to it's high altitude performance.

However what both Glider and FlyboyJ are telling you is correct too.

While there are multiple reasons why we can establish a design Vne, the two major reasons are q-limits and mach limits.

Q-limits are also termed our "flutter limits" and generally form our lower altitude restrictions. Our designs harmonics are such that the aircraft structure will most likely fail. There are generally two zones of restriction placed on the aircraft. First is the area of damage and second restriction is at the failure point.

Now some might erroneously think this gives a pilot license to violate the damage zone. It does not, for damage to an airframe will obviously weaken the structure. One harmonic or loading condition that would not normally cause damage to an intact airframe may now cause total failure in the damaged one at a much lower loading or different harmonic.

At high altitudes though the mach limits are our major restriction.

As FlyboyJ points out, our high TAS due to density effects means we are traveling at a higher mach number for the same Equivalent Airspeed.

M = VTAS/a
a = a<sl> * SQRT (theta)

Velocity in TAS divided by local speed of sound.

Local speed of sound equals the speed of sound at sea level multiplied by the square root of the temperature ratio.

For example, lets take an aircraft traveling at 250KEAS at sea level and see how mach changes between sea level and FL33 or 33,000 ft.

250KEAS at sea level = 250KEAS * SMOE(1) = 250KTAS

250KTAS/661.74KTAS = Mach .37

That same 250KEAS at FL33 becomes:

250KEAS*SMOE(1.7291) = 432.28KTAS

432.28KTAS/581.85KTAS = Mach .74

At mach .74 a subsonic airfoil most definitely is experiencing shock build up and supersonic flow. We are beginning to experience divergence effects on both our drag and lift forces.

Some of the effects of force divergence are:

1. An increase in Cd for a given Cl <our L/D shape is changing>
2. A decrease in CL for given AoA <L/D curve change>
3. Change in the pitching moment as the Aerodynamic Center shifts <stability and control points shift>

So even though the aerodynamic forces on the aircraft are exactly the same at altitude and 250KEAS, the Mach number is much higher.

This is an environmental effect that all aircraft have to deal with at high altitudes. High aspect ratio wings are ideal because they develop low induced drag and higher efficiencies in high CL low velocity flight. As you have seen from our airspeed computations, aircraft at high altitudes will spend the majority of their time at Equivalent Airspeeds that represent the low velocity flight realm to the aerodynamic forces due to mach restrictions of the environment.

All the best,

Crumpp

[Soren]

I know all this very well Crumpp, but you can't compare a glider to a fighter a/c.

The Ta-152H would ofcourse experience shock stall before an a/c with more stubby (lower AR) wings, but at 760 km/h there were no problems, and since the Vne was 850 km/h I'd expect no such problems until then. The U-2 is a jet aircraft of very low drag so the Vne can be reached quickly by this a/c, and thus problems with shock stall would've been very apparent to the engineers when designing the a/c, they knew it was going to have problems at very high speeds.

PS: I noticed Glider said he was warned about shock stall when released at high altitude, which I understand, I missed that part to begin with. Starting at high alt you have to be careful when descending in a glider, no doubt.

[FLYBOYJ]

Originally Posted by Soren

I know all this very well Crumpp, but you can't compare a glider to a fighter a/c.

The Ta-152H would ofcourse experience shock stall before an a/c with more stubby (lower AR) wings, but at 760 km/h there were no problems, and since the Vne was 850 km/h I'd expect no such problems until then.

Only if the OAT was such that TAS will remain in sync to the operating limitation of 850 Vne. Also consider that prior to exceeding Vne you're in a "caution" range where any abrupt maneuvers or turbulence can damage the aircraft. Just because you're at altitude at 700 km/h doesn't mean you're pulling 3 or 4 Gs.

[Soren]

Roger that FLYBOYJ and no objections from me about that either.

My point is that at all the normal flight envelopes of WW2 fighters the Ta-152 wouldn't be experiencing any problems with shock stall, but approach the Vne of 850 km/h and then we can begin to talk about the possibility of a shock stall.

[Crumpp]

Hi Soren,

I wasn't trying to come across as a know it all or talk down to you. Just to explain the effect to all of high AR wings on a subsonic airfoil and why they are important to high altitude performance whether you are in a glider or a fighter. The reason for that explanation is so that there are no misunderstanding's in the conversation.

I apologize if I came across as talking down to you.

Nobody is putting out any wrong information. What glider is saying is very true AND what you are saying is very true.

Our mach characteristics are primarily dictated by airfoil choice. Critical mach is a function of the Coefficient of pressure of the airfoil section and the free stream mach number. Shock stall is a function of critical mach number.

Getting the most out of our airfoil choices at a given aerodynamic force is affected by Aspect Ratio and is a property of the wing design. At high altitudes we want a wing that performs well at low velocity aerodynamic forces if we use a subsonic airfoil.

Just because you're at altitude at 700 km/h doesn't mean you're pulling 3 or 4 Gs.

Absolutely. AT 700kph and 33,000 feet, we are traveling at ~210KEAS and mach .65 using NACA 1922 standards. Just hazarding a big guess, I imagine a Ta-152H can still quite well especially in comparision with a design that is not optimized for high alititudes.

All the best,

Crumpp

[Glider]

Originally Posted by Soren

PS: I noticed Glider said he was warned about shock stall when released at high altitude, which I understand, I missed that part to begin with. Starting at high alt you have to be careful when descending in a glider, no doubt.

'When released at high altitude' Ouch that hurt. It took me about 2.5 hours to get up there and about 3.5 to come down again.

I retire bruised