question on (109) elevator compression

[jodgi]

In what way did the elevators compress on the 109?
Were the stickforces too great for the pilots, and/or did the elevator loose effect?

The way AH models compression leads me to believe that it is stickforces only. Trim can always get you out of dodge.

Some planes had issues with elevator effectiveness at high speeds, not only great stick forces. This may only affect higher speed regimes than in AH/ww2 planes.

Any experts in here?

[_Schadenfreude_]

Size of the surfaces, fabric or metal......probably have a influence...

[jodgi]

Sure...

but what about the 109's, what happened on that aiframe?

[GScholz]

The 109 suffered from high stickforces at high speed, not lack of elevator effectiveness.

[Blooz]

As speed increases the control surfaces get heavy due to the airflow over the wing. Once the speed gets to a point where the airflow over the wing starts to interfere with the airflow over the tail then the tail becomes ineffective.

[Angus]

I only heard (so far) that the 109 just suffered from very high stick forces at hig speed. You could still pull it out with a lot of G's as soon as the speed popped under a certain limit.
Some pilots entering close to 1000 km/h in a dive might also miscalculate and hit the ground, or even break their wings, but the elevator was still working.
Reminds me of Gunther Rall's famous dive to escape P-47's. By pulling out he cleaned some of the paint of his wings!
BTW, the P47 easily followed him.

[Charge]

And if you dive fast enough the pressure waves remove the airflow from the elevator control surface and then the elevator control becomes loose without the contact to airflow. In this situation the only way to contol the plane is to move the whole elevator assembly as is the case eg. in modern jets. If U happen to be in a propfighter without control to whole elevator assembly in high speed dive the only thing U can do is to cut the throttle and hope the speed to decrease in time before the ground catches U. :-) In 109 the elevator trim helped the pilot to contol the plane because the elevator assembly was movable even in high speeds because of its mechanical assembly although the contol surface wasn't.

I think Blooz describes a bit different case there. Starfighter and the prototype of F4 Phantom suffered of the ineffectivenes of the elevator just because of the reason Blooz described. That is why Phantom has its elevators "bent" downwards to keep them in the airflow during high speed maneuvering.

-C+

[MiloMorai]

Charge, on the Me109, and on the Fw190, it was not elevator trim but stab trim(changes in the incedence angle).

[Batz]

I sniped this together a while back from several posters on this subject (gripen, hohun, tango and a few others). Correct it as necessary.

The 109 suffers from heavy controls at speeds starting about 640kmh.

The closer airflow approaches the speed of sound the more it becomes compressed. Compressibility problems arise for aircraft when airflow in a local region of the aircraft gets very close to or hits the speed of sound.

Because of this airflow on the top surface of the wing can reach the speed of sound before the free stream air does. The velocity at which this occurs is called the critical Mach number. When critical mach is reached shockwaves form resulting in turbulent airflow behind the shockwave resulting in loss of lift, severe trim problems, and violent vibrations.

Critical Mach number for the Spitfire, P51, 109 and 190 was about 0.75.

It was about 0.70 for the P-47D and about 0.65 for the P-38.

I was about 0.64 for the Typhie and  0.73 for the temp.

Critical Mach number has an aerodynamic definition like "speed of sharp drag rise", but there are different definitions so that Mach numbers can't be compared precisely.

There's a difference between "maximum achievable Mach" number and "maximum tactical Mach number" and critical mach. Critical mach is the onset of the "sharp drag rise".

Maximum achievable Mach number can include an aircraft diving out of control, like Mach 0.73 for the P-47D (without dive flaps) and Mach 0.79 for the 109. Recovery is possible only at lower Mach numbers. As you move into lower, denser air, the Mach number drops a bit allowing pullout if you're not too fast.

mach 1 corresponding alt/mph

Alt, MPH
0 761.52
500 760.21
1000 758.90
1500 757.58
2000 756.27
2500 754.94
3000 753.62
3500 752.30
4000 750.98
4500 749.65
5000 748.32
5500 746.98
6000 745.64
6500 744.31
7000 742.96
7500 741.62
8000 740.28
8500 738.93
9000 737.58
9500 736.23
10000 734.87
10500 733.51
11000 732.16
11500 730.79
12000 729.43
12500 728.06
13000 726.69
13500 725.32
14000 723.94
14500 722.56
15000 721.18
15500 719.80
16000 718.41
16500 717.02
17000 715.63
17500 714.24
18000 712.84
18500 711.44
19000 710.04
19500 708.63
20000 707.22
20500 705.81
21000 704.40
21500 702.98
22000 701.56
22500 700.15
23000 698.72
23500 697.29
24000 695.86
24500 694.43
25000 692.99
25500 691.55
26000 690.10
26500 688.66
27000 687.21
27500 685.76
28000 684.30
28500 682.85
29000 681.38
29500 679.94
30000 678.45
30500 676.98
31000 675.51
31500 674.03
32000 672.55
32500 671.07
33000 669.58
33500 668.09
34000 666.59
34500 665.10
35000 663.60
35500 662.09
36000 660.59
36500 660.59
37000 660.59
37500 660.59
38000 660.59
38500 660.59
39000 660.59
39500 660.59
40000 660.59
40500 660.59
41000 660.59
41500 660.59
42000 660.59
42500 660.59
43000 660.59
43500 660.59
44000 660.59
44500 660.59
45000 660.59
45500 660.59
46000 660.59
46500 660.59
47000 660.59
47500 660.59
48000 660.59
48500 660.59
49000 660.59
49500 660.59

[straffo]

I remember this discution and I allways wondered why the typhoon can dive so well in  regard to this :

Critical Mach number for the Spitfire, P51, 109 and 190 was about 0.75.

It was about 0.70 for the P-47D and about 0.65 for the P-38.
I was about 0.64 for the Typhie and 0.73 for the temp.

Then I searched on the BBS and found a quite different figure :

Gripen provided the Typhoon's critical Mach number as 0.64 (see below). That works out to 487 mph TAS at sea level, or 422 mph TAS at 20000 ft. Eric Brown's "Testing for Combat" on the other hand gives the critical Mach number as 0.81 and the limiting Mach number as 0.79, which is suprisingly high.

From this thread : Typhoon diving speed

That's another story !

[Batz]

that's the thread where I gathered most of the info in my post above.


look at duma quote in that thread

'The speeds given in the Typhoon's table (of 'limiting indicated airspeeds against height bands') were, after allowing for position error, equivalent to a Mach number of 0.79, which was higher than for any contemporary piston-engined fighter except the Spitfire IX. Our job at RAE Farnborough was to determine how critical this limiting Mach number was if taken to the ultimate loss of control. These tests were normally started at the highest possible altitude, so that if loss of control did occur in the dive the Mach number would automatically reduce as height was lost, provided the dive angle was kept constant, and thus allow control to be regained.

The aircraft to be used for the compressibility dive tests was Typhoon IB EK154, fitted with a Machmeter and powered by a 2,200hp Sabre IIA. THe aircraft was climbed to 32,000 ft and after a 3 min level run at full throttle at that height was half rolled and the nose allowed to drop 30 degrees before half rolling again to maintain that dive angle. The indicated Mach number (IMN) had built up to 0.82 by 27,000ft, with moderate buffeting, then at 0.83 a noticeable nose-down change of trim occurred and at the same time the buffeting inceased. Finally at IMN=0.84, the nose-down trim change increased dramatically and even a two-handed pull on the stick could not effect recovery. I could just manage to keep the dive from steepening, and held on with considerable effort until, at 20,000ft, the nose began slowly to rise; by 18,000ft recovery was complete. From these tests it was clear that the true limiting Mach number of the Typhoon was 0.79 and the true critical Mach number was 0.81.

Maybe we need a new thread?

[jodgi]

Originally posted by GScholz
The 109 suffered from high stickforces at high speed, not lack of elevator effectiveness.

rgr, ty

[MiloMorai]

Originally posted by jodgi


Originally posted by GScholz
The 109 suffered from high stickforces at high speed, not lack of elevator effectiveness.

rgr, ty

How effective can the elevator be if the pilot due to excessive force cannot readily make the elevator move?

[Angus]

Milo: It's a different problem alltogether, although the results can be the same.
There is onething here to think about however.
Wouldn't the 109's high stickforces at relatively high speeds limits ability in high speed breaks and turns. Must be really.(not talking about lockups or a screaming dive, rather a shallow dive or max level speed)
Would be interesting to see some charts of this, if they exist

[MiloMorai]

I know Angus, but wanted to make people think a little more deeply.