Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: jodgi on January 15, 2004, 03:17:00 AM
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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?
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Size of the surfaces, fabric or metal......probably have a influence...
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Sure...
but what about the 109's, what happened on that aiframe?
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The 109 suffered from high stickforces at high speed, not lack of elevator effectiveness.
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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.
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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.
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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+
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Charge, on the Me109, and on the Fw190, it was not elevator trim but stab trim(changes in the incedence angle).
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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
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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 (http://www.hitechcreations.com/forums/showthread.php?s=&threadid=74338&)
That's another story !
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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? :p
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Originally posted by GScholz
The 109 suffered from high stickforces at high speed, not lack of elevator effectiveness.
rgr, ty
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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?
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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 ;)
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I know Angus, but wanted to make people think a little more deeply.
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Originally posted by MiloMorai
I know Angus, but wanted to make people think a little more deeply.
You fascinated by Socrates?
;)
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One thing is the force needed to move a control surface, and other is the force that you can really apply due the stick and cockpit design.
AFAIK The problem with the 109 was not related to very hi forces on the surface control, but to the lack of room to apply enough force to the stick laterally (aileron control). Here you will find a clear view of the 109G6 cockpit design and certainly there is very little lateral room, but, on the other hand, the space to apply forward and rearward forces to the stick seems more than enough, so, elevators should not suffer of the same effect.
109G6 cockpit (http://www.kitreview.com/reviews/bf109cockpitbg_1.htm)
Even better view:
109G6 cockpit (http://hkkk.fi/~yrjola/photo/planes/bf109/cockpit.html)
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Hi Milo,
>How effective can the elevator be if the pilot due to excessive force cannot readily make the elevator move?
Tough question :-)
What the high control force actually does is to limit the throw of the control surface - it can be deflected, but only by a small measure.
However, at high speeds, small deflections can actually have large results anyway, so large control force doesn't necessarily mean poor control response.
With regard to the Me 109, there's a bit of a contradiction in the reports regarding its aileron effectiveness at high speed. It's generally considered poor, yet at very high Mach numbers the ailerons actually became overbalanced.
(In other words, they but they actually deflected themselves if left alone!)
The funny thing is that this means that at Mach numbers slightly below the speed where over-balancing began, I'd expect the Me 109 to have balanced (and accordingly very light) ailerons.
I don't know what to make of this, I've just stored it mentally in my "unresolved" folder :-)
Regards,
Henning (HoHun)
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Originally posted by Batz
that's the thread where I gathered most of the info in my post above.
look at duma quote in that thread
Maybe we need a new thread? :p
ouch :) I don't think so .... I should have read slower :D
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So the Gearing on the stick regarding elevators was as unfavourable as on the aileron side?
Somehow I'd presume that the exact gearing on the "pull" side would not be as acute, or rather depending on your position really. Tug-of-war vs. armwrestling really.
All makes you wonder.Must have something to do with airflow as well, and even C of G. I recall reading that the 109 had a tendency to nose down while building up speed in a steep dive.Some planes did not, some may have pitced up, and some would be over-responsive to aileron control at too high speed, giving the pilot the possibility to push the plane into disintegration at exessive speeds.
Anyway, still curious what the 109's stick forces were at some certain speeds ;)
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Problem with the 109s elevator at high speeds was the force required on the control stick. If I remember correctly, the value being at about 50 lbs at around 400 mph increasing. At higher speeds, you need less elavator movement. As the speeds drop down, more elevator movment is required. Someone had posted a graph a while back showing the stick force required on the 109(G10?) if I remember correctly. Shows the force at various speeds.
In AH, proper trimming helps greatly when flying the 109.
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50lbs is a big force?? You can pull much than that with a single hand. 50Lbs may be a problem if you need to apply that force to the left or to the right, but pulling the stick with both hands? Even a child is able of that.
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50 lbs is not heavy but then it is substantial enough that repetative action could wear down the average pilot.
In regards to that graph, I remember looking at it and comparing it to the speeds I sometimes fight in AH and the stick forces in my 109 would have been 75-90 lbs for 400-480 mph range during dives etc... However at those speeds you dont need full elevator deflection.
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I know Angus, but wanted to make people think a little more deeply.
Make people think deeply?
Or provocating Luft-enthusiasts to start hails of uproar? :D
Just kiddin' :D
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Originally posted by Kweassa
Make people think deeply?
Or provocating Luft-enthusiasts to start hails of uproar? :D
Just kiddin' :D
:):) Only one luft-enthusist or should that be fanatic, would start an uproar. :eek::aok
Just don't get him started on Flettner aileron tabs.;)
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Originally posted by MiloMorai
How effective can the elevator be if the pilot due to excessive force cannot readily make the elevator move?
Your attempt at intellectualism is noted. The 109 pilots that have mentioned high stick forces that I have read about say that they needed both hands to pull out of a steep dive, the elevator never "locked up". If the elevator was ineffective they could have pulled the stick to its limits and nothing would have happened. I believe AH limits stick forces to 40 or 50 lbs, which is incredibly weak considering the pilots are adults who easily could have pulled a lot more.
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To be fair I must say that the new 109G10 in AH2 beta seems to handle much better at high speed, so HTC or the new FM might have changed the characteristics of that plane a bit. However it is still beta so we won't know for sure until final release.
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In AH2 the 109G10 can pull blackout turns at a little over 500 mph without any trim change (combat trim is on) and I have partial control up to about 550 mph. Aileron control is much better at high speed than in AH1 which is nice indeed.
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I had the opportunity to speak with a 109 veteran a few weeks ago about this question (109`s elevator/ailerons). I asked him wheter the controls were heavy at high speed, and he replied that yes, and described the elevators movement at high speeds as if the stick would be bolted into the floor. He could still move it, but he preferred the trimmer to help. Then I asked him about wheter this was the same with the ailerons, and he said that those, unlike the elevators were perfectly nice, there was no heaviness etc. He said it was like this at around 800 km/h.
It`s also interesting what the British found on a battered 109F they tested. It also seems to underline that the elevators were much heavier than the ailerons, yet despite the increase of control forces, the control surface`s effectiveness was still quite good:
" Manouveribility
No manouveribility trials were carried out against other aircraft but the Me.109F was dived up to 420 mph IAS, with controls trimmed for level flight, and it was found that altough the elevators had become heavy and the ailerons stiffened up appreciably, fairly tight turns were still possible. "
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That would be any 109 after 109E right?
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Certainly after the early F or the poor me109 would have lost her tail during the testing :p