109 Elevator effectiveness

[Venturi]

I have seen some other comments in a similar thread here (http://forum.il2sturmovik.com/topic/4948-fw-190-and-bf-109-longitudinal-stability-and-control/), that is locked. I have always been told that the 109 elevator lacked the ability (either through lack of effectiveness, or through the difficulty in overcoming the compression forces IE lack of leverage) to bring the 109 into the realm of high speed turns.

 

Now, this other thread had some very interesting points. First off, it seemed to me from the evidence presented therein, that the elevator on the 109 actually was as effective as on a Spitfire, but was made to have less leverage (IE harder to manipulate at high speeds) to save the airframe from ripping the wings off from overzealous yanks on the stick. The point was not made, (so I shall make it) that this is in direct contradiction of the current state of affairs in the sim - where a fast, 700kph dive in a 109 takes at least 1km of altitude to pull out from safely.

 

What say you, experts? Let's keep the personal attacks and baiting to a minimum, please, some of us are actually interested in the impersonal truth. This is a big deal for BnZ in the 109.

Edited April 17, 2014 by Venturi

[Kurfurst]

What is the 700 kph metioned above is referring to, TAS or IAS?

 

The 1943 Lukas dive trials with the 109F confirm that the aircraft can be recovered by the stick alone from a 70-80 degree dive at full power and near Vne within 1100 meter altitude, at about 850 kph TAS. Or perhaps less with a guy with more physical effort on the stick than Lukas.

 

Keep in mind that the actual pullout altitude is very much dependent on the tail plane settings - 109 manuals prescribe that dives are to be entered into with normal horizontal speed trim, and the aircraft should be kept in the dive by pushing the stick forward, and the plane is not to be trimmed into the dive. In this way, upon releasing the stick in dive the trim will aid the recovery.

 

And indeed, it is not really about control "effectiveness" (the 109s elevator remained effective up to fairly high Mach numbers, only marginal force increase was experienced up to Mach 0.73), but control forces. The Spitfire represents probably the most extreme case of all fighters, with excessively light elevators (about 5 times lighter than on the 109), which may enable pulling a lot of gs in dive with minimal physical effort, as well as snapping the plane just as easy in half due to exceeding the airframe's break g limits (which was about 10-12 g).

Edited April 17, 2014 by VO101Kurfurst

[DD_bongodriver]

Actually the evidence provided proved that a modified test airframe was capable of recovering from the dive with many of the improvements discovered from the tests not manifesting until late variant G models, the reason for the tests made clear that the 109 was suffering from a chronic lack of elevator authority and directional stability as well as failures of the wing.

Though the Spitfire is completely irrelevant to the discussion it seems to make an ominous appearance every time these discussion crop up..........strange.

Edited April 17, 2014 by DD_bongodriver

[DD_bongodriver]

First off, it seemed to me from the evidence presented therein, that the elevator on the 109 actually was as effective as on a Spitfire, but was made to have less leverage (IE harder to manipulate at high speeds) to save the airframe from ripping the wings off from overzealous yanks on the stick. The point was not made, (so I shall make it) that this is in direct contradiction of the current state of affairs in the sim - where a fast, 700kph dive in a 109 takes at least 1km of altitude to pull out from safely.

 

What say you, experts? Let's keep the personal attacks and baiting to a minimum, please, some of us are actually interested in the impersonal truth. This is a big deal for BnZ in the 109.

 

In the interest of keeping on topic, I don't know if the 109 elevator was made deliberately stiff for the reasons claimed, so far it seems to be a pure hypothesis but maybe somebody will bring along a useful document, but it is plain to see it was considered insufficient in authority in MTT's own tests, it's also plain to see they failed completely to figure out the directional stability that was the larger problem until finally from the G5 onwards it got a bigger fin, or at least they failed to address the ailerons which through over-zealous yanking on the stick were ripping wings off.

[MiloMorai]

 

 

109 manuals prescribe that dives are to be entered into with normal horizontal speed trim, and the aircraft should be kept in the dive by pushing the stick forward

 

Even more interesting is the fact that they tried different positions of the trimming. With the wrong trimset - the one for cruising at high altitude it was not possible to pull out of the dive just by using the stick. They needed to use the trimwheel to recover the plane from the dive. This happened in such violent manner that the testpilot had to push the stick foreward to be not blacked out...
If the trim was set to +1.15° it was possible to recover without using the trimwheel - both flightpaths, with and without the trimwheel, are very similar. So even with the concrete stick the limitating factor seems to be the pilot.
Also interesting in the dive the canopy iced, also the mechanism of the trim, so it was not possible to set it smooth, but in \"jumps\", but it was still adjustable...
- Source: Hochgeschwindigkeitsversusche mit Me 109, Messerschmitt AG, Augsburg.

[Crump]

Germany had stability and control standards like the NACA. 

 

Here is the relevant portion from Gilruth's NACA standard.

 

 

Here is the RAE report on the handling qualities of the Bf-109E3:

 

Above 250 m.p.h. the elevator becomes definitely too heavy for comfort, and between 300 m.p.h. and 400 m.p.h. is so heavy that maneuvrability in the looping plane is seriously restricted; when diving at 400 m.p.h. a pilot, pulling with all his strength, cannot put on enough g to black himself out if trimmed in the dive.

 

http://kurfurst.org/Tactical_trials/109E_UKtrials/Morgan.html

 

I love that statement.  The test pilot makes it out to be a negative trait of the airplane but  I wonder if the test pilot ever tried to fly a plane unconscious or if he really ever thought that indepth about what he was actually saying.

 

Airplanes do not fly very well with broken wings or unconscious pilots.

The elevator forces recorded in the report posted in that thread plainly show the Bf-109 required a push force of anywhere from 48lbs at 2Km to 88lbs at 7Km to reach Vne.  That is far below the NACA measurements of 105lbs of push force the average pilot could exert.

[Crump]

 

The point was not made, (so I shall make it) that this is in direct contradiction of the current state of affairs in the sim - where a fast, 700kph dive in a 109 takes at least 1km of altitude to pull out from safely.

 

Depending on the angle and speed attained, that does not sound wrong.  If the load factor is under 5G's that sounds correct.  I am sure the developers are capable of doing the math and checking to ensure there is not a bug. 

 

 

 

Personally, I think this is just realistic behavior.  Players are spoiled by gameshapes that do not act like airplanes.

 

For example, a typical gamer will dive his P-51 gameshape at 70 degrees to Vne and pull 6(+) G's on recovery like it was normal.  In reality, you would risking having the aircraft damaged and the pilot incapacitated.

 

Here is a the dive performance chart for the real P-51D.  Loads were limited to 4G's on pull out because of the physiological effects on the pilot.

 

A 70 degree dive to Vne that was started at 10,000 feet requires 7,000 feet of altitude to recover!!!

 

A 70 degree dive to 450mph IAS requires 6000 feet of recovery altitude to reach LEVEL flight again.

 

 

 

Edited April 20, 2014 by Crump

[Crump]

How much altitude do the Lagg and the Yak require to recover from the same speed, Venturi? 

[Venturi]

This was a maximum effort pull out in a dive at 700 kph IAS. I would have expected the aircraft to give at least 7-8 g acceleration, if your info is correct and I initiated a maximum pull effort. It may have been more than 1km altitude loss, I can't recall just now. But In reality it did not give that much g on initial pull, the elevator seemed quite ineffective, and I only started to black out after I had pulled out enough to slow the aircraft to 500kph and had regained elevator use. Took quite some time, much more than I expected from similar situations in other sims like CLoD. Lost a lot more altitude than I expected. Have not flown enough lagg to say definitively, and no yak yet, but the lagg certainly seems to have more elevator effectiveness and (although you may black out) it will pull out of a fast dive much quicker than a 109, in less altitude.

[Crump]

 

I would have expected the aircraft to give at least 7-8 g acceleration

 

I can see where one might think that.

 

The reality is pulling that much acceleration puts all of these aircraft into the damage limits.  Doing so can destroy the airframe as it is progressive.  A damaged airframe is a weakened and will fail at a lower acceleration rate.  Bend the wings in the initial pull up and it fails before recovery is complete as it cannot maintain the same acceleration. 

 

The Bf-109 is designed to maneuvered at the limits of performance and keep the pilot from going places the airplane or he cannot go.  Unfortunately, those limits of performance are set by real events.  One of the largest limits which is typically been unrealistically portrayed in games is the pilots physiology. 

 

Stability and control was control engineering was just gaining ground in many countries and was still fairly new.  Gilruth's and Gates work really set measureable qualifications. 

 

Aircraft routinely came out design firms that easily took the aircraft and pilot places they could not fly.  It was up to the pilot to fly within the airframe and his own limits.  If he did that, it was not anymore maneuverable than the Bf-109.  The Bf-109 was just designed to do it without thinking about it.

 

The pilot who pulls 7-8G gradual rapid onset rate as experienced in a dive recovery would be an easy target nursing his bent airframe and trying to reorient himself.

 

A realistic pilot physiology model would benefit both BnZ tactics by limiting the turning ability of turn fighters.  It would also benefit the turn fighters as it eliminates the cartoony 70 degree dives from a ten thousand foot height advantage.  It would realistically narrow the gaps bringing the fights in closer raising the excitement level. 

[Crump]

Kurfurst says:

 

The 1943 Lukas dive trials with the 109F confirm that the aircraft can be recovered by the stick alone from a 70-80 degree dive at full power and near Vne within 1100 meter altitude, at about 850 kph TAS.

 

 

Looking at 1 degree 15 minutes trim setting dive it appears he initiated recovery  at an altitude of ~4.5 Km and recovered to level flight ~2.6-7Km. 

 

The Germans did not accurately record the dive angle as there is a big difference between 70 degrees and 80 degrees for recovery altitude requirements but that puts the dive recovery altitude in the same 6000 foot required for recovery as most World War II fighters.

 

In other words, the Bf-109 required the same distance as any other airplane at those speeds.  The elevator was just as effective as the Spitfire or P-51's.

Edited April 20, 2014 by Crump

[Venturi]

So, let me get this straight. You are saying that, taken as a whole, pilot physiology and plane acceleration limits together, the elevator was effectively equivalent on the 109 vs other similar planes of the era. That although the (for ease of example) Spitfire had astonishingly effective elevator control, sims to this point haven't properly taken into account the true limiting factors for planes with effective high speed controls such as the Spitfire: The airframe and pilot inability to withstand such severe acceleration. That these limits which were structural and physiological, rather than engineered limits to control effectiveness such as on the 109, would tend to level the playing field for all planes in such maneuvers.

 

Makes sense to me. Although, like all engineered solutions, there are always times when the limits need to be able to be pushed, consequences be dammed. And there is always the previously documented statement saying that in the tested 109, a full pullout from a fast dive failed to elicit a blackout from the pilot. Etc. Thoughts?

[Kurfurst]

So, let me get this straight. You are saying that, taken as a whole, pilot physiology and plane acceleration limits together, the elevator was effectively equivalent on the 109 vs other similar planes of the era. That although the (for ease of example) Spitfire had astonishingly effective elevator control, sims to this point haven't properly taken into account the true limiting factors for planes with effective high speed controls such as the Spitfire: The airframe and pilot inability to withstand such severe acceleration. That these limits which were structural and physiological, rather than engineered limits to control effectiveness such as on the 109, would tend to level the playing field for all planes in such maneuvers.

 

Makes sense to me. Although, like all engineered solutions, there are always times when the limits need to be able to be pushed, consequences be dammed. And there is always the previously documented statement saying that in the tested 109, a full pullout from a fast dive failed to elicit a blackout from the pilot. Etc. Thoughts?

 

Re: the statement is that the pilot couldn't black himself out when the plane was trimmed into the dive. Its quite possible for two reasons - the 109s inclined seating position improved the pilots g tolerance somewhat, so he would black out later than in other planes.

 

Second, and, the pilots handbook for the 109 specifically states that the plane should not be trimmed into the dive, but the trim should be left alone ie. for normal cruise position, and the plane should be kept in the dive with the stick. So basically the test describes what happens when you are flying the plane the opposite way you should, and make your task more difficult. The 109/190 had an adjustable stabiliser with a lot more effect than normal trim tabs and control surfaces. Anyway its plane specific, the Spitfire's manual for example states the opposite and requires the pilot to do the opposite and trim the plane into the dive - probably to avoid some nasty things happening to airframe during pullout.

 

As for the Lukas dive, the figures Mustang operating manual would suggest that Lukas was able to pull 5+ g in that dive recovery, which is as good as it gets. Forces were probably high though, but planes pulling the same g-load at the same speed will turn exactly the same, there is no difference. If plane A can do a 5 g dive recovery, then it will recover exactly the same as plane B doing a 5 g dive recovery.

 

Anything above that g load has limited use and will turn the slider towards the situation becoming Charlie Foxtrot quickly IMHO. Most fighters had a "safe limit" of about 6-7 g maximum, depending on load and condition. It was not supposed to be exceeded, bending of the airframe could be expected above that, and ultimately breaking at about 10-11 g. Not to mention that a passed out pilot is not very good at flying the plane...

 

[Venturi]

So, what you're saying is, that just like is simulated in ROF, some of these aircraft can do things mid flight they wouldn't survive. Seems like we should be seeing more bent aircraft and wings fluttering in the breeze than we currently do, and that we should be seeing a lot more blacked out pilots. Thoughts?

[Crump]

So, what you're saying is, that just like is simulated in ROF, some of these aircraft can do things mid flight they wouldn't survive. Seems like we should be seeing more bent aircraft and wings fluttering in the breeze than we currently do, and that we should be seeing a lot more blacked out pilots. Thoughts?

 

 

That about sums it up.

 

Stability and control was still a pioneering science in the beginning of World War II.  The United States did not adopt a standard until 1942 which is why there are so many NACA reports on flying qualities of various aircraft.  Once the standard was adopted, existing aircraft had to be tested, measured, and short coming fixed.

[DD_bongodriver]

https://www.youtube.com/watch?v=pele5vptVgc

[Crump]

What does that contribute to a mature discussion?  You are not adding any facts or anything of value. If you have an opinion or new information by all means add to the discussion.  

[Rama]

Same old story..... same old fate...