Allied tests of captured Bf-109's

claidemore · 03-25-2008, 10:19 AM

The slats on the 109 opened instantly, for there to be no felt effect on flight, they would have to be power assisted and open gradually.

Opening of the slots changed the lift coefficient from somewhere around 1.4 to 1.7.(arguably) That has to affect flight path and require some correction for sighting. Wolfram also mentions this characteristic.

Just off the top of my head, the RAE/AFDU trials included turns in either direction and included tests with both planes starting in trail position on the other in turns. They did not switch pilots in the 1944 AFDU trials.

Not sure about different altitudes, speeds etc, as all I've read are conclusions and summarizations in the report. I believe Kurfurst is going to put the entire reports on his site, hopefully there will be original graphs and charts there as well.

drgondog · 03-25-2008, 10:48 AM

Glider (and Kurfurst) - true and worse for heavily loaded a/c with respect to trailing turbulence.

The tip Vortex is much worse for a heavy aircraft than propwash or jet turbulence and reaches maximum 'down velocity' at centerline (and below) the aircraft... decreasing over distance because air is not a perfect inviscous fluid. If it was the lifting line vortex would, in theory, extend from point of lift before take off all the way to point of 'no-lift' after landing (or crashing)

The tip vortex for a 70,000 pound B-17 or 60,000 pound F-105 would be far more severe than behind a Spitfire, for example. The rotational flow behind the engines is dominated by the prop tip vortices but much less than tip vortex effect and disperses rapidly in comparison.

The turbulence which 'caused' a 109 slats to engage would most likely be a very high local angle of attack due to the turbulence - not a result of the normal free stream vector. Theoretically it could happen in a thunderstorm or any CAT condition with high indicial gusts...

kool kitty89 · 03-25-2008, 05:51 PM

Quote:

Originally Posted by claidemore

The slats on the 109 opened instantly, for there to be no felt effect on flight, they would have to be power assisted and open gradually.

Opening of the slots changed the lift coefficient from somewhere around 1.4 to 1.7.(arguably) That has to affect flight path and require some correction for sighting. Wolfram also mentions this characteristic.

Just off the top of my head, the RAE/AFDU trials included turns in either direction and included tests with both planes starting in trail position on the other in turns. They did not switch pilots in the 1944 AFDU trials.

Not sure about different altitudes, speeds etc, as all I've read are conclusions and summarizations in the report. I believe Kurfurst is going to put the entire reports on his site, hopefully there will be original graphs and charts there as well.

The combat/maneuvering flaps would also have a major effect on CLmax. (a feature which the Spitfire and Hurricane lacked; hence why the P-51 had a higher CLmax than the Spit even with a lower lift airfoil)

I'm also not sure about the gradual slat deployment since the Me 262 used a similar design as the later Me 109's (I think) and had gradual deployment of slats. Soren, info and corrections on this point would be appreciated.

And for refrence here's this again:

drgondog · 03-25-2008, 07:42 PM

Quote:

Originally Posted by kool kitty89

The combat flapswould also have a major effect on CLmax. (a feature which the Spitfire and Hurricane lacked; hence why the P-51 had a higher CLmax than the Spit even with a lower lift airfoil)

There are too many anecdotal references to a P-51D unable to close (but not lose ground), with a 109G/K in a prolonged turning manuever at low altitude and airspeed, by reducing flaps. The reference to the Mustang not improving its performance in turn through use of flaps against the Spit XIV in the RAF tests bear this observation out also.

And for refrence here's this again:

I have seen a lot of discussions about positive combat results obtained by dropping flaps, lowering gear, etc - but in my opinion what they do for a 51(or any other fighter) is give it a huge increase in drag, enabling a tighter turn because of the lower speed.. meaning if he didn't get his deflection shot he was potentially in trouble now that his adversary possibly had more energy (and options)..

And BTW, there were structural limitations on flap settings as function of airspeed and lowereing gear. These are all about low speed desparation tactics..

Manuevering flaps on a P-38L were much smaller and could be deployed at a higher speed to get same effect, then pulled back in quickly, to reduce the energy loss.

claidemore · 03-25-2008, 07:55 PM

Agree drgondog.

109G2 manual says you cannot operate flaps above 250kph, and it takes 4 turns of the wheel to get them to 20 degrees (takeoff position).

kool kitty89 · 03-26-2008, 02:24 AM

I think you misunderstood me, I said the P-51 had a higher CLmax with maneauvering flaps out than the Spitfire did. I didn't say it could turn better, I was just pointing out what a difference flaps can make. However, the higher CL is still far from enough to cancel the Spitfire's wingloading advantage and resultant lift loading advantage over the P-51. (lift loading= wing loading x CL)

As you pointed out, flaps are not always the best option. However, maneauvering flaps usualy have a higher max operating speed than take-off or landing settings. And, of course, slats have no such problem.

I think that most Spitfires and 109's would be able to out turn most P-51's in most conditions.

The Hurricane would out-turn all three in a fair comparison, but lets not go there... (at least in the fighter versions of the Hurri ie Mk.I/II/IIA/IIB/IIC)

kool kitty89 · 03-26-2008, 02:29 AM

Soren,

(in case you missed it) I'd still like to know if this is correct:

I'm also not sure about the gradual slat deployment since the Me 262 used a similar design as the later Me 109's (I think) and had gradual deployment of slats. Soren, info and corrections on this point would be appreciated.

Kurfürst · 03-26-2008, 04:03 AM

Quote:

Originally Posted by claidemore

Agree drgondog.

109G2 manual says you cannot operate flaps above 250kph, and it takes 4 turns of the wheel to get them to 20 degrees (takeoff position).

That would refer to TO or landing configuration, ie. 20/40 degrees down. I have a 109E 'safe flap speeds' curve somewhere, the combat flaps could be used up to quite high airspeeds.

Bill is absolutely right about flaps though. They allow you to pull a much tighter turn (radius), but neccesessary a faster sustained turn, because they also add some amount of drag. The exact characteristics should differ from aircraft to aircraft though.. if you have the speed and radius with flaps though, you can calculate the turn time.

Hunter368 · 03-26-2008, 11:37 AM

Interesting

claidemore · 03-26-2008, 12:42 PM

Quote:

Originally Posted by kool kitty89

Soren,

(in case you missed it) I'd still like to know if this is correct:

I'm also not sure about the gradual slat deployment since the Me 262 used a similar design as the later Me 109's (I think) and had gradual deployment of slats. Soren, info and corrections on this point would be appreciated.

AFAIK the 109 slats had no damping system and were spring loaded (very light spring, finger tip moves them), so they should 'pop' open.

Soren · 03-26-2008, 01:10 PM

There are no springs of any kind at all Claidemore, the slats operate by means of air-pressure, so they are in effect AoA dependant devices, that's what makes them such ingenious devices.

Koolkitty,

The slats on the late Bf-109's and the Me-262 are of exactly the same design.

Hunter368 · 03-26-2008, 03:22 PM

Hmmmm

kool kitty89 · 03-26-2008, 05:59 PM

A little off topic, but did the F-86's LE slats use the same mechanism? (It would make sence since the Me 262, and HG variants, had alot of influence on the Sabre iirc)

claidemore · 03-26-2008, 06:04 PM

Quote:

Originally Posted by Soren

There are no springs of any kind at all Claidemore, the slats operate by means of air-pressure, so they are in effect AoA dependant devices, that's what makes them such ingenious devices.

Koolkitty,

The slats on the late Bf-109's and the Me-262 are of exactly the same design.

Thanks Soren, we needed an expert opinion on this.
I stand corrected.

There's quite a few sources that mention springs, but heres a hobby site with some good diagrams.

basepage

drgondog · 03-26-2008, 06:06 PM

The 'suction' described above in this model is usually denoted as "lift" and the other regions in the model are areas of flow separation. Check the Lednicer report attached, carefully.

The P-51D for example has better laminar flow over the wings AND the canopy and hence less drag due to Profile Drag than the modelled Spitfire IX and Fw 190D9.

You will note that the predicted Lift distribution over the model P-51 is slightly better than the fw 190 but inferior to the Spit.. This is a function of both the washout as well as airfoil differences and planform geometry (spit close to eeliptical and 51/190 trapezoidal).

As to HP of 51B (with -3) versus H (-9), there is a maximum difference of about 300-330 BHP difference between the H and the B when the H is boosted to 80" with water... as noted below