DVL data on Bf 109 roll rates

[Kurfürst]

Originally posted by gripen
Hm... The data actually confirms what is allready known about the aileron characters of the Bf 109 ie the forces and effectiveness are normal at low speeds but at high speeds the forces are very high.

[/B]

*Very high* - compared to what? Not any higher than for the majority of WW2 fighters I have seen.

Let`s see in comparision, speeds up to max. aileron deflection could be maintained with 50 lbs stickforce :

Bf 109F-2 : up to 550 kph / 340 mph
Spit V : 140 mph (with 40 lbs)
P-47C : 230 mph
Typhoon : 250 mph
F4F : 235
P-63 : 280 etc.

I don`t see any particularly heavy forces compared to the others, its perfectly normal for a WW2 airplane.

Perhaps the only exception is the Mustang, which had very low deflection for the ailerons - and consequently low force/good roll rate at high speed, as well as poor low speed roll rate where it would really count.

At 3000 m (about 10k) the TAS value is roughly 20% higher than IAS value depending on conditions. As an example 400 mph IAS is about 770 km/h TAS. I

*Roughly?* Oh, now I see why it was important to switch it to IAS. Your usual handling of the primary data gripen, it gives something, then you adjust it to suit your own needs. Displacing the chart *roughly* by a whole 20% and decreasing the actual values they measured... But as Kneagel pointed out, the DVL roll chart is for IAS, not for TAS, thus it`s directly comparable to the NACA chart.

[Kurfürst]

Originally posted by Karnak
I was, but Allied tests from WWII found the same thing.  The metal aileroned Spits handily outrolled the captured Bf109s in their tests.  The question is, were those Bf109s in good enough condition to make the tests valid?

[/B]

The only direct comparisions with the Spitfire vs. 109G were done against that 'Wilde Sau' nightfighter Bf 109G-6 with the 20mm gondolas. These weighted some 250 pounds each, and the more weight on the wing carried, the worser the roll rate bocomes, as there`s far more intertia - see fighters like the P-38, Me 110 etc that all had engine gondolas in the wings, and even with boosted ailerons, the inertia remained a problem.

One other thing that report notes with comparision flight of the 109G/Spit is that the AFDU didn`t deflect the ailerons, and were rather cautious to use them. OTOH, if you compare them indirectly, ie. the 109/Tempest comparision, which was done with a 'clean' 109G-2, and the Spit/Temp comparision, oddly they note for both fighters that they fall behind the Tempest in roll at 350mph IAS in both cases.

The wing twisting that Charge was refering to is something that plagued the Spitfire until the wing was redesigned in the Spitfire F.21.  That was mostly a problem at higher speeds though and at lower speeds the Spitfire's roll rate was unimpeded.  You can feel the model of this in AH when the Spit's roll rate goes to crap above 350mph to the point where you can't really roll at all at 500mph or above. [/B]

Indeed, too bad the NACA report with that roll chart isn`t quoted entirely, for it says the wing twist would reduce the Spit roll rate at high speed by 65% (P-47 :35%, stiffer wings).

Note that both 190/Spit`s roll curve is totally different than any other roll curve on the NACA graph.It very much appears the NACA Spit/190 chart do not show at all the effect of wing twisting, the curves are totally straight, they would be curved if it was an actual measurement and showing the elastacy effect of the wing and linkage. I guess they were rough calculations based on a few measured points. Nashwan has the report, but for some odd reason, he would not show the conditions of the planes and testing methods, only some part of it. I wonder why.

See below, actual testing of the Spit/Hurri roll rate with metal ailerons, vs. the 'spiked/straight' curves of the P-36/P-40 that were shown for comparasion, and were done by using only known aileron effectiveness at a single speed and stickforce. Same thing.



Now if I compare that one for the Spit which I knew it was coming from fully measured datapoints, using 30 lbs stickforce for both planes I get (using 200mph IAS = 386kph TAS  and 15kg force for the 109, just to make Gripen happy):

at 200mph IAS/10k :

109F-2 : 73 deg/sec
SpitV :  63 deg/sec (metal ailrons)

Hardly any difference, and that`s exactly what Dave Southwood said about the roll rate of the 109G/non-clipped Spit.

[Kurfürst]

Originally posted by gripen
Something like below?

gripen

This 109 data is with 7.6 ie. half stick throw though, so not very compatible, but should give some idea.

Here`s some for the Spit :



Edited, picture too big.

[Angus]

Hihi, this tickled me a bit:
"Let`s see in comparision, speeds up to max. aileron deflection could be maintained with 50 lbs stickforce :

Bf 109F-2 : up to 550 kph / 340 mph
Spit V : 140 mph (with 40 lbs)
P-47C : 230 mph
Typhoon : 250 mph
F4F : 235
P-63 : 280 etc."

Firstly, the position in the 109 cockpit didn't allow much leverage. 50 lbs was about as much as you could do.
(Oh, I still remember you mentioning that a shorter stick allowed more force to be applied)
Secondly the comparative Spit there is at 40 lbs. Of course a full span aircraft. Not that it matters a lot, for I remember you also claiming that the clipping had very little effect.
Comes into my mind also from a similar thread that back then you used an extended Mk VIII (?) Spit for comparison.
On your list here there is no P51, no F4U and of course no 190, - why ruin the 109F's top seat.
There is no 109E for obvious reasons......

Then this one:
"Perhaps the only exception is the Mustang, which had very low deflection for the ailerons - and consequently low force/good roll rate at high speed, as well as poor low speed roll rate where it would really count."

So suddenly performance at low speeds becomes more important? Why do you think the P51 was set up this way?

[Kurfürst]

Do you have a point Angus, or you're just ranting as usual?

"There`s no 109E for obvious reasons"

Yep. It would make the contemporary Spit I look awfully poor, and that`s more than you can generally bear.

And yes, I do think low speed roll rate is more important. After all, rolls are most needed at dogfight speeds of typically 2-300mph.

[Nashwan]

Note that both 190/Spit`s roll curve is totally different than any other roll curve on the NACA graph.It very much appears the NACA Spit/190 chart do not show at all the effect of wing twisting, the curves are totally straight, they would be curved if it was an actual measurement and showing the elastacy effect of the wing and linkage. I guess they were rough calculations based on a few measured points. Nashwan has the report, but for some odd reason, he would not show the conditions of the planes and testing methods, only some part of it. I wonder why.

I don't have the report on the Spitfire roll rates. The results, and brief descriptions of them, are in the FW 190 roll rate that Crumpp has, and I believe he's posted the whole thing in the past.

They are certainly measurements, the report goes into some detail on how they were obtained, and says that measurements obtained with a stopwatch are innacurate because of the short times involved.

Here's the relevant page:


Once agaqin, this is from a report into the FW 190, and does not go into detail on the Spitfire tests, it merely provides them for comparison.

[Angus]

You know perfectly well that the curves for a Spit I actual roll rate and a 109E actual roll rate are very similar. Post the chart if you like.
The stickforces are higher in the Spit I while more force can be applied due to the stick setup, so it basically boils down to the pilot.

And since you say that low speed roll rates are more important, well, I have something to remember
In that case the 109E beats the SpitI, hehe.

Does that apply to other performance as well?

Anyway, glad you took the bait

[Angus]

OOps, the answer was for Kuffie, not you Nash

[Knegel]

Hi,

Angus,
"Firstly, the position in the 109 cockpit didn't allow much leverage. 50 lbs was about as much as you could do."

If you look to the 1st document in this theatre, you will see that the test was made with 30kg = 66lb.

"The stickforces are higher in the Spit I while more force can be applied due to the stick setup, so it basically boils down to the pilot."  Why more force can be aplied?? Are british pilots more strong??


Kurfi,

"But as Kneagel pointed out, the DVL roll chart is for IAS, not for TAS, thus it`s directly comparable to the NACA chart."

Iam unsure which one is the DVL chart, but if you talk about the 1st both charts in this theatre, i did point out they are in TAS!!

But you be right that the 109 wasnt a bad rolling plane, it was absolute normal, at some speeds better at some speeds less good than most other planes, but at highspeed it did need much manpower.

Here is the NACA comparison with corrected 109F curves and the 50l SpitVa curve.





Greetings, Knegel

[Kurfürst]

Originally posted by Nashwan


They are certainly measurements, the report goes into some detail on how they were obtained, and says that measurements obtained with a stopwatch are innacurate because of the short times involved.

Here's the relevant page:


Once agaqin, this is from a report into the FW 190, and does not go into detail on the Spitfire tests, it merely provides them for comparison.

Originally posted by hop2002:

Is it a flight test or a rough calculation with "rule of thumb" methods ? It seems to be latter, ie. notice that both aircraft have perfectly straight roll lines - which point to that wing and control elastacy was not taken into account at all

It's a fully instrumented flight test. It says so clearly in the FW 190 roll rate report where the figures are used:

http://www.onpoi.net/ah/pics/users/282_1128078793_roll2m.jpg

Read the last paragraph.

Appearantly not a fully instrumented test, Hop. It appears exactly what it seemed at the first glance, a rough calculation with "rule of thumb" methods.

Your paper says on the middle about how they arrived on the data :

"Kb2 has been calculated from the the stick force measurements; it`s value is -0.11, approximately constant over the range of tests."

In the last paragraph, they noted the exact same way was used to calculate the roll rate of Spit, Mustang, Typhoon as on the FW 190.

So appearantly it`s a calculation that hypothesizes the aileron effectiveness is constant over the whole speed range - but it isn`t, wing flexing reduced this considerably at high speed especially with the Spitfire, the NACA 878 report notes 65% reduction from wing torision, and the aileron reversal point is rather low as well. The FW 190 should suffer from this as well, even though it`s wing structure must have been more rigid with the two spar design that carried heavy loads.

They simply took a constant aileron effectiveness, and displayed how much this constant would yield if it`s only limited by the stickforce. This doesn`t take wing elastacy into account,that`s why they got those perfectly straight lines going up, than beyond stickforce limit, down. That`s theoretical value, with 100% rigid wings, which no planes of the era had.

This isn`t how it looks like in real life, enough to look on the 109 roll curves, the NACA roll curves for all the other aircraft, the NACA Spitfire tests, the RAAF Spitfire tests - they are all much more smoothened out because of the wing`s flexing. The effect varies from plane to plane, and we know the Spit had too much wing flexing at hand, until it's wings were redesigned with the Mk21 and later.

Basically you dismiss all measured data from the RAAF, NACA, in favour of higher figures coming from a simplified calculation that doesn`t even consider all factors. But if you insist to compare theoretical 100% wing rigidity roll data - do it with all planes, not just the one you like.

[Charge]

"and the Spit/Temp comparision, oddly they note for both fighters that they fall behind the Tempest in roll at 350mph IAS in both cases."

The Tempest has more optimum placement of aileron (pretty much like in Spit F.21) so it's not a surprise it's better in roll than standard wing Spit and 109.

Angus take a look at Spitfire's/Hurri's controller and lets talk about leverage...

-C+

[Kurfürst]

Originally posted by Knegel

"The stickforces are higher in the Spit I while more force can be applied due to the stick setup, so it basically boils down to the pilot."  Why more force can be aplied?? Are british pilots more strong??

Actually it seems strange too. The Spit stick leverage was very short, only the upper part could be moved for the aileron - about 20 cm at best, giving very poor leverage vs. a normal flight stick. Outright stupid if you ask me, the least effective way to convert the pilot`s muscles into force.

Ie. silicon graphics representation, viewed from the back, pilot throwing the stick to the right :

Spit`s fligth Stick:

leverege:
<->
...O
./
.I
.I
.I
.I

Most other WW2 fighters :
leverage
<---->
..... //
...../
..../
.../
../

[Kurfürst]

It's seems Charge has the same thing on mind as I do. Simply no leverage on the Spit to turn that muscle into force easily. Even the NACA report notes the max. force the pilot could apply was 40 lbs in the SpitV, and that was enough to deflect ailerons fully up to 140mph ias, no more.

[Angus]

Haven't been able to stick my head into a Hurry's cockpit yet, but into a Spitfire cockpit yes, so I  can easily understand what the Pilots refer to.
The only thing I have from SpitI and HurryI is anecdotes,- they claim the Hury rolled much much easier,- controls were much lighter.
Was the leverage more favourable as well?

[Kurfürst]

Same thing I read from reports from 1940 on Spit/hurri relative roll, too. They say the hurri was ligther - I wonder the reason, perhaps because the washout on the Spit. Its effect on stickforces was raised early in its development, but mitchel turned it down.