Rollrates

[danish]

Being carefull not to read all the stuff with numbers and the funny signs it seems to me that the figure 47 (the above Figure 10.1) is drawn up of a hat, without any context to the math.

Quote: "Data have been collected on the rolling performance characteristics of a number of fighter airplanes of American and foreign manufacture." and then reference to fig 46 and 47 + tabel VI ect...page 39-40 Adobe.Sorry copy/paste dosnt seem to work.

There isnt any references as to these collected data, and a brief visual serch on the "Reference" section dosnt show anything.

Is the Holy Gral out there?Is there a number of Flight Tests waiting to be discovered still?

danish

[Toad]

Is there anything in there that indicates 50 pounds might be the max stick force you can achieve in any particular plane.

I'm thinking that if you could get 60 or pounds, the rollrates would change?

Still, really nice info there. Hope Pyro has it or is checking it out.

[funked]

Toad see the peaks on each curve?  The data on the left side of the peak is for full aileron deflection - adding more force won't help.  But on the right side of the peak the aileron deflection is limited by the stick force.  If you add stick force, the roll rates to the right of the peak would increase until full aileron deflection was achieved.


[This message has been edited by funked (edited 01-03-2001).]

[Toad]

Yeah, Funk, I saw that.

The question is can you get more stick force in some/all the cockpits?

IIRC, some (like the 109) were limited by the room available for stick movement.

I'm sure a scared, adrenline charged guy could generate more than 50lbs.  

[Bradburger]

Thanks for the link niklas. The Info will come in useful for a project I'm working on.  

Whilst you're mentioning clipped wing Spits:

   
LFIXe
   

Nath is correct.The fabric covered ailerons on the early MkI's used to balloon at high speeds making them unpleasent and very hard to move. If my memory serves me correctly they were replaced by the metal ones were during November 1940.

However they never really cured the problem and even the metal covered ones became heavy at high speeds. In fact i can think of a few modern day pilots that have flown the MkIX were suprised how heavy the ailerons were.

On the subject of stick forces, I remeber a long time back reading an article about flying the Hispano Buchon (Spanish built 109 - can't remeber who by but it was after the filming of Memphis Belle i think) and it mentioned that during medium-high speed flight a stick force of 80lb or more would be required for for the ailerons. Coupled with almost as heavy elevators and no rudder trim, one can see how demanding the 109 must have to fly been during combat.

Cheers

Paul
Bradburgers SDOE Projects


[This message has been edited by Bradburger (edited 01-03-2001).]

[Andy Bush]

Bradburger

>>The fabric covered ailerons on the early MkI's used to balloon at high speeds making them unpleasent and very hard to move.<<

What does 'balloon' mean? Is the problem due to some characteristic of fabric covered ailerons...or is this a mechanical advantage issue dependent on airspeed?

Andy

[funked]

Andy:  The pressure differential between static air inside the aileron and the moving air outside would cause the skin to swell outwards or be sucked inwards.

Bradburger:  The reason the aileron change didn't completely fix the high speed roll problem on the Spitfires was wing twist.  If you read that NACA paper they mention that the Brits found that wing twist accounted for 60% of the roll rate loss at some speeds!

All:  I sure would love to see a Spitfire LF Mk. XVI in AH someday.  I know a certain squad that flew them.    

   

[This message has been edited by funked (edited 01-03-2001).]

[Toad]

Basically, I'm wondering why they chose to run the test to 50lbs.

Physiological reason?

The max you could get in one particular plane so that became the baseline?

Obviously, you could get more than 50# in some planes and the roll rate would then show improvement at the right of the graph.

So why 50?

Just a question. Any ideas?

[This message has been edited by Toad (edited 01-03-2001).]

[Andy Bush]

Funked

OK...that makes sense.

Now, did that bind the ailerons when they were moved, or was the problem in a reduced aerodynamic efficiency of the aileron airfoil?

Andy

[wells]

The 50 lbs was a design requirement for the airforce.  That is, plane X had to have a roll rate of Y at such and such a speed with force not exceeding 50 lbs.  The Navy's force requirements were lower, 30 lbs.  You can get an idea of what the forces were like by checking out the peak airspeeds.  A lower peak means higher forces for any given speed.  It wasn't practical to design with lower forces anyway.  The F4u was limited to max aileron deflection at 300 knts, even though the pilot could get full deflection at higher speeds, it put too much strain either on the aileron itself or on the wing as a whole.  50 lbs was plenty.  Where planes had hydraulic aileron boost, pilots complained of having no feel.  Even the F-86's roll rate almost came to a stop at higher speeds, due to wing twisting, even though stick forces were comfortable.

[Toad]

Thanks, Wells.

Appreciate the info.

[niklas]

danish, i know from some NACA WARTIME REPORTS, each written for an individual aircraft. But they´re not published in the net afaik.

i.e. Flight Measurements of the flying qualities of an f6f-3 airplane   I- Longitudinal stability and control
Rollrate is here a bit better for the F6F:
79deg/sec to the right and 73deg/sec to the left.

or: Measurement of individual aileron hinge Moments and aileron control characteristics of a P40F airplane.
91deg/sec to the left and 85deg/sec to the right, maximum stick forces which occur for speeds up to 300mph 43pounds to the right and 36pounds to the left. So it doesn´t matter whether you apply 50, 60, or 100lb, over 43lb your rollrate is limited by the wing design.

i also saw many reports for the P39 and P63.

Or check this NACA report for the P47D-30: http://naca.larc.nasa.gov/reports/1952/naca-tn-2675/

Here they test the P47D-30 (yes, our P47) with only 30pounds stickforce. Maximum rollrate only 60deg/sec (page 57 acr.rdr.)
Conclusion (pg. 10) : the general characterics of the aileron controls were good but the effectiveness of the ailerons were below the army requirements....

I never believed that such big fighter with large wingspans like a P47 can roll with a 190 at normal speeds. 85deg/sec, that means 4,2 sec for a full circle. Good to know that this was considered to be an excellent rollrate. How long does it take for the AH P47?? 3 seconds or even less ...
And now imagine how good the P38 rolled with a wingspan of more than 45feet...

wells, can you tell me how do i get the maximul rollrate when i only have a chart with Pb/2V-values??

niklas

[This message has been edited by niklas (edited 01-04-2001).]

[Andy Bush]

For the sake of discussion, these roll rates when compared to a modern fighter are just unbelievably slow!

Even today's advanced trainer, the T-38, can easily generate roll rates in excess of 360dps...and without using full stick throw.

Whenever I fly these WW2 sims, I'm continually amazed at how poorly the aircraft roll. But, is roll rate all that important?

Absolutely! The whole point to effective BFM is orientation of the lift vector...and that breaks down into two considerations: (1) the magnitude of that lift vector (radial G), and (2) how quickly the pilot can get the lift vector pointed in the direction he wants.

No question...roll rate is significant!

Andy

[wells]

Niklas,

Pb/2V is the helix angle at the wingtip in radians.  In the case of the P-47, this angle was 0.074 * 180 / PI = 4.24 degrees

Then roll rate will vary in direct proportion to wingspan and forward velocity.

In the P-47's case, with a 41' wingspan, the tip must travel a distance of PI * 41' = 128.8' in one roll.

tan(4.24) * forward velocity = roll velocity

for 200 mph (293.3 ft/sec)

roll velcity = 21.75 ft/sec
time to roll = 128.8 ft / 21.75 ft/sec = 5.92s

[F4UDOA]

Wow,

That FW190 was a rolling monster.

Wells, could you explain that little equation, especially the part about Pb/2V being the helix angle of .074.

Also why is the 190 so superior in roll. Is it the aspect ratio or just the wing span? Should engine torque effect that ability?

Just as a reference. Here are some results conducted on four A/C by test pilots in 1989 for those who haven't read the report.

230MPH
-------------Roll left---------Roll Right
P-47D-40-----5.9sec61dps-------4.9sec 74dps
F4U-1D-------4.9sec73dps-------4.5sec 81dps
F6F-5--------5.9sec61dps-------4.6sec 78dps
P-51D--------5.1sec71dps-------4.8sec 75dps

Stick force measured
pounds per G

F4U-1D   5.0 lbs per G
P-47D-40 7.5 lbs per G
F6F-5    12.5 lbs per G
P-51D    20.0 LBS per G

Quite a differance when you are pulling heavy sustained G's in a prolonged dogfight.

[This message has been edited by F4UDOA (edited 01-04-2001).]

[This message has been edited by F4UDOA (edited 01-04-2001).]