Aileron reverse speed and roll rate of boosted ailerons

[spicmart]

Rate of roll was an important aspect of ACM. Focke Wulf (and Russian designers) seemed to be some of the first to put emphasis on that by building short and sturdy wings.
Later in the war wing strengthening became common because of the increased loads.
The Spifire evolution is a good example for that. I take this from Wikipedia (I know ):

"As the Spitfire gained more power and was able to fly at greater speeds the risk of aileron reversal was increasing so the Supermarine design team set about redesigning the wings to counter this possibility. The original wing design had a theoretical aileron-reversal speed of 580 mph (930 km/h),[8] which was somewhat lower than that of some contemporary fighters. The new wing of the Spitfire F Mk 21 and its successors was designed to help alleviate this problem; the wing's stiffness was increased by 47%, and a new design of aileron using piano hinges and geared trim tabs meant the theoretical aileron-reversal speed was increased to 825 mph (1,328 km/h)."

Are there any other specific speeds at which aileron reversal-appears known, especially of late-war machines?

The late P-38 had hydraulically boosted aielerons which enabled it to outroll every other fighter. Impressive if one consider its size.
Now the Fw 190D-13 had them, too. It should roll even better as it is much smaller.
Any other fighter which featured those?

 

[pbehn]

The important word is theoretical. A Spitfire will only do 600MPH in a very long dive and risks things falling off.

 

[spicmart]

The important word is theoretical. A Spitfire will only do 600MPH in a very long dive and risks things falling off.

The Mk 21 would still be well manoeverable at such speeds and its wings not be in danger of desintegrating. This is a definite advantage to earlier marks and possibly to most other late-/postwar fighters as well.

 

[pbehn]

The Mk 21 would still be well manoeverable at such speeds and its wings not be in danger of desintegrating. This is a definite advantage to earlier marks and possibly to most other late-/postwar fighters as well.

It would, I was just saying it is a calculated number. If you have reversal at 600 MPH you have problems long before. The Spitfire that did the highest speed levelled out when the prop fell off and changed the CoG.

 

[ThomasP]

Hey Spicmart,

re:"The late P-38 had hydraulically boosted aielerons which enabled it to outroll every other fighter. Impressive if one consider its size."

Do you mean above ~400 mph TAS? (350 IAS at 10,000 ft is ~400 mph TAS)

[edited for clarity and content] P-38L-1-LO test dated 10 June 1944. If this is with the aileron booster it appears to allow full deflection upto ~300 mph TAS at 10,000 ft? If you assume the booster allows full deflection upto ~Vmax and continue the slope line straight from the 300 mph TAS point, the line will intercept the 120°/sec line at about 460 mph TAS (395 mph IAS) at 10,000 ft. Either way the P-38 with boost begins to exceed all other aircraft at about 350 mph IAS at 10,000 ft, when compared to the lower chart from the NACA 868 report. (Did I figure this right?)

 

[GregP]

I've seen charts with a boosted P-38J at over 120° per second at over 420 mph. Don't have it just here, but it's out there. There is a chart on wwiiaircraftperformance.org that shows a P-38J with boost having a time to roll 90° at 0.45 seconds, which gives under 1 second for a 180° roll at 400 mph (or more since the initial roll acceleration has already been accomplished). See it here: http://www.wwiiaircraftperformance.org/p-38/p-38j-roll.jpg

You might notice the Fw 190, while blinding at 250 mph, is going to be less than 75° per second at 400+ mph, as will ALL the spitfires in the charts above. Haven't seen one for a Spitfire 21 myself, but will look for one. I'd expect it to be decent and better than earlier Spits.

Cheers.

 

[wuzak]

The Mk 21 would still be well manoeverable at such speeds and its wings not be in danger of desintegrating. This is a definite advantage to earlier marks and possibly to most other late-/postwar fighters as well.

The wings of the earlier marks survived high speed dives just fine, maybe a bit of bending from recovery manoeuvres!

What didn't fare well were things like the engine supercharger, which could explode at those speeds, and the propeller, which would sometimes break off - at the reduction gear casing.

 

[wuzak]

The late P-38 had hydraulically boosted aielerons which enabled it to outroll every other fighter. Impressive if one consider its size.
Now the Fw 190D-13 had them, too. It should roll even better as it is much smaller.

It may have had a higher ultimate roll rate, but how long did it take to get to that rate?

The P-38 had a high mass-moment of inertia, compared t single engine fighters, which slowed the initial roll.

 

[ThomasP]

hey look over there->

 

[Juha3]

I've seen charts with a boosted P-38J at over 120° per second at over 420 mph. Don't have it just here, but it's out there. There is a chart on wwiiaircraftperformance.org that shows a P-38J with boost having a time to roll 90° at 0.45 seconds, which gives under 1 second for a 180° roll at 400 mph (or more since the initial roll acceleration has already been accomplished). See it here: http://www.wwiiaircraftperformance.org/p-38/p-38j-roll.jpg

You might notice the Fw 190, while blinding at 250 mph, is going to be less than 75° per second at 400+ mph, as will ALL the spitfires in the charts above. Haven't seen one for a Spitfire 21 myself, but will look for one. I'd expect it to be decent and better than earlier Spits.

Cheers.

Spit Mk. 21 roll, don't mind the hand drawn 109F-4 line

 

[spicmart]

T ThomasP . Putting a ruler on your first chart gives about 108°/s at 400 mph which should match up about with GregP 's information of over 120°/s at a speed of over 420 mph.

But the Mike Williams chart giving over 180°/s... It's superhuman. How come?

 

[spicmart]

Hey Spicmart,

re:"The late P-38 had hydraulically boosted aielerons which enabled it to outroll every other fighter. Impressive if one consider its size."

Do you mean above ~400 mph TAS? (350 IAS at 10,000 ft is ~400 mph TAS)

[edited for clarity and content] P-38L-1-LO test dated 10 June 1944. If this is with the aileron booster it appears to allow full deflection upto ~300 mph TAS at 10,000 ft? If you assume the booster allows full deflection upto ~Vmax and continue the slope line straight from the 300 mph TAS point, the line will intercept the 120°/sec line at about 460 mph TAS (395 mph IAS) at 10,000 ft. Either way the P-38 with boost begins to exceed all other aircraft at about 350 mph IAS at 10,000 ft, when compared to the lower chart from the NACA 868 report. (Did I figure this right?)
View attachment 596243

View attachment 596080

The Fw 190 tested in the second chart. Were its ailerons properly adjusted? One of the captured Fw 190A tested had defective ailerons afaik. The earlier Antons had problems with those.
This flaw was rectified later. Allied mechanics might not have had the experience to do it.

 

[pbehn]

T ThomasP . Putting a ruler on your first chart gives about 108°/s at 400 mph which should match up about with GregP 's information of over 120°/s at a speed of over 420 mph.

But the Mike Williams chart giving over 180°/s... It's superhuman. How come?

Measuring rate of roll is difficult, it changes with altitude and also with how much force the pilot can exert, some tests specify the force applied, which doesn't guarantee the maximum rate of roll but does allow comparison to be more exact. There are also two factors how quickly it starts to roll and how fast it does at maximum.

 

[spicmart]

It may have had a higher ultimate roll rate, but how long did it take to get to that rate?

The P-38 had a high mass-moment of inertia, compared t single engine fighters, which slowed the initial roll.

Measuring rate of roll is difficult, it changes with altitude and also with how much force the pilot can exert, some tests specify the force applied, which doesn't guarantee the maximum rate of roll but does allow comparison to be more exact. There are also two factors how quickly it starts to roll and how fast it does at maximum.

I think that in general the initial rate or roll is higher the higher the aspect-ratio of the wing is. Or so I heard.

 

[pbehn]

I think that in general the initial rate or roll is higher the higher the aspect-ratio of the wing is. Or so I heard.

Well, yes. But sticking two engines in the wing does change calculations a little.

 

[spicmart]

Well, yes. But sticking two engines in the wing does change calculations a little.

With a P-38 rolling over 180°/s one could imagine how fast a single-engined fighter could go under the same conditions.
Torsional stiffness of the wing would become even more important.

Spit Mk. 21 roll, don't mind the hand drawn 109F-4 line

So the Mk 21 did not surpass the Fw 190 as expected..

 

[Thos9]

The late P-38 had hydraulically boosted aielerons which enabled it to outroll every other fighter. Impressive if one consider its size.
Now the Fw 190D-13 had them, too. It should roll even better as it is much smaller.
Any other fighter which featured those?

The Dornier Do 335 Pfeil: Flying the Arrow

 

[spicmart]

Spit Mk. 21 roll, don't mind the hand drawn 109F-4 line

So the Mk 21 did not surpass the Fw 190.

The late P-38 had hydraulically boosted aielerons which enabled it to outroll every other fighter. Impressive if one consider its size.
Now the Fw 190D-13 had them, too. It should roll even better as it is much smaller.
Any other fighter which featured those?

The Dornier Do 335 Pfeil: Flying the Arrow

The Do 335 is more a fighter-bomber not suited for fighter vs. fighter combat.

 

[pbehn]

So the Mk 21 did not surpass the Fw 190.


This is more a fighter-bomber not suited for fighter vs. fighter combat.

A Bf 109 and an Fw 190 are not the same, they use the same digits in a different order.

 

[GregP]

Thanks for the chart, Juha3. I appreciate it!

Looks like several airplanes were petty good rollers around cruise speed. At 250 mph, the roll rates are WAY different than at 400 mph. So, the question we might ask could be, "What was average combat speed?." I have no idea how to answer other than to ask. When I HAVE asked WWII fighter pilots, the answers were generally along the lines of, "If I got bounced, it was generally at cruise speed (figure 180 - 280 mph). If I was in a dogfight, I tried to accelerate to 300+ mph before the fight and never noticed the speed after that unless I was in a very steep dive." When I got the chance to ask, I usually could only ask ONE question, and then it was someone else's turn.

We all know that a dogfight in a WWII airplane bleeds speed and altitude if not carefully flown.

So, the next question might be, "What percent of the time were you bounced versus knowingly entering a dogfight?"

I have never asked a WWII fighter pilot that question, so I have no idea how to answer that one, except to say that to be bounced was more likely than to dogfight.

My impression is that they were about 60% bounced and about 30% dogfights, with the balance of 10% or so being of the variety where they knew enemy fighters were in the area or that someone in their unit was in a fight, but they may or may not have seen an enemy airplane when they were attacked. There is a LOT of room to disagree with that, and I have no ability to express an opinion on how true my impression is ... I don't know.

But we've all heard that most WWII fighter pilot victims never saw their attackers, including some rather high-scoring aces.