Bearcat roll rate

[bada]

if i remeber correctly, the famous Naca roll chart is based on calculations and not testing results.

Just to add more blurr to the mist of the subject:
From "Ending the Argument"

ROLL PERFORMANCE
Roll performance was evaluated using full aileron deflection in rolls to the right and left at 10,000 ft. MSL at 200 kts. for 1 g rolls through 360 degrees and 220 k.ts. for rolls at 3g through 180 degrees. The results are presented in Tables Ill and IV.

While the 1 g roll rates are not particularly impressive by modern standards, they were nonetheless quite respectable for their day. It is significant that all the aircraft, with the exception once again of the P-47, showed substantial reductions in roll performance when rolling under g. Eventually the P-47 lost 11 % of its roll performance in loaded rolls to the right (though nothing to the left), but this was negligible compared o 25-27% for the Mustang, 28-33% for the Corsair, and 26-38% for the Hellcat, making large changes of direction under g a fairly ponderous business. No wonder that improving roll rate was a major goal for fighter designers of the period when gaining a few degrees per second could endow a substantial advantage over the opposition. Roll rates in the landing configuration were very similar 1or all the aircraft, time to roll through 90 degrees being about 2.3-2.4 seconds with an average roll rate of about 38 degrees per second.

And from wwiiaircraftperformance.com, spitMK21: (shameless promotion of the website )

 

[smutny]

…for 1 g rolls through 360 degrees and 220 k.ts. for rolls at 3g through 180 degrees.

How were they loading up the airframes? Or was this a calculation exercise again?

 

[Holtzauge]

First of all you have to compare apples with apples: Either you look at the time it takes to do a 360 or 180 degree roll which will include the effects of inertia since you start off with zero roll velocity and accelerate up to your peak rolling speed at that velocity. The NACA charts are for the peak rolling velocity that each aircraft can attain at a certain speed, so those can't be used to compare with the time it takes to do a 180 or 360 degree roll. This is especially true for the P-38 which due to its twin engines has a very slow roll acceleration but with boosted ailerons has a very good peak roll rate. But even so the same applies for any other aircraft: Either you measure the time it takes to roll to a certain angle, or you measure the rolling velocity.

In addition, analysing video footage may be interesting, but since you have no idea about how fast the stick is moved over and what stick forces are being used its questionable if you can compare aircraft in this way. Maybe if you measure the rolling velocity after the acceleration phase and before the pilot slows down the roll you can get some idea though.

Also, what makes you say these are calculated? In NACA report 868 it states that data has been collected for a number of aircraft. What makes you think it has been calculated?

The Germans also used the same method (as NACA) to evaluate rolling performance: This was done in trials where the peak rolling velocity was measured as a function of stick force. And the below chart for the Bf 109 is therefore an apples with apples comparison since it's directly comparable to the NACA chart in report 868 given that both measure the same thing.

The German chart shows what would have been possible to achieve with stiff rod controls at 50 lb (red dot) but since these flexed, the Bf 109 only did about W=1.4 or about 80 deg/s.

So this 80 deg/s figure for the Bf 109 is directly comparable to the numbers in the NACA chart I posted earlier, and shows that the Bf 109's roll performance was quite mediocre.

So in conclusion, the roll rate of the F8F was clearly superior to the Bf 109 in that it did between 90-105 deg/s even with a stick force of 30 lb (NACA RM No L7L31).

 

[smutny]

The Germans also used the same method (as NACA) to evaluate rolling performance:

That is what my list was asking. All these charts are meaningless unless the mechanics of gathering the data is known.

 

[Holtzauge]

That is what my list was asking. All these charts are meaningless unless the mechanics of gathering the data is known.

By method I meant they measured the same thing: Roll rate defined as the stabilized rotational speed in degrees or radians per second around the longitudinal axis as a function of speed at a certain specified altitude.

There are many ways to measure both stick forces and rates of roll: The Germans used a special stick to measure force and deflection, and a gyroscopic unit to measure roll rate.

And why would this data be meaningless unless you know exactly how they were measured? NACA posted roll rate figures for a number of fighters. The German research institute DVL measured them for the Bf 109. These are two professional and respected research institutes so what reason would there be to question their numbers?

Exactly how NACA came up with their numbers is unknown to me. But if they used gyroscopic units or filmed the cockpit and horizon and worked out the roll rate from this seems irrelevant to me unless you want to question their ability to do correct measurements?

 

[GregP]

We'd know more if we knew pb/2V values and could compare them.

The variable pb/2V is avctually the helix angle of the roll cylinder as the wing tips trace a path around the roll.

p = roll rate in radians / second.
b = wingspan (ft).
V = True airspeed of the aircraft (ft/sec).

You can find some of these values, but I've not seen one for the F8F.

I HAVE seen two maximum roll rates quoted, 176° / second and 360° / second.

It wasn't noted. but I am assuming that is at 10,000 feet since most US Naval fighters of the day were quoted there for test purposes. Naval mission were planned there, too, in most POHs. Personally, I'd come MUCH closer to believing the 176 instead of the 360 number. US fightgers were mostly in the 90 to 140° / second range for highest roll rate in WWII, and it was usually in a very narrow speed range with all other roll rates being slower.

So, 176° * 3.072 rad/s. I assume 250 mph, which is 366.67 ft/s. The wingsp[an is 35.8333 ft. That gives a pb/2V = 0.15 radians or a helix angle of 8.6°. To get anything from that, we'd need to compare it with other fighter pb/2V values.

Might be fun. Cheers.

 

[GregP]

How were they loading up the airframes? Or was this a calculation exercise again?

You load up the airplane by pulling on the stick while looking at the g-meter. Most veteran pilots can easily pull with steady g-force.

 

[Holtzauge]

We'd know more if we knew pb/2V values and could compare them.

The variable pb/2V is avctually the helix angle of the roll cylinder as the wing tips trace a path around the roll.

p = roll rate in radians / second.
b = wingspan (ft).
V = True airspeed of the aircraft (ft/sec).

You can find some of these values, but I've not seen one for the F8F.

I HAVE seen two maximum roll rates quoted, 176° / second and 360° / second.

It wasn't noted. but I am assuming that is at 10,000 feet since most US Naval fighters of the day were quoted there for test purposes. Naval mission were planned there, too, in most POHs. Personally, I'd come MUCH closer to believing the 176 instead of the 360 number. US fightgers were mostly in the 90 to 140° / second range for highest roll rate in WWII, and it was usually in a very narrow speed range with all other roll rates being slower.

So, 176° * 3.072 rad/s. I assume 250 mph, which is 366.67 ft/s. The wingsp[an is 35.8333 ft. That gives a pb/2V = 0.15 radians or a helix angle of 8.6°. To get anythin g from thath, we'd need to compare it with other fighter pb/2V values.

Might be fun. Cheers.

We already got both the roll rate and pb/2V for the F8F: E eagledad posted a NACA report containing them a while back in this thread.

The roll rate is good, but not nothing special and does not come near the Fw-190's over 160 deg/s:

 

[bada]

1°First of all you have to compare apples with apples: Either you look at the time it takes to do a 360 or 180 degree roll which will include the effects of inertia since you start off with zero roll velocity and accelerate up to your peak rolling speed at that velocity. The NACA charts are for the peak rolling velocity that each aircraft can attain at a certain speed, so those can't be used to compare with the time it takes to do a 180 or 360 degree roll. This is especially true for the P-38 which due to its twin engines has a very slow roll acceleration but with boosted ailerons has a very good peak roll rate. But even so the same applies for any other aircraft: Either you measure the time it takes to roll to a certain angle, or you measure the rolling velocity.

2°In addition, analysing video footage may be interesting, but since you have no idea about how fast the stick is moved over and what stick forces are being used its questionable if you can compare aircraft in this way. Maybe if you measure the rolling velocity after the acceleration phase and before the pilot slows down the roll you can get some idea though.

3°Also, what makes you say these are calculated? In NACA report 868 it states that data has been collected for a number of aircraft. What makes you think it has been calculated?

4°The Germans also used the same method (as NACA) to evaluate rolling performance: This was done in trials where the peak rolling velocity was measured as a function of stick force. And the below chart for the Bf 109 is therefore an apples with apples comparison since it's directly comparable to the NACA chart in report 868 given that both measure the same thing.

5°The German chart shows what would have been possible to achieve with stiff rod controls at 50 lb (red dot) but since these flexed, the Bf 109 only did about W=1.4 or about 80 deg/s.

So this 80 deg/s figure for the Bf 109 is directly comparable to the numbers in the NACA chart I posted earlier, and shows that the Bf 109's roll performance was quite mediocre.

So in conclusion, the roll rate of the F8F was clearly superior to the Bf 109 in that it did between 90-105 deg/s even with a stick force of 30 lb (NACA RM No L7L31).

1° Agree totally with you
2° Also, apart the points you raised, the precision from analysing a film would be very approximative and results questionable
3°From Memory, but getting old , something in the discussions from more than 15 years , from the times with kurfy and crump.
But if you have the full Paper from Naca, i'd be happy to update wwiiaircraftperformance with it, instead of just having the chart.
4°Yes, see the Würger Dive Test (and transalation),where you can see very precise data. ( and where you can see that the 190 requiered only +/-27Kg on the stick for a recovery from terminal velocity M0.79)
5° Why always compare to the 109? why oh why?? The würger was a better plane to compare with than the old mopped.

 

[Holtzauge]

1° Agree totally with you
2° Also, apart the points you raised, the precision from analysing a film would be very approximative and results questionable
3°From Memory, but getting old , something in the discussions from more than 15 years , from the times with kurfy and crump.
But if you have the full Paper from Naca, i'd be happy to update wwiiaircraftperformance with it, instead of just having the chart.
4°Yes, see the Würger Dive Test (and transalation),where you can see very precise data. ( and where you can see that the 190 requiered only +/-27Kg on the stick for a recovery from terminal velocity M0.79)
5° Why always compare to the 109? why oh why?? The würger was a better plane to compare with than the old mopped.

3) You can get the complete NACA report 868 from NTRS from here. And good to know that you did not have some other source about how NACA derived the roll rates which I did not know about. Sometimes things are not what they seem to be and I was wondering if you had seen some other info somewhere else.

4 & 5) For sure, the Fw-190 was much better in both dive and roll but I thought the Bf 109 roll chart was good since it was directly comparable to the NACA chart and which was why I used it.

 

[GregP]

We already got both the roll rate and pb/2V for the F8F: E eagledad posted a NACA report containing them a while back in this thread.

The roll rate is good, but not nothing special and does not come near the Fw-190's over 160 deg/s:

View attachment 838935

I have seen 176° per second quoted in several places for the F8F-2 Bearcat and Eagledad's post was for the F8F-1.

The F8F at the Planes of Fame is likely even better since it is a very rare G-58 Bearcat (one of two) and never had any military armament installed ... so it very likely has less rolling inertia without guns or gun mounts.

 

[Holtzauge]

I have seen 176° per second quoted in several places for the F8F-2 Bearcat and Eagledad's post was for the F8F-1.

The F8F at the Planes of Fame is likely even better since it is a very rare G-58 Bearcat (one of two) and never had any military armament installed ... so it very likely has less rolling inertia without guns or gun mounts.

But compared to the F8F-1, the F8F-2 only had a taller vertical stabilizer and rudder for improved stability AFAIK? And if so, i.e. as in no changes to the ailerons, then this would not have changed the roll rate.

And regarding the 176 deg/s roll rate number, do you have any sources for those? From the study of WW1 performance numbers I know that sometimes a number is mentioned by someone somewhere and then simply repeated in other places until it becomes a fact so it would be good to see where it originates from.

Regarding the effects of armament in the wings such as guns and ammo, that would have a substantial effect for roll acceleration but as long as they are contained within the wing (as in no guns pods etc.) the effect on peak roll rate will be quite small.

 

[smutny]

And why would this data be meaningless unless you know exactly how they were measured?

Because it makes a difference how the roll is flown. Because it makes a difference on how the start and stop points were determined. Because it makes a difference on who made the observation.

You talked about apples vs apples. All these variables affect the end number.

 

[smutny]

You load up the airplane by pulling on the stick while looking at the g-meter. Most veteran pilots can easily pull with steady g-force.

So you're saying they did a 1/2 barrel roll. Pulling and then introducing a rolling component will give you a barrel roll.

This is why I keep saying the type of roll makes a difference in these discussions.

 

[Holtzauge]

Because it makes a difference how the roll is flown.

Didn't you read what I wrote before?

"Roll rate defined as the stabilized rotational speed in degrees or radians per second around the longitudinal axis as a function of speed at a certain specified altitude."

Because it makes a difference on how the start and stop points were determined.

Can't you comprehend what stabilized means?

It means you exclude the start and stop points and the time it takes to accelerate and decelerate to the peak stabilized roll rate.

Because it makes a difference on who made the observation.

No, we do not need to know who made the observation. They were both made by professional and well established research facilities. But if you get to know this how are you going to use that? If you know it was NACA's Msc Billy Applepie and DVL's Dipl Ing Fritz Apfelstrudel who measured this are you then qualified to give a thumbs up or thumbs down?

You talked about apples vs apples. All these variables affect the end number.

No they don't. The NACA roll rate numbers for the F8F and the DVL numbers for the Bf 109 are an apples to apples comparison.

Finally, the Washington Monument is supposedly 555 ft 5.125". But I really doubt that: I mean how did they measure that? What equipment was used? Who did it? Was he qualified to do it? And even if we learn all this, was his measurement equipment calibrated? In that case I want to see the calibration protocol and who approved that. And then how did they calibrate the calibration tool?

 

[GregP]

So you're saying they did a 1/2 barrel roll. Pulling and then introducing a rolling component will give you a barrel roll.

This is why I keep saying the type of roll makes a difference in these discussions.

Actually, I'm not saying that. The data posted above (post #21) give a table at 10,000 feet, and for a 360° roll at 200 KIAS and 1 g, and for a 180° roll at 220 KIAS and 3 g.

To me, the only way 1 g and 3 g makes any sense for a roll is if it was a barrel roll, which was and is a standard combat maneuver. Most WWII fighter do not have inverted fuel and oil systems, so they keep at least low positive g on the airplane during combat sp they don't have engine cut-out or oil starvation damage. Actually, I have seen oil starvation damage in a T-28 when the pilot forgot about the 5 seconds inverted limitation. It was pretty or cheap. Basically, it was time for a new engine.

 

[Holtzauge]

Actually, I'm not saying that. The data posted above (post #21) give a table at 10,000 feet, and for a 360° roll at 200 KIAS and 1 g, and for a 180° roll at 220 KIAS and 3 g.

To me, the only way 1 g and 3 g makes any sense for a roll is if it was a barrel roll, which was and is a standard combat maneuver. Most WWII fighter do not have inverted fuel and oil systems, so they keep at least low positive g on the airplane during combat sp they don't have engine cut-out or oil starvation damage. Actually, I have seen oil starvation damage in a T-28 when the pilot forgot about the 5 seconds inverted limitation. It was pretty or cheap. Basically, it was time for a new engine.

That is my take as well: The 1 g numbers are probably for an "ordinary" roll around the longitudinal axis. In addition, the roll rate numbers in the article for the P-47 and P-51 (have not looked at the other aircraft) are in the ballpark you would expect given the peak roll rate numbers for these aircraft given in the NACA report 868 which is around 80-85 deg/s at this speed.

And I also think the 180 deg roll times at 3 g must be for a half barrel roll. Difficult to understand what else they could be. And to pull 3 g's in the Mustang requires quite some pull on the stick. I have recently tried wingovers myself in the "Jersey Jerk" two-seat P-51D Mustang at Sywell in England and while the ailerons were very light and crisp at 180 KIAS, you had to pull back with quite some force to reach 3-4 g's at 260 KIAS. So if you have to divert some of your strength to get the nose to move in pitch, that would of course slow you down somewhat in roll.

 

[smutny]

Didn't you read what I wrote before?

"Roll rate defined as the stabilized rotational speed in degrees or radians per second around the longitudinal axis as a function of speed at a certain specified altitude."

I can ask you the same thing. As I mentioned, there are two types of horizontal rolls. What we today call the slow roll and the aileron roll. One rolls around a point requiring top rudder in segments the other starts with a pitch up before the roll is initiated with little or no rudder movement. Which one was used for the various tests? Did they strive for a straight trajectory or did they allow a more parabolic one? There's not a big difference in roll rate between them, there there is one.

Can't you comprehend what stabilized means?

It means you exclude the start and stop points and the time it takes to accelerate and decelerate to the peak stabilized roll rate.

No need to get huffy about it. I missed that nuance of your post. But it still raises the question for me did they do a sequence of rolls and use the middle for the data or did they calculate the start/stop sections out of a roll by just using (for example) from 90 degrees to 270 degrees?

No, we do not need to know who made the observation. They were both made by professional and well established research facilities. But if you get to know this how are you going to use that? If you know it was NACA's Msc Billy Applepie and DVL's Dipl Ing Fritz Apfelstrudel who measured this are you then qualified to give a thumbs up or thumbs down?

You missed the point of my question. Not who as in name, but who as in role. Was it the pilot, an observer of the maneuver or did they work with film?

Finally, the Washington Monument is supposedly 555 ft 5.125". But I really doubt that: I mean how did they measure that? What equipment was used? Who did it? Was he qualified to do it? And even if we learn all this, was his measurement equipment calibrated? In that case I want to see the calibration protocol and who approved that. And then how did they calibrate the calibration tool?

You are absolutely correct, and this is the basis of my questions. As technology moves forward, more accurate instruments and methods of measurement have been developed.

My issue is that, 80 years on, there are still fantastical performance numbers tossed around as witnessed or fact, for example the recently mentioned Bearcat 360 degree/second roll rate. When these charts and reports are thrown around as 100% definitively accurate, I have to take issue with that. While most, if not all, were done in good faith, technology has moved forward in methods to more accurately determine data like this. If all testing was identical, or near identical, great, then the numbers may be close and ranking may be correct. But if one used one method and another a different method, then it's all good for hangar talk, but must be taken with a grain of salt for accuracy.

 

[smutny]

Actually, I'm not saying that. The data posted above (post #21) give a table at 10,000 feet, and for a 360° roll at 200 KIAS and 1 g, and for a 180° roll at 220 KIAS and 3 g.

To me, the only way 1 g and 3 g makes any sense for a roll is if it was a barrel roll, which was and is a standard combat maneuver. Most WWII fighter do not have inverted fuel and oil systems, so they keep at least low positive g on the airplane during combat sp they don't have engine cut-out or oil starvation damage. Actually, I have seen oil starvation damage in a T-28 when the pilot forgot about the 5 seconds inverted limitation. It was pretty or cheap. Basically, it was time for a new engine.

Flying along straight and level, you're at 1G. Doing a 1G barrel roll, you'll see 2G on the G-meter. Trying to do a barrel roll with only 1G on the G-meter requires extremely slow control movement and takes a very long time. I've never done one like that but now I'm curious to try it.

So were the 1 and 3 G's on the report indicative of the load added to the airplane or what the G-meter was indicating? If indication, then 1G would be a horizontal type roll and 3G would be a barrel type roll.

I'm not trying to be a ass, I'm trying to understand how these numbers that we're throwing around were determined.

 

[Holtzauge]

I can ask you the same thing. As I mentioned, there are two types of horizontal rolls. What we today call the slow roll and the aileron roll. One rolls around a point requiring top rudder in segments the other starts with a pitch up before the roll is initiated with little or no rudder movement. Which one was used for the various tests? Did they strive for a straight trajectory or did they allow a more parabolic one? There's not a big difference in roll rate between them, there there is one.

No need to get huffy about it. I missed that nuance of your post. But it still raises the question for me did they do a sequence of rolls and use the middle for the data or did they calculate the start/stop sections out of a roll by just using (for example) from 90 degrees to 270 degrees?

You missed the point of my question. Not who as in name, but who as in role. Was it the pilot, an observer of the maneuver or did they work with film?

You are absolutely correct, and this is the basis of my questions. As technology moves forward, more accurate instruments and methods of measurement have been developed.

My issue is that, 80 years on, there are still fantastical performance numbers tossed around as witnessed or fact, for example the recently mentioned Bearcat 360 degree/second roll rate. When these charts and reports are thrown around as 100% definitively accurate, I have to take issue with that. While most, if not all, were done in good faith, technology has moved forward in methods to more accurately determine data like this. If all testing was identical, or near identical, great, then the numbers may be close and ranking may be correct. But if one used one method and another a different method, then it's all good for hangar talk, but must be taken with a grain of salt for accuracy.

I think we are just going round in circles now and I think I've addressed these questions of yours a number of times now so with that I will call it a day. And as is sometimes the case in forums such as this we just have to agree to disagree and leave it at that.