Bearcat roll rate

Holtzauge said:

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.

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Fine. If you can provide the document on the 109 tests, or a link to them, I'll read it myself. Yes, I'm fluent in German. Already download the other two documents linked earlier.

Holtzauge said:

I think we are just going round in circles now…

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Sorry, that first line broke me up. I wish I posted that.

That' called a dogfight or a political / religous discussion ...

smutny said:

Fine. If you can provide the document on the 109 tests, or a link to them, I'll read it myself. Yes, I'm fluent in German. Already download the other two documents linked earlier.

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It's not available online, but the methodology and instrumentation employed in FB Nr. 1951 is given as follows:

III. Versuchsaufbau und -durchführung.

a) Meßverfahren und Meßanordnung.

Als Maß für die Rollwirksamkeit wurde die bei einem bestimmten Querruderausschlag ξₘ erreichbare stationäre Winkelgeschwindigkeit um die Längsachse ωₓ gewählt, die gleichzeitig für die Flügelbeanspruchung für den Fall der gleichförmigen Drehung maßgebend ist. Die Winkelgeschwindigkeit wurde mit einem Kreiselgerät gemessen, das hinter dem Sitz des Flugzeugführers angebracht war. Um auch den Fall der beschleunigten Drehung mitzuerfassen, war noch ein Gerät zum Messen der Drehbeschleunigung eingebaut. Bei den Versuchen zeigte sich jedoch, daß den Schrieben dieses Gerätes so große Störamplituden überlagert waren, daß die Auswertegenauigkeit unzureichend war. Die Drehbeschleunigungen mußten daher aus den Drehgeschwindigkeitsschrieben durch Differentiation ermittelt werden.
Um den Einfluß der Schieberollmomente abschätzen zu können, wurde im Zusammenhang mit der Geschwindigkeits- und Höhenmessung der Schiebewinkel mit einer DVL-Winkelstaudüse gemessen. Bei den hohen Geschwindigkeiten (etwa ab 560 km/h) mußte jedoch aus Sicherheitsgründen der Mast mit der Winkelstaudüse wieder abgenommen werden (s. Skizze 1).

Der Knüppelausschlag ließ sich durch eine Kette auf 3 verschiedene Werte begrenzen (s. Abb. 2), die im Mittel über den gemessenen Staudruckbereich ungefähr einem mittleren Querruderausschlag von ξₘ = 3º, 6º und 9º entsprachen. Der Bügel mit Kette konnte auch bei gespannter Kette durch einen leichten Druck mit dem Daumen oder Zeigefinger von dem Knüppelkraftschreiber gelöst werden. Die Ausschläge beider Querruder wurden gemessen, wobei die Geräte an den Querruderstoßstangen in unmittelbarer Nähe der Querruderhebel angelenkt waren.
Die gemessenen Größen, sowie der Einbauort der Geräte und ihre Meßgenauigkeit sind aus Tabelle 1 und Abb.1 zu entnehmen. Der Vorschub der Geräte wurde durchweg so groß gewählt, daß eine zeitliche Zuordnung der einzelnen Meßgrößen auf 0,01 Sek. möglich war.

b) Versuchsausführung.
Der Meßvorgang ist folgender:
Der Flugzeugführer fliegt mit einer vorgegebenen Geschwindigkeit in einer bestimmten Höhe geradeaus, wobei das Flugzeug weder schieben noch drehen darf. Dann gibt er einen plötzlichen Querruderausschlag bis zu dem durch die Kette begrenzten Knüppelanschlag und läßt das Flugzeug bis ungefähr zur Nesserlage drehen. Nach Erreichen der Messerlage wird das Flugzeug sofort wieder in Normallage gebracht. Während der eigentlichen Messung soll das Seitenruder nach Möglichkeit nicht betätigt werden. Um Höchstwerte für die Drehbeschleunigung zu erreichen, soll die Betätigung des Querruders möglichst rasch erfolgen. Hierbei wird auch ein annähernd geradliniger Anstieg des Querruderwinkels über der Zeit erreicht, was für die Nachrechnung der Versuche eine analytisch einfache Ruderschaltfunktion ergibt.

Tabelle 1

Roll, roll, rock'n'roll...
My head was spinning after watching this video. I need to do a brain scan!
Hey, pilots, how can you discuss graphs and formulas after flying like that?

View: https://youtu.be/NlE8_dvAJ7Q?si=h2pdRdJpgSEATRsZ

Well, looks like the Fw-190 finally met its match!

Hey guys,

I am not a pilot, so I do not know all of the proper and informal terms for the various aspects of flying. I would appreciate a critic and explanation/correction of what I am about to type.

My understanding re rolls are that there are 3 types of rolls that could be considered to have a maximum roll rate.

1. An axial roll

2. A barrel roll

3. an outside roll

An axial roll could be defined as roll about an axis (line drawn) approximately through the aircraft from nose to tail.

A barrel roll could be defined as the aircraft describing a spiral around an axis (line drawn) in the forward direction of flight, said axis (line drawn) being some distance above the pilots vertical, said vertical intersecting the axis.

An outside roll (of necessity being a barrel roll) with the pilots vertical toward the outside of the spiral.

My understanding re the outside roll is that only a few specially designed or modified aircraft can perform outside rolls at any high rate or for any length of time - partly due to the standard aircraft not being able to maintain fuel and/or oil flow due to the negative Gs, and partly due to pilot inability to tolerate negative Gs. So probably not of concern to this discussion?

My understanding of axial rolls is than many (most?) aircraft cannot do true axial rolls - due to the centers of gravity and wings being off centerline? Also, doing a true axial roll might starve the engine(s) of fuel and/or oil due to 0 or very low Gs.

This leaves most aircraft to do barrel rolls, although at least a significant minority of aircraft can do fairly tight barrel rolls (ie near axial rolls)?

In addition to the above, maximum roll seems to be described either in terms of maximum roll acceleration (such as time from initiation of roll to 90° in x seconds left or right), or what I have been calling a developed roll (ie the time from 0 to 90° is ignored as such and it only matters what the maximum rate of roll reached over a relatively greater period of time or over a number of rolls), and possibly a third description which seems to blur/combine the two.

In addition to any appreciating correction of the above, I have a couple of questions.

1. Would the measurement of the rolls rates in the numbers upthread where one rate was measured at 1G and the other measured at 3G be due to the aircraft measured not being unable to do axial rolls? Or did they eliminate the axial roll of one or another due to the other aircraft not being able to perform an axial roll?

2. How many WWII aircraft (or prop jobs in general) were/are able to do axial rolls?

3. Although the various roll acceleration tests to be found online are (I think) somewhat self-explanatory in that they are timed tests from 0 to 90°, or from 90°L to 90°R, etc - am I missing something?

4. Is there some accepted number of rolls that is used/should be used to measure what I call a developed roll? Basically, I am wondering if any of the countries seemed to be consistent in their measurements. How did they measure a developed roll? I know that some tests done by RAE/A&AEE used cameras mounted in the cockpit that had the roll indicator instrument and a clock in the FOV. Sometime they had G meters installed for various maneuver tests, such as turn rates, but I do not know if they used them for roll tests.


In addition, here a couple of bits of info which I think are pertinent ot the discussion:

On WWII aircraft, boosted ailerons such as those on the P-38 would help with roll acceleration (ie time from 0 to 90°) but not with maximum roll rate (ie sustained °/sec) - unless the pilot was not able to manually hold the stick over upto the maximum developed roll rate of the aircraft. Another way of saying this is if the aerodynamic forces on the ailerons were too high for the pilot's strength and control linkage system to allow full deflection above a certain speed, then the boosted ailerons might allow the ailerons to be kept at full deflection to a higher speed and hence the developed roll rate might be increased - but not necessarily since the increased drag on the rolling aircraft might prevent a higher developed roll rate. Changing (usually reducing) the aileron deflection, and/or adding trim tabs to reduce the stick forces, could also help maintain/deveop high roll rates to higher speeds. An example of this is the P-51, which ended the war with a significantly higher roll rate at high speeds than at the start of the war, although sid mods reduced the roll rate at lower speeds (I think).

Per the evaluations of the Fw-190 performed by the RAE/A&AEE and USAAF, both agencies commented that the Fw-190 was able to perform snap rolls that would tear off the wings on the UK or US aircraft. Nearly all war-time US/UK aircraft had a prohibition against snap rolls in their pilot's note/handbooks. It was only very late-war that a couple of US/UK aircraft did not have this prohibition. I do not know enough about the Soviet aircraft to know if this held true for them as well?


re jet aircraft

I do not have any numbers for aircraft like the F-104 (which was supposed to have a high roll rate), but the A-4 Skyhawk (ie the 'Scooter') could do over 360°/sec in a developed roll.

With modern jet aircraft, particularly those with fly-by-wire controls - both the roll acceleration and maximum roll rates can be very high and very much higher than WWII prop jobs. A couple examples that I am familiar with are the F-16 at over 480°/sec developed, and the F-15 at over 360°/sec developed.

Even the F-14 (pre FBW mods) could do over 240°/sec with its wings forward at subsonic speeds, and over 360°/sec with its wings at full sweep at transonic/supersonic speeds. I do not know how the FBW mods affected the F-14.

All of the numbers I quoted for the jets are for clean aircraft.

??

You are quite correct that you can't do a "true" axial roll in most aircraft for any extended period of time since you will begin to "wobble" around the roll axis both due to aerodynamic and inertial effects. I went back and looked at the German Bf 109 test report and there they read off the peak roll velocity within a second of initiating the roll in the example they showed, after which the sideslip angle ß starts increasing and the roll rate slows down due to the resulting increasing "wobble" around the roll axis. The whole roll sequence there was a bit more than 2 s and the sideslip angle increased from 0 to more than 10 deg in that example so quite some "wobble" on the end there. Have no idea how NACA measured their numbers though, but roll rate is a well-established metric in the study of aerodynamics and you can find roll rate versus speed charts from many major aeronautical research institutions.

smutny said:

A few years ago there was a very lively discussion in the aerobatic chat channels about roll rates. One intrepid individual, Spencer Suderman, spent a lot of time analyzing video footage, frame by frame, to determine roll rates on a wide variety of aerobatic airplanes. Unfortunately, no Bearcat pilots sent in any video, but here are a couple of the warbird numbers:

	Video FPS	Roll 1 Frames	Roll Rate degrees/second		Roll 2 Frames	Roll Rate degrees/second		Notes
War Birds
AT-6D	60	190	57		193	56		150 mph reported by pilot
Harvard Mark IV	24	65	66					160 Kts reported by pillot
T-6G	30	74	73					Metal Ailerons
P-51 Mustang	30	58	93					Pilot reported 200 kts
F4U Corsair	30	67	81					Pilot reported 160 kts
T-33	30	74	73

A couple of the general consensus outcomes were that pilots often over-estimated aircraft performance, and modern digital cameras with high frame rates are far better suited for this analysis than older film based cameras. The data isn't scientific accurate, a lot of variables, but makes for some good hangar flying.

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Thank you. For comparison, the A-4 Skyhawk (various iterations) usually was rated at 720 dps.

Hi ThomasP,

The only thing thath stands out to me as maybe slightly questioable above is the asseretion that the Fw 190 could do snap rolls that would tear the wings off other aircraft.

My understanding is the Fw 190 could do either axial, or as close to axial as it could get, or barrel rools fas enough to leaver most other aircraft behind, at least up until it got over 400 mph, when it rolls rate was much closer to Allied aircraft. No fighter, or other aircraft for thath matter, does snap roll at high speed such as might be encountered ina dogfight. If you are over the corner speed of the aircraft (see VG diagram), you will exceed the limits of the aircraft before you stall. Not good.

Under corner speed, you can snap roll if the aircraft is stressed for it.

But, all the claims I have seen for the roll capabilities of the Fw 190 series have been for normal rolling maneuvers, not snap rolls.

Not trying to nitpick, more to clarify. No dog in the hunt, here, Cheers.