High Roll Rate

[SpitLead]

Was wondering what airplane attributes give some aircraft a faster roll rate while others don't. Is it related to: wing loading (high vs. low), wing area, wing aspect ratio, aileron size, aileron boost (I think P38 has boost) and/or combinations of all these factors??  Is there a predominant factor?

And, what ACM can be used to take advantage of the high roll rate in a dogfight against a better turning airplane.   I know the F4U and FW190 have GREAT roll rates. I use a flick roll and then pull thru to change directions quickly in a scissors type move.  I've found this to be especially effective to shake off a tailing nme and get separation.

[Drano]

Roll rate is definitly related to turning. Here's why:

Most turning is done with the elevator. You basically are pulling. The direction you're turning(pulling) in is called your Lift Vector. When you roll your plane, you're changing the direction of your Lift Vector. Planes with superior roll rate can get themselves oriented in the desired direction of turn faster than others by changing the direction of that Lift Vector.

So what's important about that?

Turn rate is measured in DPS or Degrees Per Second. If you're flying a plane with superior roll rate--such as the F4 or FW--you can get yourself rolled around inside your opponent's turn faster than he can. This is why it works so well in scissors type manuevers. Basically you're pulling into your turn before your NME has rolled into his. What it does is cuts a bit of the "Per Second" part of your NME's turn rate--you got there before he did. Make sense?


Hope that didn't confuse ya too much : )

        Drano

<still a semi-idiot but I'm workin on it>


[This message has been edited by Drano (edited 05-17-2001).]

[flakbait]

Well, roll rate is primarily a function if aileron design. Take the Fw-190; that aileron runs about 1/3 the length of the wing on some models. It's superb balance, light weight, and design give you one hell of a roll rate. Then you take something like a Yak. I call Yak ailerons "shoulder mounted" types. Instead of the hinge being in the center of the aileron, it's near the bottom of the wing. Like this (it's rough but works):

   

Finnish pilots supposedly prefered the Yak over the Spitfire because when the Spit got above 350mph the ailerons got stiff. The Yak actually gets the best aileron performance at this speed, oddly enough. When you roll in a Yak the aileron "shrugs" and the nose goes either above or below the wing. This lets air flow through, reducing pressure on the aileron and thus, pressure on your hand. As for maneuvers, pretty much anything when you need to change direction fast is where roll comes in. If you're a die-hard vertical fighter then you won't bother with roll. Me? I like to mix things up (flat-turning in a Yak) so roll helps. Scissors, split-S, immelman; any time you have to go from this direction to that one FAST. That's when roll comes in dang handy.

Forgive me for going on about the Yak. It's my baby and has an aileron system that's simple to explain. Hey, I coulda run through the calculations to figure how fast an aileron of a given type will roll!!  

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Flakbait [Delta6]
Delta Six's Flight School
Put the P-61B in Aces High
"With all due respect Chaplian, I don't think God wants to hear from me right now.
I'm gonna go out there and remove one of His creations from this universe.
And when I get back I'm gonna drink a bottle of Scotch like it was Chiggy von
Richthofen's blood and celebrate his death."
Col. McQueen, Space: Above and Beyond
   

[This message has been edited by flakbait (edited 05-17-2001).]

[SpitLead]

Thanks guys!  Great info. I love that high roll rate :-)

[Tyro48]

roll rate is directly related to the length and width of the aileron, after that its rudder authority to quickly over come the adverse yaw, bigger aileron more adverse yaw.

[Jekyll]

 

Originally posted by flakbait:
If you're a die-hard vertical fighter then you won't bother with roll.

Ooh wrong I'm afraid flakbait.  Some of the very best offensive moves in the fast rollers come from being able to go vertical, snap into a fast roll to establish lead pursuit on a flat-turning opponent, then pull the lift vector through into a guns solution.

------------------
Jekyll
9./JG 54 "Grünherz"
Aces High Training Corps

[Lephturn]

Jekyll is right on.  Roll is the key to using the vertical effectively versus better turning planes.

Lets say your in a Spit IX, and I'm attacking you in my Jug.  I have an altitude and hence an Energy advantage, but you can out-turn me.  I press an attack, and you do a horizonatl break turn in the Spit to evade.  I pull up into a loop.  Now as I'm coming back down from the loop, all I have to do is roll in the vertical and adjust my heading so I pull out of the loop where you are going to be.  If I have enough energy advantage at this point, I can use lag pursuit and high yoyo's to stay with you for the kill.  Or, I can take the snapshot if I've lined it up right.

Asside from snapping into scissors faster, a fast roll rate will let you "out turn" better turning planes by rolling in the vertical.  You can adjust your heading this way much faster than any bogey can flat turn.

A fast roll rate is also great for getting or preventing a guns solution.  To make a tracking shot on a bogey, you must match your plane of flight with his.  If you are the attacker in this case, a fast roll rate means you can match your plane of flight to his very quickly if he rolls.  If you are the defender, you can quickly roll out of the enemy's plane of flight, and use short hard pulls to stay out of his gun sight.  If your plane rolls better, he won't be able to keep up with your constant quick rolls and will be unable to get a solid tracking solution.

------------------
Sean "Lephturn" Conrad - Aces High Chief Trainer

A proud member of the mighty Flying Pigs
http://www.flyingpigs.com

Check out Lephturn's Aerodrome for AH articles and training info!

[flakbait]

Thanks Jekyll and Leph. So I was a little caught up in explaining my Yak's aileron system and screwed up. When it comes to maneuvers and mechanics I've got a one track mind. It's either maneuvers or mechanics, not both at once!  

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Flakbait [Delta6]
Delta Six's Flight School
Put the P-61B in Aces High
"For yay did the sky darken, and split open and spew forth fire, and
through the smoke rode the Four Wurgers of the Apocalypse.
And on their canopies was tattooed the number of the Beast, and the
number was 190." Jedi, Verse Five, Capter Two, The Book of Dweeb
 

[Jekyll]

I once had a great film of an engagement in the TA between myself in a 190A8 and another guy in a Spitfire V.

This guy had refused to believe me when I said that under the right circumstances the A8 could comprehensively outmaneuver the Spitfire.  So we set up an engagement.

I came in hard on his 6 .. he performed the usual Spit V hard break defensive turn, whilst I pulled pure vertical, rolled onto his new heading, then pulled through back onto his 6.

Two or 3 of these and his energy had bled down to critical levels, making him easy prey for 4 Mg151/20 cannon.

Roll and vertical performance are powerful weapons.  After all, during 1941 the Fw 190 was regarded as being a 'highly maneuverable' aircraft.  The British pilots were told that the Spitfire could still outturn the 190, to which one of the pilots retorted, "But turning does not win battles".

[wells]

All things being equal, roll rate is a function of wingspan and airspeed.  Twice the wingspan = 1/2 the roll rate for a given helix angle (and airspeed), which is largely determined by aileron design.  Using the P-51 as an example, it's ailerons deflect 10 degrees up and down compared to 15 or 20 for most other planes.  This is because the laminar flow airfoil has a steeper angle down to the trailing edge as the thickest point is farther back.  If the aileron deflects too much, it can stall, reducing it's effectiveness.  The P-51 is at a disadvantage  because of this.  They tried bevelled ailerons at one point to get a pressure recovery over the aileron, which allowed them to deflect a bit more and be more effective, but I think the idea was scrapped for some reason, maybe because it adversely affected cruise drag or something.  

The Yak rolls well  because it's wing is 7' shorter than a P-51 or Spit.  It used a clark-yh airfoil, which many may recognize as having a flat bottom, which means the upgoing aileron can deflect more than the downgoing one without stalling.  The benefit of that is reduced adverse yaw.

Smaller wing = smaller aileron = less force to move = higher speed for max roll