min. radius vs max. rate turns

[chicken6]

Entering a max rate turn, we teach full power and pull to the start of the stall warning or just before the start of the buffet. This gives the best rate of turn by providing the most lifting force you can get from the wing at the time (the reason for the stall warning), without the induced drag slowing you down too much (the reason for the power).

Questions.

1) Does adding flap increase the rate? It certainly gives more lift, but the drag increase would, I think, nullify or override any gains there, and you wouldn't be able to roll in as far, and not pull as hard.

2) Does an increase in power available increase the rate if you are pulling at the stall anyway? As far as I can tell it would have to increase the lift from the wings...

1b) What about effect of flap on radius? I think it would decrease the radius simply because of the resulting slower speed.

3) I think in the USA you teach min. radius turns, what's the recipe for one of those?

4) How does all this fit into the v-g diagram?

From a "studying too hard" instructor (me). Got too many words in my head at the moment! I could read "Aerodynamics for Naval Aviators" again, but it wouldn't make any more sense even though it is a GOOD book :frown:.


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Confident, cocky, lazy, dead.

[Genghis the Engineer]

Please take my comments as those of an engineer who has done some performance work, not of a QFI...


1) Does adding flap increase the rate? It certainly gives more lift, but the drag increase would, I think, nullify or override any gains there, and you wouldn't be able to roll in as far, and not pull as hard.

> Turn rate and radius in a balanced level turn are functions of speed and g, g is a function of bank angle. If the flaps allow you to turn slower or bank more without stalling, they may help. If you turn at the same bank angle and speed - it'll make no difference.

2) Does an increase in power available increase the rate if you are pulling at the stall anyway? As far as I can tell it would have to increase the lift from the wings...

> Best turning performance may be limited by either lift or thrust. If you can't pull any more g anyway, thrust won't help. If there is more g in the envelope, thrust will allow you to keep speed on and use it.

1b) What about effect of flap on radius? I think it would decrease the radius simply because of the resulting slower speed.

> at the same g, yes.

3) I think in the USA you teach min. radius turns, what's the recipe for one of those?

> Do the sums.... Basic O'level physics will do it.

4) How does all this fit into the v-g diagram?

> V-N diagram if you don't mind. At the point of stall, you are somewhere on the curved section at 9 to 12 O'clock on the diagram.

From a "studying too hard" instructor (me). Got too many words in my head at the moment! I could read "Aerodynamics for Naval Aviators" again, but it wouldn't make any more sense even though it is a GOOD book :frown:.

> Never met it, why not try getting hold of Def-Stand 00-123 "Flying", which is the RAF equivalent.

G

[Smooth Torquer]

Chicken6 me'old, you take me back to the depths of my CFS groundschool a few moons ago. I will do my best to answer your questions in simple terms as that is all I work in.

First the requirements of a max rate turn are;

1. C/L max, i.e highest possible AOA without stalling which means the light buffet.
2. Max AoB, the more bank, the higher your rate of turn.
3. Full power, more power means more speed, more speed means more g for any given AOA, more g means smaller radius / higher rate of turn.
4. Low altitude, the lower you are the more power your engine will produce and the lower you are the thicker the air is hence more lift for a given AOA. Think about the equation for lift, Lift = 1/2*Rho*Vsquared*Cl*Wing area.

To your questions;

1. I can't remember off hand what flap will do to the rate but it is really irrelevent as most a/c dont have flaps stressed to more than 2g and trying it with flap will simply overstress the a/c either in g or in IAS.

2. See point 3 above.

1b. Radius is affected by g and IAS at the time which often vary as the a/c slows down. Also radius is not important, rate is. More rate means you can turn faster (more degrees/sec) than the other guy so you can get on his tail and not vice versa. Guns Guns Guns!!!!!!!!

3. Gengis answered that one.

4. Again Gengis speaks the truth. Basically its the top of the hill without going too far and down the other side.

Hope this has helped you out and Merry Christmas all. My head has just exploded. Principles of Flight and hangover dont mix.

Doh!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[chicken6]

Aaaaaaahhhh

Deep sigh of relief! Now I know I was getting confused, thanks for clearing it up. Too many words in my head!

Genghis - I don't mind if you're an engineer, pilot or kayaking instructor or librarian or whatever, thou Speakest the Truth and it is Good.

To summarise:
min. radius = max g and max AOB, if you can extend flap and pull the same g then do so.

Flap will reduce radius at the same g as no flap; only g (directly related to AOB for a level turn) will affect rate.

Rate is affected by g and the limits of the v-n diagram. If you are not limited by g (stress) i.e. you are stalling before the max g limit, excess power will enable you to pull more, therefore rate increases.

*Another deep sigh*

Feels good to clarify things.

Smooth Torquer

You might be able to help, I've noticed in Combat FlightSim that you can line the other guy up quicker if you use a grossly uncoordinated turn using mainly rudder to yaw around quicker than a coordinated turn, why didn't they make the aeroplane able to turn tighter? (I'm talking Spitfire, Mustang etc.) GUNS GUNS GUNS!!!!! I like it!

Safe flying

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Confident, cocky, lazy, dead.

[grade_3]

G'day,

When writing my own lesson plans for Max Rate / Min Radius turns I found using the formulas to calculate radius and rate useful to demonstrate how changes in AoB and Speed effect the performance. Kinda like using the Lift formula for the first few Ab-initio briefings.

(pls excuse odd formatting)

Radius (ft) = (V^2) / (11.26 tan AoB)

Rate (°/sec) = (1091 tan AoB) / V

where V = TAS in Knots
and AoB = Angle of Bank in degrees.


From these you can quite easily see the performance changes Ghenghis and Smooth Tourquer described above.

HTH

Cheers,


Grade 3

[grade_3]

Forgot to respond to this in my other post, guess that's what the holidays do... ;)

<font face="Verdana, Arial, Helvetica" size="2">You might be able to help, I've noticed in Combat FlightSim that you can line the other guy up quicker if you use a grossly uncoordinated turn using mainly rudder to yaw around quicker than a coordinated turn, why didn't they make the aeroplane able to turn tighter? (I'm talking Spitfire, Mustang etc.) GUNS GUNS GUNS!!!!! I like it!</font>

Primarily, forget the BS about MS flight sims being "As Real As It Gets" - they're most definately not. For something for "meaty" in the flight modelling department, have a look at Aces High (http://www.hitechcreations.com) Free download etc. etc. and after flying this you'll never touch CFS again :)

Cheers,

Grade 3

[John Farley]

Chicken

I’m glad you are happy now with the basic theory of turn performance.

But before you set yourself up to win beer from others who may not have got it sorted, stick a caveat in that you are talking low speed low power aircraft.

Please be aware that this basic theory diverges from reality as speed increases. At 150 kts you would be pushed to measure the difference between theory and practice. By 200 kts if you were good enough you could show the difference, by 300 kts the difference will be so great as to make you wonder what happened to the theory.

The reason is of course that air is not incompressible (as we always assume it is for basic aero stuff) At what speed (or mach number) we must start to modify our ideas is a rather variable feast as some topics are more affected than others. Sticking with our turning topic, a good old fashioned straight winged jet like the Meteor would DEMONSTRATE that the min radius turn was achieved at circa 240 kts but the max rate at circa 350 kts.

This difference between theory and practice was the result of the available CL max reducing as compressibility effects came into play. Hardly Concorde speeds eh?

Never forget the value of min radius compared with max rate when you are trying to miss an obstacle – like the ground at the bottom of a loop…..or a pylon at 12 o/c on a nav ex.

Sorry to go on a bit but the grandchildren were snowed in so I had the afternoon off.

JF

[Genghis the Engineer]

What I would like to know is how Chicken knows that I used to be a kayaking instructor?

[chicken6]

Grade_3

When I first started instructing I used to put in so many formulae it looked like a 3rd year physics paper. Then I started dispensing altogether with certain formulae and people started understanding me, coming back, and I got paid more! Now I'm figuring out which ones to bring back in and how, thanks for the simple ones. AS for Aces High, I'll get onto it after my upgrade test next week! Bit busy (don't ask "why are you here then", this is research ;))

John Farley

I'll cross that bridge once I can see it! I want to get this stuff absolutely 110% right first.

Genghis

Are you serious? You didn't put a smiley in...it was an off the wall occupation that I once thought of doing until I realised how little I enjoyed being upside down under water.

Safe flying all, Happy New Year!



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Confident, cocky, lazy, dead.

[Genghis the Engineer]

Utterly, I still have four boats in the Garage, although I only get them out once or twice a year these days. I used to teach, mainly whitewater kayak - slalom skills and suchlike. I pretty much gave up after I bought my first aeroplane.

Being upside down underwater isn't that bad; it's staying there that's bad.

G