Author Topic: Why corner velocity is important (Read 1158 times)

Widewing · « **on:** August 20, 2003, 10:53:14 PM »

One of the denizens of the rec.aviation.military newsgroup is a fellow named Vlado Lenoch. Vlado is a warbird owner and his collection includes a P-51D (Moonbeam McSwine) and a T-33.

We were discussing a post that referred to a Spitfire XII executing a split-S from 1,000 feet. I didn't believe it and tested the AH SpitV SpitIX and SpitXIV. None could come close to pulling a split-S from that height. Vlado mentioned that he needs at least 2,000 feet for that maneuver in his Mustang to ensure adequate margins of safety. So, with Vlado's info that the P-51's corner velocity was 270 mph, back I went to AH (offline) for some testing.

I started testing at 200 mph, and concluded with the 270 mph corner speed.

According to Vlado; "Maximum G limit AND minimum TAS provide minimum radius "loops". The maximum G is the structural
limit and the minimum speed at which the maximum G could be obtained is the target TAS. This target TAS sometimes requires the addition or subtraction of power to obtain and or sustain. In the Mustang it is 270 mph."

I filmed the exercise and reviewed it later. As you will see by the test results, the tightest radius was obtained at the highest speed.

Here's what I tried. I took a P-51D with 25% fuel. I climbed to 2,000 feet and adjusted throttle till airspeed was stable. After rolling inverted I pulled off the power and pulled through the half-loop. Testing was done over water so that I had a consistant and reasonably level surface below.

All airspeeds where verified before pulling through.

At 200 mph TAS, I cleared the water by 8 feet! Visual estimate via film. I was less than a single prop blade length off the water.

At 250 mph TAS, I cleared the water by about 85 feet. Better but still little margin.

At 270 mph TAS, I cleared the water by about 220 feet. Much better.. plenty of room.

Unlike the first two, I was able to pull 6G+ at 270 mph (was blacking out).

Tonight in the MA, some guy was whining endlessly about having his Spitfire Mk.XIV out-turned by a P-51B. In all likelihood, the fight occurred right in the Mustang's sweet spot between 250 and 300 mph, where it can hang with just about anything long enough to get a killing shot in.

So, you Mustang guys who don't already know, keep it near corner velocity and you will find yourself having more opportunities and surviving more fights with the so-called turnfighters.

My regards,

Widewing

Tarmac · « **Reply #1 on:** August 20, 2003, 11:14:49 PM »

Good stuff.

So how do you figure out the ideal corner velocity in other planes?

john9001 · « **Reply #2 on:** August 20, 2003, 11:15:11 PM »

all you spity an lala drivers , pay no attention to widewing

Toad · « **Reply #3 on:** August 20, 2003, 11:28:43 PM »

You use a chart like this one for each aircraft.

Unless you can get someone to post them or or tell you.

Or you can also do a LOT of semi-accurate offline testing.

Widewing · « **Reply #4 on:** August 21, 2003, 12:03:42 AM »

Let's post one with greater relevancy:

Notice that between 260 and 320 mph the P-51D can turn with the Spit IX.

My regards,

Widewing

Steve · « **Reply #5 on:** August 21, 2003, 01:16:23 AM »

Wide, Shhhhhhhhhhhhhhhh! I've mentioned the pony's sweet spot in another thread, although relative to other plane's turning abilities at speeds, I'd rate it another 50 MPH higher. It's what allows me to get such great snap shot opportunities at spits and other turners..you know the routine: get 'em fast, watch them break turn, chew off pieces of their plane with the.50's in the snap, look for the next guy. Sweeeeeeeeeeeeeeeeeet!

Mino · « **Reply #6 on:** August 21, 2003, 02:30:27 AM »

Widewing;

Where you get those charts?

Thanks;

Load · « **Reply #7 on:** August 21, 2003, 03:05:50 AM »

WHOAOooooooo

Excellent POST !!! Thank you

I remember in and old sim everything changed when I discovered the CV of F4uD, you could outturn everything!!

In that sim CV for F4u was 190 mph with 1 notch of flaps!!!!

In the chart above......have you consider that 1 notch of flaps could give you even a better turn???

And a request...Plzzzzz CV for 190-D9!!!

Salute

Gixer · « **Reply #8 on:** August 21, 2003, 03:25:49 AM »

So if you were unable to pull off your tests in a game you wouldn't believe it could be possible in real life?

Being good or what ever you may be able to preform in a flight sim means squat really. No matter how good you may think the flight model may be.

~~...-Gixer~~

beet1e · « **Reply #9 on:** August 21, 2003, 03:37:09 AM »

Right. I'll be the first one to ask: What exactly IS "corner speed"? The only times I've heard it mentioned have been in FlightSimdom. And those charts - eeek - those charts... I never could work anything out using those damn things - preferred an aviation calculator. What are these charts telling us?

Load · « **Reply #10 on:** August 21, 2003, 04:20:12 AM »

Corner speed is the velocity at where you achieve your maximum turn ratio in degrees per second.

As diagram shows..P-51 will get its best turn at 260 mph. It means that as you are driving faster or slower than that you are turning worse.

As you go faster than that your turn radious gets larger and you spend more time to turn the same degrees. As you get slower...you are losing drag and you cant pull so hard to achieve those dps.

So, if you mantain your P51 at 260 mph and you turn with a spit at 300, you can out turn him and kill him, as you get faster or slower the spit will begin to gain dps on you.

Salute

Kosk

Load · « **Reply #11 on:** August 21, 2003, 04:24:05 AM »

Ahhh forgot it.....

I am pretty sure that with flaps you could have a chance of getting a better CV.

And, plzzzzzzzz..190-D9 CV now!!!!

Kosk

beet1e · « **Reply #12 on:** August 21, 2003, 04:49:41 AM »

Thanks, Load. That makes sense. I remember all that business about tracing a line on the chart until it intersected another line, and then moving across to find the next line etc.

How I ever pased the PPL writtens - well, I just had to make sure I got all the other questions right! The blue line drops back after corner speed, but then comes down vertical - why is that? And the charts seem to show two corner speeds - is that for WEP and nonWEP? What is the meaning of the altitudes that are shown?

Load · « **Reply #13 on:** August 21, 2003, 05:24:39 AM »

Well, the line drops vertically because structure cant hold more than 6gs turns over 350 mph....mmmmm I think.

Bottom line is the speed for sustained turns.

And the feet are not height......they are turn radious.

Salute..

PLZ 190-D9 CHART!!!!

GScholz · « **Reply #14 on:** August 21, 2003, 05:45:21 AM »

Quote

Originally posted by Load
Ang you got me..I dont know why there are 2 lines. From the draw I suggest it is turn at 6gs and the other 1 means stall speed...but some1 should confirm.

The 6g lines are the max instantaneous turn rate, the lower lines are max sustained turn rate. At 225 mph the Pony can achieve a 6g turn for a brief moment as speed will drop, however it can sustain a 3g turn as the chart shows without losing speed.

EDIT: Sorry, I was looking at the SPIT IX lines, not the Pony's.