Turn rate and radius questions

[F4UDOA]

If an aircraft has a 3G stall speed at it's gross weight of 160MPH and another has a 3G stall of 200MPH which one should be able to complete a 360 degree turn faster?

I did 3 360 degree turns then divided by 3 to get an average.

Tested the F4U-1D vrs the FW190A5 and found that they are virtually identical both with 75% fuelin both and a heavy load for weapons in the 190.

The F4U-1D = 20.8
The FW190A5= 21.06

How is this possible?

Does anyone the FW190 3G stall numbers? Annecdotally from Navy test the F4U could get on the tailof the 190 in 1.5 turns.

[TimRas]

Turning rate = Acceleration / Speed.

So if the acceleration ("g") is the same, the plane with lower speed has better turn rate.

Turning radius = Speed squared / Acceleration.

Note that from the curves you posted  you can calculate instantaneous turn rate (which is mainly related to wing loading). What you actually measured is sustained turn rate (where the thrust/weight -ratio is more important). Note that the curves are applicable to both F4U-1 and F4U-4 (same wing loading with same gross weight but very different power loading).

[Badboy]

Originally posted by F4UDOA
If an aircraft has a 3G stall speed at it's gross weight of 160MPH and another has a 3G stall of 200MPH which one should be able to complete a 360 degree turn faster?

I did 3 360 degree turns then divided by 3 to get an average.

Tested the F4U-1D vrs the FW190A5 and found that they are virtually identical both with 75% fuelin both and a heavy load for weapons in the 190.

The F4U-1D = 20.8
The FW190A5= 21.06

How is this possible?

Does anyone the FW190 3G stall numbers? Annecdotally from Navy test the F4U could get on the tailof the 190 in 1.5 turns.

Hi F4UDOA

Here is an Aces High Energy Maneuverability diagram for the F4U-1D overlaid with the Fw190-A5.



You can see that the sustained turn rates are very close to each other with a slight edge to the F4U. You will also notice that the F4U-1D can also achieve a slightly smaller turn radius than the Fw190-A5 when they are both fighting on the edge of the envelope. The diagram also shows that the F4U-1D has an advantage in instantaneous and sustained turns at all speeds below corner velocity, but the advantage is only small.

You can use the that diagram to read off the 3g stall speed for the Aces High aircraft by following that line of constant g until it cuts the stall limit curve on the envelope for the each aircraft.

To answer your original question, the aircraft with the lower stall speed should be able to complete its turn more quickly, because it will have a higher instantaneous turn rate, speed for speed, than the other one. However, you have to be careful in general terms, because if the aircraft in question has a very poor sustained turn, it may lose its energy very quickly then be out turned by an aircraft with a higher stall speed.

That's why energy managment is considered to be such a valuable skill in aircombat, and also why you need to consider instantaneous and sustained turning ability together... that's why EM diagrams are so useful

Hope that helps

Badboy

[Badboy]

F4UDOA,

Just to mention that the chart you posted gives acceleration limits, but the equivalent limit in the charts I produce is based on the 6g pilot physiological limit modelled by blackouts in Aces High. I use that 6g limit on the basis that if you lose sight, you lose the fight, so most folk don't max perform beyond 6g often, even though you sometimes can.

If you want to compare the 7g values, the 7g curve is shown on my diagram (but not noted) so you can still project a 7g corner speed if you want to.

Hope that helps.

Badboy

[F4UDOA]

Badboy,

Thanks for responding to my question.

I think the main problem I have in AH is some historic issues such as that the 1G stall for the F4U is just too high and some A/C like the FW190A5 is just to low. The 1G stall I have for the FW190A5 with a full load is 110MPH and the 1G stall for the F4U-1D at 12,000LBS is 100MPH both gear and flaps up. As you reduce weight the stall should come down but they seem to stay to high relative to weight.

I guess my main question should be if the F4U-1D has a three 3G stall at 160MPH and the 190 has an estimated historic 3G stall of 180MPH the why can't the F4U fly a 160MPH circle at max G and clearly turn inside the 190?

BTW, in the Navy comparison between these two same A/C the F4U could from a head to head merge be on the tail of the 190A5 in 1 turn.

TimRas,

Your testing really sparked my question.

It seems to me that their is to much parity in the abilitys of some A/C in AH for what reason I do not know.

Does anyone have FW190 stall test?

[F4UDOA]

Did some more off line testing.

In low 2000RPM 20"MAP reduced speed and attempted some low speed intentaneous turns. Could not get 2G's at chart indicated 126MPH. In fact I couldn't get two G's at 135MPH.

Does anyone have the same chart for other A/C?

I have the P-51D and P-38L. The P-51D list is at 8,000LBS so it harder to tell but the P-38L is definitely high as well.

[dtango]

F4UDOA:

Instantaneous vs. sustained turn performance- they are not the same things.  There isn't a simple linear relationship between the two.

Instantaneous turn performance is essentially the maximum turn performance you can get at a given point and velocity in time.  

Once you start holding that turn for any amount of time it becomes a sustained turn.  In sustained turns all sorts of other consequences of aerdoynamics emerge such as energy bleed from the drag induced by the turn etc.

The 3g limits you noted are instantaneous turn performance figures.
 
The 360 degree turns you did represent sustained turn performance.

Just because an a/c has a better instantaneous turn performance vs. another you shouldn't expect that it translates to a better sustained turn performance.  There is no linear relationship between the two.  Another one of those tricky things with aerodynamics.

Tango, XO
412th FS Braunco Mustangs

[Zigrat]

neat-o a v-n diagram. it is for sustained performance, don't usually see that but nice info. thing that jumps out at me is that like f4u says the 1g stall speeds from badboy's chart and f4us don't match at all.

[F4UDOA]

CC Zig,

I have had an ongoing conversation with HT about stall speeds. There are two others that are off for sure. The F6F and P-38.

Does anyone have these diagrams or similar for the 190 series or any other bird?

DTango,

I am aware that they are not the same. But if you try to attain those instentanious figures in AH it is impossible at that weight.

[Zigrat]

one thing you shoudl consider is the conversion from badboys chart of MPH (TAS) and f4u's chart of KPH (IAS) there will definitely be substantial differences, and I am slightly confused by the 10k and below thing because there is a big diff between 10k and the deck in terms of ias-tas conversion

[F4UDOA]

Zigrat,

I have the CAS conversion table for the F4U-1.

At 130Knots the error is 2Knots, at 140Knots the error is +3Knots.

So your looking at 164.5MPH instead of 161MPH. Not really very much to scream about. And when you consider the 140Knots is for 10K you have to figure that number is lower at sea level.

I just received a large document from the UK on the test of F4U's that the Brits had in WW2. In other sections of the report it mentions the 4G stall occuring at between 140knts and 150Knts at approx 11,700LBS.

[dtango]

F4UDOA wrote:
I guess my main question should be if the F4U-1D has a three 3G stall at 160MPH and the 190 has an estimated historic 3G stall of 180MPH the why can't the F4U fly a 160MPH circle at max G and clearly turn inside the 190?

Your question was this no?  You're assuming the F4U's instantaneous turn rate advantage means it should have the same advantage in sustained turn rate.  There's no linear relationship between the two.

The lift-limit curve of Badboy's EM chart is based on knowing the stall speed of the AH a/c in level flight for the given alt and weight config.    It's governed by:

V = Vstall * sqrt (g-load)

It's really hard to flight test against the lift-limit curve because below corner velocity the g-load is determined by the angle of bank of your turn that is less than the maximum bank angle you can achieve of ~80 degrees.  Too much bank (probably above 50-60 degrees somewhere) and you've already exceeded the lift capability of the wing at that speed.  You also need to make sure you have combat trim off as well.

Tango, XO
412th FS Braunco Mustangs

[F4UDOA]

Dtango,

Let me re-phrase my question.

The F4U-1D has a 3G stall of approx. 160MPH and the FW190A5 3G stall of Approx 190MPH.

Why is it not possible for the F4U to sustain a 3G turn of say 170MPH (10MPH above it's instentanious turn rate) and simply turn well inside the 190?

This the outcome of the Navy test.

It is also the outcome of Zigrats spreadsheet:)

It is on my webpage here

http://mywebpages.comcast.net/markw4/FW190A5.xls

[F4UDOA]

BTW Zig,

Are the EM diagrams sustained or instantanious?

One thing that your spreadsheet doesn't take into account is this.

The 1G stall speed for the F4U is based on 18"MAP and low RPM. Increasing power increases prop wash and Cl max.

At full or partial power the 3G stall speed Cl max should be much higher lowering accelerated stall speeds.

Sorry to pic Knits. Just read that myself.

Do you mind me putting your work on my Webpage? I gave you credit

[TimRas]

Originally posted by F4UDOA

BTW, in the Navy comparison between these two same A/C the F4U could from a head to head merge be on the tail of the 190A5 in 1 turn.

As 1 turn takes some 20 secs, it means that if F4U gained 180 degs in that time, it has about 9dps advantage over A5. Even Spitfire cannot do that. I have great doubts about "anecdotal evidence" if we don't know exact circumstances of these tests.