Cornering Speed Chart Methodology

[dosequis]

I am thinking of putting together a chart that shows optimal cornering speed per plane at different speeds at different altitudes.

The key pretty much to all of AH is how fast a plane can turn at a given speed at a given alt.

I think a chart with altitude in the Y-axis, and speed in the X-axis in true airspeed with different color lines for each plane is the way to go here. But then I thought a lot of the lines would overlap and be hard to distinguish. So I am asking how should this data be sampled and represented.

Any comments?

XX

[wells]

Corner speed will always be the same in the cockpit.  It's a function of G-limit and stall speed.  If you know you blackout at say 6G's, and you know the stall speed to be 100 mph, the corner speed is then

sqrt(g-limit) * stall speed = 245 mph (in this case)

[Jekyll]

Since stall speed increases with altitude, would you not need to plot corner speed in indicated airspeed?

------------------
C.O. Phoenix Squadron
http://www.users.bigpond.net.au/phoenix
Aces High Training Corps

[Andy Bush]

Well...let's take this one by one!

>>I am thinking of putting together a chart that shows optimal cornering speed<<

Optimal is sorta open to definition. In most cases, 'optimal' means 'sustained'. Since few aircraft have a Corner Velocity that is sustainable (no WW2 aircraft do), then your graph will have to deal with sustained speeds only.

>>So I am asking how should this data be sampled and represented.<<

Rather han a single graph, perhaps a chart will be easier...with best performance on top.

>>Corner speed will always be the same in the cockpit.<<

This is only true of a specific gross weight, altitude, and configuration.

>>It's a function of G-limit and stall speed.<<

Yes, in a manner of speaking. CV is an academic term...it is seldom attained in RL and in air combat has only marginal relevance. By definition it is the minimum speed that max Gs can be pulled instantaneously for the given conditions of weight, altitude, and configuration.

>>if you know you blackout at say 6G's...<<

CV has nothing to do with blackout Gs. It is an academic term best suited in comparing relative maximum performance between different aircraft. It is only one of a number of comparative terms used to define fighter performance.

>>you know the stall speed to be 100 mph, the corner speed is then sqrt(g-limit) * stall speed = 245 mph (in this case)<<

I gotta admit I have never seen this equation before...but it seems good for the a/c that I flew.

>>Since stall speed increases with altitude, would you not need to plot corner speed in indicated airspeed?<<

CV is usually plotted on a diagram that shows both TAS and IAS. You are correct that stall speed increases with altitude...but that's TAS, not IAS.

Guys, people put too much stock in CV as a panacea for good BFM. It has its place as a measure of comparative performance, but as a tool to be used in an actual engagement, it has a limited value. The max sustainable G is a much more valuable number to know and use.

Andy
 

[miko2d]

 With constant speed, the more G, the better is your turn.
 With constant G the slower you go, the better is your turn.

 Contrary to what Wells says, you do not use the stall speed for calculations, because there is no plane that can pull 6G at stall speed.
 Stall speed can give you best turn radius (feet), but not turn rate (degrees per second or seconds per 360% turn).

 Your corner speed is the slowest speed at which you can pull critical Gs (assume 6).
 So just experiment (decending turn at full stick deflection) at which speed your G-meter reaches 6. That is your corner speed.

miko--

[wells]

Miko, I never meant that 6G's could be pulled at stall speed, but stall speed is relevant because that's your maximum lift coefficient.  Then G's are a simple function of speed as you said.  If you double the speed, you quadruple the lift/G force.  If a plane stalls at 100 mph (1G), you can pull 4G's at 200 mph, 9G's at 300 mph etc...get it?

[Andy Bush]

miko

No, no, and no. Please...unless you have some academic qualification in this area, my suggestion is that you remain on the sidelines.

>>because there is no plane that can pull 6G at stall speed.<<

Absolutely false. You are thinking one G stall speed. An aircraft stalls at a given angle of attack, not airspeed...depending on G, this angle can be reached at speeds greater than the one G stall speed.

 
>>Stall speed can give you best turn radius (feet), but not turn rate (degrees per second or seconds per 360% turn)<<

In the context of Corner Velocity, this is not true. CV is the max turn rate for the a/c, by definition, and occurs at the stall point at max G.

>>So just experiment (decending turn at full stick deflection) at which speed your G-meter reaches 6. That is your corner speed<<

No. First of all, the academic description of CV usually assumes level flight. This is because CV is a function of radial G, not cockpit G...radial G varies with your bank angle. To minimize confusion, the idea is to take radial G out of the consideration by turning level...ie, radial G equals cockpit G.

In your descent, you are getting an advantage from your lift vector being oriented below the horizon...ie your radial g is greater than it would be in level flight. A larger radial G value means a higher turn rate...your CV reference is no longer valid because one of the two parameters for CV, radial G (the other being TAS) is skewed.

I apologize for being this blunt...but you are making assertions that are not correct. The other readers of these posts might take your words to be gospel, and that would be unfair to them.

This a nifty hobby that we have...but the foundation of BFM is rooted in considerable academic detail. Unfortunately, this level of detail is not provided in the typical sim manual or on-line Help doc. The average simmer is best advised to turn and burn to his heart's content...but leave the instruction to those better qualified.

Andy

 

[Zigrat]

I have been for some time been thinking of making a web page that explains the basics of flight to perople. I am certainly no expert (i will be a senior in Aerospace engineering undergrad this coming school year) but I have picked up the basics of aerospace design concepts   Any of you other guys like wells or funked interested in doing such a thing? It wouldn't be so much like andy's articles but would deal a little more with mechanics of flight, stuff like the different kinds of drag etcera. I myself am very weak when it comes to knowledge of engines and power when some of you guys talk about all this turbo supercharge water injectioion stuff so i would like to learn from it as well  I mean i learned about the otto and brayton cycles and all that but in class they dont really teach you actually how to build it, just the theoreticals  

[miko2d]

 Andy,

Stall speed:
 I am definitely lacking quaifications, that is why I am using Shaw's definition of a corner velocity.

 If you are using the "stall speed" as "a speed at which a stall could occur", which could mean any speed, then "stall speed" does not mean anything.
 It has been my impression that a term Stall Speed is a technical term specifically meaning "a speed at which lift is lost in level flight" or something like that.
 In all the magazines they list the stall speed with flaps retracted and the stall speed with the flaps extended as a property of an airplane, not mentioning anything about pulling Gs. I guess they have confused me... May be you should write them a letter and correct their use of "stall speed".
 If you have seen any mention of a "stall speed" meaning anything other then "one G stall speed" anywhere other then in your posts, I would appreciate a reference.

 I do not have my Shaw with me now in my office, so I cannot quote, but there is nothing academic in his definition of the simple terms and knowledge of a basic geometry is sufficient to understand his book.
 We are not talking about why the lift is lost - that would involve the properties of the airfol and other sophisticated matters.

 Your statement that "An aircraft stalls at a given angle of attack, not airspeed" cannot possibly be true. At the same angle of attack a plane can stall because it is flying too slow - regular stall, or too fast - accelerated stall, but be perfectly flyable in between. Speed definitely have something to do with that, unless you are in a helicopter   - that one flies because it is too ugly and the Earth repells them, right?

Regards,
miko--

[Andy Bush]

miko

This situation really isn't fair to you...and the many other sim fans that have had a similar experience.

Understanding air combat fundamentals is a bit more than looking thru Shaw's book or a couple of magazine articles. I sympathize with you...you like this hobby. Your enthusiasm takes you beyond simple sim flying...you want to know and understand what its 'really like'. More power to you. Enthusiasm is what keeps our hobby alive.

But please don't let yourself get led astray in this enthusiasm. It's not necessary to be an aero major to appreciate the sim.

You asked this question:

>>If you have seen any mention of a "stall speed" meaning anything other then "one G stall speed" anywhere other then in your posts, I would appreciate a reference.<<

Here is a reference...an excerpted figure from the USAF P-51 pilot operating manual:

 

Note the different speeds for the stall at varying bank angles. If you understand why, then you are on the way to understanding the answer to your question.

Andy

[Andy Bush]

miko

This situation really isn't fair to you...and the many other sim fans that have had a similar experience.

Understanding air combat fundamentals is a bit more than looking thru Shaw's book or a couple of magazine articles. I sympathize with you...you like this hobby. Your enthusiasm takes you beyond simple sim flying...you want to know and understand what its 'really like'. More power to you. Enthusiasm is what keeps our hobby alive.

But please don't let yourself get led astray in this enthusiasm. It's not necessary to be an aero major to appreciate the sim.

You asked this question:

>>If you have seen any mention of a "stall speed" meaning anything other then "one G stall speed" anywhere other then in your posts, I would appreciate a reference.<<

Here is a reference...an excerpted figure from the USAF P-51 pilot operating manual:

 

Note the different speeds for the stall at varying bank angles. If you understand why, then you are on the way to understanding the answer to your question.

Andy

[miko2d]

 

Originally posted by Andy Bush:

You asked this question:

>>If you have seen any mention of a "stall speed" meaning anything other then "one G stall speed" anywhere other then in your posts, I would appreciate a reference.<<

Here is a reference...an excerpted figure from the USAF P-51 pilot operating manual:

Andy

 Where did you get an impression that they are talking about anything other then 1 G flight?
 Do you assume that after banking a plane they are also pulling on a stick? It is not obvious from the charts.

 I concede that they use the term "stall speed"  meaning something other then "sustained speed in a level flight at which the wings lose lift". They use it as "speed at which stall occurs under certain conditions".
 They may not use the term right but it is clear from their context what they mean.

 It does not invalidate a term "Stall Speed" as a unique and specific characteristic of a plane. A plane could have more then one of them specified - clean, flaps out, flaps and gear out and maybe different fuel loads - 0%, 50% and 100%, but always a level flight.

 If you see a statement "Car X develops 200HP" or "car X has 160 mph top speed" you could argue that a car develops variable power depending on how hard you press the pedal, or that it has different top speed depending on the weight and incline and you would be corect.
 Still, when we layman speak of those things we assume certain test conditions, like fully depressed pedal and 5600 rpm for power and flat paved road and zero headwind for speed.

miko--

[Andy Bush]

miko

Quit before you get further behind. Your lack of understanding of basic aero is appalling.

You missed the point of the diagram.

Andy