Quickest time around a closed course ?

[bdk]

OK, lets try another basic course in aerodynamics. Hopefully I've got this right since it has been so long since I have done any of this. If anyone sees any errors by all means speak up!

Lift = 1/2 air density (rho) * velocity squared (in ft/sec) * wing area (sqft) * the coefficient of lift (textbook stuff).

If you assume the lift is an 8,000# Mustang (probably a bit heavy) pulling 6 Gs, you have 48,000# of lift resulting in a racing turn.

At 500 MPH and 80 degrees F at Stead Field's elevation, you find that a coefficient of lift of .431 results with a stock Mustang's 235 sqft wing area.

I couldn't find a graph showing the lift to drag ratio of the NACA 45-100 airfoil section (I've lost my copy of "Theory of Wing Sections"), but a similar laminar wing I was able to find showed that was well within the drag bucket. If 35 sqft is removed by clipping the wings (a guess as to the area of the wing extensions), the coefficient of lift would be at .506, near the edge of the drag bucket. At 6000# that clipped wing Mustang is back down to a coefficient of lift of .380, once again well within the drag bucket.

My conclusion is that at 6 Gs at those speeds, a Mustang will see an imperceptible increase in drag because the angle of attack to obtain 6 Gs is still so low (Dudley's corner speed graph evidence would support this I think). You probably lose more drag from the deflection of the control surfaces than you do from the G-forces.

If someone can find an online resource or can post a scan of the L/D graph for that airfoil section, we can get a more precise calculation of the drag. In any case, the drag increase would still be very small.

Any anecdotal evidence from a race pilot would be appreciated.

[bdk]

Why don't you see any P-47s racing ?

Not enough around to cut up? It would be a real goer with an R-4360! The SuperBolt!

[warbird1]

Why don't you see any P-47s racing ?

My guess would be for the following reasons:

1) It's too rare.

2) It's too big and heavy and not known for having a tight turn radius.


If I'm not mistaken, I believe the CAF brought one of their P-47's to Reno back sometime in the mid 70's. I seem to recall that Lefty either brought it up there and raced it, or was part of the contingent that did. My ancient CAF history is not the best, perhaps Gary Austin can fill in the details.

[warbird1]

If someone can find an online resource or can post a scan of the L/D graph for that airfoil section, we can get a more precise calculation of the drag. In any case, the drag increase would still be very small.

Any anecdotal evidence from a race pilot would be appreciated.

FWIW, John Penny, the pilot of Rare Bear, wrote this a while back on another aviation forum on his opinion concerning the original question in relation to "G" loading, turn radius, optimal race course profiles, etc.:

Your short question has several parts to the answer, some with lengthy portions.

The short answer is: it depends.

You are right that a lower aspect ratio will typically result in more energy loss anytime Gs are applied in a turn, be it in combat maneuvering or around a pylon. But reducing wing span also results in less wetted area and usually results in a lower overall drag coefficient allowing better speed during the “unloaded” portions of the racecourse. In some cases, the amount of span reduction is driven more by the geometry of the existing wing construction, available aileron hinge locations, etc., than by rigorous aerodynamic analysis.

Course design at Reno also dictates, at higher course speeds, G loading at the pylons that may otherwise not be optimal for the actual layout of the course. When coming off outer six, a more efficient line would take the higher speed racers outside the west deadline. Off of pylons one and two if a very healthy level of G is not maintained, one runs the very real risk of violating the east deadline.

The above being said, there is also a tradeoff between, flying a line that results in the lowest energy bleed that is geometrically much longer, and a much shorter, tighter course that incurs higher energy bleed when rounding the pylons. Again, the ability to strike the proper balance is sometimes constrained by the west, south, and east deadlines that define the outer limits of the racecourse. When Jimmy Doolittle broke the “250 mph barrier” at Cleveland in 1932, film clips show him flying a very high, very loose course line that allowed a minimal energy bleed. He was a magician at the controls of the “Gee-Bee”.

Another influence in energy bleed is the airfoil cross-section. The sharper radius of the leading edge of the P-51 results in a higher drag rise at the angles of attack reached in the pylon turns, as opposed to the more round profile of the Bearcat, or a Corsair. But, the coefficient of drag of the P-51 airfoil is less than those others on the straight-aways.

Energy bleed will also depend on the efficiency of the propeller design and how close the helical tip Mach is to approaching the blades’ critical Mach number.

Then there is other racecourse traffic. Because of our safety rules in the Unlimited Division, we are usually constrained to make a pass outside or above the plane being passed. The line they are choosing to fly may have an impact on the line the passing aircraft has to fly during the pass, and the subsequent geometry of the line at an upcoming pylon turn.

So, because of course constraints, at the very high race speeds approaching 500 mph, it is very difficult to avoid G levels of four and a half to five and a half at various pylons. The course constraints hinder being able to fly an “optimal” G at some of the pylons.

To answer your original question – 10 to 20 KIAS.

“Bear” Driver

Regarding the last sentence there, the question is how much airspeed loss is there associated with the turns on the Reno Race couse. The answer is 10 to 20 KIAS.

[bdk]

Regarding the last sentence there, the question is how much airspeed loss is there associated with the turns on the Reno Race couse. The answer is 10 to 20 KIAS.

But that begs the question, what causes that?

One of the features of a laminar flow airfoil is the drag bucket, an area where small changes in the coefficient of lift have little to no drag impact. With the Bearcat's NACA 23000 series airfoil that drag bucket is not present (again, from memory). This means that a Bearcat would suffer more from drag rise under heavy G-loadings than would a Mustang.

Also not considered by the airfoil analysis is the impact of fuselage drag at a higher angle of attack (since it isn't as well stramlined) as well as the control surface deflections and the download on the horizontal stabilizer subtracting from the lift of the wing (Gary posted a photo of Rare Bear showing lower fuselage skin buckling that I attribute to this force). Furthermore, as I mentioned previously, the anecdotal evidence of Tsunami losing manifold pressure in turns from the design of the carburetor air inlet. All these things can add drag or cause a loss of thrust.

[aseanaero]

I got to do Reno and see (and hear) all this for myself !

I would imagine the pilots would be totally exhausted after a race , hard work physically and mentally

[RyanShort1]

Regarding the last sentence there, the question is how much airspeed loss is there associated with the turns on the Reno Race couse. The answer is 10 to 20 KIAS.

But that begs the question, what causes that?

Induced drag... ?

Ryan

[warbird1]

Regarding the last sentence there, the question is how much airspeed loss is there associated with the turns on the Reno Race couse. The answer is 10 to 20 KIAS.

But that begs the question, what causes that?

I assumed it was induced drag.

[RyanShort1]

Any time you are pulling G's, you have to increase the AOA - however slightly - and that moves a tiny bit of your horizontal component of lift in a slightly aftward vector... at 400 mph that could be just a small percent, but enough to cause a loss of airspeed as mentioned above. I got a really really good explanation of this the other day from the CFI I'm working with as I get ready for the CFI checkride.

Ryan

[Dudley Henriques]

Any time you are pulling G's, you have to increase the AOA - however slightly - and that moves a tiny bit of your horizontal component of lift in a slightly aftward vector... at 400 mph that could be just a small percent, but enough to cause a loss of airspeed as mentioned above. I got a really really good explanation of this the other day from the CFI I'm working with as I get ready for the CFI checkride.

Ryan

This is basically correct. It also depends on aspect ratio and most of all wingtip vortices. Low aspect ratio wings create more drag than high aspect ratio wings and low aspect ratio is common in fighters.
The more g you're pulling in the corner, the deeper into drag you are pulling the airplane and this is exactly what you don't want to do when max airspeed and optimum path through the corner is the optimum result.
If it was just a matter of radius and rate, flying a fighter hitting the airspeeds you have at Reno, you would most likely have to actually SLOW the airplane down from it's straightaway airspeed to meet it's corner velocity at the pylon.
Naturally in a race situation, this isn't the name of the game.
The key for a race pilot flying a fighter at these airspeeds on a closed course is to PLAN AHEAD! The trick is to know where you are on the course and where those closest to you are on the course.
With this in tow, the prime factor in rounding a pylon is to seek the path that gives you the SMOOTHEST line through; pulling as little g as possible doing it. You're also playing the vertical plane in these turns so energy management is extremely important in the mix.
If you had to put a single word on all of this, that word would be SMOOTH!
Dudley Henriques

[bdk]

Regarding the last sentence there, the question is how much airspeed loss is there associated with the turns on the Reno Race couse. The answer is 10 to 20 KIAS.

But that begs the question, what causes that?

I assumed it was induced drag.

I did too, until I did the calculations above. On a Mustang at least, an aircraft with a laminar flow airfoil and a pronounced drag bucket, it does not explain a significant loss in speed.

[steve dickey]

Yeah after a couple laps behind the BIG BOYS the "smooth" goes away and you fight the wake turbulance But some guys can stay low and stay away from all that messy air and stay "smooth"

[Dudley Henriques]

Yeah after a couple laps behind the BIG BOYS the "smooth" goes away and you fight the wake turbulance But some guys can stay low and stay away from all that messy air and stay "smooth"

This is part and parcel of the race equation as it applies to "smooth".
Avoiding that disturbed air is a lot of what makes the planning ahead that constitutes the essence of "smooth race technique", and you're absolutely right..........getting a prop fighter in behind that air can get REAL interesting! I've not raced at Reno, but I've been caught up in that kind of disturbed air more than once playing tag with a few Bearcats at full song down low in the marbles )
Dudley Henriques

[warbird1]

Regarding the last sentence there, the question is how much airspeed loss is there associated with the turns on the Reno Race couse. The answer is 10 to 20 KIAS.

But that begs the question, what causes that?

I assumed it was induced drag.

I did too, until I did the calculations above. On a Mustang at least, an aircraft with a laminar flow airfoil and a pronounced drag bucket, it does not explain a significant loss in speed.

What were your calculations based off of? Did you calculate them based off of 4 to 5 G's - which would be common around most of the pylon turns?

Also, notice that the 10 to 20 KIAS loss was for a Bearcat, not a Mustang. In addition, Rare Bear has been heavily modified, including some mods for the leading edge of the airfoil. So, anything published by NACA on the Bearcat's airfoil probably wouldn't be 100% accurate. Also, IIRC, the Bearcat does not have a laminar flow wing, so your Mustang calculations wouldn't apply in this case, I don't believe.

[bdk]

Regarding the last sentence there, the question is how much airspeed loss is there associated with the turns on the Reno Race couse. The answer is 10 to 20 KIAS.

But that begs the question, what causes that?

I assumed it was induced drag.

I did too, until I did the calculations above. On a Mustang at least, an aircraft with a laminar flow airfoil and a pronounced drag bucket, it does not explain a significant loss in speed.

What were your calculations based off of? Did you calculate them based off of 4 to 5 G's - which would be common around most of the pylon turns?

Also, notice that the 10 to 20 KIAS loss was for a Bearcat, not a Mustang. In addition, Rare Bear has been heavily modified, including some mods for the leading edge of the airfoil. So, anything published by NACA on the Bearcat's airfoil probably wouldn't be 100% accurate. Also, IIRC, the Bearcat does not have a laminar flow wing, so your Mustang calculations wouldn't apply in this case, I don't believe.

I think I used 6 Gs in the calculation above, which sounds a bit high based upon the discussion. I wanted to use a worst case though until I got better data. Please reread what I wrote earlier as most of your questions are answered there.

If you assume the lift is an 8,000# Mustang (probably a bit heavy) pulling 6 Gs, you have 48,000# of lift resulting in a racing turn.

At 500 MPH and 80 degrees F at Stead Field's elevation, you find that a coefficient of lift of .431 results with a stock Mustang's 235 sqft wing area.