Question for Unlimited pilots

[dvddude]

For anybody that flies Unlimiteds or Fury's, Mustangs, etc.:

When you fly around the pylon, on average how much airpseed do you lose in the turn? I'm really curious, because in high performance jet planes, when you pull G's, you have a huge amount of induced drag due to the typically low AR wings. This translates into a large amount of energy loss. Most W.W. II type aircraft are characterized by high AR wings. This would seem to result in much lower induced drag and consequently less energy bleed off in a high G turn. Can anyone elaborate on this on what it's like in your typical Unlimited racer?

Also, what is the average or I guess I should say "optimal" G to use in a turn for a pylon to minimize energy loss? I know it depends on bank angle, but what is typical for most Unlimited racers?

Thanks!

["Bear" Driver]

Re: Question for Unlimited pilots

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

[WVRACEFAN]

Re: Question for Unlimited pilots

WOW! I didn't ask the question, but thanks for the info! I've wondered much the same thing. BTW, congrats on a great race/win this year.

Regards,

WV hillbilly displaced to Dayton, OH.

[dvddude]

Re: Question for Unlimited pilots

Wow, awesome response! Thanks, Mr. Penney!

Now, a follow-up question. Out of all the typical Unlimited racers, which airfoil design has the most efficient for preservation of energy in a turn. With all things being equal, is it the Mustang, Bearcat, Fury, Yak, or some other airplane?

Thanks again for anyone taking the time to respond!

[ebutner]

Re: Question for Unlimited pilots

Yes thank you for answering the question... Great information.

[Whiteside]

Re: Question for Unlimited pilots

When not hindered by traffic or a whole bunch of wake from other aircraft, I will see 10-15 Knots variance in SteadFast depending on the course while flying my optimal line. Pylon 5 being the slowest if I stay tight on it. You can really feel the airplane when it is unhappy around the course. I was seeing indicated of around 315 or so this year and that really seems to hold itself up there with the new prop better than the DC3 prop we took off. I'm sure the more speed we gain, the easier it will be to keep it!
Great info John, thanks.
Will

[Whiteside]

Re: Question for Unlimited pilots

John, What is the Mcrit of a typical warbird prop airfoil section?
Will

["Bear" Driver]

Re: Question for Unlimited pilots

Dvddude,

Dunno...you'd have to research mounds of NACA technical data.

Will,

Varies, but usually in the low to mid .9s

[Whiteside]

Re: Question for Unlimited pilots

Thanks John, that is what we will be shooting for. We have been running close to .84 according to my calcs. With a 400 course speed next year we will be close to .95 unloaded between 5 and 7. That should sound nice from the ground.
Thanks again,
Will

[Whiteside]

Re: Question for Unlimited pilots

Whoops, 7500' D.A. raises mach, how about .92!
WW

[John]

Re: Question for Unlimited pilots

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

Nice flying there on Sunday John, many of us could not have predicted that you would be able to get around the September Fury. It made it a great race! We saw how hard the team had worked too.

[Whiteside]

Re: Question for Unlimited pilots

What i meant to say is that its hotter than standard as Mach is purely temp related.
WW