Aerodynamic modifications

[Curt_B]

Curious about the aerodynamic modification history enabling the unlimiteds to go fast. As an example, can initially see extended wing/fuselage fairings on Roto-Finish from 1972, and various versions have been used throughout the years.

http://www.flickr.com/photos/10846656@N03/2232321114

Would like to know the history behind these modifications, i.e., who, what, why, where, when, etc., and what people think is the reason they work. Some of the mods are pure genius and it would be good to know if they were thought out, or resulted from trail and error. Seems the visible technology has been stagnant for a decade or more.

Thanks,

Curt

[John]

Re: Aerodynamic modifications

...was hoping some of the more knowledgeable and experienced would answer some of your questions...
Aerodynamics is a very interesting subject. Perhaps we should ask you, due to your study of transonic and supersonic aerodynamics. What is your take on the speeds these aircraft are now approaching? Obviously massive HP is required...

[Idaho_cowpony]

Re: Aerodynamic modifications

Maybe a good idea to get in touch with Gunther Balz?

[Curt_B]

Re: Aerodynamic modifications

...was hoping some of the more knowledgeable and experienced would answer some of your questions...
Aerodynamics is a very interesting subject. Perhaps we should ask you, due to your study of transonic and supersonic aerodynamics. What is your take on the speeds these aircraft are now approaching? Obviously massive HP is required...

It's impressive some of the planes are getting into compressibility effects, especially in the turns. Instead of just induced drag at 3-4 g's in the turns causing deceleration, the compressibility drag is chipping in. Says a lot about the crew chiefs, the crews, the engine builders, the engineers, and the owners knowing who to listen to, hanging onto everything to be able to go this fast.


Some of subsonic mods are straight forward and common sense, like stiffening wing panels and smoothing the surface, etc. But the scoop mods and the wing/fuselage trailing edge fairing are interesting on the Mustangs, and was curious about how they came about and the minds that figured it out. Would also be cool to find out about those mods that were tried and didn't work.

From inspection, seems like the last step forward aerodynamically was sweeping the prop tips. Was that done a decade or two ago.

An area of modern development might be to introduce an oblique shock wave ahead of the existing shock wave to lessen it's strength and reduce the rapid boundary layer growth through the shock, i.e., drag.

[Idaho_cowpony]

Re: Aerodynamic modifications

Some interesting things were being tested in the F-1 hangar this year, regarding electric shock/drag...

[Curt_B]

Re: Aerodynamic modifications

Some interesting things were being tested in the F-1 hangar this year, regarding electric shock/drag...

To control the boundary layer?

Expanding to other classes, which is fine, talked to the designer of the fast biplane, Phantom, about his prop. Asked if any body else was flying it and he said negative, but the props are/were available. Couldn't figure out why not unless it wouldn't work at lower speeds.

[Big_Jim]

Re: Aerodynamic modifications

Curious about the aerodynamic modification history enabling the unlimiteds to go fast. As an example, can initially see extended wing/fuselage fairings on Roto-Finish from 1972, and various versions have been used throughout the years.

http://www.flickr.com/photos/10846656@N03/2232321114

Would like to know the history behind these modifications, i.e., who, what, why, where, when, etc., and what people think is the reason they work. Some of the mods are pure genius and it would be good to know if they were thought out, or resulted from trail and error. Seems the visible technology has been stagnant for a decade or more.

Thanks,

Curt

Gunther wouldn't know anything...he just bought the plane 'as-is'. The guy who did the modifications to #5 (when it started life as Miss R.J. with Chuck Hall) was Boeing engineer Jim Larsen. He designed the clipped wings (copied from Mel Cassidy) as well as those wing fillets. He designed similar wing fillets for Precious Metal, Foxy Lady, and the Oogahonk Special...designed to straighten out the airflow coming off the wing/fuselage. It was also his idea to put that smaller canopy on...which if you look at it is a stock Mustang canopy rail....but the windscreen itself is a stock Mustang canopy mounted backwards.

He also designed the modifications for Miss Foxy Lady/Sumthin' Else.

Jim was out at the pylons shooting again a couple weeks ago.

[Curt_B]

Re: Aerodynamic modifications

Gunther wouldn't know anything...he just bought the plane 'as-is'. The guy who did the modifications to #5 (when it started life as Miss R.J. with Chuck Hall) was Boeing engineer Jim Larsen. He designed the clipped wings (copied from Mel Cassidy) as well as those wing fillets. He designed similar wing fillets for Precious Metal, Foxy Lady, and the Oogahonk Special...designed to straighten out the airflow coming off the wing/fuselage. It was also his idea to put that smaller canopy on...which if you look at it is a stock Mustang canopy rail....but the windscreen itself is a stock Mustang canopy mounted backwards.

He also designed the modifications for Miss Foxy Lady/Sumthin' Else.

Jim was out at the pylons shooting again a couple weeks ago.

Thanks, would like to sit down with him someday. Maybe I can run into him next year somehow. The fillets are also keeping the fuselage boundary layer away from the radiator afterbody fairing so the afterbody presents itself to the air in actual size, as opposed to actual size + boundary thickness.

[IF1#13]

Re: Aerodynamic modifications

Some interesting things were being tested in the F-1 hangar this year, regarding electric shock/drag...

Please do tell.... electric shock/drag?

Brian

[RAD2LTR]

Re: Aerodynamic modifications

You might try and chase down forum member "Blue Foam" he came up with many of the aero mods on PM this year. He seems to know his stuff (from long running posts on here in the past) and has reasons/opinions why some mods work and others don't.

Will

[L.E.D.]

Re: Aerodynamic modifications

The other big name in aero in the racing world is Bruce Boland. There's a nice biography on him here:

http://www.warbirdaeropress.com/articles/Boland/Boland.htm

Sadly, he's no longer with us.

Bruce Lockwood may also have some insight the share into aero mods; he's posted in the past about tests with Dago Red and Miss America done by comparing speeds at known power settings, though off the top of my head I don't remember the specific mods. He does give a summary of some of the things done to Dago Red here:

http://www.aafo.com/hangartalk/showthread.php?7676-No-no-not-Dago-and-or-September-Fury&p=74752#post74752

This thread is also interesting:

http://www.aafo.com/hangartalk/showthread.php?7714-Ridge-Runner-III-The-Road-to-Reno

Much of what I've observed is as much about feeding and cooling the engine (cooling drag) as it is about reducing airframe drag. Of course, with the mustangs the belly scoop is the big question. Both Strega and Voodoo did away with the boundary layer splitter. Presumably the radiator doesn't mind BL air and removing the intersections cuts down on the drag.

One thing that I've noticed is that the mustangs by and large have gone back to the stock spinner - nobody uses a pointy one anymore, and it seems to me that I've heard that was because of a loss in manifold pressure (or was that the induction 'smile?'). Wonder if that had any effect on the Bear, given the persistent rumour that they had lost MP with the cowling scoop. Rumour and innuendo...

Way back when NACA did tests on the P-51 to determine critical Mach - (maybe even with the NACA P-51 that attended this year) and found it to be about 0.7. Even with the 520TAS mentioned for some planes this year, the racers are just getting there, and that's probably the limit with the basic airframe.

However. digging around in Hoerner does give an idea of how much just cleanup is worth: A presumably 'clean' P-51 has a sharper 'knee' at the drag rise than a 'dirty' Bf-109; likewise the higher the basic drag coefficient, the lower the critical Mach number. Hoerner also advocates for large fillets to cut down on wing/fuselage drag.

Wish I had more answers than questions. Hopefully this'll get to be a good discussion.

[RichH]

Re: Aerodynamic modifications

Much of what I've observed is as much about feeding and cooling the engine (cooling drag) as it is about reducing airframe drag. Of course, with the mustangs the belly scoop is the big question. Both Strega and Voodoo did away with the boundary layer splitter. Presumably the radiator doesn't mind BL air and removing the intersections cuts down on the drag.

Actually... the scoop on Voodoo still has somewhat of a boundary layer splitter, as the front of the scoop still hangs down and away from the bottom of the wing. It's just much smaller than stock. The scoop on Strega blends right up against the bottom and doesn't do this...

[L.E.D.]

Re: Aerodynamic modifications

Actually... the scoop on Voodoo still has somewhat of a boundary layer splitter, as the front of the scoop still hangs down and away from the bottom of the wing. It's just much smaller than stock. The scoop on Strega blends right up against the bottom and doesn't do this...

Well.. oops, you're absolutely right. Maybe I was thinking of the Dago Red/RRIII scoop.

[Curt_B]

Re: Aerodynamic modifications

Very informative. I knew Bruce back in the Tsunami days, great guy, passionate about the sport.

More accurate information in testing mods can be achieved by flying what I call a speed triangle at different altitudes and recording gps speeds. The ground speeds, or gps speeds, at three different headings can be resolved to provide true airspeed and removes instrumentation error.

For RR III to reach 490mph on the course, sounds like removing the BL splitter from the scoop configuration, paying attention to oil cooler duct routing, extending the afterbody fairing, and the trailing edge fairing help more than installing a tiny canopy. Of course ingesting the BL in the scoop will generate duct rumble, but there are ways to mitigate that internally. The scaled Mustang guys running in sport would see a speed increase simply by installing the wing trailing edge fairing, and keeping the BL splitter wouldn't detract from the visual presentation too much I would think.

Roundy spinners are best because the air flowing around them accelerates early and the pressure integration produces a thrust. The pointy spinner delays the acceleration toward the back end of the spinner and can see how that would incrementally lower the pressures at the 'smile'.

Drag divergence Mach number reduces with increasing lift coefficient, or g, in the turns, and clipping the wings reduces wing area and the lift curve slope. There's no appreciable compressibility drag for the Mustangs in the straights, yet, but they're bouncing up against it in the turns.

The link is a simple compressibility primer,

http://adg.stanford.edu/aa241/drag/cdcintro.html

The large fillets on the Sea Furys are a wonderful thing. Looking at the exhaust, oil trace flow after a race depicts nice, tight flow.

As a general, and encouraging observation, there appears to be a good knowledge base here.

[John]

Re: Aerodynamic modifications

Roundy spinners are best because the air flowing around them accelerates early and the pressure integration produces a thrust. The pointy spinner delays the acceleration toward the back end of the spinner and can see how that would incrementally lower the pressures at the 'smile'.

Drag divergence Mach number reduces with increasing lift coefficient, or g, in the turns, and clipping the wings reduces wing area and the lift curve slope. There's no appreciable compressibility drag for the Mustangs in the straights, yet, but they're bouncing up against it in the turns.

It's remarkable how good those engineers were back in the day!
...perhaps they should put the "Tiger Claw" prop back on Strega sans pointy spinner... lol

Makes one wonder about the prop tips on the unlimiteds(cambered airfoils). PM looks awesome in that respect... Strega has the slightly clipped and raked tips...

A leading edge extension(wing airfoil mod) was installed on the Rare Bear at one time in her life. Also, some years ago Matt Jackson provided us with interesting info on Bears wing(stock airfoil) reaching critical mach number in flight.

Lots of interesting things have occurred over time. One wonders what will be next... The freedom of experimentation is a beautiful thing.