Aerodynamic modifications

[Curt_B]

Re: Aerodynamic modifications

Speaking of prop cuffs, it seems Rare Bear's 3 blade should be better than the 4 blade due to the formers very nicely designed cuffs.(by the way, who designed and built the cuffs for the modified P-3 3 blade that was once used on the Bear?)

Also, what was your opinion of the Risky Business wing tips during the days it was raced at Reno?

Except you have to look at the number of blades. If you remove one from a four blade, the remaining three have to get, 'wider', so to speak, to get the most from the engine. If diameter is decreased at the same time, then the have to be wider still. There's an engineering term for that, but this is a good layman's explanation without creating confusion. I think the P-3 blades have exceptionally small t/c's if I remember. As far as the cuffs ramming the intake, the intake has to be right up against the back of the blades to be effective. Are the old bear intakes on the wing leading edge? Also reducing the number of blades unevenly, like 3 instead of 4, throws the blade pass frequencies for a loop, and might screw with some airframe vibrations.

Would you have pictures of Risky Business's wingtips. I went to a few races in the early to mid 80's and then skipped them all until 2012 or so. Too busy working and all to go, but now I've got time, sometimes, to go, so excuse my ignorance.

Thanks for your help.

[bflynt]

Re: Aerodynamic modifications

Let me rewind and ask a question about this post on page 6 of this thread:

"......Rear Bear. Pretty sure they know what they're up against and have heard about a new, extended leading edge designed to decrease the t/c of the root section and smooth the upper surface curvature changes to mitigate compressibility drag. A good way to smooth out the area rule would be by shaping the canopy, if they haven't already."

Please tell me what "t/c" means in that sentence? I know it's probably obvious, but it's driving me crazy!

Noticed that some Bonanzas have a similar sharp edged wedge at the wing root, which I am told is to enhance stall warning.

Thank you for a terrific thread, I am learning a lot.

"t/c" is the ratio of the wings thickness to chord length. By extending the leading edge of the wing they would be adding to the wings chord length and in turn lowering the t/c.

[BD4Flyer01]

Re: Aerodynamic modifications

Thank you for your prompt response.

[Curt_B]

Re: Aerodynamic modifications

Noticed that some Bonanzas have a similar sharp edged wedge at the wing root, which I am told is to enhance stall warning.

Thank you for a terrific thread, I am learning a lot.

That makes sense. Heard the Bear has a narrow airspeed range between lift-off speed and gear speed. The pilot could fly the buffet nibble, and drop the airspeed scan from his workload during the gear transition. That has my vote so far. Collectively, keep this up and this might be the first sport where the racers solicit fan advice. Lol.

Reminds me recently of flying my Cub. Whenever I slip to landing, the airspeed wants to be 70 mph so I let it. Been flying it since I was 16, and after flying many other types since then, forgot why in the interim. Took it to altitude and it stalls at 60 indicated in a slip. Has something to do with the pitot being at an angle and the static pressure being cabin pressure in the leaky cockpit. Thought I remembered it being 50. Funny the things you forget. Been thinking about aero so much, forget the important digital stuff every now and then. Lol.

[John]

Re: Aerodynamic modifications

Would you have pictures of Risky Business's wingtips. I went to a few races in the early to mid 80's and then skipped them all until 2012 or so. Too busy working and all to go, but now I've got time, sometimes, to go, so excuse my ignorance.

Thanks for your help.

Should be some here: http://www.unlimitedair.com/reno_2002_rb.htm

[Curt_B]

Re: Aerodynamic modifications

Should be some here: http://www.unlimitedair.com/reno_2002_rb.htm

Getting close. Would have to be careful that the aft stub winglet doesn't just entrain the vortex generated from the forward part of the tip. the upseeep should dissipate the vortex a little though either through skin friction effects, or just being in the way.

The vortex is generated from the pressure difference between upper and lower that is maximized on the forward part of the tip.

For zero aoa the pressure distribution looks like this typically;

http://digital.library.unt.edu/ark:/67531/metadc55231/m1/18/

and at 4 degrees aoa the pressure differential is larger;

http://digital.library.unt.edu/ark:/67531/metadc55231/m1/22/

The difference in pressures can be used to calculate the, 'vertical', velocity component and when combined with the freestream velocity can be used to determine the upflow angle around the tip generally. When the flow gets to the top, it wraps around into a vortex, starting further and further forward, and gets stronger and stronger.

Wingspan extensions are an excellent opportunity to displace the vortex out of the wing plane by canting up the tip a little since it would apply to the whole tip chord. Special treatment/shaping at the tip itself would buy a little more gain. And also, minimizing the tip chord does wonders.

Hope this isn't too confusing.

[BD4Flyer01]

Re: Aerodynamic modifications

I just saw that Aerochia has a speed mod for the Lancair that extends and sharpens the leading edge at the root, and droops down slightly. It's under the heading of "speed mods". Is it just hiding the thicker root on a tapered spar? Does it lessen the mysterious "horseshoe vortex", something I just heard about on this thread? You can see pictures on Andy's web page, www.aerochia.com.

Thanks,

Craig

[mayday51]

Re: Aerodynamic modifications

Call Andy he isn't that shy.

[John]

Re: Aerodynamic modifications

Getting close. Would have to be careful that the aft stub winglet doesn't just entrain the vortex generated from the forward part of the tip. the upseeep should dissipate the vortex a little though either through skin friction effects, or just being in the way.

The vortex is generated from the pressure difference between upper and lower that is maximized on the forward part of the tip.

For zero aoa the pressure distribution looks like this typically;

http://digital.library.unt.edu/ark:/67531/metadc55231/m1/18/

and at 4 degrees aoa the pressure differential is larger;

http://digital.library.unt.edu/ark:/67531/metadc55231/m1/22/

The difference in pressures can be used to calculate the, 'vertical', velocity component and when combined with the freestream velocity can be used to determine the upflow angle around the tip generally. When the flow gets to the top, it wraps around into a vortex, starting further and further forward, and gets stronger and stronger.

Wingspan extensions are an excellent opportunity to displace the vortex out of the wing plane by canting up the tip a little since it would apply to the whole tip chord. Special treatment/shaping at the tip itself would buy a little more gain. And also, minimizing the tip chord does wonders.

Hope this isn't too confusing.

Not too confusing, ...looks like there can be serious secondary flow at the wingtips during lifting.
The angle of attack at race speeds must be very little(even flying the course under G) -if any, due to the very high speed, dynamic pressure, and slight wingtip washout on a Mustang; and we know any cambered airfoil produces lift even at zero Alfa.
BTW, the wing tips on the 787 look awesome!

[Curt_B]

Re: Aerodynamic modifications

I just saw that Aerochia has a speed mod for the Lancair that extends and sharpens the leading edge at the root, and droops down slightly. It's under the heading of "speed mods". Is it just hiding the thicker root on a tapered spar? Does it lessen the mysterious "horseshoe vortex", something I just heard about on this thread? You can see pictures on Andy's web page, www.aerochia.com.

Thanks,

Craig

Neat stuff. The reduced root t/c decreases interference drag and the wing profile drag drops since the stagnation pressure on the leading edge decreases by the cosine of the sweep angle. That's why I like the P-51D wing planform. Might be able to squeak out a little more with such a mod on the Mustang, but it'd be low on my list of things to try since the leading edge is already swept. Wouldn't think that there'd be a horseshoe vortex forming on a low, or high, wing configuration. What are the performance gains of the Aerochia mods.

Birds have wing root fairings, as well as fish. Less pronounced on fish since the fins are swept. Even the Albatross has a little leading edge sweep across the wing and they unsweep the wing tips for landings. Oh, and the high performance birds and fishes have very small tip chords.

Aerochia seems to be legit, I can't vouch for them one way or the other, since this if the first time I've seen them. Thanks. Their mods look good. Look out for other people though and try to verify performance increase claims beforehand before you buy. I'd ask for a money back guarantee from some of the companies. Saw one mod that I tried on another one of my little airplanes that resulted in no speed increase, but it increased flaps down stall speed. Lol. Glad I didn't buy it. Some people market items for the buck sometimes it would seem.

[Curt_B]

Re: Aerodynamic modifications

Not too confusing, ...looks like there can be serious secondary flow at the wingtips during lifting.
The angle of attack at race speeds must be very little(even flying the course under G) -if any, due to the very high speed, dynamic pressure, and slight wingtip washout on a Mustang; and we know any cambered airfoil produces lift even at zero Alfa.
BTW, the wing tips on the 787 look awesome!

The clipped Mustangs have a reduced lift vs alpha slope, so pulling 4 g's requires a higher alpha than a stock Mustang. They would still benefit from tip treatment.

Just noticed the 787, is this the configuration. Racers are much more interesting;



The high twist at the tip is a geometric phenomena. Highly tapered wings require these high twist values geometrically to get the desired twist at 80% and 90% span right. The high sweep is to force the shock sweep since the shock wants to unsweep at the tips due to the vortex aerodynamically uncambering the the tip airfoil section. Back in the sixties, they rounded the tip leading edge to alleivate that problem on the C-5.

Even the birds are learning something from us, lol, and the sweep means something subsonically too;



There's something to the minimal tip chord.

Maybe someday we'll see a formula racer modeled after the varying leading edge sweep changes of birds.

[John]

Re: Aerodynamic modifications

The clipped Mustangs have a reduced lift vs alpha slope, so pulling 4 g's requires a higher alpha than a stock Mustang. They would still benefit from tip treatment.

Just noticed the 787, is this the configuration. Racers are much more interesting;

[ATTACH=CONFIG]20378[/ATTACH]

The high twist at the tip is a geometric phenomena. Highly tapered wings require these high twist values geometrically to get the desired twist at 80% and 90% span right. The high sweep is to force the shock sweep since the shock wants to unsweep at the tips due to the vortex aerodynamically uncambering the the tip airfoil section. Back in the sixties, they rounded the tip leading edge to alleivate that problem on the C-5.

Even the birds are learning something from us, lol, and the sweep means something subsonically too;

[ATTACH=CONFIG]20379[/ATTACH]

There's something to the minimal tip chord.

Maybe someday we'll see a formula racer modeled after the varying leading edge sweep changes of birds.

The design in nature is awesome! ...one can also take a closer look at the fluke of a Minke, Fin, or Blue Whale and be very humbled by the advanced hydrodynamic shape.

[Curt_B]

Re: Aerodynamic modifications

The design in nature is awesome! ...one can also take a closer look at the fluke of a Minke, Fin, or Blue Whale and be very humbled by the advanced hydrodynamic shape.

Pretty neat stuff. The flukes are evolved for propulsion, in water, and while they should be studied for understanding; fins, and wings are more applicable. We're on our own transonically.

After understanding all this so far, we can see why clipping the wings on a Sea Fury is a bad idea - it leaves a longer than normal tip chord due to the planform.

[John]

Re: Aerodynamic modifications

Thats interesting about the SeaFury wing clip,...makes sense.

This has not been mentioned here, but of all the Unlimiteds I'd say Rare Bear has the best wing tip treatment for racing. How say you?

[Curt_B]

Re: Aerodynamic modifications

Thats interesting about the SeaFury wing clip,...makes sense.

This has not been mentioned here, but of all the Unlimiteds I'd say Rare Bear has the best wing tip treatment for racing. How say you?

The Sea Fury already has a thin tip section if I remember, so clipping would eliminate a reduced profile drag, and really just get rid of the skin friction drag. But the ramp-up of induced drag in the turns is disproportionately large.

I see a bunch of different tips for RB over the years, can you supply a picture?

Thanks,