Aerodynamic modifications

[Curt_B]

Re: Aerodynamic modifications

Also, some years ago Matt Jackson provided us with interesting info on Bears wing(stock airfoil) reaching critical mach number in flight.

Would like to see that if anybody can dig it up. Can't remember if I analyzed the RareBear wing or just looked at the geometry and didn't bother. That poor engine having to contend with that, though there are some things aerodynamically that can be done to help some.

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

But the costs with current fuel prices have to be horrendous. Helps a little to schedule aero flight testing with regular maintenance flights when possible since the sponsorship isn't there. Drags out development time and it's good to be right the first time because second chances are hard to come by.

[RAD2LTR]

Re: Aerodynamic modifications

Perhaps Wild Bill Kelso will chime in on how well the aero mods on PM worked this year. I've heard in testing they went very fast (at Reno). If you look at PMs wing tips, then look at a few of the sport planes and some of the f1 planes, you might see some similarities. They also changed the canopy, the scoop, and added strakes this year. It seems to me that these guys are looking at new ways to address issues that have been deemed a good enough fix by the other major players, the difference being the number of prop blades up front and the additional heat generated by the much larger engine.

Speaking of interesting mutations of the P51, MA2 had some creative ideas for lowering drag such as the NACA ducts for both the carb intake and for the radiator scoop. According to the book "Griffon Powered Mustangs" once they had a few things sorted out, both worked very well. I can't say if the NACA duct for the radiators would work well with a stock Mustang wing, but it might. I think if you are interested in seeing an unlimited P51 evolve into a more modern era, keep an eye on what the PM guys do. They seem to be forward thinking and not that afraid to try things that have been said "will never work on an Unlimited even though they might pay large dividends on F1s and sport racers.

Great thread.

Will

[Curt_B]

Re: Aerodynamic modifications

Perhaps Wild Bill Kelso will chime in on how well the aero mods on PM worked this year. I've heard in testing they went very fast (at Reno). If you look at PMs wing tips, then look at a few of the sport planes and some of the f1 planes, you might see some similarities. They also changed the canopy, the scoop, and added strakes this year. It seems to me that these guys are looking at new ways to address issues that have been deemed a good enough fix by the other major players, the difference being the number of prop blades up front and the additional heat generated by the much larger engine.

Speaking of interesting mutations of the P51, MA2 had some creative ideas for lowering drag such as the NACA ducts for both the carb intake and for the radiator scoop. According to the book "Griffon Powered Mustangs" once they had a few things sorted out, both worked very well. I can't say if the NACA duct for the radiators would work well with a stock Mustang wing, but it might. I think if you are interested in seeing an unlimited P51 evolve into a more modern era, keep an eye on what the PM guys do. They seem to be forward thinking and not that afraid to try things that have been said "will never work on an Unlimited even though they might pay large dividends on F1s and sport racers.

Great thread.

Will

I enjoy the F1, Biplane, and Sport hangars because of the ideas, which are transferable to other classes since air is air. The people are refreshing as a lot of them don't have aero degrees I imagine, are always learning and come up with great concepts. Goes to show that drive and desire can be more rewarding than degrees and computers I imagine. The unlimiteds are neat too, but the development seems to have stopped years ago - development costs?, recession?, everybody's happy at ~500mph? Did I hear the jets have a speed limit now?

Wouldn't think that NACA scoops would work well in those applications, but I've been wrong before - sometimes.

[RAD2LTR]

Re: Aerodynamic modifications

Apparently the NACA intake scoop doesn't work well on a Merlin as the Tsunami team found out, but can work well on a Griffon due to a different mounting location (lower allowing the airflow to straighten out before entering the carb.) The radiator scoop allowed the radiator and oil cooler to sit deeper in the fuselage of MA2. Another interesting thing I just noticed while looking at some pics of MA2, the wing tips are somewhat similar to the ones on PM now. Obviously not identical but similar. It would be interesting to see what MA2 would look like now had the accident never happened. Looking at race speeds of MA2 and PM from they were in the same ball park. Had Gary Leviz run props like what PM has now, the results might have been pretty impressive. They were good for what, 60 mph on PM last year? MA2 was cleaner with a potentially faster wing, it certainly makes me wonder, what if...

I agree, the Unlimiteds have sort of reached a point of stagnation to some degree. The new Rare Bear program might show some good results in time. Its a new crew trying far different things, and a few that were explored in the past but were possibly deemed as dead ends. With the new crew and a different way of looking at ideas, they brought back the leading edge mod that was tried awhile back, but did it better this time around. The intake block off idea seems to have worked this year. I think given more time to really massage the beast, we could see it back on top.

The PM team still seems to be the ones doing all the serious innovation and boldly going in new directions that very well could pay off big time. This year they went slower than they did last year, but I'll bet they learned a huge amount and brought home tons of data that will likely prove ideas out, disprove a few (like the carbide valve fingers that ate cams) and come next year assuming they get some good luck (they were a little short on that this year) they might be right there pushing Strega and Voodoo right to the breaking point. (Yeah I'm sure a few people are laughing at that thought. All I can say is time will tell. ) They certainly have people putting some serious effort into making it happen. There are a lot of bright guys on that team who all want to prove the naysayers wrong. I really look forward to seeing what these guys do next.

Will

[L.E.D.]

Re: Aerodynamic modifications

I found Matt Jackson's comments on the Bear at critical Mach:

http://www.aafo.com/hangartalk/showthread.php?5770-MR-AWESOME-FROST-BITE-4-SALE&p=54182#post54182

And some other stuff:

http://www.aafo.com/hangartalk/showthread.php?2159-Wing-attachment-and-a-spinner-!&p=15231#post15231

And this thread, while just plain long, is worth the reading. The link starts in the middle with discussion of
Sea Fury 3350 cowlings, but the whole thing is gearhead heaven:

http://www.aafo.com/hangartalk/showthread.php?5320-Critical-Mass-Blind-Man-s-Bluff-SPLIT-THREAD&p=49780&highlight=rare+bear+airfoil#post49780

I haven't read this paper yet but maybe Curt_B will like it:

http://aero-comlab.stanford.edu/kasidit/publications/jameson.aiaa.06-0048.pdf

However, what's got me hitting the books tonight is the subject of change in Mcrit with lift coeff.

If we start with an 8000lbf P-51 with 220ft^2 of wing, at 5000ft at 500mph (733fps; M = 0.66), it needs a Cl of 0.07.
3.5G would require Cl = 0.25. Mcrit for the NACA 66-210 goes from about 0.77 to 0.75, which doesn't seem like it would hurt too much, at least for the wing, but it's clearly not the whole story. Lots of assumptions there: wrong airfoil, guessed at the weight, guessed at the area, wing alone with no interference effects... I'm out of my depth, here; how much does Mcrit for a whole airplane depend on Cl and/or alpha?

In any event it seems clear that keeping Cl low pays - which makes Precious Metal's wing extensions all the more interesting.

[Curt_B]

Re: Aerodynamic modifications

I found Matt Jackson's comments on the Bear at critical Mach:

http://www.aafo.com/hangartalk/showt...4182#post54182

Matt's comments give good data points on when certain events occur when the shock becomes so strong that it becomes noticable to the pilots. ( Thanks for finding that.) A lot of drag has been added between when the drag rise starts, and when the pilot notices something's different. The drag lowering concepts extend that out to higher Mach numbers, i.e., higher speeds.

And this thread, while just plain long, is worth the reading. The link starts in the middle with discussion of
Sea Fury 3350 cowlings, but the whole thing is gearhead heaven:

http://www.aafo.com/hangartalk/showt...foil#post49780

Good to get these scattered aero links in one place, for posterity if nothing else. Those that come years after us will have something to keep them occupied.

I haven't read this paper yet but maybe Curt_B will like it:

http://aero-comlab.stanford.edu/kasi...aa.06-0048.pdf

Another good contribution for the thread. Dr Jameson is the guy that made this CFD stuff possible and he's an unbelievable mathematician. He even designed the high speed Gulfstream wing for the manufacturer, or helped their guys. The objective of these grad school papers is to demonstrate the student has a grasp on the technology, writing/running computer cfd program technology in this case. Unfortunately, they used the thick Mustang root airfoil at the tip too in the geometry definition so their effort has limited practical usefulness. The bump idea is a single design point concept, and unfortunately will create a double shock off-design, which is even worse drag rise wise.

how much does Mcrit for a whole airplane depend on Cl and/or alpha?

The fuselage cuts out the wing span loading. It's typical to increase wing CL 5 to 15 percent to compensate for that. The wing lift also has to be increased by the amount the tail lifts down for trim. And the lift curve slope decreases with wing clip. Any comparisons to the old NACA reports have to be compensated for wing clip. Converting the drag rise from 'vs CL', to 'vs AOA' is required because of the lift curve slope change.

Any local flow accelerations due to the fuselage shape in the proximity of the wing will be magnified in the supersonic flow field above the wing. The effect is more pronounced for low aspect ratio configurations, and especially for low aspect ratio/swept wing geometries. So much so that a compromised wing design can be made into a good design by shaping the fuselage of a fighter. Helps to compensate for any constraints the party spoiler designers, , impose. The first order effect of this is the area rule.

Here's another link that draws the drag divergence Mach number line along the drag rise curves at different lift coefficients to make it easier to see. This is more of what the Bear looks like.

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

Opps, that was peak pressures or something. Visually, and changing the labels, and maybe drinnking some beer, that could graphically depict decreasing MDD with increasing CL.

[Curt_B]

Re: Aerodynamic modifications

Had some time and dug 23015 section drag divergence Mach Number, Md, and critical Mach number, Mcrit, data with aoa. Figure 5 in;

http://digital.library.unt.edu/ark:/67531/metadc55116/m1/22/?q=drag%20rise

Mcrit is where the first air molecule on the surface reaches Mach 1.0. The 23015 section is about the average Bearcat section after the clip.

[John]

Re: Aerodynamic modifications

Good stuff, thank you. The paper on a solution for Dago Red's wing is interesting. For many years thought the Mustangs might also someday require an airfoil leading edge extension mod. to delay the drag rise. It looks other solutions are possible.

If the Rare Bear has Naca 23018 at the wing root, it must be a challenge to solve drag rise there. New Bear has interesting mods in and around the wing root. One thing that was beautiful about the 3 blade prop for the Bear was the white blade cuffs and large spinner. It looked very efficient.

[Curt_B]

Re: Aerodynamic modifications

Hope this stuff isn't getting too complicated. Provides a new appreciation for all the chiefs and crews that have gotten the Bearcat to go fast. Also adds some talking points for the people trying to figure out if radials or v's are best. In RearBear's case, it includes the more powerful unseen spoiler drag effect of the shock wave, but they got it to still compete with the Mustangs that have a lesser effect. It's good the fans can have an appreciation for this effort. Pretty impressive I would say in anybody's book, and they should be proud.

Good everybody contributed, learned some stuff.

If there's anymore, that be great.

[bflynt]

Re: Aerodynamic modifications

Interesting thread.
Back in 2009 I inquired if the mods in that paper were ever implemented.

http://www.aafo.com/hangartalk/showt...g-Optimization

At the time Prof. Jameson was my advisor and "Blue Foam" had just visited and gave a talk about designing a unlimited racer with a mid-body mounted propeller. I never got a solid answer but was invited to come see for myself. Unfortunately, I had just moved a 1000 miles away and then the plane changed hands. Would still be interested in finding out if the mods were ever done and made a difference.

[Curt_B]

Re: Aerodynamic modifications

Interesting thread.
Back in 2009 I inquired if the mods in that paper were ever implemented.

http://www.aafo.com/hangartalk/showt...g-Optimization

At the time Prof. Jameson was my advisor and "Blue Foam" had just visited and gave a talk about designing a unlimited racer with a mid-body mounted propeller. I never got a solid answer but was invited to come see for myself. Unfortunately, I had just moved a 1000 miles away and then the plane changed hands. Would still be interested in finding out if the mods were ever done and made a difference.

Wouldn't know about being tested on that airplane, but it's a single design point modification. Off-design will give two shocks, one in front of the other, which is bad. If the concept worked for all conditions, and since it was thought of so long ago, it'd be on Boeing airliners. The Boeing guys are pretty good and wouldn't have missed this opportunity. Besides, they got a bump for something other than a Mustang wing due to using the root airfoil at the tip in the geometry definition, so if was tested, it would have been the wrong bump.

The continuous spanwise bump would be better off by breaking it up like a dotted line and using something other than bump segments. If you get it right, you'll get an oblique shock in the sideview, or airfoil view, ahead of the normal shock, and shock scallops, or sweeps in planform view between the bumps that arent bumps. This dotted line configuration, and using something that aren't bumps, will give better off design, and design, performance - I would think. Helps make a straight wing think it's a swept wing with a bunch of little segments to delay drag rise.

The adjunct equation is neat and all, as well as inverse and qausi-inverse design methods, but the most efficient method is to simply take the difference between target, or desired pressures, and the current calculated pressures for geometry perturbations. You can change the scaling during the design iterations to keep the code on the verge of divergence, as I like to call it, and get the answer in 8 or so steps. Constraints can be imposed by freezing the geometry where it's fixed, and alter the target pressures if you can't get there.

[LoveOldPlanes]

Re: Aerodynamic modifications

If you look at PMs wing tips, then look at a few of the sport planes and some of the f1 planes, you might see some similarities. They also changed the canopy, the scoop, and added strakes this year. It seems to me that these guys are looking at new ways to address issues that have been deemed a good enough fix by the other major players, the difference being the number of prop blades up front and the additional heat generated by the much larger engine.
I think if you are interested in seeing an unlimited P51 evolve into a more modern era, keep an eye on what the PM guys do. They seem to be forward thinking and not that afraid to try things that have been said "will never work on an Unlimited even though they might pay large dividends on F1s and sport racers.

Great thread.

Will

My thrill of this last year has been working with Thom on Team PM doing these mods. The great thing about it all is his excitement and passion to do better than has been done before. He loves air racing and the challenge of the engineering of the aircraft itself. The excitement is invigorating to be around. The scoop extension and strakes started life on Ridgerunner 3 and had to be adapted/ fitted to PM's airframe. Rather than poke new holes in the airframe, I spent when a fair amount of time doing fiberglass/ composite work to extend edges to accommodate existing holes in the airframe. Another Team member spent a fair amount of time getting the scoop extension to mount properly, so as to give the intended advantages. Its using the best of what we can come up with on our budget.

The wingtips were a new design that Thom came up with himself. He knew what he wanted, had the engineering work done and the tips created. The filling of the flush rivets in the wing was treated as sacrilege by many fans of the aircraft...until you remember it IS a Racing Aircraft and the mod was to make it faster. Lots of labor for small gains, but every little bit counts.

The canopy profile is actually close to the last one, with a differing hinge system and more glass to have a better view for the camera project. That said, I am still laughing to myself that thus far, everybody has missed a major aerodynamic mod to the airframe. A few months before the Races somebody in one of these threads was even going on at length about how bad the old design was. I had to bite my tongue to not talk about the mod were directly in the middle of making. I still wonder why nobody has mentioned it.

So far, the Team is recovering from last year and starting to get the excitement back for this year's challenges. I suspect only a couple of people have direct access to the data gained this year. I also think its important to note how PM, as a No Bucks Team was in the Gold next to Mega Bucks Teams. Hats of to all the Teams approaches, but I keep thinking about Team PM when I remember the line from the WW2 Seabees, "The Impossible Will Take Just a Little Longer....". I am most impressed with what Thom has done in just a few years of owning the aircraft....against Teams with decades of racing under their belts. While we have our shining stars like Wild Bill, others of us are getting the hang of thinking outside the box to help the program. As the program gets its feet under it, I am certain great things lay ahead- for the aircraft, the Team and Racing itself. Am I hooked worse than ever on Air Racing...? Oh heck yeah!

[AAFO_WSagar]

Re: Aerodynamic modifications

Thom is a very exciting guy! He's got the fever and he has managed to gather a really high quality group of people around his effort.

He's showing a lot of qualities of a great leader!

Oh, yea.. besides that... he's a kick ass pilot with gonas' made of of titainium!

Really...

Imagine strapping on the extreme machine that Precious Metal is, after all of the last minute work that had to be done.. then, "sallying forth" to RENO '13... Let's hope everyone actually tightened that fastener!

It not only shows what a great pilot that Thom is, it is an extreme example of his confidence and faith in his crew!

Much much more to come from this team!

[L.E.D.]

Re: Aerodynamic modifications

The canopy profile is actually close to the last one, with a differing hinge system and more glass to have a better view for the camera project. That said, I am still laughing to myself that thus far, everybody has missed a major aerodynamic mod to the airframe. A few months before the Races somebody in one of these threads was even going on at length about how bad the old design was. I had to bite my tongue to not talk about the mod were directly in the middle of making. I still wonder why nobody has mentioned it.

Smaller dorsal... ?

[MRE]

Re: Aerodynamic modifications

The PM guys also added pieces to smooth out the line by the coolant exit door. Used to come to a squared off end.