Warbird Information Exchange

You're right BDK, I had forgotten you wrote what the assumptions were.

I still think it's induced drag. All airplanes have induced drag, but some are more prone to it's effects than others. Low aspect ratio airplanes, like modern fighters are NOTORIOUS for losing HUGE amounts of airspeed in pulling G's. In fact, it's how most fighters lose airspeed when they report initial for an overhead break. It's not uncommon for Navy planes like the F-18 to lose 400 to 500 KIAS in a "carrier break" by simply losing that energy through mostly induced drag from the increased lift through pulling "G"'s.

High aspect ratio airplanes like your typical W.W. II fighter will still lose airspeed in heavy G's due to induced drag, but it's effects are much, much less pronounced.

I did take a couple years of Aerodynamics in college, but it's been so long, I don't remember any of the equations or how to analyze your above math work. Obviously, we're missing something here, and I don't know what it is, but I still say the airspeed loss is due to induced drag.

The only other thing I can think of is:

Perhaps the Mustang's airfoil, due to being laminar flow, somehow reduces the effects of induced drag.

Any other Aeronautical engineers care to pipe in?

I would love to hear from any of our current WIX members who are current on both the Bearcat and Mustang to pipe in here to talk about the effects of induced drag on a turn when pulling G's. I know that we have at least one - Jim Beasley - who is current on both.

Jim, if you're reading this, how much airspeed will the Bearcat lose in a constant G, level flight turn compared to a Mustang at the same speed? Since we're talking about the applications in regards to Reno racing, say, somewhere in the neighborhood of 400 to 450 mph?

Pulling 6 Gs at 500 MPH (where my calculations were done) is a lot different than pulling 6 Gs in the overhead break (which is way too high anyhow). In the overhead you are going much more slowly (200-250 MPH?) so you achieve a higher angle of attack which gets you up into higher coefficients of drag and slows you down. At 500 MPH you can't pull enough Gs without either blacking out or pulling the wings off for the increased induced drag from the very minor increase in angle of attack to be a large factor. Don't forget that the velocity term in the equation is squared, so if you cut the speed in half the lift is reduced to 1/4 so you need a much higher angle of attack for the same G-force. This is why a 3-G turn at cruise will never kill you but a 3-G turn on base to final might.

If you started with a clean sheet of paper would a single or twin engine design be faster ?

I was imagining a big twin boom version of something like the Pond Racer/P38 with tricycle undercarriage , carbon fibre composites where necessary but go for a titanium centre structure and wing with twin R-4360s !

Perhaps some canards on the nose controlled by a flight computer to help balance out the loads on the tail and elevator

One R-4360 exceeds the minimum weight limit of 4,000 lbs

One of the limiting speed factors may also be the props , maybe a design using ducted fans , grab the intake shroud and C-1 fan from an engine like the JT9 hi bypass jet engine and drive it with an R-4360.

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Aussie expat lost in Indonesia

Ah yes, you've discovered the concept of corner velocity. Below Vc you can't over-G the aircraft, but above it, you can!

Also, realize that the only reason I brought up the overhead example was to show how pilots can use induced drag to their advantage - to lose airspeed very quickly, in this example, for the overhead break to get below the limiting airspeeds for gear and flaps. Keep in mind also, that when those pilots in their F-18's are trying to lose 400 KIAS so they can lower their landing gear, the throttles are at idle and they are using the huge amount of induced drag to slow down. I really didn't mean to use this example and apply it to Reno air racing, it's just for illustrative purposes. Of course, at Reno, the Unlimited racers have their power up pretty high, not at idle as my example shows.

I'm not so sure that a twin racer with two 4360's would be the best way to get fast airspeed for a few reasons:

1) The 4360 weighs a LOT and doesn't have the best power/weight ratio.

2) The 4360 has a HUGE frontal area and would expose any potential racer to a great deal of parasitic drag which would be VERY pronounced at 500mph.

3) Any racer that would be built to accomodate those huge engines would have to be very big, and heavy just to retain structural integrity to pull the G's required on the race course.

I like the twin idea, but I think that a twin with inline engines would be the best way to go because: 1) it has a small frontal area, 2) it has good power/weight ratio and 3) it is much lighter and would create a smaller, more aerodynamic racer.

It's no secret that year after year, typically speaking with a few exceptions, the Mustangs seems to win the most. HHHHmmm, there must be something to that in-line design!

If I were to start from scratch, I would develop a twin, either along the lines of an F-82 type airframe or a push/pull combo along the lines of the Do335. Put a souped up Merlin in each with Allison rods, Nitrous, etc, and you have a winning combination, IMO!

Now, all you need is about 5 Million dollars and you're in!

Inline twin ... now there's an interesting idea

They would have change the rules to allow on onboard flight engineer to keep the twins engines in one piece , imagine 2 tweedle valves to play with while doing 550 mph at 50 ft around the pylons !

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Aussie expat lost in Indonesia

1) The 4360 weighs a LOT and doesn't have the best power/weight ratio.

Dreadnought has a number of Reno wins and the Super Corsair even won once (no offense to Corsair fans, but that is one draggy airframe!), beating Dreadnought due to a pylon cut. Where were the Merlins then? The radials seem to stay together better than the Merlins and can often pull full power for the entire race where a Merlin would overheat. The Super Corsair was a perennial 3rd place finisher with a basically right out of the can stock 4360

2) The 4360 has a HUGE frontal area and would expose any potential racer to a great deal of parasitic drag which would be VERY pronounced at 500mph.

No more so than an R-2800 or R-3350. The cooling drag can be offset with thrust just like a Mustang does with it's radiator.

I like the twin idea, but I think that a twin with inline engines would be the best way to go because: 1) it has a small frontal area, 2) it has good power/weight ratio and 3) it is much lighter and would create a smaller, more aerodynamic racer.

Twins are not aerodynamically desirable because of the drag at all the intersections (nacelle to wing, fuselage pod to wing in the case of the P-38 or Pond Racer). The Pond Racer had no choice because of the small and unproven engines used- they needed two.

It's no secret that year after year, typically speaking with a few exceptions, the Mustangs seems to win the most. HHHHmmm, there must be something to that in-line design!

I think you'll find that radials have done better than inlines at Reno, although I stopped counting a few years back.

***Note - my original comments in black and BDK's in blue, even though the quote block says BDK***




True, but how many round motor engined airplanes have won Reno recently besides Rare Bear and Critical Mass a while back. In the last 10 to 15 years, inline engines have won most of the Reno Championships. You're right about the radials though, those things are built tough and they last! The Merlin is certainly a very finicky, intricate piece of machinery. The 4360 is like a Buick - rugged, reliable and not as much maintenance required, while the Merlin is like a Porsche or Mercedes - intricate craftsmanship that requires some maintenance and breaks down often.

As far as my original comment regarding the 4360 power/weight ratio, apparently Gary Austin agrees with me:







My comparison is the 4360 vs. the Merlin, not other radials. As an example of the huge drag and not much power added aspect I talked about, just look at Dreadnought. It has a 4360, but yet it is NOT the fastest Sea Fury out there. Critical Mass, with it's 3350 was much faster. If the 4360 really was a much better race engine, we would see it in many, many more racers. It's only been used in what, 3 racers in Reno history - 1)Dreadnaught, 2) Super Corsair, 3) Furias. The F2G Super Corsair doesn't count since it was built that way originally, and is an original, essentially unmodified design. Why have virtually every single Sea Fury owner put a 3350 in their planes instead of a 4360? Lots of reasons, but primarily the extra weight is not worth the small extra horsepower and the huge frontal area is very draggy. With the 3350, owners can keep the cowling and firewall forward section (QEC) looking somewhat like a normal Sea Fury since it doesn't have to have the huge oversized cowling to accomodate the 4360. Huge oversized cowling = huge amounts of drag.



Perhaps the drag issues are not desirable, but I don't think those can't be overcome with good engineering. Things like fillets, compound curves at wing/fuselage intersections, "coke bottle" designs to minimize transonic drag and efficient use of NACA airfoils, I believe could overcome those issues. In addition if you put the pilot in one of the fuselage's like an F-82, you wouldn't have to worry about any pod drag or issues. I think I mentioned that in my original quote! Perhaps a twin isn't the most optimal solution, but if North American could design the F-82 to be as fast as it was, why can't a modern designer with the benefit of CAD, and advanced computational fluid dynamic programs, etc., design something just as fast or faster?




Perhaps that was true during the early years of Reno with the Bearcat and Greenameyer/Slovak/Shelton dominating, but in the last 10 to 15 years, it seems the inlines have the edge. Why? I don't have an exact answer, but I suspect it has something to do with the many years of trial and error on perfecting the perfect "Race Merlin Motor" has finally matured. Is there anyone out there now who has perfected the 3350 or 4360 to such a degree as your Thorn's, Nixon's, etc.? If we were to see any engine builder that was able to squeeze as much extra horsepower out of those 4360's as the Merlin, they might be more popular in the Unlimiteds currently.

I'm still in awe of the engineers from the 40's to 60's who built things like V2 rockets , SR-71 , Valkyrie and Saturn V's with slide rules.

I think modern design teams are missing that rebel element with guys like Kelly Johnson and the independence they were given to control the design process.

This has been a really interesting topic so far , it would be great to see some new designs again to attempt to break 500mph.

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Aussie expat lost in Indonesia

True, but how many round motor engined airplanes have won Reno recently besides Rare Bear and Critical Mass a while back. In the last 10 to 15 years, inline engines have won most of the Reno Championships.

Do you mean September Fury?

My comparison is the 4360 vs. the Merlin, not other radials. As an example of the huge drag and not much power added aspect I talked about, just look at Dreadnought. It has a 4360, but yet it is NOT the fastest Sea Fury out there.

It was for quite a while though and it has multiple wins. How many other Sea Furies have won Reno? One? Once only? Dreadnought is also a two seat sport plane with the long canopy.

If the 4360 really was a much better race engine, we would see it in many, many more racers. It's only been used in what, 3 racers in Reno history - 1)Dreadnaught, 2) Super Corsair, 3) Furias. The F2G Super Corsair doesn't count since it was built that way originally, and is an original, essentially unmodified design.

No, the Super Corsair raced at Reno was a one off design and used nothing from an F2G. Not the engine, not the engine mount, not the cowling, not the oil tank, not the oil coolers, not the propeller. It was built from scratch using a stripped F4U-1 Corsair airframe. The engine was set back to within an inch of the firewall.

Why have virtually every single Sea Fury owner put a 3350 in their planes instead of a 4360? Lots of reasons, but primarily the extra weight is not worth the small extra horsepower and the huge frontal area is very draggy. With the 3350, owners can keep the cowling and firewall forward section (QEC) looking somewhat like a normal Sea Fury since it doesn't have to have the huge oversized cowling to accomodate the 4360. Huge oversized cowling = huge amounts of drag.

Here's the answer: Nelson Ezell sells a well engineered 3350 swap kit. Dreadnought was first, then Sanders made parts for Furias. The 3350 Sea Furies came much later. The same cowling was used for the 4360 only the side cowling was extended a couple of bays to make it longer. There is no additional frontal area from a stock Sea Fury.

Perhaps the drag issues are not desirable, but I don't think those can't be overcome with good engineering. Things like fillets, compound curves at wing/fuselage intersections, "coke bottle" designs to minimize transonic drag and efficient use of NACA airfoils, I believe could overcome those issues...<SNIP>...why can't a modern designer with the benefit of CAD, and advanced computational fluid dynamic programs, etc., design something just as fast or faster?

Well, that was supposed to be the Pond Racer. Some of the greatest minds in the disciplines you suggest were on that program. I think they would have been farther along with a Merlin powered single, but the goal was to not use any warbird parts. You just can't overcone intersection drag in any manner other than eliminating the intersections.

Is there anyone out there now who has perfected the 3350 or 4360 to such a degree as your Thorn's, Nixon's, etc.? If we were to see any engine builder that was able to squeeze as much extra horsepower out of those 4360's as the Merlin, they might be more popular in the Unlimiteds currently.

A lot of work over the years has gone into the Merlin and to a much much lesser extent the 3350. Virtually every 4360 racer has used an engine right out of the can (except there is one mod to keep a bearing from spinning but that doesn't add any power). I guess that nobody has needed to upgrade the 4360, it was good enough as-is.

I think you'll find that the key to winning isn't Merlin vs. Griffon vs. 3350 vs. 4360, but $$$$$$$ and planning with a lot of development thrown in. You just have to be prepared. These aren't formula one teams with multi million dollar budgets for wind tunnel testing and dyno testing, these are a bunch of rich guys playing once a year. The quickest way to win Reno is to buy an established winner and crew!

Are the Rolls Royce or Packard versions of the Merlin used for racing ? Is there any real difference ?

Why are Allison rods used in the Merlin ?

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Aussie expat lost in Indonesia

Merlin with the intercooler (reduced charge air temperature increases air density and reduces the chances of detonation) and the fact the Packards are more available in the US where the races are and the fact they are typically installed in Mustangs anyhow.

The Allison rods are stronger.

You will notice that I mentioned "Super Corsair" twice by accident. The first mention of "Super Corsair" was in reference to the Maloneys'/POF's purpose built air racer modified with the 4360. When I mentioned "F2G Super Corsair", I should have left the "Super" part out. That was in reference to Odegaard's Corsair. So my original statement is correct. Sorry for the confusion.



While that is correct, the original reason that the 3350 was used in the first place, was strictly for economics, parts availability, good power/weight ratio and keeping the lines aesthetically similar to the original powerplant. Parts and overhauls for the Centaurus were getting harder and harder to find and more expensive. The 3350 was a logical choice back then, since they were relatively plentiful, cheap and easy to overhaul. The 4360 was not chosen for this common conversion for reasons discussed above. My mention of "oversized cowling" was primarily in reference to length. With the 4360 it has a longer nose. I wasn't aware, however, that the cowling diameter was the same for both the 4360 and 3350. That's interesting. How does the cowling on that compare to the diameter on the original Centaurus cowling? I had always thought that the diameter on the American engines were larger than the Centaurus diameter. Is this not correct?

You're right that the Ezell's produced that easy swap 3350 QEC kit. They, probably more than anybody popularized the conversion. I was told by someone close to the Ezell camp a while back that the Ezell's severely undercut the price on that conversion to directly compete with the Sanders' "perceived" over-priced conversion kit. This is what has made it so popular, along with the reasons mentioned above. I don't remember, but who did the first 3350 conversion - the Sander's or Ezell's?



The Pond Racer, IMO was destined to not ever be as competitive with the Unlimiteds. Anything that flies with a car engine, just can't put out the horsepower as consistently, and without breaking to compete with the proven W.W.II technology of the Merlin's and Allison's. The Pond Racer had constant problems with applying those auto engines to airplanes. I think they could have gotten a lot further and perhaps even broken some records if they would have made an F-82 like twin with Merlin's or Allison's. IMO, the greatest and fastest potential purpose-built Unlimited ever which never realized it's potential was Tsunami. It's unfortunate it's career was cut short.




I believe the reason for that is because: 1) a lot of the early races were won by Mustangs, 2) Bearcats were much rarer even back in the 60's and 70's when a lot of the "Merlin engine gurus" were learning their craft. Mustangs were plentiful in the years before the Sea Furies came flooding onto the market from Iraq and Germany, 3) the 4360 was still not considered a serious contender for applications for Air Racing primarily because of it's weight, the largeness of the motor with it's large frontal area, and there was no airframe large enough, except perhaps the slow airfoiled Corsair, to accommodate it's girth until the Sea Fury became more popular in Air Racing. I don't think that it was so much that people thought it was good enough as is, IMO.



I agree 100%. Most technologies can be improved on, given enough funding for research and development. Money is the single, largest factor in deciding the fastest Reno racer. Whoever has the most resources can pour the time, research, and effort to really developing a winning team. That's why, IMO, I believe that Rod Lewis will, over the next 10 or so years, become one of the winningest Unlimited owners around. He has unlimited resources to pour into his airplanes and racing programs.

Great discussion, by the way!

If the diameters are different, it's not by much. Nelson's 3350 conversion utilizes the original engine cowlings for the Sea Fury. The only change I can remember doing on the cowlings (other than the mounts themselves) is the location of the baffle seals on the inside of the wrap around portion of the cowlings.



I believe it was Larry Burton who made the first 3350 conversion for the Sea Fury, but the engine mount was crooked. Nelson "fixed" one of the old Burton mounts to begin with, which is what got him started making new mounts of his own. The rest of the conversion kit followed, with induction trunks, cowling mounts, exhaust kit (made by Sam......crap...forgot his last name ), etc..

Anyway, I'm pretty sure I have the facts right there. I hope that info is more help than it is confusing.

Gary

Sam Davis?

On Dreadnought (and later Furias), Frank Sanders merely added some bays to the length of the original cowling. The Super Corsair used an A-26 cowling that was extended and used an extra set of cowling latches.

An intersting note is that the later 4360s used in the C-124 had the accessories mounted radially on the accessory case, not mounted longitudinally behind the engine. This allowed the engine to be pushed back closer to the firewall on the Super Corsair. The oil tank was also put behind the pilot to make more room. My understanding was that the 4360 in the Sea Fury application could not be moved aft, that is why the nose is so much longer than stock and why the vertical stabilizer needed to be enlarged.

Dreadnought also has lower fuel flow at takeoff and in cruise, at the exact same speeds, than does a stock Sea Fury (with the Centaurus).

The Pond Racer met all the requirements on paper, but suffered from numerous development challenges related to the engines. They had nothing in common with passenger car engines however. They were GTP based engines built by Electromotive as I recall.