P-47 Top speed without wing Pylons?

[wuzak]

I'm not too sure where the limit for HP was for a stock Merlin, but the limit would come from the stock rods. According to Lovesy they ran one at some 2,650 HP.

Stock rods on Merlins changed with time. The Merlin I rods wouldn't have survived at the powers that the 2 stage Merlins were capable of producing.

The Merlin RM.17SM ran 2,640hp on the test bench running +36psi, 3,150rpm and ADI. When corrected for air temperatures, it was 2,620hp.

The first attempt at the endurance test failed because the rods broke. The reason for this was that the rods used were of an earlier specification.

In 1943 a Merlin 66 being used to prototype the 100-series Merlins ran at 2,380hp @ 3,300rpm and +30psi dry.

The RM.17SM was rated at 2,200hp @ 2,000ft and 2,100hp @ 15,000ft, again without ADI.

The Merlin 66 with +25psi boost was rated at 2,000hp @ 5,250ft.

 

[GregP]

The BEST of them give up at between 2,500 and 2,700 ... maybe 2,800 HP. They break and go through the crankcase. So the serious guys use Allison G-series rods. They are good for well over 4,500 hp before they break ... IF you can drag it out of the engine.

Joe has a few Allisons in Europe on the tractor circuit with fuel injection and twin turbos, spinning 4,500 rpm without problem. Of course, this IS for a short tractor pull run, NOT an 1,100 mile round trip mission in an aircraft.

The main point is Allison rods are VERY strong. It is NOT that Merlin rods are weak, they aren't. If you are running an airworthy stock Merlin in a stock warbird, there is no issue at all with Merlin parts. It's only when you get to high racing horsepower that it shows up. That was NOT the case in WWII, or even with the early "R" engines that were hot-rodded and raced. This is NOT a knock on Merlins ... it only has to do with aftermarket air racing engines today.

 

[wuzak]

My point being that 100 series Merlins had stronger rods than 60 series Merlins, but they would be more rare than rods for 60 series Merlins and, probably, G series V-1710s.

 

[GregP]

I understand. Point taken.

 

[grampi]

Greg, did you notice your Rare Bear was bested by a Mustang at Reno...again!

 

[GregP]

Hi grampi.

Yes I noticed. I was sentimentally pulling for Voodoo since Stevo Hinton was flying Voodoo, and he had engine trouble in the Gold Final race. Stevo lost the championship for the first time in seven years. One time for engine troubles in seven years isn't bad at all considering the power levels they are running. In fact, it is pretty good!

The Bear finished pretty well in second, thankfully with no engine woes. The P-51's have a higher aspect ratio than Rare Bear. The density altitude at Reno means that aspect ratio is important. The Cassut racers in Formula 1 have the same trouble with the longer-wing, more narrow-chord Formula 1 winners.

In a straight line, Strega, Voodoo, and Rare Bear all have about the same top speed but the P-51's turn a bit better at Reno and lose a bit less speed due to aspect ratio. Rod Lewis, Rare Bear's owner, isn't running Nitrous Oxide, and that would buy them some speed at the expense of possibly blowing an engine. I think he probably has enough money in Rare Bear and Reno without possibly blowing an engine. Let's not forget he is also usually running a Sea Fury in Race 232, and a Tigercat or two. He also sometimes flies the P-38 Glacier Girls to Reno. So collectively, he is spending a great deal on money on Reno. There is probably some speed left in Rare Bear, but it remains to be seen whether or not he will go after that speed or be content with the speed he is going.

I have met Rod twice and I can say he has a fabulous collection of warbirds and isn't afraid to fly them frequently. Whatever else Mr. Lewis may be, he is a warbird collector of the first magnitude. I have occasionally wondered if he needs to adopt a "son" who is older than he is …

Nice to see Rare Bear back in healthy form flying at characteristic speeds. And I think that Stevo Hinton Jr. will probably see another Reno where he doesn't have engine trouble. That is NOT to say he'd have won if he hadn't suffered engine woes. Strega is FAST and Hoot Gibson is one of the genuine nice guys. Couldn't be happier for him. But it WOULD have been nice to see a good head-to-head race all the way. If Rare Bear was running Nitrous, it might have been interesting three ways. But perhaps the P-51s would have just stepped it up a bit. Usually in the past, when they did that … they blew up. But it looks like Team Strega and Team Voodoo have figure that one out … for the most part.

 

[grampi]

I just find it funny since you claim the Mustang's engines get het soaked and therefore can't maintain the same power levels for the entire race, and you claim Rare Bear actually gets faster as the race goes on, but yet Rare Bear gets beat every year by a Mustang...

 

[Balljoint]

I just find it funny since you claim the Mustang's engines get het soaked and therefore can't maintain the same power levels for the entire race, and you claim Rare Bear actually gets faster as the race goes on, but yet Rare Bear gets beat every year by a Mustang...

Heat soaking, like most engine hot rodding challenges, is not an intrinsic, unsolvable problem. Just a tough nut to deal with. As with rods breaking they may have found a bit of a fix. Even with an old and mature engine there's still an experience curve even if it's a bit flat.

If they're faster/live longer that usually means something new has been learned/used.

The above is submitted from a deep reservoir of ignorance of the specifics.

 

[drgondog]

With all the modified wings and weights that deviate far from 'stock', I suspect wing loading as a function of the current wing area compared to stock is the first thing to look for - before AR.

Induced Drag IS a function of the inverse of AR*Oswald efficiency - but Induced Drag is extremely low at 500mph TAS at 5000 ft AGL. I would look to W/L first to explain the difference in turn..

The second thing I would look to closely is the Drag Rise behavior and Compressibility factor where those guys are running ~ .66M for those separate airfoils.. Rare Bear would have to have a far different wing than stock. So would Strega/Voodoo but in the near same family of laminar/low transonic type airfoils?

 

[GregP]

Hi grampi,

When Lyle Shelton was flying Rare Bear that's the way he ran it, more slowly in the first 2 - 3 laps. The, when everything was in the green, he'd power up. John Penney flew that way when he flew for Lyle, but may have changed his ways when Rod Lewis bought the Bear. Rod is not having them use Nitrous Oxide in the last 2 laps and I don't know the individual lap speeds this year.

The part about the heat soaking Merlins comes from Stevo Hinton Jr., Hoot Gibson and a few others. They all say they slow down as the race proceeds as long as nobody is catching them. Their race average speeds bears this out and Stevo had a fast lap in Strega once of 512 mph, but won at something like a 486 average. For all I know they might have more water in the oil cooler boil-off these days. It LOOKS like they got the liquids figured out, but lap speeds will tell all when they are available.

This year the Bear was running about as fast as it ever did without nitrous oxide use, so it looks to be back in healthy status. According to Steve Sr., Setvo 's engine went flat at the start and he soldiered on for some laps before basically running out of oil, and doing a mayday down safely. You might recall that Steve Hinton Sr.'s engine went a bit "flat" in 1979 and the Red Barron didn't make it all the way to the runway safely. He was quite lucky to survive the crash when the prop blades went flat and he basically lost flying speed while trying to land it. Six prop blades create a LOT of drag.

I wasn't there this year as I had and am still having some important times in personal life just now. But if the situation happens to be good in 2016, I hope to be back for the race next year. If so, I hope Voodoo is back healthy so we can see a great race. Good racing is what I want to see ... not emergencies. These are good guys and safer is better.

Meanwhile, I'm sure Hoot Gibson is happy to have had the chance to fly Strega. Salute to Mr. Gibson and Team Strega. It would be great to see them BOTH back healthy in 2016. I think his fast lap was 501 and the average was 488.8 or so. Fast lap is usually lap 2 - 4 for a P-51 but, again, I haven't seen the individual lap speeds for this race yet and can't say yet.


Hey Bill,

I'd love to do wing loading but these top racers won't tell you the weight or the wing area or the airfoil, so it would all be a big "estimate." Rare Bear doesn't have hardly any Bearcat systems left in it, and the airfoil is definitely far from stock. I KNOW that Strega and Voodoo's airfoils have been profiled, but nobody will tell me to what airfoil or how many systems have been removed. Both run boil-off oil coolers like the Bear, but the race weight would be another SWAG.

Rare Bear has a span of 30 ft 6 in and gross weight of 8,500 lbs ... but no race weight, empty weight, or wing area. In 1995 he qualified at 489 mph (on nitrous oxide).

I know Jon Sharp said that aspect ratio was a big thing at Reno for keeping speed up, but it may have been misdirection for the masses. He was usually near the front of whatever class he happened to be racing in and retired as the winningest pilot of all times. Nemesis NXT certainly has a higher aspect ratio than a Cassut, but I don't know the weight of a racing NXT. The airfoil is a "modified natural laminar flow" unit. The kit specs say empty weight is 1,600 lbs. and gross weight is 2,600 lbs., but no "race weight." His record speed was 406 mph on a Lycoming IO-540-NXT putting out an estimated 750 - 800 HP ... but he never did confirm the power or the weight or the airfoil or the AR. The effective AR is 8.23 (24 ft span, 70 sq ft area).

A Cassut has a span of 15 ft and an area of 67.5 sq ft., so the effective AR is 3.333 .

Quite a difference in AR at what is usually a pressure altitude of some 6,000 - 6,500 feet or so on race day. Empty is about 500 lbs and gross is about 900 lbs, but no race weight.

There's a lot of missing data ... as you might expect for racers on active teams.

 

[wuzak]

I guess the heat soak issue is due to running at 500mph and 3,500hp using a cooling system designed for cruising at ~300mph and ~800-1,000hp.

 

[GregP]

It could be. It could also be that the engine was designed to produce the heat of 1,500 - 2,000 HP and the components are just not quite up to the heat of 3,850 HP. It's likely the fluid flow cannot absorb that much heat, but I am not sure at all if that is correct and don't know anyone who is other than probably Pete Law and his type of people. I haven't asked him since hopped-up engines have NEVER been really reliable. It should be no surprise when one goes away ...

I AM pretty sure that if I took a 150 HP automotive eninge and dropped the comrepssion ratio and suoperhcarged it t put out 385 HP, it probably would show the same signs of weakness. I HAVE taken a 90 HP rotary and made it into a 220 HP rotary. It lasted one season and when it did go, it was rather spectacular.

Most engines aren't too tolerant of being run at power levels of twice the deisgn power level and beyond. As long as they're cheap, why not do it if you are so inclined? But when they cost hundreds of thousands of dollars like a Merlin, it becomes very limiting when you blow them up regularly unless the pockets are VERY deep.

 

[drgondog]

Hey Bill,

I'd love to do wing loading but these top racers won't tell you the weight or the wing area or the airfoil, so it would all be a big "estimate." Rare Bear doesn't have hardly any Bearcat systems left in it, and the airfoil is definitely far from stock. I KNOW that Strega and Voodoo's airfoils have been profiled, but nobody will tell me to what airfoil or how many systems have been removed. Both run boil-off oil coolers like the Bear, but the race weight would be another SWAG.

That is my understanding also.

Rare Bear has a span of 30 ft 6 in and gross weight of 8,500 lbs ... but no race weight, empty weight, or wing area. In 1995 he qualified at 489 mph (on nitrous oxide).

If the plan form didn't change other than reducing span it should be easy to calculate. The span reduced 2'-9" out at the tip - but I haven't fount the root/tip chord data yet. Empty weight without GFE was 7,070 pounds - so Oil, coolant, race fuel and pilot seems to be the round up for GW - would guess no more that 7800 pounds Max - but still a guess. 7.6% reduction in wing area. If same plan form the tip to root chord ration is ~ 40%. Gotta go for now but should be easy to narrow down the wing area.

I know Jon Sharp said that aspect ratio was a big thing at Reno for keeping speed up, but it may have been misdirection for the masses. He was usually near the front of whatever class he happened to be racing in and retired as the winningest pilot of all times. Nemesis NXT certainly has a higher aspect ratio than a Cassut, but I don't know the weight of a racing NXT. The airfoil is a "modified natural laminar flow" unit. The kit specs say empty weight is 1,600 lbs. and gross weight is 2,600 lbs., but no "race weight." Race GW probably 400-500 under GW when considering fuel and oil for Race rather than X Country? His record speed was 406 mph on a Lycoming IO-540-NXT putting out an estimated 750 - 800 HP ... but he never did confirm the power or the weight or the airfoil or the AR. The effective AR is 8.23 (24 ft span, 70 sq ft area).

A Cassut has a span of 15 ft and an area of 67.5 sq ft., so the effective AR is 3.333 .

Quite a difference in AR at what is usually a pressure altitude of some 6,000 - 6,500 feet or so on race day. Empty is about 500 lbs and gross is about 90 lbs, but no race weight.

There's a lot of missing data ... as you might expect for racers on active teams.

There is zero question that AR is critical for increase/decrease CL directly affecting Induced Drag and that the turns are where CL peaks.

So, as you know, the trade off is to balance reducing the parasite drag of the wing for the straight runs (shorten the span, clip wing tips, smooth wing surfaces and polish - maybe get clever about Boundary layer control - but that effectively reduces AR and god knows what to Oswald efficiency change for the worse)- or improve the turn by increase area/AR (in comparison to change above), modify tip to increase plan form induced drag effects but both of those mods should increase parasite drag and reduce the straight run performance.

I received an interesting related question from a friend who knows Steve,Jr very well, regarding 'effect of changing thrust axis' to which I answered and heard no more on the subject.... The racing teams that win have always had top industry expertise like the Ex-Lockheed guys Boland and Law (and consultants like Lednicer)plus the powerplant gurus.

 

[grampi]

I guess the reason I question the claims of the engine getting heat soaked is because a Mustang wins every year. If it were true that the Mustang pilots have to bring back power due to heat soaking as the race goes on, and Rare Bear is just as fast and does not suffer from getting heat soaked, then why doesn't Rare Bear overtake the heat soaked Mustangs and win?

 

[GregP]

Hi again grampi,

If you follow Reno, Rare Bear has been plagued with mechanical and engine woes since Rod Lewis bought it. This was the first year in a long time that it ran well the entire weekend with no glitches. Glad it is looking healthy again. One year the new crew managed to hook things wrong and pumped water into the hudraulic system! So Rare Bear flew with the main gear about 7/8 up that time.

Mustangs don't win every year or Rare Bear wouldn't have so many Reno Chamionships. They HAVE been winning recently because ONE guy, Tiger Destefani, had a very fast and very reliable Mustang. Stevo is a very smooth stick and KNOWS the racing engines. He won 4 years straight in Strega and the next tine Tiger competed in it (2014) he blew the engine trying to catch Stevo in Voodoo. Rare Bear's top qualifying speed is around 489 mph or so, and the two top P-51's can sprint for a lap or two at 500+. Their race-winning speeds haven't been very impressive for the most part, though there WAS a 499.9 average in there, and mostly have not been faster than Rare Bear's winning speeds some years back.

If Rod Lewis would allow the use of Nitrous Oxide, the Bear might be right there with Strega and Voodoo as far as average goes. Stew Dawson is a very good pilot but when the owner says "no Nitrous," Stew probably doesn't turn it on. If he did, everyone would know it since the exhaust would turn dirty brown.

If they flew in a straight line, I think the Bear is good for about 535 mph, Strega for about 545 - 547 and Voodoo probably about 540 - 545. It is horrendously expensive to try for a world record, so none of these guys have tried for it, and there is NO REASON I can think of that makes any sense for them to get together and have a straight-line race. The probability of expensive damage is just too great. Somebody would blow an engine ... and for what? Bragging rights? They already get that at Reno.

If Reno continues as an event, we may see the Bear back in the wnner's circle. Right now the three fastest unlimiteds are Strega, Voodoo and Rare Bear. I think Dago Red is being converted back to stock configuration. Sherman Smoot may surprise us all one day in his Yak. Somehow he is always getting faster ...

Time will tell.

As far as heat soaking goes, you either believe the top pilots or you don't. I do. There is no other way for me to find out ... I'm not a Reno race pilot and have zero chance of flying any of them. I know a lot of people have seen the in-cockpit video from Voodoo. Please note that the public telemetry does not have a manifold presure gauge in the frame.



Hi again Bill,

I think I could make a very close estimate of wing area for Rare Bear and Voodoo and might try that in the future. Right now I'm preparing to teach a year of industrial electronics and have little in the way of free time. I'm sure Stevo knows the span of Strega as he grew up working on it for a lot of years before he ever flew it. Not too sure about the estimate of race weights. I MIGHT get someone to tell me, but your guesses are probably as close as any.

They removed EVERYTYHING from the Bear and only put the systems back in they required. So there is no wing fold mechanism, no hydraulic system for the landing gear (it's air operated), and almost nothing inside the rear fuselage except the oil boil-off system, and it only carries tankage for 180 gallons of fuel. We all can see it has no flaps. I do not know exactly what equipment has been installed. Probably only Dave Cornell and the current crew know that. Well, you can probably throw John Penney and Stew Dawson into that group, too since they must know the systems to race it and be safe in an emergency. I DO know the systems are nothing like a stock Bearcat's systems.

We might find all this out when they quit racing but, since they're active racers at this time, there is no reason for anyone to tell their secrets to the public.

 

[wuzak]

Greg, where do they keep the water for the cooling system?

(I understand that they spray copious amounts of water onto the engine to cool it.)

 

[drgondog]

Greg - I had not considered flaps and wing fold mechanisms being removed from the Basic weight. good catch. I suspect Voodoo is close to 7800-8000 basic weight before Hinton and Fuel/oil/coolant load so the Bear probably has a lower W/L as it started out with more wing area/lower W/L in stock versus stock - and the F8 has more removable 'stuff' -----------> meaning I am leaning to increased Induced drag due to planform mods to reduce AR and likely also reduce 'e' due to tip geometry.

Having said that, the Bear should have gained some benefit in dash speed - or why bother? Later

 

[GregP]

Hi Wayne,

There is a water tank for the spray bar. My estimate is they go through something like 8 - 10 gallons per lap for 8 laps and probably don't start the spray bar until the temps get well up into the green. That probably takes something like 1/2 of the first lap or so .... I'd guess the spray tank at something like 60 - 80 gallons of water, give or take a bit. Might get away with 50 gallons. Depends on flow rate. Only the teams really know.

Hi Bill,

As for the P-51's Voodoo and Strega, I'd assume no armor, no armament, minimal hydraulic system, both have carbon fiber cowlings and other bits and pieces including the belly air scoop area, no incidence on engine, wings, or tail, evaporative oil boil-off system rather than a standard oil cooler, proprietary airfoils, very GOOD surface interfaces for things like aileron ends, gap seals, formula 1 type canopies, probably props that are too short for a limited category aircraft, well-sealed fuselage joints to eliminate as much leakage as possible, and both have trailing edge fuselage-wing fillets of carbon fiber. So the basic weight is probably 500 or more pounds lighter than stock. Both also probably have only the minimum fuel and oil tankage they think is reasonable for flying to and from Reno on the ferry engine.

Nothing you didn't already think of, I'm sure.

 

[dedalos]

Polishing my motorbike s engine s (1000 cc capacity) flow surfaces gave me a 5% gain. It is a 2008 constructed model. A serial production ww2 engine , i assume would be of worse building quality. Would be possible for the macanics of a front line unit ,if they had the time, to achieve similar gains? 5% on a db 605 would be almost 75 ps.
Of course such modifications require very specialized and skillful technicians