The Pond Racer.....Rutan's Watergate

[Tin Man]

Re: The Pond Racer.....Rutan's Watergate

Juke
You're throwing out alot of numbers there, what is your background in aerodynamics and propulsion? I'm under the impression you're a model airplane builder. Not that there's anything wrong with that.

[First time Juke]

The Pond Racer...inspiration for a light twin-racer !

Tom,

Like I said on my reply to Michele, I am an architect and an aviation enthusiast. I do time to time build models and draw some plans of them too.

Propulsion is interesting and I think PR had lots of it.

I read at another site that a Mustang scoop/radiator created 700 kilos ( 1500 pounds ) of thrust. Correct me if I am wrong. I can see that the PR radiator exhaust is not directed as it is in a Mustang. I assume it does not create as much ram-air effect as it could have.

I have read several books about piston aircraft history and details memorized from there.

I have also hanged around here at AAFO.com for several years and info has been exchanged by several guys at the site.

My estimates for a new twin for a car engines is purely imaginative or very uneducated guesses. No mathematical calculations to back them up. Just plain cold reasoning.

There was a time when I did dream about being an aviation engineer, but hey finns were flying Mig-29s back then and the future did not seem very bright back then as an aviation engineer.

I have these imaginary racers drawn up. I can enclose my entry for the " twin contest ". I think it does utilize the ram air to some extent...the square box on top of the nacelle is supposed to be the radiator position. I am glad to help if someone shows real interest for it. The weight estimate of my twin is wrong....it has been calculated in my head for two V-8:s. I have a slight intention to make a flying model of it soon. It has been inspired by PR and several american twin fighters like Grumman Skyrocket http://www.wpafb.af.mil/museum/research/p50.htm and http://www.fiddlersgreen.net/AC/airc.../skyrocket.php .
I also find Westland Whirlwind very sporty: http://www.cbrnp.com/profiles/quarter2/whirlwinds.htm + http://www.constable.ca/whirlwind.htm

I have the "Reno Gold" book and thus Rick Brickerts caracter is familiar. I was very sad for his loss. I also did loose a friend in an aviation accident ( collided with an other sailplane in World Champs in Texas ).

Am I asking too many questions Tom ? I think I internet too much, maybe I ought to take a brake ? Have a good day anyway.


rgds,

Juke

[AirDOGGe]

Re: The Pond Racer.....Rutan's Watergate

I read at another site that a Mustang scoop/radiator created 700 kilos ( 1500 pounds ) of thrust.

Too high. The numbers I usually see in texts under ideal conditions were closer to 300-400 pounds of thrust, which roughly counters most of the drag induced by the scoop and radiator. This article at Air & Space has some good discussion on the topic:

http://www.airandspacemagazine.com/ASM/Mag/Supp/JJ99/Mustang.html

I agree the turbo exhausts possibly only would have gained 1 mph more, but placing the stacks behind one another could have given ( along with being shorter ) 4-5 mph more.

That doesn't sound correct to me (another "layman", so to speak).

If I recall correctly, drag increases to the square of velocity. This means doubling your speed increases drag by a factor of four. Because of this, increasing thrust has less effect on your velocity the faster the aircraft is flying



For that reason I believe the direction of the exhaust of the PR's little nissans would have very little effect at unlimited race speeds, even if the exhaust velocity had not been reduced by the turbocharger and regardless of the position of the stacks. 1 MPH maybe if that, but 4-5 mph sounds very optimistic.

[King]

Re: The Pond Racer...inspiration for a light twin-racer !

I also did loose a friend in an aviation accident ( collided with an other sailplane in World Champs in Texas ).Juke

I think we discussed this, but I knew Ansi Pasilla <sp> from the worlds in Texas. Ansi had a mid-air with a Japanese pilot while thermaling in a gaggle. In fact I presented the country flag to the Finish Team Captain after the memorial service after his accident. I was an Official for the Soaring World Championships when held here.

[First time Juke]

Re: The Pond Racer.....Rutan's Watergate

Too high. The numbers I usually see in texts under ideal conditions were closer to 300-400 pounds of thrust, which roughly counters most of the drag induced by the scoop and radiator.

Thanks for this information AD. I am wiser now.It may have been then 700 pounds the figure...not kilos.

For that reason I believe the direction of the exhaust of the PR's little nissans would have very little effect at unlimited race speeds, even if the exhaust velocity had not been reduced by the turbocharger and regardless of the position of the stacks. 1 MPH maybe if that, but 4-5 mph sounds very optimistic.

In a Spitfire they gained 2 mph just by sticking them out and turning them behind pointing. Also germans made a special arrangement to gain more speed.

Regarding the position and lenght of the stacks. Ever tried putting hand out of the car at 60 mph ? I bet one would loose his/her fingers trying to do it at 520 mph.

Finnair changed the position of the windscreenvipers on all they MD 80s when someone discovered how much drag the older stationary position caused. I heard it once. It was a sizeable cut in travel expenses per flown distances.


Ok Airdogge. I rest my case..there would then be a too big gap for a car engined twin to catch up with the BEAR even if all of the ram-air would be used ( and possibly an incease of drag in the less propulsion possessing airframe ). Unless there was an engine that weighed 500 lbs and produced that 1000 hp:s like the Nissan engine was supposed to deliver.

I am a layman which was now proved by Airdogge.

[51fixer]

Re: The Pond Racer.....Rutan's Watergate

I agree the turbo exhausts possibly only would have gained 1 mph more, but placing the stacks behind one another could have given ( along with being shorter ) 4-5 mph more. Insignificant when going after Bear record for sure. What was the role of Bruce Boland in the PR team anyway ?

When Steve Hinton took over the project he brought many of his brain trust. Workers, engineers and the like he had worked with over the years to bring a different, real world perspective to the persistant issues that it had. Bruce was one of those guys.

Was the highest speed ever recorded by PR on a flyby around 440 mph ?

I worked on it during it's last year of existance. That Reno was the 1st time I crewed on the PR. I really don't have that info.

How did the 6-8 inches change forward of the engines affect the flying caracteristics. Did Rick ever comment on that ?

Part of the real world changes the Steve and his crew performed were to incorporate a spray bar system for the radiators, cut down the intakes size for the radiators (inboards were eliminated), install a varible door outlet for cooling exit air and install an ADI system. To do all that required tanks and adding weight. To offset the CG changes the engines were moved forward. Spray bar tanks were install on the firewalls in the space created by moving the engines. A bladder was made and installed aft of the pilots seat in the center pod for ADI. These items were also required as running av gas blends of fuel make more heat so the ADI was required. The spray bar was needed to reduce the drag of the cooling system. Rutan designed it with large itakes which he kept increasing in size as the thing ran hot on the ground as all warbirds do. Instead of understanding this they kept trying to fix it by increasing the drag while flying.

Were the engines performing better or worse...using methanol or A-10P fuel ?

I didn't work on it when it ran on meth. It was a pain from what I was told. Certain epoxies were not compatible with the fuel. You would fuel, run, de-fuel, flush with av-gas, run and then drain that fuel. Anytime the plane was ferried it was flown on avgas. The engine computer chips were changed and away you went. When you race or run on the meth you would change to the meth fuel chips. You got holes in alum fittings, I repaired fuel leaks years later in small panels in the wings that had gotten softened by this fuel. The engines ran fine on the A-10P from a operating standpoint. They required a whole new set of engine chips. Prior to that Reno dyno work was carried out on a different fuel blend which gave promising results. It never flew using that fuel.

Previously you also said all the wires ( ie the wires were very heavy ) made the AC heavy. How much do you estimate PR weighed empty ?

That has left my memory banks. My point was that hoses, lines and wiring were not put in in a clean, well thought out manner. It was a mess. Many lines were ss braid hoses that could have been an alum hard line. This could have lightened the weight some.

Rich P

[First time Juke]

Re: The Pond Racer...inspiration for a light twin-racer !

I think we discussed this, but I knew Ansi Pasilla <sp> from the worlds in Texas. Ansi had a mid-air with a Japanese pilot while thermaling in a gaggle. In fact I presented the country flag to the Finish Team Captain after the memorial service after his accident. I was an Official for the Soaring World Championships when held here.

I remember someone said Anssi had complained about the flying behaviour of the same japanese pilot he collided with the day before the accident. What really happened remains a mystery. I valued his friendship alot.

He really enjoyed flying and one aerobatic soloflight with a sailplane he performed during an airshow once really was breathaking. I had never realized a sailplane can pull out such fantastic maneuvering at low altitude.

------------------------

Rich,

Thanks for the input.

[HiredBitSlinger]

Re: The Pond Racer.....Rutan's Watergate

The engines were designed for methanol, that's what they used in F1 racing.

I have seen this before. This is incorrect on two accounts. First, F1 does not burn methanol. They use their interpation of gasoline. True, a few years ago it got way out in of control, but the sanctioning bodies got them under control. Second, the engines were not from an F1 project. They were the engines used on the Nissan GTP. This was raced, among other places, the IMSA series in the US. The engines were built by Electromotive. The Nissan was also raced in Europe, but I do not know who did the engines. I believe that Electromotive were the suppliers for the Pond Racer.

Dan Plunkett

[AirDOGGe]

Re: The Pond Racer.....Rutan's Watergate

In a Spit they gained 2 mph just by sticking them out and turning them behind pointing...

That validates my point somewhat. The Spit has the thrust of 1650+ cubic inches of engine displacement (27 liters) to push it along, and it only gained 2 mph. .... 27 liters of cylinder displacement produces quite a large quantity of high velocity hot gases and a significant amount of thrust...

...But even with a smaller airframe the Pond Racer would only have the exhaust thrust of a total of 366 cubic inches (6 liters, or 3 liters x 2) of displacement, so their thrust would have much less affect on the P.R.'s top speed. 1 MPH increase with any exhaust pipe system sounds more likely to me.

-

As far as a 4-5 mph increase not helping much in beating other aircraft, true when looked at by itself...

But sometimes it's a 5 mph mod here, 3 mph there and small increases from numerous other improvements that total up and make the difference between 1st and second place. Every little bit can count big time in the end.

.

[First time Juke]

Re: The Pond Racer.....Rutan's Watergate

Airdogge,

You have to be careful now. That 2 mph has been gained in a comparison to nothing...original Spit ( 5054 ) had only holes as exhaust in the fuse and gasses came in at 90 degree angle from the fuse.

What I suggested was making an existing two large tubes to be shortened and put into a row. Compared to a situation if the fuse was clean without the potruding stacks the Pond would have gone 10 mph faster ( an assumtion ). It couldn't because the heat would have caused melting in the nacelles. Also the thrust of the exhausts meant it caused a thrust vector to bring the plane down ca 1 mph...this had to be compensated by more lift.

Also as I see it the radiator exhaust caused small vector of thrust..unfortunately into wrong direction....down. If Pond had taken full advantage of the Meredith effect it would have been according to your link about 220 lbs worth of thrust...not much. Do you agree ?

I don't think even if these details had been correct that PR could have gone 500 mph; 450 mph at most.

If the engine cooling problem was caused by the inadequate airflow in the cooler...then maybe the PR would have created 100 more hp. But AD all this is pure speculation....I dunno much about engines and their cooling in air racers with ADI etc.

Then again I don't also know how much the propulsion in PR was worth..it was very sleek.

Se ya later dudes at a better time.


regards

[440_Magnum]

Re: The Pond Racer.....Rutan's Watergate

You have to be careful now. That 2 mph has been gained in a comparison to nothing...original Spit ( 5054 ) had only holes as exhaust in the fuse and gasses came in at 90 degree angle from the fuse.

Which for all I know *might* be better than hanging stacks out in the breeze regardless of which way they're pointed.

I read a lot of talk about thrust from Merlin stacks and I have no doubt that the stacks push forward on the airframe when exhaust is flowing, but I sometimes wonder whether it is much of a net gain. Each stack produces a pulse of thrust every other crankshaft rotation. The rest of the time its just hanging out there causing drag. I've never really seen any comparison between having 12 individual stacks versus an exhaust manifold internal to or at least faired into the cowling and a single exhaust dump.

Now with a Bearcat or Sea Fury its a different deal, because the stacks all lead to an ejector chute and the exhaust flow is more-or-less the combined flow of all the stacks, is combined with cooling air outflow, and gives a much more continouous flow. Even then, I have to wonder if the "super stock" Sea Furies are all that effective with a line of individual stacks leading almost to the point where the airflow from in front of the ejector has to merge with the exhaust flow. Something like Pardue's Fury, Critical Mass, or the Bearcat where the mixing of gasses from individual pipes and engine cooling air happens upstream of the ejector opening makes more sense intuitively. But my REAL point is that intuition is sometimes (usually?) a lousy engineer , so I'm not making any real firm assertions there.

What I suggested was making an existing two large tubes to be shortened and put into a row. Compared to a situation if the fuse was clean without the potruding stacks the Pond would have gone 10 mph faster ( an assumtion ).

Well, if we're going to pull numbers out of our ears, I'll pick zero. The Pond engines were turbocharged, so the exhaust had already been expanded through the turbine, slowed in velocity, and given up a *lot* of its energy. If you put enough back-pressure on a turbocharger so that the exhaust is producing any thrust, then you're impairing the function of the turbocharger and losing power that could have been used to compress intake air instead of give jet thrust. One of Kelly Johnson's bulleted list items of shortcomings of the P-38 was that they couldn't even put a hood over the turbocharger to direct its flow aft in search of a *little* thrust without causing enough backpressure to reduce its performance. I'll admit that my "zero" is a complete s.w.a.guess, but I think its about as well-founded as "10 mph."

Then again I don't also know how much the propulsion in PR was worth..it was very sleek.

It LOOKED sleek. How "sleek" it actually was is (obviously) still being debated.

[speeddemon]

Re: The Pond Racer.....Rutan's Watergate

I read a lot of talk about thrust from Merlin stacks and I have no doubt that the stacks push forward on the airframe when exhaust is flowing, but I sometimes wonder whether it is much of a net gain. Each stack produces a pulse of thrust every other crankshaft rotation. The rest of the time its just hanging out there causing drag. I've never really seen any comparison between having 12 individual stacks versus an exhaust manifold internal to or at least faired into the cowling and a single exhaust dump.

A very well respected crew chief, who currently works on a round-engine, but has amassed bocoup success in the past with one white, and two different red Mustangs, had a discussion recently with me about JUST THAT.

I was discussing the shape and placement of exhaust stacks, and the theory behind them, and he said that his research determined that something like 18% of the total thrust generated by the engine/prop came from the exhaust. That was a shocker. I knew that there was something to gain, but I was thinking low, single digits.

I'd say that 18% is a pretty hefty 'net gain'...wouldn't you?

[51fixer]

Re: The Pond Racer.....Rutan's Watergate

All one needs to look at is the head and stack setup. The port around the exhaust valves on the Merlin has a large area as does the outline of the port where the stack attaches. Compare that with the area of where the gases exit at the end of the stack. Anytime a large volume is compressed into a smaller area you generate an increase in pressure.
The racer motors use stacks with a larger ID oulet than stock to flow at a higher rate. Tennis balls are used as plugs on some of these which makes for an interesting event when you see these balls rolling through the pits when someone forgot to remove them before starting the engine.
Don't ask as I have forgotten who, just that it happened in the 70's for the time I witnessed.
On the PR the outlet of the stacks were a foot or so above the turbos and not a hard, solid mount as I recall. (Some movement) Using the every action has a opposite reaction rule these could not have been putting out much thrust as the structure wasn't there to support much of a load. Compared to the structure of the stack, head mounting of a merlin or allison you can tell they will absorb the forces. Many a horizontal leading edge of a P-51 has impacted from chunks of an exhaust stack that was overworked and overlooked. Over time the upper and lower surfaces of a merlin stack will bulge from heat and pressure.
Rich P

[440_Magnum]

Re: The Pond Racer.....Rutan's Watergate

A very well respected crew chief, who currently works on a round-engine, but has amassed bocoup success in the past with one white, and two different red Mustangs, had a discussion recently with me about JUST THAT.

I was discussing the shape and placement of exhaust stacks, and the theory behind them, and he said that his research determined that something like 18% of the total thrust generated by the engine/prop came from the exhaust. That was a shocker. I knew that there was something to gain, but I was thinking low, single digits.

I'd say that 18% is a pretty hefty 'net gain'...wouldn't you?

More than hefty! I was thinking single low digits also. I'd like to know how that was actually quantified. Like I said, intuition is often a bad engineer and I love hearing about cases where fact and intuition are at opposite extremes.

[speeddemon]

Re: The Pond Racer.....Rutan's Watergate

More than hefty! I was thinking single low digits also. I'd like to know how that was actually quantified. Like I said, intuition is often a bad engineer and I love hearing about cases where fact and intuition are at opposite extremes.

I would not be the one to have the fact and intuition NUMBERS, and I'm sure that those are probably proprietary...if not TOP SECRET. But the theory in which he was describing his experiments and such was quite eye-opening. And you can't argue with the success. I guess it all has to do with how much $$$ you want to spend.

But lets just say that since the time that Rolls Royce/North American designed the way the stacks on the Mustang were shaped in 1943, there have been some significant research discoveries about high velocity exhaust, and how to gain maximum efficiency from it.

18% was just a jaw-dropping number. And his comment was "and it's such a freebie...I don't know how anyone could pass something like that up".