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  #31  
Old 05-20-2004, 08:46 AM
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Clutch Cargo Clutch Cargo is offline
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Default So...you ran some tests eh?

Just see what kind of boost you have from a turbo at 800 rpm on a 13B (lets say mild street porting because anything more probably wont go as low rpm). At what point does the turbo begin to "break even" from being a "drag" to being a power producer. Remember: A rotary's combustion chamber is more sensitive to exhaust effieciency because of the shape and because it doesn't have valves.

A supercharger has straightline "drag" and boost that doesn't have to wait for the ineffeciency of the exhaust gas force to build to become efficient as a turbo does, the drag it creates is quickly compensated during low rpm acceleration, whereas the turbo has to break even first, if the speed that is the "break even" point is not acheived during use, then the turbo is in "debt" until it passes it's efficiency threshold rpm. The SC isn't limited by this and produced boost immediately. So peak power, load and pre-enhancement exhaust data have to be figured in as well..

Then there is the cooling load the turbo produces...

At a given altitude at a given temp, the turbo at higher rpm will always be efficient.

But which is more efficient:
A Honda Civic with a 16V engine and 5 spd ?
A Peterbuilt tractor with a 425 Cat engine and 15 spd?

Think about THAT one...
If you need to find efficency, you need 100% of the load data

But as John says: "That's my opinion, I could be wrong"
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  #32  
Old 05-20-2004, 09:11 AM
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Hello No. 4,

You probably used to dust my house in Meekatharra as you went past...

Superchargers: Can be clutched, and are more an air-pump than a blower, so can be setup to work at lower rpm. No high-temp input, but it takes engine power to make it work.

Turbo: Works all the time, so (for cars) optimised for high revs when the motors working, for really high revs vent the excess. At low revs, not doing a lot. If the turbo wasn't there the energy would just blast out the exhaust pipe and be wasted.

Conclusion: Turbo is more efficient coz its powered by recycled energy, not engine power. But it doesn't work all the time.

The Deltahawk (and, I think, the Zorche) have a supercharger AND a turbo. Without the sc the motor wouldn't run at low revs, at high revs the turbo does all the work. Buy a Deltahawk and you can sniff at both camps...
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  #33  
Old 05-20-2004, 10:44 AM
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mtorzews mtorzews is offline
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Turbo's are not a free lunch. They compress air by plugging up the exhaust. This reduces engine output. How much ... I don't know, I guess it could be looked up, but its probably in the 10 - 25 hp range for the 13B. Now of course the compressed air the turbo creates more than makes up for this loss. But before spooling up power is reduced.

A SC creates compressed air by taking hp off of the crank shaft. How much ... I don't know but its more than a turbo. and it can be clutched to give no drag at low rpm. Efficiency is dependant on SC type, but a centrigul SC approaches the effieciency of a turbo (however it operates like a turbo too and takes several seconds to get boost).

The big benefit of a SC is it gets instant boost and thus better low rpm acceration. This is good for a car, but worthless in a plane.

If it takes a turbo 4 - 5 seconds to spool up would you care when ...
... When driving a car during a 1/4 mile drag race that lasts 15 seconds. Of course the turbo spool time can significantly affect the result.

... When flying at 15,000 feet during. Nope!

... When rolling down a runway for take off. Maybe but not likely. 4 or 5 seconds of reduced boost is minor during a take off roll. You could always compensate by increasing throttle while still on the brakes. Once past 3000 engine RPM the turbo will be spooled up.

Most high efficiency constant throttle applications use turbochargers.

The same argument can be made against twin turbochargers. The purpose of twin turbos is to reduce spool time by using a small turbo that spools quickly. The big turbo then provides max power later. In a plane or constant RPM application this isn't needed. Your better off with 1 large turbo.
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  #34  
Old 05-20-2004, 10:53 AM
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Yes, in theory, one big honker, but look under a cowling when the plane is flying under full boost and you see pipes that are 1400 degrees continious. My Continental came with a single turbo and 5 extra feet of pip to put it all together.

I am using two, to minimize that occurance, one on each side feeding an intercooler
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  #35  
Old 05-20-2004, 02:19 PM
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Dust when I mentioned "twin turbo" I wasn't referring to your setup. Both your turbos are the same size right? Your just are using two to increase boost, and not trying to eliminate lag. One larger turbo would work, but you may have problems like the heat that you mentioned as well as fitting everything.

I was really referring to the mazda twin turbo or other high performance automotive twin turbo applications. These use a small and large turbo to eliminate lag but still give good max boost. Setup like this acceleration is better than either single turbo or supercharger. Its the use of a small and large turbo together that I think is worthless. Planes don't need acceleration. They need high peak output and efficiency.

Its not that any of these setups are bad. Even Superchargers would perform well. I believe in WWII superchargers were used frequently on Allied planes. I just think for a plane operation a single big turbo would be optimal.
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  #36  
Old 05-20-2004, 02:26 PM
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hey a single turbo would be simpler in the controlls, just not the plumbing and heat loss and controll
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  #37  
Old 05-20-2004, 03:28 PM
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Quote:
Originally Posted by mtorzews
Its not that any of these setups are bad. Even Superchargers would perform well. I believe in WWII superchargers were used frequently on Allied planes. I just think for a plane operation a single big turbo would be optimal.
This begs the question why didn't the turbo those planes. The answer is Turbochargers didn't become practical until high speed bearings and compressible flow calculations (1950's), hence the use of superchargers.

Edit- I need a history lesson, it seems the turbo was invented 1909 and used widely in WWII, so I guess my assumption regarding compressibile flow calculations dates is off quite a bit.
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  #38  
Old 05-21-2004, 09:43 PM
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Hello Aussies,
Sorry we had to beat you in the Rugby World Cup, you being at home and all, but I guess it makes up for the cricket.
Strangedays:- Nothing wrong with the Kenworth bro, you should try a Bedford 4 tonner. I still have scars from cracking my head on the wing mirror bolt. The only flat front with no tilt cab. criminal.
Spodman:- Meekatharra eh? Blimey! I used to work at Gifford Creek Station, which is about 300 km's nor' - west of you. I used to haul cattle from the Pilbara and Gascoyne to either Port Headland, Geraldton, or Perth.

Hello Dust, I don't see how two turbo's are cooler, surely the exhaust gas temperatures will be the same, but with half the mass flow to each turbo?

Hello Clutch Cargo,
"But which is more efficient:
A Honda Civic with a 16V engine and 5 spd ?
A Peterbuilt tractor with a 425 Cat engine and 15 spd?"

Too Easy , Gearbox's are irrelevant, the CAT is much more efficient.
I guess 0.22 kg/kw/hr for the CAT, and 0.25 kg/kw/hr for the Honda

I think spool up and boost at low rpm are a red herring, when do you ever want high manifold pressure and low rpm in a plane? Anyway, a wastegate by passes the exhaust turbine, so drag on the exhaust flow is not a problem.

The spool up time on a 200 - 400 hp single turbo is only 2-3 seconds max, so it is hardly a problem enough to justify twin turbo's.

At altitude the turbo or supercharger is flowing say 200 hp worth of air, the same as at sea level, yet it is now compressing at up to 3:1 ratio. The turbo has manifold pressure, plus combustion pressure on one side, but on the other has the reduced atmospheric pressure. This makes the turbo even more efficient at altitude, whereas the supercharger will have to work harder, ie draw more hp from the shaft.


Regards
Adam
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  #39  
Old 05-21-2004, 10:50 PM
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No4 said
"Hello Dust, I don't see how two turbo's are cooler, surely the exhaust gas temperatures will be the same, but with half the mass flow to each turbo?"

I get rid of a nasty 5 foot of 1400 degree pipe from one side of the engine to the other and i can just localize and shorten the distance to the turbos from the exhaust ports
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dust

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  #40  
Old 05-21-2004, 10:51 PM
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LargePrime LargePrime is offline
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the thinking is every square inch of exhaust tubing radiates heat in the cowl.

Reduce the square inches, reduce the heat under the cowl.

put the turbo 6 inches from the exhaust valve and you have as little radiated heat you can. Then start sheilding and managing the heat.

Then there is plumbing. On a flat six you have to cross the engine with a bunch of tubes and whatnot. I dont know if it will save weight with two turbos, by eliminating a lot of tubes, but the plumbing will be a lot simpler.

Every case I have seen they turbo improves BSFC. A blower will cost you BSFC. From a fuel consumption point of view, a blower sucks.

The exhaust restriction comment is a red herring. A turbo adds air, which adds power. That fact that you may not quite get the scavaging of the Exhaust that you can with a blower dont matter. You still get more power, and it dont COST you BSFC, it GIVES you a BETTER BSFC.
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  #41  
Old 05-21-2004, 11:04 PM
no4 no4 is offline
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Hi Dust and Largeprime,
I'm with you, and I like your thinking.

I guess it depends on which you consider more of a problem, complexity, weight, or heat.

Personaly, I still plan for one turbo with the ceramic coating on the header pipe.

cheers
Adam
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  #42  
Old 05-21-2004, 11:29 PM
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damn great to have you back, i am most concerned with heat, both radiant and ahhhhh ahhhhh the other one
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Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

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  #43  
Old 05-21-2004, 11:30 PM
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dust is trading weight for reduced complexity and heat.

I imagine he will ceramic coat both the headers too. And the turbo.

I have the idea in my mind of putting one turbo between the cylinders above the oil pan.
But then the pipes would have to bend 90 coming out of the cylinder, to parallel the block toward the other side, and another 90 into the turboat the middle.
Unless...
Have you ever seen a turbo with Two exhaust gas entrance flanges?
I was thinking one could just turn 90 out the head and point right at the turbo flange for that side. This would eliminate about 5 inches per side of pipe vs the two bend layout. Only about 4" of pipe total longer than the two turbo set up.

Oh, and does anyone know if you can run a Cont TIO 360 upside down? Make where the current oil pan is the top of the engine and put a oil pan, or dry sump, on the other side?
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  #44  
Old 05-23-2004, 04:04 AM
no4 no4 is offline
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Wow, sounds like some serious plans for the TIO.

Some Questions.
1/ Do you actualy have a heat problem?
Surely the TIO makes only 20 bhp more than an IO-360, and then only at take off.

2/Reduced Complexity?
I'm sorry I can't see how two turbochargers, with two wastegates, can be less complex.
Two stories of partial / full engine failures are already on this site. Both involve oil lines, won't you now run twice the risk?
If one wastegate or turbo fails won't you lose all boost, as it backflows through the dead turbo?

I can't comment on inverting the engine and dry sumping it, it certainly is possible, they do exist as factory options for the aerobats. Sounds expensive and rather like a lot of hard work.

I asked Dr Hans what he thought, and he said "no4, I'd go to a custom muffler shop and get them to make me a lovely six into one header pipe, and get a simple manualy controlled wastegate."
I asked him would he run it above the engine or below the engine, and he said " no4, If I wanted to get lowest possible pressure on the outside of the exhaust turbine, and divert the noise upwards, I would have it on the top.; If I wanted a ram air duct straight onto the turbo inlet, I'd mount it below. Mainly it would depend on which side has more space available."
Then we went out for some beer, and got in trouble with the Royal Society for the Protection of Virgins and Innoccent Females (RSPVIF).

Cheers
Adam
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  #45  
Old 05-24-2004, 01:07 AM
no4 no4 is offline
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Hello All,
Two posts in a row. I've been thinking about your proposed set up Dust.
Looking at the title of this thread, the "Hanger Queen", I asked myself, If I was to choose between two aircraft, which would be more likely to be a hanger queen, and the options are ;

Plane A: Standard Cozy, Steam gauges, 3 mechanical engine levers, and an out of the crate recon TIO- 360 , attached to recon constant speed prop

and

Plane B: Standard Cozy, EFIS, single electronic engine lever, upside down dry sumped TIO - 360 twin turbo, with experimental ignition and injection, complete with "black boxes" controlling every thing from the nose gear to the prop rpm.

I would have to put my money on Plane B.

I can only foresee a nightmare of glitches until everything works properly, and then something or other failing during it's whole life. Thus the "hanger queen".

Without being rude, it seems you choose a "black box" to replace simple good airmanship. Might I suggest that you either get a rating in a Piper Seneca, or even go as far as to do your Instrument rating in one.
This will benefit you by:-
a/ Getting used to handling two TIO's, with the old fashioned levers, thus giving you extensive knowledge of manifold pressures, rpm settings and fuel flows.
b/ Get you used to 2 constant speed props
c/ Get you used to a retractable undercarriage
d/ Get you used to joining Instrument approaches at some speed similar to a Cozy, which, even in a much slower plane can very soon go to custard if the numbers stop adding up.
e/ Get you used to high altitude flight by taking a portable oxygen set up

As you are considering very fast speeds, you would want to be very good at keeping on track. If you end up on a converging track with a jet at Fl 250, you can have a closing speed of up to 900 mph.

Going from 2 engines to one will be a step back, as will only having 2 or three levers compared to 6. Thus I would say you would be qualified to decide actualy what black boxes you need, and what improvements you need to make to your engine, without having to listen to outspoken Englishman like me on the other side of the planet.

I look forward to being told" Shut up no4, you're talking rubbish!"
Best Wishes
Adam
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