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  #16  
Old 05-16-2004, 04:18 PM
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JungleJet JungleJet is offline
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Default Turbo vs Super

There is a really good article in the July 'Custom Planes'. It discusses the pros and cons of turbos and superchargers. The way the article was written, the supercharger seems like a better option, sans cost. It also had a big article on the five seat Velocity.
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  #17  
Old 05-16-2004, 06:26 PM
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I Have not read the artical, but just on principal a supercharger makes no sense in an aircraft.
A turbo can reduce or at least break even with BSFC, a super charger will always cost you more fuel.

Supercharger only make sense in an automotive application because throttle resonse matters in cars. If not for that they would never have been invented.
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  #18  
Old 05-16-2004, 11:21 PM
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I also read the article in Custom Planes. The comparison made was that both use about the same hp, so fuel consumption would be about the same assuming the author was correct. The plus side of the supercharger is it does not have the heat issue the turbo has, as its belt driven. The downfall side is that it does not quiet the exhaust as a turbo does. Cost wise for our "experimental" classifaction, cost wise to install should be about the same. If not for the exhaust muffle the turbo creates, I would be seriously be looking further into the supercharger for my 13b Cosmo.
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  #19  
Old 05-17-2004, 09:56 AM
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Quote:
Originally Posted by David Clifford
The plus side of the supercharger is it does not have the heat issue the turbo has, as its belt driven.
That is true, but you realize you're trading a "bearing failure" mode for a "belt failure" mode. 1 for 1.

From an efficiency perspective, it seems a waste to let all that exhaust gas velocity go unrecovered into a muffler (especially for rotaries). Since turbos recover wasted energy from the exhaust, they are more efficient than superchargers.

Large has good points re dust's application, but keep in mind dust's aircooled engine was designed and cert. for a turbo, does the original engine design include an afterrun pump?
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  #20  
Old 05-17-2004, 11:30 AM
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Just another thought

i was thinking that maybe i should disable turbo operations when the nose gear is down, may take quite a few failure modes and make them smaller issues.

On what was certificated, i view certification process as antiquated, thats why all of the controlls are being replaced.

And remember the certificated ones are the ones that are considerred "hanger queens" and my wife, the goddes won't allow me to have any queens hangin around
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  #21  
Old 05-17-2004, 12:33 PM
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Quote:
i should disable turbo operations when the nose gear is down
I wouldnt recommend that. There are times when you want all the power you can get right now, and don't care if it hurts the engine a bit. - like on an emergency go around, perhaps, or a heavy hot day take off thats running short of runway. Any safety feature like that needs an override.
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  #22  
Old 05-17-2004, 01:03 PM
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Yes, but remember i am normalizing so at below 2-3000 i will have almost no boost and i should still be able to get over 200hp for a go around, normally aspirated
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  #23  
Old 05-19-2004, 02:51 AM
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Hello All,
Just my ten cents worth,

Dust, that sounds like a good idea, but what if you plan to go and visit Joe, I think it's 7,000 feet plus at Taos, and lots of other places. You'll basicaly have an NA engine for Take off and go around.


I didn't read the Custom planes mag, but it's just wrong to say there is no difference in efficiency. The supercharger takes horsepower from the crank, the turbo uses hot air and mass flow from the exhaust.

I agree with the simplicity argument, and the boost versus normalisation. My Nissan Skyline has an RB25DET motor (2.5 litres 6 cylinders, 350 bhp), which is regarded as the ultimate to come from Japan. They are sold in Japland only, and were banned from racing in Australia because they smoked the GM Holdens and Fords too badly.
http://www.turboclub.com/makes/nis/Skyline/nisgtr.html
I rarely exceed 29 in hg manifold pressure, mainly because it means the speedo will be passing 100 mph very quickly, and there will be flashing red and blue lights in the mirror. All the latest Jap cars like the Subaru WRX, Mazda RX7, and Misubishi Evo VII, if driven hard (boosting) will blow black smoke sooner or later, and have knackered engines. Anyone considering boosting manifold pressure for any period other than take off above 29 in hg, I think is making a mistake.

I'd agree with Aaron, to keep it simple, my Skyline has automatic wastegate, an oxygen sensor, blow off valve, inlet temp sensors, egt sensors, etc, etc. Under the bonnet is a nightmare of wire$and pipe$, when one fails it shafts the whole electronic ignition and misfires badly( and empties my wallet); also moisture can have the same result. I agree all you need is a turbo, manual wastegate, intercooler and voila! I guess a blow off valve is fairly fail safe and can help prevent detonation.

Anybody have any ideas on how to link a supercharger and turbo in "series" , so as to normalise to Fl 440? I've got this plan with twin intercoolers, supercharger first, then intercooler, then turbo, then another intercooler, then the manifold.

Best Wishes
Adam

PS not photos of my car, but mine is very similar to the second photo, the third photo is an RB26, which makes 1300 bhp @ 11,000 rpm, with 3kg/cm3 boost, not bad for a 2.6 litre!
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Last edited by no4 : 05-19-2004 at 03:13 AM.
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  #24  
Old 05-19-2004, 09:32 AM
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The concept of combining superchargers and turbo's has been used on heavy vehicles for a while.
Many of the prime movers running the triple trailer road trains we get out west have 2 turbos feeding the blower. I am unfamiliar with the finer points of the setup, but I believe the throttle goes in front of the whole lot, allowing the compressor to spin freely in (near) vacuum state with the throttle closed, with the wastegate control taken from the blower intake, to prevent turbo overboost into the blower.
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  #25  
Old 05-19-2004, 11:22 AM
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Point well taken, just a newby thinkin, and i know i'll have to visit joe, i'll go back to thinkin, the only problem, i'll be doin REAL soon
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  #26  
Old 05-19-2004, 11:23 AM
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Default heavy boost...

I personally like the concept of the supercharger as opposed to the turbo which has a drain on the cooling system and lube system in an aircraft application (among other things). The SC is cooler and more efficient (especially in a rotary) and easier to control without adverse effects. I like the exhaust to be tuned and to leave the area as soon as possible..

Some of the above points are more matters of opinion when one wants to boost HG for more power at altitude, which is where the turbo does it's thing as well as an SC (which does it well from the beginning of RPM climb, almost a straight line whereas the turbo does better at higher RPM because of using exhaust gas). So one can argue either way in this regard.

However, unless someone has invented a new and different type of "blower" (roots or axial) they are VERY heavy. You all know what Burt said about throwing things up in the air....I wouldn't want to be under one of those blowers when it came down....of course I wouldn't get it very far into the air...

When the superchargers were used in recip aircraft (big 12 cylinder Rolls-Royce engines etc...) they already had crossed the line HP / weight, it was a small trade-off. The EZ/Cozy aircraft wing design doesn't have as much to give to make adding that much weight worth it IMHO.
Now if there was an engine that weighed about 125 lbs that would boost up to 300 hp at MSL then it might be worth it.

Of course with the SC you have to put a muffler on a rotary anyway....
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  #27  
Old 05-19-2004, 11:35 AM
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And by doin, it will be a single lever controll for everything, i'm old fashioned, lazy, i don't want a prop,throttle,boost,mixture controllers, i want a dammmmmmmmmmmm go control.
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  #28  
Old 05-19-2004, 06:45 PM
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Quote:
The SC is cooler and more efficient (especially in a rotary) and easier to control without adverse effects.
Sorry Clutch, I'm not reading you here, how is a SC more efficient?

For illustration purposes I ran some compressor calcs on 700 scfm of air going from 9.3 psia and 16F (conditions at 12,000ft) to 16psia.

Wether you use a SC or TC, you need to compress the air, doing work. the amount of work done here will take 23 hp. No SC or TC is 100% efficient, usually they're closer to 60-80% efficient, so best case around 29 hp. This is just for normalization, keep in mind. For boosting to 23psia you'd be using 40-50 hp.

An SC will take this hp directly from the crank (plus losses in the beltdrive), a TC will take it from the exhaust gasses with only a minor exhaust gas restriction ( perhaps as much as 5-10 hp).
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  #29  
Old 05-19-2004, 11:15 PM
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Hallo Dust,
Well we all want lots of things, but I'm not sure you may get it old chap. Unless you have drasticaly changed your prop governor, you will need at least two levers, one for prop/ engine rpm, and one for power. If I understand correctly, your chosen engine management system replaces the fuel flow and manifold pressure levers with a single item. The only single lever constant speed props I have heard of are on the Thielert diesels, and the innards of which are Gekados!(thats Top Secret in jermun).

Hallo Clutch Cargo,
I'll have to agree with Aaron that there is no way a supercharger can be more efficient. Secondly I'd point out that you would never want high manifold pressure and low rpm. There are some superchargers available now which are centrifugal compressors driven by a belt from the crank.
http://www.capa.com.au/kits_holden.htm

Hallo Strangedays,
I used to drive a double from "The North" down to Perth. For those who havn't been to Land of Oz, "The West" is anywhere past 100 km from Sydney on the East coast, and "The North" is anywhere past 100 km north of Perth. That describes about a 6.6 gigillion acres of red dust, kangaroos and flies.
I think what you are referring to are the two stroke Detroit Deisels. They need the supercharger to vent the cylinders; I never had the pleasure, my rig was a flat front Kenworth with a 600 hp Cummins and single turbo.

Best Regards
Adam
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  #30  
Old 05-20-2004, 05:09 AM
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StRaNgEdAyS StRaNgEdAyS is offline
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Good evening No.4
Hmmm a cabover kenworth... I never liked the cabovers, the bumps just seem to travel rightup your ....... spine .
The unit I saw so configured was one used exclusively for the Adelaide to Darwin trips (on of the KTM trucks I think), it was not allowed into any other states (I don't know the details, but their authorities didn't like it one little bit), and used to have to be driven VERY gently when unloaded, or it would break stuff. It was a beast.
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