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  #61  
Old 05-26-2004, 07:09 PM
rui rui is offline
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This may be out of topic, if so please move it to a new thread.

While readng those turbo articles (btw, I love reading Deakin's work, he seems to be a no nonsense kinda guy who likes to get to the bottom of things) a thought flashed into my head. Why don't we power the turbo compressor with an electric motor? I couldn't think of a good reason not to (other than maybe that the power required would be too much, but other than this....) and could think of at least a couple of good ones.

-removing the heat associated with the exhaust would lessen the need (maybe eliminate) for intercooling. Also would eliminate the heat from the bearing area making it possible to run only oil cooling to the bearing.

- reduced complexity in the engine bay since the exhaust pipes could be routed independantly of the intake pipes.

Some people on the rotary list are experimenting with electric water pumps, why not electric air pumps?

Anybody ever think of such a thing? Is there some fatal flaw in the idea? I can't help but wonder why it hasn't been tried before..
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  #62  
Old 05-26-2004, 10:20 PM
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It’s a matter of power.
A supercharger does just that, takes power from the engine and uses it to compress the air. This can take 10-50+ HP to compress, depending on HP produced.

An electric motor with this capacity would weigh much too much. The power requirement would be outrageous.

A turbo has the advantage in that it uses waste energy (exhaust energy equal to the HP produced) to compress the air. This recycled waste energy is basically free to drive the compressor. A well-engineered turbo can actually increase the fuel economy (BSFC) of and engine AND add HP.
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  #63  
Old 05-26-2004, 11:25 PM
rui rui is offline
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Ok I just did a google search for electric turbo. I found a couple of links mostly to pages saying why this wouldn't be practical. Just as LargePrime said, its a power thing.

They can be useful in cars for low end power before the main trubo spools up, but this is pointless for airplane use.

Back to your regularly scheduled thread....
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  #64  
Old 05-27-2004, 01:41 AM
Aaron Aaron is offline
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Default intercooler and turbo's (rui)

Just to be clear here, intercoolers remove the heat of compression basically because you are compressing a gas it heats up. Given the same amount of compression from whatever source (turbo, sc, squirrel fan, leaf blower, whateva) you have the same heat to contend with.

That being said, turbos do cause undercowl heat issues if they increase the length of the exhaust plumbing, and they usually do.

LP is (as usual) correct, the amount of power required for the "E-ram" type superchargers is around 50 amps, and they give a boost of about 1 psi at 600 CFM, AND they are not designed for continuous loads. Plus you have to take crank HP, convert it to electricity, convert the electricity back into shaft work, and then use that shaft work to compress the intake charge. Energy is lost at step adds, therefore lower efficiency.
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  #65  
Old 05-27-2004, 05:19 AM
no4 no4 is offline
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Good Evening Ladies and Gentlemen,
This is a very interesting thread.

Oversquare,
"When the manifold pressure exceeds the RPM/100".
Strictly not allowed for me, If I try it I get either a/ a slap across the knuckle with a clipboard, b/ yelled at profusely, c/ "I have control" come into my headset, or d/ all of the above.
Over torques the motor, risks detonation, etc, stricktly VERBOTTEN!!
Undersquare not any problem at all, common for descent, approach etc.

Increasing Power with Costant Speed Prop, and injection
Fuel flow to desired rate, pitch to desired rpm, throttle to desired manifold pressure. ( Right to Left)

Decreasing Power with csu,
Throttle to desired MP, pitch to desired rpm, fuel flow to selected rate. ( Left to Right)

Wrong way round = bang, bang, rattle rattle, clunk, clunk, ........silence.......

Auto pitch imho = step backwards/ playing with fire

Largeprime said, /"If we have an automajical system that holds 30" boost always infront of the throttle plate, then we eliminate a nob.1 down, two to go."

Think you're quite wrong with this one mate, sorry. A normaly aspirated has 29.92 " on a standard day at the air intake, as the throttle is opened and the valves open, the piston sucks the air all the way from first constriction. Hence 28" for take off in the IO.

A turbo pressurises the whole intake system, putting a throttle in the way will only control the flow rate. I absolutely guarantee detonation the first time you tried to crank your system.

NA motors have a volumetric efficiency of 70% for old pushrods, 85% for multi valves, whilst turbo's get 100+ % because of no drop from intake to cylinder. I think someone made the same point about 20 posts ago, turbo superchargers are pumps as well as pressure increasers.

The Seneca comes with fixed or manual wastegate. The fixed gate by passes say 25% of the exhaust around the turbine.
Take Off - Fuel flow full forward, pitch full forward, throttle slowly to 31 " over three seconds ( low compression pistons) using Mk 1 eyeball.
Climb - Throttle back, pitch back, fuel back
During next 5,000 feet Throttle BACK further to maintain MP , because turbo becomming more efficient.
Climb next 10,000 feet Throttle advanced to wide open, to maintain mp
Cruise - set and leave for next three hours , Auto pilot on
Descent, retard levers Left to Right; throttle reverse of climb sequence
Circuit - rpm up
Finals- full fuel flow, full rpm, throttle to meet required power
Numbers- close throttle and csu acts like a big air brake

Too Easy

I was wondering about making the upper surface of the wing and fuselage out of solar panels, to drive E-ram compressors.

Maybe next time

respect
Adam

Last edited by no4 : 05-27-2004 at 05:41 AM.
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  #66  
Old 05-27-2004, 08:49 AM
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John Slade John Slade is offline
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No4 makes a good point. It's all about pilot responsibility to control the MP. If they do it that way in certified ships, surely we can do it in our birds. Combine this discipline with a blow-off valve and you have a satisfactory and relatively KISS solution. No?

Quote:
turbos do cause undercowl heat issues if they increase the length of the exhaust plumbing, and they usually do
Not necessarily in aircraft use. My exhaust pipe is all of 6 inches long. Shroud the manifold and turbo with stainless and vent the entire thing out of the back of the cowl.
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  #67  
Old 05-27-2004, 11:43 AM
Aaron Aaron is offline
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Quote:
Originally Posted by John
Quote:
Originally Posted by Aaron
turbos do cause undercowl heat issues if they increase the length of the exhaust plumbing, and they usually do.
My big mistake there is the word "usually" has no place in this discussion

Johns system is simple and elegant (lucky wankler!). In fact I think Johns setup is shorter because he can use the turbo as a muffler. Dusts on the other hand will be a bit more complex.
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  #68  
Old 05-27-2004, 12:14 PM
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LargePrime LargePrime is offline
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Quote:
Originally Posted by No4
Oversquare,
Over torques the motor, risks detonation, etc, stricktly VERBOTTEN!!
But you didnt address the reason WHY it is "VERBOTTEN". Its not about "overtorque"ing, as the motor does just fine producing more torque, like at full throttle. I have never seen a motor "overtorqued".
I belive it does risk Detonation, because it is a carbed motor, and will run lean, risking detonation due to over lean condition.
Fuel injection eliminates that problem, allowing oversquare operation. Thats my theory and I am sticking to it.
Untill its shown wrong.
Of course.
Then i'll change.
Of course.

Quote:
Originally Posted by No4
Quote:
Originally Posted by LargePrime
If we have an automajical system that holds 30" boost always infront of the throttle plate, then we eliminate a nob.1 down, two to go.
Think you're quite wrong with this one mate, sorry. A normaly aspirated has 29.92 " on a standard day at the air intake, as the throttle is opened and the valves open, the piston sucks the air all the way from first constriction. Hence 28" for take off in the IO.
A turbo pressurises the whole intake system, putting a throttle in the way will only control the flow rate. I absolutely guarantee detonation the first time you tried to crank your system.
I am confused. Any restriction will lower pressure down stream of the restriction, right? Its called a venturi. It is how dusts engine is set up now.
All dust is doing is holding 29.92 (can we call this 30?) from takoff to 30K
At 30K his system behaves just like its at 500FT. I see no reason for a detonation risk.

Quote:
Originally Posted by John Slade
If they do it that way in certified ships, surely we can do it in our birds. Combine this discipline with a blow-off valve and you have a satisfactory and relatively KISS solution. No?
Most humbly, no.
Unless there is a good REASON for them to do it that way, outside of beauracratic mandates.
I see no reason to bother the pilot with a wastegate. Automajicaly hold standard atmosphere and forget about it. The engine will act like a normally asperated engine with no fail modes due to pilot error, the number one killer.
A standard spring blow off valve is a differental pressure device. It will not function correctly at 30K AND at 500FT. It will do one, but not the other without an absolute referance, like a Standard Atmosphere bladder.
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  #69  
Old 05-27-2004, 12:53 PM
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mtorzews mtorzews is offline
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I don't know if this is right or wrong, but in cruise at lower altitudes you may want to reduce MP before the throttle.

scenerio cruising at best economy at 10,000 ft.
You have an auto waste gate giving you 30 before the throttle plate, and you want to reduce fuel burn. Best economy is with WOT, so full throttle and 30 before the throttle and after. You need to reduce power for economy so you lean out, but now you are risking detonation. So you throttle back. The throttle reduces the pressure from 30 to 22 which reduces power and fuel burn. Your turbo is still working to provide 30 before the throttle (which is back pressure) but it is being wasted by the throttle which reduces effiency.

I would think for best economy you would need control over boost. Now you can again run WOT. Open waste gate to boost before throttle pressure to 22 which partially reduces turbo work (and back pressure). WOT and you get 22 at the intake valve. Lean out but not to detonation.

Does this make any sense?

I know Dust won't care about economy cruise at 10,000. I see him running WOT with 30 MP at about 25,000 feet and caring less about fuel burn.

Just food for thought.
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  #70  
Old 05-27-2004, 12:55 PM
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I don't know if this is right or wrong, but in cruise at lower altitudes you may want to reduce MP before the throttle.

scenerio cruising at best economy at 10,000 ft.
You have an auto waste gate giving you 30 before the throttle plate, and you want to reduce fuel burn. Best economy is with WOT, so full throttle and 30 before the throttle and after. You need to reduce power for economy so you lean out, but now you are risking detonation. So you throttle back. The throttle reduces the pressure from 30 to 22 which reduces power and fuel burn. Your turbo is still working to provide 30 before the throttle (which is back pressure) but it is being wasted by the throttle which reduces effiency.

I would think for best economy you would need control over boost. Now you can again run WOT. Open waste gate to boost before throttle pressure to 22 which partially reduces turbo work (and back pressure). WOT and you get 22 at the intake valve. Lean out but not to detonation.

Does this make any sense?

I know Dust won't care about economy cruise at 10,000. I see him running WOT with 30 MP at about 25,000 feet and caring less about fuel burn while considering what to order for dinner at the Phoenician that night .

Just food for thought.
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  #71  
Old 05-27-2004, 03:36 PM
Wayne Hicks Wayne Hicks is offline
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It's an old wives tail to believe that you can't run oversquare. The OWT comes from radial engine operations of running square or undersquare to reduce the failures of the master rod bearings.

Read: Avweb's John Deakin
http://www.avweb.com/news/columns/186778-1.html


...Wayne Hicks
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  #72  
Old 05-27-2004, 03:39 PM
Wayne Hicks Wayne Hicks is offline
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In a plane with a constant speed prop, the throttle is used to manage the manifold pressure and the prop control is used to manage the RPM.

In applying power( as in to climb), the order is mixture forward, prop forward, throttle forward.

In reducing power, the order is throttle, prop, mixture.
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  #73  
Old 05-29-2004, 08:39 AM
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"I came away with is that it is heat that kills engines, not "overstressing" by running them near their red line. I think this is especially true of the rotary since it has so few moving parts. RUI"

I'm no engine expert either but my training told me that a turbo generates heat in the air its compressing.

http://www.fact-index.com/t/tu/turbocharger.html
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  #74  
Old 05-30-2004, 01:53 AM
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LargePrime LargePrime is offline
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If you read the artical you would understand RUI ment that it is most important to keep the CHT and EGT at lower temp.

Although intake temp can effect the EGT, the biggest effect is fuel ratio.
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  #75  
Old 05-30-2004, 10:35 PM
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John, I read about your yesterday's adventure. Do you have a big tree you could nose up to? (One they don't mind you pushing over.) I'm not shaking fingers at you, I'm hoping and sure you'll get it worked out so I can just copy it.
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