Quantcast

Supercharged engine

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

nheistand

Member
Joined
Mar 4, 2011
Messages
23
Location
Vinton, Iowa / USA
I have an AMR300 small supercharger on my Predator 670cc V-Twin. See it running on YouTube:
http://www.youtube.com/watch?v=3gVygOvU83A


The same type of setup would work on any similar small engine as well. Half VW, 2A042, 4A032, Kohler CH27, Honda GX690, etc. For a 1600cc VW or 4A084 I would use an AMR500. All stock engine, just a v-belt pulley on the flywheel and Mikuni carb on the supercharger and a custom intake manifold. Since it is not easy to increase the displacement with more cost and more work, the supercharger is a simple and low cost way to go. $300 for a used AMR300 from Japan. The AMR300 weighs 7 lbs.

A 1600 VW longblock and a used supercharger could be a 50hp stock engine boosted to 70+hp with 10psi of boost with a used AMR500 supercharger from Japan. This is a very low cost combination that would power many experimental and Light Sport Aircraft. I would love to build one and run it on my test bench, only waiting for the $$:)



Norm Heistand
 

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,352
Location
Everywhere USA
There are also small turbochargers available new for under $1000 that are used on many scooters. But boosting power might not be much of a good idea, and larger displacement VWs are available for very little extra.

The real use for a supercharger/turbocharger is to keep power at altitude (called "normalizing"), and many members live above 6000 feet, and have to fly at 10,000 or more. This easily cuts power by 15-20%. And regaining this power would allow a fairly nice increase in true airspeed.

A small amount of boost above normalized would probably do pretty well. Anything else would be risking issues with reliability.
 

Topaz

Super Moderator
Staff member
Log Member
Joined
Jul 29, 2005
Messages
14,272
Location
Orange County, California
... A 1600 VW longblock and a used supercharger could be a 50hp stock engine boosted to 70+hp with 10psi of boost with a used AMR500 supercharger from Japan. This is a very low cost combination that would power many experimental and Light Sport Aircraft. I would love to build one and run it on my test bench, only waiting for the $$:)...
VW's don't really lack for power - as Doggzilla said, there are larger-displacement versions to handle larger power requirements - but they struggle with heat rejection, especially in heads. That's far more often the limiting factor in their power output for a given displacement. If you're going to go the supercharged route, you're also going to have to figure out how to get rid of the heat the extra power the engine is producing as well.
 

cheapracer

Well-Known Member
Log Member
Joined
Sep 8, 2013
Messages
6,290
Location
Australian
Just a small correction, a supercharger does not maintain your performance as you gain altitude because it's speed is fixed to the engine's speed.

A turbocharger will maintain performance as you gain altitude because it is free to spin faster independent of the engine's speed.

So if you play near sea level then either are a choice, but if you're up in the mountains then you should be looking at turbochargers.
 

cheapracer

Well-Known Member
Log Member
Joined
Sep 8, 2013
Messages
6,290
Location
Australian
Well, you could do it with a supercharger too, but it wouldn't be very efficient and you would be blowing a lot of air overboard at low levels and high power.. :)
I believe some supercharged WW2 planes had to be careful on the ground with their rpms when the boost was set for high altitudes.
 

rv6ejguy

Well-Known Member
Joined
Jun 26, 2012
Messages
4,079
Location
Calgary, Alberta, Canada
Many WW2 aircraft had 2 speed, 2 stage supercharger drives to produce and control boost with altitude changes. Complicated and heavy. A turbocharger and wastegate is elegantly simple by comparison plus turbine efficiency and drive energy increases as altitude increases due to reduced atmospheric pressure acting on the discharge side.
 

mcrae0104

Well-Known Member
HBA Supporter
Log Member
Joined
Oct 27, 2009
Messages
3,647
I believe some supercharged WW2 planes had to be careful on the ground with their rpms when the boost was set for high altitudes.
Yes, and this was as much for control during takeoff as to it was to protect the engine.
 

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
Just a small correction, a supercharger does not maintain your performance as you gain altitude because it's speed is fixed to the engine's speed.
Many pre-turbo era WW2 planes had superchargers. Most of those, had clutches and gearboxes. With anywhere from one to three boost settings. "on/off" or "neutral/low/high" Or "low/high".

I suspect an intake restrictor could reduce load on the supercharger at low altitudes, without needing a dump valve. With the lower exhaust complexity, and potentially lower heat load, you might even come out ahead weight wise with a supercharger.

A belt also provides a convenient clutching mechanism. If you don't like that, there's also the electric clutch option like on the early MR2s. They had what was essentially an a/c compressor clutch on their supercharger. Any supercharger should have a bypass flap, so in the event of belt, or other mechanical failure the engine still gets atmospheric air.

... It doesn't sound stupid to me...
 

N8053H

Well-Known Member
Joined
Jan 31, 2013
Messages
2,523
Location
Right here in front of my computer
A supercharger can be over or under driven. They do not turn at Crankshaft speed. A turbo will only spin as fast as the exhaust can exit. Both designs have their draw backs. The Turbo needs a heat exchanger where a supercharger does not... ect.
 

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
A supercharger can be over or under driven. They do not turn at Crankshaft speed. A turbo will only spin as fast as the exhaust can exit. Both designs have their draw backs. The Turbo needs a heat exchanger where a supercharger does not... ect.
I don't understand where you're going with the gearing point. Any centrifugal supercharger is going to need a gearbox to achieve useful rpm at the rotor. Gear ratio determines the pressure ratio of a roots of screw type supercharger.

Turbochargers run when there's sufficient exhaust velocity to spin them... the "as fast as the exhaust can exit" doesn't make a whole lot of sense.

At similar pressure ratios, the need for a charge cooler, inter cooler, or heat exchanger is the same between similar types of compressor. Centrifugal compressors, run in their efficiency island, being the best of the bunch, while any of the contact style compressors all fall beneath them. Factory supercharger installs frequently include a intercooler of some sort. Being somewhat less efficient than a centrifugal compressor the needs for charge cooling are greater than a centrifugal compressor.

I'm just talking about the compressors, as a the need for charge cooling is dependent on compressor efficiency, intake air temperature, and compression ratio. Not how the compressor is driven.

A supercharger does not need the belt to run. They run just fine without the belt. The rotors will free spin. No need for any flapper. The only valve you have is a relief valve in case of over boost. Take it from someone who runs superchargers.
Sure, a supercharger might freewheel, but that's going to be a fairly hefty intake restriction. A flapper valve would allow almost all of the available air pressure into the cylinder head. I'm going to take my cue from OEMs who made thousands of installs with variable boost devices on their engines. The majority of those installs over the years, do have an atmospheric bypass valve to get full pressure to the engine when the compressor isn't running.

Now that I think about it.. I wonder how many CFM spiral compressors are up to.
 

nheistand

Member
Joined
Mar 4, 2011
Messages
23
Location
Vinton, Iowa / USA
Many pre-turbo era WW2 planes had superchargers. Most of those, had clutches and gearboxes. With anywhere from one to three boost settings. "on/off" or "neutral/low/high" Or "low/high".

I suspect an intake restrictor could reduce load on the supercharger at low altitudes, without needing a dump valve. With the lower exhaust complexity, and potentially lower heat load, you might even come out ahead weight wise with a supercharger.

A belt also provides a convenient clutching mechanism. If you don't like that, there's also the electric clutch option like on the early MR2s. They had what was essentially an a/c compressor clutch on their supercharger. Any supercharger should have a bypass flap, so in the event of belt, or other mechanical failure the engine still gets atmospheric air.

... It doesn't sound stupid to me...
Since the supercharger is simply an air pump, it would be easy to install a hose/tube from the blower output to the blower input. A variable shut off valve on the tube would allow changing the boost pressure "on the fly" with no other parts needed. Probably a way to have a control knob in the cockpit to change the boost level to keep it optimum as desired.

Supercharging is the only way to get desired power at the lowest cost, $300 for blower, $50 for pulleys and belt. I am thinking of building a 1600cc VW 4 cylinder for longblock $1400, supercharged $400, ignition $50, exhaust $50, carb $100, prop hub $150, and ready to go for $1150. I challenge anyone to match that price for a zero time engine with reliable 70 hp.

Norm Heistand
 

blane.c

Well-Known Member
HBA Supporter
Joined
Jun 27, 2015
Messages
4,492
Location
capital district NY
I believe some supercharged WW2 planes had to be careful on the ground with their rpms when the boost was set for high altitudes.
You have to reduce (occasionally and rarely increase) manifold pressure adjusted for density altitude when using Pratt R2,000's and R2,800's. This is done using a chart usually attached to the takeoff checklist. The "idea" behind turbochargers is that you get some free power from the exhaust gases to drive the turbo charger, this is often offset by the reduction in exhaust diameter (choke point) at the turbocharger. The main difference in performance between exhaust driven centrifugal turbochargers and gear driven lobed or screw superchargers is that centrifugal turbochargers are not really efficient at lower RPM's and do not add significant boost until the engine is in the upper power-band while geared superchargers are more effective through a broader power range. Centrifugal turbochargers can be set up to be efficient at cruise power and excess pressure (boost) can be relieved (automatically) at takeoff power settings. Geared superchargers can also be set up to relieve pressure automatically so for aircraft applications I see no clear advantage for either system. The P-47 Thunderbolt of world war two fame had the Pratt R2,800 with geared supercharger and multiple shift points to increase supercharger RPM for various altitudes, it also had exhaust driven turbochargers and could fly well into the 40,0000 foot levels.
 

mcrae0104

Well-Known Member
HBA Supporter
Log Member
Joined
Oct 27, 2009
Messages
3,647
The Turbo needs a heat exchanger where a supercharger does not... ect.
Either a supercharger or a turbocharger may need (or at least could benefit from) a heat exchanger depending on the application because both increase the temperature of the intake charge. There are also some applications for each that do not strictly need one (e.g. many draw-through turbos get by fine without one).
 

rv6ejguy

Well-Known Member
Joined
Jun 26, 2012
Messages
4,079
Location
Calgary, Alberta, Canada
Lots of misinformation here from the supercharger advocates.

For aircraft operating at very different altitudes, you need to increase the pressure ratio to maintain manifold pressure as you climb. If you bleed air off it to control boost, you generally heat the charge more on a centrifugal type- bad idea and a waste of input power. Transmissions/ clutches are complicated, heavy and maybe need quite a bit of maintenance. With a turbo, you close the wastegate as you climb, N1 increases- voila higher pressure ratio and infinitely variable, not coming in big steps.

As Nerobro stated, the need for intercooling is directly related to compressor efficiency and pressure ratio and modern centrifugal compressors are about TWICE as efficient as a straight lobed Roots supercharger. Apples to apples, turbos produce much higher hp than superchargers, not that that is important for aircraft usually.

Compressing air takes power, lots of it at the flow rates engines need so no belt on a blower = no hp increase. Not sure what the point of that was...

Modern turbos can generate torque peak anywhere you want, many cars have TP down in the 1400-1750 rpm range these days and can carry 80-90% of that torque right to redline- very broad powerbands indeed.

Look at the number of production supercharged GA aircraft compared to turbocharged. That pretty well sums it up. They work but just are not a good choice for aircraft applications.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
5,758
Location
US
Supercharging is the only way to get desired power at the lowest cost, $300 for blower, $50 for pulleys and belt. I am thinking of building a 1600cc VW 4 cylinder for longblock $1400, supercharged $400, ignition $50, exhaust $50, carb $100, prop hub $150, and ready to go for $1150. I challenge anyone to match that price for a zero time engine with reliable 70 hp.
If you want to build a supercharged 1600cc VW engine, go ahead. But in aircraft use it will give you no advantage over a naturally aspirated VW.

Power: Your 1600cc supercharged engine will produce less power than a 2180cc engine. You say you can make 70HP, NA 2180cc engines make more power. Unless you work some magic on the heads, the heat rejection is the limiting factor for cruise power.
Cost: Your installation will cost more--the VW parts cost about the same regardless of displacement (if they are comparable quality), and then you've got to buy the blower, etc.
Weight: All the VW engines, if configured the same (drive end, accessories, etc), weigh about the same regardless of displacement--within a few pounds. Your supercharger weighs something.
Reliability: You'll be running at higher effective compression ratios--that means a higher risk of detonation and other issues.

Why do it? Maybe there are other good candidates out there to be supercharged--maybe a watercooled motorcycle engine with excess cooling capacity and the ability to run at high CR without any problem. Get a reduction drive, turn it at 6000 RPM, and try things out. But this VW engine is not a good candidate for what you are planning. If you like VWs (I do), just use more displacement if you need more power than a 1600cc can give. If you need more than 70-80HP, then look at a different engine.
 
Last edited:

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
You have to reduce (occasionally and rarely increase) manifold pressure adjusted for density altitude when using Pratt R2,000's and R2,800's. *snip* The P-47 Thunderbolt of world war two fame had the Pratt R2,800 with geared supercharger and multiple shift points to increase supercharger RPM for various altitudes, it also had exhaust driven turbochargers and could fly well into the 40,0000 foot levels.
It goes a bit further than that. Centrifugal superchargers and radials happened sort of by accident. Getting good mixture delivery to the cylinders on a radial is not easy. Between long runner lengths, and gravity issues, bottom and top cylinders see very different mixtures. So, the logical solution was a mixing device. That mixing device was crank driven, and had this funny byproduct of producing some pressure.

That mixing device ended up being developed into centrifugal superchargers.

Now, eventually, engineers got interested in what they could do with the exhaust gasses coming off the engine. That lead to the turbo-superchargers we know and love. When applied to a radial, there was no reason to remove the mixing device.... :)

Stacked superchargers and turbochargers are not unheard of. Most commonly you'll find hybrid turbo/supercharger setups on locomotives. They tend to be two strokes, and are dependent on a supercharger for scavenging. By using a sprag clutch, they can use the same turbocharger as a supercharger at low power settings. Also some engines just had the conventional supercharger behind a turbocharger setup.

Lots of misinformation here from the supercharger advocates.

*snip*

As Nerobro stated, the need for intercooling is directly related to compressor efficiency and pressure ratio and modern centrifugal compressors are about TWICE as efficient as a straight lobed Roots supercharger. Apples to apples, turbos produce much higher hp than superchargers, not that that is important for aircraft usually.

Compressing air takes power, lots of it at the flow rates engines need so no belt on a blower = no hp increase. Not sure what the point of that was...

*snip*

Look at the number of production supercharged GA aircraft compared to turbocharged. That pretty well sums it up. They work but just are not a good choice for aircraft applications.
I'm only an advocate in the "it's potentially easier to do" bracket. Turbochargers are essentially ideal for aircraft use. As long as money and injection/carburation isn't the question.

Screw (which look a lot like roots..) superchargers come pretty close to centrifugal designs. Enough so, that they can afford to use them on modern cars. Unless I had one handy... I wouldn't be looking in that direction though.

I mentioned running the engine without the supercharger active, to cover for hardware failures. If a turbocharger fails, you're looking at potentially a very large oil leak, reducing your flight time, and likely the need to rebuid the engine. Most superchargers are self contained, and a supercharger failure will just lead to a reduction in altitude (providing your were doing normalization) as opposed to total engine shutdown. It's potentially somewhat safer.

Have there been any supercharged O style engines? I can't think of any.
 

mcrae0104

Well-Known Member
HBA Supporter
Log Member
Joined
Oct 27, 2009
Messages
3,647
It goes a bit further than that. Centrifugal superchargers and radials happened sort of by accident. Getting good mixture delivery to the cylinders on a radial is not easy. Between long runner lengths, and gravity issues, bottom and top cylinders see very different mixtures. So, the logical solution was a mixing device. That mixing device was crank driven, and had this funny byproduct of producing some pressure.

That mixing device ended up being developed into centrifugal superchargers.

Now, eventually, engineers got interested in what they could do with the exhaust gasses coming off the engine. That lead to the turbo-superchargers we know and love. When applied to a radial, there was no reason to remove the mixing device.... :)
Where might one read up on this story? It is at odds with the history I have read. Would like to hear more if you can point me to a source.
 

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
Where might one read up on this story? It is at odds with the history I have read. Would like to hear more if you can point me to a source.
I hope I can find it. I remember reading about it in a book when I was in college.... That's a long time ago now. :) But.. I'll try. And i'm open to being wrong.. it happens.
 

Latest posts

Top