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The 100HP VW--Reliable? Practical?

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Vigilant1

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Given the dearth of affordable 100HP engines, I'm reviewing the approaches to obtaining 100HP from the Type 1 VW for limited periods (takeoff and 5 minutes of climb). What I've seen or what seems possible:
-- PSRU: By allowing a higher engine speed while keeping prop speeds reasonable, these appear to give good results in draggier airplanes (105 HP for about 5 minutes). I'm not quite understanding why the same setup wouldn't work just as well with cleaner airplanes if the right prop were selected. After all, the RPM and torque are close to an 0-200, and these have worked will on slippery planes.
-- Smaller prop: Allows higher engine RPMs before the tips reach critical mach. While this might allow the engine to make more HP, the higher profile drag from all the "junk" in the way of a small prop (esp the fuselage), as well as the lower efficiencies due to higher disk loading, make this fairly unattractive.
-- Turbo: Not widely done in airplanes, but Revmaster sold a turbonormalized setup for their 2100 engine version for many years (along with an available two-position prop). A nice by-product of a turbo used to get 100HP at SL would be this ability to maintain a constant 75 HP or so at 8000 ft MSL.
-- Nitrous oxide injection: I know cars have used it and I'm aware of at least one seaplane that has used NO boost to get off the water. Simple, relatively cheap, and would seem to involve about the same engine stresses as turbocharging.

Anything I'm missing?

Limits on all of the above come from the ability of the little VW engine to shed waste heat. A short-duration run gets around this by just using the heat capacity of the engine and oil--things get hotter and hotter, and you need to back of at 5 minutes or you'll break something (exhaust valve stems, valve seats, etc).
Ways to increase the available higher HP running time (or reduce thermal stress on the engine within that 5 minute run time):
-- Run rich (use the excess fuel to cool things off). It probably works okay to keep head temps lower. Simple, cheap. Diluton of oil with fuel likely to increase wear.
-- More oil, increase size of oil cooler. Limited impact on cooling the critical valves and valve seats.
-- Improved heat transport from fins: From what I've read, the "Fat Fin" heads have done a good job of making practical, sustained 75HP operations possible. But even with this, the guys in the know aren't suggesting that 100 HP ops can be conducted for more than about 5 minutes. Nikasil cylinders also provide slightly improved heat transport. I wonder if still higher heat rejection can be accomplished:
--- Copper brazed to the fins?
--- Water jacket attached to the fin tips
--- External water spray to incoming cooling air (even a gallon of water requires a tremndous amount of heat to convert from liquid to vapor)
--- Heat-pipe to carry heat from the spark-plug holes to a remote location, etc).

Again, are there other approaches that might help keep temps in check, at least for a limited time? Ideas, other installed approaches, etc are welcome.
 

autoreply

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-- Smaller prop: Allows higher engine RPMs before the tips reach critical mach. While this might allow the engine to make more HP, the higher profile drag from all the "junk" in the way of a small prop (esp the fuselage), as well as the lower efficiencies due to higher disk loading, make this fairly unattractive.
This would be my personal favorite. Simple and straightforward.

I don't think the drag at cruise will be that much worse as with a bigger prop. Induced velocity during cruise is typically very low.

Sure, static thrust will suck (not suck enough actually) and so will initial take-off roll, but at climb speeds (say 65 kts) the difference is a lot smaller.
Anything I'm missing?
Water injection? Saves the complexities of turbo's and nitro and also keeps your cilinder heads a lot cooler.
Again, are there other approaches that might help keep temps in check, at least for a limited time? Ideas, other installed approaches, etc are welcome.
A big cowl flap? Looking at typical cooling setups they're not exactly efficient and for most, a good cooling set-up can double the Cp over cooling inlet/outlet. That's 41% more airflow through your engine and shutting the cowl flap will make the extra drag go away.

You could also ask yourself whether you really need that much climb performance. A Super Dimona climbs just fine at 1700 lbs with 80 hp.
If you manage a reasonably streamlined design, you'll climb exactly as well as an LSA if you're flying at 1000 lbs. That's not a rocket ship, but it's plenty for normal flights.
 

Vigilant1

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Google to read the late Bob Hoover's articles on RAH and his blog. Don't bother debating- just follow his advice.
I am a big fan of his writing style and articles, and he surely knew VW's very well. But he held for a long time that there was no way to get more than about 40 HP from them due to these cooling limitations. I'll have to go back and look at his work because I do recall he might have changed his position on this at a later point, agreeing that that the "Fat Fin" modification, along with his lubrication modifications, etc, made higher sustained HP possible.
 

Topaz

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I am a big fan of his writing style and articles, and he surely knew VW's very well. But he held for a long time that there was no way to get more than about 40 HP from them due to these cooling limitations. I'll have to go back and look at his work because I do recall he might have changed his position on this at a later point, agreeing that that the "Fat Fin" modification, along with his lubrication modifications, etc, made higher sustained HP possible.
Bob Hoover (the engine builder, not the pilot) knew a lot about VW conversions. I entirely respect his work. Unfortunately, his writing didn't live up to his engine knowledge. The series of blog posts referenced by Harrisonaero contain some very poorly worded passages - and one in particular - that are commonly mis-read to mean that VW engines in general cannot sustain more than 40hp reliably. Which even Bob Hoover never agreed with, and he regularly built 60-65hp (takeoff) power engines for clients. The confusion came in when he was telling a story about a client coming in with a 1600cc Type I, asking for 65hp out of it. Which can't be done, reliably. It can be done just fine with a larger displacement VW, but Bob didn't do a very good job of saying it that way, and people have been misquoting him as a result for years now. We've had some really rocking debates about this myth here on HBA. The fact remains that, no matter what anyone says, there have been reliable 65hp (takeoff) VW conversions since the late 1970's, that have powered hundreds, if not thousands, of homebuilts. Those airplanes were never falling from the sky with broken, burned out motors. Never have been, and never will be.

Moving back to the subject at hand, I'm obviously a HUGE fan of the VW for aircraft conversion, but the success of high-power operations, as you note, is going to depend entirely on how much you modify the engine. Oil coolers help a lot, as do the modified heads that Great Plains and the others use. Spraying water over the cooling fins (especially on the heads) is an interesting idea, but I question if the heat transport through the metal is sufficient to reject heat building up quickly near the valves inside the engine when run at this power. I think nitrous is a thoroughly bad idea for an engine that would already be struggling with heat rejection at this power level. More displacement is a better answer.

I think if anything's going to allow a VW to run at this power level for even a short time, it's highly-modified heads (more metal near the valves as a sink) and a well-sized and effective oil cooler.

Personally, I remember that the 100hp variants that Revmaster and others used to offer back in the early '80s seemed to be very temperamental. Personally, I think this is asking too much for this little engine. I think the various VW variants are good and reliable up to about 65-70hp (takeoff) without radical modification, and developing your own modifications seems like a huge project unto itself. Great Plains offers a 105hp (takeoff) rated Type I with a reduction drive, punched out to 2276cc and with completely custom heads and if you're bound and determined to use a VW, I'd go with that since they have so much experience. But I imagine that the allowed time for running WOT is going to be five minutes or less, not a full climb-out. Can your chosen airplane climb adequately in a high-density-altitude situation on 75hp or less? That's what you'll have to work with once you've used the takeoff power time allotted and have to back off the throttle. Whether or not the engine lasts will depend upon your discipline with that throttle. TBO will plummet if you regularly run takeoff power longer than specified. I don't think there's a lot you can do to extend the WOT running time safely, and certainly not into the range where you could cruise at that level of power.

Honestly, in this power range, I think you're better off to find a used O-200 somewhere and use that. Or a Corsair, if you're pinching pennies. As much as I like 'em, I just don't think pushing a VW this hard is a really great idea.
 

autoreply

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Just a general thought, but how long would it take to overheat a VW if you're running it at 30-40% above max (heat rejection) power? A minute? More?
 

bmcj

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Google to read the late Bob Hoover's articles on RAH and his blog. Don't bother debating- just follow his advice.
You said "the late Bob Hoover"... Don't shock me like that. From now on, his name should officially be "Bob Hoover: No, not THAT Bob Hoover".
 

TFF

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For as much power as you want I think you are now in the Subaru range with the watercooling. I dont think you can do it economically. You could see if Rotaway Helicopter would sell one of their watercooled fadec engines. They started out with VWs when the Scorpion came out and refined it to their own engine. It still has VW DNA even if not one part interchanges.
 

Topaz

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Just a general thought, but how long would it take to overheat a VW if you're running it at 30-40% above max (heat rejection) power? A minute? More?
Probably depends mostly on how long it takes to warp or melt an exhaust valve seat. Without some pretty extensive mods, not long, I'm guessing.
 

BBerson

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First, what is the mission? (Race plane, bush plane)
My VW derived Limbach 2000 only works on the heavy motor gliders because of the controllable prop that allows low pitch for climb.
Otherwise, hardly anything near max power will be available in climb with any fixed pitch prop set for reasonable cruise.

So, a manual two position prop (like my Hoffmann but lighter) is another option for your list.
Another option is electric motor boost for takeoff.
 

rheuschele

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I can't give you technical reasons of why I didn't go this route, but after doing research on what and how much I would have to add to a VW to get the 100 hp it added up
to more weight, and more money than just using a corvair. Then I decided that the corvair has 6 cylinders and a smoother feel.
ron
 

Vigilant1

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First, what is the mission? (Race plane, bush plane) . . . So, a manual two position prop (like my Hoffmann but lighter) is another option for your list.
Mission: LSA-legal two-place, hard-runway operations, 1200 lb MTOW. Mostly solo recreational flying with the occasional option for two-up trips (not serious cross-country, but 350 lbs of people, 100 lbs of bags, 100 lbs of fuel). A Sonex meets almost all my requirements (good handling, fairly fast (170 MPH) cruise at altitude, affordable price and economical operations) but I could use about 100 lbs more useful load than the stock Sonex provides. The structure is strong enough for it, I can place the weight within the allowable CG range, but the limiting factor appears to be climb performance on 80 HP. Even at 1100 lbs, according to reports, climb is marginal at anything but very low density altitudes. 20 additional HP for takeoff would provide the climb performance needed to overcome this single limiting factor.

Unfortunately, a controllable pitch prop puts the plane out of the LSA category. That's not a showstopper, but it's a negative factor. I don't know how those will price out--it might be cheaper to buy a Jabiru 3300 instead.

The series of blog posts referenced by Harrisonaero contain some very poorly worded passages - and one in particular - that are commonly mis-read to mean that VW engines in general cannot sustain more than 40hp reliably. Which even Bob Hoover never agreed with, and he regularly built 60-65hp (takeoff) power engines for clients.
Thanks, I must have read that single exchange and gotten it stuck in my bit bucket. His HVX mods and other things made it clear he was building engines capable of a lot more than 40HP sustained, so the 40 HP limit didn't make much sense (along with the fact others have obviously been getting more than 40HP for a long time).
Spraying water over the cooling fins (especially on the heads) is an interesting idea, but I question if the heat transport through the metal is sufficient to reject heat building up quickly near the valves inside the engine when run at this power.
I don't know either. But here's a back of the envelope calculation on the overall situation: 25 HP needed (beyond the 75 HP that can produced continuously). Most auto engines shed about the same energy to the coolant (air or water-then-air) as they produce at the shaft, so we need to get rid of about 25 HP worth of heat, or 63600 BTU/hr. For 6 minutes, that's about 6400 BTU. Latent heat of evaporation of water is 965 BTU/lb, so it would take about a gallon of water to get rid of the excess heat in this case. It would seem a straightforward issue to get the water to the fins that need it most (near the exhaust port), but I know there would be devilish issues with differential expansion, stresses, and the issue you mention about the ability of the metal right at the valve seat to conduct the heat away regardless of the temperature of the fins or the head in general.

You could also ask yourself whether you really need that much climb performance. A Super Dimona climbs just fine at 1700 lbs with 80 hp.
If you manage a reasonably streamlined design, you'll climb exactly as well as an LSA if you're flying at 1000 lbs. That's not a rocket ship, but it's plenty for normal flights.
The Super Dimona's 164 sq ft of wing and 52 ft span help a lot. For unrelated reasons I'd thought about the pros/cons of adding stub wings to a Sonex, which would increase the span by 3 feet (22 ft to 25 ft) and increase the area by 13 sq ft (98 sq ft to 111 sq ft). This would improve the plane's climb rate (amount? unk), and might even improve cruise at altitude, but would also decrease the roll rate and probably require changes to the tail, etc.

I wish Revmaster would finally come out with the long-promised R3000 100HP model. But it has been a long wait already . . .
 
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TFF

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I have seen what I would guess is a 80hp Sonex takeoff solo a couple of times. Not a rocket; closer to a C150. I was surprised.
 

autoreply

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Unfortunately, a controllable pitch prop puts the plane out of the LSA category. That's not a showstopper, but it's a negative factor. I don't know how those will price out--it might be cheaper to buy a Jabiru 3300 instead.
A ground-adjustable one will not. That gives you the choice of slow cruise and good climb, or slow climb and good cruise.
The Super Dimona's 164 sq ft of wing and 52 ft span help a lot.
Obviously and it's an extreme example. The Dimona has a lot of drag, so a much cleaner and lighter design could climb at much higher forward speeds during climb, negating the need for both a high aspect ratio and a variable pitch prop.
For unrelated reasons I'd thought about the pros/cons of adding stub wings to a Sonex, which would increase the span by 3 feet (22 ft to 25 ft) and increase the area by 13 sq ft (98 sq ft to 111 sq ft). This would improve the plane's climb rate (amount? unk), and might even improve cruise at altitude, but would also decrease the roll rate and probably require changes to the tail, etc.
You mentioned 170 mph cruise, but that's considerable higher than the LSA speed limit isn't it?
 

Himat

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You have forgotten the non practical possibility to make the engine a turbo compound engine.

Back to the more practical solutions. I have got an old Norwegian book on car tuning. This book is again based on a German book, Autos schneller machen, by Gert Hack. One chapter is devoted to the air cooled VW engine. A maximum of 170hp from a 2234cm^3 engine is stipulated, this at 6000rpm. A side note is that the valve train make it difficult to obtain anything more than 6000rpm with this engine. But I doubt a VW engine screaming at 6000rpm would last very long. And the specific fuel consumption would probably be bad. Assuming a linear power curve, 3000rpm gives 85hp. A guess without digging out graphs is that 100hp is obtained close to 4000rpm. I’m not sure the air cooled VW is well suited to that either.

I am no fan of the old KDF Wagen or its engine, would rather search for an automotive, motorcycle or “recreational” engine that have 100hp at peak toque that could be used/converted.
 

Autodidact

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What about a turbocharged Ecotec? You'd have to make some kind of prop drive and it would be best if it weren't eyeballed:

ecotec.jpg

[h=2]Ecotec Gen II[/h] [h=3]2.0[/h] [h=4]LNF[/h]
Ecotec LNF in a Pontiac Solstice


A turbocharged direct injected (redubbed Spark Ignition Direct Injection) Ecotec was introduced in the 2007 Pontiac Solstice GXP and Saturn Sky Red Line. In these applications, the engine is mounted longitudinally. Displacement is 2.0 L—1,998 cc (121.9 cu in)—with a square 86 millimetres (3.4 in) bore and stroke. Compression is 9.2:1 and maximum boost is 1.4 bar (20.0 psi), delivering 260 hp (190 kW) at 5300 rpm and 260 lb·ft (350 N·m) of torque from 2500 to 5250 rpm. Engine redline is at 6300 rpm and premium fuel is recommended. The sodium filled exhaust valves were based on technology developed for the Corvette V8 powertrains. The sodium fuses and becomes a liquid at idle, which improves conductivity and draws heat away from the valve face and valve guide towards the stem to be cooled by the engine oil circulating in this area. The camshaft-driven direct injection systems pressurizes the fuel to 31 bar (450 psi) at idle, and up to 155 bar (2,250 psi) at wide-open throttle. The "Gen II" block is similar to the 2.4 L and also features VVT technology. The Gen II block was developed using data from racing programs and computer simulations. The bore walls and bulkheads were strengthened with a weight increase of 1 kg (2.5 pounds). The coolant jackets were expanded to improve heat transfer, resulting in a coolant capacity increase of 0.5 liters.
In December 2008, GM released a Turbo Upgrade Kit for the LNF engine which increases horsepower to 290 hp (220 kW) and torque to up to 340 lb·ft (460 N·m), depending on the model. The kit retails for $650 and includes remapped engine calibration and upgraded MAP sensors. The kit is covered by the cars' existing GM warranties.[4]
Unique LNF features[5] include:

This engine is used in:
Year(s)ModelPowerTorque
2007–2009Opel GT260 hp (190 kW) @ 5300 rpm260 lb·ft (353 N·m) @ 2000 rpm
2007–2009Pontiac Solstice GXP260 hp (190 kW) @ 5300 rpm260 lb·ft (353 N·m) @ 2000 rpm
2007–2009Saturn Sky Red Line260 hp (190 kW) @ 5300 rpm260 lb·ft (353 N·m) @ 2000 rpm
2008–2010Chevrolet HHR SS260 hp (190 kW) @ 5300 rpm260 lb·ft (353 N·m) @ 2000 rpm
2008–2010Chevrolet Cobalt SS260 hp (190 kW) @ 5300 rpm260 lb·ft (353 N·m) @ 2000 rpm
2009Elfin T5264 hp (197 kW) @ 5300 rpm259 lb·ft (351 N·m) @ 2000 rpm
2012Fisker Karma260 hp (190 kW) @ 5300 rpm260 lb·ft (353 N·m) @ 2000 rpm
[h=4]LDK[/h] A high-performance version of the LNF with 9.3:1 compression. This engine is also known as A20NFT and A20NHT by GM Powertrain Europe.
This engine is used in:
Year(s)ModelPowerTorque
2009Opel Insignia162 kW (220 PS; 217 hp) @ 5300 rpm350 N·m (258 lb·ft) @ 2500 rpm
2010–presentSaab 9-5162 kW (220 PS; 217 hp) @ 5300 rpm350 N·m (258 lb·ft) @ 2500 rpm
2011Opel Insignia 4x4184 kW (250 PS; 247 hp) @5300 rpm400 N·m (300 lb·ft) @2400-3600 rpm
2012Opel Astra J OPC206 kW (280 PS; 276 hp) @5500 rpm400 N·m (300 lb·ft) @2500-4500 rpm
 

Himat

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Interesting numbers, just to show how interesting, here is the power at "peak" torque rpm:

TorqueRPMPower [kW]Power [hp]
35320007499
35120007499
350250092123
4003600151202
4004500188253

This engine is in the 100hp class in direct drive configuration. Spin the engine at at 2500rpm as is done with a "Lycosaur" and the engine give 123hp.
 

autoreply

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Vigilant1

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A ground-adjustable one will not. That gives you the choice of slow cruise and good climb, or slow climb and good cruise.
Yes, and that might work well for me since most of the time I won't be at max gross weight and it won't be very hot.

You mentioned 170 mph cruise, but that's considerable higher than the LSA speed limit isn't it?
It can be done, at altitude. The US regulation says:
(2) A maximum airspeed in level flight with maximum continuous power (VH) of not more than 120 knots CAS under standard atmospheric conditions at sea level
So, they measure calibrated airspeed, in knots, at sea level. By the time you convert to MPH and TAS at higher altitudes, 170 MPH is possible (and the 120 HP Sonex's do it). Another area for creative interpretation of the rules I suppose is the "max continuous power" provision. I'm not sure who gets to say what the "max continuous power" is of an engine that a homebuilder has put together from bits. I suppose you could tell the FAA "At sea level standard day, this engine is only good for 2800 RPM continuous, and at that RPM the plane does 120 KCAS. But the engine can run 3400 RPM for 8 minutes at sea level."
 
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