The big engine small plane problem

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Jay Kempf

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Back to the topic at hand- I'm looking at the typical overpowered two place design for my own needs. I have been going along the big inch NA powerplant (540 Lyc or V8) route so far. I wonder though, if you took something like a 300 HP Rocket and replaced the engine with a normalized 180, how it would perform?

As I sit in my fuselage mockup and ponder the V8 integration, I can't help but consider the 180 Lyc sitting in the corner. If I add a turbo, would I come out ahead...
Only one way to find out... math model for both on a fixed mission profile of your choice. You would break the NA 540 into mission chunks like climb, cruise, yadda and did individual estimates for fuel flow and HP at each altitude you could start to figure out time down range for each event and fuel flow during each segment. For each though you have to look at fuel consumed along the way and the original weight difference on MTOW between events. It really isn't all that bad of a spreadsheet. If you don't factor in the cost of the engine choice it would be an interesting operating cost and performance investigation on it's own. If you factor in lifcycle costs it is another animal altogether. But you knew all that. For a small plane that 540 is a big chunk of metal to both house and lift. Fortunately on a small airframe the lift part isn't as strong in the mix. You can fly a freight car if you have a high enough trust vector value :)
 

Toobuilder

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Interesting. If you only neaded the hp at alt, and climb, etc. was still acceptable, that might be a good option. Just out of curiosity, what are you building?
"Building" is a strong term... I want a fast two seater with long legs - a Rocket is close, but with plenty of limitations. An Extra 330LT is also close, but WAY out of consideration for me. So I'm toying with something close to both, but custom fit for my wife and I. I currently have a full scale fuselage mocked up in EMT, and am playing with a direct drive LS based V8 to power it. Still a long way from building flyable parts, the stuff I'm doing now helps me think and ultimately will narrow down the final product. Paper and computer renderings are cool, but I think better when I can touch it.

 
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Toobuilder

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Only one way to find out... math model for both on a fixed mission profile of your choice...
Couple of problems with that, I think. Trying to accurately predict the weight difference would be one; and the second is the simple fact that the Rocket wing is really bad up high where the turbo engine would start to shine. From a theoretical standpoint, the fuel burn between the two should be easy to figure. That in itself should get you close enough to see if it makes sense from a speed and range standpoint.
 

akwrencher

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Sweet. I'm sort of in the same spot. Learning as much as possible so I can hopefully start building next year. Leaning towards a Pegazair 80 or 100 plans built. Toying with the idea of building a j3 kitten ultralight first. Can't decide, but don't have to yet:)


So, back to the topic, what would be the weight diff for say, that 180 lyc and a LS DD? Is the plane going to be light enough for it to help? Interesting how many factors go into figuring all this stuff out, isn't it:)
 

akwrencher

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I have to say It doesn't look like something I would like either, unless I knew someone who had one I could fly to change my mind. Just put up the link 'cause it has pricing, etc.
I know there are fans of the Aeromatic, but I have a buddy who put one on his 125 HP Swift without success. Despite spending several days with the company owner fiddling with it, the prop never performed all that well. Maybe others have had better luck, but the Aeromatic is off my candidate list. BTW, if anyone wants the Swift or prop, it's available for the taking at the bottom of Cheasepeak Bay.
 

Monty

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Back to the topic at hand- I'm looking at the typical overpowered two place design for my own needs. I have been going along the big inch NA powerplant (540 Lyc or V8) route so far. I wonder though, if you took something like a 300 HP Rocket and replaced the engine with a normalized 180, how it would perform?

As I sit in my fuselage mockup and ponder the V8 integration, I can't help but consider the 180 Lyc sitting in the corner. If I add a turbo, would I come out ahead...
Assuming same airframe.

The NA V8 with a CS prop will probably have a better initial rate of climb. It will probably have higher cooling drag, although the intercooler on the Lyc may offset this.

You will be able to run a leaner mixture with the water cooled engine in cruise.

The weight difference between the V8 and the LYC will be useful load-ie more fuel for the lyc.

If you fly high, and use oxygen....it may be a wash, with a slight speed advantage to the lyc, at a higher fuel burn. Range may be equivalent with a transit time advantage to the lycoming. (more speed, higher fuel burn, but able to carry more fuel, lower initial rate of climb)

Cost advantage-V8 if your time is free+cool factor.

Lowest risk development program - Lycoming.

If it is already in the corner......hmmmm.

How soon do you want to be flying?
 

Jay Kempf

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Assuming same airframe.

The NA V8 with a CS prop will probably have a better initial rate of climb. It will probably have higher cooling drag, although the intercooler on the Lyc may offset this.

You will be able to run a leaner mixture with the water cooled engine in cruise.

The weight difference between the V8 and the LYC will be useful load-ie more fuel for the lyc.

If you fly high, and use oxygen....it may be a wash, with a slight speed advantage to the lyc, at a higher fuel burn. Range may be equivalent with a transit time advantage to the lycoming. (more speed, higher fuel burn, but able to carry more fuel, lower initial rate of climb)

Cost advantage-V8 if your time is free+cool factor.

Lowest risk development program - Lycoming.

If it is already in the corner......hmmmm.

How soon do you want to be flying?
Are you sure the Lycoming would be lighter? I have an io470 here and it is a porker.
 

Monty

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Are you sure the Lycoming would be lighter? I have an io470 here and it is a porker.
Not sure. I assume about 100 lbs more for the V8 if they both use CS props. Radiators and all for the FWF.

So you could carry about 16 gallons more with the Lyc.

It is definitely dependent on the weights.
 

akwrencher

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Stock A1A about 260lbs. dry. Push that over three for the stock turbo model. IO 360 came in two hundred horse, don't know how hard it is to convert......Maybe a FADEC is in the works, auto mixture, etc.....:)
 

Jay Kempf

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Not sure. I assume about 100 lbs more for the V8 if they both use CS props. Radiators and all for the FWF.

So you could carry about 16 gallons more with the Lyc.

It is definitely dependent on the weights.
I thought we were talking direct drive as the comparison. If you have to take the V8 and fit it out with CS, prop controls, and reduction drive to compare I think you are correct. Direct drive I think the v8 will be close or less weight and especially if you buy an aluminum block.
 

Toobuilder

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Couple of thoughts over the last few posts:

Monty - how do you figure on running "leaner" with water cooling? With the electronic ignition on the Lyc, it will run all the way down to 100+ LOP and remain smooth... This setting is only for experimenting, as the power is down so low that you have lost any speed utility, not to mention the cylinder temps are hard to keep warm enough.

Jay - you mention the IO-470 as being a porker... It is, but it's also a Continental... The Lycoming sixes are much lighter, even the ancient O-435. If we are talking about the four bangers vs. the V8, I think Monty is in the ballpark - the V8 is going to be heavier by a significant margin.

To another point, the V8 running DD can have a CS prop if you build that function into the drive extension. Sure it's a bit heavier, but it is not nearly like a complete redrive. This has been my plan all along. You need a bearing cartridge anyway, might as well pressurize it for propeller control.
 
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Jay Kempf

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Jay - you mention the IO-470 as being a porker... It is, but it's also a Continental... The Lycoming sixes are much lighter, even the ancient O-435. If we are talking about the four bangers vs. the V8, I think Monty is in the ballpark - the V8 is going to be heavier by a significant margin.

To another point, the V8 running DD can have a CS prop if you build that function into the drive extension. Sure it's a bit heavier, but it is not nearly like a complete redrive. This has been my plan all along. You need a bearing cartridge anyway, might as well pressurize it for propeller control.
Yes a DD v8 can have an electric CS prop with almost no mods other than the DD bearing/shaft extension adapter. So that isn't much of a weight penalty. And Monty's original premise was a Harmon Rocket as a platform to compare engine choices. It was AKwrencher that introduces the 4 banger in the mix. I was reacting to the original comparison and using the io as a 6 cyl example. A 300HP 6 was the original point of comparison and whether it was a reasonable way to put HP at altitude. My premise is that if you are trying to shove a large amount of HP in a small airframe you are better off with a smaller, lighter engine with a turbo and direct drive and a cruise prop for overall simplicity and the excess HP at sea level will make it perform fine.
 

Monty

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Yes a DD v8 can have an electric CS prop with almost no mods other than the DD bearing/shaft extension adapter. So that isn't much of a weight penalty. And Monty's original premise was a Harmon Rocket as a platform to compare engine choices. It was AKwrencher that introduces the 4 banger in the mix. I was reacting to the original comparison and using the io as a 6 cyl example. A 300HP 6 was the original point of comparison and whether it was a reasonable way to put HP at altitude. My premise is that if you are trying to shove a large amount of HP in a small airframe you are better off with a smaller, lighter engine with a turbo and direct drive and a cruise prop for overall simplicity and the excess HP at sea level will make it perform fine.

You won't be able to fly much over 10-12K ft without overspeeding the Turbo, or the prop. Probably will need an intercooler if you go higher than that as well.

Flying high with the turbo is not as simple, you would be better off with the large engine and a CS prop. If you are going to turbo, then the smaller engine with a CS prop would have the advantage up high.

I would not start with the rocket wing for high altitude work.
 

Monty

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Couple of thoughts over the last few posts:

Monty - how do you figure on running "leaner" with water cooling? With the electronic ignition on the Lyc, it will run all the way down to 100+ LOP and remain smooth... This setting is only for experimenting, as the power is down so low that you have lost any speed utility, not to mention the cylinder temps are hard to keep warm enough.

Jay - you mention the IO-470 as being a porker... It is, but it's also a Continental... The Lycoming sixes are much lighter, even the ancient O-435. If we are talking about the four bangers vs. the V8, I think Monty is in the ballpark - the V8 is going to be heavier by a significant margin.
You can run the NA liquid cooled engine leaner than the turbo engine at altitude. You don't have to worry as much about the reduced cooling due to the thinner air, or the turbo heating the intake charge. Therefore you can advance the timing and run a lean mixture without fear of detonation. You have to push the smaller air cooled engine harder to get the same power output at altitude. The NA V8 that makes 300 hp at SL-will be making somewhere in the 150 hp range at altitude, maybe 135-140 LOP. equivalent to running the lower HP turbo engine at 75% or so.

Ball park #'s of course.
 

Toobuilder

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Turbos are not my forte', but the Turbo Alley guys and the latest factory turbo Cirrus' run LOP at altitude... The only conclusion my limited experience leads me to is that a TN engine is simply allowed to run at SL power settings while up high. So going "too" lean simply reduces power and temperature. After all, the 300 HP NA engine is 150 at altitude, while the 180 TN engine stays at 180.

...or am I missing a significant point?
 

Jay Kempf

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You won't be able to fly much over 10-12K ft without overspeeding the Turbo, or the prop. Probably will need an intercooler if you go higher than that as well.

Flying high with the turbo is not as simple, you would be better off with the large engine and a CS prop. If you are going to turbo, then the smaller engine with a CS prop would have the advantage up high.

I would not start with the rocket wing for high altitude work.
10-12k is fine for me. Maybe doesn't give the best overall mission fuel consumption and speed but way better than sea level and no oxygen really required. That get's you over most of the mountain passes and trouble most places in the US and gets you high enough to get some benefit out of the density altitude and keeps you in the boost range of most off the shelf stuff without staging turbos. Staging turbos is a good option for going up higher which brings more complexity requirements with it if you want to get serious about being up there.
 

Toobuilder

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Yes, I'm thinking mid teens is about the highest I'd want to go. Physiology gets a little dicey above that.
 

SVSUSteve

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Maybe doesn't give the best overall mission fuel consumption and speed but way better than sea level and no oxygen really required.
Just because it's legal to fly at 10-12K without supplemental oxygen, it doesn't make it a good idea. There are significant deleterious effects on the cognition, reaction time, etc. If you're above 8K you really need to be on O2 or in something pressurized to a lower altitude.
 

Jay Kempf

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Just because it's legal to fly at 10-12K without supplemental oxygen, it doesn't make it a good idea. There are significant deleterious effects on the cognition, reaction time, etc. If you're above 8K you really need to be on O2 or in something pressurized to a lower altitude.
OK, a canula then combined with cabin heat. Not a significant' system. My point was if you want to dabble in that altitude regime then it is less complex than much higher. Somewhere right around 10k is where most people start having effects.
 

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Water cooled are more detonation tolerant because the cylinder can be kept at a more homogeneous temperature. There is a lower potential to remove heat on aircooled. Look at motorcycles. When watercooled became standard in the 80's, it doubled the horsepower of the same size 70's air cooled. Overnight life also went from 20,000 miles for an air cooled to 100,000+ to water. There is just no money to do it right in aviation. If they sold one million planes a year like they do with Ford F150 trucks, you would see water cooled. What do they sell in GA, 1000-2000 planes a year?
 
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