The big engine small plane problem

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SVSUSteve

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Somewhere right around 10k is where most people start having effects
That they recognize. The human factors literature, NASA research, etc is pretty clear that someone who lives in a non-mountainous area will start to have effects somewhere between 4,000 and 8,000 feet ASL. That's the reason why airliners are pressurized to what they are. More importantly, that's why NASA treats a 5,000 ft cabin altitude as only marginal.

OK, a canula then combined with cabin heat. Not a significant' system
Of course. It doesn't need to be fancy to work.

My point was if you want to dabble in that altitude regime then it is less complex than much higher.
I know. I just wanted to point out a couple of things. Sorry for the derail.
 

Toobuilder

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Water cooled are more detonation tolerant because the cylinder can be kept at a more homogeneous temperature...
Detonation is one thing, but we're talking stable, LOP ops. Once LOP, detonation is not possible. Getting to LOP is the trick, and as long as you pass through the detonation range (75-25 ROP) quickly, you're generally in the clear.
 

Jay Kempf

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It's for model airplanes and doesn't estimate a cruise prop stalled at 0 MPH. Which I am guessing what the intent of the question.

Jarno in answer to your question: I think if you are asking because you are wondering if you can get one of your designs moving the answer is yes. The initial takeoff roll might be a bit slow but it isn't that many meters before you have sufficient airspeed to make the prop get out of the stalled zone. Even working badly with that much HP it is still going to produce 300+LB thrust maybe closer to 400. And still 250 plus even at pretty high speeds. That little prop will most likely get happier at higher speeds as well. Even if you call it 200 lbs of drag that is a pretty healthy budget at a pretty high speed for even a modest sized airframe.
 

SVSUSteve

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It's for model airplanes and doesn't estimate a cruise prop stalled at 0 MPH. Which I am guessing what the intent of the question.

Doesn't RTFM's version of the Roncz spreadsheet also include a calculator for this sort of stuff?
 

autoreply

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It's for model airplanes and doesn't estimate a cruise prop stalled at 0 MPH. Which I am guessing what the intent of the question.
Exactly.
Jarno in answer to your question: I think if you are asking because you are wondering if you can get one of your designs moving the answer is yes.
No, not one of my designs. The fuel cost would short me down with our prices. :speechles
The initial takeoff roll might be a bit slow but it isn't that many meters before you have sufficient airspeed to make the prop get out of the stalled zone. Even working badly with that much HP it is still going to produce 300+LB thrust maybe closer to 400. And still 250 plus even at pretty high speeds. That little prop will most likely get happier at higher speeds as well. Even if you call it 200 lbs of drag that is a pretty healthy budget at a pretty high speed for even a modest sized airframe.
I was thinking along the lines of designs you and other are working on. Fast, light and big engine. 1000-2000 lbs MTOW, big engine. I feel that a very fast (and thus small, tip-speed limited), fixed pitch prop might work well and simplify things a lot. Obviously doesn't work for most designs since they have less HP and more weight, so they need the static thrust to get off the ground.

Theory works fine, but estimating static thrust from such a highly pitched cruise prop... not at all. We know that static thrust is proportional to:
T==power^(2/3)*A^(1/3).

So if we have the static thrust of a fixed pitch prop on a very fast plane, we might make a reasonable estimate. It seems to me that about 0.25-0.3 is acceptable since many LSA's and C172's fly with that type of thrust ratio (MTOW/static thrust). 0.2 or so still flies (many motorgliders and VLA's like the DA20, Aquila A210), but might be a slouch with the higher stall speeds of such a fast design.


In short, can we throw a PSRU, turbo's, CS props etc overboard and make a reasonable propfan-like pocket rocket?
 

Dan Thomas

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. 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?

1453 in the US last year, including all the King Airs and bizjets and everything. The biggest seller was the Cessna Skycatcher, at 168 units.

Go here: General Aviation Market Data | Aircraft Sales & Shipments 2011/2012

Scroll down to "Top-10 Best-Selling General Aviation Aircraft Models"

Note the numbers on such airplanes as the 172, 182, and Cirrus. Note that the American Champion aircraft aren't even mentioned; they must have produced fewer than 53 of any model.

Very, very few new engines being built these days.

Dan
 

Monty

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...or am I missing a significant point?
Cooling. You are asking the same engine to cool at 1/2 the air density. The NA engine is making <1/2 SL power, the Lyc is making SL power.

V8 heat rejection temp = 200 degrees

Lyc heat rejection temp = 400 degrees.

With the NA engine you can afford to radically advance the timing, so you can run leaner mixtures and still make power. Not true with the TN engine. Temps are too high and detonation margin too slim.

Look into some of the things Klaus Savier has done with advanced timing and very lean mixtures at high altitude.

I've taken a chamber ride, so I know the risks. I'd be willing to fly regularly up to 18k with O2 without too much concern. Higher than that is definitely much riskier. I'd probably still do it....No way I'd go over 18K with any regularity...no time to react to O2 system failures.

If you go over 16-17K the cooling issue becomes severe, and the turbo/intercooler situation is more critical.

One of the reasons I like the big engine solution is your margins get better with altitude. The TN engine margins get worse with altitude.

One is simple, the other complex.
 

Monty

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Exactly.

No, not one of my designs. The fuel cost would short me down with our prices. :speechles

I was thinking along the lines of designs you and other are working on. Fast, light and big engine. 1000-2000 lbs MTOW, big engine. I feel that a very fast (and thus small, tip-speed limited), fixed pitch prop might work well and simplify things a lot. Obviously doesn't work for most designs since they have less HP and more weight, so they need the static thrust to get off the ground.

Theory works fine, but estimating static thrust from such a highly pitched cruise prop... not at all. We know that static thrust is proportional to:
T==power^(2/3)*A^(1/3).

So if we have the static thrust of a fixed pitch prop on a very fast plane, we might make a reasonable estimate. It seems to me that about 0.25-0.3 is acceptable since many LSA's and C172's fly with that type of thrust ratio (MTOW/static thrust). 0.2 or so still flies (many motorgliders and VLA's like the DA20, Aquila A210), but might be a slouch with the higher stall speeds of such a fast design.


In short, can we throw a PSRU, turbo's, CS props etc overboard and make a reasonable propfan-like pocket rocket?
Yes it can be done. The prop makes about 50% thrust stalled. Propulsion efficiency is terrible. The problem is packaging. You need a nice smooth transition into that little prop which favors pushers...driveshaft.....yuck. Just ask Billsky.

Noisy.

and like you said...can't afford to feed the darn thing. I lean the crap out of my 172 and still manage to burn way too many $100 bills.

The sweet spot for cruise at altitude seems to be around 200 mph. If you start going much faster than that the compromises make for an unsafe landing speed.

200 mph gets you there in a hurry, and I like to look out the window!

Have you seen the V8 long EZ? He runs a short prop and spins it up to about 4000 rpm IIRC. Good performer too.
 

akwrencher

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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.
Wasn't trying to veer off topic, I was refering to Toobuilder's Lyc 180 sitting in the corner......Pretty sure that has to be on of the 0-360's. Looked up some average empty weights just for fun.
 

bmcj

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A little off-topic, but I have an Aeromatic on mine. It's 93" diameter on a 260 HP engine. The Aeromatic has a very wide blade and thick airfoil section, so you cannot expect to turn it efficiently at high RPM's, but at 93" diameter, high RPM's is not the goal. For mild aerobatics, it seems to work fine... lots of low end thrust and doesn't run away on the descent.

I apologize for going off-topic. My original mention of Aeromatic was in response to a comment about adjustable props.
 

Himat

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1453 in the US last year, including all the King Airs and bizjets and everything. The biggest seller was the Cessna Skycatcher, at 168 units.

Go here: General Aviation Market Data | Aircraft Sales & Shipments 2011/2012

Scroll down to "Top-10 Best-Selling General Aviation Aircraft Models"

Note the numbers on such airplanes as the 172, 182, and Cirrus. Note that the American Champion aircraft aren't even mentioned; they must have produced fewer than 53 of any model.

Very, very few new engines being built these days.

Dan
Thanks for sharing!
Interesting reading. The biggest seller was the Cessna 162 Skycatcher. Of all Cessna sales it look like just about one third was piston singles and about half was jet's with the 208 Caravan making up the rest. Globaly it's the same trend, turbojet/turbofan sales are almost half of the new GA sales.
 
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