$20 hour Cessna 172?
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benyflyguy
En-Route
Neat article. I missed where they discussed the costs of the new engine with all add ons and cost of testing all this?? It seems like or sounds likes he could easily have more than 100k into that conversion
CharlieD3
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Looks like that was gas cost alone compared against avgas, not mogas.
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jsstevens
So his V-8 is burning 10 gal/hour? (Assuming $2/gal mogas).
bnt83
Final Approach
Have been flying a 150 horse lycoming O320 powered 177 for about 10 years now, the last 5 years have been almost straight mogas for the last 400 hours. It doesn't average 8 GPH per flight but lets say its 8 GPH rounded up from 6.5 to 7.5 average, 87 regular is $2.49 where I buy it right now, 8 x 2.49 = $20.98 an hour without a $100k engine conversion.
Not to mention this engine is just about to hourly TBO of 2000 hours. If I spend $20k on this overhaul its essentially $10 an hour. A brand new prop is around $4500, I don't need one so not buying one.
Not to mention this engine is just about to hourly TBO of 2000 hours. If I spend $20k on this overhaul its essentially $10 an hour. A brand new prop is around $4500, I don't need one so not buying one.
RussR
En-Route
This surprised me, that gas would be so expensive in Nebraska, compared to here in OK where it's almost a dollar cheaper! I looked at the gas price map on gasbuddy.com, and sure enough, the metro areas in Nebraska are much higher than the rural areas.
bnt83
Final Approach
Its a flipping rip here. I heard on the local news "Lincoln is one o the most profitable gasoline markets in the midwest" IOW we are dumb enough to pay....
Tantalum
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San_Diego_Pilot
Great article!
Kudos to this guy
Also, this part
"
After just a few calls, nothing had seemed to change except that the same 1970 vintage 172s were now renting out at $115-$125 per hour. Even more unbelievable was that the same engines were used and still required leaded gas—the EPA and FAA seemed hell-bent on eliminating lead’s poisonous emissions in the early 1980s. Somehow aviation became an inverted pricing model compared to all other industries, wherein the older and more worn a plane is, the more it cost to rent, and remained immune from any emissions rules that required all other engine industries to evolve.
"
..a man after my own heart
Kudos to this guy
Also, this part
"
After just a few calls, nothing had seemed to change except that the same 1970 vintage 172s were now renting out at $115-$125 per hour. Even more unbelievable was that the same engines were used and still required leaded gas—the EPA and FAA seemed hell-bent on eliminating lead’s poisonous emissions in the early 1980s. Somehow aviation became an inverted pricing model compared to all other industries, wherein the older and more worn a plane is, the more it cost to rent, and remained immune from any emissions rules that required all other engine industries to evolve.
"
..a man after my own heart
Crashnburn
Pattern Altitude
Um, AFAIK, there is no limitation where you can land an EAB aircraft. You’d need a LOA, though for any revenue operations.
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jsstevens
Yes. He cited a lot of nice benefits. I'm still trying to decipher if efficiency is one of them. And I wonder how much investment money he needs to get to a general STC?
Did he have an answer for the coolant system being a single point of failure? He did for fuel delivery and ignition.
Tantalum
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San_Diego_Pilot
Pray? I'm not sure. To get an STC would be a financial disaster most likely, but it didn't seem like he was interested in that. I think he was just dissatisfied with what present GA offers for his mission so created his own solution for it.. which is pretty cool
I think that also speaks to why the EA world grows
I would be curious how likely one is to have an engine failure due to a coolant system issue. Biggest risks are what, broken pump, leak, and bad thermostat. The thermostat could fail safe open (a cold engine is better than a hot one), and I would think the plumping and pump aren't huge obstacles
Nothing perfect out there. I just thought it was funny that this guy was "surprised" that they're still using the same engines
DaleB
Final Approach
Not in my experience... we road tripped across the state a back in August, and once last summer as well. Once we left Omaha, the gas prices were never that low again. Aside from the challenges of even finding 91 or better octane gas for the rocket sled, it was anywhere from a dime to 30 cents a gallon higher in rural areas than we paid at home.
OK is a lot closer to the refineries... lower transportation costs.
Dan Thomas
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Dan Thomas
Conversions like this one typically have gearbox failures. It is VERY difficult to create a gearbox that won't destroy itself, and it is not at all like the transmission in a car. The gears have to be much heavier, not only because the loads are high and constant, but because the propeller wants to turn at a nice steady rate while the crankshaft doesn't. That crank surges forward every time a cylinder fires and lags back on every compression stroke, and those gears have to take that. There are resonant RPMs where the thing can abrupty destroy itself, and many geared conversions have done just that. Propeller Speed Reduction Units, they're called, PSRUs, and they're a frequent topic of discussion on homebuiltairplanes.com. There have been far more failures than success stories.
So that's why we're still using the same engines. The technology to change, and the certification costs, are very high. And those costs are spread over a tiny market, so it mostly doesn't get done. Add liability to the headache.
Then cooling can be an issue, and fuel systems are another problem area. It takes a capable cooling system to take the waste heat away at extended full power, and it has to do it without causing a lot of drag. Most engines now don't have anywhere to put a mechanical fuel pump, so you end up with at least two electric pumps, along with electric ignition of some sort, so you have to have a robust generating system and some form of backup if you don't want a simple alternator failure to bring you down.
I speak from experience. I did the design and installation work of a PSRU'd Subaru into a Glastar over 20 years ago. It's not easy or cheap. By the time it was done we could have had a nice new Lycoming in it, and the resale value of the airplane would have been approximately double.
Tantalum
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Yes! Didn't the yellow flying wing demonstrator (the one that unfortunately crashed out here in California a few years ago, something like the "n1"), use automotive style torque converters to solve that issue going from the engines to the propellers?
FormerHangie
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Even if all the coolant drains out, the engine will continue running at a significantly reduced power setting long enough to get to an airport. It may very well destroy the engine, but you'd be able to make a landing.
I think back on what cooling system failures I've experienced over my now nearly 50 years of driving. They were either caused by poor maintenance (clogged core, should have been replaced), or poor selection of material by the manufacturer (crummy plastic cooling system parts). I've never had one fail bad enough to stop me in my tracks. It would be important to know immediately if something were going wrong, I'd want some sort of annunciator for that.
If you noticed there's a significant weight penalty versus the Lycoming. This engine would be more suited to something bigger. since it can produce more power.
Looking at the marine world, Honda and Mercury use 3.5 liter V6s in their 200 hp outboards, while Yamaha uses a 2.8L inline 4. You don't really need a V8 to power a Skyhawk, either of these would work fine, but as long as we're using the legacy airframe designs, we're going to be using the legacy powerplant designs as well.
A PSRU is a demanding thing for someone to develop while working out of his garage, but it's well within the capabilities of an engine manufacturer. i. e. Rotax.
RussR
En-Route
No personal experience, just going from what I saw on gasbuddy.com - https://www.gasbuddy.com/gaspricema...=41.13001294893101&lng=-98.97720584745383&z=8
Shows that the metro areas are around the $2.49 he quoted, but the rural areas can be as low as $1.77 if I get my colors right.
It is interesting that there is a definite change in gas price at the Kansas/Nebraska border. I'd guess that has to do with taxes.
GaryM
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We drove most of the way across the country in October (long story, long drive), but in a number of cases we found it very useful to use a gas price app (in our case, the free GasGuru app) to look for stations on either side of a state line, and also to see what was available a mile or two off of the interstate. The biggest delta we saw between a station we almost used, and a convenient alternate found with the app was $0.75/gallon, similar to what Russ noted above. I figure the app saved us about $150 over the course of the trip.
First off, I'm admitting my ignorance on this; I'm genuinely curious:
I see that the track record for speed reducers had been abysmal, but Rotax doesn't seem to have trouble. Do they have some magic, or is that the reason they haven't gone beyond the 130hp level?
Also it seems like belt drives are pretty reliable? I assume one big enough to reliably transfer 200hp would be too big to be practical? The junkyard guys who put a jacobs r755 in a pickup used a belt drive, but with no cooling they couldn't run the engine long, so the reliability of the belt drive was probably the last thing they worried about.
genna
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ТУ-104
I find it hard to believe that PSRU(or anything else in this conversion) is that much of an engineering challenge for a serious engine manufacturer. Boats use such devices on more powerful engines and those have to shift(I get the weight issues). Race cars run and shift much more complex transmissions connected to much more powerful engines for hours at the time. I find it very easy to believe that nobody who can wants to do it because there is no money at the end of it. In part because the market is tiny, in part because only a very small percentage of this tiny market is willing to trust anything different. Basically how one can describe most innovation attempts in piston GA that cannot be sold as a safety feature.
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jsstevens
"The project received a FAA G1 issue paper for an STC to install the engine on other 172s, but certification cost requires outside investor funding and we have not found the right partner yet. "
So I think he would IF he found the right investor. Which seems doubtful given the potential ROI.
David Megginson
Pattern Altitude
When I'm flying at 65% power in my PA-28-161, I'm burning about 7 gph LOP, so let's try to figure that out:
7 gallons = 26.5 litres * CAD 1.83/litre (taxes in) = CAD 48.50 * 0.75 =~ USD $36.50/hour
So with the conversion, I'd save about USD 16.50/hour on fuel costs with the $20/hour number quoted. Presumably, I'd save the same if I just did the Petersen mogas STC for my Piper's O-320-D3G.
I'm managing to fly about 50 hours/year these days (life and all that), so switching to mogas would give me a saving of USD 825/year — at best, 10% of my flying cost. I don't mind paying that 10% for the convenience of just taxiing up to a fuel pump on the field (or calling over the truck) instead of hauling up to 10 5-gallon cans of mogas onto the field every time I need to fuel up.
Tantalum
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San_Diego_Pilot
You are able to run LOP on a carbureted engine?
David Megginson
Pattern Altitude
Yes. It's hit or miss with carbureted engines (especially six-cylinder ones), but four-cylinder the O-320 does pretty well. Without an engine monitor, the best technique is to leave the throttle wide open and lean to your target RPM at cruise — that means you're as lean as physically possible (at that power setting and density altitude), and if the engine runs reasonably smoothly, that means there's not too wide a spread among cylinders (the power curve drops off very steeply on the lean side, so any significant spread will cause very noticeable roughness). Here's what Piper recommends in the PA-28-161 POH (1982 edition, section 4.7):
The Lycoming O-320 Operator's Manual (2007 edition, section 1) also references the relatively-smooth fuel/air distribution for this engine:
Of course, your mileage may vary. You might find that one plane with the O-320 just won't run smoothly LOP no matter what you do, while another of the same year and model might run smoothly right to idle cutoff.
bnt83
Final Approach
Here it would be pretty close to 78% more to buy blue gas. Depending on which FBO you use it may be 100% more.
David Megginson
Pattern Altitude
In my example, it was 82% more to buy the blue gas, but since fuel is such a small part of the overall cost of flying (at least unless you own a turbine or thirsty twin), the net impact on flying cost is tiny.
Someone who flies a C172 or PA-28 50 hours/year is probably paying between $150 and $200/hour total flying cost (maybe $120/hour if you fly 100 hours/year) when you divide up all the fixed and variable costs, so saving $16.50/hour on gas doesn't amount to much in the bigger picture, except maybe bragging rights in the hangar.
Crashnburn
Pattern Altitude
When I got my A&P I did a paper on torsional resonance and how to address it. Four cylinder four stroke engines have torsional resonance because there are gaps in power output because of intake/exhaust valve overlap. The propeller acts like a spring and pushes energy back into the engine. That doesn’t happen with 6 or more cylinder engines as the engine applies power to the propeller all 360 degrees of operation. I’ve never heard anyone talk about how smooth a 4 cylinder LycoSaur is, but I have heard numerous people talk about how smooth the Continental 6 cylinder is.
Torsional vibrations occur even in direct drive applications. When a LycSaur is winding down, the propeller sometimes kicks back. That’s not a backfire but torsional resonance.
Rotax solves the torsional resonance problem with slipper clutches. They engage above idle and are disengaged at idle, so when the propeller tries to turn faster than the engine, it doesn’t supply any energy to the engine.
I had the opportunity to look at a Rotax powered plane. One of the builders said that before they added the then optional slipper clutch, the engine would sometimes kick back so hard the air cleaner would pop off. They never had that problem after they added the slipper clutch.
I’m not saying you don’t need a PSRU for engine conversions, but you shouldn’t need to worry about torsional vibrations from 6 or more cylinder engines.
Torsional vibrations occur even in direct drive applications. When a LycSaur is winding down, the propeller sometimes kicks back. That’s not a backfire but torsional resonance.
Rotax solves the torsional resonance problem with slipper clutches. They engage above idle and are disengaged at idle, so when the propeller tries to turn faster than the engine, it doesn’t supply any energy to the engine.
I had the opportunity to look at a Rotax powered plane. One of the builders said that before they added the then optional slipper clutch, the engine would sometimes kick back so hard the air cleaner would pop off. They never had that problem after they added the slipper clutch.
I’m not saying you don’t need a PSRU for engine conversions, but you shouldn’t need to worry about torsional vibrations from 6 or more cylinder engines.
Dan Thomas
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Good luck with that. When the cooling system fails in your car, you're not running at 75% or 65% or 55% or even 45%. You're running at maybe 20 or 25%. In an airplane a coolant system failure means imminent seizure. You're not cruising to the nearest airport at 25% power unless the airport is very close and you have plenty of altitude.
FormerHangie
En-Route
There are a few small companies who make reduction drives for airboat use. Some use belts and some use gears. Clearly, someone with some knowhow and adequate resources can engineer a PSRU, but I can see why this would not be within the reach of the average homebuilder.
genna
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ТУ-104
An engine failure mode where I have 25% continuous power and 100% short power would be pretty dreamy actually. Opens up a lot more options and possibility of correcting an error on landing. I’ll take it.
Dan Thomas
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It's not torsional resonance at all. It's just the compression pushing the prop back as it stops. Torsional vibration in direct-drive applications is pretty much absent. The prop is the flywheel and is connected directly and solidy to the crankshaft. With gearing, the prop is still the flywheel, and at certain RPMs the gears are going to suffer unless there's some means of damping the vibrations. With geared aircraft engines (both Lyc and Continental built them) there are torsion shafts that absorb the worst of the resonance by twisting. Rotax uses a clutch. On airboats, where weight isn't much of a factor, the heavy cast iron flywheel can be left on the crank to damp out the vibration. Even in cars there are springs on the clutch plate to absorb the bad stuff. Torque converters do it, too, but a heavy thing like that isn't welcome in any airplane.
The Continental GO-300 crankshaft:
#1 is the crankshaft. #13 is that torsion shaft I talked about. It flexes to reduce the torsional vibration loads on the gearing. #14 is the crank gear and the torsion shaft drives its forward end, and the other end of the shaft inserts into the crank. The driven gear, the one that the prop is bolted to, is this:
Setups like this have RPM ranges that are verboten for cruising in. You can pass through them but you don't stay there. Those ranges are where the vibration is the worst.
Belts are easier, as they can accomodate more vibration, but they have failed as well. That Subaru I installed used a wide timing belt, and at 1400 and 2800 RPMs you could feel and hear that belt getting hammered. It was less at 4200 and 5600 (redline). That engine had an aluminum flywheel; without it, the system wouldn't survive.
Chains have been used. Geschwender used the Morris Hy-Vo chain, which had zero lash. It ran on special gears, not sprockets, and it had teeth that fit into the gears and which spread as the chain curved around the gear, filling the gaps between the gear teeth and removing the lash. Geschwender installed Ford V-8s with these things on a 172 and a Piper Pawnee. Seemed to work OK. Dates back to the late '60s. It takes a lot of time and money to make anything like this succeed. For those of you convinced you can make a go of it, see this: http://users.owt.com/worden/alternateairpower/
Dan Thomas
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25% power in a 172 will be around 1600-1700 RPM at most. It takes 1900 or so to maintain altitude when running light. Like I said, you're going down.
genna
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Not disputing that fact. But you are going down a hell of a lot slower than with a stopped propeller. And you will have max power for a minute or a few before landing. Or even a few short bursts along the descent. I will take that.
Matthew Rogers
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But again, you are going down with a failed legacy engine as well, but the comparison is going down with 0 power or with 20% power. 20% power is plenty to make an approach to landing in a field 10x easier than a true dead stick landing. Plus, as stated, if you need 100% power last minute to clear a power line or fence, you have it, regardless of if it seizes after that burst.
I had a partial power emergency landing and partial power made all the difference in making it back to an airport 10 miles away from 2500’ AGL vs choosing a field and hoping I didn’t make a bad choice of landing site.
Bacho
Pre-takeoff checklist
Personal experience would disagree with that. It would depend on the application. You might be due for an O/H by the time you land though.
There are ways to convert all of the rubber/plastic parts in these LS engines over to very high quality stuff. The cooling failure would not be a bigger concern than anything else IMO.
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AlphaPilotFlyer
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The airfacts article says the $20/hour is operating cost with fuel, oil and reserves..... not just the fuel. Big savings over a O-360 at about $60/hr. There are plenty of experimentals flying with car engines safely now and seems logical to apply to old certified aircraft. But didn’t Porsche make and certify an engine for Cessnas and Pipers back in the 80’s?
David Megginson
Pattern Altitude
Reserves for what? Even leaving out engine overhaul (since that would be a different cost with for him), if you're paying $1,500/year insurance, $3,000/year maintainance, and $1,000/year tie-down (all improbably optimistic low-end estimates) that's $110/hour at 50 hours/year (most owner-pilots don't even manage that), or $55/hour at 100 hours/year before we even get into variable hourly costs. So unless fuel, oil, and engine reserve are between negative $35/hour and negative $90/hour — again, in an unrealistically-optimistic case — it's hard to see how you could land at $20/hour.
AlphaPilotFlyer
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Reserves typically refer to engine overhaul. Not sure I see your point. Cost of flying is absurd, seems something like such new thinking in this ancient industry is a huge step in the right direction. If cost can drop to $20/hr, or even $50, for something like a C172, there would be less aircraft being parted out and returned to rental fleets and flying clubs which can really make a difference in allowing more to fly.
my flying club rents a C172 out for $110/hr which is about the lowest around. If something like putting a new engine design on the same old airframe and drop the cost to about $50/hr, it would be huge. It may not cure the other cost factors, it’s a good step in right direction.
my flying club rents a C172 out for $110/hr which is about the lowest around. If something like putting a new engine design on the same old airframe and drop the cost to about $50/hr, it would be huge. It may not cure the other cost factors, it’s a good step in right direction.
David Megginson
Pattern Altitude
In the article, he compares the cost of renting a C172 to the his claimed $20/hour cost. That's apples to oranges, because the cost of renting (or owning) is mostly not fuel, oil, or engine reserve.
The US $50 fuel+oil+engine-reserve saving seems improbable, because that's about the total hourly variable cost for the O-320 in my PA-28-161. USD $25–30/hour saving seems more realistic (maybe less in the U.S., where 100LL is a bit cheaper than in Canada). I could get most of the same fuel-cost saving by applying the Petersen mogas STC to my plane, without spending tens of thousands of dollars to retrofit a car engine, but I'm not interested in hauling a carload of 5 gallon gas cans out to the airport every time I want to refuel.