Avgas Substitute

[mugaliens]

I'm not getting this: They claim a 100LL substitute to be called G100UL. Same performance/octane as 100LL, commonly known as "avgas" as it's the fuel used in most general aviation piston aircraft.

What I don't get is:

1. Here in the Springs (and elsewhere), 100LL already costs about $0.45 to $0.50 more per gallon than Jet A

2. Turbo-diesels for general aviation are substantially more efficient during cruise while offering better performance during climb, reducing overall fuel consumption.

Sure, I understand there are tens of thousands of general aviation aircraft owners who which will not convert to diesel and need a replacement for the 100LL that's going bye-bye very soon. Several times, however, the fuel industries have said they would soon discontinue 100LL even if the EPA continued granting extentions, nor would they support a substitute if one were developed.

Since Jet-A is so widely available, and perfomance is that much better, I think a financial case could be made for conversion to diesel for the majority of the fleet.

A napkin calculation shows that for a Cessna 172, a diesel conversion would break even around the 3,000 hour point, which is a lot of hours for your privately-owned 172. Not so much for one used at a flying school.

Points? Comments?

[NEOWatcher]

Points? Comments?

All these decades of unleaded, you would think the aircraft manufacturers would have been phasing out these engines.
Or even, the FAA telling them they should be phasing them out.

I didn't even know that this leaded exhaust is being sprayed around in the air. Not that I worry about it, it's miniscule compared than all the lead I inhaled before the cars switched.

[swampyankee]

All these decades of unleaded, you would think the aircraft manufacturers would have been phasing out these engines.
Or even, the FAA telling them they should be phasing them out.

I didn't even know that this leaded exhaust is being sprayed around in the air. Not that I worry about it, it's miniscule compared than all the lead I inhaled before the cars switched.

The aircraft engine manufacturers have been phasing out gasoline engines, which is why turbines are used on just about every aircraft requiring more than about 400hp/engine. The big radials -- which were rated up to about 3500hp -- and V-12's are relics; the few being used are on museum aircraft, like this one. About the only spark-ignition aircraft engines remaining in production are the various air-cooled, opposed engines produced by Lycoming and Continental. Some aircraft are being converted, via an STC, to use one of the certificated aircraft diesels, which run on Jet-A, but it's not currently cost effective for the majority of operators.

There used to be several grades of avgas: 80/87 (no longer produced), 100/130 (aka 100 octane, and no longer produced), 100LL, 115/145 (which hasn't been produced for at least 30 years).

[NEOWatcher]

The aircraft engine manufacturers have been phasing out gasoline engines, which is why turbines are used on just about every aircraft requiring more than about 400hp/engine. The big radials -- which were rated up to about 3500hp -- and V-12's are relics; the few being used are on museum aircraft, like this one. About the only spark-ignition aircraft engines remaining in production are the various air-cooled, opposed engines produced by Lycoming and Continental.

This talk of 172's made me think it was more common.
So, in the article they mention 200,000 piston aircraft. Are they inflating the number because many pistons don't require it?

[Larry Jacks]

A napkin calculation shows that for a Cessna 172, a diesel conversion would break even around the 3,000 hour point, which is a lot of hours for your privately-owned 172. Not so much for one used at a flying school.

There are only a few aviation certified diesel engines available. There are a few R&D projects that I know of but some of them (like DeltaHawk) have been R&D projects for over 15 years. Continental won a NASA contract back in the 1990s to develop a diesel engine but never did anything with it after the prototype work. The currently available engines that I know of are from Thiebert (sp), SMA, and Astra. Thiebert burned a lot of customers when they went bankrupt, charging outrageous prices for parts with a 300 hour lifetime. SMA is more tailored to planes like the Cessna 182 (>220 HP) and hasn't had a lot of sales success. The Astra engines are now certified in Europe and soon in the US for planes like the beautiful Diamond DA-42.

The last time I checked, the cost of putting a diesel engine in a plane like a Cessna 172 or Piper Cherokee was about $70,000. That's more than the value of most of the planes out there. That's more than twice what I paid for my Cherokee. As much as I'd love to have one of those engines in my plane, I just can't afford or justify it.

The issue of 100LL is a serious one in the general aviation community. Just about all piston-engined planes built since the late 1970s require 100LL and many of the earlier ones do, too. This is reportedly the only leaded gasoline still sold in America so it can't be transported by pipeline. It's such a small niche market that there is no economy of scale. The last avgas I bought (3 weeks ago) was $4.15 a gallon self-serve. Sooner or later, it's going to be very hard to find avgas if things continue the way they are. There are proposed alternatives like 92 octane unleaded but no one is making that right now and it remains to be seen if it will work in engines that require 100 octane. It might require a modification such as reducing the compression ratio but that also means lower horsepower.

Alternatives like the one you linked to are very interesting but it remains to be seen if they can produce and distribute the quantities required at a competitive price.

[swampyankee]

This talk of 172's made me think it was more common.
So, in the article they mention 200,000 piston aircraft. Are they inflating the number because many pistons don't require it?

The numbers may not be exaggerated; the 172 is the most-produced aircraft in history, and general aviation aircraft have remarkably long lives.

Just about all current piston aircraft engines require 100LL. There are some non-certified engines which can use automotive gasoline, some experimental conversions to use ethanol, and the few diesel aircraft engines, which use Jet-A. Only the last category has any with certification, so only those can be used on aircraft with full certification. Larry Jacks mentioned that there are only a few current manufacturers of aircraft diesels; they probably don't have the combined production capacity to fill the engine mounts of the piston-engined aircraft in current production.

[NEOWatcher]

The numbers may not be exaggerated; the 172 is the most-produced aircraft in history, and general aviation aircraft have remarkably long lives.

I know the 172 has been around for quite some time (I even had a chance to fly one in 1980*), so are you including it in the comment you made above about museum pieces and relics?

* no license or anything, just a crazy teacher in an aviation class in High school who said "come down any saturday with 10 bucks for gas, and I'll let you fly my plane".

[swampyankee]

I know the 172 has been around for quite some time (I even had a chance to fly one in 1980*), so are you including it in the comment you made above about museum pieces and relics?

* no license or anything, just a crazy teacher in an aviation class in High school who said "come down any saturday with 10 bucks for gas, and I'll let you fly my plane".

No; I was saying that the aircraft that used the big radials or V-12's were.

[Glom]

I know the 172 has been around for quite some time (I even had a chance to fly one in 1980*), so are you including it in the comment you made above about museum pieces and relics?

* no license or anything, just a crazy teacher in an aviation class in High school who said "come down any saturday with 10 bucks for gas, and I'll let you fly my plane".

The 172 family has been around for quite some time, but it keeps up with the times. The latest model, the S, comes with G-1000 as standard to highlight are more superficial thing.

It is surprising that aero piston engines have kept leaded for so long. For the record let me point out that the LL in 100LL stands for low lead, so it's not like your old four star. I love the smell of 100LL more than Jet A-1. I like the blue colour to it too. Still, it would be nice if we could get away from that just to keep everyone happy. If this new stuff can really be casually phased in to our existing fuel supplies, then that is really great.

Of course, you know me. Where's my fission engine?

[Glom]

Cessna's next model will be diesel. It is delayed because to stupid engine manufacturer went belly up, but Cessna are committed to the project because they say the market is strong with this one.

It will have FADEC and automatic VPP. That's just like the PA-28D I've flown. What is it about Jet A-1 that means you need to automate the mixture and the prop?

[swampyankee]

Cessna's next model will be diesel. It is delayed because to stupid engine manufacturer went belly up, but Cessna are committed to the project because they say the market is strong with this one.

It will have FADEC and automatic VPP. That's just like the PA-28D I've flown. What is it about Jet A-1 that means you need to automate the mixture and the prop?

Nothing about Jet A itself. The primary reason is that the single-lever control reduces pilot workload. I suspect that the other, unstated, reason is that FADECs can control the engine more reliably than a human.

[captain swoop]

Diesel Engines inject fuel into the cylinder where the heat of the compressed air ignites the fuel, they don't use a spark plug. I would say that a modern engine will use sensors and an engine management system to control the mixture and keep it at optimum.

[hhEb09'1]

I know the 172 has been around for quite some time (I even had a chance to fly one in 1980*), so are you including it in the comment you made above about museum pieces and relics?

My first airplane flight was in one of those, before that time even.

I jumped out with a parachute.

[hhEb09'1]

I know the 172 has been around for quite some time (I even had a chance to fly one in 1980*), so are you including it in the comment you made above about museum pieces and relics?

My first airplane flight was in one of those, before that time even, 1973.

I jumped out with a parachute.

[swampyankee]

My first airplane flight was in one of those, before that time even.

I jumped out with a parachute.

Why would anybody jump out of a perfectly good airplane?

[hhEb09'1]

Well, it was almost twenty years old at that time. It was one of those things like NEOWatcher had--if I showed up on a Saturday morning with ten bucks, three of us could jump out, one for free and he provided the chutes.

Come to think of it, my second flight (jump) was from a 172, the first was from a 180--which has been around longer than the 172, right?

[NEOWatcher]

My first airplane flight was in one of those, before that time even, 1973.

I'm not suprised. They started in '55.
My dad got his license in a paper cup...er piper cub.

I jumped out with a parachute.

I'm glad you mentioned the parachute, I was a bit worried until I finished reading the sentence.

[Larry Jacks]

Why would anybody jump out of a perfectly good airplane?

I was a paratrooper from 1975-77, just after the end of the Vietnam War. Some of the planes I jumped from were so worn out, I figured having two parachutes gave me better odds than staying with the plane. I love airplanes more than most people (read that as you wish) but I was happen to take my chances with the chutes.

The Cessna 172 design dates back to 1956. Really, it was little more than a tricycle landing gear version of the Cessna 170 which dates back to the late 1940s. Properly maintained, those early Cessnas are very good planes. I recently saw an immaculate 1956 Cessna 182 at my local airport. It was beautiful and probably performs better than most newer ones because it was significantly lighter and even the fuselage was 4 inches narrower.

The new models have glass cockpits (Garmin G-1000) with capabilities that make some military and airliner cockpits look bad. One of my neighbors is currently in Iraq. His unit is flying the T-6A trainer, the Cessna Caravan (basically a flying pickup truck with a turboprop engine and Hellfire missiles!), the Cessna Mustang light jet and the Cessna Citation X. He says the cockpits in the Cessnas are far more sophisticated than the glass cockpit in the T-6. They have synthetic vision and a host of other capabilities that the T-6 lacks.

[swampyankee]

When my brother was in the service (he was a USAF combat controller), one of his tasks involved jumping out of airplanes. I still don't understand why people would do that for fun.

I remember reading a piece by a homebuilder a few years ago. He had just landed his Vari-viggen in Cat 2 conditions, and had a DC-9 pilot come over and take a look at the cockpit. The DC-9 pilot's comment was (reportedly) "Wow! Your cockpit is better equipped than the airliner's I fly."

[Glom]

Nothing about Jet A itself. The primary reason is that the single-lever control reduces pilot workload. I suspect that the other, unstated, reason is that FADECs can control the engine more reliably than a human.

I'm sure. But why wait until the plane was given a diesel engine to do it? Why are the avgas engines equipped with FADEC and such?

[swampyankee]

I'm sure. But why wait until the plane was given a diesel engine to do it? Why are the avgas engines equipped with FADEC and such?

I can't give a definitive answer, but a lot of 172's are used for flight instruction, and most aircraft would still have the throttle-mixture-prop triad. A pilot trained with a single-lever control could have difficulty transitioning to the traditional set up.

As for the spark-ignition FADEC question? Probably the size of the likely market and the cost of getting the certification work done.

[Glom]

I can't give a definitive answer, but a lot of 172's are used for flight instruction, and most aircraft would still have the throttle-mixture-prop triad. A pilot trained with a single-lever control could have difficulty transitioning to the traditional set up.

As for the spark-ignition FADEC question? Probably the size of the likely market and the cost of getting the certification work done.

I don't think that holds up. It was flying schools that wanted the diesels most of all. Their airframes naturally do a lot of hours and so the fuel cost savings can be significant for them. My old flying school now operates PA-28D's. The Cessna 172TD reportedly had strong demand from flying schools.

Unless you envision that the future will become mostly diesel very quickly, I can't see why the market for FADEC on avgas engines would be smaller than for diesel engines.

It is true that too much FADEC means we could get a generation of pilots who can't operate a mixture knob if they found one (then again, I never fly high enough to need to operate it other than as part of the startup). That's why it is a bit of a shame. The quadrant on a Piper Arrow with black throttle level, red mixture control and blue prop control looks cool.

[Larry Jacks]

Aircraft engine manufacturers are extrement conservative. That's why they still use magnetos that belong on a 1930 tractor instead of electronic ignition. I've read that part of this is due to legal liability. If they upgrade the engines with newer technology, that's admitting that the old technology was inferior and would open them up to lawsuits.

TCM did certify a FADEC system but didn't sell very many of them. Lycoming is working on one now but only for large engines.

[hhEb09'1]

Aircraft engine manufacturers are extrement conservative. That's why they still use magnetos that belong on a 1930 tractor instead of electronic ignition. I've read that part of this is due to legal liability. If they upgrade the engines with newer technology, that's admitting that the old technology was inferior and would open them up to lawsuits.

Why wouldn't they be afraid of what is now known as the Toyota Syndrome: push technology to the edge and it will develop new and interesting ways to fail.

[swampyankee]

Why wouldn't they be afraid of what is now known as the Toyota Syndrome: push technology to the edge and it will develop new and interesting ways to fail.

Because they were afraid of it when Toyota was still trying to figure out drum brakes

Neither Lycoming nor TCM have had much reason to push the technology: their engines were completely adequate to satisfy the market. It's also possible that they did not have the capability (financially or technically) to bring replacements to market.

[mugaliens]

I don't think that holds up. It was flying schools that wanted the diesels most of all. Their airframes naturally do a lot of hours and so the fuel cost savings can be significant for them. My old flying school now operates PA-28D's. The Cessna 172TD reportedly had strong demand from flying schools.

That checks - the Academy's using them for the cadets.

Unless you envision that the future will become mostly diesel very quickly, I can't see why the market for FADEC on avgas engines would be smaller than for diesel engines.

Retrofitting an avgas for FADEC definately improves efficiency. Not enough to justify the cost, though, unless one flies an awful lot.

It is true that too much FADEC means we could get a generation of pilots who can't operate a mixture knob if they found one (then again, I never fly high enough to need to operate it other than as part of the startup). That's why it is a bit of a shame. The quadrant on a Piper Arrow with black throttle level, red mixture control and blue prop control looks cool.

That scares the heck out of me - if they can't operate a simple mixture control knob, they've no business operating an vehicle in more than two dimensions! Not to mention weather, communications, and the fact that the air doesn't hold still like the road does!

In the states, most general aviation aircraft are fixed pitch. The few that aren't require an additional rating (complex), which covers both VP and retracts.

[mugaliens]

Aircraft engine manufacturers are extrement conservative. That's why they still use magnetos that belong on a 1930 tractor instead of electronic ignition. I've read that part of this is due to legal liability. If they upgrade the engines with newer technology, that's admitting that the old technology was inferior and would open them up to lawsuits.

TCM did certify a FADEC system but didn't sell very many of them. Lycoming is working on one now but only for large engines.

That's a shame, really, considering I have one on my 210 HP 4.0 L V-6 that runs like a champ from sea-level all the way to the top of Pikes Peak, 14,110 ft! Not only that, but a replacement engine and all electronic engine controls cost less than $2,000.

For a while there back in the 1990s, a lot of 150 owners were switching to Honda engines with gear reduction systems. I flew one owned by my former IP. Very smooth.

[captain swoop]

Did the gear reduction make it quieter?

[Larry Jacks]

That checks - the Academy's using them for the cadets.

The AFA isn't using diesel powered Cessnas, just ones with bigger engines to make up for the high density altitude.

Cessna was testing a diesel powered 172 using the Thiebert engine. That project died when Thiebert went bankrupt. It might be revived if they can get their hands on the new Austro diesels Diamond is putting into their DA-42 Twinstar NG. Diamond was probably the company worst burnt by the Thiebert bankrupsy (they sold versions of the DA-40 and DA-42 with the engines) so they worked hard to get the Austro engines certified and operational. They're charging over $140,000 to convert a Thiebert DA-42 to the new engines. It's an expensive modification.

Did the gear reduction make it quieter?

Some auto engine conversions for homebuilt aircraft require a gear reduction drive because car engines produce their power at RPMs too high to directly drive a propellor. The faster the RPM, the smaller the prop has to be in order to keep the tip speeds from getting too close to Mach 1.0. Most props are designed for a maximum tip speed of approximately Mach 0.8. Spin it much faster and the noise goes up while the efficiency goes down.

[captain swoop]

I thought a slower prop might be quieter although I know tat wouldn't be the main reason for gearing.