Counter Rotating Props ?

[N801BH]

Right, but the Jet-A producer has already done his thing before the Prist gets added. Prist isn't needed for the Jet-A to meet Jet-A specs.

Yeah... But Prist needs to be added to Jet A in a predictable amount or it is ineffective.

 

[Trapper John]

But some airplanes require Prist or some other anti-icing additive because they don't have fuel heaters. In the same manner, if a lower octane fuel were manufactured for a bulk of the GA fleet couldn't an additive be used for the airplanes which need it?

Without knowing the chemistry, I couldn't tell you if it's possible to take something like 91 UL and dose it with something to make it act like whatever the 100 LL substitute fuel is supposed to act.

But I do remember way back when 80/87 got killed off it was because the oil companies didn't want to bother with it any more. I have a hard time seeing the oil companies now wanting to take on producing two different avgas products unless there was enough money to be made to make it worth their while. If anything, I think the solution will be one fuel, a 100 LL replacement of some kind, and everyone that doesn't need that will be paying for something they don't need, just like they have been for the last 35 years since 80/87 was eliminated.

 

[kyleb]

Because one of the main complaints from the industry was any new fuel would attack fuel bladders that are in certain aircraft...

I understand that, but question the apparent premise that because it doesn't attack bladders, it'll be OK for wet wing (i.e. prosealed) fuel tanks as well.

 

[N801BH]

I understand that, but question the apparent premise that because it doesn't attack bladders, it'll be OK for wet wing (i.e. prosealed) fuel tanks as well.

I agree 100%.. All it takes is some testing..... Seems alot easier then formulating a whole new brew....

 

[Capt. Geoffrey Thorpe]

With the advances in automotive technology that we see today, I would be surprised if very little came out of aviation science. Even if that is the case, with the kind of fuel efficiency advancements that have been made such as those in diesels and more efficient ignition systems in gas there has to be something better that can be applied to aviation. Am I just being ambitious?

One of the Taylors of "Taylor and Taylor" (They wrote the book) designed aircraft engines before he went to MIT.

Maybe. Aviation engines are much more "on the edge" than automotive engines are. I'm not sure what the car guys are doing for increased efficiency, but at the end of the day, like Ted says, the physics of combustion are the limiting factor, and aviation engines operate much closer to the limits than auto engines do.

The big, big, big, thing that aircraft engines don't do is change the spark timing with speed / load / mixture.

What automobile engines don't do is run lean (aftertreatment doesn't work to reduce NOx when lean unless you spend bucks on something like SCR catalysts and urea tanks)

Some things that automobile engines do are real good at improving efficiency at low loads (like cam timing games) - where aircraft engines hardly run.

Heard about the AF blend...seems promising.
What I meant about the automotive stuff (should have ellaborated a bit more) was the computerized control of valve/ignition timing and air/fuel ratios for different performance. Obviously, aircraft have a much broader environment to contend with than the average auto, it just doesn't seem far fetched that its POSSIBLE...whether I personally would trust a computer is potentially another story:wink2:. Im somewhat out of the loop here, just wondering how far piston engines have really advanced.

I would argue that aircraft engines run under a much less broad range of conditions - purd near constant speed / load except for idle. You can't really "lug" an aircraft engine... That's why they get away with a fixed spark timing. Altitude is no big deal with current auto technology - FWIW the road up Mt. Evens gets up to 14,240 feet MSL. That's higher than I've ever PICd an airplane...

The issue with aircraft engines is that they turn at low RPM and have large cylinder volumes. That creates perfect conditions for detonation. The flame front doesn't move quickly enough through the large cylinder volume to burn all of the fuel before the unburnt fuel gets hot enough and compressed enough to detonate.

Auto technology (other than the smaller cylinder volume/higher RPM Rotax approach) won't fix that problem.

Big cylinders are good for fuel consumption - lower surface to volume ratio = lower heat loss. Not so good for knock (as you point out) but they do have dual plugs which reduces the total burn time quite a bit (and is good for knock). They could be made much more lean tolerant by changing the intake port configuration to generate swirl (air motion around the circumference of the cylinder) or go to two intake valves and generate tumble (air motion down the cylinder wall, across the piston, up the other side and across the heads). But until you start changing the spark timing to take advantage of the lean capability, the value would be limited.

Lots of auto technology is devoted to reducing emissions. I've probably spent nearly half of my 35 years in powertrain controls on improvements to mixture control - keeping the average value very close to the chemically correct ratio while performing some controlled modulation - in order to maximize the efficiency of three way catalysts.

 

[airbornejohnny]

I don't mean to get away from one fuel for all, but it seems JET-A is very similar to JP-8, which does not gel up like diesel does. JP-8 is used by the military in everything from Humvees to Blackhawks (and burning human waste).
There are inherent lubricity issues when using it as a direct replacement to diesel, but I'd wage to guess it is a step in the right direction except that gas is a much more common need...

 

[Henning]

Are there any aviation diesels that have the same power output at the same weight as an air-cooled gasoline aviation engine?

There is the 230hp SMA diesel that is certified and operating on the 182. This is a 4 cylinder that Continental bought and said they were also going to develop a 350hp 6 cylinder from. This was a couple of months before the Chinese bought them stating this was the reason and everyone was happy because the Chinese were supposed to throw a boatload of money at the project. I'm not quite sure where the project is at these days.

Not sure on exact weight either, but it shouldn't be too far off, the 182 I have seen reports on still had >1000lbs useful load IIRC. I think any improvement on gasoline engines is a waste of time and marketing strength as well as compromising economies of scale for us. China and Russia are about to open up GA, and they need these engines in quantities large enough that we can benefit by going there. Diesel stroke engines are much more fuel tolerant. Most of the world where these planes have a major market, the ability to use a variety of oilstocks is a huge benefit, and in the developed world where fuel prices are rising, the fuel savings make it the obvious choice.

I'd bet that Lycoming also has a toe in this that they aren't tipping hand on.

 

[Henning]

I don't mean to get away from one fuel for all, but it seems JET-A is very similar to JP-8, which does not gel up like diesel does. JP-8 is used by the military in everything from Humvees to Blackhawks (and burning human waste).
There are inherent lubricity issues when using it as a direct replacement to diesel, but I'd wage to guess it is a step in the right direction except that gas is a much more common need...

There are additives to use to easily overcome which fuel you are running. Gelling is overcome in diesel with the same substances that Jet A uses.
Lack of lubricity of Jet A can be modified if needed as well, but with modern electronic common rail systems, it's not really as much of an issue as it was with rotary and piston pumps, still easily compensated for.

 

[Henning]

Or simply be grounded. Again - Think warbirds here. And, frankly, a whole lot of other airplanes that might not be "worth" spending the $$$ to adapt to a 91UL solution, but that you don't want to see grounded.

We need the 100% solution because we can't afford to alienate the 20%. Aviation is too small as it is.

91UL isn't a "solution" at all. I'd be reluctant to even call it a "kludge." It's a cop-out, nothing more.

Warbirds can run on 91UL for the most part. You need to "detune" them some, but that's ok. They already do run detuned from their wartime fuel if they needed higher octane. It's not really going to be a huge hit for the warbird community because most of those guys aren't even using all the power they can if they don't have to. Very few of them need even a fraction of what they needed to carry a wartime load on a wartime mission.

The guys racing these mills are already buying racing fuel for high power ops so no big difference there.

 

[Ted]

Or simply be grounded. Again - Think warbirds here. And, frankly, a whole lot of other airplanes that might not be "worth" spending the $$$ to adapt to a 91UL solution, but that you don't want to see grounded.

We need the 100% solution because we can't afford to alienate the 20%. Aviation is too small as it is.

91UL isn't a "solution" at all. I'd be reluctant to even call it a "kludge." It's a cop-out, nothing more.

This, by comparison, is both accurate and well thought-out.

 

[Henning]

This, by comparison, is both accurate and well thought-out.

But provides no solution.... Saying "There is no solution" over and over is not going to change the situation that we will lose our current leaded fuel.

I'm wondering if many larger aviation engines couldn't be converted to use diesel fuel. There's really been a quantum leap in diesel technology over the last decade. With the way that the high pressure common rail EFI injectors work, the fuel can be delivered in such a way as to minimize the pulse and rattle and really smooth them out reducing smoke and fuel consumption at the same time. CNC billet machining has produced the other side of the equation of being able to build lightweight diesels.

I'd like to retrofit an R-2800 or 985 with a HP Common Rail EFI system similar to the way GM put a mechanical injection system in the Olds 350. I think those 2 engines have a reasonable chance with modest mods.

 

[Ted]

But provides no solution.... Saying "There is no solution" over and over is not going to change the situation that we will lose our current leaded fuel.

I didn't say there wasn't no solution. I believe quite to the contrary.

 

[Henning]

I didn't say there wasn't no solution. I believe quite to the contrary.

What do you see as the solution?

 

[Rob Schaffer]

wow,.. going on page 4 here,...