Twin engine or Single engine? (Dumb question)

[N747JB]

There are some discount card programs, like Air Boss, but I don't know of any contracts for 100LL. The big difference is the volume, it costs almost the same to have the fuel truck and the lineman put 12 gallons in a 172 as it does to put 300 gallons in a Citation, or 1000 gallons in a Gulfstream. The only difference is the extra 10 minutes of labor. Let's say it's $10.00 to crank and move the truck, and the lineman makes $15.00 per hour. He pumps 12 gallons with a mark up of $2.00, grossing $24.00 profit in the transaction. Same guy pumps 300 gallons with $.40 mark up and grosses $120.00 Volume makes the difference in fuel costs, with even the thirstiest piston twin holding a maximum of 250 gallons, most piston airplanes will probably take 20-50 gallons at a fuel stop.
When I had my Citation I had a fuel card that worked like contract fuel, for smaller operators. The company went out of business, but it was a great deal on Jet-A, I remember in ADS buying fuel about $2.00 less than the posted rate!

I've heard rumors from some folks that if you have one of those contract fuel cards, you'll be paying around $3.50/gal for Jet A.

Anyone know if that's true? What is required to get into such a program? I assume there are no such programs for 100LL...

 

[Dr. O]

Ahhhh, ya bunch of pansies.
Real men (and women) fly twins. There is nothing like grabbing a fistful of throttles.
Even Dirty Harry would understand.

 

[bluerooster]

deleted.... better replies already made B)

 

[gismo]

The only reason for a diesel engine to flame out is lack of fuel. The reason gas aircraft engines run out if fuel is the medieval fuel system on most aircraft. TBMs for example have an automated system thst balances fuel draw from the wing tanks, a header tank is a different option. Really not an issue.

AFaIK some diesels rely on turbocharger boosted MAP in order to generate enough cylinder pressure and induction air temperature for self ignition. I don't know if any of the aviation diesels are designed this way but if so restarting at altitude could be a problem.

 

[Henning]

You need to get around more. Europe definitely has plenty of diesel rentals.

AFaIK some diesels rely on turbocharger boosted MAP in order to generate enough cylinder pressure and induction air temperature for self ignition. I don't know if any of the aviation diesels are designed this way but if so restarting at altitude could be a problem.

Those are pretty much all two strokes, and large. Fail a turbo and you lose a bunch of power and make huge plumes of black smoke, but the engine will not lose the ability to ignite fuel, at least not any I'm familiar with in the size that would go on a plane.

Modern Diesels though are completely reliant on electronics to function correctly.

 

[weilke]

AFaIK some diesels rely on turbocharger boosted MAP in order to generate enough cylinder pressure and induction air temperature for self ignition. I don't know if any of the aviation diesels are designed this way but if so restarting at altitude could be a problem.

Yes, it would be a problem. But so is re-starting a turbofan engine after it has flamed out. There is a 'restart window' and it requires descent below a certain altitude, usually somewhere in the teens (some light diesels also keep the glow-plugs on maintain ignition while the engine is cold and idling).

Just like a turbofan/turboshaft engine, a diesel has no reason to flame out as long as it receives fuel*. The fuel systems are designed in a way that provides that fuel on a consistent basis. An aero-diesel operated above re-start altitude should have a similar fail-proof fuel system.



* and as long as the power to the fuel valve solenoid hasn't been cut off or the anti-shudder valve hasn't failed in the closed position (says the man who still has soot unter his fingernails from pulling a failed anti-shudder valve friday night )

 

[flyingcheesehead]

Twin-engine aircraft have two engines because they can't fly on one.

Not true. There are very few twins that *can't* fly on one (that old tube-and-fabric fixed gear one with fixed-pitch props that Tony Condon likes comes to mind, but I can't for the life of me remember what it's called).

Now, if you look at the worst of the certified light twin bunch, the Piper Seminole, it has a single-engine service ceiling of 3800 feet. That's the density altitude at which it can climb 50 fpm on one engine at max gross weight. But it can maintain an altitude (i.e., "fly") above that indefinitely.

Sure, if it's hot, high, and heavy it's not going to keep flying - But that doesn't mean it "can't fly on one" in a multitude of other conditions (lower, lighter, or cooler).

You can always provide conditions under which any particular light twin can't fly on one, but the majority of them can fly under the majority of conditions provided the pilot does things right.

 

[weilke]

Not true. There are very few twins that *can't* fly on one (that old tube-and-fabric fixed gear one with fixed-pitch props that Tony Condon likes comes to mind, but I can't for the life of me remember what it's called).

Champion Lancer.

 

[flyingcheesehead]

On typical piston twin you have 12 cylinders. On a typical single you have four cylinders. Assuming a cylinder failure at 2000hrs for a 4 cylinder that will put the twin at a cylinder failure at every 700hrs.

Actually, it's more likely to be eight on the twin vs. six on the single for comparable birds (Bo vs. Travel Air, Twin Comanche vs. Comanche 250/260/400) - Or at least the same number of cylinders per engine (Bo vs. Baron, Twinkie vs. Comanche 180, Seneca vs. Lance, etc). So, the failure rates won't be as far off as you say, and I'd much rather be flying a twin if there's a catastrophic cylinder failure.

 

[flyingcheesehead]

Champion Lancer.

YES! That's the one!

Kind of an ugly duckling, and I'd bet it flies on one only in a very limited set of circumstances if at all. According to Google's find of Some Guy On The Internet, its single-engine service ceiling is -2000 MSL.

 

[flyingcheesehead]

So.... what about the stories I have heard about the tendancy of twins to flip over on take off if you loose an engine? Do we have any concerns about that?

They'll flip over in any phase of flight with one engine if you fly them wrong. So, don't fly them wrong.

 

[flyingcheesehead]

The plain fact is that FEDEX opted for the Caravan. The Caravan is a money maker not a money spender. And when you are in business you are in for profit.

And how many Caravans are operated as charter airplanes compared to King Airs? Very VERY few.

Forget this argument for single vs. twin. Airplanes are generally designed for a mission. There are plenty of twin-engined cargo planes as well. At my old home field, you were more likely to see a Cessna 402 hauling cargo than a Caravan.

 

[weilke]

YES! That's the one!
Kind of an ugly duckling, and I'd bet it flies on one only in a very limited set of circumstances if at all. According to Google's find of Some Guy On The Internet, its single-engine service ceiling is -2000 MSL.

The things the quest for goverment money will create !

I believe the number of flyable Lancers is in the single digits. A curiosity to look at at Oshkosh.

 

[weilke]

And how many Caravans are operated as charter airplanes compared to King Airs? Very VERY few.

There are a fair number, some on part 135 EAS contracts, some on floats, some to shuttle crews to drilling sites etc. I dont think there are many in the 'fly mr big pooba to his important meeting' charter business.

 

[weilke]

Actually, it's more likely to be eight on the twin vs. six on the single for comparable birds (Bo vs. Travel Air, Twin Comanche vs. Comanche 250/260/400) - Or at least the same number of cylinders per engine (Bo vs. Baron, Twinkie vs. Comanche 180, Seneca vs. Lance, etc). So, the failure rates won't be as far off as you say, and I'd much rather be flying a twin if there's a catastrophic cylinder failure.

A cylinder failure will not rip the plane from the sky, neither a single nor a twin. My current Bo was landed by one of my partners after one of the cylinder heads fell off the barrel about 8 years ago.

 

[flyingcheesehead]

There are a fair number, some on part 135 EAS contracts, some on floats, some to shuttle crews to drilling sites etc. I dont think there are many in the 'fly mr big pooba to his important meeting' charter business.

Yes, but those are all "specialty" charters, where the mission is somewhat more defined. Your average charter op at your average local airport that serves anyone who walks through the door probably isn't going to use a Caravan. There may be examples, but I know of precisely zero.

 

[flyingcheesehead]

A cylinder failure will not rip the plane from the sky, neither a single nor a twin. My current Bo was landed by one of my partners after one of the cylinder heads fell off the barrel about 8 years ago.

Yeah, but you've got more options with the twin, provided you keep it flying.

 

[weilke]

Yes, but those are all "specialty" charters, where the mission is somewhat more defined. Your average charter op at your average local airport that serves anyone who walks through the door probably isn't going to use a Caravan. There may be examples, but I know of precisely zero.

Isn't that what I said ?

 

[flyingcheesehead]

Isn't that what I said ?

You were trying to rebut my statement that Caravans are rare in charter ops. I'm reasserting that in a traditional charter op, Caravans are exceedingly rare.

 

[N747JB]

You were trying to rebut my statement that Caravans are rare in charter ops. I'm reasserting that in a traditional charter op, Caravans are exceedingly rare.

Our local FBO had a Grand Caravan on it's 135 certificate for a couple years, they used it for fairly local stuff, 200 miles or so. I'm not sure why, but the owner sold it. It seemed to fly on a fairly regular basis, but I don't know how much one needs to fly to justify keeping it. I don't think the owner replaced it, so he might have learned all he needed to know about buying an airplane and putting it on charter at an FBO.

 

[FloridaPilot]

Ahhhh, ya bunch of pansies.
Real men (and women) fly twins. There is nothing like grabbing a fistful of throttles.
Even Dirty Harry would understand.

I have to go up in a twin one of these days. Never been up in a twin but quite a few singles.

 

[weilke]

You were trying to rebut my statement that Caravans are rare in charter ops. I'm reasserting that in a traditional charter op, Caravans are exceedingly rare.

All part of the 135 world. There are also few TBMs but plenty of PC-12s. Whatever the local market is able to sustain.

 

[FloridaPilot]

Yeah, but you've got more options with the twin, provided you keep it flying.

A Single and a Twin take off from the runway, The engine dies on the Single and one of the engine dies on a twin and you just passed the runway and just reached 300 feet on both airplanes. What advantages does the twin have that the single does not?

 

[Ted]

A Single and a Twin take off from the runway, The engine dies on the Single and one of the engine dies on a twin and you just passed the runway and just reached 300 feet on both airplanes. What advantages does the twin have that the single does not?

The single is going to land straight ahead, regardless of what's there. The twin, if properly loaded, can fly back around and land on the runway.

 

[Ted]

Just like a turbofan/turboshaft engine, a diesel has no reason to flame out as long as it receives fuel*. The fuel systems are designed in a way that provides that fuel on a consistent basis. An aero-diesel operated above re-start altitude should have a similar fail-proof fuel system.

On a Common Rail Direct Injection FADEC diesel, there are plenty of reasons why it could flame out while still receiving fuel.

 

[JHW]

A Single and a Twin take off from the runway, The engine dies on the Single and one of the engine dies on a twin and you just passed the runway and just reached 300 feet on both airplanes. What advantages does the twin have that the single does not?

I've done exactly that. Whereas the single would have landed in the lake off the end of the turnway, I just turned around, landed, moved the boxes from the 310 to the 421 and we were on our way with maybe an hour's delay.

 

[weilke]

On a Common Rail Direct Injection FADEC diesel, there are plenty of reasons why it could flame out while still receiving fuel.

In the absence of emissions control requirements, there is really no reason to put that particular technology on an aircraft diesel.

 

[JHW]

In the absence of emissions control requirements, there is really no reason to put that particular technology on an aircraft diesel.

for the precise thing we are discussing here: easier restarts

most engines fail in flight because they don't well run on air. After switching to a fuel tank with less air in it, the engine needs to be able to start.

 

[mtuomi]

In the absence of emissions control requirements, there is really no reason to put that particular technology on an aircraft diesel.

So far, unfortunately, airplane diesels have been based on common rail with FADEC control, because it has been much much cheaper to develop. They have been based on automotive engines, with rather minor modifications.

If you ask me, the best would be a prechamber engine. 100% bulletproof after it has been started, no power required to keep it running, and so on.

Commo rail has very few plus sides on airplane use.

 

[JHW]

So far, unfortunately, airplane diesels have been based on common rail with FADEC control, because it has been much much cheaper to develop. They have been based on automotive engines, with rather minor modifications.

If you ask me, the best would be a prechamber engine. 100% bulletproof after it has been started, no power required to keep it running, and so on.

Commo rail has very few plus sides on airplane use.

you're missing a key point. Considerable structure (weight) is needed to drive injection pumps for most diesel engines. With common rail the pump to generate the pressure is divorced from pressure waves of individual injections, making the torsional ugliness in the geartrain largely go away. That allows smaller parts to be used. Reduced weight is good for cars. Maybe it's good for airplanes too but you wouldn't guess by the amout of useless crap people lug around in their planes.

 

[mtuomi]

you're missing a key point. Considerable structure (weight) is needed to drive injection pumps for most diesel engines. With common rail the pump to generate the pressure is divorced from pressure waves of individual injections, making the torsional ugliness in the geartrain largely go away. That allows smaller parts to be used. Reduced weight is good for cars. Maybe it's good for airplanes too but you wouldn't guess by the amout of useless crap people lug around in their planes.

Err? Not sure I understand what you mean.

The considerable structure for a Bosch VP37 for example is a belt and pulley, and just a tappet the size of your little finger.
Common rail pumps normally take their "power" from the camshaft.
Bosch CP3 producing 1600bar produces more parasitic losses than a VP37 or VP44.

To compare the mechanics, crankshaft for Volvo D5244T engine weighs more than D5252T(same as VAG AAT engine). Weight difference between the engines comes from the block, not the injection system.

A common rail engine runs slighly smoother but thats only because the combustion process can be controlled more accurately (mainly pre-injection can be shorter so the ignition is smoother), not because the injection system has different mechanical characteristics.

Perhaps I misunderstood what you mean by the structure?

 

[weilke]

So far, unfortunately, airplane diesels have been based on common rail with FADEC control, because it has been much much cheaper to develop. They have been based on automotive engines, with rather minor modifications.

The Thielert and Austro engines are the only ones that description fits for.

The SMA is an aviation design, and as far as I can gather uses a electronically controlled but mechanically operated distributor type injection pump (similar to the Bosch VP units used up the VW ALH engine).

The 4 cylinder Deltahawk is also a mechanical pump.

If you ask me, the best would be a prechamber engine. 100% bulletproof after it has been started, no power required to keep it running, and so on.

Direct injection was available with mechanical pumps a long time before CR came around. They just run at a higher pressure.
I wouldn't want to give up efficiency by going with a prechamber design.

Commo rail has very few plus sides on airplane use.

Agreed.

Cam driven unit injectors or a VP pump seem to make a lot more sense.

 

[mtuomi]

The Thielert and Austro engines are the only ones that description fits for.

The SMA is an aviation design, and as far as I can gather uses a distributor type injection pump (similar to the Bosch units used up the VW ALH engine).

The 4 cylinder Deltahawk is also a mechanical pump.



Direct injection was available with mechanical pumps a long time before CR came around. They just run at a higher pressure.
I wouldn't want to give up efficiency by going with a prechamber design.

I haven't looked into the SMA or Deltahawk constructions. I just know the Thielert and Austro engines and they are pretty sad if you ask me.

Mechanical direct-injection pumps are pretty rare, and they aren't very efficient either. To get the best efficiency out of direct injection technology, it needs very accurate control. Without this, the difference really isn't that massive. I would be happy to fly behind either.

Common rail is of course much more than just a higher pressure. CR technology makes stuff like 7-phase injection etc possible. But this is mainly emissions stuff which really doesn't matter on an airplane use. It does add unnecessary reliability concerns, and that is why currently it is not a very suitable technology for airplane use.

 

[Henning]

A Single and a Twin take off from the runway, The engine dies on the Single and one of the engine dies on a twin and you just passed the runway and just reached 300 feet on both airplanes. What advantages does the twin have that the single does not?

Twin I'm flying it back around and landing on the runway.

 

[Henning]

In the absence of emissions control requirements, there is really no reason to put that particular technology on an aircraft diesel.

Oh yes there is, smooth running light weight engines. The FADEC/digital injection technology smooths out the power pulses to the point where you can build the engine light enough to make practical for small aircraft use.

 

[Fearless Tower]

Twin I'm flying it back around and landing on the runway.

Exactly. In my Baron, I'm well above Blue Line and cleaned up by 300 AGL. With the exception of gross weight at fairly high DAs, I will be able to return to land (provided I don't do something stupid like feather the wrong engine).

 

[weilke]

I just know the Thielert and Austro engines and they are pretty sad if you ask me.

Well, they work great at what they were designed for: Propelling a taxicab around the streets of barcelona at 15-20% of rated power.

Mechanical direct-injection pumps are pretty rare, and they aren't very efficient either. To get the best efficiency out of direct injection technology, it needs very accurate control.

The early VP series pumps are mechanically timed. The electronic control only affects the stroke-volume. They did have a solenoid to retard the injection pulse for startup and a fuel-cutoff solenoid for shutdown (a long time ago in a galaxy far away from here I was one of the people assembling VE and VP series pumps in the Bosch plant)

Without this, the difference really isn't that massive. I would be happy to fly behind either.

About 5% difference in BSFC as I remember it.

 

[weilke]

Oh yes there is, smooth running light weight engines. The FADEC/digital injection technology smooths out the power pulses to the point where you can build the engine light enough to make practical for small aircraft use.

I dont think anyone has put theory into a design at this point. For the most part, the CR technology is used to make the engines run quietly at low power without the usual diesel racket and to fulfill emissions requirements.

 

[Ted]

I dont think anyone has put theory into a design at this point. For the most part, the CR technology is used to make the engines run quietly at low power without the usual diesel racket and to fulfill emissions requirements.

I remember hearing a story some years ago from a reputable fellow who'd been working on an aviation diesel. He basically came to the same conclusion as Henning. The project was scrapped because without CRDI technology the weight penalty was too high due to higher pressure pulses from a mechanical system. It created too small of a box that the engine needed to run in without electronics to keep it there. At the time, he was unwilling or unable to take on the added burden of designing and certifying a FADEC and CRDI.

 

[weilke]

I remember hearing a story some years ago from a reputable fellow who'd been working on an aviation diesel. He basically came to the same conclusion as Henning. The project was scrapped because without CRDI technology the weight penalty was too high due to higher pressure pulses from a mechanical system. It created too small of a box that the engine needed to run in without electronics to keep it there. At the time, he was unwilling or unable to take on the added burden of designing and certifying a FADEC and CRDI.

The limitations of the Thielert and Austro is in the conversion part, not the technology of CRD. You could put two high-pressure pumps and two sets of piezo injectors on there if you want redundancy. I have electronically controlled mechanical unit injectors in my car, not a single breakeown related to that system in 190k miles (tandem pump just got replaced due to a leak).