Most fuel efficient twin?

[Hodja]

Not to mention, that jerrycan refilling is a bit of a mess, and potential safety hazard. A lot of airfields even prohibit jerrycan refuelling on the ramp.

I agree. Unless mogas becomes directly available on the airfields, mogas isn't really a viable option. I see mogas as a great "fallback option", ie. if you're stuck somewhere w/no avgas options for hundreds of miles.

Mogas is available everywhere.

So is diesel btw. (good for the SMA's/Thielert-Centurion and probably the Austro as well)

[peterh337]

I see mogas as a great "fallback option"

What would actually happen if you put normal car petrol into the tank, for an IO-540-C4 for example?

Presumably, detonation would not occur at the low CHTs present during takeoff, IF you transitioned to a cruise climb ASAP.

[AdamFrisch]

Any old twin worth it's salt is going to guzzle 25-30gph Avgas. Add to that a minimum cost of $25-30k per engine on overhaul, plus all the rest of the stuff you get stung with on old twins. I've shelled out $35K this year alone in maintenance (bless her heart). Even a financed Tecnam at 5% interest is going to be more cost effective at just 100-150hrs. Everything above that is gravy.

On a LA to NY trip of 2100nm, the Tecnam will burn $825 in Avgas, or $525 (this is airline competitive prices) in Mogas. Compared to my Commander at $2062 in Avgas. Same speed, same power setting. It doesn't take many hours before you've saved enough to pay for that monthly payment...

And come overhaul, you're looking at half the price or less compared to any Lycosaurus

[peterh337]

Any old twin worth it's salt is going to guzzle 25-30gph Avgas

Should not be as much. I am below 10GPH on high altitude flights, so 2x that. 30GPH is just being ignorant of engine management, or flying a turbo installation at 75% to 85% of max power.

But cost savings are not much good if you are stuck in icing conditions.

[Hodja]

What would actually happen if you put normal car petrol into the tank, for an IO-540-C4 for example?

That's a good question. An acquaintance of mine flies mogas in his IO360 DA40F. (covered by a mogas STC) But I'd personally be wary of doing this on a IO540.

Any old twin worth it's salt is going to guzzle 25-30gph Avgas

Should not be as much.

I'm not sure why, but I generally hear even higher consumption figures quoted for these old twin guzzlers. A friend of mine flies a C340, and it's running ~35gph at 75%. Try that with non-US avgas prices, and you're talking serious cash for even trivial trips. Although as people have mentioned in this thread, what's really killing the old twins are the damn maintenance bills.

I've shelled out $35K this year alone in maintenance (bless her heart).

Adam, please tell us it's been worth it after all!

[peterh337]

I'm not sure why, but I generally hear even higher consumption figures quoted for these old twin guzzlers

I suspect it is because the ones you heard about are flown by pilots who are ignorant of modern operating procedures.

The engine doesn't care if it is in a single or a twin.

But yes an old twin will be relatively expensive to run because

- you have 2 engines and some ~80% of the 2nd engine is used to pull along that engine, plus the now substantially larger aircraft (longer wings are needed because the engines take up a fair bit of them, for example)

- most twins are very old and an old plane will tend to have a significant appetite for airframe parts (true for old singles too of course but a twin has more bits on it)

[Big Pistons Forever]

Originally Posted by peterh337

I suspect it is because the ones you heard about are flown by pilots who are ignorant of modern operating procedures.

Yup everybody is ignorant about the operation of engines except you

Adam flies an Aero Commander 520. It has GSO 435 Lycoming engines fitted with pressure carburators. His reported fuel flows are the best you are going to get from this engine. All the modern engine analysers in the world are not going to make any difference as this engine won't run smoothly at LOP.

In any case all the private pilots I know who operate twins are quite aware of how to run the engines economically because they are the ones who have to pay the big bucks when the fuel truck pulls up! They all have and use engine analyzers.

[peterh337]

I don't think you got what I was getting at, BPF

[AdamFrisch]

Adam, please tell us it's been worth it after all!

Yes it has for sure for me personally, but it's like people say: if you buy an aircraft cheaper, be prepared to spend as much again the first year to bring them "back". This has proven to be the case. Even though I knew that, it's only when you're actually faced with the bill that it hits home. But no regrets at all, even though this is money you can't get back if you sell it.

My squawks are pretty much all eliminated and ironed out now, so this year the costs will only be cosmetic, hopefully. But just to give an idea: a new paint job done right is $18K, an interior is $5-10K. Any new avionics installation is in the thousands etc. So it's not for the faint of heart.

[silverknapper]

On a LA to NY trip of 2100nm, the Tecnam will burn $825 in Avgas, or $525 (this is airline competitive prices) in Mogas

With how many stops? 4 minimum, with all seats full 7? Obviously flying in the US is more reasonable but 7 stops in Europe starts to stack up. Especially if one has to utilise proper airports, which on a long international flight one would have to to be assured of completing the mission. Providing icing isn't an issue. Also the 2100 nm will take a looooong time.
The right avgas burner should be around 20-24 gph. Anymore than that would be discounted in my search for cost reasons.

[englishal]

If I wanted a twin (well I do...but...), I'd buy something like an old Seneca II (as it has turbos on and is pretty capable if you get de-ice boots etc...) relatively cheaply. I'd then overhaul the motors, put 3 blade props on, re-upholster and paint. Then depending on how flush I felt, I'd fit a new avionics suite.

So for £150,000 you could end up with a sweet "as new" aeroplane with modern avionics in great known condition.

Yep it will burn significantly more than a DA42 but at the end of the day if one buys a new aeroplane, you're going to lose a shed load of money in the first few years anyway, and that is more then equivalent to the fuel saving.

[peterh337]

I believe both have the same 8.5:1 cylinders

That is what I was getting at. I cannot see a problem (apart from it being illegal).

Don't forget the 1999kg STC, Englishal

[Jan Olieslagers]

if you fly to a real airport, I don't know of any airport that offers Mogas

I don't know your definition of a REAL airport, nor why anyone should want one. But there's plenty of aerodromes with mogas available, especially round yours. Check it out at http://www.dulv.de/app/so.asp?o=/_ob...gas_170111.pdf for just one source. Have to admit I know of no airfield with a Mogas pump in my own country.

[Pilot DAR]

I'd buy something like an old Seneca II

Oooo, though I'm generally a fan of some "legacy" types, NOT a Seneca II, or a number of other Pipers of that era. I have had first hand experience with very expensive repairs required for corrosion damage, because Piper would not support that type, with the required replacement parts. I quote the Piper Tech Rep: "Sir, that's a 40 year old airplane, we have not seen it in 40 years, and we don't want it in the air."

With that policy toward product support, I'm really happy I own the second most common Cessna ever!

[421C]

an old twin will be relatively expensive to run because

- you
have 2 engines and some ~80% of the 2nd engine is used to pull along that
engine, plus the now substantially larger aircraft (longer wings are needed
because the engines take up a fair bit of them, for example)

- most twins
are very old and an old plane will tend to have a significant appetite for
airframe parts (true for old singles too of course but a twin has more bits on
it)

Neither of those reasons are true.
Two smaller engines mounted on the wings are less efficient in weight, drag and specific fuel consumption than one larger one, no doubt. But it's nothing like 80% of the 2nd engine. That's ridiculous. Take a basic airframe available in twin and single versions. A 2x200hp Seneca vs 300hp Saratoga. The Seneca is faster. It is not substantially larger, it is about the same size. For that matter look at the Tecnam 2x100hp vs. 160-200hp singles.

I have never understood your theory that an old plane is expensive to maintain because of airframe parts. I have owned 2 old twins and the airframe parts cost has been negligible. I don't believe a properly maintained old twin cost more to maintain today than it did 20 years ago. However, they do cost a lot to maintain because they are complex and labour-intensive. There's more to go wrong and even trivial things can take a few hours labour before anything has happened. What is hugely expensive is taking a badly maintained old twin and fixing it. The other mistake is to base maintenance cost expectations on what the purchase price of the airplane is. The old twins have depreciated a lot in real terms but that hasn't changed the maintenance cost from the time in the 70s when they were the equivalent of $1-2m corporate airplanes.

Oooo, though I'm generally a fan of some "legacy" types, NOT a Seneca II, or
a number of other Pipers of that era. I have had first hand experience with very
expensive repairs required for corrosion damage, because Piper would not support
that type, with the required replacement parts. I quote the Piper Tech Rep:
"Sir, that's a 40 year old airplane, we have not seen it in 40 years, and we
don't want it in the air

There are thousands of Senecas flying about giving dependable service. In my 10 years of ownership I never had a part problem. And at least Piper didn't succumb to an equivalent of the SID debacle which has cost twin Cessna owners $100k each in some cases - ask any Australian C310 owner...

I have yet to hear of any consistent set of anecodotes about parts cost and availability for any old aircraft. They always contradict themselves. One person says
"the factory was struck by a giant meteorite in 1971 and vaporised. The company then went bust and all the drawings were burned. Parts sourcing is thus a nightmare for this Type"
Then someone replies
"Nonsense. The owners' association has a list of PMA suppliers and every single part can be sourced just as quickly and cost-effectively as for a type still in production"

[Pilot DAR]

I agree that different owner's experiences with airframe parts availability can vary greatly.

I was not involved in either of the two mentioned parts availability problems as the owner, but as the DAR (like FAA DER) asked to provide approval for a "made part", when Piper would not support the aircraft with the required parts. The quote I reference was spoken by Piper to me.

The Seneca II I was involved with was unairworthy as a result of corrosion - just certain parts, but critical ones! If there were any alternative sources for the required parts, a great effort expended, before I got the call, would probably have revealed it/them.

Similar challenges with Cherokees, and in particular an Arrow I was asked to inspect, have resulted in a similar response from Piper.

Yes, Cessna has mandated comprehensive inspections, which, in the era of "aging aircraft" for larger types, does have some merit. I believe that Cessna will still provide the required parts. (though I have not personally checked this). I attended a Cessna presentation on this subject, and nothing in that presentation lead me to think that Cessna did not want it's legacy twins flying, they were just intent on assuring their airworthiness. I understand it's beginning to filter down to the singles soon too.

I did check with Piper myself, and was twice told "No". That makes an impression upon me....

[Contacttower]

My vote goes for the Twin Com; great aircraft.

[peterh337]

I have never understood your theory that an old plane is expensive to maintain because of airframe parts.

Obviously that's not true, so it could not have been a theory of mine.

It is the accumulated cost of poor maintenance (specifically poor lubrication, and corrosion) which makes an old plane potentially much more expensive to bring up to a "perfect" standard after it is bought by the next punter.

There are obviously exceptions, depending on whether the previous owner was diligent or not, but most owners do not maintain on a money no object basis. Most let things wear out and then they flog the plane. Same with cars.

But firstly few people are going to "totally fix" a 30 year old plane they have just bought, so they will be running along with a part of the legacy they bought, and secondly corrosion is something that does get increasingly expensive with airframe age (relative to hangarage history obviously, etc). That is just actual practice out there.

I have owned 2 old twins and the airframe parts cost has been negligible

After the total-stripdown rebuild you had done on your 421C (ballpark cost £100k plus avionics?) I would have expected it to be close to zero for the rest of your flying life

Re the 80% fuel burn overhead, what figure would you offer?

[AC-DC]

The Twin Com is the aircraft that will do the job for you in the most efficient way. Fuel consuption will be 15gl total @ 160 knots (indicated at low level). In Oz there are some very knowledgeable people who will be able to you if you have problems, more over, they even produce their own parts (due to CASA rules). As for parts, some are more difficult to obtain than other but all are available, especially as Piper said that they will start to produce parts as needed, even if they have to reverse engineer them, price unknown.
If you decide to go for the twin Com feel free to contact me (by email) and I will introduce you to some people that will make sure that you won't get burnt, they can find the aircraft for you, will inspect and repair it as needed if you instruct.

Pilot DAR
These 3 bladed props, are they FAA STCed or just during development? How much are they? Some people will give their right arm to have these on their aircarft.

Thanks

[peterh337]

If you are a really good engineer (like you are) and you live in a reasonably dry climate then there is no reason why 50 year old airframes should not be fine.

Being in the USA also helps. One of the things which costs money in Europe is that there is no authorised procedure for replacing bushes which are push-fit inserted into aluminium brackets. You have to either buy the whole bracket with the bush (typ. £1000) or you do a job off the books whereby you either (a) ream out the bush a bit and machine up a new pin or (b) push the bush out and machine up a new one and just buy the usually cheap bolt which goes into the middle of it. Some 99% of airframe parts are trivial to fabricate if you have a lathe and possibly a turret mill, but cost a fortune to replace officially. Under the right regulatory regime you just machine them up and an A&P/IA signs it off.

The other factor is whether there is a CMM (component maintenance manual). If you are totally anal about it, no CMM means the component cannot be worked on at all. I bet the 50 year old planes in question here were flying before anybody could spell "CMM". On things like Spitfires (AIUI) you can fabricate replacements if you have the manufacturing drawings, and for a Spit they do exist.

But then a Spit is not on an ICAO CofA which alone makes a massive difference to what you can do. We need to be comparing like for like.

Here in Europe, EASA-reg, the flexibility is gone unless you do stuff off the books. Put that together with crap lubrication (just squirting an aerosol lube into the bearings/bushes, without dismantling them and cleaning them) and that's why people with 30 year old C152s may be paying £7k to get them through the Annual.