An affordable twin??? [Archive]

Sciolistes

27th Nov 2008, 12:08

I think there could be a market for this amongst the safety concious who would prefer a twin for regular overwater / montain flying.I have a modest 70hrs on piston twins, I tend to agree with IO540 in supposing that theoretically you have double the chance of engine failure with a twin. If that is the case then a single would probably be preferred as most normally aspirated twins would struggle to hold 4,000' AMSL on one engine, probably more like 3,500; which is less than the MSA over just the hills of the UK. Add turbocharging and you're probably well to the right of relatively 'affordable' compared to a decent high performance single, even then don't expect much above 8,000'.

However, I wonder if you really do have double the chance of failure in a twin. I suspect that a significant number of engine problems/failures are due to maintenance, misuse, mismanagement or missing fuel. Suggesting that if one goes, the other may well follow soon suggesting that to most practical purposes the extra expense of a twin really probably is about peace of mind rather than any significant strides in terms of safety.

Mr Grimsdale

27th Nov 2008, 12:18

An ex-RAF chap at one of the clubs I'm with gave pretty much the same summary of the safety aspects of having a second engine. Apparently some twins cannot climb on a single engine, they can only maintain height. So if one engine fails at a point where you need to climb you are stuffed.

englishal

27th Nov 2008, 12:30

normally aspirated twins would struggle to hold 4,000' AMSL on one engine, probably more like 3,500; which is less than the MSA over just the hills of the UK. Add turbocharging and you're probably well to the right of relatively 'affordable' compared to a decent high performance single, even then don't expect much above 8,000'.
Should read "most knackered old training type twins...";) I agree the BE76 or Seminole have pretty crap SE performance.

I'd rather fly a decent twin any day though. With a SE if the engine fails you have one option, go down. Most light twins I've flown can fly quite happily on one engine, even when moderately loaded. Turbo's make a great difference though and even the likes of a Twin Star with 3 POB and overnight baggage and lots of fuel (probably at Max UUW) will happily climb on one engine to a good altitude.

what next

27th Nov 2008, 12:46

Hello!

Should read "most knackered old training type twins..." I agree the BE76 or Seminole have pretty crap SE performance.

Our flying school Seminole (non-turbo!) easily maintains 6000ft on one engine. With the exception of the Alps, you can fly anywhere in central Europe at that altitude. And other than with some more complex twins like the C340 or C421B, all the fuel on board is available to the remaining engine, so longer overwater flights can safely be completed.

At this time of the year with poor weather and early darkness, I feel much safer in the lightest of light twins than in any piston single.

Greetings, Max

vanHorck

27th Nov 2008, 12:47

Thank you Englishal for fighting against the twin bashing.

The higher up the flying ladder you go, the higher the requirements for currency, eye hand coordination and systematic handling of the craft.

Those who can only fly less than 25 hours per year should not fly twins or even complex singles, even less so if one wants to fly at altitude with oxygen or in marginal weather.

But those that can afford to fly regularly in a modern proven twin and who have the eye hand coordination, the urge to fly accurately and who by their very nature enjoy the renewal stress could do a lot worse than flying something like a good modern Seneca, a Baron or a DA42

Those people can afford to fly high over the Alps, Pyrenees, Carpats etc or at night over the sea with more confidence at speeds close to 200 knots true, often well above the weather and feel not too distant from the professional flyers.

I have found flying my twin mch more usefull than the PA28's i flew before, more enjoyable and indeed more people now fly with me.

B2N2

27th Nov 2008, 13:02

Small "cheap-ish" turbines are available for the home built market..
Innodyn :: Aviation :: The Innodyn Turbines (http://www.innodyn.com/aviation/products.html)
Article on them here:
Aero-News Network: The Aviation and Aerospace World's Daily/Real-Time News and Information Service (http://www.aero-news.net/SpecialContent.cfm?ContentBlockID=6fa04bb0-c0bc-4704-a2e4-29954de7674e&cat=17)

Here is an RV with an Innodyne:

http://www.jeffsrv-7a.com/PLANES/innodynRV6.jpg

IO540

27th Nov 2008, 13:32

The biggest problem with these twin v. single debates is that they usually fail to separate the two very different things

1 - stuff which only a twin gives you

A spare engine
At the top piston end (e.g. a C421) loads of payload and speed

2 - stuff which a single can give you but is more common on twins

Full de-icing
Redundant electrical systems (see Cessna 400 for an example)
Good capability versus weather
Pressurisation

One would be a fool to be flying a twin to get a high operating ceiling for example, when any half decent SE IFR tourer can go to 20k and the turbo ones can do 25k.

If I recall right, the NTSB data shows SE turbines about 5x less likely to go down than piston twins. Now, this could be hiding a lot of factors, for example the population of SE turbines is likely to be younger and better maintained than the population of piston twins (just look around your airfield for ample evidence of this).

The extra cost of a piston twin is high. I reckon the total operating cost of a Meridian and even more so a Jetprop is going to be similar to the OC of a Seneca or something similar. Well, after the capital cost has been set aside :)

LowNSlow

27th Nov 2008, 13:47

Bringing it back to the realms of affordable VFR day-only twins I can see why Chris Heintz isn't putting any effort into developing the Gemini. The extra cost of the 2nd engine isn't offset against the potentially increased risk of an engine failure. The reason I looked at this initially was that then I had the potential to be flying across to Ireland regularly and for that I would like two engines. I know the Rotax 912 or Jabiru engine that the Gemini would potentially use seem as reliable as your average car engine so the actual risk is relatively low, but half way across the cold Irish Sea I would feel greatly reassured looking past my 10-year old daughter at the spare "get out of jail free" card sitting on the wing!

patfitz

27th Nov 2008, 14:07

the future of GA?
On the bottom of the PDF it gives a table comparing the Tecnam with 2 rotax engines to its GA rivals, cessna 172,Cirrus,Piper,Da 40 ect

http://www.tecnam.com/PDF/schede/twin.pdf

Fuji Abound

27th Nov 2008, 23:14

Twins versus singles - now here is an old chestnut.

The first comment people usually make is that twins are less safe. That statement is wholly erroneous without qualification. Twins are, on the whole, used for quite different mission profiles. Far more poor weather sectors are flown in twins - because on the whole they can cope with worse weather.. The general statistics also pay regard to the experience over the last forty years. Particularly in the States it dawned many years ago that twins were susceptible to asymmetric accidents in particular, and accidents in general with pilots flying in conditions for which they had inadequate training. Twin training has improved enormously in that time and even more importantly the insurance companies had made it increasingly difficult for inadequately trained pilots to find cover. There is no evidence in the current environment that twins are less safe, and if you take account of the mission profiles flown they are more safe than singles.

There are many similarities with high performance singles. In the early years the accident rate in the Cirrus was far higher than you would have expected. Pilots with inadequate training were lulled into a false sense of security by the fancy avionics, performance and promise of a state girdling light single. Of course the Cirrus was still a single, and with its added performance less forgiving in poorly trained hands than a Cherokee. The training has improved enormously, and in the States at least the insurance companies have set the standard. The accident rate is probably now better than that for other singles. (Probably because statistically it is still early days).

It is true that the climb performance of many twins on a single engine is poor or almost non existent. It is equally true that for many twins the climb performance is acceptable. How many critical engine failures do you read about each year in the UK? Of these how many singles do well in terms of avoiding injuries?

I have quite a few hours on 42s. An engine failure immediately after take off before you have cleaned up the undercarriage is an issue, but not unmanageable. An engine failure a few moments later is also an issue but far less of one. As long as you are on the ball the aircraft continues to climb quite nicely even at MAUTW - I have flown singles that barely do much better. An engine failure in the cruise is a complete non event. I had one last year. If I had to we would have flown on for as long as necessary. Personally I don’t subscribe to the school that a failure is anything other than an emergency and I don’t subscribe to flying home on one engine - but if there is no alternative one could and would. Had I been in a single which might easily have developed exactly the same fault I would have landed in a field. With luck I would not have been uninjured, with a whole lot more luck the aircraft might have survived without a reasonable amount of damage, but probably not.

In the last two weeks two Cirrus have sadly been lost due potentially to engine failures. In once case the pilot lost his life, in the other one crew member escaped without injury, the other was injured. The aircraft is a write off. In a twin with a current pilot if the accidents were caused by an engine failure neither the aircraft or crew would have suffered any consequence.

On the whole twins carry more weight. On the whole twins are better equipped to cope with weather. That does not mean to say singles cannot be so equipped but in reality few are. Twins will typically be certified for flight in known icing. Twins will typically have boots rather than fluid which is only “lifed” for as long as the fluid in the reservoir lasts. Twins on the whole have significantly higher cross wind limits and are more stable both on the approach and in flight. If you care to fly an Aztec in turbulence, and a single in the same conditions you may well wonder why the passengers are throwing up in the single. Twins on the whole have significantly more redundancy. Twins are on the whole are faster and perform significantly better - at least when both engines are working!

Some modern high performance singles attempt to emulate twins on some of these counts but none emulate twins on all counts.

In defence of twins you therefore get a great deal more than just an extra engine. On the whole you get better performance, greater comfort, more redundancy, improved all weather capability and, with a current and well trained pilot, more safety.

One last thing - you worry a whole lot less. I know engine failures are remarkably rare. I know the engine doesn’t know it is over the sea or the Alps or it is night or there is a 800 foot base. Never the less it still doesn’t stop me worrying in a single half way to the CI in the middle of February with a cold 5 foot swell beneath that an engine failure will definitely ruin my day. I would only fly twins if safety was the sole issue - as it is singles are good fun to fly for other reasons, and a whole lot less expensive.

So to answer your question Diamond were brave enough to try and prove there was a market for a modern twin - inspite of the ill informed bad publicity with which they had to contend - I think they have been very successful in that regard if let down by the choice of engine. Tecnam will hopefully apply the same formula to powering a mdern twin with a much cheaper Rotax already used in loads of non certified aircraft. They apparently have a pretty good order book. I hope others try.

IO540

28th Nov 2008, 11:19

I think the DA42 was a great formula which would have eventually been very successful.

Total flow rate is identical to my TB20, at the same cruise speed of 140kt (11GPH) but you get a spare motor in that.

I say "eventually" because Diamond p*ssed off so many people and that was before Thielert went bust. The reliability was so poor that one needed the second engine! I know of a number of owners and almost none of them dared to fly them anywhere too far. Defeats the point of a twin, completely.

I am sure 5-10 years from now it will be a well shaken down airframe with reasonably reliable engines. Shame it will have taken that long. That is longer than most private pilots' flying career.

Fuji Abound

28th Nov 2008, 11:54

I say "eventually" because Diamond p*ssed off so many people and that was before Thielert went bust. The reliability was so poor that one needed the second engine! I know of a number of owners and almost none of them dared to fly them anywhere too far. Defeats the point of a twin, completely.

IO540 - That isnt my experience, or the experience of owners I know, so perhaps the experience of owner / operators has been variable.

I have not had any failures on the 42 (other than the engine :)) which made be nervous about going far, and the failures that have occurred have been minor. That is the experience of others to whom I have spoken. I guess with any new aircraft (and I dont mean in the design sense) there is some inevitable beding in - I have had the coms fail for example, but I think in the early days you had similiar issues with your TB20. Whether or not these issues should arise at all is debatable - perhaps it is just poor quality control. Everyone is pi**ed over the issues with the engines but that is well rehearsed. 42s have had a lot of "heavy" use with the schools and have been used and abused as only a training aircraft can. As we have discussed how well they will really stand up to the test of time once they have been left out on the pan in all weathers remains to be seen - but that is another story.

I think the 42 with twin Lycomings as now been rolled off the production line could be a great twin fro anyone needing just 4 seats.

I would be interested to know what specific reliability issues people have had with 42s?

IO540

28th Nov 2008, 12:03

It is the engines, mostly.

Which is more than sufficient to deter serious usage.

Fuji Abound

28th Nov 2008, 13:35

Ah yes IO, you are right.

You dont really want to go anywhere in a twin if you are going to spend the whole time wondering when the engine is about to quit on you. I was at FL95 from Ireland having just got on top after a climb up through solid IMC from about 1,100 feet, and I recall thinking I would prefer to make my way down with the same number of engines as on the way up. :)

wsmempson

28th Nov 2008, 14:13

In answer to the original question, how about Gabriela Irimia?:8

liam548

28th Nov 2008, 14:19

SNS3Guppy

28th Nov 2008, 14:21

I tend to agree with IO540 in supposing that theoretically you have double the chance of engine failure with a twin.

That's really not the case. The truth is you have the same chance with everything, every time. Either it will, or it won't. Period. This doesn't increase with engines, with numbers of takeoffs, with anything. Either it will, or it won't. Either it will run, or it will fail.

One would imagine with four engines we'd be having failures right, left and center with odds and chances increasing in proporition to the number of engines...but suprisingly, no.

In a light piston twin, the second engine isn't there for safety. It's there for performance. Specifically, climb performance. Many light piston twins won't maintain altitude on one engine, let alone positive climb performance, and have very low single engine service ceilings. While this is often cited as a big disadvantage for the light twin...it's a given that singles don't have many options during a power loss, either.

One of the big advantages of a twin is redundancy of systems; additional hydraulic pump, additional vacum pump, additional generator, etc. Learning to fly a multi engine airplane, or any advanced or complex airplane for that matter, is learning to fly it with engines and systems failed...learning to handle it in less than ideal conditions.

Mr Grimsdale

28th Nov 2008, 14:48

In answer to the original question, how about Gabriela Irimia?

Cheeky boy!:}

Fuji Abound

28th Nov 2008, 14:50

In a light piston twin, the second engine isn't there for safety. It's there for performance.

Yet another fallacy, we are on a roll.

Singles have been around that can match the performance of nearly every light twin for as long as I can remember.

Even today, you would have to go a long way to find a twin that can out perform a Mooney or even an SR22 in every practical sense. I can go faster in the SR22 than I can in either the 42 or an Aztec (two generations of twins in regular use), I can fly as high as makes no difference, and whilst I might get 200 feet more of climb performance out of the Aztec it as good as makes no difference.

I doubt the second engine was ever fitted for pure performance.

However passengers and regulatory authorities (and even some pilots) take comfort from the extra engine. The CAA has never approved single engine turbines (or anything else for that matter) under JAR-ops or before for IFR ops. Passengers are on the whole horrified when you let slip there is only the one fan.

Even the multi world started out with the 60 minute rule, that evolved into any transoceanic aircraft being required to have four engines. Whilst this has evolved again into ETOPS and will shortly evolve into LROPS the second engine is considered a prerequisite for safety, and even then, under ETOPS a second engine is still not quite considered as stacking the odds sufficiently in the passengers favour, hence the ETOPS requirements which are not, as many think, restricted to only transoceanic crossings even if in practice this is effectively the case.

No body wants to carry around an extra engine for performance, even if their was any truth in the fallacy, and everyone is desperate to see ETOPS evolve in LROPS but I don’t think even the commercial world will ever persuade the general public to get in an aircraft with one engine unless perhaps they think there is half a chance of landing it in a friendly field about the size of their back garden!!

Pace

28th Nov 2008, 14:55

I think the idea that you have twice the chance of a failure in a twin has grown from the conception that as you have two you have two engines to potentailly fail which doesnt mean twice as likely to fail.

One safety factor of a twin which is often missed is that the engines are on the wings rather than infront of you as in a single.

Aircraft design is attrocious regarding crash protection and a head on with a single on ground contact inevitably means that giant lump of metal in front of you joins you in the cockpit!

Normally aspirated twins do have a poor single engine ceiling but something like a Seneca Five turbo charged intercooled unit has a service ceiling single engine of 16500 feet which is pretty good.

Pace

Fuji Abound

28th Nov 2008, 15:26

I think the idea that you have twice the chance of a failure in a twin has grown from the conception that as you have two you have two engines to potentially fail which doesn’t mean twice as likely to fail.

Is this yet another fallacy? I thought we were on a roll.

If an engine fails once in every 1,000 hours, and never goes beyond a thousand hours, and the failure rate is linear, then there is twice the probability of one engine failing on twin in a given time frame because both engines eventually must fail on the twin whereas the single has only got one engine to fail.

In reality there are other factors involved that even where the same engine is concerned the probability of a failure in a twin will be different from in a single. Moreover engine usually dont fail before they become either time expired or have adequate work to enable them to continue to operate on extension where this is permitted.

In reality, if you were to plot hours against failure rates (or at least problems identified requiring remedial action) would you end up with a bell curve? If so is that also why it is common to see twins with engine hours that are not the same?

Chuck Ellsworth

28th Nov 2008, 15:29

However passengers and regulatory authorities (and even some pilots)

Hmmm let me think about this for a while......

.......I am flying over water at night far from land and the engine fails....

.......would I want to be in a SR22 or an Aztec? :confused:

Fuji Abound

28th Nov 2008, 15:31

Chuck

You have had enough thinking time .. .. ..

;)

Chuck Ellsworth

28th Nov 2008, 16:32

The SR22?:ok:

smo-kin-hole

28th Nov 2008, 16:57

I have a friend with a Cessna 337 Skymaster. Under certain conditions, he does shut down the front engine and rides a good tailwind to his destination. These things are old, hard to work on, noisy, cramped,but really are quite slick in concept. Adam tried to build one and there are a few Rutan Defiants out there. Its a great idea that might be executed on a cheaper level if somebody had the time/money.

What about having the nose engine much smaller than the tail one? Use the front just for takeoff and loitering,but otherwise shut it off? Maybe make it water cooled so there is no thermal shock? Solid-fuel booster fired by a big red panic button for takeoff emergencies? What about a belly mounted micro-turbine with just enough power to maintain altitude?

Do I have too much time on my hands or what?:}

vanHorck

28th Nov 2008, 17:54

Could anyone enlighten me on the service ceiling of singles when their first engine fails?

Duchess_Driver

28th Nov 2008, 18:38

The performance calcs for the Duchess, IIRC, give about 15 or 16,000 as the maximum 'cruising' line. Can't recall what the 'service' or absolute figures are - would need to check the books - but it's not really relevant for this discussion.

What is important here is that mid channel when one donkey goes tilt - I've got another one! That's where the benefits are. A single may be faster, easier to manage, cheaper to operate but here's the real benefit - when my engine fails my DRIFTDOWN is significantly higher than yours!

Thats what I call a performance benefit. :ugh:

(And I'm not too sure I want to go long distance over water or over mountains in a Cirrus at the moment!)

IO540

28th Nov 2008, 19:42

how do aircraft engines compare to car engines for reliability generally?

This is not possible to compare.

The reason is that car engines spend most of their time at around 10% to 30% of max rated power. A typical 2 litre saloon, 130mph top speed, is running at about 30% power at 70mph.

Whereas an aircraft engine is running at 65% or maybe even 75% power continuously.

When one sees normal car engines used in real competitions e.g. rallying they tend to fall to bits really quickly. I gather the rally teams have a pile of spare engines.

Car engines have the big advantage of water cooling, which keeps temperatures under close control, but I think they are way less reliable than the old Lycos.

And they are not more efficient, either. They are much more efficient over a wide range of power settings, which is what one needs to sell cars, but if one compared constant operation at say 65%, the two would be very close.

SNS3Guppy

28th Nov 2008, 19:57

You can't really make a comparison based on percent; the power percent for a horizontally opposed aircraft piston engine is based on propeller limitations, not what the engine can do. Aircraft engines typically operate in the 2000-2500 rpm range in cruise. So do cars, give or take. Aircraft engines are capable of far more power and far higher RPM's...the truth is that aircraft engines, while exposed to thermal stresses, generally operate far less harder than car engines.

madlandrover

28th Nov 2008, 20:48

I would be interested to know what specific reliability issues people have had with 42s?

Only seen a few so far, but... Head gasket problems seem fairly rare, unlike Thielert installations on other aircraft. Some aircraft have the odd ECU problem which seems to affect original and replacement ECUs on just one engine - possibly due to faulty injectors. Other problems are relatively minor stuff like worn autopilot gyros, faulty KAP140 autopilots, and the odd minor avionics issue, often related to the plugs & power supplies for the factory supplied Sennheiser headsets. The only other grounding fault I've seen recently was a couple of props either missing 1 of the 3 rubber protection strips, or 1 blade delaminating. I haven't got anywhere near the experience of many on here, but of the 50-odd DA42 hours I've done both in training and solo ferrying I haven't had a single heart stopping moment, only the odd "Hmmm, I wonder where this might going" query!

They are quite sensitive to decent maintenance, so can be a bit fragile if poorly maintained, but in general the work I've seen so far from a certain centre of excellence in the south west results in very few faults - and better still no new scratches on the gel coat.

Given the option of the simple and normal complex singles that I teach on, or the few light twins I've flown (DA42 and PA44) I would take the twin for pretty much every mission, for the confidence as much as anything else! The average school PA44 can be a bit limited in single engine performance at higher levels, but simultaneous twin engine failures are still reasonably rare...

Fuji Abound

28th Nov 2008, 21:20

how do aircraft engines compare to car engines for reliability generally?

Most car engines will make over 100,000 miles without any mechanical rectification. That is about 2,500 hours of operation, ignoring periods at idle, which adds to making a comparison complicated. Most aero engines will do well to get to 1,600 hours without a top overhaul, and a major overhaul by 2,000 hours. On that basis the car engine is vastly more reliable.

The engines are, as others have said, operating in very different environments.

However, my knowledge of performance cars would leave me to believe that lubrication and heat are the two most important factors in determining the life of a well built engine. While a road car may operate a great deal of its time at low rpm the aim of a race car is to operate continuously in its maximum power band. That will almost certainly mean between 5,000 and 8,000 rpm. In the case of a car add a few G in corners and it is all to easy for the engine to be starved of oil. For this reason we fit dry sumps, in some ways not dissimilar to the Christen systems on aircraft. Without these systems it is quite possible to destroy an engine in a single race. In a similar way light weight alloy car engines are hugely susceptible to excess heat. A loss of coolant will destroy a hot engine in a minute or two. We cringe when you watch novices starting the engine from cold and immediately applying throttle. Not only has all the oil found its way to the sump but it takes 5 seconds or so for oil pressure to have established even with a dry sump. In this 5 seconds a great deal of damage can be done.

The engines we use day to day in our cars are way short of the power the engine is capable of producing. The tolerances are large and the stress on the components is kept to a minimum. Despite what the advertising agencies may like to tell us the name of the game is to deliver an engine that is no where close to its peak performance capability, because by doing so it will be reliable. My 1600 engine in its usual road going guise develops less than 100 bhp, in some sportier cars that is pushed to 120 bhp. The same engine with hot cams, ported head, forged pistons and properly mapped will produce over 200 bhp - twice the power.

In some respects aero engines are no difference. On the whole the mapping is rudimentary and the engine is not designed to operate close to its potential. However, there is an equally big difference. I can easily apply +6-4g to my aero engine. I can easily chop the power, and without any thermal buffer from the water cooling system in my car engine expect the air flow to dissipate all the heat from beneath my tightly cowled engine. I can easily expect the engine to sit idle for two or three or four weeks, start the engine, and expect it to provide maximum power within 10 minutes of startup whilst also expecting it to reach its full operating temperature in the same time. In short even when we are kind to aero engines we give them a load of abuse. As to the original topic of the thread this is one of the reasons twin engine aircraft should be more kind to their engines - it is far easier to dissipate excess heat in a twin than in a single.

I reckon if you used your aero engine every day, always allowed at least 5 minutes to fully establish oil pressure, avoided shock cooling and any manoeuvers likely to restrict oil flow aero engines would do nearly as well as car engines.

IO540

29th Nov 2008, 10:47

The subject of "why we don't have car engines in a plane as they would obviously be so much more reliable" has been done to death on every pilot forum going :)

As Fuji suggests, one cannot do a direct comparison for a number of reasons.

But there are also others.

Car engines are designed to deliver their rated HP at high RPM, 5000-7000, while direct drive aero engines deliver a similar power at much lower RPM, say 2500 (my car and my plane are both 250HP, funnily enough) so the aero engine has to deliver an appropriately much higher torque (HP=rpm*torque). On an engine, everything incl crank stroke being equal, torque comes from piston surface area which is why my IO-540 is 8.8 litres whereas my car engine is only 3 litres.

But there is no way one could make the IO-540 rev at 7000rpm. It would shake itself to bits, I reckon. They have enough problems with dynamic stress on the crank at 2500rpm and have to add movable balance weights to reduce this.

So, the engine designs are very different.

I reckon every IO-540 would make TBO without any work, if it ran constantly at say 65% power, with good airflow. There are plenty that do make TBO in normal operation.

But I just don't believe that a car engine would run for 2000hrs at 65% power without something breaking. Not mechanically in the engine but on the ancillaries e.g. cooling hoses.

The basic mechanical reliability of some car engines is awesome. I gather Toyota spent USD 400M developing a certain 4 litre V8 engine for the U.S. market (as used in e.g. the V8 Lexus Soarer) and one just doesn't see any investment like that in aviation. But one cannot escape the fact that 99.9% of these engines will still spend 99% of their lives doing 10-30% of rated HP and that is bound to massively slant the figures.

SNS3Guppy

29th Nov 2008, 11:42

Most car engines will make over 100,000 miles without any mechanical rectification. That is about 2,500 hours of operation, ignoring periods at idle, which adds to making a comparison complicated. Most aero engines will do well to get to 1,600 hours without a top overhaul, and a major overhaul by 2,000 hours. On that basis the car engine is vastly more reliable.

Most people reckon their car longevity by miles (or Km, whichever you prefer). A car making 200,000 miles is doing well. An airplane which sees 1,600 hours in it's powerplant, at 150 nm/hr, has made 240,000 miles.

IO540

29th Nov 2008, 11:46

Physics is physics.

The prop is no more than a screw which screws itself into the air around it, and the variable pitch mechanism is the gearbox :)

So a plane isn't going to magically do 10,000,000 miles while a car would do only 200,000 miles, on the same kind of propulsion device technology.

Dr Jekyll

29th Nov 2008, 12:15

There is also the consideration that an elderly car engine which splutters to a halt occasionally will still be acceptable to some drivers for many thousands of miles until they can afford to replace it. A pilot will try to replace/overhaul before the first breakdown.

jxk

29th Nov 2008, 15:01

There seems to be certain areas on an aircraft engine and systems which cause problems. If it were possible to remedy some of these we would have better reliability and safety. Here are some of the things I've come across:
Camshaft wear (mostly Lycos).
Valve guide tolerances.
Exhaust port erosion.
Vacuum pump failure.
Cylinder Head cracking between inlet and exhaust valve seats.
Oil pump failure.
Pushrod tube sealing.
Crankcase cracking (Continental).
Crankshaft rust/pitting.
Of course, a lot of these things are down to lack of use but perhaps that should be factored in as well.

SNS3Guppy

29th Nov 2008, 22:23

Physics is physics.

The prop is no more than a screw which screws itself into the air around it, and the variable pitch mechanism is the gearbox

So a plane isn't going to magically do 10,000,000 miles while a car would do only 200,000 miles, on the same kind of propulsion device technology.

Right. Which is why a piston aero engine has already fulfilled more than it's share of work when it comes time for an overhaul, compared to an auto engine.

If the auto engine gets overhauled (or more often junked) at 200,000 miles, then the aircraft engine which goes to 240,000 miles, gets overhauled, and then flies another 240,000 miles, is doing quite well.

Each of my cars, including my current Dodge Grand Caravan, have been over 200,000 miles. My Caravan, which just went over that last month, is on it's fourth transmission.

Then again, the engines on some of the airplanes I'm flying have well past 25,000 hours on them.

I think aircraft piston engines do quite well. There's certainly room for improvement, but with such a small market (and it is small), putting the money into development and certification is somewhat of a losing proposition, to say nothing of product liability.

LowNSlow

1st Dec 2008, 07:52

My original intent with the "as reliable as a car engine" was that I would prefer the engine to be as dependable as the 2.5l one in my BMW rather than the 1.3l one in my Triumph Spitfire! I have no qualms about driving anywhere in my 104,000 mile BMW but I have my doubts about driving to work in the Spit as I don't feel that my arrival is guaranteed! I regard my Auster in much the same way as I do the Spit even though it has never let me down in a big way. I certainly have my doubt about flying over any large bodies of water even though a lot of members of the Auster Club regularly attended fly-ins in France and Holland. Maybe it's my perception of danger that needs revisiting here!

IO540

1st Dec 2008, 10:36

There is a huge spectrum of operating practices and a huge spectrum of maintenance practices. And another huge spectrum of engine ages, and in that I include the # of years (or decades!) since the engine was last opened. Plus undeclared prop strikes, many years ago perhaps...

Put these factors on top of each other and you are going to get a huge spectrum of engine reliabilities.

The funny thing is that while cars have improved on both engine designs and the reliability of electrics (electrics used to be the thing responsible for the big majority of breakdowns), planes have not improved on the engines for many years and their electrics are generally still in the Vauxhall Viva territory. I therefore reckon that while cars of 40 years ago were truly crap (as in the Triumph Spitfire), planes probably were way ahead in reliability in those days.

The reliability hassles one gets on a plane are mostly small things - just like with a car. One very rarely gets con-rods flying out of the crankcase - same with a car.

LowNSlow

1st Dec 2008, 10:49

IO-540 you are certainly right about the Spit. The number of built in rust traps is unbelievable as I have discovered to my cost. Got a fair bit of practice in with the MIG welder though! It is usually the ancilliaries that give the bother with the wiring being truly atrocious. Regarding the Vauxhall Viva analogy I was once advised to fit the voltage regulator off a Mini (BL not BMW) to my Aerobat as it was identical to the original.......

Fortunately my Cirrus was rebuilt by Norvic a few moons ago and I have recently invested one arm and most of a leg in a top end and magneto overhaul by Vintech so the old girl is getting the best of care. I'm still nervous about flying over anything bigger than Grafham Water though!

Rod1

1st Dec 2008, 11:26

There are some very interesting LAA twins. The first and most famous is the Cri Cri. This is a single seat twin which is stressed +12 – 6 G and fully aerobatic on two very small engines. I have seen one aerobated on one engine and the jet version is absolutely outrageous. The second is the Phillips Speedtwin which is much more conventional, fast and also aerobatic. The Mk2 version of this is in final approval with the LAA and kits should be available eventually.

Rod1

Fuji Abound

1st Dec 2008, 12:10

LowNslow

I think you have hit the nail on the head.

I spent over three thousand hours on one single I liked to fly sitting behind the controls or involved with the maintenance. In that time I only had two issues with the engine. In fact both of those issues were not strictly engine related. One was entirely due to an error made by the maintenance company which manifested itself on the very first flight after they had got their spanners involved. The second issue related to the fuel injection system and while in theory could have resulted in an engine failure would probably have only done so if all the warning signs had been ignored. The route of that problem was also probably down to poor engineering practise.

However despite the evident reliability and my insistence on scrupulous maintenance there was always that irrational nagging doubt that the best place to be wasn’t over a cold windswept expanse of sea.

Irrational, certainly, but, it is a bit like spiders, you can tell someone that this particular one isnt poisonous and wont bite, but they still wont hold it! I think that is why all other factors aside if you have one engine, you would prefer to have two, and if you have got two, there is no substitute for three and if you have three .. .. ..

snowfalcon2

1st Dec 2008, 20:47

Well yes but the cost is a bit of a problem, and cheap turbines are nowhere near being even on the horizon.

What's wrong with the new RR500 turbine? Other than having more than enough HP for the average 4-or 6-seater?

Best,

IO540

2nd Dec 2008, 06:53

Fuel flow.

Cost is the other problem. It drives the aircraft price well beyond the £300k kind of range, into the category where most punters expect pressurisation and club seating with a cocktail bar, which is why we don't have any SE unpressurised turboprop IFR tourers; the marketing men then load up the airframe with gizmos, grow it in size so it can carry the extra weight and you have a Meridian or similar... shame really. The Grob 140 looked very interesting but Grob felt they had to justify the price by loading it with pricey avionics and the end result was £1M which was pointless except as a military trainer.

I'd like nothing more than a turbine. Solves the huge avgas problem which one finds when going further out.

flybymike

2nd Dec 2008, 11:23

I suppose at a stretch a Cessna Caravan could be regarded as a SE unpressurised tourer ( for those with the brass... ;))

LowNSlow

4th Dec 2008, 09:37

Seems like the Russians reckon there is a market for a very light 3 seater twin powered by a pair 80hp Jabiru engines with electric VP propsDescription / Aviakom (http://www.aviakom.ru/m12/description/) which has been reviewed in Todays Pilot this month. Looks very nice but there is no mention of cost and it's certified as Experimental in the USA which could be a real pain for the first people to certify it in the UK.

Justiciar

4th Dec 2008, 10:50

which is why we don't have any SE unpressurised turboprop IFR tourers

Doesn't the turbine SF.260 come into this category? Not that I know much about this, but the certified SF260s are IFR capable so presumably the same applies to the turbine version. I guess that there may be other reasons why you would not tour long distances and don't know what their endurance is, given their design as trainers.

ika

22nd Dec 2008, 00:02

I used to fly a single comanche (and still do). I wanted something that would carry 6 people occasionally, and was thinking of getting a bonanza or cessna 210 but wanted peace of mind when flying with small children across to France for the day. I got an aztec for the same price as a basic single (under £50k) and it flies wonderfully, happily in and out of 600m boggy fields (it will stop in a couple of hundred metres lightly loaded, very docile landing), it feels like a grown-up plane compared to most singles but is fun to fly with 500hp, although obviously a bit less sporty to handle than some singles, nice and stable even in nasty weather (it's the first plane I've had with an autopilot and I never use it after the novelty wore off), carries anything you put in it in terms of both volume and weight (lots of fuel,6 adults and several cases of wine, or 2 adults, 4 children and back of an estate car full of baggage for a week's holiday) and it's almost impossible to load out of C of G. I happily flew to Sweden 350nm over water non-stop landing at night, which I wouldn't have dreamed of doing in a single. Yes my annual bills are a bit higher, say 50% more and fuel is 90-100 lph at 160-170 knots which is 50% more compared to comanche's 60 at 150 but not that much worse mpg than many typical singles - if you work out what portion of the cost of flying fuel for a typical private pilot doing 50-100 hours a year is, it's not that big a deal - with all the flying I'm likely to do, it will never match the capital cost of say a £100k single. It only took a few days to do my ME a couple of years ago and since then I've done 50-100 hrs multi, got my multi-IMC. Doing the ME renewal, flying on 1 engine is a non event in the Aztec compared to e.g. the Seneca I did my ME on (might be more interesting at gross weight, but that's a lot of weight). The only complaint I have is that if I ever want to trade up, I'd have to spend close to 20 times more for something a bit nicer and faster and then I won't be able to get into short grass fields. Try one!

vanHorck

22nd Dec 2008, 06:32

My story is similar but on a Seneca.
I do not find the single engine control of a Seneca an issue.

If I am not mistaking the EFATO climb rate of the Aztec as is the single engine max altitude. That's a serious downside alongside your benefit of load capacity.

Does your Aztec have a critical engine? Cos my Seneca doesn t.

Finally when i spend tens and tens of thousand of euros or pounds on a capital investment I like to have something that looks good, so I would always buy a completely repainted, recovered interior one, possibly including a new panel facia.

The Aztec is also showing signs of "vintage", that can be nice too

ika

22nd Dec 2008, 21:47

When I said single engine was a non-issue in aztec compared to seneca, I didn't profess to be an expert - quite the opposite as the only time I flew a seneca was doing my ME rating and I suspect you are a much more proficient pilot than me. I just found that asymmetric you had to nail the blue line speed pretty accurately even lightly loaded (2 people plus the bag of ballast you have to carry for CofG) or the ground quickly got closer! I understood why low time private pilots sometimes get into trouble in twins - if an engine fails, it's likely to be an unexpected and somewhat disconcerting experience and I can see someone out of practice getting flustered and the old cliche of the second engine simply getting them to the scene of the crash faster, which was a good thing to appreciate.
In the aztec doing my IMC multi renewal, I can sloppily sort out controls while peering under goggles to see what I'm doing to the engines, work out approach etc and it keeps flying happily upward with only a casual glance to check that the ASI and blue line are still acquainted. I've had the benefit of a bit more time in the Aztec but it just feels to me as if it there's more time to take a deep breath and calmly enjoy a bit of unscheduled asymmetric practice and instructors have agreed it's much more forgiving.
The left is supposedly the critical engine and that's not really a problem for control but what is a problem is it also operates the hydraulic pump - I've practised manually pumping the gear down with it fully shut down but I don't fancy doing a late go-around on the right engine for real - I hope I'm not tempting fate by saying this!
On takeoff, it zips past red and shortly after blue lines so you'd have to time it really spot on to lose an engine between being too late to abort and blue line. I'm not sure how single engine altitudes compare but I take published figures for a 30 year old aircraft with some scepticism, the point is that if you need to maintain say 8000 feet to clear mountains, it's unlikely to be terrain full of friendly fields to glide a single into and anyway you can cover more ground looking for one with one engine than with none!
The seneca does win though on eurocontrol charges!
As for cost, I saw a pristine aztec F for double what I paid and I suspect your aircraft looks a lot prettier than mine, but the 70s charm - a friend described it as like an old Ford Cortina, and more importantly the fact that the elements attacking the paintwork aren't knocking thousands off the value, have grown on me.
I think we'd both agree though that the negative things people say about twins are generally somewhat misguided - at least in a twin you normally have to take a positive step to kill yourself by your own stupidity if you lose an engine whereas in a single there are circumstances in which no matter how good a pilot you are (unless you are cautious enough to avoid them all), it's going to be a very bad day.
Finally, the other benefit of flying a twin is that ATC assume you are a more proficient pilot and are more helpful to you and let you through when they might turn a single away!

Sciolistes

23rd Dec 2008, 02:14

My story is similar but on a Seneca.
I do not find the single engine control of a Seneca an issue.
Well it is and it isn't. The Seneca 1 is comparatively an affordable twin, but a very weak one. It is true that you really cannot creep below the blue line and have much hope of maintaining a climb (however slight) in normal conditions and the sort of loads one would associate with a decent run to Europe (what one would buy a twin for?).

The Seneca III performs much better, but is much much heavier on the rudder and can be trickier to stabalise, but not difficult when you're expecting it! E even the mighty Seneca III, as I found out during my IR test, with a decent fuel load and two on board will not climb OEI (one engine inoperative) at 600 AMSL and 30 deg C. Something you are likely to encounter on Southward forays during the summer.
but the 70s charm - a friend described it as like an old Ford Cortina
I know what you mean, there is a certain something about that era.

flybymike

23rd Dec 2008, 09:34

Rust, mainly.

Justiciar

23rd Dec 2008, 10:09

I know this is kicked about a lot, but has anyone actually done some figures to compare buying new as against old? I mean the whole spectrum of expenditure, including depreciation and cost of use. What promptd this is seeing a Mooney for sale at £30k! Ok, it is 1966 vintage but that means nothing really with relatively low airframe hours and good maintenance. It occurs to me that the only advantage of a new aircraft is low operating costs (if diesel or it runs on mogas) but you tend to have high depreciation.

It seems to me that you could buy cheap, spend £30 or £40k on repaint, new avionics etc and still have an aircraft which in absolute terms will cost you far less in total over a period of ownership than buying new or nearly new (unless you fly huge amounts per year). Is an old Astec cheaper in the long run than a nearly new TB20, for example.

This is all a gut feeling and unsupported by actual figures. It would be interesting to hear from those who have done one or either or both and know what the actual figures come out at. Some views of course already expressed here.

411A

23rd Dec 2008, 10:37

I know this is kicked about a lot, but has anyone actually done some figures to compare buying new as against old?

Why certainly, at least with the cabin class piston twin.
Twelve years ago I purchased my 411A.
It had 1800 total airframe hours on it, with mid-time (600 hour) engines.
After an extensive annual inspection, IRAN'ed cylinders, overhauled propellors and an IFR approved (enroute, terminal, approach) GPS installed, the total cost was $110,000.
It has seven seats (pilot and six passengers), a bar and a potty.
It can fly for over 1000 nautical miles, and being turbosupercharged, can fly all day long in the mid-high teens, in quiet (geared engine) comfort.
It consumes 30 US gallons/hr and flies at 190KTAS.

It has provided unsurpassed reliability in the last twelve years, having missed only one planned flight due to maintenance issues.

To purchase this type of airplane today (provided it was available at all) would take at least $1.5 million.

Face it folks, if you shop carefully, very good value can be found today with the purchase of an older piston twin, in good condition...with many reliable flying hours remaining.

vanHorck

23rd Dec 2008, 12:52

As with cars or anything else people buying new still pay a hefty premium.

The smart buyer will buy an older airframe and do it up completely like the 411 earlier on, with full refurbish, new panel (and wiring if needed), things like a Colemill conversion or Ram conversion, new paint.

Those who cannot wait to fly but are still smart will opt for a low hours well maintained twin and still get most of the benefits without forking out twice as much for the factory new.

I bought my pristine 10 year old Seneca IV G-MAIK with just 1000 hours on the engines. The lady didn't have a scratch, the inside still smelled like new, sh had mainly been hangared so the paint looked good and the panel was how I like it, analogue dials but with a good moving map and color radar, good autopilot with altitude preselect. The only thing I added were Gami injectors with JPI760, updated the KLN90B's database and never looked back.

The only reason I see to buy new are those pilots who like the integrated glass cockpits, but i like the non-integrated classic panel with part digital equipment so this choice worked for me.

The day I got her, i baptized her with a bottle of Veuve Clicot Brut sprinkeled over her wings to the horror of my FBO's owner Derick Gunning who was horrified but understood...

She's a good girl!

IO540

23rd Dec 2008, 14:55

Is an old Astec cheaper in the long run than a nearly new TB20, for example.

The two don't compare on load carrying capability, and for that the Aztec will use double the fuel of the TB20 (twice as many IO540 engines).

Otherwise, an old Aztec is likely to cost £10k-£20k p.a. on maintenance whereas a newish (say 2002; the latest possible) TB20 might cost £4k p.a.

It's the same old argument which has been done to death on all pilot forums many times.

There is no doubt that buying old means that you have loads of money to spend on fuel and maintenance and upgrades.

But what value do you place on hassle and downtime?

It is arguably foolish to buy a new car because even a 15 year old Toyota is still extremely reliable. But a 25 year old plane probably won't be, or (putting it another way) you have to spend loads of money on it because if you don't it will not be airworthy, you won't get it signed off on the return to service, and it will be worth scrap.

I think that on average if one buys something old and keeps it say 10-20 years then one spends as much on maintenance as the extra amount one would have spent on the extra purchase price of something newer.

But as with cars there are smart strategies and there are dumb strategies. You want to buy a plane which is old but still has 5-10 years before it starts to fall apart, so you probably want one which is about 10 years old. That should give you 10 years before you need significant airframe replacement/repair parts (which are the really expensive bits). You also want to buy one with the avionics you want already installed because the money the previous owner spent on avionics is almost a total loss.

And, personally, I would prefer a plane with a runout engine because it will be sold at a massive discount and you can then send the engine off to a really reputable American engine shop (there are no really reputable engine shops in the UK) so I have a known quantity up front (engines being quite important on a plane).

SkyHawk-N

23rd Dec 2008, 15:03

you have to spend loads of money on it because if you don't it will not be airworthy, you won't get it signed off on the return to service, and it will be worth scrap.

Yet another IO540 sweeping statement, without any figures to back it all up.

IO540, how much has your aircraft depreciated in the last year? Add to that your maintenance costs?

My VERY old aircraft (1977) has cost approx £800 in maintenance in the last year and has not been out of service for more than 3 days at a time (for annual, and forgetting it's crating to the USA.) in the last 6 years. I know many others who have the same experience of running 'old' aircraft. :ugh:

IO540

23rd Dec 2008, 15:36

I am not going to debate this, Skyhawk-N because

My VERY old aircraft (1977) has cost approx £800 in maintenance in the last year is infeasible in the UK where an Annual is some £2000-£3000, plus any actual "work".

You either live in some aviation heaven, or you do your own maintenance and place zero value on your time.

Actually I know how to get an Annual done on my TB20 for £800, using a freelance A&P/IA but for that I would need a hangar where he would be allowed to work, and I don't know of such a hangar.

Justiciar

23rd Dec 2008, 15:42

Otherwise, an old Aztec is likely to cost £10k-£20k p.a. on maintenance whereas a newish (say 2002; the latest possible) TB20 might cost £4k p.a.

This is what I was trying to get at. There is a general perception that old = more maintenance, but where is the hard evidence to back this up? Obviously two engines tend to cost more than one, so my old Mooney vrs new(ish) TB20 may be a better straight comparison. Each aircraft will need an ARC and each will in due time require overhaul of engine. This may happen sooner in a £50k Arrow rather than a £150k TBx or nerly new Archer or C182, but then there is around £100k of price difference - an everage of £10k per year if you keep the aircraft for 10 years, say. Would I spend £10k a year more on maintenance and upgrades than the owner of the new hardware? Seems to me that the case is not proved.

SkyHawk - hope the C172 is flying well - no fly-in at Tibs this year that I have heard of :sad:

SkyHawk-N

23rd Dec 2008, 22:48

IO540, the reason I stated the £800 was to answer your point about "one spends as much on maintenance as the extra amount one would have spent on the extra purchase price of something newer.", this need not be the case. Having an old aircraft does not neccessary mean big maintenance bills. A well maintained and owned aircraft should not degrade to a large extent, if you buy an old pig, then yes you will get big bills. I'd rather own a solid, older aircraft and spend small amounts replacing the odd vacuum pump here and carb there than suffering 10's of thousands of pounds on depreciation.

You did not answer my point about depreciation.

Justiciar, hi there. Skyhawk is going very well thanks (for a 31 year old ;) ) Shame about Tibs not having a fly-in, I tried to encourage a few to get something arranged but it seems like nothing is being done.

Vee1Kut

23rd Dec 2008, 23:52

This is the kind of drivel that is perpetuated by those that just don't do this for a living..A light twin will climb and maintain altitude, granted like most planes, your flying it within it's performance limitations. If that wasn't the case, my NASA test pilot examiner wouldn't have signed my ATP ride off, doing single engine missed approaches in a 150hp/per side Apache. If you want to load up a 310, fuel of fuel, with 5 people and bags, and trying to climb out of ASPEN on one engine...yes Guppy, the plane won't climb.As far as chances of blowing and engine..... statisticaly your chances of a well maintained, catastrophic non-pilot induced engine failure are very slim. Statisticaly both engines failing in a catastrophic non-pilot induced engine failure at the exact same time, are so slim it's almost impossible to calculate. The safety in twins is for that 5 minutes it takes lose one engine, feather it, fly out and land on the remaining engine, means you will still fly on one engine, enough to get the plane back down, versus a forced landing on in a single.I will be the first to admit that on many twins the single engine climb rate on a most light twins, including many turboprops is abysmal, like in the 300 FPM range, but again, if you adhere to performance limits and aren't lazy in the areas of weight and balance and density altitude, and or telling boss too many people are slated for the trip, ...then the plane will fly. Having had 4 engine failures in my career, in all categories, ect helicopters...my reliance on statistics in the hope 'that it won't happen to me' is wishfull thinking. Personaly I believe if you fly enough, often enough, you will encounter your share of mechanical, electrical, pressurization, hydraulic, braking, ect failures....with most all of these situations, hashed out so much by the manufacturer, schools, lawyers, that it pretty much holds that the only reason a plane seems to crash is if the pilot allows it to happen.