An affordable twin???
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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.
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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.
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.
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.
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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.
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.
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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.
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.
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.
Thread Starter
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!
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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.
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.
Thread Starter
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!
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!
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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.
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Rod1
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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 .. .. ..
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 .. .. ..
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IO540
Well yes but the cost is a bit of a problem, and cheap turbines are nowhere near being even on the horizon.
Best,
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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.
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.
Last edited by IO540; 2nd Dec 2008 at 07:32.
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Thread Starter
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 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.
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which is why we don't have any SE unpressurised turboprop IFR tourers
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I would unreservedly recommend an aztec
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!
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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
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
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Re Seneca
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!
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!
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My story is similar but on a Seneca.
I do not find the single engine control of a Seneca an issue.
I do not find the single engine control of a Seneca an issue.
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