Another through Bolt gone

[rankamateur]

however this makes me think twice before purchasing a Jabriu

in reply to your post

 

it makes me think twice before I would get into one who ever owns it, come to think of it, on the second thought I never have got into one. Oh well nothing lost.

 

 

[facthunter]

I think you will do more dangerous things than go flying in a Jabiru, unless you live a very sheltered life. Left to my own devices I probably wouldn't have flown one but if the plane is the only one and the student is booked you go...... If I get into one it is just another plane now. I like to think that it is well serviced whatever it is. Quite frankly I would think that the average two stroke is more likely to fail these days as they are getting a bit long in the tooth and are in the hands of people who don't get as much advice from people on the field as they are not common and do require a bit of extra care. Any single engined plane can lose an engine, so you must be prepared to cope with that. A non centreline thrust multi engine becomes a handfull if you don't do the required actions too and can be lethal if you get slow. Nev

 

 

[damkia]

...The engine in my Minicab is putting out 23hp per litre. Politely, thats sod all in the way of engine stresses.....

Not necessarily.

It may well be the upper limit of what the engine could take due to the heavier reciprocating masses involved, when combined with the limits of metallurgy/technology of the rest of the structure of the engine. You could probably get more out of the engine but you would need to add weight in the fixed parts of the engine to strengthen it.

 

A more realistic measure would be how many thousand hours per hp per kg engine weight (apologies for the mix of measurements)

 

A very good example of what I am referring to would be drag car engines. Light weight, powerful (high hp/litre), BUT need an overhaul after about 10 minutes at full throttle (20 runs), and only last less than 2 hrs before being disposed of (if they haven't spectacularly scattered their parts to the earth by then).

 

Motorbike engines tend to be towards this end of the reliability scale, rather than the ability to go for thousands of hours like aircraft engines (and diesels). Something has to give in the big equations....

 

 

[alf jessup]

Can second that - have switched from Avgas to Mogas in my A-65-8 powered Minicab and love it. Easier starting and seems to run very much smoother after 20 hours or flying time. Only downside is it leaves a slight soot deposit out of the exhaust, apparently this is common on Continental 65's run on Mogas though.My point is that the last owner recommended it as it did not stick up the valves, nor leave as many deposits, nor cost as much. This was a fellow who had had the engine rebuilt from the crank out and wasn't afraid to take everything out and rework if needed, too; he knew what he was talking about.

 

Not a big fan of Avgas myself, especially in my little 65 which was rated for 75 octane and recommended to use 80 octane! Using 95 octane Mogas almost seems like overkill when you look at it like that.

 

- boingk

 

EDIT: Just for the record, I don't have a lot of faith in 'Aviation' branded oils. I'm heavily into motorcycle and automotive mechanics - maintain all my vehicles myself - and working with aviation oils is like taking a step back 50 years. Very conservative, very costly, very marginal. Yes, they work, but I believe there are better options out there. Personally I like the modern diesel oils such as Gulf Western 'Top Dog' 10W-40 or Dello 400 10W-40. Incidentally these oils can be bought for very reasonable sums when buying in bulk - I recently paid $90 for a 20L drum of GW 10W-40, for example.

Boingk,

 

The difference with automotive and motorcycles oils is they can change the addatives anytime without having to tell you for which in my case might not go well in the gearbox of a rotax, aviation oils can''t be from what I have been told by a reputable person in the aviation industry.

 

Alf

 

 

[turboplanner]

Not necessarily.It may well be the upper limit of what the engine could take due to the heavier reciprocating masses involved, when combined with the limits of metallurgy/technology of the rest of the structure of the engine. You could probably get more out of the engine but you would need to add weight in the fixed parts of the engine to strengthen it.

 

A more realistic measure would be how many thousand hours per hp per kg engine weight (apologies for the mix of measurements)

 

A very good example of what I am referring to would be drag car engines. Light weight, powerful (high hp/litre), BUT need an overhaul after about 10 minutes at full throttle (20 runs), and only last less than 2 hrs before being disposed of (if they haven't spectacularly scattered their parts to the earth by then).

 

Motorbike engines tend to be towards this end of the reliability scale, rather than the ability to go for thousands of hours like aircraft engines (and diesels). Something has to give in the big equations....

Good example Boink

 

Long distance trucks, which need a life cycle to in-frame rebuild time of around 10,000 hours weigh a little over a tonne and cruise at around 1.100 rpm these days.

 

Increasing power from standard is going the wrong way for aircraft if you don't want constant forced landings.

 

 

[damkia]

Good example BoinkLong distance trucks, which need a life cycle to in-frame rebuild time of around 10,000 hours weigh a little over a tonne and cruise at around 1.100 rpm these days.

Increasing power from standard is going the wrong way for aircraft if you don't want constant forced landings.

No problem, facthunter.

 

 

[turboplanner]

Brainfade moment

 

 

[boingk]

Not necessarily.It may well be the upper limit of what the engine could take due to the heavier reciprocating masses involved, when combined with the limits of metallurgy/technology of the rest of the structure of the engine. You could probably get more out of the engine but you would need to add weight in the fixed parts of the engine to strengthen it.

 

A more realistic measure would be how many thousand hours per hp per kg engine weight (apologies for the mix of measurements)

 

Motorbike engines tend to be towards this end of the reliability scale, rather than the ability to go for thousands of hours like aircraft engines (and diesels). Something has to give in the big equations....

Definitely, every engine design has a maximum optimal output before things start going 'boom' prematurely. Hell, you can even get different opinions on what 'prematurely' is... such as the guys with Cassut air racers that get 200 hours out of an o-200 conversion thundering along at 140kt and 3200rpm. Given the state of tune, design of the engine and its usage (ie mostly high throttle settings) 200 hours is acceptable.

 

As for motorcycles, they actually tend to be very nicely engineered. Average road speed for most vehicles in Australia over their lifetime is around 60 to 80kmh. Calling it 70kmh, that gives you around 1500 hours of time before you hit 100,000km on the odometer. Many motorcycles I know have acheived this with nothing more than routine servicing - the ones that aren't are usually neglected or simply thrashed at the racetrack until something gives. It is certainly within standard manufactuerer design limits. BMW in particular has a working design lifespan of something like 500,000km for its modern big aircooled twins - 7500 hours run time at 70kmh. Motorcycle engines aren't particularly heavy, either, especially seeing as most modern sport motorcycles tip the scales at a scant 200kg ready to roll.

 

Anywho, my point is that many aircraft engines I have been around seem to be particularly modest in their technical specifications. Rotax 912's seem to be pushing comfortably into the modern era, though, with 100hp from a relatively simple 1.3L engine giving around 75hp/L - more than three times what the A65's put out.

 

As for oils... why would you trust what reps and salespeople tell you? They are *given money* by the *companies that they are promoting products for*... bit of a conflict of interest. I tend to trust what works. In some cases, yes, that is what salespeople and reps are telling you. In many cases I have found it is not.

 

Cheers - boingk

 

 

[damkia]

Definitely, every engine design has a maximum optimal output before things start going 'boom' prematurely. Hell, you can even get different opinions on what 'prematurely' is... such as the guys with Cassut air racers that get 200 hours out of an o-200 conversion thundering along at 140kt and 3200rpm. Given the state of tune, design of the engine and its usage (ie mostly high throttle settings) 200 hours is acceptable.As for motorcycles, they actually tend to be very nicely engineered. Average road speed for most vehicles in Australia over their lifetime is around 60 to 80kmh. Calling it 70kmh, that gives you around 1500 hours of time before you hit 100,000km on the odometer. Many motorcycles I know have acheived this with nothing more than routine servicing - the ones that aren't are usually neglected or simply thrashed at the racetrack until something gives. It is certainly within standard manufactuerer design limits. BMW in particular has a working design lifespan of something like 500,000km for its modern big aircooled twins - 7500 hours run time at 70kmh. Motorcycle engines aren't particularly heavy, either, especially seeing as most modern sport motorcycles tip the scales at a scant 200kg ready to roll.

 

Anywho, my point is that many aircraft engines I have been around seem to be particularly modest in their technical specifications. Rotax 912's seem to be pushing comfortably into the modern era, though, with 100hp from a relatively simple 1.3L engine giving around 75hp/L - more than three times what the A65's put out.

 

Cheers - boingk

Most motorbike motors are only used at the very low end of the hp range (circa 5-10%? on acceleration) for very short periods of time before effectively "idling" in terms of potential power output. Simple maths of power requirements to keep a 100kg rider on a 250 kg bike at 100 km/h including a drag factor of say 0.4 would give you a rough idea. This is clearly evidenced by the 250-350 km/h most modern bikes are capable versus the pottering around at 100km (or as in your assumption, 70 km/h average). Quite literally it is a very lightly loaded scenario. Note that a 1.5t car takes about 15kw to keep it going at approx 100km/h, and a bike has a hell of a lot less weight and frontal area to push through the air.

Compare that with an aircraft engine that is rarely used below 80% of full power...

 

If you subjected the M/C engine to the same test standard as an aircraft engine I think you would see the reliability and effective "TBO" reduced significantly.

 

 

[turboplanner]

Most motorbike motors are only used at the very low end of the hp range (circa 5-10%? on acceleration) for very short periods of time before effectively "idling" in terms of potential power output. Simple maths of power requirements to keep a 100kg rider on a 250 kg bike at 100 km/h including a drag factor of say 0.4 would give you a rough idea. This is clearly evidenced by the 250-350 km/h most modern bikes are capable versus the pottering around at 100km (or as in your assumption, 70 km/h average). Quite literally it is a very lightly loaded scenario. Note that a 1.5t car takes about 15kw to keep it going at approx 100km/h, and a bike has a hell of a lot less weight and frontal area to push through the air.Compare that with an aircraft engine that is rarely used below 80% of full power...

 

If you subjected the M/C engine to the same test standard as an aircraft engine I think you would see the reliability and effective "TBO" reduced significantly.

 

I just guessed the height and width of a motor cycle, and at this frontal area, your figure for power demand at 100 km/hr is roughly the same, but the demand is exponential with speed.

 

So at 140 km/hr or 76 knots air resistance power has jumped to 37 kW - or nearly three times the power demand

 

100 knots is 185 km/hr so power demand is much more again

 

67 knots is still 124 km/hr, requiring nearly twice the power demand

 

However, that's only the power demand to overcome wind resistance.

 

To this power demand you have to add things like alternator, mechanical efficiency, rolling resistance etc. which all take their piece of available power.

 

So depending on the desired cruise speed, a motor bike engine could have to contend with quite a large power demand in an aircraft.

 

What saves the motor cycle's engine on the ground is that power demand is usually intermittent with the engine backing off through the gears and for speed restrictions.

 

Aircraft use is a constant speed demand application, so there is no relief for the engine like there is on a motor cycle. Under those circumstances one of the design issues is to ensure the aircraft application does not exceed what the engine can live with at a constant, heavy load.

 

 

[fly_tornado]

I prefer the comparison between boats and planes, most bike engines are built too light to be effective as plane engines.

 

 

[Gentreau]

There's one company in France who think motorcycle engines make good aircraft engines .....

 

http://www.vija-engines.com/images/2010/ENG%20presentation-2010.html

 

.

 

 

[facthunter]

High performance type engines have never worked in planes. Porsche build great race and endurance engines but their aeroplane engine never made it. The geared Bugatti engines were a disaster too. Honda haven't built one

 

Pumps compressors and boats have the constant load that aeroplanes have. Aircraft engines don't get a rest. They are FLAT out at the beginning for FIVE minutes or so on some engines. This is when the engine is not really warmed up to anything like the temps and heat gradients that it gets to on full power. I'm talking piston engines. Often the engine is used as a heat sink and at full power the temps just keep rising. That is why they have a time limit at certain power outputs

 

HP/ Cu in is usually from 1/2 to 3/4 on an aircooled engine. If you can get the power/weight to 1 HP/ lb you are doing well.. . The motors are specially built for aircraft. While some speed records were established with some aircraft engined cars. Napier etc, driving a car with an aeroplane engine in it, wouldn't be very satisfying or competitive generally.

 

One Mercedes engine prewar had a design life of around 3,000 kms. That doesn't mean it is a BAD engine, just specialised.

 

There is supposed to be a lot of quality control in an aero engine as there is no more metal than necessary, so you have less margin for error. Nev

 

 

[damkia]

There's one company in France who think motorcycle engines make good aircraft engines .....http://www.vija-engines.com/images/2010/ENG presentation-2010.html

.

84 - 88kg (+ exhaust???, wet??? - not noted...) is more than a Rotax and Jabiru for the equivalent HP and both those have the safety of twin spark plugs per cyl...

 

 

[rankamateur]

I prefer the comparison between boats and planes, most bike engines are built too light to be effective as plane engines.

But the propeller is too small on a boat engine, you would never get off the ground!

 

 

[Thruster87]

But the propeller is too small on a boat engine, you would never get off the ground!

Don't be so density about it.

 

 

[M61A1]

There's one company in France who think motorcycle engines make good aircraft engines .....http://www.vija-engines.com/images/2010/ENG presentation-2010.html

.

That looks like my Gixxer engine. I thought about an aero conversion for one of those, but I was thinking about dumping the transmission (which they seem to have kept, and is a lot of weight), and running my prop shaft off the secondary drive gear, which would also provide a good reduction. They are extremely hardy and will take a flogging without breaking. Probably would be wise to run a larger than factory oil cooler as they use a second stage on the oil pump to run a large volume of oil over the heads for cooling, advanced stuff for early '80's.