Which Engine???

[pmccarthy]

Somewhere along the way This thread lost the plot. There is nothing wrong with a Bass Strait crossing, thousands have done it, just be prepared and do the risk assessment.

 

Whoops, I’m the one who lost the plot. Wrong thread. But I think the discussion is anal. Though I wouldn’t do The crossing on a vee wee donk.

 

 

[Jethro Belle]

In my case it was cooling designed for Canada ( at best) on a plane built in South Aus trying to live in Western Qld... I believe cooling was mentioned earlier as a problem with VW installs.. though even the early 'Beetle' suffered a similar fate out here once cooling was compromised ...usually dust. I did 150 hours in 6 months before it succumbing.. but still didn't fail/stop … just slowed down with plenty of warning

Thanks for posting about your ex-Sonerai. It looks/looked like a nice one. Do you believe it is possible to 'cool' any VW enough for service in Australia without derating power output IYO? Academically I am interested about how much the power output from an air-cooled engine (say the 2 L factory rated at ~70hp for intermittent full power and prone to overheating on the road) can be increased for WOT application in an aircraft without the inevitable top end overheating. You can increase power output by increasing BMEP, boring, stroking etc, but you can't change air-cooling fins much, so that limit is built in. Only increased forced/ram air will raise the cooling effectiveness.

 

My experience with road VW beetles and Kombis is WA is that motors failed if you drove them hard for long distances on a hot day. I did it twice, but they were not pristine engines, so not saying all were so prone. I grew up in one of those 1100cc reduction hubs split screens that now fetch a gazzilion dollars, and can't see how such a heap of s$@t has improved that much since then Before I am flamed, it was brilliant in some ways, but it was without doubt a SLOW with a death trap swinging rear axle, drum braked cross-ply shod .... Oh and the carbon monoxide poisoning heater option

 

 

[Bruce Tuncks]

The very first Jabiru engine had a head that looked like a VW head. Every revision of the Jabiru heads has increased the cooling fin size until now those heads look quite different from the VW heads.

 

Those old VW engines in cars had a blower which absorbed a lot of power. But I liked the noise it made. Of course aero versions don't have the blower. I should have been very interested in the CHT's they were getting but in those days I was too young and silly. I don't think they had a CHT gauge.

 

Personally, I would stay away from using one. I know of 2 first-flight disasters with VW engines, but to be fair, the Limbach engine has been ok on motorgliders around here. But one motorglider I know of was much better after changing to a Jabiru engine.

 

 

[turboplanner]

I am interested about how much the power output from an air-cooled engine (say the 2 L factory rated at ~70hp for intermittent full power and prone to overheating on the road) can be increased for WOT application in an aircraft without the inevitable top end overheating.

The diagramme I posted a couple of days ago showed a stable temperature at operating rpm for an engine designed for constant power.

If you think "more power" = "higher compression" = "higher temperature", it follows that you can have some control over the temperature gradient.

 

I all my training, WOT has only been used for the take off phase, and then power is reduced to cruise rpm, or less for approach and landing.

 

So it could be that the 70 hp engine you describe has a climbing temperature during the short take off phase, and would exceed safe temperature if you continued at WOT, or would achieve a stable cruise temperature at cruise revs. The reports could be as simple as some people are trying to wring 70 hp (which you've noted is intermittent), for cruise.

 

You could get a lot more power using racing techniques but at the expense of a lot more fuel consumption and a lot less reliability - that's not the way to go for an aircraft engine where you can't just pull to the side of the road.

 

If you've brought your prerequisite for maximum safety along to engine choice, put a Rotax into it and have it serviced by a qualified person.

 

 

[facthunter]

The Kombi's over revved often . Oil leaks and dust grunge made then run hotter. They frequently broke crankshafts, pulled rocker posts out of heads and dropped valves. The flywheel was held on by a single large bolt. In aircraft they often drive from the front and the prop parts from the aircraft. By the time you make one good ( IF that's really possible) you would have been better making them from scratch. You may glean from my post I'm not a fan They may resemble an aircraft motor but are not really one unless you don't demand much from them. Might power a VP 1 OK. Nev

 

 

[Jethro Belle]

If you've brought your prerequisite for maximum safety along to engine choice, put a Rotax into it and have it serviced by a qualified person.

 

Yes. That was my starting opinion. I wish it wasn't so obvious and boring I hope Jabiru can challenge Rotax, but suspect lengthening the fins any more is chasing diminishing returns and physics rules the day.

 

Rotec water cooled heads on the Jabiru would change the physics. I have found some limited discussions initiated by @Yenn on the Jabiru Engine 2200 Mechanical Problem Reporting but no posts since from anyone using them. Anyone have/heard good reports?

[facthunter]

Just liquid cooling the heads is a part job. As I said earlier I would do it on a pusher but it requires all the extra pipes and radiator cost and complexity. Having a six cylinder engine is a plus. They are much smoother than a four.. Air cooled in an aeroplane has a natural "thing" about it. It saves a lot of problems Running an engine too cool is not efficient either. Setting up the airflow through the cowl is not just making a streamlined cover. Overcool it slightly and make adjustable cowl flaps and use baffles to get the air where it's needed and avoid extra drag .Nev.

 

 

[Jethro Belle]

Having a six cylinder engine is a plus. They are much smoother than a four.. Nev.

Agree about smoothness and desirability. Acquiring a six cylinder Jabiru was a serious consideration me, but when reading about them I came across threads discussing the problems six owners have with uneven temperatures and "thermal shock" from touch and go training! Some where fitting CHT to every cylinder to keep them 'safe'. That is when I became aware of the Rotec WC heads!

 

I think the "thermal shock" discussion was UK based, where they may encounter far colder conditions than average for Australia.

 

 

[facthunter]

Thermal shock as a problem in small motors may be a little over stated. You can't get much worse than feathering an engine in cruise at high altitude and while that may not help them it doesn't usually ruin them either. Para drops and glider launching takes a toll on cylinder heads with some engines but that is an extreme application of full power on extended climb with a large payload to a power cut and steep dive at idle from maybe 8,000 feet.

 

When you have a six you have the extra power usually to increase your climb speed to 80 knots + when it's real hot outside and that is a recommended technique. You don't wait till it gets hot. If the temps are rising a bit quickly do it then. Nev

 

 

[Jethro Belle]

Thermal shock as a problem in small motors may be a little over stated. You can't get much worse than feathering an engine in cruise at high altitude and while that may not help them it doesn't usually ruin them either. Nev

I think it probably is also (more like rapid thermal changes), but clearly there is some issue with at least the older Jabiru heads and the centre cylinders (from memory) of the six, or the 'fixes' would not be dreamed up/ marketed.

 

My reply was pointing out that adding two cylinders seems to make the thermal control more problematic, not better. More is not always better

 

 

[facthunter]

I don't believe the problem is as big as it's made out to be. Jabiru made 8 cylinder flat engines that were cooled the same way in principle as the fours are. Few jabiru engines apply baffles between the cylinders in contrast to MOST other makes that tend to apply them universally. This creates a higher pressure Plenum like space over the entire top of the engine and the baffles regulate and direct the air to the parts as needed depending on how they are orientated. and the gaps control the amount (mass ) of air. Further airflow regulation is done by exit cowl gills/ flap. Nothing new in any of this and once its done properly you don't need temp sensors all over the place. Just select the one cyl you have found to be the hottest Temp indicating paints can be used to check max temp reached.. Nev

 

 

[OZJohn]

I have a friend who flies behind a 6 cyl. Jabiru and does not have any overheating problems if he avoids a certain (narrow) rev range.

 

Sorry can't remember that rev range but could find out.

 

John.

 

 

[facthunter]

There's plenty of them flying around... Not as if they are rare. Nev

 

 

[turboplanner]

Why would yoube trying to swueeze a 6 cyl engine into a CH-701?

 

 

[Jethro Belle]

I have a friend who flies behind a 6 cyl. Jabiru and does not have any overheating problems if he avoids a certain (narrow) rev range. Sorry can't remember that rev range but could find out.John.

Yes please John. I haven't heard overheating in a rev range Keen to learn about real experiences and how problems are avoided by some and not others. Unless Jabiru owners are a different breed to Rotax owners, it can't all be down to maintenance and operational factors (IMHO). My preferred engine would be a reliable Jabiru.

 

A VH registered J430 would allow me to take my children flying and second hand ones are available at 'good' prices, but the engine issues put me off. I suspect the 'good' second hand prices are related to the engine issues. I am unaware of other problems.

 

 

[Jethro Belle]

Why would yoube trying to swueeze a 6 cyl engine into a CH-701?

Yes the starter post was about CH-701 engines. Sorry for subverting the thread to a wider engine discussion

 

 

[turboplanner]

You could just about describe the 701 as a ride-on RC.

 

 

[Yenn]

I know of one owner who fitted Rotec water cooled heads to a Jab, then removed them as they were no improvement.

 

 

[Marty_d]

Why would yoube trying to swueeze a 6 cyl engine into a CH-701?

Only if you want to turn it into a single-seater.

 

You could just about describe the 701 as a ride-on RC.

Oi!

 

 

[turboplanner]

Might have been a slight exaggeration.

 

 

[frank marriott]

Yes please John. I haven't heard overheating in a rev range Keen to learn about real experiences and how problems are avoided by some and not others. Unless Jabiru owners are a different breed to Rotax owners, it can't all be down to maintenance and operational factors (IMHO). My preferred engine would be a reliable Jabiru.A VH registered J430 would allow me to take my children flying and second hand ones are available at 'good' prices, but the engine issues put me off. I suspect the 'good' second hand prices are related to the engine issues. I am unaware of other problems.

Short answer from my experience, they don’t like operating in low RPM range. 2900 - 3000rpm seems to be ideal. In a couple I have flown with full EMS instruments you get differences in temps below about 2900rpm. Use 2900 and plan 25ltrs/hr seems about right (3300 motor) - I have limited exposure to the 2200 motor.

 

 

[Old Koreelah]

...make adjustable cowl flaps and use baffles to get the air where it's needed and avoid extra drag .Nev.

...but make sure you never forget to open them when needed.

 

 

[Jethro Belle]

I know of one owner who fitted Rotec water cooled heads to a Jab, then removed them as they were no improvement.

 

Thanks for confirming @Yenn. I noted your post in #158. I was hoping you may be able to shed more light since it was a while ago. What sort of improvement was expected? Was it a problem with operation due to head quality?

 

After searching more I found the Liquid cooled heads thread which is probably where any reply should be posted (sorry TP). Reading both that thread and Rotec Liquid Cooled Heads for Jabiru Engines clearly indicates that water cooled heads solved overheating problems (

If I do that I would almost certainly use the 3300. But only with LC Heads. I have worked on a 3300 from new , and the struggles we have had with overheating are almost unbelievable

) even for those who felt Rotec quality was very inadequate. The fact that quality sand casting of aluminium is difficult, and requires inert gas blanketing to avoid porosity and other problems, seems to be a major issue (Something D-Motor is struggling with also), but some simple machining quality reports leaves me wondering .

 

Most people seem to claim their system over-cooled! While Nev believes in air-cooled simplicity, he also states that a leaner mixture is possible when heat is not an issue, and so better fuel economy should be possible with LCH, offsetting some of the additional weight. I take it your friend noticed no improvements in fuel economy either?

[skippydiesel]

"Placing equipment in the duct may look neat, but it will be in the highest velocity region = high drag. Ducts around the fuselage doubles the area exposed to high velocity so more drag."

Not in the high velocity air flow - in the actual structure of the duct (utilising what would otherwise be an aerofoil/hollow space) cooling would be from external/slow speed air in front of the duct.

 

"Original turbo-fans were direct drive from the power turbine. Striving for increased efficiency has seen gearboxes added to drive larger bypass fans in the high-bypass designs filling the gap up to turboprops. My understanding is the turbo-props don't do near sub-transonic speeds (probably because the tip speed must be kept subsonic)."

 

I assume that if the engine drives the fan directly (1:1 or close too) the tip speeds would go sonic as in a high bypass jet engine, hence the need for a duct.

[Jethro Belle]

@skippydiesel You seem to have included your reply in my post :-P

 

Not in the high velocity air flow - in the actual structure of the duct (utilising what would otherwise be an aerofoil/hollow space) cooling would be from external/slow speed air in front of the duct.

Good idea, tricky fitting and making.

 

I assume that if the engine drives the fan directly (1:1 or close too) the tip speeds would go sonic as in a high bypass jet engine, hence the need for a duct.

The duct has no bearing on tip speed going supersonic, except maybe accelerating the airspeed making it worse. Even high bypass fans are smaller in diameter than a turboprop equivalent power, so their tip speed is lower. Not sure if gearing is to keep their tip speed down of for efficiency. It is a specialist field & I am not familiar with it.