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A little gem about the Rotax 912

I would agree with pretty much everything FAA Inspector says in his comment. There are many down sides to this little engine.
 
I think if "FAA Inspector" is that concerned, he should probably not buy a Rotax 912 series engine.

The 912 series have been around long enough, and there are enough in production (and flying) that I think if the so-called "downsides" were real issues, we'd be hearing a lot about them. I think there are some real misconceptions "Inspector's" epistle, like his understanding of the alternator and regulator and whether you can design an engine to run reliably at higher RPM than a desk fan. But, as he says, it's all his opinion and everyone is welcome to theirs.

Yes, they are different than Lycomings and Continentals. The overhaul and repair procedures are different. The design philosophy is certainly different. That doesn't mean they are something to regard with fear and trepidation, but if you do, well, by all means go buy an O-200D. For the rest of us, despite their obvious differences from more traditional GA piston engines, it's hard to argue with the demonstrated success over the past few decades.
 
Decent overview on the 912 engines if a bit long.

Couple points on the video:

The Continental O-200 is not a dry sumped engine, it simply has an odd shaped oil pan.

The maximum boiling point of a water/ EG mix is not reached at 50/50, it's reached at 100% EG 0% water. Evans non-aqueous PG coolant is little different in characteristics from 100% EG coolant but a ton more expensive.
 
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I think if "FAA Inspector" is that concerned, he should probably not buy a Rotax 912 series engine.

The 912 series have been around long enough, and there are enough in production (and flying) that I think if the so-called "downsides" were real issues, we'd be hearing a lot about them. I think there are some real misconceptions "Inspector's" epistle, like his understanding of the alternator and regulator and whether you can design an engine to run reliably at higher RPM than a desk fan. But, as he says, it's all his opinion and everyone is welcome to theirs.

Yes, they are different than Lycomings and Continentals. The overhaul and repair procedures are different. The design philosophy is certainly different. That doesn't mean they are something to regard with fear and trepidation, but if you do, well, by all means go buy an O-200D. For the rest of us, despite their obvious differences from more traditional GA piston engines, it's hard to argue with the demonstrated success over the past few decades.

Well said. The piston speed is not much different between a Lyc 360 at 2700 rpm and a 912 at 5500 rpm. Combine this with similar barrel and piston expansion rates, Nikasil bores and liquid cooled heads which keep the heads well below any temperature where strength may be affected and guess what? They last just fine as Lockwood said.
 
I haven't watched the whole presentation yet, but I wonder if this FAA inspector might be like a lot of motorcyclists that think that Harley Davidson (Lycoming/Continential) is the only "real" motorcycle. ;) After all their design is about the same vintage. And yes I have owned a Harley and I loved it! Along with a lot of the "less vintage" motorcycles that I've owned. :)

Jim
 
After all their design is about the same vintage.
Kinda sorta but not really. The general layout may show its heritage, but at least Harley has advanced their technology. Even my 14 year old H-D has electronic fuel injection, and a few years later they started using water cooling in the hot parts of the heads. It's driven by emission requirements. They have to burn leaner and leaner to meet emission regs, and that makes it run hotter and hotter (here we go with that again, right?) and requires better control of mixture and timing. I haven't kept up enough to know if they now run closed loop; mine is open loop.

My pickup is a full size crew cab land yacht that will seat six in glorious comfort and weighs over 2-1/2 tons empty. They manage to get 365 HP out of a 3.5 liter V6 with twin turbos, and the speed limiter is easy to hit if you're, umm, "spirited" with it. Times change. It's been 100.0% reliable with zero repairs or adjustments since the day I bought it new in early 2011. If you'd told me that in the 80s I'd have laughed at you.

The presentation was Mike Bush talking about how, by golly, this new Rotax engine is pretty good. Welcome to 2017, Mike. :) The other stuff was just some anonymous guy posting his opinions on Youtube.
 
Prop drag?

I enjoyed the presentation, thanks for posting. I found it a helpful instructional as to what the Rotax, maintenence, and it's install is about.

But which does create the most drag with a damaged engine? (No power)
A freewheeling prop...or one that's stuck in one position?:confused:


Regards,
 
I enjoyed the presentation, thanks for posting. I found it a helpful instructional as to what the Rotax, maintenence, and it's install is about.

But which does create the most drag with a damaged engine? (No power)
A freewheeling prop...or one that's stuck in one position?:confused:


Regards,

My understanding has been that, although perhaps counterintuitive, the best strategy is to try to get the prop stopped (stalled) if you have a dead engine. Reason is that it takes energy to keep it turning (think of the effort needed to start by hand propping). That energy is coming from the air against the prop (drag) and is stealing your airspeed and altitude at the worst possible time while you're trying to get max glide. Seems like I recall at least one POH that said if no luck restarting, then pull up to slow down in an attempt to let the prop stop. Kind of a twofer, you (might) gain some altitude (don't stall!) and get a better glide after it stops.
 
Yes, I have practiced complete engine out landings in the kitfoxes and RV-12's. Letting the prop come to a complete stop does make a difference in drag, and it's considerable smoother, allowing you to concentrate on the landing.
There is no doubt that the engine is NOT producing power.

Vic
 
My understanding has been that, although perhaps counterintuitive, the best strategy is to try to get the prop stopped (stalled) if you have a dead engine. Reason is that it takes energy to keep it turning (think of the effort needed to start by hand propping). That energy is coming from the air against the prop (drag) and is stealing your airspeed and altitude at the worst possible time while you're trying to get max glide. Seems like I recall at least one POH that said if no luck restarting, then pull up to slow down in an attempt to let the prop stop. Kind of a twofer, you (might) gain some altitude (don't stall!) and get a better glide after it stops.

Excellent point, Dave and convincing argument. I just wonder if I would think of it in the quite stressing situation of engine loss? Well, I am not too much concerned, I am flying behind a Rotax 912, not a Lycoming or Continental engine!:D
 
I experienced the same effect in my twin engine days. Feathering a windmilling prop stopped it and produced a noticeable surge forward.

If unable to stop windmilling in a single-engine with a constant speed prop, pulling the control full out results in less drag.
 
But which does create the most drag with a damaged engine? (No power)
A freewheeling prop...or one that's stuck in one position?:confused:
We did the math in University to figure this out, and then I tried it in flight after I got my license and verified it... On a Cessna 150 with a metal prop, and a homebuilt with a wooden prop.

A windmilling, fixed-pitch prop creates about the same drag as a flat disk the same diameter as the prop circle. A stopped prop creates the same drag as a 2x6 the length of your prop. The difference *is* significant, so if you can get it stopped, you'll be better off.

However: Unless you have a wood prop, or maybe composite, it'll be hard to get it to stop turning. A wood prop will stop with only a little loading via pitching up. The metal prop on the Cessna took a very high deck angle and low speed to get the blades to stop moving.

Once it's stopped, you have to rely on engine compression keeping it there. If you've blown a cylinder, or cracked a shaft, and have little or no compression available, you *can't* stop it. If you have a constant speed prop that's gone to coarse pitch, it'll be hard to keep it there as well. And if you get your RV up over 100mph or so in the descent, it's likely that airflow over the blades will start it spinning again.

So yes, there are benefits to stopping it, but there are a lot of practical limitations that might make it not worthwhile.
 
Some years ago ABC WideWorld of Flying did a demonstration with a C-182.
He demonstrated both glide ratios and minimum sink with engine at idle, engine idle with prop in course and fine positions and with the prop stopped.
Results were very impressive. If I'm remembering correctly, delta between engine at idle, prop at fine pitch and prop stopped, the glide improved something like 26%.
I'm pretty sure I still have the tape. I could dig it out and run it again.
 
Since this is the RV-12 forum, I will suggest that the discussion of stopping it doesn't really matter because as is the case with pretty much all RV's with a light weight (wood or composite) propeller it will stop all by itself if the engine quits unless the the airspeed is kept quite high (not likely if you are using best glide speed).

This can be seen in THIS VIDEO.
He mentions slowing to 65 so that the prop will stop, but with the geared engine and low mass (low rotational inertia) prop, I am pretty sure it will still stop at quite a bit higher airspeed.
 
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