Author: eaainc@... Time: Sun Jan 20, 2002 7:12 am PST Link
In a message dated 1/19/02 7:00:24 PM Pacific Standard Time,
zrxordeath@a... writes:
> 1) Design. This is simple, if you need an engine to produce maximum torque
> at low RPM (like 2700), You don't engineer a short stroke, high revving
> engine for the job,
>
> And why then did ROTAX design the 912 and 914 this way? They now sell more
> aircraft engines than anyone I can think of. The engine is smooth and very
> light. Continentals new series of Tierra engines were going this route as
> well.
You would use a large displacement, relatively long > stroke engine,
Very old fashion and outdated way of doing things. Short stroked and
> balanced engines have the same or higher life expectancy if water cooled and
> operate under less internal stress and much smoother. I am not taking
> about 12,000 RPM motorcycles but rather 3-4800 RPM opposed 4 cylinder
> engines with 5 main bearings in 11" of crankshaft and a 18 LB flywheel.
and keep the piston speed well below the theoretical limit of
>
> 4000 feet per minute.(ok, engineer types, check me on that, school was 10
> years ago, might be 3000, LOL)
The piston speed of the Lycoming is close to that of the Subaru due to the
Lycomings long stroke so this is not an issue. The internal tolerances of
the Lycoming are not even close to that of the Subaru and the water-cooled
engine has reasonable cylinder head temperatures and don't have to run with
choked bores and 400 degrees F head temps. as a design compromise.
> 2) Liquid cooling, and belt driven overhead cams are great, but they offer
> 2
> extra points of failure. Most of the engine failures I have seen on modern
> engines are related to failed cam drive belts.
>
> When I see statements like these, just thrown out for the aviation world to
> read, brainwashing builders not to try something new, due to these half
> truths written from a negative viewpoint only and don't shine any light on
> the positives, I feel obligated to respond. If the cam belt is the
> strongest argument against using this type of engine, well I have good
> news. Car manufacturers have learned a lot as well on this. Belts are now
> reinforced with Armid fibers (Kevlar) and therefore are strong enough to
> lift a house. We don't replace the belts every year during the annual
> inspection because it is overkill. People just don't fly enough to even
> wear off the factory lettering on the belts. But this could be done,
> replacing the belt during the annual inspection every year would also give
> you the opportunity to spin the idler pulleys by hand to check for proper
> operation. The belt can be replaced in 15 minutes in the airplane. It is
> very accessible behind the engine and not the kind of job it would be if
> the engine was still in the car.
>
> The water cooling is very safe and obviously should not be compared with
> that found in cars, even though modern cars are reliable as if maintained.
> In an aircraft, rubber hoses are replaced with silicone and the diameter is
> less than half for great strength and long life. Clamps are expensive band
> type and not the worm-drive type. The oil cooler provide 35% of the total
> cooling so even if a total liquid cooling system failure were to happen,
> the engine could be operated at reduced power for a long time.
You break one of these, its
>
> All over, you are landing. Soon. This is usually due to a lack of
> preventive
> maintainance, but I have seen new ones fail too. And, there is no highly
> inspected aviation grade alternative, its Shucks, or the dealer.. I
> recently
> looked at a Lycoming in the shop that had eaten one of its exhaust valve
> guides, and probably the valve too. It was still running, And we just had a
> Lacair 4 make an emergency landing yesterday outside the door from breaking
> the crankshaft in flight ???? This engine was designed for aircraft use
> and the crankshaft just breaks? and got the owner
> back to the airport. You won't get that from an equivalent failure in a
> subaru, at 5500 RPM. Here is a great example of you throwing out negative
> information. By saying nothing more than 5500 RPM, you are conveying to
> those trying to make an educated decision, that the Subaru has to run at
> this RPM to fly. This is not true, the Subaru engine have the capability
> of operating at this RPM (I have test flown my engines and gear drives to
> 7000 RPM) but a normal flight situation is 3000-3900 RPM. Holed pistons,
> and bent valves, are the order of the day
> here. I'm not real keen on the idea of electronic ignition, every seen a
> battery break a plate? 10 volts wont do good things for your spark, a
> magneto
> driven engine dosen't care. An over-volt will fry the little black box real
>
> quick, too. Wow, and on we go??? Ever heard of dual battery systems and
> over voltage protection? The Subaru ECU would operate to 36V and as low as
> 9V.
>
> 3) Another member mentioned something about the bearing at the front of a
> Lycoming. This is a very good point. An automotive engine's crank is not
> subjected to much side load at all. I would think the asymetrical thrust
> produced by a propeller, would put a hell of a side load on the crank, that
>
> was never anticipated by the designer. A gear reduction would dampen this,
> but I ASSume There you go, yes you are assuming a bunch of things while
> writing this. You first introduce yourself and back up your credibility by
> stating that you have done a lot of work on engines, and then you throw out
> all of this non substantiated and speculative negative information that has
> kept aviation from moving forward for 50 years. Oh, yes, about the
> engines. Did I mention the Lancair 4 that broke the crank? Well,
> "Aircraft" engines have a terrible design in that they have to drive a
> propeller at the front of something that further aft has tremendous
> reciprocating motion introduced to it. I don't care how big of a front
> bearing you put on it, it there are harmonics going through the shaft like
> you would not believe. Why do you think it is so critical to only run with
> an approved propeller? The engine will see all of the funny forces the
> propeller is capable of generating. All of the thrust forces and all of
> the radial / gyroscopic / centrifugal forces. In the Subaru installation,
> all the engine has to do is turn. It was designed to turn and that is what
> it does, it turns. Very few of the forces generated by the propeller can
> reach the engine crankshaft. The only connection between the crank and the
> reduction drive is through a 2" long splined shaft. This shaft drives the
> input gear of the reduction drive. The drive is fully enclosed, has it's
> own oil supply and does not use a single sealed bearing. All propeller
> forces are handled by the drive unit. The reciprocating motion from the
> engine is transformed into rotary motion and then dampened by a 18 LB
> flywheel (Never saw one on a bike or Lycoming) to further help the engine
> achieve a long life. The flywheel spins 1.82 X faster than the propeller
> so tremendous force is developed. The carbon fiber propeller blades only
> weigh a few pounds each and are no mach for the inertia built up in the
> spinning flywheel. the reduction unit uses a sealed ball bearing on the
> output
> shaft. No I have seen too many dirtbike engines that spit the cage from the
>
> crank bearing race, to be too excited over having one of these on my plane.
> So now we are comparing 2 stroke very high rev. engines to the Subaru. I
> now know that you have never seen the internals of the Subaru engine. So
> why then this letter???
>
> 4) I am eagerly awaiting the introduction of a well tested, lightweight
> diesel engine for aircraft, this seems like a perfect solution! Maybe I am
> missing something obvious, as to why there isnt one already, but it sure
> seems like the answer to me! In the meantime, I will hopefully be able to
> buy
> a 0-360, and put it on the nose of my plane. I am accepting donations from
> guys upgrading to Subarus, I will happily take your old Lycoming..He he
> he..
> I could ramble on, but I'm not sure if there is a limit to the amount of
> space I should take up here, I am brand new to this posting thing as well
> :)
> Take care guys, and good luck on those RVS!! Kyle
Great to have you and I am happy that we can talk about the different angles.
Jan Eggenfellner <A HREF="http://www.subaruaircraft.com/">www.subaruaircraft.com</A
[Non-text portions of this message have been removed]
Author: "wallaceenga" <wallaceenga@...> Time: Sun Jan 20, 2002 12:15 pm PST Link
--- In RV7and7A@y..., eaainc@a... wrote:
Hi Jon
Have to tell you, that your reasoned factual responses to shoot
down the "experts" with their myths on the Subaru engine conversion,
definitely does make my day.
Still chuckling over your last couple of responses :)
Now get back to work making them.
Wally Enga
RV-7 QuickBuild
N757E (Reserved)