Why hasn't a simple carb balance been engineered?

[Buckaroo]

What would happen if the ratio were changed to allow 2600 rpm?????

[gbigs]

Great post Fred! Now with all things taken into consideration I wonder which engine would go longer? I'll bet Rotax! Water cooled heads, tighter tolerances, less pressure impulses and the biggest reason it's what I currently own!

 

The Continental 550 has a 2200 hour TBO.  The Rotax 912 has a 2000 hour TBO.

[ctfarmer]

What actaully does limit life on each engine.

An example. As i understand, the dog drive system in the rotax sheds metal. That is a life limiting issue for the whole engine. Not only for the gearbox but the engine on account of oil contamination.

Reciprocating masses per se, large or small, don't in themselves affect component life. Stresses, vibration and other design related matters do. It is a fact that large pistons and bores can have proportionally greater wear before compression loss and oil use appears. But design, metallurgy and better lubricants have pushed those far into the background compared to even 30 years ago.

It worth noting that larger or heavier pistons stopping and starting dont waste more energy. It's like a pendulum. A piston returns energy on the slow down which is taken up again on the speed up. And friction results in waste by virtue of movement, not acceleration.

[ct9000]

At Rotax school we worked on an engine with over 4500hrs. that had only an oil leak as the reason for work on it but the owner decided to have it overhauled anyway . It still showed the crosshatch pattern in the bores . My first 912 I put over 1000hrs on it , it already had 700hrs since overhaul  ( it was 1200hrs TBO back then ) and it was as new condition inside . My CTSW I put approx. 1000hrs on and no problems . I believe from asking around that the average Lyc. or Cont. does not make TBO without work when in private use . They normally get to TBO ok only in commercial situations where they get lots of hours in a short time - always warm . 

[gbigs]

At Rotax school we worked on an engine with over 4500hrs. that had only an oil leak as the reason for work on it but the owner decided to have it overhauled anyway . It still showed the crosshatch pattern in the bores . My first 912 I put over 1000hrs on it , it already had 700hrs since overhaul  ( it was 1200hrs TBO back then ) and it was as new condition inside . My CTSW I put approx. 1000hrs on and no problems . I believe from asking around that the average Lyc. or Cont. does not make TBO without work when in private use . They normally get to TBO ok only in commercial situations where they get lots of hours in a short time - always warm . 

 

Let's see some data on the claim Continental engines don't make TBO.   There are anectdotal stories for all three engine makes.  Rotax engines are perfectly capable of frying with abuse and poor maintenance too.

[Doug G.]

Hmm... think you touched a nerve on our Cirrus owning friend.

[Buckaroo]

????????????

[FredG]

CTfarmer - thanks for the clarification re. piston mass and engine power.

[Tom Baker]

What would happen if the ratio were changed to allow 2600 rpm?

The propeller would be less efficient, and make more noise.

[Buckaroo]

The propeller would be less efficient, and make more noise.

That's interesting but based on what study?

[Tom Baker]

Let's see some data on the claim Continental engines don't make TBO.   There are anectdotal stories for all three engine makes.  Rotax engines are perfectly capable of frying with abuse and poor maintenance too.

 

Based on 30+ years working as a aircraft mechanic, it has been my experience that the big Continentals will need cylinder work before reaching TBO. The bottom end of the engine will likely be okay.

Lycoming can have problems with the bottom end and less likely with the cylinders, but the cylinders are not completely immune to problems.

[Tom Baker]

That's interesting but based on what study?

I don't have a specific study to quote, but I'm certain you could find one if you want to do the search.

[Roger Lee]

I agree that many Cont. & Lycomings need a top end job before TBO. Some of this has to do with using 100LL. A top end job on a Rotax before TBO is rare and usually caused be extensive use of 100LL and or the wrong oil and or filter use.

[Buckaroo]

I'm googling as we speak. I'm sure Rotax tested every variation of ratio, prop pitch, size etc. it be fun to read those tests.

 

I'm guessing that with more aggressive ratios and prop tweaking they found things get wild like vibes, heat, engine life, noise, effeciancy problems etc.

 

If I find something interesting I'll share.

[Buckaroo]

Somebody told me they use Rotax in military drones. He said they go thousands of hours with very little maintenance.

 

Anyone know about this?

[Doug G.]

Yes, the Predator uses a Rotax engine. I believe it is a 914. I don't know anything about the longevity, but I would not be surprised with teams dedicated to their maintenance and the type of flying they do.

(The local Air Guard flys them everywhere in the world. They have Reapers at our local airport and are working on approval from the FAA to fly them in the pattern for training. They currently use the Air Base in Grand Forks. The Reapers and FedEx putting an air terminal here will probably move us from class D to class C. At least that is the rumor.)

[Buckaroo]

Maybe when they switch to fuel cells we'll find an abundance of boxed brand new 914 engines for cheap!????

[Roger Lee]

Rotax used to supply a lot of 914's to the military. They look nothing like we get. They are very stripped down to a bare minimum and then the military modifies them. The military has cut way back on Rotax orders and are moving towards diesel engines. They don't want to handle two fuels and the diesels can stay in air much longer. If I remember right the military rebuilds the engine once, but after it gets to the second TBO they toss them in the garbage.

 

Coppercity here on the forum works directly with them. Maybe he can chime in and make corrections here or give more info.

[gbigs]

Somebody told me they use Rotax in military drones. He said they go thousands of hours with very little maintenance.

 

Anyone know about this?

 

A Rotax 914 turbo was used in predator drones up until last year.  The military does not want to use them anymore because they do not want to stock 100LL.   Again, Rotax makes a good engine but it is not markedly better than a Continental or Lycoming if maintenance and care are equal. 

[Tom Baker]

A Rotax 914 turbo was used in predator drones up until last year.  The military does not want to use them anymore because they do not want to stock 100LL.   Again, Rotax makes a good engine but it is not markedly better than a Continental or Lycoming if maintenance and care are equal. 

 

Even with the best care available I would bet that your Continental doesn't make it to TBO without needing cylinder repair or replacement of some type. It is simply normal and accepted for these engines.

[Runtoeat]

Anectodal....my neighbor A&P fixes a lot of Continental, Lycoming and Franklin engines.  In the last 10 years, he has not worked on one of these engines because it has reached TBO.  He does a lot of work replacing/repairing cyinders before these engines reach TBO.  Burnt valves, worn rings and worn out valve guides.  

[gbigs]

Tens of thousands of TCM and Lycomings in operation, a few hundred Rotax engines.  How these engines are operated and maintained dictates the life of an engine, not the make.

 

Both Lycoming and Continental say the most important key to a long engine life is flying frequently. Commercial operators, who fly frequently, fly long past TBO routinely. Aircraft that are not operated for days or weeks at a time can collect moisture causing a loss of effectiveness in the oil layer and rust forms. Corrosion in the engine is the leading cause of diminished engine life.  This is especially true of aircraft not hangared.

 

With Lean of Peak operations, the pilot has a lot of control; regardless of the engine they fly.  Keeping CHTs under control is a big factor in engine life (below 400f for TCM).   Does the CT have a mixture control?  We know the 912iS fuel management tries to strike a balance in fuel managment/CHTs, which may not always be optimal.

 

Preventative actions such as oil analysis, oil consumption tracking, regular oil changes, compression checks, cylinder bore inspections, and baffle inspections can add to engine life.  Those that forgo regular maintence may not catch a problem early and thus destroy their engines prematurely.

 

A majority of engines (including Rotax) do not reach TBO.  This is more likely attributed to the above factors, especially the infrequent flying scenarios.  Lycoming adds 200 hours to their engine TBOs if the engine is run more than 40 hours per month for example.

 

Here are 8 tips to making sure your engine reaches TBO:   http://blog.aeroinstock.com/tbo

[Roger Lee]

"a few hundred Rotax engines"

 

How many.  50K engines with 5 million run hours and BRP /  Rotax has been making engines since the 1920's and the 912 since late 1989. They supply 80-85% of the world's small aircraft engines. 

 

"A majority of engines (including Rotax) do not reach TBO."

 

Actually this isn't true. Most Rotax do reach TBO

 

"Does the CT have a mixture control?"

 

It doesn't need it. just like most motorcycles without fuel injection.

[Tom Baker]

Gbigs, you are the one who brought up TBO in this conversation. No one has said the Continentals won't make it to TBO, what has been said is that they will need cylinder repair before they get there. Having cylinder work done, does not mean the engine did not make it to TBO. Lycoming and Continental engines are more likely to need cylinder repair to be able to reach TBO, compared to Rotax.

[ct9000]

When I started flying (with a 912 ) I thought that an engine that revs. at these speeds will not last and in fact must be some sort of hand grenade .However after a while you get used to the fact that these 912 engines just keep on singing along for a very long time with little problems . Then you learn more , go to Rotax school , overhaul a couple , realise that technology has come a long way have a different viewpoint and so on . Fly a 912 for a couple of thousand hrs. you can't help but be impressed .