Another question about alternative engines

[YankeeClipper]

I am only a student of 25 hours at this point, and while I fully appreciate the need to get more time in single engine, non-complex aircraft first, the Skymaster has remained at my 12 O'clock these last few years. In that time I've read numerous threads about alternative engines that discuss, among other things, what has already been done and the risks of trying to component-engineer new solutions in general. What I haven't read (and perhaps just missed), is discussion about replacing the native power plant with the other IO-360. I am of course referring to the Lycoming.

I understand that this is ten HP shy of the TCM, but with commensurate adjustments to one's mission (e.g. mtow) I'm wondering if there aren't any advantages to this. The weight is about the same, the cylinders fewer (i.e. fewer points of failure), the manufacturer's TBO 33% longer, the rebuild cheaper by about $3-5k. It is also smaller (i.e. more room under the hood). I suppose I could also raise the specter of crankshaft issues but I'll leave that debate to the myriad other threads on the topic. There is also the TIO variant which isn't much larger (same dimensions as the TCM), that returns the aircraft to original power, and has the altitude benefits as well (though not of course the maintenance/cost ones). Finally, folks can go many rounds on this brand vs that, but the digest of many, many hours of reading seem to indicate that they are at least comparable in quality and reliability. If anything, my reading has favored Lycoming ... though again, I'm only a student, and it is only the digest of one man's reading.

My other thoughts:

* with similar performance specs, no torque, vibration, weight distribution changes to airframe

* Needed changes include engine mount redesign and possibly prop offset if fitment in cowling requires it.

So the question is simply, what are your thoughts?

[Ernie Martin]

The engineering, certification and FAA approval would be a MAJOR endeavor, way out of proportion to the benefits, which I view as negligible to none. Then you'd be flying in a one-of-a-kind airplane that didn't benefit from the systems engineering that Cessna put into mating the TCM IO360 with the rest of the airplane. As a very young man I modified cars for racing. They never had the reliability of the factory (read: well engineered) models. The thirty subsequent years in space systems and jet engines reinforced the value of systems engineering. Sorry, but you would be far better off spending your money on a standard Skymaster that has been well maintained, and then keeping the aircraft in top shape.

E

[YankeeClipper]

Thanks for the prompt reply, Ernie.

So tell me, why do you view the benefits as being minimal to none? I get what you're saying about trying to modify engines, but that seems quite different from supplanting one altogether. And in a car, one has the transmission, drive shaft, axle-shaft, and rims & tires to engineer into the system. Then there's the exothermic heat, the cooling, etc. to deal with. But I'm talking about taking out one solution that has been factory engineered to be installed in any number of aircraft, that is much more independent in nature than an automotive engine (I think), and swapping in another.

To be sure, I don't question your logic--I just want to come a little closer to an understanding of these types of aircraft and the dynamics in play.

Thanks again.

[hharney]

First as Ernie indicated the costs of the certification (STC) would be a huge burden to bear let alone having an unknown final cost. Then in order to justify the costs you need an audience to believe in your application. So the believer is not just paying for a new engine but has to pay for the certification burden. To get what? The same performance or reliability. Personally I think the two engines are to similar to really entice someone to pay extra to make the switch. When Jack Riley made the Rockets you were buying a whole new airplane with new avionics, interior, paint, and on and on. These modified Skymasters had a market. I don't know if you have noticed but Skymasters are a dime a dozen compared to 10 years ago. There is hardly a market out there for these slower, gas guzzling light twin engine airplanes. So those of us that have them are just trying keep them in the air and be able to afford some fuel to burn through them once in a while. My use has dropped 50% in the last 6 years just because of fuel costs. I am know operating LOP to justify using the airplane for some trips. There's a lot of Skymasters out there but most of them are idle and folks are not going to spend a lot of money on them.

My Continentals have been fantastic. I would not want to trade them for a shakey Lycoming. The Continentals have always run smoother than the Lycomings. I get way over the published TBO so that indicates that Cessna failed at increasing the TBO as the engines got better. Cessna did not see a market for the Skymaster so why pay more to certify the engines for hight TBO. But the engines will go beyond TBO easily.

If one is going to spend money for better engines then maybe that would be diesel. The future of AvGas is unstable. Shame on Continental and Lycoming for not evolving with the situation we are in now with leaded fuel. They could see it but sat on their hands, my opinion. The Skymaster is a great airplane and those that have them either really love them for what they are or they are burdened with the cost of ownership because they could buy them so cheap. These light twins are very reasonable to buy but are not cheap to maintain and use. If you can't afford to maintain them and use them you are going to have a real burden, an albatross. When this happens the Skymaster ends up deteriorating and it's all over. There are to many of those Skymasters out there. I have searched the FAA registrations quite extensively and there are a lot of Skymasters that have expired registration. It's usually only a matter of time for those airframes to be no longer airworthy or not feasible to get back into the air.

I agree with Ernie, find a clean airframe and pay the extra to find one with every option you want. With the low cost of Skymasters today it's a bargain to buy best one out there. The cheap ones will just cost you more to make equal to the best one out there.

[Ernie Martin]

Herb has largely answered for me. I wouldn't call the Lycoming "shakey", but it's not better, just equal or comparable. The Rileys had a new engine and got added horsepower, so added speed and margin. What does the Lycoming add? TBO? That's an illusion. A properly maintained and operated TCM IO360 lasts just as long between overhauls. So, in my book, you've made a huge investment (I'm going to guess tens of thousands of dollars) and got nothing in return. Well, actually not nothing, you got the potential for lots of headaches. Yeah, unlike cars there is no transmission, U-joints, differentials, suspension and brakes, but there is an entirely new exhaust system, an entirely new motor support assembly (not just motor mounts, but all the tubes and brackets), an entirely new cooling arrangement (just look at the image below to see all the parts -- metal and rubber -- that Cessna designed and tested to ensure proper air flow around the engine). Incidentally, while I show the image as possible headaches if some of the parts are improperly designed (not only allowing some parts of the engine to run too hot or too cold, but maybe breaking because they were designed too weakly), it will also give you an idea of the huge design effort, just in baffling; in fact, maybe my guess of tens of thousanda of dollars is low and it's closer to $100,000.

This mental excercise was fun, and I hope you benefited from our responses, but because I think this is a pie-in-the-sky concept -- huge cost, no payback -- I will sit on the sidelines and let others continue the dialogue.

Ernie

[YankeeClipper]

That diagram reminds me of my 1976 912E. Hugely complex engine pan system. And yes, that does shed quite a bit of light--those engines aren't just "floating" around in there.

As I said, I'm just student--a neophyte really--but the more I understand about the aircraft (and GA aircraft in general) the safer I and my passengers will be. "Exercises" like these are indeed very helpful ways to do just that.

Fair warning: I'm a relentless brain picker.

Thanks again for the input.

[H H]

Cessna came out with a 182 diesel, what do you think ??? Would it work on a 337g??? I know it is $75,000 x 2. Would it be worth it???

[YankeeClipper]

Just the sound of a diesel pounding from within the cowls would be worth it.

[hharney]

It's already been done .....


http://www.337skymaster.com/messages...ghlight=diesel