New engine question

[JayT]

Sorry if this is a silly question, but...

Is it possible to install IO-520's on a pressurized '73 or later model?

If so, would this be easier/less expensive to maintain than turbos?

Thanks in advance

Jay

[Ernie Martin]

Take a look at a thread titled "Different engines possible?". BTW, it's always a good idea to do a Search of this forum to see if your question has been answered before.

The following are excerpts from that thread, where someone asked a question similar to yours.

Roger answered, in part: I've always had a bit of a problem with various "rocket scientists" scabbing "better ideas" onto Skymasters. Inevitably the scabbed on projects either fail to live up to the hype, or end up literally crashing and burning into yet another pile of metal.

I added: I have an MS in engineering from Caltech, spent 30 years in the aerospace industry and have consulted for both GE and the FAA. And one thing missing from any discussion in this Message Board -- not just this thread but the whole Message Board -- is "Systems Engineering". The aircraft as a whole is a "system". Everything is interelated. It was designed as a system. Change one item and it affects everything else. Often adversely. Change the engine and it affects the loads on the airframe, on the prop, on the prop governor -- maybe even the harness.

None of us has the money or resources to make sure that a change in one area will not adversely affect another area. So it doesn't get checked. Or it gets checked poorly.

I read this thread when it started and I wanted to jump in and say "are you crazy?" I didn't because I'm one of the site administrators and did not want to discourage full discourse. But now that Roger voiced his views I wanted to say "save not only the money but also the grief".

Before I went into engineering I spent five years in a business that souped up cars for racing. The typical client had limited resources. So he changed the carb from a 2-barrel to a 4-barrel. Never was the desired performance achieved. The compression ratio, cam timing, valve size and exhaust system -- which were designed for the 2-barrel -- remained, so there was now lots of fuel but the combustion efficiency sucked. Even clients who modified the whole engine ended up unhappy. Yes, the engine was a rocket but the drivetrain (transmission, rear axle, etc.) was designed for the wimpy engine, so elements of it kept failing.

Your safest aircraft is a well maintained certified aircraft. Limit your changes to the avionics suite.

Further questions and responses dealt with engines that were STC'd for the Skymaster (such as the Riley Rocket and AirScan Skymasters), and I was asked whether I would find these acceptable. My response follows: A different engine with significantly greater horsepower or one with radically different characteristics (read: diesel powered and water cooled) would be acceptable to me only if there have been dozens of such installations spanning several years and they have been without trouble.

Two other thoughts.

First, it's possible that I'm more conservative than most, because a) I fly mostly my family and principally over water, and b) I spent 19 years on communications satellites, where the designs had to be perfect since you can't fix a satellite once in orbit.

Second, my opinion is based not just on good engineering principles, but on hands-on observations. When you look in the area of the rear engine, you see how cramped and well designed are all of the elements associated with the engine. The engineering effort that went into the design of all mounts, control cables, hoses, etc., must have cost millions in 1960s dollars, and I just cannot believed that kind of robust design can come from an STC. Just think of the consequences if a throttle control cable fails on take-off or landing, because the STC design gave short thrift to that element. And you, being an early user, are the guinea pig.

Not for me. I'm not a test pilot.

In the thread "Another question about alternative engines" I posted an image of the baffling used to keep all of the cylinders at the proper temperature, to give you an idea of the huge design effort spent by Cessna just in baffling. Take a look at the image and ask yourself if an STC would have an equally robust design.

My apologies for the long answer.

Ernie

[hharney]

Ernie, why no link to the thread you copied above? Also you referred to an image?

JayT
My thoughts on your question; I understand you question is in consideration to a NON-TURBO 520 conversion. There are a couple STC's out there for the bigger engines but as far as I know they all utilize the TURBO version of the 520 and 550 engines. You would be far ahead to purchase a Riley Super Skyrocket than to wait or develop a conversion for a normal aspirated big engine. I have seen some really low prices on the Riley converted aircraft lately. Don't think we will be seeing any new conversions in the near or distant future for the Skymaster.

[Ernie Martin]

Here's the link to the first thread: http://www.337skymaster.com/messages...ead.php?t=2888

And here's the second thread cited, with the baffling image on the fifth message:
http://www.337skymaster.com/messages...ead.php?t=3505

Ernie

[JayT]

Ernie

Great answer, I certainly understand the concept of unintended consequences.

Herb, I have seen some of the Riley's for sale, thanks.

Ernie, do you feel the Riley's fit into your above reply too?

Thanks guys

[Ernie Martin]

I have never looked at or know much about the Riley, so I don't have an opinion. Of the large-scale STCs for the Skymaster it seems to have been the most successful. Perhaps it's a question you should pose to others in this forum with Riley experience. If you get a large enough sample (say, 10?) and it's predominantly positive, then I would consider it. But make no mistake, for me it would always be second-fiddle to a well-maintained standard Skymaster, because for the flying I do (no mountains, short hops) a Riley would add little. For others a Riley may provide a significant benefit, and should be considered if owners with Riley experience are generally satisfied.

Ernie

[Ernie Martin]

Sorry to beat a dead horse, but another point occurred to me. If you limit yourself to adding a bigger engine, what useful load are you left with? Might your aircraft, certified for 6 people, become a two seater? It's not just the heavier engine but the additional fuel required.

Ernie

[JayT]

Ernie

I totally see your points, of course everything is a trade off.