A.  "912 Trouble? No Problem! - Day after day the phone lines light up with anxious 912 owners, certain that they have invested in a lemon of an engine. It is running poorly, they have checked everything imaginable and soon they turn to me. There are very few ways to make a 912 run poorly, but many have tried and even more have succeeded. I know the clear lines coming off the carburetors sure look like overflow tubes. Why not put a longer line on each carb, tee them together and vent them overboard? Sounds good, looks safe and professional. There’s one small problem - this concept is WRONG, WRONG, WRONG!

"If you have fallen victim to this, don’t feel too bad, you’re not alone. Everyone assumes that the clear lines coming off the carbs are overflow tubes. Wrong! Actually, these lines are air vents that control fuel pressure in the float bowls. They will vent fuel, but very rarely.

"In the event that your installation puts this tube in close proximity to the exhaust system, it’s an easy fix. Get a suitable length of half-inch (I.D.) hose, overlap the open end of the vent tube by one-quarter to one-half inch. Use tie wraps to keep it in place downstream and the vent will work properly. Be sure not to put a tie wrap at the overlap; you need to have the tube sense the same air pressure as the carburetor intake tract.

This has been the most common trouble spot for the 912 installer, and luckily can be remedied rather easily."

Q.  Dear Engine Q&A - I have an idea I’d like to get some feedback on. Currently, all of the liquid-cooled engine installations I’ve seen are cooled by some form of a conventional radiator. The result is a radiator which is always out hanging in the breeze and generating drag.

In the past there have been systems which used the leading edge of the wing for cooling. What if you did the same thing with the top half of your engine cowling?

You’d lay sheet metal about 1/4 inch below the engine cowling, seal up the edges, and pass the water between the two sheets of metal. The advantages are you’re using metal which is already exposed to the outside and so adds zero additional drag. The metal you’re using is already in the airstream of a big fat cooling fan (the prop). Anytime you’d need the cooling, the prop would be running and keeping it cool. The additional weight of the sheet metal would be less than any radiator it replaced. Overall, this should be more effective, lighter cooling than anything I’ve seen to date.

The same scheme could be used to cool the oil on a different part of the cowling.

It would also heat your windshield on cold winter days. - Dan Riebs, Reedsburg, WI

A. Dear Dan - Hmmm, some interesting thoughts! Let’s see what other readers have to say. - M.J.

Q.  Dear Engine Q&A - Upon picking up a copy of the November ‘95 EXPERIMENTER, I was deeply saddened by Mr. Bertran Copp’s comments concerning the performance of the Corvair motor in an aircraft. From my perspective, the remark, "The hopelessly weak Corvair, rated at 150 hp in a car has 145 ci like the 65 hp Lycoming, and that’s about all it can do." is misleading, grossly oversimplified and indicates a general lack of understanding of the internal combustion engine and aircraft propeller design.

One would have to assume that the particular motor that Mr. Copp was referring to was the 1962-3 turbocharged model. Yes, this particular motor is rates at 150 hp, complete with turbo and at 4400 rpm. Now, I have only been going to Oshkosh for about 10 years (which is honestly a relatively short time), but I have never seen a Corvair motor that was installed on an aircraft with the turbo included. Also, with that motor needing to turn up to 400 rpm to achieve that kind of power, propeller design in a direct drive application would be challenging to say the least.

It is just not a fair comparison to pick the highest output motor of a four-model product line and then say that motor is "hopelessly weak."

NOBODY uses a turbo on a Corvair motor in an aircraft. Nobody uses the 4 carb model, either. It’s just not practical.

However, that same motor without the turbo is rated at 80 hp at 4400, still a somewhat high rpm for a direct drive application. If we take this motor and install a direct drive 60-inch propeller and run the motor at approximately 3000 rpm, the motor will be making about 60 hp.

But that may not be usable. The factory cooling-charging system that is retained by most builders imposes a load of approximately 17 hp on the motor during normal operations at 3300 rpm. This would leave us with 43 hp to pull our airplane along if the stock carbs were retained, but usually they aren’t, so it gets worse from here. Not a very good return considering the 235 lbs. weight of the motor.

The simplest way to increase power output is to just go to a 1964 or later motor. The lower rated output of that time frame is 95 hp. Primarily because the cid was increased to 164. That model is a few pounds lighter and easier to find.

There are many options available to anyone wanting to tap into the Corvair motor’s generally unused potential. The more you invest (not necessarily monetary), the greater the return. More information on this is available.

Back to Mr. Copp’s comments, it is important to remember in comparing the 750 Hisso to the O-320 Lycoming that the long stroke Hisso was never designed for hp, but for torque. It was comfortable turning a big prop at a relatively low rpm in a high drag aircraft. On the other hand, the Lycoming was designed for more aerodynamically clean, modern aircraft. It’s not really a question of one motor being "weak" or "strong," but of two good motors doing exactly what they were designed to do. How weak would a two-stroke motor appear if we bolted a 60-inch prop right on the end of the crankshaft? Obviously, that comparison would be unfair.

Let’s go the other way with the Corvair motor. Suppose that we take a 164 cid turbocharged model rated at 180 hp at 4000 rpm with 265 foot pounds of torque at 3200 rpm. Then we install a PSRU with a ratio of 2:1. We will use an eight-foot prop, with the motor rpm of 3200 to 3500. This powerplant would easily pull any airplane that the Hisso ever did. I know just as sure as God made little green apples, that this powerplant would generate more than 650 lbs. of thrust, no problem. Every motor is built with a purpose in mind at the time of engineering. The Corvair motor is no exception. The designers never envisioned this short stroke motor being used direct drive. It can do it, but it may not be able to do it well.

There is a tendency in the aviation community to want to sort and file everything, as if this motor is good and that one is bad. I can’t help but think that we are shooting ourselves in the foot when we do that. We must try to look beyond the "motor of the month" mentality and see each potential powerplant (and plane for that matter) for how it would perform in any given task that we may be asking it to achieve.

For instance, there is one type of powerplant that is extremely popular, yet it seems to have a relatively high failure rate. I know where there is a former Oshkosh grand champion light plane just sitting in storage. It’s owner will not give the powerplant manufacturer one more dime of his money for repair parts. He has had the motor repaired several times, and he’s just disgusted. We are all proud to be members of the Experimental Aircraft Association, but still in some areas true experimentation is the deviation and not the accepted practice.

One motor is heavy, while another is light. Still another tends to have carb icing problems, while its counterpart has a problem with sticking valves. Some have very low tbo’s; others seem to run forever. But none of them are perfect, and any of them will quit without warning. To beat any of them up is futile because it is really a question of matching up advantages versus shortcomings relative to any particular application.

Very fortunately for all of us, we are currently living in a time frame where information has never been more readily available. Custom machining can be had in most any small town in America. We are in the midst of a very fertile timeframe for aircraft construction and alternative powerplant research. But we must be sure to guard against complacency if we are every going to realize our full potential.

Thank you very much for the opportunity to be heard. - Rich Dietrich, Morrice, Michigan

Q. Dear Don (Bouchard) - I would like to have your opinion on turbo-charged direct drive Subaru engines (EXPERIMENTER January, ‘95, p. 45), versus the same engine with a reduction drive and normal aspiration. How do you think they would compare in cost, performance and complexity?

Also, is it possible to find and use a more compact (brick-shaped, like an oil cooler) radiator for the Subaru, as I plan to install mine in or under the wing.

I look forward to your column every month. (Editor’s note: Enclosed with Mr. Girard’s letter was the following newsletter excerpt written by Reg Clarke regarding his experiences with a turbo-charged Subaru.)

"Due to the many inquiries I have had from all over I felt perhaps you would be interested in this information on my experiments with an E81 Subaru turbo charged direct drive plane. I own a Dragonfly Mark II which previously had a VW engine in it. I was looking for a more reliable and stronger engine that could be turbocharged safely, therefore I installed a used E81 with approximately 30,000 miles on it. I flew it direct drive and no turbo.

"I found the power to be the same as the 1835 cc VW. Advantages are: quieter, smoother, and less fuel burn. Then I installed a used turbo, flew it to Arlington and back, it ran great. I then flew it to a Dragonfly-Quickie fly-in in Kansas in September ‘93; again it ran A-1. The direct drive works great because we are using a shorter prop, 54-inch. Cruise speed is now 170 mph. The VW was 145 cruise.

"Since the fly-in, there have been numerous phone calls from the U.S., Netherlands, Australia and Canada about the direct drive turbo charged Subaru. We have made a video showing how to zero time, balance and blue print. Also a second video showing how to convert from auto to aircraft plus all modifications and installation of engine firewall forward. We are aiming at the numerous homebuilts that could use this information. This Subaru has plenty of power without turbo and can be run with a reduction system. The reason I went to turbo is so I could run direct drive at lower rpm which translates to engine longevity and high altitude power. . . . We are presently building engines for anyone who might want one or our videos.

"P.S., I had logged over 100 hours on the engine and that was with high compression pistons. I then took the engine apart and plasti-guaged all bearings for any wear and found none at all. Also checked for cylinder scoring and there was none. Crank was still at factory specs. I could have just put it back together, but decided to rebuild. I have now totally rebuilt it using turbo pistons and a new water-cooled turbo." -

Pierre Girard, Mississauga, Ontario

A. Dear Pierre - Regarding the turbo-charged direct drive Subaru engine, reading the article you enclosed about Mr. Clarke from Wetaskiwin, he certainly seems to have it all together on the turbo charged conversion for the Subaru, which is very impressive. He does a beautiful job! I’m glad he’s sharing his experiences.

Regarding your question on direct drive, you would use a shorter prop because of tip speed and would give you around 350-400 lbs. of thrust. With redrive, it would allow you to use a longer prop and also allow the engine to increase rpm to be more efficient in its hp range. The cost would be more with redrive.

The radiator to use, if you have room, is off a VW Rabbit; it’s lightweight. For the oil cooler, you could use a motorcycle oil cooler.

Mr. Clarke’s video would be a great help to you. I hope I’ve answered your other questions. - Don

Editor’s Note - For others interested in the video from Mr. Clarke, his address is: Air Ryder Manufacturing, Inc., Box 6896, Wetaskiwin, Alberta, Canada T9A 2G5, phone/fax 403/352-5001.

 
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