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|Subj: Little Wing Autogyro|
I have recently become interested in the Little Wing autogyro. I am wondering if you have any direct experience with this machine. More generally, can a Corvair fly in an aircraft that can slow down like the gyro can? Ron Herron, Little Wing's designer and builder, e-mailed me saying his opinion is that the Corvair is too heavy and doesn't put out enough power for its weight, also that it overheats and needs a fan! (Maybe he hasn't had any recent experience...) Thing is, the radial he has on his single-place gyro weighs around the same as the Corvair, but it sits real close to the firewall. He has a two-place that is longer; builders have used the Rotax 914, the Hirth F30 and various VWs. What do you think?
Thanks, Jonathan Cartford, St. Paul, Minnesota, Manual 6417, no airplane, lots of dreams!
|Reply from WW:|
|I have not followed the Little Wing extremely closely, but here's what gyro people who we're friends with share
with us: |
I can assure you that a direct drive Corvair will produce more static thrust than a Rotax 912S. The 914, being turbocharged, is slightly heavier than the 912S and even more expensive. The Rotec radial is a beautiful engine, but again, it's astronomically priced. I haven't seen a Rotec on a scale, but I'm willing to bet a Corvair has a lighter installed weight. You could build three or four very nice Corvair engines for the price of either one of these imported engines.
|Subj: Crank and Cylinders
I took my crankshaft to the shop and it has to be turned .030 under on the rods and .010 on the mains. I've heard several comments saying that using .010/.010 cranks are good, but don't believe I've seen anything on what the limits of a grind are. I see that Clark's has the bearings for them up to .030. Also the cylinders have a .005 taper. Would you recommend boring the minimum (.020) piston or going to .030 for a little larger displacement? I was discussing the crank grinding with the shop when I asked how far they recommended grinding the crank without going thru the nitriting or Tufftrided. He said that crank isn't nitrided anyhow....because it has some rust on it, and nitrided cranks don't rust. Is that correct? I suppose the nitriding was just on the journals only anyhow.
|Blue Skies, Bob Unternaehrer
||Reply from WW:
||Almost every Corvair crankshaft we've dealt with would be perfect if ground .010/.010. I have a lot of flight
time on .010/.010 cranks. I'd be reluctant to fly a .030 under crankshaft. The availability of crankshafts for Corvairs
is so good that I would get another which could be ground only .010/.010. .030 under might work perfectly fine, but
that's a theory, not a flight proven fact. For building your own engine, I suggest you stay within previously tested limits.
The nitriding on Corvair cranks is only a few thousandths of an inch deep. Most crank grinders will tell you that it is ground off by the time you do any type of work other than a light polish. The only Corvair cranks that were nitrided by the factory went into 140hp and turbo engines. Your crank grinder is quite wrong; I have several rusty 140 cranks in the scrap bin awaiting conversion to a mailbox post. The cubic inch difference between a .020 over and a .030 over engine is less than 1cid. That's roughly half a horsepower difference between the two engines, very negligible. In the past, the main reason we bored engines to .060 over was for weight reduction. They are three to four pounds lighter than engines with stock bores. .060 over adds 7cid to a stock engine, and makes a slight difference in power that we can actually measure on the dynamometer. If you have a 1964 engine, we recommend .030 as an overbore, and a 1965-69 engine can run .060 over. In the most recent Corvair Flyer newsletter, we have a bore vs. displacement chart for the nine most popular bores on a Corvair, and a discussion on the combinations and recommendations.
|Subj: Engine teardown
I'm in the process of tearing down, oiling, and bagging the parts of my core engine to preserve it for a future build. After removing all of the headnuts and rocker studs, the heads are still VERY stuck. I hit the heads as hard as I dared from every direction I could get at them using a block of wood and heavy ballpeen hammer, but they just won't come free from the cylinders. Do you have any hints or tips for getting them free without breaking anything?
|Thanks, Douglas Eatman, St. Augustine, FL, No airplane (yet!), Manual #6307
||Reply from WW:
||I'm glad you went straight from Corvair College #8 to purchasing a core. One of the reasons we recommend the best
condition core engines for purchase is the fact that some of the more corroded or stuck engines represent a real challenge
to disassemble. My gang in the shop have given up on only two engines in the past three years. With patience and
perseverance, virtually any engine can be disassembled with minimum harm to the engine, your tools and your fingers.
When a head is reluctant to come off, start by removing the pushrod tubes. Six pushrod tubes with dried out original O-rings
can put a surprising grip on a head. Look in the Clark's catalog or Richard Finch's book to see what a pushrod tube
removal tool looks like. Spray a lot of WD-40 down the sparkplug holes, and at the joint between the head and the
cylinders. I use a block of hard wood and a 2 pound hammer to get the head off. Watch the joint between the head and
the cylinders closely to ensure you're taking the head off square. If it's cocked at an angle, it's only going to bind up.
Tap around the perimeter of the head in order to keep the opening between the head and the cylinder uniform and square.
Keep in mind that many engines will want to stick the cylinders in the head, and have them slide out from the case.
This is OK, but you may need to unbolt the rod caps if the respective pistons will not slide out the bottoms of their
bores. Study it carefully and take your time. You may break a cylinder fin or inflict some other replacable damage. Don't
be discouraged: Some engines are just a bigger challenge than others. Write back and let us know when you get it all apart.