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Building Tips and technical articles. => 1/2 A building. => Topic started by: Dave Moritz on September 30, 2023, 11:00:54 AM
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Am hoping that the good brethren can provide some insight here. Whenever cool weather and higher humidity set in, I find it a major challenge to get good needle settings and decent power out of my 1/2A engines. I'm beginning to think that as Fall comes on, I ought to shelve my little critters and fly the bigger guns.
What do you all think - operator malfunction or just a reality I need to face?
Dave Mo...
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I can't say that I have noticed much difference but I haven't flown a lot of 1/2A in recent history. Between the extra humidity and the air being cooler and more dense, maybe add a head shim or two, or maybe a bit less nitro if you are running a lot. experiment with those and see what you get.
Dan McEntee
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Operator malfunction...but no barb from me. H^^
I've got a jewel of a 1/2A plane (flapped Keil Kraft Radian) built by a British chap. He wanted a surrogate flier and sent it my way. While I could bench run the low hours Medallion .051 with high compression glowhead, any time it got in the air it absolutely floundered. I mixed a bunch of different blends from 15% Vitamin N up to the latest ~23%-25% brew. If it ran a tank out, it flat raced out the lean run at the end of the tank. Needling for just off lean was almost impossible. I changed fuel lines, flushed the tank and NVA and bench ran it some more.
I talked the runs over with FredV4 last weekend., and he asked "any chance you have too much compression?" Hmmm.
This morning I added two glowhead shims, and ground ran another couple of short tanks, each time I wound the needle valve in 1/8 turn. After three tanks, I checked tach at 16,700 and lined up the camera...and ripped off four solid flights. I ran the needle in maybe another 1/2 turn or so. The engine needed a prime to start now. The worst part is knowing I was scared to fly it for the last four years because I couldn't trust the powerplant. The best part is I can really play with the plane now! Yes, I have video to prove it.
I will mix up some 30%N for the next outing. Don't be afraid to make changes to your engine...add a few shims, change your nitro ratio, change your oil. But adding/removing shims is easy and fast, so it can be done at the field.
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Dave Moe,
Well, there's "a little cooler in the fall," and then there is "Wisconsin frozen lake cold."
Keep the nitro. Keep the fuel somewhere so it is warm. Too cold and the oil viscosity can give you trouble, especially on a small engine with small holes. Fiddle with head shims if needed. Use a prop with some mass to it to get it warmed up. That all works down to 50ish. For a Wisconsonian, you might need some heat on the head if you are frozen-lake-flying? Dunno. I try to stay off frozen lakes even if they say the fishing is good....
Stay warm,
The Divot
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There were only 278 Medallion .051s ever made, and they were sold to free flight guys for nostalgia events. Are you sure what you have? And if so, it is a collectors item. Look at the piston and see if it has a copper colored ring ground into it. 🤠
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Ah, but many of you good gents have come through in the usual fine form. The consensus is shims, so shims it'll be. Will chalk the whole snafu up to operator malfunction a la the mystery Jim!
Will report back in due time. Thanks!
Dave Mo...
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Mr. Dave,
I wanted to back up what I said earlier. This was some time ago. I couldn't trust the engine to try anything.
https://youtu.be/pvEUoF8VFJE?feature=shared
Here it is this last Saturday with two extra head gaskets (three total-the only change) under a Cox high compression glowhead. There are several others from Saturday if you care to look/listen. It is as if it were a completely different engine!
https://youtu.be/y97zhUvS6Dw?feature=shared
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Wowza, Jim what a difference those three gaskets made! Thanks for the video links.
Best,
Dave…