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Engine basics => Engine set up tips => Topic started by: Steve Helmick on September 05, 2009, 11:42:38 PM
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Our last contest was a bit on the breezy side, and I had a problem with windup on outsides. It doesn't seem to do it on all outsides, but the rounds and the outsides of the H8. The outside squares are ok, and so are the outsides of the OH8. I read Randy's anchored Engine Tips post at the top, and could try a Thunderbolt 4-cycle glowplug (the old type, of which I still have some), tho I don't see that as a solution on a side mounted engine. But maybe?
The setup is this: Fancherized Twister, heavy at 47 oz, side-mounted Magnum XLS .36, TT Cyclone 11-4.5, 10-22GMA, Thunderbolt R/C long, .272" venturi with PA Nv Assy., OS .46LA muffler (stock), Hayes 4 oz tank (stock) on muffler pressure, 60' eye to eye .015's. I usually launch at 9.7k/9.8k rpm, and it'll typically peak at 10.2k. In good conditions, it's a pretty good setup. However, it'll windup to about 80mph on outside rounds on a windy day. Yow! Doesn't do that, normally, and insides aren't a problem, nor are outside squares (I think the corners keep the speed down enough).
So, I'm looking for ideas for a windy weather setup. I've got a Wilks carbon 3-blade 10-4 Tornado copy, figure on pitching it down toward 3.5" or less. I'm hoping that the blade area is adequate to load the engine enough so that I can launch the engine about 200rpm below peak. Maybe put a Bruline air filter back on, fine or coarse. We're having enough trouble getting decent fuel, so I'm not sure I could drop to 5% nitro if I wanted to, but could cut some 10-22 with FAI fuel. I got a set of 59' eye/eye lines for windy weather, but haven't tried them. More castor might help? Restrict the muffler outlet? Could add a "rubber ducky" to the muffler outlet, but not sure if that would do anything good or not. Other ideas welcome!
I want to test this setup and have it in my box of tricks, not wait until a windy contest to try something willy-nilly. How can I test a windy weather setup without waiting for windy weather? My usual flying sites are pretty much unflyable if the wind is up, due to turbulence off adjacent buildings, trees, or terrain. It seems to me that it will have to work reasonably well in average conditions in order to work in windy conditions. It is logical that I'll need to decrease the lap time a little, and run the engine closer to peaked, so it won't have much more rpm potential. The engine will usually peak at 10,200 and launch at 9,700. In the heat in Canada (about 100F) it would peak at 10k and I launched at 9.8k, but it wasn't windy. Odd weather this year, but it ran ok and lead me to think about the possible setup for wind. Eugene was windy, but not hot enough to make the engine lose rpm (darn it!). ??? Steve
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If I remember right, Big Art told me one time to go to a lower pitch prop for windy weather. ??? ??? DOC Holliday
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That's an easy one, put your Stalker 76 on it...problem solved
Nyet, Greg! Bad dawg! Sit! Stay! mw~ Steve
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there's two ways to look at it, Lean and low or rich up pitch up. I've used both and definately prefer the richer engine and higher pitch prop approach. Especially on non piped setups.
FWIW
B
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Well for what it's worth, you want an engine/prop combo that has good braking properties, since the plane is picking up energy from the wind during the maneuvers, so it is an engine and prop issue assuming the airframe is not to be changed.
I know from some calculations ~^, that everything else being equal, a lower pitch prop at a higher rpm will have better braking response than a higher pitch prop at lower rpm (the rpms in my calculation were selected to provide the same thrust). Of course in my case, the rpm is being held constant by my speed control for the electric motor. In your case you need to worry how the engine likes to unload. I would think that a smaller engine might not be as good as a larger engine in that regard, but I am not sure on that point at all.
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Thank you, Bruce and Alan, for your comments. I got the Wilk CF Tornado 10-4 clone on the plane last weekend and again last night. It's easily the best results I've gotten with a 3 blade CF prop, but still needs some pitch tweeking. I hope that will improve things, and not make it worse! Have a few other props to try, hopefully this weekend, and maybe I'll get the 10-4 repitched for Saturday's Fun Fly. ~> Steve
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I haven't gotten back to the Wilks/Tornado 10-4 on the XLS .36 yet, but did test the 11-4 Master Airscrew SCIMITAR S-2 and 11-4 TF Power Point to my satisfaction. Launch rpm for both was up around 10.5 to 10.6k, performance was reasonably good, but the howling as it pulls out of the dives (RWO, OH8 and Clover) is unsettling! I'm wondering if this could be a "good thing" with the OS .46LA muffler with its trick "cone of silence" and all. On the whole, the TT Cyclone won the battle of the blades on the XLS .36.
One thing I'm missing is those wonderful Prather noseweight washers...1/2 oz, 1 oz, etc. "Grape Lanes" has 1 oz and 2 oz on their list...I'll have to cut some meat off them. Meanwhile, the Prather product was a wonderful product for our needs. Sure would like to see somebody put them back on the market. :! Steve
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I think the reason for this is it is not being flown by the guy that built it. There is a reason he gave it away! I would give it back to the guy that built it and fly one of your other arfs that you usually fly. y1 y1
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Steve, hate to say it, but a big part of your problem is the weight. High wing loading doesn't turn as fast, and when the wind speeds up the plane you have very little time to do anything. The control loads go up very fast as the plane speeds up too, so you lose a lot of leverage to make any kind of corner. Adding some tail weight and/or modifying the controls to get more leverage would help.