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Engine basics => Engine set up tips => Topic started by: Steve Helmick on May 27, 2015, 03:31:31 PM
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I'm running an AAC (Nelson made, Randy Aero assembled) OS .46VF, 10% Wildcat Premium with a dose of Randy Smith's Aero-1 "Snake Oil" added. Plug is a no longer in production Thunderbolt 4-cycle. Prop is a Brian Eather 12-4 3-blade with undercamber, cut to 11.5" diameter. Launch rpm is 10.5k.
It seems to be running leaner than my previous prop, needing about 10-15cc's less fuel, yet launching at the same rpm. At NW CL Regionals this past weekend, my pit tootsie (Keith Varley) said it pulled really hard before release, a good thing.
I'm thinking that (because it's burning less fuel) the prop is less load than the previous prop. But then again, I have to set the NV about 1/4 turn leaner to get up to the same launch rpm, which then suggests that maybe I need to add some pitch or clip the blades down another 1/8" or so? Any ideas? Why? Yes, I'm confused on this! ??? Steve
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Bump! H^^ Steve
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Sounds like is less load.. based on my experience with the .40VF. I'm assuming you are comparing it to a cut down 12.25x3.75 APC? vs the 3-blade BE 11.5x4.. Are you getting the same lap time with this prop? or its slower.
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Thanks for answering, Joe! Well, launching at same rpm (but in more on the NV), it flies about the same speed...but I don't check lap times. I think they are highly overrated as a goal. The plane has a minimum speed where it flies well, and that's about all there is to it. But the engine is obviously running leaner, also observable by the way it quits now...slight leaning out, not for long, and not all that obvious a signal. I've had to reduce my fuel load about 10-15cc's on the same fuel.
I'd like to richen the engine up and burn a full 6 oz again. It's a clunk tank and holds a bit more than 6. Using my mustard pump, I can accurately put in 6.0 even. It's kinda surprising how different the plane flies with the 3 blade CF prop...took some retraining of the pilot! Part of that would be the CG shift, but a lot is just the prop. In general, I like it. But I need to get the engine running richer and increase the fuel burn. I'm just not sure where to go with the prop. I have one more of these props, but it's a full 12", and on the PA .51. I'd like to leave it there, and certainly don't want to squander either (pun intended!) of these. LL~ Steve
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So , Im your pit tootsie eh. If Im to be branded with a cute nick name ,let me have a say just what it is ,please. Actually I prefer Pit Puppy.Yes thats it.
As far as props and fuel are concerned, I have One stellar suggestion. Change it out for an electric motor. Thats where your troubles disappear , and true everlasting happiness comes rushing in. Keith , Pit Puppy,Varley.
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Ok, Keith, you're a Pit Puppy!
I haven't figured out yet why electron burners want everybody to change to electrons. I'd rather eat worms! Yes, that's it, worms. Yucky worms and yucky electrons. Ewwww! Castor oil is good for the skin, you know... y1 Steve
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Why not try pitching the prop to 4.25?
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Why not try pitching the prop to 4.25?
Well...I thought this was the prop from the PA-51, so thought it'd be ok, trimmed to 11.5". Turned out it wasn't the same prop. Plus, I'm not very good at re-pitching props. It's the logical thing to try, of course. I appreciate your suggestion. Maybe I can get to it by Thursday night; at least I know where my pitch gauge is. I think. H^^ Steve
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Ok. So, I checked the pitch at stations 7, 10 and 12. Could have gone to 13, but it appeared to me that all three blades are actually at 4.25" at those stations. Mike H. said to pitch up the 12 & 13 to 4.75" or so.
I guess I'll try it sometime in the future. Not happening tonight, anyway...it's beer-thirty, after CD'ing Stunt-at-Auburn today. If I drank as much beer as I should (I won't), I'd run out. And where the heck is dinner? LL~ Steve
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Reporting back after pitching the last 2" (8-10-12 stations) to 4.75". It reduced the launch rpm to 10.30K to 10.35K and pulls much better in the verticals and overhead stuff (previously launched at 10.5k) John Leidle launched for me both rounds at The Scobee, and clocked my level laps at 5.2 sec. both upright and inverted. The engine run is still too long on 6 oz, landing at 7:55 on my first round. It still doesn't give as strong a signal of shutdown as I'd like. Fuel was changed to 10-22 made by Howard Rush. I'd like to just pump in 6 full ounces, and I want a strong shutdown signal. I have deleted the pipe pressure and instead have a tube run from the uniflow into the backplate cavity, hoping for a constant pressure. I like this, and see no reason not to run it this way all the time. Brett says he has this option for the wind, but why not all the time?
Since changing trucks ('06 Tacoma to '08 Chevy), I have been transporting the plane in the backseat, with the nose down. Previously, I had it on a shelf in the back of the truck bed/canopy. This nose-down thing is a bad deal, as a lot of oil runs into the engine and locks it up. I've never bothered with "burping" the engine before. I need to make a trip to the hardware store and get some PVC pipe and a bunch of fittings to make a new rack for the back of the truck. I can't find the one that I used in the '97 GMC...but it may be in the compressor shed or just lost in the garage. It could be in there, somewhere. I may have given it away, but I hope I find it. I have a new one sketched up to figure out fittings and pipe lengths. y1 Steve
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Steve , sorry about the 4 chapter story of my past with locked up pipe engines a simple " normally the pipe oil flows back into the engine " would have done.
From where I stood your .46 sounded to be in a deeper 4 stroke than before , normally when you load these things up as you have the none or shorter shut off happens at least if its working properly.
John
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John, I knew the exhaust oil residue would run into the engine, but just didn't think about it, and didn't have an alternative way to transport the model. Oldtimers kicking in?
I'm not sure I understand what you're saying about the 4 stroking and shut off signal. Are you saying that I have a lot of prop load or too much prop load on the engine? That was the original question I posted.
I think I can tell if the engine is loaded too much, but don't know what signs to look for if not loaded enough. As the .46VF is now, I think it could be a little on the heavy side of ideal. Seems to me like if the engine is running rich, it'll come on strong as it gets to the last lap or three. If it's running pretty lean, it should just run ok until it's out, being an AAC. That's what I'm seeing, pretty much. I'm thinking about modifying the blade tips to scimitar shape to reduce the load, instead of just clipping the tips. If it works, fine, if it doesn't, I'll clip them more and repeat the scimitar shape again. Does this sound logical? ??? Steve
PS: I just dropped $46 on PVC pipe and fittings at McLendon's... :o
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My experience is that when running loaded the engine will have a more abrupt "quit" not sure why I have guessed about it for a long time because I have run rich or loaded for a long time.
When you asked about the locked up engine I figured you never had to deal with it so I figured to say all I know on the subject. I suspect moving up from a foreign car to a Big Boy American made Chevy is worth a few locked up engines.
Did you spend $46.00 American to make a long exhaust outlet?
Gotta go Paladin is on , John