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General control line discussion => Open Forum => Topic started by: Terry Caron on October 15, 2015, 06:53:44 PM
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On 52' .015 lines w/8-4 MAS prop, my Sterling P-40/Fox .15 Rocket does about 4 sec laps.
How can I slow it to 5.5ish sec lap time?
Will just a prop change do it?
Terry
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Less nitro in the fuel and open the needle.
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How about keeping the air speed and using 60' lines instead of the 52'??
I'm a newbie, but I would think that might be good.
R,
Chris
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Or..... Put that rascal on .012 x 60' lines. That should do it. We fly our .15 and .19 trainers etc. on 60' lines.
Dave
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First, why are you using .015" lines, when you can use .012's and make the airplane happier? It will have to fly faster to make enough line tension with the .015" lines. Longer lines would be a good option. Smaller planes don't like flying at slow airspeeds. That's why everybody says bigger models fly better.
I never had a .15X, only earlier "steel fins" (Rockets). What I read about the .15X at the time was that they didn't like as large a prop as the steel finned Rocket. Admittedly, I have a poor opinion of MAS props, but I'd suggest trying an 8-3 APC, perhaps even with more nitro and not less. Even the 8-3 APC might be too much prop, so I'd look at their lists (not what's available at the LHS!!!!) and see if there's a 7.5 x 3 or something in that range. APC's might look scary, and they might not look like a Y&O, but don't be surprised if they work real well.
Remember that the more "power", the slower you can fly the plane. We're looking for thrust, not horsepower, and not really static thrust, but I must say that static thrust is a good indicator of something good about to happen. Then again, if your P-40 is from a genuine Sterling kit, it may be so heavy that it'll never be "happy" flying slower. I had one of the "Me-109's" when I was a kid, and it was a dog compared to a Jr. Flite Streak. Ah, those were the days! :'( Steve
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At the same airspeed, going to 60' lines from 52' should get your lap times to 4.6-4.7 seconds, not taking into account any extra drag for the longer lines, if my math is correct.
But I would drop down in line size as well, and I would guess that might keep the drag about the same, even with the longer length.
Please report your findings for the rest of us, and good luck.
R,
Chris
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Wow - thanks for the response guys!
FWIW, the plane weighs 17.2 oz on my scale. It came with a .15X that I changed out for my Rocket (I'm familiar with it).
I've not flown a .15 before but read 52" lines as "correct"; not having anything that length, my Bud Mike Londke gave me a set of his 52'/.015".
I do have 58'/.012" but thought that too long/draggy.
So I assume a smaller prop isn't the way to go - I'll use the 58'/.012", richen it and see that works.
I run mostly APCs on my larger engines so I'll see if I can find a suitable size/pitch if needed.
I'll update results.
Terry
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It might surprise you how well the 15X runs on a zinger 8/4. I used them for years with 012X60 lines and had a ball with the small models. As stated dump the .012X52 and get the correct lines, you will appreciate the difference it makes.
15% nitro is /was my usual fuel for them as like all small displacement engines I found tipping the nitro can was beneficial. You don't need 29% oil if your shaft is free with no drag. I ran 15/22 on one of my X's for a long time and it is still in prime condition. No 15% available then 10/22 is fine. Do not get the engine screaming lean no Fox engine survives too many of those runs no matter what percentage of oil you use. When they are running well they are thirsty use a 1.75 or 2 oz tank and adjust to your preference.
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We fly .15's on 60' lines all the time at the turkey ranch.
MM
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With no previous .15 flight experience, and not a clue as to a good launch rpm, it was running near peak.
But toning that down and using the longer .012" lines should be more to my liking.
Terry
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BTW - what would be a good launch rpm w/8-4 prop and 60' CTC lines?
Terry
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BTW - what would be a good launch rpm w/8-4 prop and 60' CTC lines?
Terry
Pretty hard to predict! What brand of prop? FWIW, when I flew the Twister (Magnum XLS .36) on 59' eye to eye .015's, I launched it at 9,700 rpm on a TT Cyclone 11 x 4.5. When I experimented with TF PowerPoint 11-4 and MAS Scimitar 11-4, I had to launch at about 10,400 rpm and still had very little line tension up top, so I gave up on them. I regret not trying the Scimitar 11-5, and some APC props. Various companies under or overrate their pitches. I don't think anybody knows why, but this has been going on for many decades, starting with TF paddle blades and RevUps.
Basically, various brands of 8-4's are going to have to launch at different rpms. I'd suggest starting with backing the engine off 500 rpm from peak rpm. Make sure you know what rpm you launched at, so you can adjust from there. One of the (few) lovely things about plastic clunk tanks is that you can launch with 1/4 fuel load until you get your launch rpm pretty close. H^^ Steve
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8-4 APC is on it right now Steve, and your comments remind me that the MAS 8-4 is likely an 8-2.5 or something.
On the ground it peaks ~12.8K w/either.
APC website lists 7.625-3.25, 7.8-4 & 8-3.75 available.
Terry
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I always used Zingers as they were cheap and available. Being from the old school I never did tach small engines that were on sport models. I just got top rpm and backed off what I considered enough. My considering is really pretty good after all these years.
dennis
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BTW - what would be a good launch rpm w/8-4 prop and 60' CTC lines?
Terry
you really need to find out what rpm the motor is happy at,, THEN decide on what prop gets you the speed,,
typically you either want a 424 run, or a wet 2stroke run,, seldom run it peaked or at max rpm
Most x4 pitch props are going to want to be around 10,000 rpm,,
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OK, I can tell a wet 2, so go up from there 'til it flys to suit.
Thanks guys.
Terry