mrcoolpop

I have the Seagull 540 with the 66.9 in wing span. I had been flying it about 2 months ago and it was fine. Went to the field today and had major problems. I have the O.S 120 FS 4 stroke engine and my RPM get up to 9700. I have a Master Airscrew K-Series 14x6 propeller. My CG is 6.5mm from the leading edge it balance good. Now the problem I'm have is when I take of it flies like its under power real slow and sort of tail heavy. Can only make one lap and have to land it. Please!!! any help will be greatly appreciated.

Thanks,

speedracerntrixie

My Feedback: (29)

Try an APC 16X6

Gray Beard

My Feedback: (-1)

I used either a 15X8 or a 16X6 APC with my OS 120s. I did a lot of prop testing though with each new plane to see what worked best for me. The MAS props didn't work so well and a 14 is a bit small. Also as our temps start to go down the engine may also need to be fine tuned too.

JohnBuckner

My Feedback: (1)

Have the same engine on a Stearman and even aero tow two meter gliders with it and just checked and an APC 15x6 has done a creditable job, in fact its the original prop since I started flying it few years.back. a 14x6 sure sounds under propped to me.

I am not really a fan ot those Master K Series and if you look at them carefully in comparison to the same size APC and look at the blade planform you will find it has about fifty percent more blade area compared to the APC, Its a humongous difference. Also not convinced its just a prop problem since you said it was not the same last time. Could it not be a simple tuning problem and did you retune from two months ago? That's enogh for a season change and definitely may require a simple retuning.

John

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mrcoolpop

Thanks for all the info and I will go to my local hobby shop and the the APC prop. For as the tuning I think its fine because my RPM gets up to 9700. Base on the manual it tops out @ 9500 RPMs. Will let you know how it flies with the new prop.

mrcoolpop

[h=1]One last question, my flying buddy has a Xoar Beechwood Propeller 15x8 prop. Will it compare the same as the APC[/h]

JohnBuckner

My Feedback: (1)

Depending upon some manufacturers published rpm to define whether or not your tuning is ok is a mistake. To properly tune to the high speed the engine is leaned out to peak then backed off a given RPM margine or as I do is use the pinch method and a brief pinch of the fuel line at full power. If that imediately kills the engine then the main needle is too lean or if the pinch results in a brief increase in RPM then the needle is too rich.

The 15x8 may be a bit to much pitch.

John

speedracerntrixie

My Feedback: (29)

Go with the APC it is a proven performer. Not to mention wood props on an Edge just don't look right. LOL. You can dye them black to Mach your color scheme. Mix up a 50/50 solution of water and vinegar, get it to a boil add Rit dye and throw your props in for an hour as it cools. Using black, the props come out looking like CF.

Gray Beard

My Feedback: (-1)

The only way to know what works well for a pilot is testing. I really like the Xoar props but only one shop in town stocks them but everyone has APC. When I had the 120 in a big bipe I tried several props to see what worked best for me. It just turned out to be the 15X8. I'm no longer using the OS 120s and have gone over to YS engines and my Extra with the YS 120 likes the 15X8 and didn't fly the way I wanted it with the 16 inch prop in any pitch?? Only by testing different props will you find the one that works for you. I liked the way the 16X4 APC flew my Kaos with an OS .91, a bit over propped but it worked for me. I tested props from 14 to 16 inch with different pitches until I found what worked for me.
With our weather now cooling down I will start to fine tune my engines until our winter really sets in. I tune for several months of 100+ but it gets down into the 20s and 30s pretty fast here and the engines need to be adjusted as it drops.
I tune differently then John but there are several ways to do the same thing. Pinching is a good way though and I use it on two strokes sometimes.

Gray Beard

My Feedback: (-1)

I was once asked how I managed to find matching colored props at a fly in. I said I had a guy that made them up special for me. I had guys wanting me to sell them colored props for big money then told them to just drop them in the dye when they were tinting there canopy. Works well with any dark color.

flyinwalenda

My Feedback: (5)

If you have immediate access to the wood 15x8 prop I say try it.
Re-tune so it reaches max rpm and then back the needle out just a bit to make the mixture rich and fly it. If it "sounds' like it's stumbling or not reaching full rpm at high throttle you may be to lean or too rich on the high speed needle. Bring it in and feel the engine and if it's really hot you are too lean back out the HS needle a bit ; if it's not really hot then it may be too rich so turn in the HS needle a click. May need to do this a few times until you get it right. Also the low speed needle may need to be adjusted as well depending if it stumbles from idle to full throttle(too lean) or if it bogs down and throws out a lot of fuel/smoke(too rich) The low speed needle will affect the high speed needle setting.
When you get it tuned and if it still doesn't fly well then get the 15x6 APC and repeat the process.

daytonarc

My Feedback: (5)

I like the APC 16.5 X 5W for the 120-125 FS sized engines in an aerobatic/3D plane.

drac1

My Feedback: (4)

It flew OK 2 months ago and it still makes maximum RPM on the ground.

If it was the prop, it wouldn't have flown OK previously. If it is too rich, it wouldn't make maximum RPM. Also if it is too rich, once in the air it would lean out and run better.

The only thing it can be is too lean. Run the engine at full throttle, then point the nose straight up. If the mixture is correct, you will hear the engine RPM increase slightly. If it is too lean it will die off.

kiwibob72

If your getting that 9700 RPM while the plane is stationary and on the ground, your over reving the engine due to your prop being too small, as the engine will unload and rev a lot harder in the air (ie well past the recommended max rpm).
You should look to get only about 8600-8700rpm on the ground if your motor's maximum rpm is 9500, as it will unload and reach those maximum RPM's while in the air.

Gray Beard

My Feedback: (-1)

I get about the same as Bob with both the OS and YS 120s. I can push them a bunch farther but I really hate floating the valves. I run them about 500 rpm fat but some of that is our heat we have here. Another thing is the tack your using, some are a bit better then others but as long ad it isn't bouncing around your OK.