Help With Prop
 

Hello Everyone
OK...I have a Supertigre .40 with 1/4 shaft. I am working on my 4th prop and still can't get this right.

When I place the spinner back-plate on the shaft, there seems to still be about an 1/8th of the unthreaded portion of the shaft exposed between the back-plate and where the threads start. I am using a Zinger Wood prop and the problem is that the prop fits very snug up to the point where this shaft is unthreaded. This is as far as it will go unless I ream a portion out to make the prop fit snug against the backplate.

Should I ream the prop out by the 1/8th inch to allow it to fit snug against the back plate??

I am afraid if I try and force it on the larger portion that I will break the prop.

Any help would be appreciated.

Also had the same issue with Master Airscrew props.

Thanks,
Lamar

RE: Help With Prop
 

Yes, you should ream out the prop so that it can fit all the way back on the shaft. See the attached diagram for how you should set all of this up.

Hope this helps

Ken

RE: Help With Prop
 

Yup, it needs to fit up against the backplate. If you're using a prop reamer, you shouldnt have any problem taking off just a hair more to make it fit perfectly.

RE: Help With Prop
 

Get one of these and keep it in your flight box. You'll get a lot of use out of it.
http://www2.towerhobbies.com/cgi-bin...?&I=LXK248&P=0

RE: Help With Prop
 

OK....I have a prop reamer and have reamed just enough into the back side of prop to make it fit. I was afraid that this would weaken the prop by only doing a partial ream. Guess it's just beginners jitters or something.

After I reamed it partially, I rechecked the balance and everything seemed good.

Has anyone ever tried the Du_bro metal Prop Nuts?? I am assuming that if you use one of these in place of a plastic spinner you can eliminate the backplate??

Also, how tight is tight when you tighten down the prop nut onto the shaft. The last prop worked itself loose...no damage to the plane but it did happen. Can I overtighten and damage the prop??

Thanks for your help.

Happy New Year

RE: Help With Prop
 

tight real tight i use a 6in cresent on my props and i put the torque on never had a prop come loose yet. I guess you figured out not to stand in line with hte prop while starting
good luck have fun

RE: Help With Prop
 

The ST's are a bit tricky because, while they use the usual 1/4"x28 thread, the plain part is actually 7mm (1/4" is 6.35mm) so if you're going to ream it properly you'd need a metric reamer. I just run a drill through far enough to give a clearance. If you use a tapered reamer then the prop is located by the threads which is no biggie because the threads are very accurately cut. A lot of props (APC, Master etc) come with the back end already more than large enough to fit over that plain section. All wood props have a plain hole (usually 1/4") so they definitely need to be opened out at the back.

I'd better add that with a wood prop they need to be tightened firmly but don't overdo it. And recheck the tightness fairly often because the wood will compress for a while and the nut will be looser.

RE: Help With Prop
 

Thanks DownUnder,

You are right on the money with the ST's. You know exactly what I am talking about. Didn't realize the smooth part of the shaft was metric.....I have a standard reamer. I am gonna get a metric one this week. I tried reaming the back side of the prop (enough to slide over the smooth section but it was larger than the shaft. This bothered me as I was looking for a snug fit. Now I know!!

You have any thoughts on this engine vs. the U-Can-Do 3D?? I have about talked myself into the 4 stroke.

Are the ST's finicky to adjust or no more than any of the rest?? The .40 seems to load up when coming from low idle up to speed.

Thanks so much for the insight on the prop and thanks for understanding the question.

HAppy New Year

Lamar

RE: Help With Prop
 

Idle mixture sounds too rich. Carefully, and in small increments until correct, adjust it leaner with the IDLE mixture adjuster. A slight readjustment of hi-speed mixture may be required when done. Once you get the idle mixture set, you should never have to fuss with it again. All future adjustments will be with the hi-speed mixture only. Be very careful of the prop if done while running. [:@]

See page 25 here for more guidance:
http://www.supertigre.com/manuals/sup-manual-v1_1.pdf

Pinch test mentioned works well on both needles.

RE: Help With Prop
 

One thing not mentioned in that link above (although it's in the ST instruction leaflet) is that the ST carb has a midrange adjustment if the idle mix doesn't fix the transition problem. There are two screws holding the fuel inlet spray bar where the main needle screws in and by loosening these two screws you can rotate the whole assembly to alter the angle the fuel nipple points. This is quite convenient for getting a neater run of the fuel tubing but it also happens to be the midrange adjustment! ST recommend starting with the nipple pointing straight at the front mount hole (this is basically how it's set from the factory). Rotating the nipple up leans the midrange and rotating down richens it. Don't forget to tighten the two screws after making an adjustment.