Dan Grunloh's Prop Tips:

Date:         Fri, 11 Jun 93 16:20:25 CDT
From:         Dan Grunloh (GRUNLOH@vmd.cso.uiuc.edu)
Subject:      Prop Tips
To:           Ultralight Mail (ultralight-flight@ms.uky.edu)
Message-ID:  (9306112120.aa15852@s.s.ms.uky.edu)



---- PROP TIPS, some advice on care and feeding thereof -----------

  In the area of safety as discussed recently re Daves bent tube,
I thought I would post some notes I took at the 13th Annual Illinois
Ultralight Safety Seminar held this year in Springfield.

  | Sorry I don't participate more in the discussions on this mailing
  | list.  I have a severe lack of time.  I do read EVERY word you
  | folks post so keep it up and thanks very much.

#2.. If you propeller is mounted in front (tractor), paint the back side of the prop FLAT BLACK. This will improve visibilty through the blurred prop arc, and reduce reflections when landing with your back to the sun. It should also help with the problem of a strobe light illuminating the prop when you are landing in those nearly dark conditions 30 minutes after sunset on an overcast day. Hairy!

#3.. Balance your propeller often!! (once or twice per year) It can go out of balance gradually so you don't notice how bad it has become. Besides pilot fatigue, long term wear on all the engine and airframe components is an important consideration.

#4.. Retorque the prop bolts at least twice a year. Wood props can swell or shrink and result in prop failure. Various charts of torque values have been published. Don't quote me, but I think our wood props on ultralights go about 14-18 foot-lbs. I prefer to torque by feel, (don't laugh) because with experience, you can get the perfect value for YOUR individual prop. The idea is that by going very gradually you stop just before the point where you begin to crush the wood. Then back off and retorque again. Use a torque wrench if you want and find out what values you are using. Torque composite props strictly according to the manufacturers specifications.

#5.. If the prop cannot be made to "track" correctly you can try shims under the prop hub to straighten it out. Paper card stock is preferred to brass shims as it is less likely to slip out. (You track a prop by removing the spark plug(s) and turning the prop to measure from each tip forward or backward to a fixed point. Get it as close as you can but din't get too carried away. I had prop which was 3/8 inch out of track so I shimmed to turn correctly and then it exhibited a strange fluttering vibration in flight. Perhaps it's out of track when static but flexes under a load to come out OK. The proof is in the flying!

#6.. To add some easy protection to the leading edge of your prop, add an epoxy leading edge. Mask off a narrow strip along the leading edge and paint on a couple coats of epoxy glue.

#7.. According to the propller expert at this seminar, a wood prop should have at least 5 coats of varnish (polyurethane). With me, it takes at least that many before the finish starts to get really smooth when using cheap spray cans. If the varnish wears off you will get water damage and unsightly stains which are permanent. I found that old varnish can be removed by scraping with a razor blade or other sharp tool. Let one-part polyurethanes harden for a couple of weeks before you use the prop.

------------------------------------------------   *                  ^^
 Dan J. Grunloh      | grunloh@vmd.cso.uiuc.edu   \|/       __|__        ^^
 Research Specialist | University of Illinois     \|/   -----(.)-----
---------------------------------------------------|----------------------