GT propeller repair (fibreglass cover over wood)

[pluessy]

Hi everyone,

 

I have a 2-blade fixed-pitch wooden GT propeller (from my Tecnam P92) where the fibreglass sheeting on one tip has delaminated. I had a slight vibration and some funny noise, when I checked back on the ground the glass/paint had lifted just behind the leading edge protection. Pulling on it, a 12cm section pulled off easily, see attached photos.

 

Does anyone have any experience with this type of repair or know of a repair shop (Australia)? GT has been of no help so far, referring me to the prop manual (the prop manual states to contact the manufacturer!).

 

Thanks for any help, Thomas

 

 

 

 

 

[Soleair]

If that was my prop, I would repair it with epoxy & glass cloth. Polyester resin, typically used in 'fibreglass', does not bond well to wood - that's prolly why it was easy to peel off the tip section.

 

Epoxy - preferably WEST system - is made especially for wood. It has a lower viscosity, & ISTR diluents, to allow it to bond better to bare wood surfaces.

 

I would feather the edges of the old encapsulation back, as fine as possible. Then wet the bare wood with neat WEST & allow to cure. Then re-wet with neat epoxy, & laminate glass cloth up to the same thickness as the original - always applying the resin first, & drawing it up through the dry cloth by stippling with a brush. Overlap the feathered edge. Let it all cure, then dress it by hand with sandpaper & a cork block. Note that to cure properly, you should be working in warm dry conditions.

 

For the other end, that just has the ding, I would prepare as above, apply a coat of neat WEST, allow to cure. Then apply subsequent epoxy thickened with colloidal silica or microlite. Let it cure, sand it flush, give it a another coat of neat WEST. Finally sand to profile.

 

When you have done all that, you must check the balance of the prop. If you don't have (access to) a dynamic balancer, you can balance satisfactorily statically.

 

Make a channel of 100 x 25 softwood, about 200 long. Screw it to the bench. Fix a couple of straightedges to the upper inside edges (e.g. steel rules), so you have 2 level steel edges parallel to your workbench top. Use a spirit level to check this carefully. Make a spindle that is a good fit in your hub, then balance in 4 positions. Remove excess resin, or add more, to get the blades to hang level. Fine balance with paint if necessary. Both profiles should be the same.

 

 

[pluessy]

Thanks Soleair. As this is from an LSA, I was looking for someone who can sign off on this repair. I have bought and installed a Bolly BOS3, so I'm not grounded and have time to source the repair (or sell it).

 

 

[DGL Fox]

Thomas,

 

Call Dieter I am sure he will be able to help you...

 

Dieter Sedlbauer

 

Mob. 0414504116

 

David

 

 

[pluessy]

Thanks, will try him.

 

 

[Blueadventures]

Hi everyone,I have a 2-blade fixed-pitch wooden GT propeller (from my Tecnam P92) where the fibreglass sheeting on one tip has delaminated. I had a slight vibration and some funny noise, when I checked back on the ground the glass/paint had lifted just behind the leading edge protection. Pulling on it, a 12cm section pulled off easily, see attached photos.

Does anyone have any experience with this type of repair or know of a repair shop (Australia)? GT has been of no help so far, referring me to the prop manual (the prop manual states to contact the manufacturer!).

 

Thanks for any help, Thomas

Hi Thomas

 

I'm no expert in aircraft propellors. And my next comments are just my thought if it was my prop and considers that the manufacture has offerd no helpful assistance, comment or repair/refirb option.

 

I would not use that propellor ever again unless it had been stripped by an authorised (by the manufacturer) workshop and re covered. To me it looks like either the timber surface was not correctly prepared just prior to the application of the resin mat layup or the resin mix or curing was done out of spec. THe way that has let go suggest movement in the resin to timber and will extend further along the blade towards the hub.

 

Up to you but I'd get a new GT or a Bolly etc if thier OK. (Would not like to see a worse delamination failure in flight.)

 

Cheers

 

Mike

 

 

[cscotthendry]

Thomas:

 

I agree with Mike completely. I wouldn't repair the GT prop myself. I'm guessing that somewhere somehow, the wooden core of your prop has got moisture in it that may have made it swell, and the swelling and the aerodynamic forces have made the prop shed the coating.

 

I had a Woodcomp prop on my LSA and I changed it for a Bolly, because I'm a bit hesitant about props with wooden cores and laminate sheathing. Also in my factoring, Bolly are local (to Oz) and so it is easy to get service AND they are great people to deal with.

 

In my case, I wrote to the factory of my LSA and sought a letter of approval for the prop swap and they were quite willing to do this. I believe this is all you need for LSA.

 

 

[pluessy]

Thanks everyone for their input. I'm thinking along the same lines, having to replace the complete sheeting. But I'm also not comfortable with a prop up front that can develop a hidden failure eg you don't know that the sheeting is delaminating until it is visible from the outside or is already peeling off. I have bought a Bolly BOS3 and the approval request is under way.

 

I think a wooden prop should be covered with clear glass or varnish so that any damage to the core or cover is visible (check out the Jabiru prop manual). This GT might just become a very expensive clock

 

 

[GTProps]

!).

Thanks everyone for their input. I'm thinking along the same lines, having to replace the complete sheeting. But I'm also not comfortable with a prop up front that can develop a hidden failure eg you don't know that the sheeting is delaminating until it is visible from the outside or is already peeling off. I have bought a Bolly BOS3 and the approval request is under way.I think a wooden prop should be covered with clear glass or varnish so that any damage to the core or cover is visible (check out the Jabiru prop manual). This GT might just become a very expensive clock

Thanks everyone for their input. I'm thinking along the same lines, having to replace the complete sheeting. But I'm also not comfortable with a prop up front that can develop a hidden failure eg you don't know that the sheeting is delaminating until it is visible from the outside or is already peeling off. I have bought a Bolly BOS3 and the approval request is under way.I think a wooden prop should be covered with clear glass or varnish so that any damage to the core or cover is visible (check out the Jabiru prop manual). This GT might just become a very expensive clock

G'Day Thomas

 

My name is Chris and you did indeed speak to me about your GT prop.

 

I recall that at the time I advised you that the best person to speak to would be Dieter to repair the prop as he has the facilities to do so.

 

In general a damaged prop should where possible go to the factory or to a authorized prop repair shop. In your case a person such as Dieter who also manufactures wood propellers.

 

 

[Bruce Tuncks]

Yes, good advice about seeking expert help with that prop. And if it is to be repaired, the new resin needs to be compatible with the rest. Even among epoxies, this is not always the case. I think the Jab prop is polyester resin but this is no help to you.

 

Your problem is very serious and you are lucky to have escaped so easily. I have seen 2 Jabirus brought down by prop failures. The first was because they had taxied through weeds and worn through the tape protecting the prop leading edge. In flight, it peeled back and produced enough drag to ground the aircraft due to lack of prop rpm.

 

The second was more like yours. Our maintenance man of the time had removed the tape and in the old Jab props, the rubber leading edge was butt-jointed to the glass-covered wood. Air got in under the glass and ripped off some of it with the resulting out of balance so bad the engine had to be shut down at 300 ft after take-off.

 

 

[pluessy]

I have decided not to have it repaired as I don't need it anymore. More than happy with the Bolly. I will need a much smaller prop for my single-seat project and I might use the GT as a core for that prop.