REFLECTOR: Leading Edge Prop Damage Advice

[Bob Jackson (Jax Tech)]

Thanks, Sid -- I remember and highly respect your suggestions from the last
time, and you obviously successfully made some big repairs to your prop.

I'm only asking again because our latest damage is to the leading edge
sheath itself, it's ~8" in from the prop tip (where there would be a lot
more load and stress than on the prop tip, as in your case), and the damage
caused the sheath to delaminate somewhat from the wood where the sheathing
ends (about an inch back from the leading edge).

We're not sure how much the steel sheathing provides structural/longitudinal
strength to the blade compared to how much it is there primarily just as
protection of the leading edge (for an 'erosion sheath' as they call it on
their website).

We just want to make sure that if we repair it ourselves we won't be
seriously risking the loss of the last 8" of that blade due to the load and
how we've weakened the sheathing in that area.

Thanks for the help!
Bob


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of sbjknox
Sent: Monday, June 20, 2011 10:44 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Leading Edge Prop Damage Advice

Here is a 'reprint' of a related MT discussion from last Fall... the damage 
is different but you may find some useful info there:

**************************************************************

From: "Bob Jackson" <bobj at computer.org>
Subject: REFLECTOR: Prop Damage Advice


> We damaged our prop (FOD on takeoff?) and would appreciate any suggestions
> you might have concerning:

> 1. Can we safely repair it (ourselves)?
> 2. or, would it be better to just send it back to MT?
> 3. If we repair it, what risk do you think there would be of the tip
> breaking off and 'departing' later on?
> 4. If the tip departs in flight, what damage do you think it may cause
> to the engine (TNIO-550N)?
> 5. How would you recommend repairing it, if we do it ourselves?

> Our first thought is to repair it ourselves, with careful work 'coaxing'
> and
> soaking epoxy down as deeply into the frayed wood as possible -- then
> covering that with a thin layer of JB Weld.  We have other (smaller) nicks
> already in the prop that we've repaired this way, but since this one is
> larger - should we also use some fiberglass?  We will probably send it off
> eventually for a complete overhaul job in the next couple of years.  We've
> got 300 hours on the prop so far.
>

> Thanks for the ideas,
>
> Bob Jackson
>
> N2XF XL-RG
>

I have repaired my MT on two separate occasions... both from digging the
tips into the runway.  The attached photo is from the first time.  The
second time was not as bad but again got all three tips.  This was many
years ago and the repairs are still intact.  The balance was not as good,
esprcially after the second repair so this past summer I had it dynamically
balanced and it required only a small weight.  Feels noticably smoother now.
I used JB Weld and glass and resin.  Yours is an easy fix.  Here is how I
would do it if it were mine:
1) With some coarse sandpaper, clean out all the loose debris and around the
edge to get thru the paint.
2) Drill a dozen or so small holes all the way thru.  Spead them throughout
the damaged region.  The reason for the holes is to ensure that the JB Weld
is anchored into the blade and not just stuck on the one side.
3) Work the JB Weld into the holes until it comes out the other side.  Work
it well into the damaged wood.  Smooth it out and let it cure.
4) Sand as required.  A second or third application (with cure and sanding)
may be required to get it really smooth.

Discussion:
In step 4), if there is a significant excess of JB Weld after it cures, it
may be easier to use a flat file to knock the excess down to the face of the
blade.

I used glass to wrap around the tips on mine but you don't have that kind of
damage.

Depending on the ambient temperature, the JB Weld may initially be soft
enough to try to 'slump'.  There are a couple things you can do:
1) Every few minutes rotate the prop such that the material flows back the
other direction.  This can get rather tiring waiting for the JB Weld to
kick.
2) Cut a small piece of glass into 'very' small lengths and mix into the JB
Weld before you apply it.  This a great trick that thickens up the mix and
even better, makes the repair stronger.

In specific answers to your questions:
1) yes
2) no
3) very low
4) none
5) as discussed.

Please understand that I am by no stretch an expert at MT prop blade repair
but I know what worked for me.   $0.02

Sid Knox
Oklahoma

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