Hatz Biplane Association

Found this on the old forum...... quite a few years old.
Jurg is still active but I don't know about Paul Brown.
Jeff Moore
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I have recieved a couple of requests for information on Jurg Muller's reccomendations for a spar upgrade for upper front spars on the Kelly-D, I would be happy to mail or fax a copy to anyone interested in reading the whole report, I recieved the report along with my new set of plans a few weeks ago (have no plans # yet as the records were missing at time of shipping)
Briefly Jurg reccomends the following:

FOR EXISTING AIRPLANES. Do not perform aerobatic maneuvers.

Limit maximum take-off weight to 1,400lbs

FOR NEW AIRPLANES. Use Douglas fir for upper front spars.

Increase the height of upper front spar.

Jurg also reccomends extending the 1/4 inch plywood doublers on bay inboard and outboard. He states that it is important to use high quality 5-ply birch plywood and to bevel it generously.The face grain of the plywood should run parallel to the spar.

Have you noticed that we now have more topics on the Kelly-D forum than the CB forum does.


Paul Brown
Ridgefield WA

Greetings All,

I was reading through the archives, and came across several references to the Kelly D Spar upgrade...

I'm flying from Washington to California this Wednesday to take a look at a Kelly D that looks very promising. Can anybody tell me how to tell if this upgrade has been done? The owner is unsure. It was originally built in 1989, but recovered in 2001. If it hasn't been done, is it a mandatory item to be worried about? This plane has an O-235 and weighs 975 empty.