The KRnet PropBank was created as a "matchmaker" for those with unused props to be able to loan out their prop to other builders, in an effort to help determine the best fit for flying (or soon-to-be flying) KRs. The ability to bolt on and static or flight test a prop that should be in the ballpark for your engine and airframe will go a long way in making first flights safer, as well as giving you a good idea of which diameter, pitch, and manufacturer can give your airplane best performance. Once a good fit is found, you can either buy the prop you have, or contact the manufacturer to build a new one for you. To get an idea of where to start, see the KR-info chart first. Keep in mind that most props will turn 150-300 rpm faster at top speed than they do on the ground (static).

Props are loaned out for $50, paid direct to the owner of the prop. The fifty dollar charge is intended to compensate the guy who was nice enough to loan you the prop, pay for shipping from his end (probably about $15 of that), and also to serve as a deterrent to checking out 20 different props looking for the perfect one. The shipper (guy who loans out the prop) will ship the prop in a box he feels is good enough to protect the prop. Rolling it up in bubble wrap and cardboard will probably do, but a box built out of 1x4 framing with 1/4" top and bottom skin works really well too. Make sure it's insured for the full value both ways!

When requesting a prop, send a check for the "value" to the prop owner, just in case you trash it or never send it back, but the owner will not cash the check for 60 days (negotiable with owner). If you like it, keep it, and both owner and borrower will be happy. Otherwise, ship the prop back at your expense, along with a check for $50, and the owner will tear up the first check you mailed him (we hope). It is advised that you photograph your prop before loaning it out, so there will be no disputes regarding damages incurred, such as spinner cutting into the blades or overtightening prop bolts. Typical torques for wooden props are in the neighborhood of 10-15 lb-ft, but in no case should the prop be torqued past the point of hearing wood crushing noises and you should ALWAYS use a metal crush plate under the prop bolts! It might be a good idea to send a crush plate out with your prop, just to make sure. A recommendation on bolt torques would be good also.

And if you need a prop immediately, the PropBank may have one that will get you in the air day after tomorrow, rather than in 3 months when you can have another one made for you by one of the few prop makers out there. I'll even see if I can get the prop manufacturers to throw some props in there. Maybe some "rejects" that have vibration problems (for static testing), or new props that were made but never shipped.

Above is an image showing the current state of the PropBank. The hotlinks to photos and email addresses won't work in the image, so visit the PropBank webpage for the html version with embedded hotlinks to pictures. I expect this to grow considerably in the next few weeks. If you'd like to try out one of the props listed above, contact the owner directly to make arrangements. Please remember that you are borrowing something with a very high monetary value, so take care not to overtorque the bolts or crush the wood. Carefully inspecting the prop when you receive it and before you return it will go a long way toward resolving any issues that arise.

We should probably work up a standard legal document that both lender and borrower sign to make sure everybody knows the rules. I'll work on that. The bottom line though is that if you damage a prop that you have borrowed, you may very well have just bought it for the full price of the check you wrote to the lender, so keep that in mind. The lender is doing you a huge service by allowing you to home in on the perfect prop for your airplane. Please don't abuse him.

If you'd like to add a prop to the bank, or change your prop description, contact Mark Langford with pertinent info and I'll update it (n56ml "at" hiwaay.net).

Something else we can do is capture the information from your prop test and put it on the web. For example what RPM a certain prop was turned by a certain engine statically, or better yet, while flying, and at what speeds. That sort of thing.

Coming soon: Links to prop manufacturer's webpages with contact info...

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