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Author Topic: Interchangeable props for small models  (Read 435 times)
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Pete Fardell
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« on: November 09, 2014, 07:14:30 AM »

I just came across the attached in an old Aero Modeller (June 82).
As someone with an increasing collection of slightly too short to use, snipped off prop shafts I thought it might be a useful idea. As well as making it easy to try different props during trimming, it could also mean not having to make a whole extra nose block to accommodate the scale prop.
The question is, would/does it work as reliably as stated? Or would it end up being just another thing to go wrong?
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Interchangeable props for small models
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« Reply #1 on: November 09, 2014, 08:34:09 AM »

It works fine if you can wind the coils tight enough!
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« Reply #2 on: November 09, 2014, 03:42:04 PM »

I have been using a similar arrangement since 2007 for my indoor models The attached image which I recovered from my post on Small Flying Arts in 2007 (http://www.smallflyingartsforum.com/YaBB.pl?num=1170766951/17#17) gives you an idea.

The stud earring retainer is not needed to keep the prop on the shaft. It is used to retain a spinner. The shaft can be cut close to the the prop hub otherwise. The 0.014" hook over the prop hub is sufficient to retain the prop. Distances are very short so that size wire is stiff enough.

I made a dedicated coil winder to create the coils. The 0.014" wire is tinned with silver bearing electronics solder before winding using acid flux. The prop shaft is also tinned the same way. The acid flux is removed by submerging the wire in a hot solution of baking soda in water. The two parts a sweated together on assembly.

The winder will create snug coils for 0.025" and 0.032" prop shafts. Larger shafts can be accommodated with exchangeable winder components if I ever need to do so. So far I have found 0.025" shafts perfectly adequate for indoor bostonian models.

I now use my version of a "Czech" hook and I intend to change the mushroom shaped PTFE bearing to a nylon sphere which I have purchased from Amazon.

My Observer bostonian can be found here, http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=10463.0 The prop is not removable but the shaft is 0.025" wire. I tried to show the three thrust-line adjusting grub screws but they are very tiny and hard to see in the photo. This model has been flown many times indoors without incident (crashing or snagging). The motor is a single loop of 1/8" 'sport' rubber which gets the model just below the ceiling hazards (gas heaters, pipe work, etc.) in a basketball gym.

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Re: Interchangeable props for small models
« Last Edit: November 09, 2014, 04:04:26 PM by RolandD6 » Logged
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