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Author Topic: PT-1 conversion  (Read 468 times)
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aerotrope
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« on: March 27, 2021, 01:59:20 AM »

I built this 20" rubber powered PT-1 from the John C. Winter plans printed full size in Flying Models back in the summer of '70.
After about 50 trim flights I was unable to find a fix for spiral instability, and as I wasn't willing to go as far as rebuilding with more dihedral, it sat on a shelf for a season.  Then I found a broken ParkZone P-51 for $20 at a garage sale, so I pulled the motor and receiver and put them in the PT-1.  Didn't think to take pix of that surgery, but it wasn't too awful - I removed a bit of tissue from the bottom, glued the receiver to a piece of 1/16" sheet and glued the assembly in between the lower wing and the engine bay.
I made a new fin/rudder and elevator, keeping the existing stab, and temporarily replacing the tail bracing wires with struts under the stab.

It has turned out to be a slow, easy flier, capable of loops and spins.  Still has the instability and is not hands-off trimmable.
Only the last picture is post-conversion; the sewn elevator hinges can be seen, as well as the electric prop and the faint glow of the receiver LED down in the cockpit.
Next time I have it out I'll try for some flight pix.
Attached files Thumbnail(s):
PT-1 conversion
PT-1 conversion
PT-1 conversion
PT-1 conversion
PT-1 conversion
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kaintuck
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« Reply #1 on: March 27, 2021, 07:06:11 AM »

Yours is a nice one, very clean!
I too have a biwing that is a booger...a sopwith camel, electric, .....she sits on the shelf waiting for someone quicker on the sticks than me!
Marc
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aerotrope
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« Reply #2 on: March 27, 2021, 10:17:46 AM »

Thanks - it's actually the third from these plans I've built over the years.  First was when I was 14; it glided ok but I had no idea about free flight and no place to fly so I put a bit of sheet around the nose and converted it to .049 control line.  Got maybe 25 flights before it broke up in the air.  Altogether great fun and very exciting at the end.
The second, twenty years ago, was enlarged to 30" span with a PeeWee .020 for free flight power.  It flew a few times, but had trouble with wing warps.
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Tiger Tim
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« Reply #3 on: July 02, 2021, 06:20:02 PM »

Beautiful work, and I’m always a sucker for sewn hinges.
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simpsd
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« Reply #4 on: July 02, 2021, 07:20:21 PM »

Wow, that is a beautiful little plane.  The finish is what I aspire to. It sounds like it flies a lot like my Wiley Post A that I posted about here a little while ago. Did you use nitrate dope thinned and brushed on? It came out so even & smooth. I love the close-up picture of the cockpit.
 
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aerotrope
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« Reply #5 on: July 05, 2021, 01:39:33 AM »

Yes, two coats of Randolph nitrate, thinned by half.  The tissue markings were applied with the second coat.
I've had as good results with low-shrink butyrate, but the vapours are even more obnoxious than nitrate.
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freeman
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« Reply #6 on: September 02, 2021, 07:09:34 AM »

Wow, that's a lovely project! I would love to see it flying. Do you have any videos that you can share? My very first model was a PT-3 and it was quite a challenge to build it into something that can fly. I think I have just chosen a difficult project for a starter. But now whenever I fly it in the backyard of our property in Cannes I'm enjoying the same old feeling of success that I felt at the first time.
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dosco
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« Reply #7 on: September 02, 2021, 07:33:16 AM »

+1

That's a beauty. Very clean!

Best-
Dave
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Konrad
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« Reply #8 on: September 02, 2021, 08:45:02 AM »

Sorry I missed this when it was first posted.

That is a great fix for an unstable FF model.

Well done!

All the best,

Konrad
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Cut it twice and it's still too short!
aerotrope
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« Reply #9 on: September 18, 2021, 12:28:27 AM »

Thank you, all.  Flying season isn't quite done around here, so I'll try for a session with video.
Here's a pic of it in its free flight days, just starting left spiral.  Photo by lens wizard Craig Limber.
Attached files Thumbnail(s):
Re: PT-1 conversion
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TimWescott
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« Reply #10 on: September 18, 2021, 11:40:22 AM »

I'm wondering if there's anything you can do with stealth surfaces that would fix this -- either a clear vertical surface from fuse to wing (which supposedly adds some dihedral effect, by damming up the air on the bottom of the top wing), or clear surfaces between the front & back flying wires that you so thoughtfully installed, to make it into a tripe with lots of dihedral.

I'm wondering if the original had this problem, or if it was fine as long as you didn't hold on to the stick -- then I wonder if you built a FF version with an articulated rudder on really free hinges (i.e. thread hinges) if it'd reduce the vertical stab effectiveness enough to regain spiral stability.
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Konrad
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« Reply #11 on: September 18, 2021, 10:34:44 PM »


I'm wondering if the original had this problem, or if it was fine as long as you didn't hold on to the stick -- then I wonder if you built a FF version with an articulated rudder on really free hinges (i.e. thread hinges) if it'd reduce the vertical stab effectiveness enough to regain spiral stability.
Don't know about the full size. But a free flopping rudder (tube and pin hinge) often solved the spiral instability issue.
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Cut it twice and it's still too short!
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