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Author Topic: Zippiee Repair Pictorial—Rescuing a Hollow Log  (Read 2031 times)

Offline Dave Hull

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Zippiee Repair Pictorial—Rescuing a Hollow Log
« on: March 07, 2023, 10:52:21 PM »
Larry Renger (AMA--L9246) campaigned his own-design 1/2A hollow log racer in the Knights of the Round Circle 1/2A Proto Hollow Log Races. It is in the spirit and tradition of the Scientific-Musciano hollow log designs. With these, you could get practically any type of airplane you wanted, so long as it was 18” wingspan and had a partially hollowed balsa block fuselage, all for $3.95. At least, that was what was advertised in the magazines for a couple of decades. Larry’s Zippiee design is a bit more refined. Elliptical surfaces all around, internal bellcrank, very streamlined fuselage for maximum racing speed, and short landing gear to reduce drag. According to Larry, that short gear might well have been the plane’s downfall, as discussed later.

This particular design in my opinion is easily the most beautiful of the genre, with only the Golden Hawk coming close. As such, it was well worth it to me to do a bit of work to restore some of its original beauty. It had been thru a pretty bad crash or two. I believe Larry said it torque-rolled on takeoff and came in on him, perhaps because of the lack of propeller ground clearance.

Here is what we started with. The fuselage had been epoxied back together, maybe to make another try during the contest? The rudder and aft fuse didn’t quite line up and needed some work. The outboard wingtip was lost. Perhaps it was windy that day, and it blew off the field and into the grass? Follow along and see how things turned out.

Figure 1. The first picture I took of the Zippiee repairs. Here, I have already stripped off the engine, then cleaned off the plane to get rid of any oil and dirt. A template of the intact wing was made from my favorite template material—a Corn Chex box. Don’t use high-sugar cereral box cardboard because then the planes always come out heavy! The piece of balsa has been scientifically selected for the exact proper density for the new wingtip. Actually, it is what was left over from making a couple of new biplane wings barely visible under the sanding block at the top of the picture. But those are part of a different rebuild story!

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #1 on: March 07, 2023, 10:55:05 PM »
Figure 2. Once the new wingtip was traced onto the perfect racingwood, the wing was cut to ensure a clean butt joint. This one actually had two angles as you can see in Figure 1, since more of the leading edge was missing. Once the replacement tip was exactly matched to the wing, some 30-minute magic stuff was applied to make it all one piece. The wing is flat-bottomed, which made it easy to achieve proper alignment while curing. A steel block and my “sandpaper eraser” hold down the inner portion of the wing and I grabbed the first thing I could find to weight down the tip. Waxed paper keeps the work surface clean. This was the easiest part of the overall repairs, so to get up some momentum, I did it first.

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #2 on: March 07, 2023, 10:57:39 PM »
Figure 3. After the epoxy cured and the wingtip was definitely going to stay on, the template was used again to mark the wing outline. Note that the grain in the replacement tip was aligned roughly tangent with the leading edge. Since I was not planning on refinishing the entire plane—I wanted to preserve the original graphics—I needed to carefully sand to blend the new tip without causing more work.

Offline Paul Wescott

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #3 on: March 08, 2023, 01:15:08 AM »
Slightly out of chronological order (Sorry Dave)…

Pictures from December 1st, 2018 at the Toys for Tots Control Line Speed and Racing event at Whittier Narrows, El Monte Calif.

The back Story:

Larry Renger brought an amazing custom 1/2A airframe with an amazing Larry-built Cox .049 engine (might even have been a Venom).  Larry described that he keeps most of his good balsa the way most of us do on shelves or in drawers.  But he keeps his best balsa on the ceiling, implying that his best balsa is so light that it floats to the ceiling like an abandoned helium balloon.  So Larry said he scraped a block and some sheet off of his ceiling and built the Zippiee.  It’s a beautiful little airplane.  But its maiden flight in the speed circle didn’t go so well.  Either the airframe was too light, or a tad too small, or the engine was too powerful.  My daughter who used to go flying with me and I volunteered to time the flight.  The flight was Amazing!  Fastest 1/2A I’ve ever seen.  However instead of flying around the circle Immediately upon launch the little airplane took off ACROSS the circle.  Never even made 3/4 of a lap.  When it got to the other side of the circle the lines parted and the model headed straight for the chain link fence which stopped it cold, although not undamaged as you can see in the last picture.

The model hasn’t been seen since until it turned up in the hands of the talented builder/rebuilder Dave Hull.

Pre-flight:


Offline Paul Wescott

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #4 on: March 08, 2023, 01:17:22 AM »
Also pre-flight next to Howard Doering’s stable including two Dale Kirn Torquette biplanes for scale:


Offline Paul Wescott

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #5 on: March 08, 2023, 01:18:20 AM »
Just before the flight, accident, both:


Offline Paul Wescott

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #6 on: March 08, 2023, 01:19:19 AM »
Post-accident damage:


Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #7 on: March 08, 2023, 03:44:39 PM »
Paul,

Thanks so much for some additional history of this little plane. And especially the pictures! What they show is that I'm missing the cowling! So I'm going to have to try to recreate that....  Looks like a molded glass shell was on it originally.

After the wreck that you showed with the broken aft fuselage, it was tacked back together with epoxy. I don't know if another flight was attempted or not.

And yes, Larry told me that the engine is an authentic Venom. I cleaned that up and will reinstall it.

More details to follow....

The Divot McSlow

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #8 on: March 08, 2023, 03:57:23 PM »
Figure 4. Time to look at the tail. The break goes from the rudder and down thru much of the fuselage. Note the pushrod, which engages with a one piece formed-wire elevator joiner/horn, like many F2C racers.

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #9 on: March 08, 2023, 04:02:21 PM »
Figure 5. The damage on the outboard portion of the tail looks a bit more dramatic. Here, I have already started sanding down flush some of the temporary epoxy repair, but still have a way to go. The goal was to blend the surfaces back to the original shapes and re-establish structural integrity.

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #10 on: March 09, 2023, 10:42:17 PM »
Figure 6. As sometimes happens, the nature of the damage tells you it will be easier and make a better repair if you entirely replace something. In this case, the rudder had epoxy between the two pieces from the temporary repair and there was no way to close up the gap or fair the rudder back together. So, make a new one! On a plane this small, even the smallest pieces from the scrap box are big enough.

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #11 on: March 09, 2023, 10:43:43 PM »
Figure 7. A template was made from the old fin/rudder and a new one was cut out. Here, it has been epoxied onto the fuselage, which was dressed down flat with a sanding block. Square, flat, and rectangular joints are much, much easier to achieve a good fit than irregular surfaces! An epoxy fillet was applied afterwards. You can also see some more progress on blending the fuselage repairs and the wingtip repair. The light-colored band inboard of the wingtip glue joint is Elmer’s wood filler. The tube is in the upper right in this picture. Good stuff.

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #12 on: March 10, 2023, 12:49:32 AM »
Guys, someone was nice enough to point out that the original build history of the Zippiee is documented here on the 'hanger. It has good info....

https://stunthanger.com/smf/12-a-building/not-stunt-but-12a!-zippie-hollow-log-racer/msg229902/#msg229902

And the plans are posted here:

https://stunthanger.com/smf/12-a-building/zippiee-racer-information/
« Last Edit: March 10, 2023, 01:16:17 AM by Dave Hull »

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #13 on: March 11, 2023, 01:23:20 AM »
Figure 8. The wingtip was then glassed with .58 oz/yd2 to reinforce the joint, sanded to blend to the contour of the existing wing surfaces and then given two coats of primer. KlassKote primer is thick and won’t easily go thru my airbrush. So the primer was reduced a bit and applied by brush. To get the surface to blend, the new wooden wingtip needed to be sanded down below flush to leave a few thousandths of an inch for the lightweight glass. I used EZ-Lam 30 minute epoxy, which is my favorite for glassing models. It sands extremely well—not all epoxies do. At this stage, Zippiee looks like a Dalmation/Chilipepper cross, or maybe a red-headed appaloosa? (Don’t pay any attention to the plane that Zippiee is sitting on. That’s the CroMagnum which has had waaaay more attention than it deserved this past year involving bellcrank/leadout/pushrod replacement and is still hogging all the bench space. But it is ready for paint now.)

Offline Juan Valentin

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #14 on: March 11, 2023, 06:15:16 PM »

 Hello Dave
                       You are doing great with the repair!
                                                                                                                                                                   Juan

Offline Paul Gibeault

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #15 on: March 12, 2023, 09:02:06 PM »
Hi Dave,
Sorry, I don't follow Stunt Hangar that much.  It seems to me from this flight description that your leadout guide is too far forward + not enough tip weight for initial testing. On my proto's I use a tip guide with 5-6 holes just so's I can start with the most AFT position & gradually move it forward. I also recommend lead tape as is sold in golf stores. Wrap some around the OB wingtip & after successive fligts keep removing a bit until takeoffs become too light on the lines.
Such precautions are necessay with a lightweight model with a rudder on top which causes the model to turn into the circle. I agree I wouldn't have expected that with a L/H prop...

Great job on documenting the repairs.

Cheers, Paul

p.s the photo of my wingtip L.O. guide is apparently too large for this site.


Fastest 1/2A I’ve ever seen.  However instead of flying around the circle Immediately upon launch the little airplane took off ACROSS the circle.  Never even made 3/4 of a lap.  When it got to the other side of the circle the lines parted and the model headed straight for the chain link fence which stopped it cold, although not undamaged as you can see in the last picture.

The model hasn’t been seen since until it turned up in the hands of the talented builder/rebuilder Dave Hull.

Pre-flight:
« Last Edit: March 15, 2023, 11:41:58 AM by Paul Gibeault »

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #16 on: March 13, 2023, 12:22:26 AM »
Thanks for the comments, Juan and Paul.

A bit more info to come. One of the likely causes of the torque roll was that the gear was very short. Larry was running a left-hand prop and believes that it may have touched when the tail rotated, which would have "walked" the nose into the circle at contact. The gear issue has been rectified during the repairs.

As far as tip weight, I agree. In fact, tip weight doesn't have much impact on the top speed, but does affect the proto speed. But if you can't get off the ground, then you really aren't even in the race--you just paid contest fees to crash. I most often will tape a tungsten washer, or even just a quarter onto the bottom of the wing for testing. I haven't tried golf tape--since I am doing my level best to avoid "duffer" status....

I will be sure to consider the leadout guide location before any attempt to fly it. Based on Paul W's research, the plane is missing a cowling and a spiffed-out spinner. Going to have to find/build those....

Dave

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #17 on: March 13, 2023, 12:24:04 AM »
Figure 9. The other side of the broken fuse after a couple coats of primer and almost dry enough to start sanding. Larry painted the plane originally with KlassKote primer and KK epoxy paints. I used the same materials in order to best duplicate the finish. But, since painting is not one of my skills, the results are more than a bit off. The KK primer comes in white and gray. I always use white for brighter top colors. But Zippiee had a much deeper red finish, and despite checking the primer as I sanded thru old finish and thought I saw white….

Offline Larry Renger

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #18 on: March 13, 2023, 07:03:38 AM »
I think I still have the cowl, but the spinner was ruined.  H^^
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #19 on: March 13, 2023, 03:07:49 PM »
Good to hear from you, Larry!

Unless you are keeping the cowl as a souvenir, I can try to do any needed repairs and get it back on the Zippiee. Or, I can recreate one based on the forms shown in the plans plus the picture. Whichever you think would be best. Hate to see a naked motor on such a smooth airplane....

Do you recall what type/brand spinner it was? I might go looking for another one.

I also saw your comment in one of the threads describing the original construction that you were thinking of installing gear fairings. I thought about doing that too. What shape were you imagining? And, just out of curiousity, did this plane originally have wing-mounted gear? There are some "artifacts" that suggest that might have been the case.

Dave

Offline Larry Renger

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #20 on: March 14, 2023, 04:28:39 AM »
I think the spinner was a Froom.

And yes, the original gear was wing mounted.

Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #21 on: March 14, 2023, 04:55:09 AM »
Ahhh. The plot thickens....

Thanks, Larry!

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #22 on: March 17, 2023, 11:10:49 PM »
Figure 10. There came a day when the dreaded painting could no longer be postponed. Even the rainy weather wouldn’t cooperate—it wasn’t even foggy enough to leave it for another day….  I mixed up about ½ oz of red, let it go thru the required 30-45 minute induction period, then thinned about 50% with KK reducer and loaded my Badger airbrush using the large size tip.  A final wipe down with a microfiber towel to get off any remaining dust and you just have to muscle up and pull the trigger on the airbrush. I have heard car painters talk about blending a repair. They tell you not to mask off a hard new "paint/old paint" line because you will never get it to match. With the airbrush, I hoped to have the control to aim across from old paint to new areas to control the overspray. That worked well. In some places, a bit of rubbing compound on the old paint brought up the shine and helped the blend. In other places, it looked like I would go thru the paint before it started to even up. As a super-light proto-speed plane, there wasn’t a lot of paint thickness to work with. Maybe I can do a bit more buffing?

(Don't be fooled by the red overspray on the "paint stand." That was from restoring old Ford 2N tractor parts...not from prior Zippiee paint attempts....)

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #23 on: March 19, 2023, 05:52:45 PM »
Figure 11. The landing gear needed more than restoration—it needed new geometry to help prevent future takeoff incidents. Something both Larry and I agreed on! Note the notch in the firewall for better engine breathing. Still working to clean up the oil-soaked firewall before doing touchup painting.

edit--I probably should have said, this is the "before" configuration. Only a tiny bit of prop clearance for even a short, short prop....
« Last Edit: March 19, 2023, 09:10:17 PM by Dave Hull »

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #24 on: March 21, 2023, 03:14:57 PM »
Figure 12 & 13. After a couple of consultations with Badger, Binks and Paasche the legal remedies are (mostly) behind me. Two coats of KlassKote red overtop the KK white fast primer--but the colors don't match. I used a bit of rubbing compound to try to blend the old paint adjacent to the repair and it helped some. But, we are preserving what's here, not restoring the entire plane. I needed to preserve the graphics and keep things authentic. So I'll live with the results...dang it!  In the second picture, you can see the prior installation point of the wing-mounted gear that Larry confirmed earlier in this thread. The bottom view of this design really shows how clean it is. And that's a dehavilland stabilizer if I've ever seen one....

Offline Juan Valentin

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #25 on: March 22, 2023, 08:59:28 AM »
Figure 12 & 13. After a couple of consultations with Badger, Binks and Paasche the legal remedies are (mostly) behind me. Two coats of KlassKote red overtop the KK white fast primer--but the colors don't match. I used a bit of rubbing compound to try to blend the old paint adjacent to the repair and it helped some. But, we are preserving what's here, not restoring the entire plane. I needed to preserve the graphics and keep things authentic. So I'll live with the results...dang it!  In the second picture, you can see the prior installation point of the wing-mounted gear that Larry confirmed earlier in this thread. The bottom view of this design really shows how clean it is. And that's a dehavilland stabilizer if I've ever seen one....

 Hello Dave
                      I think it needed grey primer for the red to match but I`m just guessing.
                                                                                                                                                                                juan

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #26 on: March 22, 2023, 05:26:49 PM »
Juan,

I think you are right, but here's why that was not obvious to me. First, the primer that I could see around the firewall seemed to be the white primer if you look at the earlier photos. However, and this is debatable, I only found out thru this thread when Paul posted a picture of the plane originally before paint, that Larry had covered the wing in carbon veil. So if he used the least amount of primer buildup possible, the surface before color coat might have had a grayish tint. And I would have been better served either duplicating the veil--which I did not know about--or using a bit of tint in the white primer. Paul's picture doesn't show any veil on the fuselage, and the paint does match better there. There is also the possibility of the color aging. I give that some credence since the bottom of the plane seems to be a brighter red, not the deeper color of the top...? That said, I have "cleaned up" older models that were painted with K&B epoxy paints and they brightened up a bit. I didn't have much luck doing that with the Zippiee. Finally, I thought multiple coats of red would deepen/darken the color, so I went with two coats. But it was still very bright red and not wanting to keep adding layers (the airbrush is a pain to clean each time) and not believing that Larry put down six coats of KK (who would?) I called it D-U-N done. So, I will enjoy it with some scars from flight test....

Dave

Offline Dave Hull

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Re: Zippiee Repair Pictorial—Rescuing a Hollow Log
« Reply #27 on: March 26, 2023, 08:37:43 PM »
Figure 14. After the paint and body work was done, it was time to work on the gear. The plane was originally equipped with 1” diameter Williams Brothers skinny (antique?) wheels but the short gear just didn’t leave enough room for the 4” diameter prop. So I straightened out the axles making them part of the gear leg, and then “stretched” the gear by splicing on some more 1/16” music wire. I didn't cut any of the original landing gear struts off, I straightened them out! The new gear leg has a 5/8” overlap wrapped with 36 AWG copper, then soft soldered. 

The plastic hubs in the original Williams Bros wheels were getting wallowed out, and the last thing this plane needs is another ground accident! Therefore I “borrowed” the really nice 1" diameter wheels from a concurrent restoration project and installed them. At this point I still need to solder a retaining washer on the axle, but the inside shoulder washers are on. Foremost Products makes exact-fit brass washers that are perfect for this. The revised gear should allow plenty of clearance for a 5" prop and maybe a bit more. That leaves room for experimenting with props in the future.

I’m still toying with the idea of making some gear leg fairings to clean things up. Yes, I’d have to get involved with the dreaded paint process again, but I need to repaint the firewall anyway, and now I know that the original plane had a cowling I will need to build, so….


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