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Sep 27, 2015, 09:05 PM
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PaulBrad's Avatar
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Jetco Hawk


I was recently pouring through my collection of digital model airplane plans and had one jump out and say build me. It is a model from my youth that I built back in the 50's. Namely, the Jetco Hawk. A nice 25" span model that is fairly easy to build.

I have found that many digitized plans have either sizing errors, or have some part fit issues. For that reason I normally redraw the plan using CAD tools to make sure things will go together as intended by the designer. In some cases I will also tweak the structural design to reflect more current build practices.

Once I completed the plan redraw I built another example of this model that sits in my fond memories reservoir. A couple of photos of the completed model are included here. Weight without rubber is 33.6 grams. The covering is ink jet printed tissue with three coast of 50/50 clear dope.

The original plan calls for a motor made from 9 1/2 feet of 1/8" rubber formed into four loops (8 strands). The plan includes a prop blank layout for carving an 8" prop. The prop I have used is an 8" prop I made on my 3D printer. I am using a slightly higher pitch to diameter (P/D) than would be achieved using the plan prop block. My prop has hypotwist with a P/D of 1.2 out to the 75% radius point and then increases linearly to 1.8 at the tip. The average P/D is 1.5.

I have not yet had an opportunity to fly the model under power, but hand glides look quite promising. I hope to get some powered flights with the model fairly soon.

Since this model is relatively easy to build, I am thinking it would be good for someone with limited stick and tissue building experience. For that reason, in addition to redrawing the build plan I also created a set of illustrated build instructions. The plan/instruction package is available for free download from my web site at parmodels.com. Just go to the downloadable plans section.

Paul Bradley
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Sep 28, 2015, 12:28 AM
skumgummi dave
Well done as usual! Thanks for sharing with us.

Regards;

Dave-
Sep 28, 2015, 09:43 AM
B for Bruce
BMatthews's Avatar
That's an amazing looking model with that finish on the tissue.

The size is an excellent one for a model that is large enough to trim out easily and be able to easily handle a DT system for duration/distance control in limited fields. But the bottom mounted tail makes adding a normal style of flip up tail pretty well impossible. Perhaps some sort of flip up wing controlled by a bottom mounted viscous button timer? If some thought is used it could be done quite neatly.
Sep 28, 2015, 12:15 PM
Registered User
It definitely looks nice and 3d printed prop is really interesting.
Sep 28, 2015, 01:44 PM
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PaulBrad's Avatar
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I very much appreciate the positive comments.

I have not rigged a DT for this model and I fear it will be lost as a result. As was noted, a pop up stab is problematic with the location of the stab.

I am thinking a pop off wing, Embryo/P-30 style, would be the way to go. A wing that tips up would also work.

Paul Bradley
Sep 28, 2015, 02:30 PM
B for Bruce
BMatthews's Avatar
For small field flying I think it would be almost essential. I've lost too many sweet flying small models over the years that didn't have DT's.

These days I want to stick to 18inch and larger just so they won't notice the weight of at least a button viscous timer. And my ideal small field rubber model would use a modified Tomy Toy works for more accurate and consistent DT operation.
Sep 28, 2015, 02:33 PM
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Trisquire's Avatar
Nice work as always Paul. Any chance you could put the printed tissue art on your website?

Tom
Sep 28, 2015, 07:19 PM
B for Bruce
BMatthews's Avatar
Speaking of doping printed tissue......

Paul, how long to let the ink dry/cure before doping the tissue over the inks? Or do you airbrush the clear on?

I ask because I'd had good luck with black ink that had dried over night. So I did up some "decals" that had red ink on them and the red ink dissolved and bled at the edges rather badly from the dope thinner. I found that leaving the coloured inks to dry for a few days seemed to minimize this.

So even if it's airbrushed I still have to wonder how long you gave the inks to really dry and resist bleeding.

Com' on. 'Fess up. Perspiring minds need to KNOW!
Sep 28, 2015, 11:45 PM
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Tom - I will get a file together of the printed tissue to place on my web site. I just need to remove my AMA number .

BMatthews - I have never experienced any ink bleed when applying dope to ink jet printed tissue. I have only used printers that used dye based inks rather than pigment based inks. Since dye based inks are not water fast, I use steam to shrink the tissue. I then brush on 50/50 clear dope.

I typically print the tissue and then apply it to the model the same day. By the time I get the entire model covered and then steam shrunk, a day or so has gone by. That said, I have on occasion printed and doped tissue within an hour after printing. In those cases I am either patching or replacing a tissue panel I am not happy with. I have not experienced any bleeding when the dope is applied.

For many years I was using an HP printer. Today I am using a Canon printer. Both use dye based ink and span a technology period of 20 years. My only thought on your experience in having the ink bleed when dope is applied is the type of ink used by your printer. I have not used pigment based inks but wonder if they may be affected by dope and thinner. Perhaps your printer is one that uses pigment based ink cartridges.

Paul Bradley
Sep 29, 2015, 12:39 AM
B for Bruce
BMatthews's Avatar
I dunno. The printer I used for it was an HP. But it was a fair number of years back. I'm not sure that your comment on HP using dye based inks applied back then.

I'll have to give it another try with my current HP printer. Thanks for your experience and information.
Sep 29, 2015, 06:14 AM
Intermediate Multi
Trisquire's Avatar
Thanks Paul.

Tom
Sep 29, 2015, 07:20 AM
Registered User
Paul, just out of curiosity what do you prefer using to adhere tissue to structure before steam shrinking? Are there any out of the ordinary complications that come with the steam method?

Thanks, Travis
Sep 29, 2015, 10:45 PM
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PaulBrad's Avatar
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Travis - I use glue stick to attach the tissue to the balsa frame. I apply glue stick to the balsa and the tissue where it will be in contact with the frame. I then let the glue stick dry.

The tissue panel is then placed on the model. and lined up. Once in position I use my film covering trim iron set on low heat to iron down the tissue. The heat re-flows the glue stick and really sticks the tissue down nicely. It is easy to heat and lift if I have to re-position the tissue to get rid of major wrinkles or puckers.

I typically use Elmer's School Glue Stick. Nothing exotic. While this is a washable glue, I have not had any issues with it lifting during the steaming process. So far I have never had any lifting either during the steaming process or over extended periods of time.

Tom - I should have the covering layouts on the web site within a day.

Paul
Sep 30, 2015, 08:48 AM
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The covering layouts have been added to the web site. These layouts are set up for printing on legal size sheets of paper (8.5" x 14"). That required the fuselage panels to be split to fit the length of the sheets. The split was placed at the forward edge of the checker board section. That lines up with the uprights and cross pieces. The black edge is overlapped to form the splice.

Paul Bradley
Sep 30, 2015, 09:12 AM
Intermediate Multi
Trisquire's Avatar
Paul, Thanks for the covering layouts. They're awesome.

Tom


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