Super Duper Pronto for CAP 2017 Build Off - RC Groups
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May 28, 2017, 05:35 AM
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Build Log

Super Duper Pronto for CAP 2017 Build Off


Even before I started building an original 48" size Pronto (Dave Robelen) for the build-off, I had in mind building a larger one at 150% or even 200%.

Having now finished my first Pronto, the urge to go larger has returned.

https://www.rcgroups.com/forums/show...TBD2-Build-Off

After checking my workshop supplies I have decided on 72" wing span or 150% of the original design, and balsa construction rather than a depron conversion.

At this size, I think it will need the electric equivalent of about a 35-40 sized glow motor (based on the original being for 15 sized glow).

I have made a start on scaling up the template parts in CAD, and have cut a set of templates for the basic components from 3mm depron. Then I can trace around these onto the balsa.

It is already apparent that although the wing components fit normal 36" balsa, the fuselage and tail components will need some joining width and length wise because they are larger than standard wood.

Name?? Well David Boddington also designed a model called Pronto, and a mini Pronto, so there is probably a Pronto Major also. I think Dave Robelen also designed a Super Pronto with ailerons.
Last edited by Gere Sport; Nov 05, 2017 at 01:53 PM. Reason: transfer build to a different build off
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May 28, 2017, 05:48 AM
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Made start on routing the wing ribs.

The outline is the same as the original, but has top leading edge sheeting and an extra rear spar. Also the trailing edge is made of top and bottom sheeting rather than solid balsa.

After cutting one sheet of ribs, the next 3 cut sheet produced firewood when the machine decided to miss out the breakout tabs. A power reset of the machine and laptop seemed to sort it out - perhaps it was just refusing to work in such hot temperatures. Never had these issues when I used a trusty scalpel.

At 150% size I need 30 wing ribs instead of 20 on the smaller one. This was part of the deciding factor to stall on going to 200%, the wing ribs would then be 16" wide and probably only get 3 to a sheet of wood, needing 40 in total. However the model shows start in a few weeks, and if I am seen doing some heavy lifting from one of the balsa shops, there could be a larger one in the future - we still have 5 months of build off left.
May 28, 2017, 09:02 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Even at 150% it'll be quite a substantial model. Name? Well as Dave Robelen, as you said, had already used "Super Pronto" how about Mega Pronto?
May 29, 2017, 07:56 AM
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J Bergsmith's Avatar
This is very cool, Pronto XL.
May 29, 2017, 09:01 AM
I like thermals
I am 90% certain that Tidewater Hobbies briefly offered a kit for an enlarged 72" Pronto, but I can't remember what they called it. Designed for a .45 glow engine I think. Would have been available in the late 1980's...company used to run adds regularly in Model Aviation for the complete kit line.

Hope you really enjoy this latest project.
May 29, 2017, 11:17 AM
RFJ
RFJ
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A couple of Tidewater ads from 1989.

Ray
May 29, 2017, 11:31 AM
I like thermals
Nice find Ray!
May 29, 2017, 01:24 PM
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J Bergsmith's Avatar
Quote:
Originally Posted by RFJ
A couple of Tidewater ads from 1989.

Ray
Interesting, I wonder if the plans exist?
May 29, 2017, 03:28 PM
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Thanks for excellent information guys. It's got me rethinking the motor to use in the scale up. Perhaps I need more like a 40-45 glow equivalent, with an estimated auw of about 5lbs. Better to know now, and make the adjustments while still at the templates stage.

SD's post about modifications got me thinking. Originally I was thinking of 3 channel and no ailerons, but this will make hitting our narrow runway with crop fields on either side interesting, so perhaps ailerons are worth considering.

Rather than strip ailerons (because I have cut the ribs already), barn door ailerons would be better. Anyone got any ideas what size they should be for a wingspan of 72" and a wing chord of 12"? Also any ideas what the dihedral angle should be reduced to? The original had 3 1/2" under each wing tip, but the scale up will need 1.5 times this amount. So any back of an envelope maths which help me decide the aileron size and reduced dihedral angle would be useful. Then I can see how much effort it is to doctor the parts to suit.
May 29, 2017, 10:09 PM
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Funny you should ask about barn door ailerons. The picture of my Pronto in your Pronto thread (and below) is really a Super Pronto. Managed to find the plans. The Super Pronto has barn door ailerons (barely visible in the pic) and tandem cockpits. The ailerons are 8 inches long and 2 inches deep, and take up the first two rib bays. Dihedral is 1 3/4 inches per wingtip. Highly recommend use of ailerons on your Super Duper Pronto.

Bud
May 30, 2017, 05:10 PM
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Thank-you of the advise, I will draw it on my plans and see what it looks like. Interesting that the dihedral is half when using ailerons. Sounds about right to avoid the drooped wing appearance.
May 30, 2017, 09:10 PM
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Here's a copy of the flyer included in the kit, c1977. The Super Pronto wing span was 50 inches.

Bud
May 31, 2017, 05:37 AM
RFJ
RFJ
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I like Dave's little touch of making the Super Pronto a tandem two seater

Ray
Jun 11, 2017, 10:52 AM
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With the help about ailerons, I have finally drawn up the wing plan and modified the dihedral angle to suit ailerons.

Now that is sorted I have prepared the kit of parts for the wing including holes in the ribs to let the aileron wires through, and it is time to get glueing.
Jun 11, 2017, 11:31 AM
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Quote:
Originally Posted by Gere Sport
Made start on routing the wing ribs.

The outline is the same as the original, but has top leading edge sheeting and an extra rear spar. Also the trailing edge is made of top and bottom sheeting rather than solid balsa.

After cutting one sheet of ribs, the next 3 cut sheet produced firewood when the machine decided to miss out the breakout tabs. A power reset of the machine and laptop seemed to sort it out - perhaps it was just refusing to work in such hot temperatures. Never had these issues when I used a trusty scalpel.

At 150% size I need 30 wing ribs instead of 20 on the smaller one. This was part of the deciding factor to stall on going to 200%, the wing ribs would then be 16" wide and probably only get 3 to a sheet of wood, needing 40 in total. However the model shows start in a few weeks, and if I am seen doing some heavy lifting from one of the balsa shops, there could be a larger one in the future - we still have 5 months of build off left.
Subscribed.

I once made a T-170 (rcm, august, 1985), a 1.7 enlargement of Al Clark's Terrier (rcm, march, 1984), which itself was a one-sixth scale of a low wing home built.
The T-170 wing was 100" long and had a 16 inch chord. Not wanting to drastically cut into my balsa stash at the time, for ribs I used 1/4 foamboard covered in paper/thin cardboard on both sides. The ribs, apart from being cheap, were easy to work with and the resulting wing strength was fine. As long as you are covering the foam ribs in leading edge balsa sheeting and balsa rib caps and a big of trailing edge balsa sheeting, there is plenty of strength. Carpentry yellow glue works fine with these materials.

I've also used 1/8" plus Depron foam, salvaged from grocery fruit/meat packaging trays, in smaller models with similar construction with no problems.

good luck

Michael in Ontario, Canada


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