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Jul 25, 2020, 06:50 PM
It's all about scale models!
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Build Log

Yak 3 "SteadFast" Reno Racer Conversion


Once again, I am listing my project under "Scale Kit/Scratch Built" in spite of the fact that the project's origin is a foamie. I don't feel most readers of "Electric Warbirds" are very interested in in-depth projects like this, and it's definitely not an ARF assembly project. Maybe someday RCG will add a category more appropriate -- or officially expand this category to include extensively modified foamies. Once again, I'll point out that I dislike the label "Kit Bash". I only "bash" models when I crash them. Modify or Convert are much better descriptions IMO.

This is my third Covid-19 project (previous projects: Black Horse Dornier Do335 and Hawk 75A-P-36 Conversion). Our city is not quite as "locked down", but my business is taking a hit, as my clients have found their business way down. Hence I have more time than I know what to do with, and much of it is being spent in my shop. My new motto is "what else have I got to do?" Know the feeling?

The basis for this project is the Taft Hobby Yak 11 trainer, which is available from AliExpress and Banggood. Sometimes they even get a few at their US warehouse, which is recommended during these days for obvious reasons.

I got one of these Yaks because I like warbirds that are off the beaten track. It assembled easily. I was surprised at how light it felt. The wingspan of 1450mm is deceptive because the fuselage is enormous. You could fit 4 large lipos in there (not that you would).

I flew this model stock 13 time according to my flight log, and was very surprised with how well it flew -- fast, and terrific vertical. Really amazing for a large 6s warbird.

But the red/white color scheme and gigantic greenhouse canopy really didn't suit me. I thought about just repainting the scheme and leaving as a Yak 11, but the more I flew it, the more I didn't like the canopy.

I looked at several Yaks which were converted to racers, and settled on a Yak 3 "reproduction" built in Romania in 2005, which raced as "SteadFast". This plane set a series of world records (including world speed record) for its weight class, and is powered by a Pratt & Whitney R-2000. The plane survived its racing career and now lives in Australia, flying for airshows and giving rides -- while it looks like a single seat fighter, it actually has two seats, both with fight controls.

As with many such projects, this became much more involved than it appeared at the outset. But this project gave me an opportunity to further explore the usefulness of 3D printing, and also large vacuformed parts made over 3D forms.

In my next entry I will go over my list of things involved with this modification.
Last edited by MrSmoothie; Jul 25, 2020 at 09:01 PM.
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Jul 25, 2020, 07:03 PM
It's all about scale models!
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What's Involved with a Yak 3 SteadFast Conversion?


Since I don't compete, I only have myself to satisfy with these projects, so I can pick and choose which features I intend to replicate and which things to skip for one reason or another. Sometimes it's an issue of "bang for the buck -- you make the change and it really stands out. Other times, it's because it presents a challenge for how to make the part or modification. Some things are skipped because I doubt anybody would ever notice -- especially if the change would involve a lot of work. Other times I'll skip the change to avoid complexity. I'm trying to end up with a model that's fun to fly and doesn't break a part every time I take it to the field.

List of changes for SteadFast:

-- Canopy. The most obvious difference. While a two-seater aircraft, SteadFast has a single-seat style canopy much different than the Yak 11. More on this later.

-- Spinner. The SteadFast Spinner is considerably larger than the Yak 11's. On the model, the Yak 11, the spinner is about 83mm dia. while Steadfast's is about 120mm dia. This is very evident in photos.

-- Prop. Most if not all Yak 11's have two-bladed props, and that's how the Taft model arrives. The motor/prop combo works fantastic. SteadFast has a more fighter-appropriate 3-blade prop. I hope when it's said and done it flies as well as the two blade stock setup.

-- Color Scheme and Graphics. Completely different and offering a few challenges.

-- Large Air Scoop over the cowl and forward deck.

-- Wing Tip Smoke Generators. Added after sale to Aussie company for airshows

-- Retractable Tail Wheel. This is one of those things that I decided to skip, for the sake of complexity and also to avoid CG issues on a rather short-nosed model.

-- Wing Root Air Intake. The Yak 11 only has one on the starboard wing root. SteadFast has two. I decided to skip out of laziness, figuring nobody would ever notice.

-- Inner Gear Doors. The SteadFast has small inner gear doors, which wouldn't be that hard to add -- but they are the kind of thing that always seems to be problematic eventually, and frankly, in flight I can hardly tell if the gear went up all the way on a model, let alone if it has inner gear doors. So... skip.

-- Control Surface Trim Tabs. The Yak 11's trim tabs would be timmed off flush -- SteadFast has "integral" trim tabs.

Other things:
- Replacing the Stock Retracts, Struts, Gear Doors and Wheels. More on the why and how later.
Last edited by MrSmoothie; Jul 25, 2020 at 08:59 PM.
Jul 26, 2020, 11:39 AM
It's all about scale models!
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The Canopy Mod that Did Not Work...


I admit that I kind of dove into this part of the project without thinking about it enough -- or doing enough research. I figured if I was only doing a basic representation of SteadFast, all I needed to do was remove enough sections of the trainer canopy to make it a single seater.

Wrong! What I was left with wasn't long enough and too tall. I realized right away that I was going to have to vacuform a new canopy much scale in profile, and that the project's success would more or less hinge on this.

On the other hand, I did get a good start at cutting out the foam "seats" and starting to fill the forward section with some foam, which I would eventually cover with plastic sheet.
Jul 26, 2020, 11:47 AM
It's all about scale models!
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Getting Good Scale Reference Before Proceeding.


I'm a fan of Air Racing enthusiast Taichiro Yamashita, who has drawn dozens of 1/48 scale drawings of famous race planes. Clearly this is a long-time passion of his, and his work is excellent.

His website is here: http://taichi56jp.g1.xrea.com/

The images I am posting are the same low-res images he makes available on his website -- you can purchase laser prints in higher resolution which he mails, which is what I have done for this and previous racer conversions I have done (RB-51 Red Baron Mustang, and Bud Lite Super Corsair).

After reviewing the drawings, I realized I was being overly optimistic about the canopy and I'd have to approach it entirely from scratch.

A note about the drawings: they depict SteadFast during its Reno racing period. I wasn't a big fan of the big winged graphic on the wing undersides. After doing some research, I found that it had been repainted once owned by FighterPilots.com.au and replaced with their logo. I felt like this was a lot cleaner and more visually consistent with the upper surfaces.
Jul 26, 2020, 12:00 PM
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3D Printed Canopy Molds for Vacuforming?


It was clear that I'd need to vacuform a new canopy which meant making molds for a canopy around 15" long. In the past, I've used balsa, but man, would that be a job. Some use foam and fiberglass over that.

I've become just good enough with Tinkercad (a beginner 3D design program) to become dangerous. I took a crack at making the canopy in 3 pieces (the reason for this will be made clear later), and printed the rear section first, as it was the largest.

It took a great deal of sanding to eliminate the faceting, a result of 3D forms without a lot of resolution. This made the walls thinner than I printed them.

The good news was that I could indeed vacuform over this -- the bad news was that after a few trial and error "pulls", I could see that the thin walls were starting to deform so as to allow the "infill" pattern (an "X" grid) to show through, which was visible in the clear part.

Clearly I needed to print the mold with thicker walls and higher percentage infill.

The size of my pulls was dictated by the fame dimensions of my newly acquired Mayku vacuum forming machine. This is a beautifully made (and very expensive) machine which provides an open frame area of 200mm square, using material 235mm square. It has the heating element, but not a vacuum. Instead, a shop vac hose is connected to the machine, and the vac plugged into the machine. When the plastic frame is dropped over the mold, it automatically turns the vac on for about ten seconds. Very cool.

https://www.mayku.me/

I experimented with putting one layer of styrene over the 3D mold first, to help cover little flaws. The actual clear part was pulled from .040" PETG, which is about 1mm thick.

The rear canopy section really pushed the limits of the Mayku, and honestly, I was surprised at how well it worked.

Then I discovered a different approach to modeling the canopy in TinkerCad that seemed like it would be more accurate in cross section and be higher resolution. Since I had to 3D print a new mold anyway, I decided to start over again.
Jul 26, 2020, 02:26 PM
Registered User
Great work Mr. Smoothie!! I have to do the same conversion to match my friends Yak-3U that is just about ready to test fly. I would like to purchase a canopy set from you, if you were willing to make a set for me. Here is a pic of my friends Yak.

Wayne
Jul 26, 2020, 03:20 PM
Big gov never Works
St. Martin's Avatar
......
Last edited by St. Martin; Jul 27, 2020 at 04:16 PM.
Jul 26, 2020, 06:38 PM
It's all about scale models!
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Second Go at the Canopy


I was able to get the profile mostly correct with my v1 mold, as well as how it looked from directly above. However, my cross section was wrong, and I knew it. The SteadFast canopy sides are mostly sloped flat areas. I didn't think it would be possible to model this in Tinkercad. However, I discovered a shape called "SVG Revolver" where you can import an SVG file -- a flat, vector piece of art. I thought maybe I could draft a more correct cross section, import that, and then... Hard to explain, but after much persistence and trial/error, I not only ended up with a canopy closer to scale, but one that had better resolution (meaning fewer facets to sand smooth later).

Sanding takes some effort -- I start with 80 grit -- the new "purple" 3m sandpaper seems to work best -- then wet sanded going through 180-220-320 3m wet/dry.

I was able to get some decent pulls -- since I was new to my Mayku, I did a lot of experimenting to see what worked best and made far more "pulls" than the three that I ended up using.

Around this time I realized the rear canopy section would start forward of the rear edge of the battery hatch. So I lopped off the rear-most section of the hatch, and integrated the piece into the fuselage. I also started lining the cockpit interior with sheet styrene. I can get nice results and never have to worry about gatoring under the glass.
Last edited by MrSmoothie; Jul 26, 2020 at 06:44 PM.
Jul 26, 2020, 09:42 PM
Registered User
Nice work on the canopies.

Looks like you rotated side view SVGs and the sliced off the sides to get your molds.
Jul 26, 2020, 09:58 PM
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Kiwi's Avatar
Steadfast has now moved and lives in New Zealand owned by Mark O'Sullivan and Ronan Harvey
Jul 26, 2020, 10:01 PM
It's all about scale models!
MrSmoothie's Avatar
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Quote:
Nice work on the canopies.

Looks like you rotated side view SVGs and the sliced off the sides to get your molds.
Thanks -- but I didn't use side view SVG's -- I drew a cross section and using the "SVG Revolver" shape (found in "Featured Shapes), basically "extruded" that cross section. Then a lot of other things until it became the shape I wanted. I really can't explain it better than that.

The center section was simply the cross section SVG extended out.

The top of the hatch was modeled separately -- not a cylinder, as the radius becomes smaller towards the tail, so a section of a cone was used.
Jul 26, 2020, 10:04 PM
It's all about scale models!
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Quote:
Steadfast has now moved and lives in New Zealand owned by Mark O'Sullivan and Ronan Harvey
Huh -- you'd know better than me. But why is it still listed on this website, which appears to be Australia-based? And with the new ownership, does it still have the FIGHTER PILOT.COM.AU across the lower surfaces of the wing?

https://fighterpilot.com.au/
Jul 27, 2020, 02:37 AM
Scale Builder
Another great project that is right up my alley Nick. I am just about finished up with a model of the modified Yak-11 racer "Perestroika" but I have a second airframe, partially built, that I hope to finish as the airplane in the picture which has airframe modifications very similar to those of Steadfast. Good luck with your bird.
Jul 27, 2020, 08:15 AM
Registered User
Nick, I tried to send you a pm, but it would not go through as your mail box is full. I can post here if you like.. Wayne
Jul 27, 2020, 10:13 AM
It's all about scale models!
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Mailbox emptied a little! Sorry.


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