JohnW

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Posting this for inspiration to anyone that is thinking about or in the process of scratch building a jet. Typical twin boom design, local group project, started in October 2009. Prototype flew in June of 2010, first “finished” plane flew in September 2010. Composite and foam/balsa build. Fuse is glass and booms are carbon/Kevlar sandwich. Carries about 130oz of fuel in three scratch built tanks in the wing. Wingspan is about 80 inches, plane weights 22.5lbs ready to fly with a P120, 28lbs on takeoff with full fuel load. Airfoil is fully symmetrical. Performance envelope is huge with the P120, stable in the air upside down as well as right side up, holds knife edge as long as you have fuel. Attached a few pics starting with very early plug stage to finished jet. - John

rcguy!

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Looks GREAT! Nice lines! Any chance of a kit someday?

Dave

ps2727

John,
Very nice work there. I know how much effort it takes to get that far with a new design.
Congrats on a nice looking sport jet!
Love the shot of the structure in the mold.

Paul

Bob.R

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Very nice work John. Like the intakes.

JohnW

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Thanks for all the kind comments.

rcguy, kitting has been considered, but there are several challanges to producing kits I haven't fully addressed.

-John

rcguy!

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John,

Damn good looking jet for sure. Has a more "modern" look to it than other pod and boom offerings. Much more "USA" type lines.... I would consider an kit if you offered one even on a limited basis.

Dave Rigotti

AndyAndrews

You did a great job on it and it looks nice. But why another boomerang? Does you're boomerang offer anything better than the existing one out there? Wings glassed? Seriously, it really looks just like a Boomerang other than the front part of the fuse.

rcguy!

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Nice Andy!
Rain on the dudes parade!
Sheesh!

Dave

JohnW

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Heh... I don't mind rain. Andy’s comment is relevant and I understand the criticism.

As to “different”, I think all planes look pretty much the same because aerodynamics dictates the shape. If I had made a sleeker sport jet, I’m sure the comment would have been it looks just like a Bobcat except the fuse is a bit different. While this plane has similar moments to an Elan, everything was designed fresh. I’ve put the two side by side and they actually look very different.

From a personal standpoint, I can take pride that I’m flying a plane of my design. I enjoy the challange of both designing and flying planes. All of my existing planes except one (Velox) were built by me and over 50% are my own design.

My individual cost was still lower than what I can get a Elan and a can make myself as many copies/parts as I want, whenever I want. This not only benefits me, but offered a less expensive entry to turbines to several others in on the project that don’t yet fly jets. Our club has a strong turbine presence, getting stronger every year with 100 members, of which I think seven have waivers and fly on a regular basis in the summer, and it will soon be more with this project. Truth be told, I was going to buy an Elan as a goof off plane last October to add to my turbine fleet, but several skilled pilots in our club that wanted into jets didn’t have the financial means to start, which convinced me to start this group project instead.

I believe it is built stronger than Elan’s I’ve seen without significant weight penalty, especially the booms which are a light but very strong carbon/Kevlar sandwich, similar to how I make pattern ship sides. I’ve seen Elan’s split booms on landings. You’d have to destroy this plane and everything in it to split these booms.

The airfoil is fully symmetrical (GOE459) and thicker than boomerangs I’ve seen. Doesn’t seem to impact the top end noticeably. I can’t prove it, but I’m pretty sure it should provide superior low speed performance. It is the same airfoil I use on my pattern ships.

Tanks are in the wings, keeping fuel load in line with the center of mass, which makes the most sense to me.

Due to time, wings/stab and all control surfaces are currently all sheeted foam. That might be resolved this winter if I have the time to make more molds.

-John

Ravivos

Hi John,
First things first - that sure is a nice plane you got there.
although it have some resemblance to other twin boom planes out there, i am sure that as for flying characteristics it is great.
i can totally relate to the "design my own" concept as for me, RC is more than just standing out there fiddling with those two little stick on my million dollar transmitter.

you said that you take great pride in flying your own design and you should, as there aren't that many like you out there.

can you share some of picture and information from the design and building process?
mainly aerodynamic consideration - Tail Volume Coefficient, Wind Cubic loading, balance and moments ect....

Raviv.

i3dm

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Very nice ! do you plan on making kits ?

grbaker

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John,

You hit it out of the park on your first try!! (I'm assuming this is your first jet design)

No worries about weak internal structures here. Everything looks very well thought out and structures look robust. This one will take a lickin' and keep on tickin'!. Sheeted foam wing and stab are just fine, too.

Please keep us informed if you deide to sell kits.

JohnW

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While not my first plug/mold/composite project, you are correct that this is my first turbine design project. It also was the most technically challenging project to date. It is amazing how complicated a “simple” looking plane can actually be to design and build.

I didn’t save most of design calcs as they were mainly back of napkin in nature, but I still have the working drawings. Not a lot to see, but I attached screen shots of the main drawing that has the basic layout and some of the formers.

-John

H.Dale

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John

Excellent job! I have been considering scratch building a jet but have never attempted making a composite. It looks like a daunting task from all I have been able to learn. I have modified a Bobcat (shown below) but would like to attempt to make it a one piece composite much like the other picture below. How hard would that be?

Hal

JohnW

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Hal, making plugs/molds, working with composites, etc. isn't hard, but it does take a special skill set you must learn. I started making plug/molds about 5 years ago, so really not all that long ago. I started small, a cowl and some wheel pants, then a 2M pattern ship, and now this jet. I found the composites section on RCU very valuable as well as other sources such as the youtube videos of the B1 bomber build, etc. The largest challange is that plug/molds are a pay up front process. Making a plug/mold can be time consuming, but the reward is the parts build fast.

cmjets

Hi John:

Great job, but why you chose that plane, I think there are another beautiful models.

See my Bandit, Bobcats and Starjet.

Best Regards from Spain.

Carlos.
____________________________
http://cmjets.blogspot.com/

dave.windymiller

Im going down a similar path with my first jet to keep cost down but its still far from flying.

Mig 1.44

JohnW

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Dave, that is a awesome looking project. Look forward to maybe catching some pics of it here when it is flying.

Carlos, very nice. I previously explained the motivation for choosing this type of plane, and now that I have put ~30 flight on it I can say it is a blast to fly. It flys a lot like a pattern ship... welll, a jet powered one anyway. Very neutral on the controls. The low speed aerobatic handling is better than I've seen on any other plane except thrust vectored models, i.e. very stable but can change direction quickly. Takeoff to a tight 1/2 loop going inverted down the runway the opposite way I've found quite amusing.

RAPPTOR

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very kool ..how did you figure c/g..??

GOGGLES PIZANO

I found this thread by accident....I love the modified might bobcat H.DALE.I would love to see more pics and detail if possible.looks awesome.thx.

turbinebuilder

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Good to know there are more scratch BUILDERS.Arfs are lot easier but there is no warm and fuzzy feeling after ASSEMBLING them.Anyway here's mine.

erbroens

Great work, congrats! To me seems wise being conservative on the airplane design as a club project..guaranteed fun for everyone.

This are two airplanes I designed some years ago thar are still around and are a lot of fun too.. The Hotcat and the JM-1

sidgates

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Below is my scratch built F-94C. Currently waiting for test flight. 82.5" long, 76" span, est. 22lbs. White will be replaced with aluminum after test flying which may be awhile do to winter weather in Denver. Build pictures available on my web: http://www.sidgates.us/HOBBIES/PROJECTS.HTM

DiscoWings

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that looks very cool.

mick15

Here's my contribution to the scratch built. Sorry it's a twin boomer! It is scale though.