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Old Jan 26, 2004, 08:36 PM
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Ron Daniels's Avatar
Kitchener, Ontario, Canada
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45" 10 cell Super Chipmunk Beta Build

After some delays caused by my personal (read: other than R/C) life, and some by some broken equipment at the laser cutter's, I finally received the 3 Beta build kits for the Super Chipmunks last Friday.

I built the first 2 Super Chipmunks from a "short kit" of just the parts I needed to make models for test-flying.

For the Beta kits, all of the parts that I want laser cut in the final version are now laser cut. I also added an optional "Art Scholl" tail for those who like to really spin their planes.

I will be framing one, for parts fit testing, and getting the rest of the photos I need for the manual ( I built # 2 in 4 days prior to NEAT and did not get the pictures due to time constraints). After it is framed, it goes to a customer, who has been waiting for a while. A friend has the other 2 kits, partially to help me with de-bugging, and partially because he couldn't wait for the production version.....

I started on the fuselage yesterday, and have decided to post a "build-along", as I go along with the assembly.

I hope you enjoy watching the plane come together!


Ron Daniels
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Old Jan 26, 2004, 08:48 PM
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Kitchener, Ontario, Canada
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Fuselage Sub-Frame

The first thing I like to build is the fuselage. I have no idea why, I just do.

In the early 1990's I made 3 fuselages for 50" Typhoons, using a half-shell method. I warped 2 of them. I like to keep my sub-structures very light in stressed skin airplanes, and I guess it was too light, and allowed the drying wood to pull itself out of shape.

I designed around this with the Hawker series, by eliminating all fuselage compound curves aft of the firewall. They hide this very well. However, the Super Chipmunk started with a buddy seeing my e-Tempest fly for the first time and saying "too bad somebody doesn't make a small Chipmunk with a scale fuselage".

I thought about it for a while, and decided that I didn't like the way that the simplified tail cones on most Chipmunks made the airplane look as though it is flying with its tail low.

So....

With the Super Chipmunk, the first thing to build is a Fuselage jig. Like the crutches that come in Jim Ryan's kits, it is stepped to mate with each former in sequence. However, I took it one step further, and made it X-shaped, to hold the fuselage very strongly in all axes. It is made of lite-ply to resist warpage.



Once it is assembled and dried, I added the formers one by one, sliding them into place from the back, forward.



I then interlocked the longerons into place, glued the canopy rail into place and installed the wing saddles. The front of the wing saddles were sanded to be flush with the former that they glue to.



At this point, I had completed the sub-frame, so it was time to admire for a while, then go in and watch TV.



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Old Jan 26, 2004, 09:03 PM
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Kitchener, Ontario, Canada
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Fuselage planking/sheeting

After finding out that an Awards Show was on TV, I decided to get back to building!

Although, a skillful builder can sheet the Chipmunk with just a few sheets of 1/16 balsa, the compound curves make it difficult for people without much sheeting experience. So, for the production version (as well as prototype #2), I opted for planking. I made sure that I got very light wood for this, as it is a bit heavier than sheeting would be.

I begun by just stringing some planks along each side.



I used Cy-A to hold the planks to the formers, but used Pica Gluit to hold the planks to eachother. This means pinning, until the Gluit dried. After a while the fuselage looks a bit like a balsa wood cactus.

When it was all planked, I headed to bed, to let everything dry overnight.

When I got back to it this evening, I took out all of the pins, gave it a rough sanding.



Then came my favourite part! It's kind of neat when the jig comes out. The jig weighs far more than the fuselage, so it is a relief when you find out just how light the fuselage is.



Hopefully, I'll get a chance to do enough building to use up another roll of film in a couple of days. I'll continue with more pictures, then.



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Old Jan 27, 2004, 10:02 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Ron

That's a really neat way to do this fuse- I was worse than you when planking- I used double glued Ambroid and Titebond to hold each plank on my P-38- took months.

Sam
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Old Jan 29, 2004, 04:54 PM
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Kitchener, Ontario, Canada
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Beginning wing

The fuselage is done and de-bugged. Some very minor problems were found and fixed. At first I though the wood was heavier than I wanted, but as I worked my way through the sticks, I found most to be the "very light" grade that I had asked for.

I actually enjoy planking, with that jig in place.

I got started on the wing, but I only had time to upload a few shots, for now.

Wing ribs attached to the shear web.



Spar complete. Sub-trailing edge and sub-leading edge in place.



Leading edge installed. Ready to start sheeting trailing edge and D-tube.



Too much snow shovelling. It is cutting into my building time!


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Old Jan 29, 2004, 06:12 PM
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Pinehurst, NC
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Ron:

Great Thread! The Super Chipmunk is a favorite of mine. Does this mean you will have these kits available through the Hobby Hangar?

Gary
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Old Jan 30, 2004, 10:25 AM
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Kitchener, Ontario, Canada
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Gary,

Thanks for the kind words.

The kits won't be available through Hobby Hangar. Like the current versions of the Hawker Fighters (10% larger, much more interlocking), these will be available through myself, or EAM.

I'm hoping to have some time to post some more pictures over the weekend.


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Old Jan 31, 2004, 07:36 AM
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Antioch,CA,USA
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Ron, I really like the jig you're using to build your fuselage. Make total sence to me. Keep up the fine work!

I do have a question though, do you wet the planking strips before gluing?
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Old Jan 31, 2004, 07:46 AM
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Kitchener, Ontario, Canada
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Hi Greg,

Thanks for the kind words on the jig. It was a LOT of work to figure out what sizes to make it (it is not symmetrical), and to make all of the ribs fit correctly. But, once I used it, I think the work was worth it.

On the fuselage I built this week, I only had to wet the last 8 " of about 3 pieces to get everything to settle into place. The wood I got with the kit was light and pliable enough that it would go around the curves without being wetted.

I removed the jig, and slid it back in. Since it went back in with no problem, this means that the fuselage retained its shape without the jig.

But, I did give the back end of the tail cone a "spritz" of water after everything was done. This is the area that I had to apply the most "force" to the planking to get it to conform (read, I actually had to pin it...) Because it is jigged so strongly, I didn't need to worry about this process causing a warp. The idea of giving it a final spritz was to relieve any stresses in the wood, so that when it is permanently removed form the jig, the fuselage will not warp over time and heat/moisture cycles.


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Old Jan 31, 2004, 10:54 AM
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I removed the fuselage from the jig this morning.

The weight (before sanding and trimming) came to 2.96 ounces/84 g.

On to more wing building!

Ron Daniels
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Old Feb 01, 2004, 07:43 PM
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The wing is now mostly done, and the panels are joined.

I am now working on the tail feathers, until I return to the mounting the wing, and then doing the cowling, and the finishing touches.

I put the Art Scholl tail over top of the stock tail. Wow! It is MUCH larger.

I only going to post one picture right now, as I'm having trouble with my photo-editor program, and the photos are HUGE and take a lot of time to load up.



Hopefully, later in the week, I'll get the photos edited so that I can post them without them taking MINUTES to load.




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Old Feb 02, 2004, 06:52 PM
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Canandaigua N.Y.
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Ron,
I really appreciate you sharing this project. I am ready to do the final sanding of a 45" low wing sport plane I designed and built using only wood from my scrap box. (it's a pretty big box...). With servos it weighs 16 1/2 ounces. It has a symetrical tappered wing that came out at 378 square inches. This is my first electric and I am on a rather tight budget for this project. I'm looking to get 9 mins. flight time so I determined I would use a Great Planes ElectriFly T-600GD ESC System w/Gear Drive (2.5:1). It comes with
One ElectriFly C-30 Mini High Power Electronic Speed Control, One 10 x 8 wood propeller for electrics (non-folding), One 0.01uF ceramic capacitor, One instruction sheet, and All mounting hardware and wrenches. Weight is 11oz (not including prop) and the Length is 1-1/8" (just the gearbox), Length 1-7/8" (from the back of the gearbox to the back of the prop). I also figured I would use 8 to 10 N.M.Hydride cells, which would make the final weight aprox. 3 lbs. The Tower hobbies price for the power system is $69.99. How does this all sound to you? Any suggestions would be greatly appreciated! Thanks!

Jim
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Old Feb 03, 2004, 09:29 AM
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Maverick_me-109, Welcome to "The Ezone"!
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Old Feb 03, 2004, 10:03 AM
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Hi Jim,

The numbers generally sound pretty good. By the wing area and weight that you quote, I'll guess you want a plane that is in the faster area of the sport plane speed range (25-75 MPH envelope).

I think, to get good performance at the wing loading range you'll be in, you will need 10 cells, or your current will need to be quite high - higher than the 30 A rating of your ESC. You have over 2 sq ft of wing area, so an increase of 1/5 ounce/sq ft for extra power won't hurt you.

The Chipmunk has 340 sq in, and puts out a bit over 300 W. Allowing for a 75% efficiency, this is an input wattage of about 400W. This means it is running around 40 A at full throttle, static.
With throttling back between vertical maneuvers, this gives between 6 and 8 minute flights on CP 1700's, depending on how hard I fly it. Performance drops significantly if I used CP 1300's, even Zapped, as they don't seem to hold their voltage at these currents.

I think the Chipmunk weighs just a tad over 3 lbs, RTF. This kind of power level gives some pretty serious performance.

Starting from level flight, I did some vertical climbs with an on-board altimeter at Ft. Wayne, this summer.

In a climb for maximum altitude, I started at 65 feet and pulled vertical, holding on until I couldn't see the plane properly, or it stopped, whichever came first. Between 100 and 500 feet, the average rate of climb was 2394 FPM. 8 seconds after 100 feet the rate of climb was still 1533 FPM.

I also did a short climb from a full-speed level pass. This time, I terminated the climb at a much lower altitude, as I was just looking for a climb rate. Starting the climb at 71 feet, the Chipmunk averaged 4547 FPM between 86 and 237 feet of altitude. (for anyone who is interested, I have an excel file of the data - Lloyd Peterson lent me an on board altimiter that records the altitude once every second, and then downloads into excel. Feet is altitude. Change in feet divided by time is climb rate. Change in climb rate divided by time is the vertical accelleration - for a number nut like myself, this was great fun!)

Because it slows, it does not have a 1:1 thrust to weight ratio, at least not at any of the speeds it drops to before it hits 600', and the limit of my vision. I think it is close enough that if I dropped to an 11 X 7, it would make it to 1:1. However, I like the extra pitch speed, and the wider envelope that gives me. I can do a scale, Art Scholl-like aerobatic flight without ever exceeding 2/3 throttle.

You will not have quite this level of performance, but then again, at even 2/3 that level of thrust to weight ratio, with a pitch speed of 60 MPH or so, you will have an airplane with performance similar to a Goldberg Chipmunk on a non-piped .60.

Just watch your currents, though. I tried pushing an magnetic Mayhem to my power levels, and melted the commutator in about 3 flights. Maybe I should have used a different gear ratio.....

Enjoy your project, and post pictures on E-zone so we can all see!


Ron Daniels
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Old Feb 03, 2004, 10:08 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Jim

Yuck....

An adage in electric- buy cheap buy twice. The best bargains out there in brushed motors have to be the Astro Flight cobalts if you can find someone to part with one used. (They last awhile.) I suspect an Astro 05 geared would do quite well- would match up fine with an 8 or 10 cell 4/5F AUP or CP 1700 pack (again, some folks are fire saling this stuff as they go to li-polys)

Bear in mind that a decent brushless system is going to be about $150-175 compared to the Tower thingie- and it'll be half the weight or less for an Axi.

You've also got a pretty light airframe- you could do fine on a 200 watt setup- really depends on your goals. (lighter weight less power, heavier, more power.)

Sam
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