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Old Nov 20, 2012, 11:20 AM
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MK Super Chipmunk 120e Design/Build

A few weeks ago a poster asked about the Carl Goldberg Super Chipmunk and its ability to fly Classic Pattern. The thread took some twists and turns and the next thing you know Bo posted a picture of the most beautiful Classic I have ever seen, the MK Super Chipmunk 120s. I was instantly in love and knew that had to be my next project.

I wasn't shy about my affection for design and the next thing you know David chimes in that wanted one too. Thankfully for me David is a CAD wizard and an all-around great guy. Off-line we decided to work together to build electric versions of this plane. As always, Kevin has been helpful in sharing ideas as well. We have been emailing ideas back and forth and are now going public to share our plans to design and build the MK Super Chipmunk 120"e".

The plane will be faithful to its original design but will be constructed with a smooth running electric motor for power. We have also decided to construct the wing and stabalizers with a foam core technique.

Bo has been kind enough to offer to send the Cowl and Canopy from his MK origiinal kit to me so that we can have them reproduced. We cannot thank him enough for his kindness and generosity on this!!

Set Up:

Scorpion 4025-12 440 KV Motor
80-100 amp ESC
15" or 16" prop
6s 5000 mAh battery
MK Mechanical or E-Flight Electric Retracts

I have been extremely happy with my Scorpion Motor so I have convinced David to design the plane with the 4025-12 in mind. In fact, he has already purchased one and has remarked how impressed he is with the quality. This motor has a slighlty lower KV than the one used on my C4e. The design of the Super Chipmunk 120e will allow us to swing a bigger prop than my Conquest IVe. We are hopful to keep the plane in the 8.5 lbs range which should give it outstanding performance.

As with all my projects it will be SLOW. Work and family dominate my time so it will take me time. I suspect David will beat me to the air but quite some time, but that's ok. It will be cool to have matching Chippys; one on West Coast and one on the East Coast.

My goal with this project is to have a one-of-a-kind plane that I can use to fly in Classic Pattern and AMA Pattern (turn-around). I just cant bring myself to fly a pregnant guppy!

David and I will share this thread and he is poised to add post #2 and reserve post #3 right after this. We look forward to input from all of you through the process. I really appreciated the support that I received on my Conquest IVe thread and hope that we receive the same here.

Doug
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Old Nov 20, 2012, 11:26 AM
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I first came across the MK 120 size semi-scale pattern classics about a year and a half ago when I opened an MK kit and found one of their glossy brochures in full colour with all their classic kits from yesteryear. I found myself eyeing them like a little kid sitting in front of a huge bowl of chocolate ice cream - my son is still like that...

While the non-scale BPA designs are beautiful, I've always had a sweet spot for the TOC style scale aircraft of the later TOC years starting with Hanno's Dalotel. It turns out this affection isn't singular and not only Doug and I share this passion but several others do too. The beginning of my inkling into the world of semi-scale pattern "TOC style" aircraft, in the context of me actually being able to build and fly one began with a set of CAD drawings that were offered to me by Obi Mapua in the Philippines (via the forum). Obi first designed a 40 size Dalo and then, years later, refined it and designed an improved Dalo 60. My immediate reaction was to say: "Hey! Here's my TOC sized Dalo - I just need to blow it up to a 90 size!"

Two to three years ago I began my venture into the CAD world and it hasn't let me rest since. Put simply, it is hard to go back to "kits" once you discover the power of CAD and how you can custom tailor just about everything to your whim and desire. Since Obi had drawn the Dalotel, I decided that I should also try and get my feet wet with CAD and I began designing a CAP 21. I made significant progress on that design but eventually I ran out of steam and decided to put it on the back burner (which in retrospect was a good thing). I conceived both the Dalotel and the CAP from the get go as foam core wing, stab and fin (in the case of the CAP) models with light wood fuse designs and electric power. I adapted Obi's design substantially making it somewhat easier to build for my application.

Fast forward a year or so and enter the Chipmunk. The MK Super Chipmunk S is unlike many other kits and ARF's on the market in as far as it is intended and conceived for pattern flying. The moments, airfoils, planforms and so forth are laid out by Mr. Kato to produce a good flying pattern model. I don't have an exact date as to when Kato's semi-scale/pattern designs were brought to market but I suspect the work began in the late 80's and kits began rolling out in the early 90's with the arrival of turn-around.

Doug and I decided that we wanted to a simple model to build specifically for e-power. I don't do glow engines larger than 60's for two main reasons: 1) They are expensive to purchase and 2) they consume a lot of glow fuel (especially if they are two strokes). To me, e-power is the "future" and while this is a "classic" forum and hence, the "past", capturing the essence of these 20 year old designs from the past and putting them into the "future" in terms of re-design, power plants, structure and materials is a fun exercise; both as a hobby and simply put, for excellent flying reliable models.

But enough on the background... As Doug put it, we are planning to build one each of these birds with the possibility of eventually doing a rather limited "kit" run primarily as a means to actually make the project viable. Viability is not a financial matter but rather a matter of "start-up" issues. There are a number of aspects that will have to be covered to bring this model to fruition. As it is, this will be a Sweden-Canada-US co-production with people in each country contributing to the project is different ways.

For myself, I am undertaking the CAD re-design of the model with changes and modifications from the ground up specifically suited to electric power. Doug has noted the general specs of the power plant we intend to use. The Scorpion motors we selected for this project, rated at 85A/2000W continuous, are excellent choices when it comes to the cost/quality equation. As Doug pointed out, I already acquired one for the project as we had the opportunity to purchase these at an excellent price. I like the quality of the motor so much that I decided to take advantage of the special offer (it's a Canadian thing) and purchase a second motor with different kV specs - a 515 kV version, just like the one Doug is running in his C4e. My application will be in a Saphir but that is another story. Suffice it to say that both Doug and I are pleasantly impressed with Scorpion and he has some flight time experience with them to boot.

I will be posting the state of our CAD design in the next post. Cowl, canopy and foam work will be taken care of by the excellent team who put together the C4e build: Doug and Kevin.

David
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Old Nov 20, 2012, 11:27 AM
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We wanted to post snaps early in the thread of our new re-design of the Chippy with the details of what and how we adapted it for our e-powered purposes. Below are the two basic drawings we've made for our laser cut fuse and foam core surfaces along with a simple 2-View of the model.

As Doug pointed out, we are hoping for an AUW of 8.5 lbs or better if possible. We're hoping to achieve this through the use of good quality foam, 1/32" balsa & CF skinned surfaces and use of plenty of 1/8" lite ply. Only the structural loading formers will be cut from 1/8" birch ply and given we are going to have 2000W strapped up front, we decided to go with a 2 x 1/8" ply electricwall. The fuse top decks are sheeted with 3/32" balsa while the fuse sides and bottom are 3/16" balsa. Substantially lightened 1/16" ply fuse side doublers are also being used. While we could have gone with a 1/32" ply doubler for our e-model, we favored going with holy 1/16" as these doublers will provide the interlocking structure for all the formers and fuse top in that area. Some of the formers and the ESC, battery and radio trays also interlock. In the design I was aiming at having a model that would frame up "dry" as much as possible to produce all alignment and expedite the build as much as possible.

I hope all Chipmunk aficionados approve of our design. Any comments or suggestions on the design modifications are most welcome. If there is something we can fine tune or improve on at this stage, we look forward to it!

David
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Old Nov 20, 2012, 10:56 PM
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With regards to the great Art Scholl's Super Chipmunk you guys have to figure out some rearward retracting gear. Not rotated, but straight back with the dangley bits covered with cuff fairings. That would be too cool!
Eric
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Old Nov 20, 2012, 11:16 PM
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Subscribed and tuned in....

I think that what you guys are doing is GREAT. The greater majority of classic Pattern enthusiasts are into the older airplanes, but there exists a small cadre of those who look forward to picking up where they left off- their creative spirit is intact. They are MODELERS. Whether this takes the shape of projects like this one, or even completely new "classic" designs, my hat is off to you, and you and your aircraft are always welcome at any event that I host. Carry on.

-Robert
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Old Nov 21, 2012, 10:54 AM
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Quote:
Originally Posted by edh13 View Post
With regards to the great Art Scholl's Super Chipmunk you guys have to figure out some rearward retracting gear. Not rotated, but straight back with the dangley bits covered with cuff fairings. That would be too cool!
Eric
Don and I are going to do a 100 inch gasser like that, Eric. All glass, foam wings, pretty darned scale.
Chris...
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Old Nov 21, 2012, 05:45 PM
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Hi,

I have now made a parcel with MK Super Chipmunk 120 cowl and canopy that will tomorrow go overseas to US for making copies of them.

Some teasers for You below.

/Bo
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Old Nov 22, 2012, 01:45 PM
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Montreal, Canada
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Bo,

outstanding! This contribution is much appreciated as Doug pointed out. We would have had that much more work to do in their absence.

Below are some pictures of where Bo has to endure his years... Filipstad, no doubt a beautiful land of Fiords.

Thanks, David

PS I just replied to your two emails.
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Old Nov 22, 2012, 02:47 PM
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Montreal, Canada
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Quote:
Originally Posted by edh13 View Post
With regards to the great Art Scholl's Super Chipmunk you guys have to figure out some rearward retracting gear. Not rotated, but straight back with the dangley bits covered with cuff fairings. That would be too cool!
Eric
Eric,

if you are referring to the retracts as shown in the photo below, I also had a quick flash of reflection on the subject. But our model will be a practical one to build and fly so we'll be using conventional inward rotating "classic" retracts.

Who knows though, maybe we'll get inspired to produce some retract well covers to smooth out the bottom of the retract bays...

David
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Old Nov 22, 2012, 02:56 PM
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Montreal, Canada
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Quote:
Originally Posted by Vertigo II View Post
I think that what you guys are doing is GREAT. The greater majority of classic Pattern enthusiasts are into the older airplanes, but there exists a small cadre of those who look forward to picking up where they left off- their creative spirit is intact. They are MODELERS. Whether this takes the shape of projects like this one, or even completely new "classic" designs, my hat is off to you, and you and your aircraft are always welcome at any event that I host. Carry on.

-Robert
Robert,

your input to the thread and comments are most well received. We thank you for your vote of confidence, praise and words of wisdom. It's nice to hear when it comes from a CPA district chief!

Who knows, maybe one day when the project is complete, I'll ship myself and the Chippy out to Cali to pose with Doug and our sleek FAI semi-scale birds!

It's too bad, I used to spend some time in San Diego in the 90's when I was out of the hobby. Anyone heard of Scripps? Used to work with folks at SIO in my previous geophysical fluid dynamics life. Said today, it sounds kind of glamorous... it wasn't. It was an exercise in seeing how to harness a few more IQ neurons to solve the problems we were trying to tackle.

In any case, nicely phrased post Robert!

David
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Old Nov 22, 2012, 07:26 PM
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Quote:
Originally Posted by edh13 View Post
With regards to the great Art Scholl's Super Chipmunk you guys have to figure out some rearward retracting gear. Not rotated, but straight back with the dangley bits covered with cuff fairings. That would be too cool!
Eric
Eric,

I think David meant to post the picture below. I was about to do the same.

The pictures below are from a MK Super Chipmunk that is for sale on the RCG at this time. It looks as though it has retracts as you have described. I have no interest in such a design. I am with David, this bird is to be practical and fly fly, fly, fly, and fly some more.

I am curious about the difference between the Super Chippy shown below and the one that Bo has in Sweden. The picture in post #1 is off of Bo's box; Super Chipmunk 120s. Can someone share with us the difference and the time frames of each design?

Thanks,

Doug

PS - I like the way David talks about "our" design. He has done the majority of the heavy lifting with me only exchanging ideas via email. David is being modest.
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Old Nov 22, 2012, 09:41 PM
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It looks as if the fuselage length on the Super S is a foot longer than this 120 MK. Interesting the Super S plan says Kato design.
I like the Super S for sure. The other one is not too pretty in comparison.
Chris...
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Old Nov 22, 2012, 10:23 PM
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Chris,

That was my first reaction too. Hard to believe but the length difference is only 1-3/4"!

The difference between the two is likely to mostly be in the fuse although the picture I wanted to post (thanks Doug), shows original rearward retracting gear - Zlin style. The canopy lengths and shapes are also different.

We don't know which one came first but the "scale" Chippy probably conforms more to the Original DHC-1 while the "special Scholl" version is tuned for FAI.

It's a good feeling that we are installing an electric power plant into a modified version that was originally designed in Toronto 6 hours away - in full scale!

David
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Old Nov 23, 2012, 03:28 AM
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Hi,

If it has not already been done, probably a good thing to add on the Chipmunk electric version is air exit hole(s) under the rear of fuselage between F8 and F10 and an angled plate there that air will hit and be directed out throuh the hole(s). Or something similar solution so cooling air can exit the fuselage. Someting like this that illustrate the principle- see images below.

/Bo
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Old Nov 24, 2012, 11:36 AM
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Bo,

Thanks for the good suggestion.

Other than the required venting, do you know if the dam to route air down and out is that important?

What kind of wood is being used in the Miss Wind for the dam? Can we get away with 3/32" balsa or does it need 1/8" lite ply?

David
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