Radical RC "Mini Intern Trainer" - RC Groups
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Mar 25, 2008, 09:54 PM
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Radical RC "Mini Intern Trainer"


At long last. We've had a number of these flying locally. I think we built the first version of this model about 3 years ago. Boy, time flys when your having fun. This model feels to me like a long neglected friendship. Have you ever had that feeling? When you meet old friends, your so relieved to freshen up those bonds and start anew.

I've had many requests to finish this one. In fact, "Dick" who helps with technical support and does all our custom electronics building and soldering continually reminds me that he could have sold 50 of these models at his flying haunts if I'd only get it done. He was involved early on testing this design with the late Jimmy Cole and reports it to be a very sweet flier. Bob (who travels to most shows with me) has had 3 of these models. One even on floats! I think Jimmy had 2 or 3 also. We logged quite a bit of time on them and made a number of key changes. EVERYBODY that has owned one of these to date and helped with this project (including Ron mentioned below) are club certified instructors. So, let me tell you, these guys know exactly what a good trainer is and they cut me no breaks on enhancing this design along the way.

Revisiting this project was a lesson in evolution. This model was probably the 4th one I ever drew for the laser. It reminded me of a V1 Micro Stick in construction which is way ahead of 95% of all the laser cut kits out there but one we upgraded to all the latest design and drawing standards lately. Soooooo, I had to start again and bring this model up to my pushbutton wing release, formerless battery compartment, space frame standards of today.

I know you'll really get a kick out of this one. It's perfect for lazy afternoon flying in the local ball field or a generous back yard. Certainly even the most inexperianced pilot will soon be wearing the wheels off this one doing touch and goes. Ahh, but don't be tricked, this model (if you know me, you know I can't help myself) has a split personality.....

Maybe you want the wing area and flight speed envelope of a trainer but don't want the dihedral interfering with your aerobatic ambitions. This idea, a wing that can be built two ways is what really hung me up on this project. After riddling out all the geometry we finally have it correct. With the change out of only 1 part (one, uno, singular) you can change the wing to your choice, trainer dihedral or aerobatic flat. Now, it was a simple idea and the way it's designed makes it very simple to build. However, from the point of view of an untrained draftsman (me) it was a real challenge.

Like many of our new works, we couldn't resist designing a new graphics package for it. This model was built, covered, decaled and equiped by Ron Lamsdale in our shop. It will be on display at Toledo. He choose the PT-19 theme for this one. Doesn't he do nice work!

I've flown this design on 14 watts (50XC brushed) through about 65 watts. This one has a Medusa 4000 on it. My original intention was 20mm inrunner, small outrunners and S300 direct. However, it takes surprisingly little power to get a nice performance out of this model. I know it wil be great on the Medusa. There is no question, once you've had Medusa, the rest of your 12mm motors will be for sale! I'll save the test flights for our most recent blue and yellow beaut' until after Toledo. But, even on the 14 watt setup (about 1/2 the power of the Medusa on 2S) it would sustain inverted flight and do basic aerobatics with a little forthought. With a S-300 (about 65 watts) or similar, you can really tear up the sky!

So, here she is. I'd like to see a couple of builders post some build threads here for the Mini Intern. I've got two beta kits to send out if you can do that. I don't have instructions or plans done at this moment, just a few sample kits so it should be somebody with a little experience building my kits as they'll understand the general logic without any instructions. It's very similar to the V2 Micro and Mini Stick kits, Mini Low and Min Bipe in construction techniques. The instruction sets from any of those will make a great guide for this one.

Happy Flying!
Dave
Last edited by radicalrc; Mar 26, 2008 at 09:37 AM.
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Mar 26, 2008, 08:00 AM
In The Sorrano Triangle
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Congrads on another winner Dave I am ready to build one or two of the "Mini Intern Trainers" . One with the 50cx and one with the medusa or even with the E-flight 250 outrunner. Looks like you need to put a tail skid on the "Show Room Model"
Will they be offered on your website soon?
Thanks for another great project.

Retired in El Dorado Hills, CA (California not Canada!)
jim
Last edited by BOZINATOR; Mar 26, 2008 at 10:48 AM. Reason: spell thing again
Mar 26, 2008, 09:01 AM
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Dave,

Another great looking bird. Im not sure where you find the time to crank all these planes out.

If you need beta builders I will gladly raise my hand.

Dan
Mar 26, 2008, 12:49 PM
BEC
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Interesting little airplane, Dave. For those of us who haven't seen it before - how big and how heavy? Judging by the pics and the description I'm guessing around 32 inch span and maybe 8 ounces all up?
Mar 26, 2008, 02:44 PM
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The cord is the same as Micro or Mini Stick. 22.5" long, 33" span. Very good guess on the specs! The one in the photo is still awaiting pushrods, RX, servos and battery. But, a flying model in the shop setup with 12mm motor is 7.2 oz including Kokam 740 pack. I expect most of these to be built withS-300, 20mm inrunners or small brushless outrunners and to have a weight range from about 7 to 8.5 oz.

Dave
Last edited by radicalrc; Mar 26, 2008 at 02:56 PM.
Mar 26, 2008, 03:38 PM
BEC
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OK - so back calculating from the Mini Stick on your site that gives about 190 square inches of wing area and therefore a loading at 7 ounces AUW of 5.3 ounces per square foot. Not a gym flyer but very reasonable for a Little League baseball field or such. This is a size that there aren't many alternatives in laser-cut wood kits.

I'd think in terms of one of the little outrunners like the AXi 2203s or their inexpensive competition (Suppo) for example, I think.

What prop are you running on that 4000 kV Medusa 12mm motor, just out of curiousity?
Mar 26, 2008, 09:16 PM
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My entire Micro and Mini series of conventional sport models, If I'm not mistaken, all the competitions kits out there today (in similar sport class) came after mine. ;-) There were a few floaty models, a few scale models, no sport models of any volume or note in this range of wing area's or weight class. I'm not aware of anything close to this size. (made for E that sold at any volume) And certainly nothing this size is as light (I might be sticking my toes out a bit to say that but I doubt it) ;-) The 50XC thru S-300 catagory (direct small props sport models) really did not exist as any commercial products until we started making kits for it. The Mini and Micro Sticks really opened it all up. Of course anybody could have done it, it's just we happened to do it and in a way that reached out all over the world with it effectively enough that the catagory stuck. It's a real catagory now with lots of participants and many high quality kits. You might notice in some of my instruction sets I even mention the movers and shakers in the laser cut kit world. I really like Doug Binders and Bill Stevens work for example. I support the expansion of high end building. I stock some of my best competitors work. Hey, if it's good I want it!

(Before somebody flames me, I didn't say nothing existed in that size, didn't say we were first, didn't say we invented anything, didn't comment on S-400 or mini wings (those might not have been around but I'm not sure) and I certainly will accept being corrected.) :-)

I've flown this design with S-300 4x2.5, 50XC 3-2,3-3,4x2.5. The Medusa didn't exist when we first started flying proto's of this model. It's one of my fav little motors so that's why it's on this fresh build. I just plane wanted to try it out. I know it will work well, we intend to run the 4.2.5 and 2S here. If I were building another with a flat wing for the express purpose of aerobatics I might run the same prop and 3S here. Make a little high wing pattern trainer out of it that way. I'd like a 2015-2800 HiMax on 3S and a 3600 on 2S as well. Really this is a 15-65 watt machine. Pick your poison in that range and you'll have a well balanced system. As you increase the wattage further at some point you run into being forced into unusable (and possibly dangerous to the airframe) pitch speeds or you run into props that are too big to absorb all that horsepower and still have a nice handlling model.

I try to wrap my mind around what a model is and plan power systems that fill that dream up well. To me outrunners start around 6" props with normal wing loading sport models. Not to say there isn't a good one out there that would turn a 4" prop just perfect for this but I would say that it's probably not as efficiant as the inrunner and you're probably getting no gain for it other than the warm fuzzy's of using the outrunner. As you get above 6" props the inrunner choices start to get narrower (presuming no gearbox) and narrower and in many ways outrunners start to look good. Certainly there are some bigger inrunners, even some that swing 12" props. Just general guidlines is all I'm talking about here. There are always exceptions. I'm not on a campaign for any kind of motor. Just open minded about what works. Heck, I'm not even ashamed to fly a brushed motor. I know some of today's modelers are not good enough to make one work well anymore but many of us still are. (oooohhhh that was a little jab at herd mentality thinking!)

The design is frienly to props from 3-6", I'll have to check to see if a 7" looks silly or not but I know up to 6" will work well. Without holding the model in my one hand a rabbits foot in the other at this moment (I'm at home), I'm guessing maybe 35-40% chance a 7" could work here. That opens up alot more outrunners.

I have no loyalty to inrunner or outrunner and generally resist the trend to presume nothing is capable of flight without an outrunner. I know your not implying that for sure. But, it seems the modeling community mind is in a one track rut on that subject. You watch, it will swing back in at some future date to inrunners and gearbox's then back to outrunners, then to inrunners and the cycle will repeat.

All the guys that said inrunners are the only way (or universally the best way) to go were wrong when they said it. (Some very famous modelers said that to me! Show Pilots, Manufacturers and sage veterans of electric flight) and to the same degree everybody that thinks outrunners are the only way to go are wrong today. Every motor has it's application where it's an ideal choice.

I think lots of these will be flying the the new 150 and 250 eflight motors (hey, I don't even sell those) and similar sized motors. I'm ok with whatever works well, has pitch speed in a reasonable range and generally fits what the model "is".

Sorry to get off on a tangent. You just brought up an important idea. Heck, I wouldn't rule out a steam engine if it was available. And yes, if you show up at SEFF or NEAT with a steam powered airplane, you will absolutely be the coolest pilot there in my view. I guarenteed a herd of onlookers around you watching the whole process and flight. And, they will love it!

Hey, anybody out there want to try a CO2 motor here? Don't giggle when you read this too much. You might think I say these things toung in check but those that know me will tell you they have no doublt that I'm 100% dead serious. I'd fly Steam or CO2 if I could just for the fun of doing it.

Where is a model engineer when you need him?
Dave
Last edited by radicalrc; Mar 26, 2008 at 09:23 PM.
Mar 26, 2008, 09:33 PM
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Quote:
Originally Posted by BOZINATOR
Congrads on another winner Dave I am ready to build one or two of the "Mini Intern Trainers" . One with the 50cx and one with the medusa or even with the E-flight 250 outrunner. Looks like you need to put a tail skid on the "Show Room Model"
Will they be offered on your website soon?
Thanks for another great project.

Retired in El Dorado Hills, CA (California not Canada!)
jim
Hey, I'm voting for the 250. You can do whatever you choose, totally up to you. It would be interesting to get that motor system tested out as I don't own one and there is no experience with it on this model. Lots of poeple have those and it seems like a great task for the 250. I bet the 150 would be great here as well. Traditionally there is a blank firwall so you can set it up easily. I like to see lots of different motors applied to my kits because it helps to outline what range is sucessful.

Our earlier proto's have the Dubro skid on them. It's a nice part but it feels too big to me. I'm thinking a little wire skid would be nice. We're a little undecided what to do here. Maybe I design a micro skid out of Delrin for the laser? Something 1/2 the size of the Dubro part.

Dave
Mar 26, 2008, 09:33 PM
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Another neat plane Dave!! But I have to say, I'm not used to seeing such a HUGE HUGE plane from you guys, I'm more used to the sub 18", zillion MPH models I've gotten from you
Mar 26, 2008, 09:38 PM
BEC
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Wow - quite a discussion. As I mentioned in my private correspondence to you, the only thing I can think of that's approximately in this size/weight class that I'm familiar with (I have a kit "on the shelf") is the Micro Telemaster. And, of course, that's a three-channel airplane. It is about the same size, if my estimate of the Mini Intern's wing area is close (192 squares quoted on the box with an AUW of 6-8 ounces).

I mentioned the little AXi and Suppo mainly because I already have them on hand....I love Medusa's products and have no doubt that that is a fine choice for many small models, either direct drive as you're doing here or dropped into an IPS gearbox for a larger model.

Actually, now that you mention it, I have a Himax 2015-2800 on hand, too.....it was last used geared in one of my Mountain Models Dandies with the Sport wing on it some time ago. AND I have a couple of the Himax 22mm diameter outrunners, too - 2208-870 and 2212-840. These have too low a Kv for a 6 inch prop, though.....

I also have a couple of LittleScreamers that have never been in airplanes - but that's overkill for sure. I'm thinking 40W or so for a ballfield calm (or near calm) evening relaxer, and quick, informal on-a-buddy-box RC intro flights, not another sport/aerobat. I have planes for that already.
Last edited by BEC; Mar 26, 2008 at 11:17 PM. Reason: spelling!
Mar 26, 2008, 09:41 PM
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Quote:
Originally Posted by Carnifax
Dave,

Another great looking bird. Im not sure where you find the time to crank all these planes out.

If you need beta builders I will gladly raise my hand.

Dan
Some of them are projects or brainstorms that were outlined long ago. It's a matter of getting off the duff and getting them done. Really Ron in the shop is the factor that's getting them all done. I keep throwing models at him, he keeps debugging them, demanding parts and fixes and even the next project. I'm not sure what I'm going to do after Toledo. We'll finish this packaging for sure. I've got a few other things on the boiler. Even one model who's slogan will be:

"If you think you can fly it, your probably wrong."

hehehehe (I'm laughing but I'm not kidding!)

I'd also like to rework the Vertigo's and make them outurnner friendly. In this model size I think the outrunner choices could be better and they certainly would be more popular with so many having these motors on the workbench.

The 80" vertigo project needs to be completed. And, I've got 2 bigger sticks flying that few have yet to see. They are killer! Probably the bigger sticks get finished next. They are fitting up prefectly, just need plan drawings and written instructions finished.

So many airplanes, so little time,

Dave
Mar 26, 2008, 09:43 PM
BEC
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On the tailskid - too bad that empennage arrangement makes a steerable tailwheel a challenge to do simply and with low weight. I've got a bunch of tailskid airplanes and while they're OK on grass, they're not much fun on ballfield infields or any kind of hard surface (like the pavement in my cul-de-sac or - gasp - at a club field with paved or mat runway).

Doing touch-and-goes is one of my favorite things, and having the transition from landing speed to takeoff speed stopped by a groundloop is kinda frustrating. A quick bounce at flying speed doesn't count .
Mar 26, 2008, 10:21 PM
In The Sorrano Triangle
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Dave,
The E-Flight 250 will be what I start with on the Mini Intern Trainer with a 6-3 or 6-5 gws slow flier prop on 2s. Will 3gr....4gr...or 5gr be enough power for the control surfaces? Or?
I put a longer shaft on the 250 so I didn't have to deal with the prop saver and could use regular prop shaft adapters.
Can hardly wait
jim
Mar 26, 2008, 10:31 PM
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I'm right with you on your read out of all those motor systems. When we were fllying this model on 65 watts I was thinking it was fantastic but I'd prefere a little less power (maybe 50 watts) if I were really training somebody with it. But, it was certainly arguably close to perfect power. At 40 watts I think you'll have a little more authority than your describing, you'll have no problem in a breeze. Heck at 65 watts on floats (heavier and draggier) it could get off the drink in about 10-15 feet. That's pretty short for a float plane.

The Mini Tele is a nice airplane, it's on the market first but several years behind the development of this kit and it post dates the catagory really. But, a very nice airplane none the less. A supurb classic. I know the guy that shrunk that for them, nothing but respect, first class master modeler and engineer.

I havn't calculated it with precision yet but a rough measurement of my drawing yeilds wing area of 186.75 square inches. I'll do it with greater precision when before it's in the box.

Tres, the DeNile Delta might be right up your alley. Imagine the nacell of the Wicked Wing continuing, nothing else. Scarey? Been working on developing a space/time warp bubble around the pilot so the eye will have time to focus and neck muscles time to swivle the noggin as the model zips in and out of sight which should only be about 100' max. If I can't get the warb bubble working perhaps 2 or 3 super energy drinks prior to flight will get the senses working at the right pace. I like a wide flavor range of airplanes. I can enjoy a white knuckle model and a lazy sailplane equally well. I just love flying machines.

Tail Skid, Hmmmm, I'll have to play around with that. This model has two features that are anti-ground looping. Few know but moving the landing gear closer to the CG greatly reduces ground looping. I'm always careful to do that with my designs. You won't find much weight on any of the tails or nose gears (in the case of the hunter) because of this. Also, it's got a long tail moment. I don't think it will be a problem but well see, that's for certain. I think a tail wheel setup could still be designed it would just need a vertical slipping component to the design of how it's actuated from the rudder. I'll have to think on that one. Aerobatic models which are generally shorter are more prone to ground looping. A Micro Stick without tail wheel might be a real chore for example.

Dave
Last edited by radicalrc; Mar 26, 2008 at 10:37 PM.
Mar 26, 2008, 11:19 PM
BEC
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Great interchange! Yeah, a long tail moment helps a great deal. But on a slick/hard surface it's usually not enough.

Main gear placement is always a balancing act between ground looping (conventional gear forward) and nosing over (conventional gear further aft). Funny, we were just talking about gear placement in a sort of "book course" I'm co-teaching at work on preliminary aircraft design today. Of course in the full scale airliner world one trades nose gear steering authority and tip back margin with nose gear loading and allowable CG range (and sufficient elevator authority for one-engine-out takeoff).....

That's the neat thing about designing airplanes to me - whether it weighs 3 ounces or 500,000 lbs., the general approach is similar and the problems to solve are similar. Granted it's rather more involved if you're going to put 250 people in it and fly at Mach .8 seven miles up, but the basics and the interactions between the various elements are very much parallel.


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