Not So Tiny Trainer

by dharkless | May 3, 2015 | (10) Posted in Projects

Hello everyone,

I am working with the local high school Physics teacher on a class module on aviation.  We are using RC airpalnes as the focus.  The kids are learning the basics of aviation theory and engineering along with learning about RC airplane and quadcopter building and flying.

We started by having a group of six students scratch build four tiny trainers.  I first kitted the planes and demonstrated the process of transferring plans to foam board to the group.  I then demonstrated the building process and had them work in pairs to complete three airplanes with the three channel wing.  We are currently waiting for a calm day to have them fly with a trainer radio.

I have flown the Tiny Trainer and it flies very well but I had some trouble with sensitivity to fairly light wind.  I was also used to flying larger trainers that respond a little slower to inputs and gave more time to react.  I thought the Tiny trainer might be easier to fly as a first trainer if it was not quite as tiny.  My first thought was to make a 150% enlarged version.  I experimented with our school printer and found it would be tedious to enlarge the tiled plans that much.  I settled on 125% because that is the largest regular increment that could be done in one step with the largest paper size available on the school's printers which is 11 X 17.

Here are a couple of photos showing the size camparison:

 

I was able to take the tiled plans that I printed from the FliteTest build article and enlarge them to 125% onto 11 X 17 paper in one step.  The margins were prortional to the original plans.  I then assembled the plans, cut the individual parts out with margins remaining and transferred them to Dollar Tree foam board.  The only difference was that the larger parts had to be oriented in the 30" direction instead of the 20 " one. I was able to get everything on 3 sheets including both wings.  I had to make the wing bottom panel into a separate piece on one wing of each pair since both wings are over 10" wide when enlarged. The separate bottom piece can be made from the end of the same sheet. The rudder also had to be made separately since it would not quite fit on with the fuselage. The rudder and vertical stabilizer had to be cut separately and then joined with tape.

There were some modifications required to the plans because of the foam board thickness.  When you enlarge the plans the slots for the folding get enlarged as well but the foamboard does not so adjustments must be made.  I started with the fusalage since it controls everything else.

Fuselage Adjustments:

The adjustments to the fuselage were pretty much limited to reducing the width of the fold slots that had been enlarged 25% along with the rest of the drawing. I just measured 3/16" from the folding side of each slot and drew in a second line.  On the top and bottom panels this results in making the fuselage 3/32" wider. The only exception was at the tail.  There I moved the lines in instead of out because the rudder still has to fit between the two sides.  The sides remained the original sizes since the fold lines are at the tops and bottoms and there were no changes there.  The rudder slot had to be narrowed to 3/16".

Here are a few pictures showing the fuselage drawing modifications.  The small arrows point to the added lines:

 

The fuselage doublers had to be adjusted as well.  The nose contour was OK but the part that inserts needed to be  enlarged slightly on top and bottom to make it fit between the top and bottom panels.  The amount is only 3/32" total between the top and bottom so it could be ignored and filled with glue but I did redraw the edges adjusting them to 3/16 offset from the nose. It really just added a little more than the width of a pencil line to each.

 

Nose adjustments:

The nose piece needed to have the fold slots reduced the same way as the fuselage but it also had to be made narrower by 3/32".  When it was enlarged the outside demensions would still have worked with the fuselage except that the inside dimension of the nose became larger as the slots were reduced.  The foam board on the drawing was enlarged 25% but in reality is still 3/16" wide.  To compensate for this I first did the fold slot narrowing the same as I did on the fuselage.  Then I split the drawing through the center of the bottom panel, overlapped it 3/32" and taped it back together.  I then reduced the top panel to match the new dimensions of the bottom one.  All of the remaining nose details work fine.

 

Power Pod Adjustments:

The power pod needs to fit inside the adjusted nose pod. The adjustments on the nose were done on the outside and the inside stayed the same.  However, the nose doublers are proportionally thinner than the drawing so the pod has to be widened 3/32".  I laid mine out from scratch after measuring the assembled nose.  You could modify the plan similar to what was done with the rest of the parts. The fold slots would have to be made narrower by moving the inner lines out.   This would also make the pod 3/32" wider to fit the wider nose inside dimension. The sides can remain the same. 

The only other adjustment  I made was to add 2 1/4" to the length of the power pod (5 1/2" long).  This still fits into the nose but it allows the battery to be adjusted for balance.  The larger 1500 mah battery can be used if it has room to move it back.  The extended part has to be notched 3/16" down at the top so it does not hit the end of the fuselage.

Tail Feather Adjustments:

The only adjustment needed on the tail is to reduce the slot in the horizontal stabilizer to 3/16" to fit the rudder thickness.  Just take a pencil width off each side and it should be close.

Wing adjustments:

The only adjustments needed on the wings are to make the spars thicker.  The new thickness should be 5/16" (9/32 theoretically) instead of the single board thickness used in the original wings.  To do this I cut strips 5/16" wide and used them vertically to make a box spar on each wing.  I suppose you could use two thicknesses of foam board instead.  That would only make the wing 1/16" thicker which is no big deal.  Doing it again I might go that route for simplicity's sake.     

 

Update 5-03-15:

One of the commenters questioned why this build should take 3 sheets of DTFB.  The reason is that I built both wings.  Each of the wings takes a full sheet with very little waste left over.  Everything else fits on the third sheet except for the vertical stabilizer which can be taken from the scrap from either of the wings.  

The little scrap that is left can then be cut up to make the spars (either version).  The spars do not have to be continuous.  They are just spacers and not real spars.  A series of 3" pieces with a 1/2" gap between would serve the same purpose.  You may need some additional scrap if you are using the full width 2 ply version. 

Here are the sheet layouts I used to make everyhting fit:

 

The Fuselage and Other Miscellaneous Parts:

Note: The rudder had to be flipped and laid out on the back to fit the space.

 

The Three Channel Wing:

 

The Four Channel Wing:

 

As you can see, the positions must be chosen carefully to get everything on the three sheets.  I did not do the glider nose.  That would take an additional 1/2 sheet if you are interested in doing it.

You could build just the 3 channel or the 4 channel version and only use 2 sheets.  I am sure that is what the commenter was thinking. 

(End of update)

 

Assembly:

The assembly methods are axactly the same as the original Tiny Trainer.  Just follow the FT Build Video.

 

The Finished Product:

Without having them side-by-side it is hard to tell the difference.

 

 

 

Other changes:

Motor:  Hextronik 24 gram, 1300 KV (Hobby King)  (The original motors would work as well)

Prop: 8 X 4.5

Servos: Increased to 9 gram

Battery: 1000 3s at nose or 1500 3s back 1 1/2"

I added a wingtip discus launching dowel with a flexible cutting board reinforcer on the bottom of the wing. 

 

Update (5-06-15):

Specifications:

Wing Span: 48 5/8"

Length: 32 3/4"

Wing Chord: 6 7/8"

Wing Area: 2.15 SF

Weight: With 1000 mAh 3S battery - 434 g (15.3 oz.)

            With 1500mAh 3S battery - 475 g (16.75 oz)

Wing loading: With 1000 mAh 3S battery - 7.1 oz / SF

                     WIth 1500 mAh 3S battery - 7.8 oz / SF

(End of update) 

 

Flight performance:

The enlarged "Not So Tiny Trainer" is 56% larger than the original  (1.25 X1.25 = 1.56) and flies like a much larger model.  I maidened it with the 4 channel set-up and found it easier to fly than the smaller version, largely due to the slower response time that comes with size.  It has enough power to do medium sized loops which are nice and uniform.  I tried a couple of rolls and some inverted which went well.  It retains all of the good flight characteristics of the "Tiny Trainer" but does everything a little bigger and a little slower (proportionally).  

After the students get some three channel time on the "Tiny Trainers" and are ready to transition to 4 channel I will have them go to the "Not So Tiny Trainer" to learn to use ailerons.  That's my plan and I am stickin' to it!         

COMMENTS

alibopo on May 3, 2015
Hi dharkless, nice conversion, and I prefer the bigger models too for all the reasons you give :)
I'd never really thought about it, but you mention the dollar tree foam board is 20" x 30" which to my metric brain is 762 x 508 mm. The foam board I buy in the UK is pure metric - an A1 sheet, which is 841 x 594 mm or 33 x 23.5 inches (roughly). I was surprised you needed 3 sheets for this build, though maybe not considering how much bigger my A1 sheet is. However I did wonder if there was a better cutting pattern for the build. I'm thinking that because currently I'm building complete biplanes with two complete wings and wingspans of 1 metre / 39" from only two A1 sheets. Possibly a tiny downscaling of the 'new' build will produce a significant economy? Not a desperate issue, if you're only paying a dollar a sheet, but it all adds up if you've got multiple models to build. I'm sure there's a department in the school that will have suitable software to lay out a cutting pattern; Photoshop is good if you use the 'Nerdnick' method or maybe some CAD software? Maybe set this as a task for the students? Could this fitting (manufacturing economy) achieve another goal in the educational process? The other thought I had, is if you start with the sheet size as a background and scalable components, you can shrink and expand them with the software to work out a 'good' largest component size. This is what I did with my biplanes using a 3 view taken from the internet - near-enough allowing the maximum achievable wingspan to dictate the final size of the model. If you set up a workspace in Photoshop equivalent to the size of foam board you use, I think you can import the original Flite Test PDF and then scale the image up and down to fit it on your page. Another trick is to import multiple copies of the PDF and then crop each version to focus on individual components, which can then be shifted around the workspace to get a good fit. Thanks for sharing. It's great to hear about this hobby finding its way into the classroom as a real-life demonstration of engineering and science in action. Cheers, alibopo.
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vikiviking on May 3, 2015
As a fellow UK scratchbuilder - where do you buy your A1 foam boards? How much do they cost?
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alibopo on May 4, 2015
Hi - I've been buying my foam board through Ebay - most recently from 'papergourmetuk' - Single sheet purchases were silly prices so I bit-the-bullet and ordered in bulk. I paid £27.60 for 10 sheets delivered to the door, but I see they are now doing it for £22.99 - so that's £2.23 a sheet!
http://www.ebay.co.uk/itm/A1-Foam-Boards-5mm-10-Pack-White-REF-FB114-/280503624029?pt=LH_DefaultDomain_3&hash=item414f51a15d
I can manage a small single wing plane - check my articles - Tribewt & Tribewt2 - with a single sheet (plans provided) and 1m wingspan biplanes use 2 sheets. I've provided plans for a Polikarpov Po-2 biplane, and I'm just about to post an article and plans for an SE5a biplane that uses 2 sheets. The last 2 bulk packs I ordered came with two 'protective' sheets either side of roughly 3mm foam at the full A1 size. I'm still wondering how to use them, but that's a 'freebie' bonus for indoor builders or someone used to working with that thickness of foam.
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SkyLark on May 25, 2015
Thanks for the useful information, Alibopo.

I have sucessfully used the Westfoam board that you can get from hobbycraft (£4.20 or 2 for £7) and Rymans (£7.99), but it weighs nearly 50% more than the dollar tree stuff. Is this the same board that papergourmet sell? If not would it be possible for you to post how heavy their board is?

Thanks.
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alibopo on May 25, 2015
Hi Skylark - yep, the weight difference is pretty fierce. HOWEVER - foam board is still a pretty light building material, even in its heavier forms. Before panicking you might look at my article on this subject;
http://www.flitetest.com/articles/don-t-let-heavy-foamboard-get-you-down
..in it you will also see a link to apnewtons exploration of different foam board weights. I have happily flown much heavier planes but there are ways around the problem. Stripping paper from one side of the foam will help - you can see Timmy P do this in his Cessna 180 article;
http://flitetest.com/articles/cessna-180-swappable-with-plans
Extra weight is more noticeable with slow flyer designs - many people have/had problems with the Old Fogey and 'wing-waving' - I think this comes from the need to fly it faster to keep the extra weight in the air. Because it has a fairly steep Angle of Incidence it doesn't like going that fast. I found this when I built the Smash Drone which uses the same wing and basic flight geometry as the Old Fogey. When I reduced the A of I my modified Smash Drone flew a lot better, though never a slow as one built from DTFB. Hope that helps, cheers, alibopo.
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SkyLark on May 26, 2015
Thanks for the reply. I hadn't seen your article; it's very interesting. I will post my comment there.
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dharkless on May 3, 2015
Hi Alibopo,
Thanks for commenting on my article. I always look forward to your input.
I needed three sheets because I built both wings. Actually the fit was very tight. Each wing took a full sheet with very little waste. Two wing halves with the bottom panels attached would not fit the 20" way so I had to separate the bottom panel from one and make it from the end that was left at the wing tips. The rest was cut up info spars. The fuselage, nose. pod and tail feathers were all from one sheet. I had to separate the bottom panel from the nose and the rudder from the vertical stabilizer to get them all on. Again there was very little waste.
Unfortunately I am not up to speed with any of the plans software that is out there. I have played a bit with SketchUp and I am aware of Photoshop but I am not proficient enough to produce usable plans with either.
We are just getting starting. The physics teacher did a little at the very end of the school year last year and got started again with it again this year only in the last month or so. I am trying to get him to introduce it earlier but we are so entrenched in "teaching to the test" here that it is hard to make changes.
I am trying to get the CAD teacher involved but so far that has not taken off.
I pretty much did what you suggested about cropping but I did it with the paper plans, I cut out each part with a small margin and then fitted them onto the board for the best efficiency. As I mentioned above, I had to separate some parts at hinge or fold lines to get everything on.
Yes. Making science FUN goes a long way toward motivation. The ideal model here in the states is the MESARCFF program (currently Author #3 Influence rating). They have a large student involvement and evidently several staff members helping in an after-school program that does spectacular things. They are a large school in a fairly affluent community. We are on the other end of the scale, being a small school in an economically challenged area. The going is a little slower. I do have a good group of interested kids and a very interested and effective teacher. That is a start.
Thanks again for your interest and your kind and constructive comments.
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dharkless on May 3, 2015
Hi Alibopo,
Thanks for commenting on my article. I always look forward to your input.
I needed three sheets because I built both wings. Actually the fit was very tight. Each wing took a full sheet with very little waste. Two wing halves with the bottom panels attached would not fit the 20" way so I had to separate the bottom panel from one and make it from the end that was left at the wing tips. The rest was cut up info spars. The fuselage, nose. pod and tail feathers were all from one sheet. I had to separate the bottom panel from the nose and the rudder from the vertical stabilizer to get them all on. Again there was very little waste.
Unfortunately I am not up to speed with any of the plans software that is out there. I have played a bit with SketchUp and I am aware of Photoshop but I am not proficient enough to produce usable plans with either.
We are just getting starting. The physics teacher did a little at the very end of the school year last year and got started again with it again this year only in the last month or so. I am trying to get him to introduce it earlier but we are so entrenched in "teaching to the test" here that it is hard to make changes.
I am trying to get the CAD teacher involved but so far that has not taken off.
I pretty much did what you suggested about cropping but I did it with the paper plans, I cut out each part with a small margin and then fitted them onto the board for the best efficiency. As I mentioned above, I had to separate some parts at hinge or fold lines to get everything on.
Yes. Making science FUN goes a long way toward motivation. The ideal model here in the states is the MESARCFF program (currently Author #3 Influence rating). They have a large student involvement and evidently several staff members helping in an after-school program that does spectacular things. They are a large school in a fairly affluent community. We are on the other end of the scale, being a small school in an economically challenged area. The going is a little slower. I do have a good group of interested kids and a very interested and effective teacher. That is a start.
Thanks again for your interest and your kind and constructive comments.
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HorrifiedPilot on May 3, 2015
Should be called the somewhat bigger tiny trainer. It doesn't quite have the same ring to it.
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dharkless on May 3, 2015
Thanks for the suggestion. It is probably more accurate, but I still like mine. Mostly because it was my idea :)
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jbing on June 8, 2015
Call it the Jumbo Shrimp

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richie2057 on May 3, 2015
This idea is brilliant. Such a nice plane to fly but bigger is better.😊
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dharkless on May 3, 2015
Thanks for the more than kind comments.. Brilliant is a stretch. I will take "practical".
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SwissFreek on May 3, 2015
Always excited to see one of your posts. Funny how it doesn't look THAT much less tiny than the real tiny trainer, and yet it makes such a big difference in flight. And it's all for a good cause!
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dharkless on May 3, 2015
Thanks for the nice comments. I flew it again this evening with the 4 channel set-up. It goes very slow and easy but at the same time is pretty responsive. Just a nice mix. A larger motor would be needed for advanced aerobatics. This one is about 85 watts. I am going to try something in the 100 to 120 range next.
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raydar on May 3, 2015
Hi dharkless, any chance you'll be releasing the modified plans for this build? Inquiring minds want to know.
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dharkless on May 4, 2015
Sorry. I am old school and not up to speed with regard to producing drawings. You can use the FT tiled plans and enlarge them 125%, The text shows how to modify them to produce the enlarged model. I know it is a bit tedious but it is the best I can do. It would be great if FT could do the modifications and offer the larger version.
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raydar on May 5, 2015
dharkless, what is the wingspan of your modified build, if you don't mind sharing? Thanks, Ray
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dharkless on May 5, 2015
It measures 47 5/8". I will do an update with specifications. Thanks for asking.
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wrayman on May 10, 2015
How does the bigger one fly compare to the smaller one
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dharkless on May 11, 2015
It flies very well. The larger one flies proportionally slower and gives you more time to react. I currently have a 70 watt motor and plan to upgrade to 100 watts for better aerobatics.
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dharkless on May 11, 2015
Correction: the current motor is 85 watts.
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Hell2Go on May 19, 2015
I was thinking about building the TT as a small performance sport plane with need for speed, do you think the airframe would be conducive to a high power, high speed setup? I thought I could use this motor( http://www.banggood.com/DYS-BE2208-1400KV-Brushless-Motor-High-Torque-For-RC-Airplanes-p-941617.html ) for the 100% version with an 8x8 prop and a 4s calculates to 120mph with over 1000g of thrust it would be a rocket! but I like the thought of the bigger version because something that small at those speeds will disappear quickly. did you use a sturdier spar in your wing construction on the 125%? do you think the larger version could handle some speed? Thanks, I know I'm kind of a speedfreak, still a few crashes short of slowing down. :)
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dharkless on May 20, 2015
I did not use any special spar. In fact used less spar than the original, Mine has two 5/16" strips on edge to make a boxed spar. If you are going for that much speed I think you should use something heavier like two pieces of arrow shaft and continue it through the through the joint. I am not sure either TT or TT 125% would hold up to those speeds. You would probably want to clip the wing and possibly make it straight to accomodate the heavier spars.
It would probably be better to go to other designs for speed. These are really designed for slow to medium.
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alibopo on May 25, 2015
There are loads of solutions, but if its speed you are after it might be worth looking at some of nerdnic's designs. He uses an aluminium flat to reinforce his foam spars. Eg;
http://flitetest.com/articles/115mph-800mm-ft-spitfire-free-plans
Cheers, alibopo.

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Valm on May 24, 2015
I am working on a 125% Trainer as well. Does the power pod still need the thrust angle at that size or will it work without it?
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dharkless on May 24, 2015
I used the thrust angle. My initial set-up was 4 channel and it flies straight and level with no trimming needed.
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Not So Tiny Trainer