Not So Tiny Trainer

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!