A Foam Board Miles Magister

by MikeRobey | October 9, 2017 | (5 Ratings) Posted in Projects


Introduction

My PT-19 was getting long in the tooth and looking more than a bit bedraggled so I decided it was time for a change.  I decided to go British this time with a Miles Magister. I wanted the same basic size and weight. I also wanted the same flying characteristics but with a different look. The Maggie had a Gypsy Major engine for a power plant so the idea of modelling the nose via 3D printing was also an attraction.  The wing has a wide centre section so I would have to design the wing so that it was similar in construction to my Hurricane design.  I figured that as it was a simple design and didn't really involve solving any problems that I hadn't faced before and so it should be a quick design and build.  In the end it took quite a long time.  I had planned to use the same motor as in my Decathlon and Simplicity designs but when push came to shove I couldn't make the motor fit and the result was I spent a lot of time trying to fit the bigger motor in and then when I realised I was beaten I had to design and print a new motor mount. Towards the end of the design process I also had some health issues which delayed things further. In the end though it all came together and I feel the magister was worth the time and effort.


Design Goals

The fuselage and wing both offered some challenges.  The fuselage sides are tapered at the bottom towards the nose so that was going to require some head scratching. The wing has a centre section with outer wing panels which are tapered and have dihedral.

The Wing:

I decided to stick with the same Bloody Baron wing section I have used before. I had to scale it as the magister's wing chord is smaller than the Bloody Baron.  I have had so much success with that wing section that it has become my default.  Dan Sponholz really came up with a winner. He said he simply based it on an Ugly Stick wing section.  All I can say is maybe that is why stiks fly so well.  The outer wing sections are tapered.  I kept the chord thickness constant and drew a wing section for the wing tip and another for the point where the outer wing panels meet the wing centre section. After that the wing design came together in a straight forward manner. I made a mistake in my plans (since corrected) which resulted in the wing spars for the outer wing panels not lining up with the wing spar for the centre section.  This meant the normal FT type overlapping join on the wing spars wasn't possible in my prototype. I corrected the plans but didn't see the point in wasting  the wings I had built so I 3D printing an overlapping joiner and managed to make it all fit together properly.  The joiner isn't required if you build from the corrected plans but there is nothing to stop you fitting it anyway for a bit more strength.

Fuselage:

The nose of the Magister was a challenge.  I designed a 3D printed nose cowling which fits over the foam board fuselage.  The shape required the fuselage sides to be angled in at the front with the rest of the fuselage side being vertical as per normal.  It took a bit of head scratching but I finally managed to come up with something that worked. I have to admit to being surprised and feeling quite a thrill when the 3D printed cowl slipped smoothly over the fuselage and with a little trimming fit perfectly. I didn't bother with side thrust but built in 2 degrees of down thrust for the motor mount which turned out to be perfect on the maiden.

Control Surfaces:

Normally I make the tail feathers 20% larger than scale but when I did that on the Maggie they looked a bit ridiculous.  I shrunk them back down until they looked okay. They ended up about 7% larger than scale.  However the area of the rudder and elevators was about the same as the PT-19 which flies fine so I figured I would be okay. I fancied a  bit more response from the ailerons than with the PT-19 so I made them a bit larger.

Weather Proofing:

I had to replace the Tailplane on the Simplicity when it got damp from picking up wet grass clippings on landing.  The result was a very banana shaped tailplane which had to be replaced.  When I made the replacement I covered the bottom of the tailplane in clear tape and the ran hot glue around the sides the way others in the FT community have done. That did the trick and many flights later the tailplane has remained perfectly flat.  I decided that I would build all my tailplanes this way and so it was with the Magister.


The Maggie Maiden

The day of the maiden arrived with strong gusty winds. It wasn't un-flyable but it wasn't good weather for a maiden flight. Also I was having second thoughts about the tail feathers. Would they turn out to be too small?  The forecast predicted that the wind would drop later in the morning so I waited.  Finally I sensed the wind was starting to ease so I turned on my trusty DX6 and reached for a battery.  As I fitted the hatch cover back onto the plane the wind gusted up horrifically as if to remind me not to take it for granted. I had second thoughts about going but I had the plane in one hand and the transmitter in the other. The heck with it I walked out to the flight line and put the plane down and stood back.  I waggled the sticks and ensured that the controls were all moving in the right direction and then quite suddenly I had no more excuses. I slowly advanced the throttle and, for better or worse, the Magister trundled forward. As it gained speed it swung a tad to the left but I corrected with a bit of rudder. Okay, I thought, at least the rudder works. The magister picked up speed and just as I was thinking it was time for a bit of up elevator she lifted off the ground and climbed away steadily with the she sun glinting on the yellow wing tape. I settled into some circuits. I kept her high because of the wind but I was surprised at how steady she was.  Perhaps the wind was less gusty up higher.  After a couple of circuits it was time for some aeros. Aileron rolls were axial and reasonably fast for a scale model. A loop proved that, even though I only had a 1:1 power to weight ratio, I could do reasonable sized loops.  All to soon it was time to come down.  As if to say “You ain't off the hook yet” the wind gusted up again as I cut the throttle and settled the Magister onto a final approach. As I descended below the tree line I added power and juggled the throttle and the controls to keep her on a steady approach path. She was getting knocked around in the wind but it was quiet straight forward to correct and keep her coming down steadily.  The landing was a tad clumsy. The wind has gusted up so that the Maggie's ground speed was almost zero as she touched down the wheels touched down and then she tipped onto her nose. After another gust of wind she settled back onto her tail skid. I attempted to taxi back to the flight line but the wind wasn't having it so I gave up and walked out and picked her up.  You can see for yourself how she flies yourself at:



Specifications

  • Wingspan: 1200mm 
  • Length: 910 mm (including spinner)
  • Flying Weight: 1018 gms
  • Empty Weight: 806 gms
  • Motor: Emax  GT2215/09 (Flitetest C power pack)
  • ESC: Turnigy Plush 30 amp
  • Prop: 10 x 4.7 slow fly
  • Battery: 2200 mAh, 3S Turnigy Graphene 
  • Max Watts: 212 watts 
  • Max Amps: 21 amps 
  • Max Thrust: 1056 grams 
  • Max C: 10
  • Flight Time at Full Throttle: 6.3 minutes


3D Printed Parts

Most of the 3D printed parts can be made via non-3D printed alternatives but some, like the nose and nose cowl, have to be 3D printed. Maybe someone on the FT forum will do that for you? There are also places online that will print for a fee.  I have to admit I was surprised at how many 3D printed parts I had incorporated into this design.

Control Horns

Pretty straight forward. You can print these or use whatever control horns you have handy.

Cowling

This really has to be 3D printed. When you do use a raft to keep it from peeling off the print bed while printing is in progress.

Nose

I took the Tiger Moth-ish nose I had done for a Mew Gull design that never eventuated (maybe one day...) and made few improvements. You could carve something from soft balsa instead if you don't have access to a 3D printer.

Motor Mount

The holes are spaced for the Emax motor I used (see specifications). If you are using a different motor then check the hole spacing and modify the Sketchup file to suit.  This mount has 2 degrees of down thrust.  You could fashion one out of lite ply if you cannot 3D print. When 3D printing, print this part solid (i.e. 100% infill).

Front Fuselage Former

Because the front of the foam board fuselage is tapered towards the bottom I decided to use this former to keep the foam board to the right shape and symmetrical.  

Cockpit Coaming

I decided to try using TPU to print the cockpit coaming. Turned out pretty well.

Undercarriage Mount

I used the same sort of design as in the PT-19. 3D printed blocks that 2mm piano wire slots into. I have since modified these to take 3mm piano wire (see later).

I haven't provided a template for the wire bending because its better to bend and fit and bend and fit into the blocks until you have a good fit.  The length is basically whatever you need to ensure the prop clears the ground on take off. Again its better for you to match your prop and wheel size.

Wheels

The wheels are 60mm in diameter.  The tyres were printed using flexible filament(TPU purchased from sainsmart.com) with 5% infill.  The result is tyres which are a bit squishy and have some flex for landing. The hub was printed using ABS and 15% infill.

Tail Skid

I elected to go for the plain tail skid which has served me well on many of my models.

Cockpit Windscreens

Technically the Magister uses a different shaped windscreen for each cockpit but I got lazy so I use the same one for both. It is modelled after the front cockpit windscreen.  I don't bother fitting clear plastic to the frames. I just tell people its the RAF and they keep their windscreens spotless!!

Hatch Bracket

This bracket is glued into the front cockpit and protrudes down into the fuselage. A skewer is pushed through one fuselage side, through this fitting and then through the other fuselage side to holed the  hatch down and secure. I don't like it and I am going to try to MacGyver something better.

Wing Joiner

This is the wing joiner I used to join the wing centre section to each outer wing panel.

Undercarriage Legs

I used piano wire for the legs but later on I printed these to go over the legs. They had two purposes. Firstly they make the legs look more scale. Unfortunately the real Magister has different shaped legs so not really authentic but they look cool. Secondly the 2mm piano wire I used for the undercarriage was too bendy. These legs help stiffen the piano wire.

Pilot

The Pilot came from thingiverse. Interestingly when I googled to find the URL I found a number of Manfreds. I think this is the original: https://www.thingiverse.com/thing:1750200

He is supposed to be WW1 and being called Manfred, presumably German but I think he makes a fine 1930's/40s Magister pilot. I had to glue a foam block underneath him to make him the right height.

Battery Holder

The CG is on top of the spar.  To balance the Magister I had to get the battery almost as far forward as it would go. The battery holder has velcro glued top and bottom and is the glued in the nose part of the fuselage so that the rear of it  nudges up against the leading edge of the wing. I used a piece of foam as a spacer, poking the foam down into the nose, putting the battery in and then latching the top and bottom velcro straps onto each other to prevent the battery sliding backwards.



The Build

Those not intending to build their own Miles Magister can skip to the conclusion. However if you envisage a Maggie in your future then read on.  My build guide assumes you are familiar with the normal Flitetest manner of model aircraft construction. If not then watching pretty much any Flitetest build video would fix you right up. However the FT-Spitfire build is probably the best one as it is closest to this in design.

As usual we start by cutting out all the parts and using your preferred method of applying the colour scheme. I used yellow wing tape.  Whatever you do it is way easier to do before assembly when everything is flat than afterwards.

The image above shows all of the pieces required for the fuselage. Start with the cockpit/battery hatch.  I apologise for forgetting to take pictures of the construction steps for that. Basically glue the formers marked A, B and C in the places specified. Then position the poster board and glue only at the tops of the formers.  Then glue each side one at a time.  Apply glue along the bottom and the formers and then roll the poster board on your build table ensuring a nice snug fit. Do the same for the other side.  I messed up with the forward part of the poster board so I cut that piece off and used a 3D printed section instead. In hindsight it would have been better to use a piece of paper to make a template, cut out some new poster board and used that.

Note also that in addition to formers A, B and C there are the formers A' and C' that are glued to the fuselage on each side of the battery hatch.  Don't get them mixed up. I marked each former with a pencil to avoid confusion and I advise you to do the same.

The above image shows the almost completed cockpit battery hatch. If you paint it make sure you weigh it down so that it is flat while the paint is drying otherwise it will bend. Originally I painted the inside of the cockpits black and forgot to do that. The hatch in the above image is the second one I had to make after the first one decided to impersonate a banana and would not straightened out in spite of trying the usual trick of wetting the other side and then weighing it down until dry.

Remember when cutting the fuselage out to only partially cut the wing slots and the openings in the fuselage top.  They need to be there while the fuselage is being glued together to prevent the foam board from creasing or breaking. If you cover the fuselage with wing tape remember to cut through the wing tape from the inside or you won't know where to cut when it comes to removing these sections.  The fuselage folds are all B folds. Start by gluing the middle of one side. Make sure the side is perpendicular to the bottom.

Now glue the other side the exact same way.

Next glue the bulkhead in position as indicated on the plans.

Next glue the rear bottom of the fuselage to the sides. After applying the hot glue press the bottom against your build table and gently slide back and forth to prevent any excess glue from gluing the fuselage to the table.

This next bit is a tad tricky. The front fuselage sides are not perpendicular to the bottom but are at an angle.  Also there is a change of angle front to rear. Apply the hot glue and push the sides into place and then rock the bottom on  the build table until the hot glue is dry to ensure the bottom is solidly placed against the side. Then repeat the process for the other side.

Glue the fuselage top onto the sides. Apply the glue, push the top into place and then turn it over and gently push the top against the build table while sliding gently back and fourth.  The tail will have to hang over the edge of your build table so take care not to damage it in this step.

When you are done the front should look the same as in the above image. Don't stress if the front is a little crooked. We will be fixing that later.

Now you can remove the required pieces from the fuselage top as shown above.

Then open up the wing slots.

Next thing to do is to glue the two rear formers into the positions indicated on the plan. These are formers D and E. Make sure they are straight and vertical.

Position the cockpit/battery hatch on the fuselage and then glue the C' former in place making sure it butts up smoothly against the hatch rear former.

The above picture shows my motor mount for the original motor. I had to discard it because the motor wouldn't fit into the nose. I included this image so you can see why there is a rectangular section cut out of the front of the fuselage top in subsequent images. When using the correct motor mount that cutout is not required.

The above image shows the nose former glued in place. If your front was a little crooked this will sort it out. In the foreground is the motor mount used. It has 2 degrees of down thrust and no right thrust.  Now the fuselage is put aside so we can move onto the wings.

We start with the centre panel.  The usual Flitetest foam spar and wing.

Start by folding the two spar sides against each other and gluing.  Wipe away any excess glue from the spar bottom and make sure you press the two halves firmly together. Cut away any excess glue that you missed when wiping.

The next step is to glue the spar in place onto the wing bottom.  As always test fit first before applying glue.

Complete the wing centre section in the usual Flitetest manner.  Use a skewer to crease along the blue lines on the wing top and then crease each one. Apply glue to the leading edge and spar top and then press the wing top against the spar top for a good five minutes. Next apply glue between the rear wing bottom and the fuselage top and again push down and hold for a good five minutes (if you watched the Flitetest build videos you know what I am talking about here). Be absolutely certain the glue is completely solid before removing the pressure.

Job done and now we repeat the same steps for each outer wing panel.

Glue the outer wing spar together in the same manner as for the centre section spar.

Glue the spar onto the outer wing panel bottom.  Make sure you have it the right way around as shown in the image above. You will really hate yourself if you get it wrong.

Before gluing the wing together check the trailing edge of the wing bottom and trim off any excess.  The bottom should meet the aileron joint.

Then crease, fold and glue in the same manner as described for the centre section.

The above image shows how I messed up on the original plans. I got the inner and outer spars out of alignment. This has been corrected on the plans so you should not have the same problem.

To correct my mistake I cut off the centre section spar ends that would normally slide over and be glued to the outer wing spars. I then 3D printed some brackets and gently carved out bits of wing spar until the bracket could be glued to both inner and outer spars creating a strong joint.

The above image shows the printed spar brackets glued in place on the outer wing panels. When gluing 3D printed parts never use hot glue as it tends to snap free under stress. I used epoxy. Using the corrected plans you do not need to use these brackets but you could if you wanted to.

I applied epoxy glue to the brackets and glued the wing panels together.  Cut two pieces of foam board 50 mm high and prop them under each wing tip to ensure the correct dihedral. When the epoxy is dry apply hot glue along each join top and bottom, smearing the excess in the normal manner. If you do not use the brackets then use hot glue to glue the panels together. I applied yellow wing tape over the top joins and clear tape over the bottom joins. If painted the use clear tape on the top joins as well as the bottom.

Carefully measure and mark the centre on the centre section on the leading and trailing edge of the wing. Then slowly, gently and patiently ease the wing into position. Make sure your marked centre positions are in the centre of the fuselage and then double check by measuring from the fuselage to the centre section/outer wing panel join front and rear and left and right. Gently nudge the wing until all four measurements are the same.

When you are sure the wing is in the right position apply hot glue to each wing/fuselage join top and bottom and left and right.

Next glue the vertical stabiliser to the tailplane making sure they are perpendicular to each other. Then slide the completed assembly into position and push the tailplane down so that the tabs on the fuselage slot neatly into the slots in the tail plane.  Eye ball the tailplane and make sure it is parallel to the wing. Gently push one side up and down until it is and then apply hot glue along the tailplane fuselage joins left and right.

Bolt the motor to the motor mount and then glue the motor mount to the cowl. The motor mount should slot into the front of the cowl and line up with the cowl front as shown in the image above.

Next trial fit the motor mount /cowl onto the front of the fuselage. Trim away sections from the front fuselage until the motor mount sits snuggly against the front of the fuselage.

Next glue the nose piece onto the cowl/motor mount. I use UHU Por for this step so that if I need to remove the nose piece to get at the motor I can simply slice through the UHU glue and pull it free without breaking or tearing anything.

Next glue the motor mount/cowl assembly to the front of the fuselage. Use lots of glue and make sure you get a strong join. Be careful not to get glue on the rear of the motor. I managed to glue the motor shaft to the motor mount and words cannot express how much fun it was removing the motor, clearing the glue and then bolting the motor back in place.  When I realised my mistake I didn't think I could get the motor on and off again but had nothing to lose by trying. After all the alternative would have been building a new fuselage and that would have made me cry a lot.

I have not provided bending templates for the under carriage as it is better to take the measurements off the mounting block.  I made the legs 10cm long but you should adjust that to suite whatever prop size you used.  I used 2mm piano wire but I recommend 2.5 or even 3mm.  Make sure the legs fit properly into the mounting blocks and then glue them in. When the glue is dry, mark and cut the holes in the wing for the mounting blocks and them glue them in place.  After the maiden I had to strengthen these up a bit (see later).

Glue the poster board over the rear fuselage formers and trim away the excess.  Mount the cockpit/battery hatch in place and glue the former A' in place against the front of the hatch.

Glue the tail skid in place. Use epoxy as anything else won't be strong enough.

Slide the wheels onto their respective axles and secure with collets.

Print and paint your pilot and windscreens and glue them in place.  Add markings, fit your electronics, glue the battery holder in place and you are almost done.  CG is on the wing spar. Balance by adjusting battery position. Remember for a low wing plane you hold the plane upside down and check the balance point on the top surfaces of the wing.


Landing Gear Leg Issues and Mods

I kept nosing over on landing. I realised that my landing gear legs were to bendy and would bend backwards on touch down. On one flight that placed the wheels behind the CG so the plane nosed over but on the last flight the legs acted like springs and bounced the aircraft back into the air. At the same time one leg broke partially free (see above image). The result was another nose over (check it out on the video). 

The following images show how I corrected the problem. I was too lazy to rip out the piano wire (although ultimately I might have to) but I recommend either 2.5 or 3mm piano wire. I have modified the models for the 3D printed undercarriage parts to suit 3mm so they should be fine for 2.5 or 3mm.

I screwed a washer down over the piano wire to ensure it doesn't break free again. I made the same fix with the PT-19 and it stood up to plenty of abuse. I used a circular servo disk to cover the washer (I thought it might look a bit neater).


I had to file a slot into the washer to make sure that it covered the piano wire properly. It will also help stop the washer from rotating as the piano wire pushes back on it.

The next thing was to add some fake legs.

The dummy legs are printed in two halves which are then epoxied together around each piano wire leg. I thought it would look better and help prevent the wire from bowing.  As of writing I haven't tested these mods out but, based on past experience, I am confident they will work.

Data Files

The full sized plans can be found here: FullSizedPlans.zip.

The tiled A4 plans can be found here: TiledA4Plans.zip

The tiled letter plans can be found here: TiledLetterPlans.zip

The dxf files can be found here: dxfFiles.zip

The pdf file of RAF markings can be found here: MagisterMarkings.pdf

The Sketchup files can be found here: SketchupFilesPartA.zip

and here: SketchupFilesPartB.zip


Conclusion

The Magister turned out quite nicely if I don't say so myself. Its a nice looking, easy to fly model that makes an excellent hack plane while still looking scale.  I am happy with mine. Build one. You won't be disappointed.

COMMENTS

glenn on October 12, 2017
Great article Mike very involved build foam and 3d printing great mix.
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MikeRobey on October 12, 2017
Thanks Glenn, glad you liked it.
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