Top Gun - CML Me109e

The Messerschmitt Bf 109 (aka Me 109) was a German World War II fighter aircraft designed by Willy Messerschmitt and Robert Lusser during the early to mid 1930s. It was one of the first true modern fighters of the era, including such features as an all-metal monocoque construction, a closed canopy, a retractable landing gear, and was powered by liquid-cooled, inverted-V12 aero engines.

 The 109 first saw operational service during the Spanish Civil War and was still in service at the dawn of the jet age at the end of World War II, during which time it was the backbone of the Luftwaffe's fighter force. From the end of 1941 the Bf 109 was supplemented by the Focke-Wulf Fw 190.  Early models had Jumo engines but later the more powerful Daimler engine was used.

 There are not many scale models on the market but Cermark in conjunction with Top Gun produced this 60 size Me109.  The fuselage is grp reinforced with ply formers and coated in matt grey finish allowing modellers more options regarding which theatre of the war they wish to emulate.  The wings are fully sheeted and pre-filmed and the model even comes with air retracts.  These are air up/spring down which in itself becomes fail safe.  The cowling is beautifully finshed using grp and the exhaust ports are pre-fixed for you.  Albiet the cowling is not true to scale or the lovely matching yellow spinner but this is usually normal in rc models.

The large cowling meant that I could hide quite a few types of engine within it, a 120 four stroke or even a 108 2T glow.  I have opted for the Jen 90 two stroke which is no bigger than a 60 size.  This engine came recommended so I went along with it.  The model should weigh in at around 8lbs or so, so a 60 motor would've been adequate but this model may become the chase plane at our club so I needed an edge on 'em. (Dastardly Smile)

It came in a rather large box and was very well packed.  Initially I had no instruction manual so for the first few steps I just used common sense.  However, managed to find a pdf version on the "net".  The box contained the fuselage, the wings each bagged and supported by poly-foam.  The rudder and stabiliser were bagged and laid flat on the bottom of the box.  Two big plastic bags contained the fuel tank, lines, wheels, air-intakes, supercharger inlet and other scale items plus screw and bolts etc.  Hinges are CA types and were pre-slotted in the wing surfaces except for the rudder hinges which are in the bags.  The other bag contained the air-retracts, and the air kit and reservoir

First job is to glue the ailerons.  I marked where each hinge's centre was and marked with a light pencil line.  Ensuring that all the hinges slid in fully and easily I then bored some 1.5mm holes at the centre point of each hinge slot.  This is enable the CA to fully soak in to the contact surfaces.  Using "T" pins pushed through the centre of each hinge I slotted them in to the ailerons and then into the wings.  The pins stop the hinges sliding in any further and also act as spacers.  After removing the pins, flexing the ailerons each way added a few drops of thin CA to each hinge on one side and ensuring the gap is constant flipped the wings over and did the same to the other side.





The Fuselage

The Fuselage in the wing mount area is enormous.  The servo tray is pre-fiitted with cut-outs for the four servos and air reservoir.  The servo slots needed no modifying to insert two JR digital for elevator and rudder.  I used two standard Futaba S148's for throttle and air retract valve.  The receiver can sit on the servo tray above the air tank keeping cabling to a minimum.
As you can see from the photos the space between the servo tray and fuel tank bulkhead is enormous.  However, the servo tray is mounted in such a position that 5mm holes needed to be drilled through the fuselage above the servos to access the rear rudder, elevator, throttle servo mounting screws.  Why they could'nt have moved the tray further forward by 15mm I do not know.

Fitting the stabilsier was a little trying.  It is a sliding fit through a slot in the fuselage.  After marking the centre line of the stabiliser and trial fitting a pencil line was drawn top and bottom where the fuselage sides meet it.  Then carefully cut away the film covering 5 mm inside these lines.  Now here is the tricky bit!  A light coating of 30 min epoxy is coated on to this uncovered area.  Then slide the stabiliser through the slot till the pencil lines align up again.  Now measuring from the tips of the stab equal distance must be achieved using the forward wing mounting recess centre and a centre point.  I found this wasn't as easy as you think.  The slightest movement/adjustment on one side tended to throw out the other side enormously.  Once happy with the alignment a thread of epoxy is then applied along the point where the fusleage sides meet the stabiliser.  Wiping off any excess adhesive carefully.  Then recheck alignment. Allowed to fully cure.

The elevators now can be fitted.  Drilling a 1.5mm hole in the centre of each CA slot ensures that the glue soaks all the way down.  Aligning the elevators with the stabiliser is simple enough ensuring that they have adequate clearance on the outer ends where the stab curves round.

With the stabiliser fitted it was time to fit the control rods for the rudder and elevator.  These are dowel rods with pre-drilled holes for the threaded wire connectors.  Once the length of wire required was ascertained for the horn ends the wires were CA'd and then the supplied shrink wrap was shrunk over the area to secure.  Placing the control rods through the pre-cut slots in the fuselage it was time to mark where the control horns would be located on the control surfaces.  Once this was done the horns where fitted and with the clevis's wound on to the threaded end these were dry-fitted so as to ascertain where the straight wires would cross the servo arms.  Marking these points, pulled out the rods again and at the mark positions made 90 degree bends.  Measuring about 10mm from bend cut off excess.  Refitting the rods and now dropping the bent ends into the servo arms which were drilled out to 2mm.  Fitting the supplied plastic "keep" clips.  Using a spare receiver and battery tested the servo travel and direction, etc of the rudder and elevator.

In the servo tray is a pre-cut power switch slot which I used with a suitable sized switch/charge line component and connected all the servo leads to the AR6200 receiver.  To oprate the switch from the outside I drilled a 2m hole in the switch lug and a 2mm hole through the fuslage in line.  Using a short piece of scrap 2mm wire with a threaded end and 90 bend in the other end fitted this to the switch.  The threaded end gives you something to grip when operating the switch!

THe air retract valve comes from the bag of air kit bits.  A laser cut piece of ply is suppplied which you break out and assemble into a valve mounting.  With this screwed in to place next to the servo a small piece of 2mm wire connects the two together.  The servo only needs to travel 7mm to operate the valve.

The throttle control is operated via a snake, supplied and some spare 2mm wires in the kit.  Once happy with its position I epoxied the outer into place plus adding a support block on the side of the fuselage and secured by a cable tie  (See Photos)

The air reservoir slides into it's location under the servo tray and I secured it with a small blob of epoxy.  Made up the airlines to the valve and to the quick-connect.  The air fill valve was located into the side of the fuselage and connected up.







The Wings

The aileron servos are fitted to the servo hatches which in turn are secured by 4 tiny screws, all painted in the same colour as the surrounding surfaces, light grey.  The servo blocks are pre-fitted but added some more epoxy for piece of mind.  The JR servos fitted nicely after a some more clearance was made between the blocks with a sharp knife.  Once fitted and checking servo arms don't foul the exit slots, which mine did, it was time to fit the wire control rods.  Again marking a line from the servo arm and where it crosses the aileron, the horn position is located.  Fitting the horn is standard with the supplied screws.

Screwing on the clevis's I now fitted the clevis to the horns and where the rods cross the servo arms, a 90 deg bend was formed.  Cutting off the excess the rods were now pushed through the servo arms and secured with supplied plastic "keeps".

Everything had gone together okay so lifting the hatches, I CA'd the screw holes and shrunk wrapped the servo lead plug and extension lead socket so they doin't come part at a later date.  Using a spare receiver and battery pack I plugged in the servos so I could set the servo direction and travel up.  With retracts already located that was it for now for the wings.  The additional scale stuff can be fitted later. ie; coolant radiators, landing gear covers and cannons.

Time to glue the wing halves together.  The supplied wing joiner is ply and has the dehydral pre-set and slided into each wing half slot.  However, the joiner needs to sanded down until it is a nice sliding fit in each wing.  The same goes with another smaller joiner that is located nearer the trailing edge.  Once the wings can slide together and the mating faces are good and in alignment on a dry-fit it is time to epoxy the two together.  I used 30 minute EP for this to allow for time to align and set.  Using strong elastic bands wrapped round the temporarily fitted the wing bolts and also wing leading edge dowel pins left the wing to set.

After the glue was set it was time to test fit the wings to the fuselage.  The twin dowels are pre-fitted but they were not located correctly which meant that they would not pass into the fuselage locating holes.  They had been glued in at an angle. (Friday night job in China!)  So I decided the quickest way round this was to drill them out and fit my own dowels.  Making up my own dowels and making them a fairly tight fit I fitted the wing into the fuselage therefore aligning the dowels correctly.  This seemed to work!  Removing the dowels again, I applied 30 min EP to dowel holes and with dowels relocated in the wings I again fitted the wing carefully till it was not quite in final position and allow the EP to set.  The wing now locates in to the fuselage easily but with a good fit.

The air retracts are designed to be secured with wood screws which I was'nt comfortable with, so using a template derived from the air retract I drill out four holes and fitted them with spike nuts from the underside.  Not easy but done!  The retracts are now secured with four 4mm socket head set screws.  The wings came with some pull throughs installed which I used to pull lengths of air-line and the aileron servo extension cables too which exit through holes at the wing root.  The airlines where connected to the Y connector which then had a short piece of line connected to the quick-connect.  In each of the wing lines a restrictor was fitted to slow the retract action





Engine and Fuel

The enormous cowl meant that I could fit virtually any power source and most of it would be hidden.  Having already built a P51D in electric I really wanted some noise so opted for a glow motor. The one I chose is a Jen 91 but the engine dimensions are no more than a 61.  Because of the scale exhaust stacks that are pre-fitted in the cowl a side on fit wasn't practical allowing the glow motor exhaust to be lowermost.  It was decided that inverted would be the best option but in this caused a headache.  An exhaust for a two stroke.  Plus any exhaust exiting from the back of the motor would be very close to the firewall and the pipes facing downwards too.  Here it must be said that thanks to Jen Engines they created me a custom Pitts style exhaust that sits real tight to the back of the glow motor with twin outlets pointing downwards from the dimensions and photos that I supplied them.  Perfect! (See Photos)

The fitting of the engine and mounting was a little trying due to the template was supplied was for four stroke I would imagine and even then it was inaccurate.  So, back to common sense, alignment with centre line of fuselage and the cowl drilled holes and located engine mount (the slotted hole type) using my own 4mm socket head screws and spike nuts to secure.  THe slotted mounting enabled me to slide the engine into the best location and clearance for the spinner to cowl. (See Photos)


Cutting the grp cowl was relatively easy to accommodate the exhaust outlets and the cylinder head.  To get the cowl to slide over the engine required removing the cylinder head and then marking roughly where it was from the outside using measurements and eyesight.  Removing the cowl then using the cylinder head as a guide marked with a pencil the outlines.  First using a small pilot drill and refitting the cowl I could see where the cylinder barrel centre was.  Relaligning the pencil marks as necessary.  Using a small drill along the pencil outlines and wiggling the holes into each other.  Pushing out the scrap and filing the hole until the barrel was central.  Refitting the head now allowed for final clean up.  The exhaust I did mainly by measurement first and using the same method of drilling and filing created two slots that allowed the cowl to slide over the outlets and drop down into position.  See Photos)

The tank supplied is 14oz and is a good fit through the bulkhead in the fuselage.  All the fittings were supplied so I used these and they were pretty standard from any model shop.  The battery is fitted under the tank.  I wrapped a 2000maH Sanyo Eneloop 4.8v flat pack in foam and located under the tank.  With lines connected and marked where they fit the tank was positioned and the fuel lines connected.  I prefer a three line system, one for exhaust back-pressure, one to the carb and one to the fuel dot filler.  The carb line has fuel filter in circuit.

With the Fuselage virtually complete I decided now was the time to fire up the glow motor.  Dropping the fuselage into my frame support I fuelled up.  Binded the receiver to the JR DSX9 and first set the retract servo to no travel for now.  Checked and set dual rates, direction of travel.  With this all as near as damn it for now, I then set the throttle travel.  Here I found I had to use a nearer to centre of servo arm hole position for the control snake.

I had opted to start with a 14x6 prop though I could have gone a few down and possibly one up to 15x7.  .  With prop fitted I flicked the crank over a few times, finger over carb to draw fuel up.  In the airframe cradle the fuselage sits upside down so the engine was now upright!  The throttle was set a very small opening after priming up.  Fuel needle at 2.5 turns out.  Snapping on the glow plug I cautiously flicked the prop about three times and she fired up lovely.  Not as noisy as I thought it might be with custom exhaust.  I let it warm up a bit before opening the throttle to about one third throttle.   Repeated this a few times and then shut down.

The one thing that did cross my mind, is priming up or starting from cold with an inverted engine at the field.  Maybe two fingers stuck in the exhaust outlets!

At this time too I decided I must cutout the cowl to access the mixture control and low jet.  With this done I made up a wire extension to fit into the mixture control so it appears through the cowl, albiet very close to the prop!






Final Stages

With the wing close by to the fuselage connected up the retract airline.  With a full charge of air and using the TX I slowly increased the retract servo travel till it just operated the valve without groaning.  I was surprised how quick the retracts operated even with restrictors.  Even faster on spring return!

With that out of the way it was time to fit the wing properly and tweak the control surfaces.  Done!

The wheels supplied are hard foam so I will replace these with Dubro scale wheels with air-filled tyres - The latter absorbs impact on the landing especially when the landing gear is not Oleos.

The coolant radiators are grp and pre-painted so it's only a matter of marking their respective positions on the wing undersides and cutting away the film 3mm inside these lines for the epoxy to key into.  The superchager intake is located on the port side of the cowl where it meets the fuselage.  I will screw rather than epoxy this to the cowl and fuselage for added security as the cowl obviously will need to come off from time to time and the intake overlaps the join.

The wheel wells are designed to have the plastic inserts as supplied but the edges do need to be sanded and champfered down to get a reasonable fit.  I may just paint in the wheel wells with black paint.  If I do stick the wheel well inserts in I'll use silicon sealer - can always pull them out at a later date for maintenance, etc.

The wheel legs need to have the covers attached.  The manual recommends clear silicon.  I have used this method but I think they won't stay on long so may take them off before maiden and find another way of securing using small clamps.

And no model should take to the field without an "Idiot" aka a pilot.  Why idiot?  Well, if anything goes wrong I can blame the pilot rather than myself...  His name is Willy, short for Wilhelm.  He may acquire other names but we will start off with this one!

Update January 2020

This warbird has now been modified and sports a DLE20 gas engine up front. The conversion was not easy due to the fact that the fuselage was moulded and designed to take a glow motor. The DLE20 sits very close to the firewall so rendering the non use of the choke. This is not a problem, I just spin it up with an electric starter until it fires. The engine sits well inside the cowl too.  The ignition module and tank are fitted to a tray that slides into the old tank area. The original tank supports and formers had to be cut and fiddled with to get the tray to fit. Behind this tray the batteries sit on the original battery tray.