Bumpy Green recently had the pleasure of building, flying & reviewing the outstanding Model Tech PSS Mustang from YT International. Now we convert the Mustang for electric flight to broaden the flying capabilities of this great model.

The Modeltech PSS Mustang is a 50" span ARTC (almost ready to cover) kit. Built with a superb colour scheme by Grot and successfully flown at Ivinghoe Beacon in it's native mode of Power Scale Soarer.



The only thing this model lacked was the ability to fly anywhere. Always keen for a challenge as well as the chance to fly this stunning plane at any of the Bumpy Green flying fields we set about the task of converting the Mustang for powered flight. The model could easily take a .15 - .20 size glow engine but to begin with we decided to take the quieter (as well as cleaner) option to fit an electric drive train.

From the first mention of conversion we knew, based on our experience, that the motor to choose would be the Overlander Typhoon. Possibly the most potent motor in this class and not a bank breaker.

Overlander will be able to supply you with all the electric components needed to convert the mustang and we highly recommend that you give them a call on +44 01524 793328 or visit there web site at www.overlander.co.uk

Unit 1 Jesmond Dene Trading Estate School lane Nr Lancaster Lancashire PR3 OAT Telephone: +44 01524 793328 Website: www.overlander.co.uk

The Overlander Typhoon 625 motor weighs 230g, is 65mm in length and 36mm in diameter. It is designed for 6 - 10 cells (7.2v - 12v range), has a free running speed of 21,000 rpm, a stall rating of 100Amps and will swing props in the 8" x 5" to 9" x 4" range which equates to around a .20 size glow engine. One unique feature is the internal cooling fan which keeps the air flowing across the coils and the dynamically balanced 3-pole armature whilst the motor is running.



Speed controller selected is the JETI Model JES 350. Rated at 35A and designed for 6 - 12 cells it weighs in at 25g. This model features 5v BEC for 3 or 4 servos, prop brake and separate arming switch.



The choice of battery packs seems endless. Opting for Overlander 8 cell flight packs of various capacity. 9.6v 1300mAh & 1500mAh NiMH, 1900mAh SCR & 2400mAh SCR-2 Ni-cad packs were the options. The only deciding factor will be the overall weight of the model with motor and pack installed compared to desired flight times. Again give Overlander a call for all your battery requirements.

Where indeed. A few evenings of discussion (usually with a curry thrown in) were had to decide the best way to approach the installation. An order of events was laid out, with a number of options and methods prepared in case of alterations along the way.



First job was to mark up the dummy spinner section to be removed. This was done with thought given to matching the nose former to the power spinner to be used and with mind to being able to replace the dummy spinner when the model is taken to the slope for unpowered flight.



Carefully working round the nose cone using a very fine tooth razor saw it was slowly cut from the ply nose former. Special care was taken here so as not to spoil the fine look of the model with either the new spinner fitted or the old nose cone replaced. Taking a few cuts then turning the model proved most accurate for removing the nose cone, taking several rotations of the model to achieve the final cut.



Removing the nose cone from the ply former took a small twist to detach the small hub of glue in the centre. The ply plate was them sanded smooth and prepared for the motor holes to be drilled.

With the nose removed and prepared the next job was to find the centre and mark it ready for the holes to be drilled for the motor output housing and mounting bolts.



A small pilot hole was already in the former so taking the largest wood drill bit we had the hole was made for the motor output housing. This turned out to be too small and a grinding stone was fitted to the ever present Black & Decker Wizard (hobby drill) and the hole enlarged sufficiently to allow the motor to be fitted flush to the back of the former.



Using a plastic 600 size motor mount as a guide, the mounting bolt holes were marked out to be drilled in exactly the right place.



Steel ferules & washers were used to spread the mounting load on the front of the ply plate, the washers were countersunk to allow clearance for the screws at the back of the prop. This also helps prevent the screw sinking into the wood allowing the motor to work loose.



Cooling holes were drilled to match the intakes on the front of the motor to make sure sufficient air passes through the motor.

One thing which is often overlooked is motor suppression. This reduces radio interference caused by the electrical 'noise' generated by brushed motors.



Overlander supply a good little kit for motor suppression. It includes 2 ceramic cap axial capacitors, 1 x radial monolithic ceramic resin dipped capacitor, heat shrink insulation and a diagram with instructions on installation. These were soon soldered into place on the back of the motor. Good quality copper wiring was also soldered to the terminals of the motor. This was carried out before fitting as the fuselage is quite narrow at the front.



The speed controller was fitted with gold bullet connectors, this not only reduces resistance in the circuit but also offers a better connection than other types available. All batteries are fitted with gold bullets, with the positive side as the female socket so it is always shielded. Small lengths of fuel tube ar used to cover the negative bullet to prevent accidental short circuits during transport.

Time to make room for the battery back inside.



The range of battery packs available to use is endless, with a wide variation of size & shaped packs. This taken into account led us to find a mounting system that would suit a wide range of battery installations. First all the internal formers were removed. The original plan was to fit the battery from below. This would involve removing the wing each pack so alternatives were looked into. Trying to fit an 8 cell sub-c pack in from the motor access hatch was not possible due to the angle of entry and the position of the wing mounted aileron servo.



Finally an access hatch from the top was decided to be the way to go. As the battery needs to go over & behind the C of G the hatch would need to be right where the cockpit was mounted - Perfect.

Following an existing panel line for the front cut and an angled cut for the rear (to avoid the insignia) the canopy area was separated from the top of the fuselage. The cuts were again made to the depth of a panel line so ensure the cutting along the sides was kept straight.



Using a sharp scalpel and a steel ruler, a straight line was sliced in the side of the fuselage. This allowed the canopy hatch to be removed in one large piece without interfering with the cockpit itself.



With the canopy removed there is a lot of room to work with inside. Next job before installing the battery tray is to make sure the hatch can be refitted and fixed with minimum effort. When refitted, the join is hardly noticeable as it follows panel lines already on the model.



A liteply tongue is used on the front of the hatch section fitting under the block in the front of the fuselage. The rear of the hatch will be held down by a screw into a block with a control snake plug to grip the thread.
The fit is secure and will provide quick and easy access to change the battery packs.

With the main fuselage modified to allow easy battery access we could now install the power train.



A few experiments will have to be carried out to determine the best thrust angle.



The prop adapter is an extra long type to allow for motor mounting adjustments & comes supplied with a spun aluminium dome nut that secures the propeller and spinner back plate to the adapter. This is a bolt on adapter using a grub screw to grip the motor output shaft as opposed to a clamping collet type fitting. The spinner matches almost perfectly both in size and colour.

Now that the motor is fitted a rough guide to the centre of gravity can be calculated.



As a large section of the upper fuselage had been removed to form the access hatch, the fuselage sides over the wings became quite weak. To counter this balsa doublers were used with a beech longeron above to add rigidity to the area. Clamped into place with a liberal dose of thick cyno all over. The longerons were angled at the ends to fit the triangle fillets of the former supports at the front and rear of the hatch area.



The battery tray is a length of 1/4 balsa sheet cut to size with a slot in the end for the elevator servo. The is strengthened underneath by a thin ply brace for the servo slot & strips of hard balsa across the width underneath.



A pair of 1/4 square fillets were fitted for the battery tray to sit on. These are fitted over the wing doubler & runs the whole length of the internal area. This allows for the battery tray to be moved (as it had to be after initial testing ) with the servo fitted.



Servo fitted & battery tray placed into the fuselage. A few quick checks with the battery pack loose inside gave a rough indication as to the amount of room needed for various cell packs that could be used. Once all the control linkage was tested for binding the tray is glued into place. Clamps help keep the sides firmly attached to the tray to ensure they are attached straight.

The re-installation of the elevator servo proved to need a bit of careful thinking.



With the servo mounted right next to the rear of the battery compartment the travel of the servo was restricted by the angle of control entry into the block holding the outer. With the battery tray & servo moved forward about 10mm it allows enough angle to move freely. The snake outer is held in a block at the front & cyno'd into place at the exit point in the fuselage.



Now that the servo was back in place & functioning correctly the final location of the radio gear could be determined. The receiver sits just in front of the canopy under the forward hatch. The aerial comes out of the same hole as before so no re-routing was needed. The speed controller is mounted under the battery tray with Velcro with the motor leads folded forward to connect. The battery leads tuck up into the battery compartment for easy connection.

The last & possibly most important component in an electric conversion - The battery.



Mounted directly over the centre of gravity the battery is held in with 2 wide strips of Velcro& held in place with 2 balsa sticks either side holding it tight in the centre. This is a 7 cell 2400mAh pack and shows there is plenty of room for 8 cells if required. Other last minute mods included the changing of the 13Amp wire on the motor to more suitable heavy duty motor wire rated at 30+ Amps.



Nice shot of Tony helping out at the Bumpy Green construction yards during the final day before flight testing. He did do a grand job of soldering up all the bullet connectors & wiring. All controls tested one more time, final check the motor is spinning the right way & refitting of all the hatches completed.
We're ready to fly...

Daren was also round shortly after lunch for a fly & was soon voted most capable test pilot therefore gaining the unfortunate honour of test flying the Mustang. This was also due to the wind being a little choppy.



Taking up position Daren prepares for launch. He doesn't look that happy with the task ahead.
Tony handled the video camera, John took control of the stills camera & we all waited with held breath.



It's away.

With a hefty chuck & full throttle the Mustang took to the air. The gusting wind didn't make life too easy but with so few days of decent weather in the near forecast the flight test went ahead. Daren levelled off & reported the model stable but may be tail heavy. With the adverse conditions & a rather fragile model it was decided that a landing should be carried out before further testing continued.



Bringing it home with few quick bursts of power to keep the airspeed up the Mustang glided well even with all the extra weight installed.
Images are stills from the video of the first flight.



Last flying shot during landing with the digital still camera on high-res-sports-action mode.



The landing was good but a tuft of long grass caught the propeller on landing & flipped the model over dislocating the motor & firewall with it. Better that this happened that the whole front end get torn off. A folding propeller system has now been acquired & more pictures will be added when weather permits. The firewall will be easily repaired as it was a clean break at the join.

The electric conversion of this model has been great success, although only a relatively short first flight was had, we will be back out as soon as possible for some more flights to check out the aerobatic capabilities of the mustang and to get some pics and video footage for a new movie.

If you are into electric flight then this model is definitely worth looking at, plus you have the added benefit of being able to slope soar it too.

YT INTERNATIONAL 15 Parkstone Close Shelfield Walsall West Midlands WS4 1QW UK Tel/Fax: 01922 684425 E-mail: inquiries@ytinternational.co.uk Website: www.ytinternational.co.uk	Overlander Unit 1 Jesmond Dene Trading Estate School lane Nr Lancaster Lancashire PR3 OAT Telephone: +44 01524 793328 E-mail: sales@overlander.co.uk Website: www.overlander.co.uk

We have now replaced the 9 x 6 graupner prop for a 8 x 4 graupner folding prop so we will no longer have the problem of the propellor catching the ground on landing. Unfortunately we did not have time to add the nice red spinner back on.

Initial flight results suggest that the model has a little too much down thrust and also the battery is still too far back making the model a little tail heavy. I would suggest having the balance point (for electric flight) at least 10mm ahead of the suggested position which is on the main spar and also make sure there is not too much down thrust, this can be achieved by holding the model by the air scoop and powering up the motor, make sure the model does not dip its nose under power.

Another thing worth noting is the control throws, these could be reduced for electric flight by about 25%.

These minor corrections will be made to our model and re-flown again soon.

Article by John Kent from Bumpy Green Model Aerodrome
4th April 2002