Old Priory Silhouette e-conversion - RC Groups
Thread Tools
Feb 10, 2005, 05:32 AM
Sloping off....
leccyflyer's Avatar

Old Priory Silhouette e-conversion

'twas the end of an era yesterday evening chez leccy.

My last remaining glow model has finally gone under the knife for conversion to e-power.

The Priory Models Silhouette is a 55" span low wing aerobatic sports model with the look of a '30's racer. She was my second model and my first low winger, being amply powered by an Irvine .46. These are a lovely quick build kit from a UK cottage industry style supplier. The model comes with the fuselage ready built, just needing addition of the foam decking and g/f cockpit moulding, fitting of the solid balsa tail surfaces and with foam wings ready to join. The end result is a very pleasing model with classic lines and great flight characteristics.

Having survived flying through a barbed wire fence with just moderate repairs some eight or nine years ago she has hardly flown since I've been flying electrics. In need of another model with wheels and being in the temporary possession of a clean workbench the time had come to finally recognise that she was unlikely to ever fly again under I/C power and to make some use of the airframe and full set of gear lying idle.

The poor old latex pilot had perished and has now gone to that great wastebin in the sky so with him out of the cockpit came the removal of the noisy bit up front. I'd laid the model up last time she was out a couple of years ago with liberal application of after run oil. This resulted in an extremely sticky model, but half an hour with the isopropanol bottle, an oily rag and some tools saw the motor, tank and cast ally mount removed along with half a ton of sticky mess over the fuselage. Some fuel soaking to the firewall had caused the film to lift a bit so the film and my metal tape repairs were stripped back to see if the fuselage itself had soaked up any fuel. Thankfully that wasn't the case and the model is in excellent nick overall.

The model has a balsa skinned foam upper fuselage deck and already has a hatch underneath for fuel tank maintenance. Though it's less than ideal to have to flip the model upside down to change batteries I think that is what I am pobably going to do- make use of the tank hatch. I could make up block packs just for this model, but would prefer to build in a battery tray that will take my 16 cell (2x8 cell) 3300's and 2400's, probably secured with velcro seatbelts.

The only internal changes I can see a need for are to hollow out the foam decking to give clearance for the battery to be inserted at an angle (the tank hatch is quite short) and moving the rudder and elevator servoes back by about their own length. Motor mounting will involve either a space frame or a ply motor box and I'm going to use a Twister 60. For once I haven't actually run the numbers as I don't have a bare airframe weight yet and that ally mount and engine make up a lot of the weight of the model.

Here's a couple of pics to start off with- the Silhouette in her former I/C days and the start of the conversion process- removing the eBay bound Irvine .46. More to follow.
Last edited by leccyflyer; Feb 10, 2005 at 05:36 AM.
Sign up now
to remove ads between posts
Feb 10, 2005, 07:25 AM
Sloping off....
leccyflyer's Avatar
Then I thought - naah, why fiddle about trying to thread a stick pack through the 4 inch hatch on an upside down model- Dereck would have kittens at such faffing about. So out with the razor saw for a few minutes butchery and instant top hatch. There is much better access to the internals now and I shouldn't think it has compromised the structural integrity at all- especially by the time I've faced out the hatch lining and added a little triangular section to the firewall to fuselage side joint and fitted the now redundant bottom hatch permanently.
Feb 10, 2005, 08:22 AM
Single-task at best...
tim hooper's Avatar

It's great to see you're back in the saddle again!

You'll be going to the flying field next..............

Feb 10, 2005, 08:44 AM
Sloping off....
leccyflyer's Avatar
Thanks Tim

This doesn't make the kit mountain any smaller though does it? Still, can't see a good airframe go to waste.

Since the clean-up last night there is a peculiar oily film in the air here now and I'm not talking about John Wayne in "Hellfighters".

I've run the numbers and there isn't anything too scary in there, wingloading is in the mid twenties, all up weight should be around 6.5lbs with 16 cells (would be a lot less with lipos ) and looking at around about 100w/lb. It should work with that same setup as the Wot 4, if there is enough ground clearance for the 13x8 prop.

Feb 10, 2005, 09:49 AM
Speed Demon
GregG's Avatar
Looking Good Brian!

I'm just about the same in that the last time I flew a glow model of my own, oops let me rephrase that if I had one was a few years ago. I don't know if I'd bother with the planes I have. They would all do so much better being built for electrics from the gitgo. It looks like your Silhouette is a lightweight one that will fly superbly under E-power.
Feb 13, 2005, 10:29 AM
Sloping off....
leccyflyer's Avatar
Just hope it works out Greg Should be okay though with the same setup as my Wot-4 as the weights and measures are about the same.

Blowing a hooley here this morning so no flying today and a chance for a bit of a tidy of the incredibly messy bench and a few more piccies before moving on to fitting the motor.

The battery tray is in place and the battery retention sorted out. In order for a battery tray long enough to fit my existing packs I've had to move all of the servoes backwards, including the single aileron servo in the foam wing. Having relocated the servoes I've got about an inch of leeway to move the battery pack backwards and forwards to balance the model, as well as a 100g reciever pack that can fit either under the main power pack in the old tank bay or behind the servos next to the receiver.

The main battery is retained by my old favourite velcro seat-belt and is then locked tightly in place in the fore and aft direction by fitting the balsa and ply crutch see in the pics below. With that locked against the end of the servo rails the pack cannot move a millimetre once it has been inserted. I'll fit a balsa block against the rear end of the pack when the proper C of G has been achieved. The battery hatch is done, save fitting a catch at the front.

Picked up my Twister 60 and Jet ESC yesterday so I can now proceed with fixing the motor. I've plumped for making up a ply motor box with a GRP front for mounting the Twister inside and the box will be bolted to the firewall. I intend to mount the esc to the side of the box, inside the fibreglass cowl, allowing plenty of cooling and keeping all of the power leads short. The battery leads will pass back through the firewall to allow connection inside the hatch area.
Mar 28, 2005, 04:56 PM
Sloping off....
leccyflyer's Avatar
Fantastic flying day today and I finally got to maiden the Silhouette e-conversion. Currently sat here grinning widely at a very enjoyable flight with a glass of cold Chardonnay . The Twister 60 works great with this model, she took off across the field like a scalded cat and was an absolute peach in the air.

The motor mount ended up as a 40mm deep box of birch ply, with aluminium angle inserts, to which is bolted a 3mm GRP motor mounting plate. The box is bolted to the firewall and the Twister 60 bolted directly to the front plate. That's a lot of bolts! It didn't prove possible to fit the motor inside of the box due to the narrow cowl but this set-up worked well.

The two 8 cell GP3300 NiMh packs to give 16 cells in series take the AUW of the model up to about 7.25lbs, which is no mean weight on 550 square inches- however the motor is more than man enough for the job and this was partly meant to test how comfortable I would be with a model with >30 oz/sq ft wing loading before flying my P-51. No actual measurements as yet but the 13x8 Master Airscrew wood prop worked well in the air.ROG from grass with ease and all the aerobatics that I'm capable of. Motocalc puts the current draw in the mid 30s amp wise with something like 85w/lb and the maiden was something like 5-6 minutes.

Here's a picture of the motor mounting box. The ESC sits through the firewall, on top of the pack, which isn't ideal, but I didn't want to lengthen any cables. For the summer I'm going to have to arrange some forced air cooling I think. The model was so nice to fly I might even be tempted by some Lipos- I've got as far as cutting a block of pink foam to the size of a suitable pack. The NiMhs are restrained by a combination of a velcro seat belt and a balsa wedge that braces the pack rigidly and stops any lateral movement.
Mar 28, 2005, 05:00 PM
Sloping off....
leccyflyer's Avatar
Here's the finished hatch area in action. I covered the front of the model in metal foil - the only silver film I had was miles away from the rest of the model in terms of colour, so on with the metal foil. complete with faux rivets and panel lines. It's just a bit of fun really.

The pilot is weightless and made from a latex mould of a commercial pilot figure into which some cavity foam insulation was squirted. It was a rush job as it's a holiday here with no shops open to source a suitable pilot- given how well he did on the maiden though this little feller is staying, despite a few moulding holes in the head.

The final picture is the completed model in it's new electric configuration. I may order up a new cowl, minus all the cut outs that the Irvine .46 required. I think I'm going to enjoy this one
Apr 03, 2005, 03:45 AM
Sloping off....
leccyflyer's Avatar
No flying shots as yet, but during a very enjoyable day's flying at Shifnal on Friday Barney took some nice shots of the Sillouette cutting the grass. I'm made up with the model, she's got wheels, all weather ability (at 7lbs plus she doesn;t notice the wind) and oodles of power.

The line up in the pits at Shifnal was most encouraging - a round half dozen electric models all with wheels fitted and all more than capable of ROG from grass. Just have to watch that we don't get caught in the 16-cell trap .
Apr 03, 2005, 06:54 AM
Single-task at best...
tim hooper's Avatar
Originally Posted by leccyflyer
The line up in the pits at Shifnal was most encouraging - a round half dozen electric models all with wheels fitted and all more than capable of ROG from grass. Just have to watch that we don't get caught in the 16-cell trap .
Looks like e-flight came of age at Shifnal on Friday!

With Silhouette, Wot4 and Cricket being fielded by Team Leccy (cricket being fielded, geddit?) and my own Decathlon in the slips, we had quite a day.

The Silhouette honked around the sky with consummate ease, just bristling with torque. It's nice when an old favourite gets a new lease of life with a civilised power train, isn't it?

Aug 26, 2005, 07:15 AM
Sloping off....
leccyflyer's Avatar
Someone was asking about fitting internal radio switches to models and as the Silhouette makes use of such a switch I'll just post a couple of pictures that I can point them to as an illustration. I think the switch is made by Du-Bro and doubles a a joystick for Major Foamheid the pilot. That's a Simprop on-board battery meter fitted into the instrment panel- a useful addition in a model that needs a separate reciever battery pack.

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Old Espirit sailplane e-conversion? RMoore Electric Sailplanes 3 Aug 17, 2002 04:38 PM
Star Cruiser e-conversion done bjsiegel@texas.net Electric Plane Talk 1 Aug 06, 2001 11:21 AM
E-conversion Observation bjsiegel@texas.net Electric Plane Talk 3 Jul 31, 2001 12:17 AM
Anyone do the E-conversion on Air Foil Aviation's 1/4 scale powered parachute? EFoil Parkflyers 0 Jul 23, 2001 06:37 PM
Anyone do the E-conversion on Air Foil Aviation's 1/4 scale powered parachute? EFoil Electric Plane Talk 0 Jul 23, 2001 06:35 PM