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Written by James Gamble   
Sunday, 08 November 2009 17:54

Osmose 50 - Build Review by James Gamble


After flying the Vertigo II through the summer months I decided to let it rest for a while and acquired an up-to-date pattern ship and having a Saito .82A Golden Knight hanging around my dad’s workshop and a Saito .91 spare, this gave me quite a few options.

My final choice came from the four-time consecutive winner of the F3A World Championships, the world-renowned French champion Paysant-Le Roux's 2007 entry Osmose in the scaled down 50 version, this seemed just the ticket.

Engine size

Well the kit does say .50cu in – .70cu in and NO MORE! So I placed an .82A up front.

Just a bit about the engine and why the .82A is not as crazy as it sounds.

The saito engines use a monolithic structure of cylinder head and cylinder with hard chrome plated inner surfaces, this eliminates the use of a cylinder liner. One of the best advantages is that it dissipates heat better but on the flip side if damaged it’s a lot more costly. The piston used is high silicon content aluminium and a compression ring which increases efficiency. The crankshaft is produced out of solid chrome molybdenum which in turn is supported by two ball bearings.

The term Hemi Head which is found on the box is basically an internal combustion engine in which the combustion chambers are of hemispherical form and therefore larger valves are possible and a straighter, less restrictive flow path can be provided for the air/fuel mixture. After Saito had produced a full range of engines they readdressed various models and expanded the displacement in the case which offered more power and without the weight penalty, hence versions like the .82A were born.

Another benefit with Saito engines is the reversible carb allowing the needle valve to be placed on the other side. The .82A features a displ.(cc) of 13.8 with a bore size(mm) of 29.0 A stroke(mm) of 20.4 and weighs in at 462g which is in fact lighter than the FA-65, FA-72 and the FA-80!

I currently have the .82A set up without a velocity stack and without pump as I’m not intending to use it for 3D but for pattern flying.

The real down side to Saito is the lack of accessories such as exhaust options, but I’ll cover that later on.



The finish of the balsa and ply were superb and the covering was nothing but eye catching but did require a little ironing on the edges. For once the manual was quite informative and self explanatory, not leaving much to contemplate. After joining the wings and installing ailerons / servos it was on to the fuselage. Note that all the required holes and cut-outs are pre drilled and all that was required was to remove some sections of covering to expose them.

I won’t bore you with the standard build but did feel that the elevator rod should be bound with cotton and super glued before heat shrinking. The reason for this is that if the control surfaces receive a knock on landing or in transport the heat shrink will stretch and located halfway down the fuselage this would be difficult to check, possibly even leading to slack in the connecting rods or even a failure in flight!

One interesting feature of the kit is the Canalizer which sits on top of the fuselage, this helps the plane track better but was a bit tricky to align.



After building the bulk of the kit, the engine cowl had to be fitted which posed a problem as I didn’t want the exhaust protruding from the side. Exhaust manifolds from other engine companies are available but expensive. I was quoted £50 for the manifold and a further £50 for the silencer!

Forget it – I’ll make my own.



After a rummage around in the garage I found some light weight steel tubing and after cutting it into several sections and welding them back together to form the curve required I took the standard Saito 2” exhaust extension, cut it in half and welded them to either end to provide the correct threads. After grinding down the welds and belt sanding I had exactly what I wanted. I sprayed the tube in heat proof satin and baked it in the oven. 200 deg C for 10 minutes – better than Jamie Oliver! Finished and all for around £2 and 1 hour of time.

Then I got carried away and fab’ed up a bracket from aluminium box section to hold the glow plug extension in place.

That’s about the complete build and a few little mods as well, so now it’s time to get the batteries charged, recheck CofG and trim settings and have some fun.

Incidentally I’m trying the new Instant batteries from Vapextech for both transmitter and Receiver, these retain their charge for considerably longer or so they say!

We will see.

The final setup consisted of:

3 HS-425BB servos

1 HS-422 servo (Used due to one of the 425BB servos juddering)

HPD-07RH QPCM Receiver

6V Instant Vapextech batteries

Saito FA-82A Golden Knight

90 Deg Exhaust manifold

Polished Aluminium Spinner

APC 13*8 Prop

Glow plug extension

2 Fuel filters and a one way valve

Twisted servo extension leads

Solarfilm Clearcoat used to stop edges of film lifting

Metal hinge clasps (soldered)


On a final note, for setting up Saito engines for best performance try saito-engines.info/



 The picture below shows dad just about to have some fun with the Osmose!



Ok, it’s time to give the ups and downs of the Osmose.

Firstly may I say that after around 15 flights the aerobatic performance is fantastic, slight adjustment to trim, mix and balance were required but that was to be expected and I’m sure that in a few months I’ll still be adjusting bits and bats.The bulk of ARTF kits seem to lack robustness in key areas with this been no exception to which I present a few solutions below.

The tail wheel fell off. The kit suggests a small piece of tubing to hold the wheel in place. In reality this is not substantial; it requires a soldered washer either side of the wheel as shown in the picture below.


After aborting a take off due to tail wheel failure, I ran the model into soft grass which resulted in undercarriage damage. The undercarriage is bolted to an inferior quality plywood plate – thankfully not too much damage had occurred. After a quick chat with dad a fibre glass plate was cut to size (MacGregor Epoxy Glass 1.6mm thick (MAC4250)) and epoxied into position along with side panels. This seems to be common fault with ARTF models and I should have had the foresight to implement such a modification before the incident but……. Anyway, hopefully people can use the idea which has been used many times before as a preventative measure.



 Whilst transporting the Osmose I clipped one of the wheel spats on the car seat allowing the spat to rotate freely (no-good). After fibre glassing a small metal plate to the inside of the spat with a predrilled hole for the wheel bolt to be inserted through I rebuilt it back onto the undercarriage. The result was superb and even though the other spat is not damaged it highlighted how flimsy the standard design is. Needless to say I will be applying this mod to the other spat.

The final problem came from my exhaust manifold creation! Ha-Ha.

Originally I made the manifold because of the lack of suitable Saito exhaust options and  the aftermarket ones being somewhat costly. Unfortunately, I had made the tube too long which created  too much load on the 90 degree aluminium exhaust adaptor. With vibration and load, the thin threaded aluminium section work hardened and sheared off in mid flight.

Both my dad and I thought about this issue for a while and came to the conclusion that the 90 degree adaptor would be far better if made out of steel. Dad offered to make one on his lathe but pointed out that the tap and the die for cutting the threads would cost more than purchasing a pre-made adaptor from ‘Just Engines’. In the end, and to save time, we decided to replace the Saito aluminium 90 degree adaptor (incidentally they now come with a small chit included stating: only suitable for use with a flexible exhaust) cut the homebrew pipe and insert about 3” of silicon tubing, to reduce load and vibration. A new support/mounting bracket was fabricated for the rear section of the pipe (and this time welded to the pipe) and shock mounted to the glass resin plate. Here are some pictures of the revised arrangement.


I also added a 45 deg silicon exhaust deflector and fitted a Saito velocity stack to the engine intake, just \for good measure!

Fingers crossed – no more problems.


James Gamble