Sparrow Hawk  Part Two

Before I start just a couple of pics from 15\02\09 Sunday Flying

 Enough of this nonsense back to the plane.  

 Having  carried out work an all the flying surfaces, as promised in part 1 I'm starting on the engine and cowl installation. Below is a picture of the fuselage prior to getting underway.

Before the engine mounts can be installed you have to mark both the centre line and the thrust line on the fire wall, as there are no plans with ARTFs this could be a little  difficult if there are no marks provided. On first inspection of the firewall I thought that this was the case, but closer inspection revealed four little marks lactated around the fuel pipe exit hole, so all that was required was to place a ruler on the firewall and draw pencil lines marking locations.  

This pic showing Centre and Thrust lines in place.

Once this was carried out into the bag of goodies to find the engine mounts and fixings.

Sorry about the poor Photo this reminds me that I need lessons 

With all the bits accounted for its time to line them up on the firewall with the engine. the way I do this is to clamp the engine mounts to the engine and then place this assembly onto the firewall aligning the mount bearers with the thrust line and the taking a set square and placing this on the centre line mark and the just move the engine and mount left or right until the centre line on the engine casing is in line with the set square. Once this has been obtained I carefully mark the mount position double check everything is in alignment and then remove the mount and engine and drill the mounting bolt holes to the required diameter.  

once these holes have been drilled the next job is to mount the engine mounts to the firewall. these are held in place with 4mm bolts that locate into captive nuts positioned on the inside of the firewall. It proved to be a bit tricky inserting these as you cannot get your hands in the fuselage to hold them in place will you screw in the bolts. I found that a magnetic screwdriver worked well in keeping the captive nuts in place until they had bitten into the fire wall enough to stop spinning. Once the captive nut are all in place I removed the bolts one by one and placed thread lock on each one and replaced the tightening then for final position. See pic  below

Tea break time

That's better. Right moving on, with the mount in place, time to see if all that lining up has worked out.  See in the picture below.

 You can also see that the engine has now been bolted in place. (forgot to take picture of lining up engine distance from firewall to prop plate Mr impatient again) Before you mount the engine to the mount you need to mark the distance from the firewall to the prop plate which for this model is 150mm. the way I managed this was to take a ruler and measure out 150mmfrom the firewall, then with a straight piece of brass plate about 6 inches long placed against the prop plate I them moved the engine along the mounts until I had obtained the correct distance and then marked mount. With this done I next marked the mounting holes of the engine and then drilled them out starting with a pilot hole first ensuring they where straight. Once this was done the engine is bolted into place. As the engine has not been run in, at this stage I have only tightened it in hand tight so that I can mark out the cowl openings.

Moving onto the cowling, another club member has purchased one of these models and had asked me whether the cowl fitted as his was very tight and would not push into its final resting place. The answer to that question sir is no it doesn't.

When trying the cowl fitting, being heavy handed I managed to damage the top balsa sheeting which in the particular area that the damage was caused was very soft, so I decided to strengthen it from inside with a couple of bits of 3\32 balsa sheet each side of the central stringer and this has made a vast improvement to the strength of the area. To actually get the cowl to fit correctly the only option was to remove the profilm covering and then sand some of the contoured edges away until the cowl fitted correctly. I have taken as much as I dare take away  without causing any structural weakness and the cowl now fits although still a little tighter than I had hoped for.

As you can see this has left the model devoid of any covering on the front underside. Fortunately I found a roll of red profilm that had be used on another project exactly the same shade of red. and this was used to recover the model.

See pics below.

With that unanticipated job done I proceeded with cutting out the cowl to accommodate the exhaust, and air inlet and outlet.
The pictures below show the cowl cut out and in place on the fuselage. All the cutting was done with a hobby drill and small sanding bit.

With all that completed its time to pack up for the day