Slingsby Petrel Project Diary

After building the Wolf, I found myself drawn by the prospect of a slightly larger vintage glider. I'd seen the prototype of this particular model and, as well as looking very beautiful to my eye, it performed very well off an aerotow. At 1/5 scale, it is easier to transport than the larger scale gliders but still large enough to have a good presence in the air so, as with the Wolf, a couple of us in the local flying club managed to talk each other into giving it a go.

This time though, it was going to be a proper Winter build so, although the design was published as a free plan in the July 2019 edition of RCM&E, to reduce the amount of dust generated I opted to start with the part kit supplied by Laser Cut Sailplanes. With this in hand, a supplementary wood list was drawn up, together with a shopping list for servos, tow release etc. and a canopy from Sarik Hobbies.

The parts kit came with another version of the plan which is much easier to work with than the sliced and diced, double sided magazine version. Unfolding this plan though brought home just how long the wings are, even on a 1/5 scale glider! Furthermore, since each wing is to be built in one piece regardless of the gull anhedral bend, the first job was to make a bigger building board. A piece of Contiplas left over from a previous kitchen project was cut down to size and faced with cork tiles.

The board rests on my existing central table (actually an original B&D dual height Workmate) so, by pushing it one way or the other I can (just!) get around to work from either side.

September 2019
The photo on the right shows the two kits ordered and gives some idea of the quantity of parts included. The parts come in a number of bags which helps keep things under control. However, they aren't bagged up in a way to reflect a particular build sequence so locating a specific part without tipping out a load of as-yet-unneeded ones can be a challenge.

The quality of wood used is good and so far the cutting has proved to be very accurate.

The wing building method is very similar to the Wolf. However once the ribs are glued onto the lower spar, trailing edge, aileron spar and false leading edges, the wing is then jacked up onto 6mm balsa spar supports to create the gull break angle. I deferred fitting the rib at the gull break (R11) until this point to make it easier to sand the right angles onto the ends of the aileron spar and the false leading edges. The top spar is then added, followed by a few of the 0.8mm ply shear webs, which sets the gull angle.

Before lifting the wing off the supports, the pre-cut ply spacer for the brass joiner box was used as a template to set the angle of the root rib. Then the wing can be lifted off the board and the remaining shear webs fitted - much easier when clamps can be applied from both sides!

With all the webs in place the 3mm square spruce spar doublers can be applied top and bottom.

Then it was a case of doing it all again! With two wings framed up, they were temporarily fitted onto the joiner bar for a dihedral check.

Before moving on to the underside sheeting, I decided to sort out the servo mounting arrangements. First the aileron servos:

Then the spoilers:

The last job before tackling the sheeting was to fit the Wing joiner boxes and rear incidence joiner tubes, once again joining the two wings together to check for proper alignment.

So, as the end of the month approached, out came the 1/16in balsa sheet and the skins for the underside leading edge section were made and trial fitted. Once again, the advice is to ignore the gull break and fit the skin in one piece. Once again, despite some initial scepticism on my part, this proved to be no problem. Next month though, we will find out whether the same is true for the upper surface!