Phase 5 by Chris Foss

After many years of procrastinating I'm finally building a Phase 5. Designed in 1978 this model is often considered to be Chris Foss's (CF) best slope model. It was never available as a kit so the only way to get one is to build it yourself. CF is still selling the plans if you fancy one. The red model is not mine, this is another example of the Phase 5 in case you're not familiar with what I'm planning to build.

The Phase 5 plan calls for a built up wing but I'm deviating from the plan and making one from foam with a balsa skin. A snow day today meant I could make a start. CF does not specify what sections are used for the root or the tip so a bit of guesswork and internet trawling resulted in the semi-symmetrical E374 for the root, modified a little to make it thinner. The tip is fully symmetrical and is between NACA 0010 and 0011. It's actually 10.67% thick so maybe it's NACA 0010.67?
Images show both left and right wing cores cut from the same block of foam, the semi-symmetrical root section and the symmetrical tip section.

Those cores look very nice Mike, you've got your hot wire cutting down to a fine art

Chris001 wrote: Those cores look very nice Mike, you've got your hot wire cutting down to a fine art

Yes they do. I think Mike could do a little business on the side and make cores for us lesser mortals with no more engineering tools than a bottle of Cyano.:lol:

I'll follow this project / subscibe with interest as I still have to make a start on my Phase 6.

Mike - Looking good so far.
Just one question - since it was designed with a built up wing - do the wing ribs give you
the required wing section ?

Colin.

p.s Welcome home Phil.

PhilF51 wrote: I think Mike could do a little business on the side and make cores for us lesser mortals with no more engineering tools than a bottle of Cyano

The final cut is quick, but there's loads of time preparing the templates and cutting blocks of foam to the right size in the first place. So it's a labour of love really.

PhilF51 wrote: I still have to make a start on my Phase 6.

Can you check whether CF uses a spar or dihedral brace on the wing at all? My guess is that it is just foam and obechi veneer and that once joined you reinforce the join with a glass bandage. This is what I'm planning to do but would modify my ideas and add a spar and/or brace if this is what CF does with the '6.

4Pedalsfly wrote: Just one question - since it was designed with a built up wing - do the wing ribs give you the required wing section ?

The plan shows the root section and the tip section but does not specify what they are. Designed in 1978 (or earlier) I doubt that a computer was used to draw/create the sections and think that CF probably went for a couple of TLAR sections.
Info from others on the net suggested that E374 and a symmetrical NACA section worked well on the Phase 5. I printed E374 at the correct chord length and it was too fat by a couple of mm. So I modified it to be the same thickness as the section on the plan and it matches very well. I'm convinced that my section will be aerodynamically superior to the original since there is some odd reflex going on on the plan because of the way he has built the flaps and ailerons from solid sheet carved/sanded to a triangular taper. That does not necessarily mean that mine will fly better, just that it will at least have a true section.
At the tip I found that NACA 0010 was too thin and NACA 0011 too thick. So I modified the thickness and created NACA 0010.67.

Hi Mike, CF has no wing brace on the P6 Wings which are pre-veneered. Just got to add balsa leading and trailing edges. They are butt jointed and then reinforced with 50mm glass fibre and resin. There does not appear to be any suggestion of any dihedral either in the instructions.

PhilF51 wrote: Hi Mike, CF has no wing brace on the P6 Wings which are pre-veneered.

As I thought. Thanks, Phil. I can proceed with the P5 as planned now.

PhilF51 wrote: There does not appear to be any suggestion of any dihedral either in the instructions.

It's common practice to join the wings inverted on a flat table so the top surface is flat resulting in a little dihedral built in because the tip aerofoil is thinner than the root.

If the snow was clear I would have had a delivery of balsa today and could have made a start skinning those wings. Instead I took the opportunity to cut some more foam, this time the tailplane.
The plan calls for a solid 3/8 balsa tail sanded to an aerofoil shape. Chris Wild (also planning to build a Phase 5) raised a concern that it would be difficult to carve/sand two identical halves. Whilst not impossible, it would certainly be a time consuming affair trying to make them and since I had some time on my hands I decided to try a technique that I'd not used before...
Cutting sharply tapered foam wings is possible with just one template if you anchor one end of the hot wire. Not only does it work, but it reduces the need to make a second template for the tip and the end results are a lot better than I could possible have made using my gravity cutter.
Images show the anchor point, the layout, the bottom template and the top template.