Keil Kraft Piper Family Cruiser

Squirrelnet wrote: Thanks Andy, no not too late - gussets at the ready Now you say that you can see the rather nasty sharp angle on the tail

My plan is to attach the tail with a light rubber band so I can adjust the tail with shims as is familiar to me in trimming vintage free flight models, once trimmed I can set in the right position. My stupidly crap maths put the wing loading at 25g per dm2 (wing area 13cm x 30 cm 390 cm2 -predicted weight 100g) ... oh hang on - two wings make that 12.5g per dm2. sounds a bit better. If it does go indoors though a gurney flap maybe the way forward

Banding the tail on is a good idea, and in practice will probably work better than moveable elevators, the latter being prone to bending in heavy landings.

When you calculate the wing area, don't forget the tailplane and also the area of the wing and tailplane within the fuselage.

ahh yes forgot about the tail and centre section that brings it down to just over 10g per dm2 if I can't get into around 100g

Squirrelnet wrote: Its all starting to come together now and weight is still around 70g

And with that lump of a motor at the front it's guaranteed to balance ok

Looking good to me.
N

Apologies if that was a bit harsh, blame it on the bottle of wine.

Seriously though, I'm still trying to get a handle on how much weight these motors will fly (all things being equal). I was hoping something like 1g per mm3 - so a Telco would fly 63g, GM-120 would fly 120g, etc, but a GM300 flying 300g / 10.5oz model (not this one!) sounds a bit hopeful. Maybe .5-.75g/mm3 ?

The G-Mot box specifications vary with size:
GM63 30-40g (= .5 - .6 g/mm3)
GM120 50-70g (= .4 - .6) seems conservative to my brief experience
GM120T 70-90g (= .3 - .4) much less than double the 120 single
GM300 80-120g (= .27 - .4)

I can't remember if you posted the auw of the Bleriot with the GM300 twin? That would be a useful point on the curve. Anyone else have a rule of thumb? Anyone remember model weights in the competition heyday? Too many sums?

No not harsh

Ok some numbers for you.

Bleriot is 141g and 28" span wing loading is around 11g/dm2

The Skycscraper vintage design is 30 " 129g and has a wing loading of around 10g/dm2

Both fly well within the power range of the GM300. The skyscraper will climb to 50' - 60' (that's a guess) on a normal power run

Today I turned my attention to the wheels. I don't have any 1 1/4" commercial ones and they would probably be too heavy anyway so I thought I'd have a go at turning some from Balsa on a drill.

Luckily 1 1/4" equates to D size battery and the positive dimple provides an easy centre so I marked some on on some light 1/2" sheet




The rough cut blanks were roughly shaped with a razor saw and sharp knife then mounted in a drill



I then used a small sanding block I use a lot for models, which is just an off cut of hardwood with some Ali Oxide paper pritt-stuck to it I rounded the sides nicely but it was not very round . Presumably the softer parts of the balsa sands way quicker giving it an egg shape ...so I got a bit more serious

With the wheel mounted on a bolt I put it in the pillar drill and used my cross vice to make a vertical lathe should have thought of this before




Ended up up with a couple of reasonable attempts at wheel shape. I made up another print stick and Ali paper tool that had a finer point to cut to make the impression of where the tyre meets the hub




The hub is a piece of carbon tube with a 1/32" ply disc either end , the whole lot is filled with 5 min epoxy and squished tight.




The airframe now finished and sanded its time to start covering

When I make balsa wheels I build up the thickness with cross lamination of hard balsa discs that helps to produce a more perfect round when you sand them and drill the centre to take an appropriate size of aluminium tube 10 mm or so longer and then you can put that in the drill chuck to spin and sand to final shape.Depron or blue foam wheels can be built similarly only just one blank.Use the glue of your choice to set the aluminium tube in place.

Thanks Firewood that makes perfect sense, I get the advantage of using laminations now

Squirrelnet
6mm Grey Depron can be made up into an excellent wheel for 'lightweights' with the advantage that it is intrinsically water proof and doesn't really need painting either.

The above is 1.75" diam and 0.9" wide yet weighs just 1.6g.
No metal tube, the axle runs directly in the plastic discs.
So cheap to make if it wears too much you just make another.

They look really good Q , the depron looks quite rubber tyre like. I shall remember that for next time

The depron wheels look great, are they easier to make than the balsa? Plus they are tyre colored already. Boz

Boz
There is really no difference except that Depron is a bit harder to sand as it 'dulls' sand paper quickly, just like it does craft knives so its brand new good quality paper and spin the blank fast.

The only disadvantage is a sheet pf Depron is big so unless you are using the Depron anyway it is relatively expensive to make just one pair of wheels or you need 32 for a AN 225!

With apologies to the Fast Show - Today I have mostly been making things Yellow

In between enjoying the nice weather, could do with some of this at the weekend

just call it mellow yellow.
he he he



Tony B

One day to go before the Mayfly and ...... I've finished it

The struts are still drying having been painted with enamel so are missing from this quick assembly. AUW is an amazing 99.5g - how close can I get to my target weight of 100g !!!.. But it does still need balancing as the CG is 1/4" or so ahead of the main spar so a little extra tail weight will be needed ..oh and I weighed it without the struts

Its finished as N5156H 'Yellow Woodbee' as is Andy's version. Its a nice simple colour scheme but also a nice one I think







I've pinned everything flat and I'll leave at least over night to properly dry out . I've warped in 1/16" washout to aid stability.




The Keil Kraft plan by Albert Hatful builds into a very attractive model but when you look at the pics and drawings of the originals it's not a very scale interpretation. I think it bears more than a slight similarity to Albert Hatful's best design, in my opinion, the first version of the Junior 60 he designed in 1946.

Here's my 1947 Reeves sparky powered Free Flight Version for comparison, pretty similar to my eyes