Piper Cherokee ( nearly)

Having got the building bug good & proper I decided this would be my next effort, for several reasons.
1. The first real air craft I flew was a Piper Warrior Reg no G- BRBE.
2. It is time to make the transition from a high wing trainer to a low wing.
3. It should be a fairly easy construction, especially the wing, which will be a uniform Clark y type.
4. It's a great looking aircraft !
Taking everything I learnt from the first build, all the good advice I got here, plus a lot of research on the net, hopefully this one will be a bit easier ! :whistle:
The first things that are different;
Using a basic design calculator that I found online, to help getting the dimensions right.
The foam covering is brown paper & a 50/ 50 mix of wood glue & water. ( as advised by Klippy) The fiberglass tissue was extremely strong but a pain to work with & it soaks up glue & paint like it's going out of fashion !
Although it is still a monocoque construction I am using thinner foam & just putting the strength where needed. Quorneng has got me paranoid about weight ! :lol:
At the moment it's going well, building is taking half the time of the Cessno.
One thing that's bothering me is I don't know whether to go for the all moving horizontal stab ( as in the original) or fixed with elevator?

All moving is a pain to arrange but much more efficient. I'd go for conventional for ease.

All-moving is a pain to get the balance right, and is prone to side-to-side rocking and flutter unless your mount is REALLY accurate and solid.
The advantage is - you can tweak the pitch setting without butchering the fuselage, if you get it wrong the first time! [badass]

All moving seems a bit to technical for me yet, so conventional with elevator it is then !

Okay guys next question.
Although this model is not entirely to scale would it make sense to scale down most of the dimensions from the original ? I will clarify that a bit.
As it stands the fuz is pretty much scale, apart from width, which is narrower, length & wing position are the same as original.
If I make the wing scale, can I make the tail position & size scale also ?

crash happy
For small models with a scale fuselage the usual practise is to make the tail 'feathers' slightly larger.
For most light planes their tails are designed to be big enough for stability within the bounds of drag and cost however a bigger reserve of aerodynamic stability for a model is no bad thing given the wing is also likely to behave differently then the full size one.

Most scale designers up the empenage sizes by about 10%

That was good timing Klippy, I am doing the calculations now. 10% it is then. Thanks.

As the weather is still doing a fair impersonation of Ragnarok & I can't maiden the Cessno ( hopefully tomorrow ) I thought I might as well get on with the Cherokee.
The first attempt at the wings was a right cock up, somehow I managed to one side of the cutter on the top of one guide & the bottom of the other ! :blink: Made for a very interesting wing shape. So after a trip to the hardware store for another sheet of foam, the second attempt turned out perfect.
Cut out the spar with 7 degrees of dihedral. The part going the width of fuz will be straight containing the joint & the two wings cut at an angle to fit. The intention is to make the wing removable, fixed by four screws from the bottom. Hopefully I will get them covered tomorrow before flying, fingers crossed !

crash happy
Is that the actual spar or just a guide?

Quorneng wrote: crash happy
Is that the actual spar or just a guide?

Unless I can find a better piece of wood, I afraid that is it. Not perfect I know.

My concern is not the type of wood so much as the fact than its thinnest depth at the centre section just where the bending forces are the greatest. That is exactly the point where it will break.
The spar would be just as strong, and quite a bit lighter, if it was the same depth from the centre section to the tip.

Your spar may of course still be strong enough 'as is' but it would mean much of the rest of it is just 'excess' wood contributing little to the actual strength of the wing.

Just saying.

"Your spar may of course still be strong enough 'as is' but it would mean much of the rest of it is just 'excess' wood contributing little to the actual strength of the wing."

I can see your point, there is a reason behind it. Being a solid wing the easiest way to fit the spar is ( as on the cessno) to split the wing & center section longitudinally. The spar then fills nearly the whole depth, leaving a 2mm gap at the bottom for servo wiring. Also I can fit a tab on each side to attach the wing mounted gear. I don't think strength will be an issue, it is rather overkill. I suppose I could run it through the planer & reduce the thickness a bit ?

Thinning it isn't going to make much difference weight wise, it is what it is and at least with that thickness you won't get any twisting moments in the wing. [badass]

I was out in the workshop this morning wondering how to get a nice sharp cut at 7 degrees for the dihedral on the wings, when Stefan turned up. A short discussion later we came up with this jig.
The two wooden blocks are machine cut at 7 degrees and are simply a guide for the hot wire cutter. Works a treat!