Wednesday, September 17, 2008

F18 Build - Part 4

I did not have a huge amount of time tonight but managed to lay up the top spars into the wing. I decided to use 12K tows for this as it is less "ropey" than the 60K tows I have and it is easier to get the epoxy to properly penetrate the carbon strands without making one moer-of-a-mess ;o)

First step is to decide how many tows to use. As I have always used spruce spars in the past in all my slope models I had no clue as to how many is enough. I just cut some small pieces and stacked them together until I got to about what I thought "looked" strong enough. Based on the "long-term" Allegro build I am also busy with, which used 4 layers of uni-directional carbon to get to the prescribed 0.7mm thickness I opted for six of the 12K tows. In hindsight If I had enought time I would have opted to use the same technique to make pre-pregnated strips (as described here) from UD carbon and just epoxy them in afterwards.

The depth of the groove was just right as the 1.5mm balsa cap I put on top stood just proud of the wing top surface.

The last bit of epoxy mix was thickened to a syruppy consistence slurry with microballoons and used as a filler to close up the tiny gaps. A maxed-out useless credit card took care of the excess epoxy to prevent too much sanding afterwards. To prevent the wing "negatives" sticking to this beautiful piece of handiwork I cut two narrow strips of Mylar which I put over the spars.

And the last task of the evening before I get some much needed sleep was to weigh the whole setup down. This is where those old UPS sealed lead-acid batteries come in very handy. Tomorrow evening I do the bottom spars.


Piet Rheeders said...

Jislike Izak,

Dis mos n' mose klomp batries daarie op vlerk, hoe lyk die speed conttroler (500 A) , en ek is amper te bang on te vrae waar is eletric motor?


Izak Theron said...

Bliksem! Praat van middernag olie brand...Wat de moer maak jy 3.30 in die oggend....!? Is die Aero Commander so groot job?

Ten minste weet ek die vlerk gaan nie krom trek in die curing proses nie.

Mike May said...

You should be able to fly that thing for several days .
What holds the batteries to the wings and are they wired in series or parallel.

Izak Theron said...

3S2P 9Ah weighing in at probably 10kg.... ;o)

Glen said...

Mike, wait until Izak has added all the armament that the Hornet carries, and then watch the weight increase. The batteries weight is nothing in comparison...