Home › Forums › Free Flight › All Gas › C gas model Revised
- This topic has 5 replies, 3 voices, and was last updated 14 years, 3 months ago by JLorbiecki.
12/27/2008 at 3:29 am #41023
With time off, I decided to rebuild a B/C gas model I had built a long time ago. The model originally had a ST 29 RR on it but was pretty heavy. So, with a fiberglass tube I had made laying around, I built up a rolled balsa tail boom (1/16 balsa/ carbon/ 1/32 balsa) as well as a new fin. I really was going to go the Berry way (non- VIT) but then decided to use stab and rudder. Hard to break a tradition…
Looked into my engine collection and found a K&B .35 that I used to love- Designed an FAI style mount- Replaced the backplate and machined up the mount. The entire front end is very FAI stylish, without a cowl. The entire fuel system will be internal and will use a Seelig timer. The front prop plate is new also- machined up one for use with the ST spinner.
The old fuselage was 350 plus grams (wing is about 240 grams). The new fuse so far is under 200 grams- only need a pylon (which will probably be built up with 1/32″ ply or fiberglass sides). So, hopefully the entire all up weight will be around 800 grams (less than 29 ounces)…
Sorry Dan about the VIT stuff….Just couldn’t figure out a clean way to mount the engine the way I wanted to and get the down and side thrust I woulda needed…
12/27/2008 at 3:30 am #46785
Here are some more pics…
12/27/2008 at 4:37 am #46786DAN BERRYParticipant
John, it looks good.
You’re are frighteningly close to having a Free Flight plane.
The machining work looks gorgeous. Is that a 3 panel wing I see?
Since its cold up there, might you have time make a tube like that for me?
What sort of carbon is in the balsa ply?12/27/2008 at 8:04 am #46787gosParticipant
Looking good. My sort of power model.12/27/2008 at 8:54 pm #46788
Yup, it is a three panel…A friend of mine from California (Russ Backer) had a design he called the Simplex and I built it. But, my fuse was tremendously overbuilt and she was a sled.
So, I decided to try some stuff and hopefully it will work.
I don’t have the form laying around anymore for the tube Dan…Let me look at what I have tho- This tube is about 4 layers of cloth with a 1.5″ ID.. The OD is about 1.59 inches. The front tube was about 10″ long and then I had to make an adapter to join the wooden tail boom. I made a really fancy acrylic former and “thought” I waxed it up good enough- but nope, I didn’t….Ended up cutting the thin in half so I could get it off the acrylic. It came out OK tho…I hate it when you glue the molded part to the tool..And, BTW, I used a pool cue for the tail boom form…
The tailboom has 5 oz carbon cloth wrapped around it. I would go with thinner cloth the next time. I would also think about doing the alum over the outside verses the balsa (I had the balsa- no aluminum). The cloth was stuff I also had laying around, so that is why I used it. I think fiberglass would work also-
I need to determine where the CG will be and then can put the pylon on…
Dan, where are you running yours? I am thinking I will be in the 60% range to begin with…I normally run about 50% on the small stab, long tail boom stuff (FAI)…I know that without VIT it can be back as far as 80% (or more)…
See ya!!12/29/2008 at 4:53 pm #46789
The fuse is probably 80% done now-The pylon is a built up version, using 1/32 ply sides, a spruce top and vertical supports, with balsa pieces inside to support it. All up weight of the pylon was about 45 grams, which is pretty equivelent to a balsa pylon, but stronger. The pylon slips thru a slot that was milled thru the tube and then epoxied in place. There is a small fillet of epoxy and micro balloons between the pylon and the fuse.
The seelig is submerged slightly and is mounted to 1/16″ thick printed circuit board material. I use alot of this material in various thicknesses and is great stuff because it super glues easily and is very simple to tap for screws.
I did make up a foam and carbon and foam fin which came out very well, but was over 15 grams when completed- very strong tho! The balsa version (built up) was about 6 grams…substantial difference.
The VIT stuff will be very simple, with a glide post and simple pull down for the stab- Again, very FAI-ish. I really like the engine mount and it should be very clean. I will be making a fuel shutoff (the thing that, after fueling, is simply closed to pinch the main feed line) just like our F1J models.
The engine, a K&B .35 has a different venturi and backplate. I plan on maybe making a new head that will use a Nelson plug as well as looking at the timing. Next, if I get really ambitious, I may make a 10-4 folding prop for it. That should help the glide a fair amount- My guess is that a folder on a F1J model may be good for as much as 20 seconds. That would make a big difference with a 10″ diameter! The fuel system is my normal deal, with a brass tee. The bladder will be surgical.To change the system, remove a screw and the entire frront end comes off to get to it.
The tail boom may also be covered with .5 oz fiberglass, glued on with epoxy paint. I am not sure yet if I am going to paint the front end or just finish it in clear. If I paint it, expect black!
All in all, this has been alota fun. I took my own advice (see the article in the Digest about using FAI techniques on an AMA model) and feel that it is far superior to the normal construction. The old fuselage weighed 345 grams and the new one, with all the aluminum and such, is a mere 220 grams. All up weight should be about 29 ounces- I was hoping for less than 30 ready to fly…
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