Estes Jetliner Build (sort of)

[ActingLikeAKid]

Put together a couple of Estes Jetliner kits with my boys. While this isn't quite a "build" post, I did discover some helpful tips:

1. Mostly this is a quick and easy build and the rockets went together really easily. Both of them had dented nose cones; I called Estes and they just shipped me two more rockets. Yay Estes!

2. The instructions recommend you glue on the big wing first, then the small fins. I'd say do it the other way round - do the smaller fins first and make sure they're straight, then it's easier to align the fins with the wing.

3. You will go through a ton of your favorite filler getting the joint between body and wing to look good. Or you can just leave it as is. I build it up not for strength but for looks.

4. A rattle can of silver spray paint would probably give this a really cool "American Airlines" look. (the boys wanted gold so that's what we did)

 

[tightwad]

Nice job. I hope your boys will enjoy watching them fly.

 

[ActingLikeAKid]

Update: DO NOT PUT ALL THE CLAY IN THE NOSE. Both flights went up about 60 feet. One corkscrewed, the other flew true. The one that flew true popped the chute about 10 feet above the ground. The other one landed under power. Amazingly, the only casualty was a snapped fin. Project this week: disembowling nose cones.

 

[Tonimus]

You will go through a ton of your favorite filler getting the joint between body and wing to look good. Or you can just leave it as is. I build it up not for strength but for looks.

Update: DO NOT PUT ALL THE CLAY IN THE NOSE. Both flights went up about 60 feet. One corkscrewed, the other flew true. The one that flew true popped the chute about 10 feet above the ground. The other one landed under power. Amazingly, the only casualty was a snapped fin. Project this week: disembowling nose cones.

I suspect these may be related.

 

[ActingLikeAKid]

I suspect these may be related.

Possibly. I was using Bondo Spot Putty, which dries pretty light. Going to have to experiment with less weight now and see what I can do that will still give me a true flight. I think I may have another Jetliner kit, I may build it up quick & dirty just to play around with the clay and see what works (I don't want to damage the boys' any more)

 

[ayryq]

I just flew this rocket, twice, on A10-3T. They both deployed the parachute just above the ground. Did you find the "right" amount of nose weight? I've managed to fish all the clay out... now how much should I put back?

 

[ActingLikeAKid]

Glad it wasn't just me. I took out about half of it but haven't retested. My advice would be to retry over grass.

 

[ayryq]

Well I tried to do some cardboard-cutout Center-of-Pressure estimates. It's not symmetrical so I made two cutouts. The top-down silhouette gave a CP at 2-3/4" from the aft end of the body tube. The side silhouette had a CP at 3-3/16". An average would be at around 3" from the aft end which on mine is at about the middle of the main wing.

Now CG: with an engine installed but no wadding, and with no nose weight installed, I got a CG at 2-15/16" from aft end of BT. That's almost exactly on top of the CP as I figure it.
With all the nose weight--about 6 grams--stuck on the outside of the nose cone the CG is moved forward by only 3/8"

Now I know that sometimes short stubby rockets have CG and CP that are closer than seems "safe" and that my CP calculation is at best a rough guess (and at worst completely wrong). However it does seem that this rocket isn't designed real well for, you know, flying. Just look at the flight logs at rocketreviews.com.

I'll reduce the clay for the next time I fly, and I'll stand well back when I hit the button And if someone manages to mock it up in a simulator, I'm interested in what the CP is calculated to be.

 

[LW Bercini]

IMHO, it is under powered with 13mm motors.

 

[ayryq]

Flew mine again, with less clay, and it still dive-bombed. So when I got home I tore out the engine mount (saved the clip to repair an Estes Gnome) and replaced it with an 18mm mount. Hopefully next time will be more successful.