Eiffel's Nightmare - Stable or not? (paging Bruce L?)

[rstaff3]

I thought I'd pose the question for Bruce and others. I built this based on a souvenir daiquiri glass. You can see more on my blog, if interested. I made a sim replacing the square features with circles of equivalent area, and used Bruce's base drag 'trick'. Anyway, the sim is a bit hosed, showing it's unstable even though the CP/CG looks ok. Opinions? I'm not as worried about fixing the sim as to see whether I implemented Bruce's method correctly.



View attachment eiffels_nightmare.rkt

 

[Micromeister]

Dick:
A long while back I did a Cone rocket using the base drag theory. Long story short it took a great deal more nose weight to get the thing to fly stabily then the CP CG margins indicated. I'd have to go back an look at the final CG but I think it was something outragous like 2 or 3 time the static margin and that was with the motor stuffed as far forward in the thing as I could.
Looks like Eiffel's has sort of the same taper with minimal acutal flat base surface area. Maybe that's why the sim didn't work?

Sure would be Neat to light that baby up.... All over!

 

[PunkRocketScience]

Dick-

Here in San Diego, Brian Moulton flies an Eiffel Tower model made from one of those plywood kits of famous buildings. It flies great, but has a TON of nose weight. Typically he uses short burn, high thrust motors. As your's has a smoother outside, I would think it'd fly better.

 

[rstaff3]

Thanks guys. I documented my latest thinking on my blog, but in summary: what you said agreed with my other experience, the form factor is very similar to the Quest DC-Y (also nose heavy); I need nose weight or clear fins. I'll probably go with the second option since the plastic glass is already fairly heavy.

Thanks again!

Oh, and with some small fins and the 'phantom cone' removed, my sim does in fact work.

 

[Hospital_Rocket]

You know that any stability you finally build into this thing will be offset by your own instability...don't you?

 

[Micromeister]

You know that any stability you finally build into this thing will be offset by your own instability...don't you?

Yeah! all us Odd-Roc'ers are just a little off....That's how we make folks laugh... ya know watch the handicapped we're fun to watch.

 

[rstaff3]

Yep :rotflol: I reckon I'm probably the court jester of MDRA. Oddrocs are the only way I can entertain people who consider an 'M' a small motor. Except maybe my F-104. (Not odd, but out-of-the-ordinary.)

 

[rstaff3]

Oh, this will prolly lead to a question for you, Micro. I think I want removable fins so I can cut them from any junk - cardboard, scrap foamboard, etc. - and still have them invisible (not installed except for flight). I remember some clear plastic runner material but for the life of me can't remember where. The stuff is like 2 angles but joined at the base. I thought I'd attach those to the side and hold the fins via pins or small plastic pop rivets. Might use rivets to attach the channel too. Since you (micromeister) are also 'Mr. Plastic' I thought you'd be a good source.