Cirrus Dart

[Anonymous]

Chris, that was an extraordinary blast. I always thought my “I” record was the safest one I had, thanks for the wakeup call 😉

15 oz. is very light. When you say “stock finish” does that mean you did not glass the airframe? I’m astounded it survived if it was not glassed… Yipes!

Tremendous flight.

JW

[Warren B. MusselmanModerator]

My Cirrus Dart was the first HPR bird I built and I wrapped three full wraps of 6oz glass around that baby. It flew successfully a three times and the forth flight was a spur of the moment attempt at L2. It dissapeared. After the fact, I simmed it at over 13K on a CTI J285 and flew it on a very windy Sunday at MHM ’04. Not surprised I lost it… given the construction though, I’m sure it probably core sampled and is fully intact and about 10′ deep in the prairie somewhere.

Warren

[Chris LaPanse]

Chris, that was an extraordinary blast. I always thought my “I” record was the safest one I had, thanks for the wakeup call 😉

15 oz. is very light. When you say “stock finish” does that mean you did not glass the airframe? I’m astounded it survived if it was not glassed… Yipes!

Tremendous flight.

JW

There were 3 items on that rocket that were glass/glassed. The fins were t2t with 6oz glass, the nose was PR glass, and the lower body tube joint had a single wrap of 0.5oz glass, more for aesthetics (a perfectly smooth joint) than for strength. Everything else was bare phenolic.

And yes, it was phenomenally light. The elimination of the brick of a urethane nose cone helped, and the elimination of the piston saved a little weight too. It also helped that I didn’t (significantly) glass the tube.

[AdrianParticipant]

Chris,

How did your Cirrus mass compare with the optimal mass for that motor?

[Anonymous]

I would’ve bet my lunch regular phenolic would have shred. I’m quite impressed / surprised that it did not. Seems like years ago I read in PML’s FAQ that 38mm and 29mm would survive pretty much anything, but you should glass 54mm and up if you pushed it.

Having a lighter cone helped a lot. That flight probably pulled 70 gees. The PML website says that cone weighs 4.3 oz. That translates into a nosecone that exerts 19# under boost. The negative gees at burnout would have been another major factor… hard to do shear pins in those solid cones.

JW

[Anonymous]

Adrian, by my calculation, 15 oz. was under optimal mass — but not by much. 15-18 oz. (in my sims) all came w/in 50′ or so of each other. The top of the curve is pretty flat. Even jumping up to 20 oz. doesn’t cost much / any altitude.

The gees were decreased with a heavier rocket, but not by much. All sims were 70+ gees.

Were it me, I’d build a touch heavier for durability and lower airspeed and gees….

[Chris LaPanse]

I would’ve bet my lunch regular phenolic would have shred. I’m quite impressed / surprised that it did not. Seems like years ago I read in PML’s FAQ that 38mm and 29mm would survive pretty much anything, but you should glass 54mm and up if you pushed it.

Having a lighter cone helped a lot. That flight probably pulled 70 gees. The PML website says that cone weighs 4.3 oz. That translates into a nosecone that exerts 19# under boost. The negative gees at burnout would have been another major factor… hard to do shear pins in those solid cones.

JW

I too got 15oz as under optimal, but close enough to not really matter. As for the acceleration, it actually did not follow the I600’s thrust curve that closely. It only pulled 57 gees in boost (never thought that I would pair that with “only”), but it also had a 1.3 second burn (compared to the 1.1 seconds in the catalog). Also, the nose cone was actually screwed on – no shear pins there. The electronics were up there, so I did not want that cone to come off.

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