Tim,
I'm sure I'm not the only one thinking this, but if one cut the double-swept delta fincan fins into elliptical fins, and except for the disturbance in the laminar airflow around the minimum diameter airframe that the fincan adds, which might be negligible or at least counterbalanced with the tailcone GLR added to it, this model would be perfect, with a more elliptical nose cone depending on the simmed speed, for the Super Single Shot Sweepstakes. I just may have to buy another one from ya. 😀 Haven't built mine yet, but it just keeps smiling and winking at me. 😉 Oktoberfest is just around the corner...

Bruce,

Hmmm. I recall a design from Estes that was BT-50 based, elliptical fins, and used an abrupt tailcone, sprint maybe? Claimed 1600' on a C6. I built a couple. But never outperformed a BT20 based rocket of the same length. But more reliable for sure.

Its stretching a comparison, but I don't think you can ever reclaim losses from drag by making the air move in two directions--first out, then in. Just making the air do a two step implies that extra energy is imparted to it, the source has to be rocket. Energy donation of course bad thing in this context.

The other notion i have is that while ellipses still rule the world of small reynolds number flying objects like hand launched gliders, it was curious to see that most of the really good kits/designs these days have the wings on backwards. In other words the LE taper is more severe. I was designing some BG's recently for Naram, and kept looking at these record holding designs thinking that can't be right.

Also, I seem to recall that Tim Van Milligan who is in the springs and is the force behind apogee (rock Sim etc) addresses this issue for rockets in one of his e-zine issues, and concludes that a rectangular fin is as good as any other. Sort of guessing, but the ellipse was based on RAF studies which showed induced drag was least with this planform. But planes always fly at a non zero angle of attack, rockets ideally do. So the ellipse may after all not be the optimal planform. Check out Apogee's site, some fantastic and free info.
Cheers,
John

Actually, a clipped delta is fine, with elliptical fins only performing ~1% better. In a contest, 1% can mean a lot. It's odd that they would, since the worst fin shape is the double swept delta, like the Event Horizon, for drag. Tip vortex and all. Don't underestimate the boat-tail. Everything in life has a beginning, middle and end. It DOES reduce drag by quite a bit, at least in a wind tunnel. 😀 Sometimes it's best to go with empirical results and not over-think things. Aerodynamics isn't always (is it ever?) intuitive.

ADDED LATER: John, just don't ask me where I read or saw this, but a boat-tail can take up to 0.2 off your drag coefficent, as I remember.

Bruce, I had the chance to fly my Thunderbolt over the weekend at Hellfire. I launched it with a Pro38 I285. It was the 2nd flight Sat. morning. It jumped from the pad, at about 2 seconds it went mach, and flat was gone. My Perfect flight read 6840ft. This weekend at Hartsel, she goes on a I300bt. It simms at 7560 @ 780 mph. The performance is there, now some DD and we should be good to go! With yours, Daves and mine in a 3way drag at Oct. we should put on a great show. The J350 sims at 47gs 1050 mph, 10,200 ft. and 20.5 sec to the top. Now thats a drag race! Not to mention the smoke and fire from 3 J350s'. Isn't this why we got our Level2's? 8)

Oh, yeah! 😀

So Gang How about what everyone is pushing to get done and fly for Octoberfest!!! ( I mean it is the topic .LOL) I really really want to hear what you all want to do for this event. I just recently ordered the Motor and Case for my L3 project I am so dang excited!!! Man thats gonna rip! So its should go very nicley!!!! I also just met with my L3CC and I have the go ahead on the next step and await it and thats the flight sign off. WOO HOO!! come on October!!!

Well, that's what we were talking about. 🙂 Best of luck, Conway, with your L3. If you need another ground crew member, just let me know. I'll be turning to you for tips within a year's time. I'm just going to fly one of Tim's Rocky Mountain Thunderbolts in a drag race with him and Dave Way, and probably a K550 in GLR's Vertical Assault. Other than that, I'll be LCO or RSO or whatever is needed.

Cool. Bruce!!! Drag race sounds fun. Can I join. My L3 may not be enough motor there to do much.You guys would prolly whip me!! Just kiddin. I must admit Im as excited as I could get. This has been a fun project. It will have Data aquisiton and on board Video as well as being a large motor with 50 lbs of rocket that should get about 13k at roughly Mach speed. I just wish it was like tomorow... LOL

Actually, a clipped delta is fine, with elliptical fins only performing ~1% better. In a contest, 1% can mean a lot. It's odd that they would, since the worst fin shape is the double swept delta, like the Event Horizon, for drag. Tip vortex and all. Don't underestimate the boat-tail. Everything in life has a beginning, middle and end. It DOES reduce drag by quite a bit, at least in a wind tunnel. 😀 Sometimes it's best to go with empirical results and not over-think things. Aerodynamics isn't always (is it ever?) intuitive.

ADDED LATER: John, just don't ask me where I read or saw this, but a boat-tail can take up to 0.2 off your drag coefficent, as I remember.

Bruce,

Perhaps I wasn't clear--my issue with the Giant leap design (which bears an uncanny resemblance to the H1000 rocket I lost at MHM) was with the notion of a fin can that adds diameter to the rocket. Sure a boattail might mitigate the damages, but in the context of ultra performance, my feeling is a single diameter tube with SM fins will do better vs a double taper to smooth a bulge.

I also don't doubt that under right conditions a boat tail might reduce ones drag coefficient by .2 and you'll find one on the booster of the L3 project I'm flying this saturday. So for the sake of argument, lets take a look at it. Nothing extraordinary, ogive nose, fineness ratio of near 20 (9.5'/6"), Nike trap fins. Say the CD w/o tail is .4. If i get the drop of .2 then I end up with .2. Meanwhile tho I have taken a potentially 4 inch min diameter and gone to 6, so the area has gone from x to 2.25X. The 50 percent reduction in Cd doesn't reclaim the losss. I end up with a 12 percent gain in drag. Now if I had a really good reason to go from 4 to 6 inches inches as in using a bigger motor or nitrous tank, makes huge sense.

Hope thats a little clearer this go round,
J

Clear and agree. No arguments from me. 🙂 I also agree that a bulge aft isn't the way to go. You have to make so many tradeoffs during the process of designing and building an altitude bird, you don't want to start with something you can avoid in the first place.

I must admit Im as excited as I could get. This has been a fun project. It will have Data aquisiton and on board Video as well as being a large motor with 50 lbs of rocket that should get about 13k at roughly Mach speed. I just wish it was like tomorow... LOL

Conway, that sounds so cool! What day do you plan to launch: Friday, Saturday, or Sunday? I wanted to get my L3 ready for Oktoberfest, but it won't be. Plus I want to fly it on an L first, which I'll do first chance I get next spring at the North site. You're using an N, right?

I planned to do on Saturday. that way I can spend all day Sunday LCO and RSO and stuff. And also on Saturday help my daughter who just turned 14 with her JR L1 cert flight on her 3" BSD Thor. Yes it is an N. I ordered the load and the case from Jim Amos just last week. I decided on the Biggets White wolf load there is to date with the N2020WT. Should be a fantastic boost. My origanal intent being somewhat of the altitude junkie i am as well was to do a N4000BB but after reading that the Cert team must see the whole flight I toned it down some. The N4000BB simmed to right at 21K in altitude and the N2020WT is around 13K. Either way should be fun. I will save the N4000BB for next may for MHM.

So Gang How about what everyone is pushing to get done and fly for Octoberfest!!! (

I'm looking forward to Oktoberfest, with the caveat that I drew an antelope tag this year (after nine attempts) so I will be gone Saturday. The good news is that I will be antelope hunting near the launch site 🙂 so if I can make quick work of things, I'll be out there Saturday before noon. We'll see.

Anyway, Oktoberfest-- I plan to fly my RATT M on a minimum diameter, and if we haven't flown by then, perhaps SSS and SSSS. Maybe (maybe!) my K altitude attempt as well. Stay tuned---

My plans are up in the air for OF. If i get the L3 ticket this w/e, some serious propellant brewing in my immediate future for an N-M shot to 30k+ at Balls. (I turned 50 this year and while I couldn't shoot my age in kilofeet, want to make sure at 60 I can). That means I need only to go up 7.5 percent a year like a good investment to double in 10. Not that my plans are exactly the same.
40K in 2007, 60 in 2008. 100K by 2010.

Assuming I get the rocket back at the Playa. i'll load it with as much commercial propellant as I can afford--probably M-L, but would like to burn more than 20KN-s.
John S

PS: If you can help pack propellant for the Balls shot let me know, APCP is an epoxy so have a pot life to contend with when packing the grains, any helpers will get rewarded for there efforts. Guessing it will take 4 sessions.

denverdoc, I'm game. I'm only a few minutes from Broomfield. I've never packed propellant but I'd love to learn how. Ya never know. I may be doing it some day...

No reward necessary. It's the experience that matters.

KenP.

BTW - my plans for OF is an L2 attempt. Was going to try it at Hartsel this weekend, but I'm really not ready. Rather err on the side of caution than push the envelope right now. I just finished a 4" x 6.5' scratch build DD rocket I'll be flight testing. If all goes well, it'll fly on a J on October.

KenP.