Delta site updated

Any idea what caused three boosters to be dropped just as they were lit?

Although the core motor was slow to pressurize, it also appears that the launch rail wasn't up to the task. In the video it looks like the delta was leaning way over before the button was pressed.

Very cool flight none the less.

-Jeff Taylor

One of the primary advantages to a rail is the ability to add a backing plate (imagine a 2 x 12 board eddgewise). This provides such profound stiffness even a 45 degree launch angle can be reliably achieved. As such it is suitable for a vertical launch of a heavy rocket.

I strongly suggest the BALLS types put together such a rail so one major failure mode is eliminated.

My name is Jerry Irvine. "Tech Jerry" :)

All too often with large projects, the launch pad is an afterthought. I'm not saying that was the case with the Delta III, I have no knowledge of that, but I've seen it happen with other projects.

Another problem that scales with project size as a square, possibly a cube, is "go fever." To haul a huge rocket out to the launch site, get it up on the pad and then scrub due to wind or other issues is extremely hard to do. Often the builders would rather see it crash than not fly that day (and in their mind it won't crash). I guilty of this myself on several occasions.

-Jeff Taylor

Launch fever is good for business :)

Nice site, Kevin. That Delta is an incredible rocket and a very cool launch. I hope it will fly again someday.

=CF

Yep, that's definitely a major selling point for rails. However, a standard rail system with a backing wouldn't have worked in this case, due to the strap-on boosters. There wasn't enough space between the boosters. The Delta used an internal rail system made of three (IIRC) huge rails that looked about as big a 2x4's.

Most of the big rockets I've seen (in person or in pics) have been flown off rails mounted to a tower or other backing. A few have used internal rods or rails, usually due to an unusual shape or booster configuration that precludes the use of more conventional launchers. For instance, Andy Woerner's huge Vostok used an internal rod, with great success. The 1/16th Soviet N1 being built for PlasterBlaster will also use an internal rod.=20

=A7

False.

I said edgewise.

I HAVE been flying rockets for a few years now Ray.

The sequencer we use to ignite the airstarts and drop the boosters is programmed via a laptop at the pad. I suspect miscommunication between myself and the person doing the programming on what the timing was supposed to be. Unfortunately, the sequencers were destroyed when the harness stripped on the lower main, so we couldn't verify how they were set after the flight.

It did have some lean, yes, and we had set some of that. The pad needs to be beefed up a bit. Minor tweaks for the next flight.

Thanks!

-Kevin

Close; the rails are 1.5x3, and spaced 120 degrees from one another, to take advantage of leverage.

-Kevin

That sounds like a version of a tower or a multi-rod.

Usually a "rail" is a singular track mounted on one side of the rocket.

Jerry

Yes, I know what you said. I've looked at the photos of the rocket and it appears that even if they used a backing narrow enough to fit between the boosters, there would be a risk of damage to the boosters if the rocket twisted even slightly while on the rail.

Of course, that's just my opinion based on a few photos from their website. If you've successfully flown a rocket that size with that booster configuration, off an external rail, please post the photos so that we can all benefit from your expertise.

Certainly no worse than what actually DID happen!!

A question on the boosters as tube fins. Do the boosters stop functioning as tube fins when the nosecones get attached?

My guess is yes because a flight of my 1/56 Delta II was akin to a land shark. Hate to have to add fins and was hoping some more nose weight would handle it.

Experience? Opinions?

Yes, they're not effective as tube fins, since the tubes are blocked.

That said, they do act somewhat as fins, the question is how much? That's what I'd love to have an answer to.

We put fins on, as I didn't have an ability to calculate how effective the boosters are as fins. For the size of our project, we decided going with fins was MUCH safer than risking wild instability.

-Kevin

They function more like a transition with the trasition CP at the strap on nose CP.

I'm curious, were the booster pistons angled up to prevent lateral forces from breaking the shear pins and causing premature seperation?

Thanks; I simmed them as a big transition.

Do you happen to know of anything that explains the math behind it?

-Kevin

No. The pistons go 1.5" straight into the airframe. It would've taken a pretty good force to break those pins early.

-Kevin

You should start with James Barroman's reports. You might also find the appendix of Nielson's "Missile Aerodynamics" of interest, as well as several other books and papers on missile aeropredictive code methodology.

Alan