How Do You Launch A 13Ft Super-roc?

[ScrapDaddy]

I Have taken some time away from my addiction from payloaders and Mach-busters and built a 13ft; 18mm/24mm powered super-roc and it just hit me after i built it, how the heck would i launch it? I dont think useing a 10 ft long rail launcher or launch rod was practical; nor could i find a tower launcher or tube launcher on the market; so how the heck will i launch the thing?:confused2:

File has been finished! Check it out!

View attachment 13 foot.rkt

 

[troj]

The first answer that comes to mind is "very, very carefully," but I doubt that helps you much.

Fly-away launch lugs, perhaps, along with a long rod?

Too lazy to open RockSim right now, so I can't look at the diameter. What is it, and how much rod/rail do you need for the motor you plan to use?

-Kevin

 

[ScrapDaddy]

Rock-sim says it will do fine off of a 3 foot launch rod
and im really debating between a 24mm and a 18mm version

 

[georgegassaway]

Well, the overwhelming choice for launching G Superrocs (nearly 15 feet tall) at NARAM-49 in 2008 was a rail.

Many people used more than 8 feet. Either two 6 foot rails end to end (12 feet), or two 8 foot rails end to end (yes, 16 feet tall). Some joined them using another piece of rail (about 3 to 4 feet long) as a sideways “splice”.

We used a 12 foot rail made of two 6 foot pieces and a sideways splice joiner.

We also used my club’s HPR pad to hold the rail, since it lowers horizontally so easily.

We had multiple rail lugs on the model, the first just 2-3 feet back from the nose, to help to keep the whole model secured to the rail. I have seen many superrocs with lugs (or rails) on the lower half only, and the upper half bending outwards due to the wind, as they sat on the pad.

BTW, our model took 1st place in Team Division (Southern Neutron Team).

Go to this page on my site and see Thursday’s pics:

https://homepage.mac.com/georgegassaway/GRP/CONTEST/NARAM/SN-N49/SN-N49.html

A page about our G Superroc R&D project:
https://homepage.mac.com/georgegassaway/GRP/RandD/Gsuper.htm


And, a must-see are Chris Taylor’s NARAMlive pages at NARAM-49. This is page 1 of the photos he shot during the G Superroc event.

https://naramlive.com/naramlive-2007/naramlive/07thursday/index.html


The ones who flew off of long rails like that, would have had the extra advantage of their models taking off straighter and safer if the winds had been up (compared to rods, or shorter rails). Turned out the winds were not to bad, but even so the long rails certainly helped. We figured we were OK even if the winds were 15 mph. And had done a lot of flight sims to predict the angle to launch it from, away from the wind, to try to get a “net vertical” flight (angled downwind some at launch to try to keep it from veering into the wind)

IIRC, NARAM-52 is going to have 10 pads with rails, I do not recall if the rails will be 8 feet or 6 feet.

I any case, forget launch rods. If there is any wind at all, rods are way too wimpy. The only thing theoretically better than a long rail, is a long tower, but that is a real PITA to do just for a Superroc model. I think at least one person claimed he was going to build a super-tower for NARAM-49, but I do not even recall if that guy showed up.

- George Gassaway

 

[ScrapDaddy]

will flex be an issue? if it is ill run full length couplers down (not flying competitively so weight is not an issue) of ill use the beefy loc version of the tube that i found on CWD, does anyone know the specs?

 

[troj]

will flex be an issue? if it is ill run full length couplers down (not flying competitively so weight is not an issue) of ill use the beefy loc version of the tube that i found on CWD, does anyone know the specs?

With a rail as long as George suggests, you should be able to have a few extra buttons to make sure it's well supported until it gets going.

Something that long, if it's really narrow, will flex some. The key is making sure it doesn't flex so much that it buckles under thrust.

But you're not talking a exceptionally powerful motor, relative to the tube, so it's likely not a huge issue.

-Kevin

 

[ScrapDaddy]

ill try to find some D3's when they come back out

 

[The EGE]

I'm not sure what your weight is, but you might want to be careful with the D3. It's got only a 2.2 lb initial spike, so only use it if you'd also use a C6.

The D10W or D13W might be a better choice for a little quicker getting to stable velocity, without being too high-thrust.

 

[MarkII]

Who is going to be making D3s? Can a D3 even lift itself? Wouldn't that be a rocket-boosted glider motor?

MarkII

 

[ScrapDaddy]

I think I like the D10 or D13 idea; and MarkII apogee is on it's way to bringing back it's composites "medalists" line of motors and the D3 has a nice intial spike it's good for top stages and alltitude attempts.... Speaking of which I'm joining the NAR soon which means the D alltitude record is mine... I have a design that will go 6000 np on a D3 and the class A record isn't thAt high.....

 

[The EGE]

Who is going to be making D3s? Can a D3 even lift itself? Wouldn't that be a rocket-boosted glider motor?

MarkII

Apogee made it a few years back, supposedly they will be back, eventually.

They were 18mm, just longer than standard, with -3, -5, and -7 delays. They were good glider and altitude motors, but they can't lift much of anything heavy. Especially not a 13-ft super-roc.

 

[ScrapDaddy]

They are 77mm long 18mm wide and the ege ; I was the one who told you

 

[MarkII]

Yes, I'm quite familiar with Apogee's Medalist line of motors (which are produced for them by Aerotech). I didn't think that we would be seeing the D3 come back anytime soon, though. They have been selling their D10, E6 and F10 motors for quite awhile. Where did you see that Apogee was going to start selling D3s again? And what is the timetable for their release?

I'm glad that you like the D3's peak thrust, because it is lower than that of a black powder B6 or B4. In fact, it is only slightly higher than that of an A8. I hope that you plan on launching your rocket in absolutely dead air.

I notice that in your design, you have five lengths of body tube but only one coupler. How are the other tubes going to be joined together? Will that make your superroc rigid enough to avoid folding?

Also, where is your rocket going to separate for recovery deployment? It appears to be hollow from the motor mount right up to the nose cone. Do you expect the D3's ejection charge to pressurize 163" of airframe in order to blow off the nose cone?

Also, I notice that you have it use a single 32" diameter plastic parachute as a recovery device. Have you ever tried to stuff a 32" plastic parachute into a length of BT-20? If you manage to get it in, how much pressure will it take to blow it out?

Finally, how are you going to keep the rocket sections together after the ejection charge fires? Or for that matter, how are you attaching the parachute to the rocket? I see no provision for a shock cord anywhere in your design. In order for a record attempt to count, the rocket must recover safely. I don't see how your design will do that.

MarkII

 

[ScrapDaddy]

Sorry i never actually go thought that i just figured that the recovery and couplers would only add questionable amount of weight ill get the updated file up; and for the record i DO care about safety i just never have enough time to finish the files op::dark::blush: oh and for the record i am not doing this for competition; i just had the urge to built a string bean i am also using the Loc version of the 18mm tube(i saw it on CWD) and MarkII, i was never planning on using a D3. however i am debating on running full length couplers through the airframe...... and i plan on splitting the airframe in half... which is still 6 feet :y: maybe ill make the lower section shorter.... this is all prototype
And ill contact tim about the medalist motors i really want to know about that

 

[ScrapDaddy]

ANd how do you recomend getting it down safely?

 

[MarkII]

Sorry i never actually go thought that i just figured that the recovery and couplers would only add questionable amount of weight ill get the updated file up; and for the record i DO care about safety i just never have enough time to finish the files op::dark::blush: oh and for the record i am not doing this for competition; i just had the urge to built a string bean i am also using the Loc version of the 18mm tube(i saw it on CWD) and MarkII, i was never planning on using a D3. however i am debating on running full length couplers through the airframe...... and i plan on splitting the airframe in half... which is still 6 feet :y: maybe ill make the lower section shorter.... this is all prototype
And ill contact tim about the medalist motors i really want to know about that

Sorry, I misread your post in which you discussed your motor choice. I do see that you talked about using a D10 or a D13 and that you ruled out using a D3. It looks like you have correctly perceived that you will need to use a motor that delivers enough thrust to get that big stack of tubes moving and going straight up without delivering such a jolt that it will cause the rocket to fold up under thrust.

Full-length couplers would add a lot of weight, because you are using several yards of tube. The LOC tubing (Semroc ST-7 is equivalent, BTW) is heavier-walled than Estes BT-20; it is quite a bit stiffer already. You can buy coupler stock from BMS and cut couplers from it that are a few inches long. These will provide the same degree of support without all of the weight of full-length liners. You can also glue some balsa stringers internally so that they span each joint and coupler. There are some creative ways of internally supporting the tubes that we can talk about if you elect to do that.

MarkII

 

[MarkII]

What is the A division D SR Alt record, anyway? On the NAR website, it gives confusing numbers (in the hundreds of thousands) and lists all of the SR Alt records as "pending" even though some of them are quite a bit older than any A division competitors now.

MarkII

 

[ScrapDaddy]

Never mind

 

[ScrapDaddy]

So what would be a good recovery system?

 

[MarkII]

So what would be a good recovery system?

One popular method is to have the rocket separate into two sections that each recover on its own parachute. If you anchor each shock cord to the outside of its respective section at the balance point so that each section descends in a horizontal orientation, you can achieve safe recovery rates using smaller parachutes. That's one way.

MarkII

 

[MarkII]

Another practical system would be rear ejection. But you wouldn't be able to use that with a minimum diameter design, at least not easily.

MarkII

 

[ScrapDaddy]

Rear ejection? I have heard of it before but hav never seen an example of one........ Is it like a blow back ejection system? Wait... I'll go look it up

 

[exprditer789]

What brand is this rocket?

 

[ScrapDaddy]

It's a scratch but all you need are 5 loc 18mm body tubes a 18mm nc and small fins and presto!

 

[exprditer789]

what does it cost to build and how high does it go?Alex

 

[MarkII]

It's a scratch but all you need are 5 loc 18mm body tubes a 18mm nc and small fins and presto!

Plus a few other parts...

MarkII

 

[ScrapDaddy]

Oh sorry MarkII i always forget you also need a recovery system

 

[ScrapDaddy]

I'm not sure what your weight is, but you might want to be careful with the D3. It's got only a 2.2 lb initial spike, so only use it if you'd also use a C6.

The D10W or D13W might be a better choice for a little quicker getting to stable velocity, without being too high-thrust.

Well to be perfectly honest my orriginal goal was to be able to fly it on a C6 but I would have to compremise integrety; on the bright side I have hade some D24 And D21 that I have been meaning to find a use for them.I was also aiming so I would not need a super long rod I was kinda hoping a 5 foot rod tops (but I would have to beef it up alot)

 

[ScrapDaddy]

A c6........ Oh Boy

 

[MarkII]

Oh sorry MarkII i always forget you also need a recovery system

Just a minor detail, Dr. Goddard.

MarkII