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bigone5500

bigone5500

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I am in the middle of a build. I have pretty much got this thing like I like it. Please take a look at the Rock sim file I have attached and let me know if this thing should fly. I want to use both 'E' and 'D' engines so the MMT will have a spacer for the 'D' engine.

The centering rings are made of 3/32 lite ply (homemade of course :D ). The bulkhead will be made from a BT60 tube coupler and a piece of the same lite ply that the CRs are made of. I'm thinking about an 18" parachute for this one.

One thing I don't know if I should do is use kevlar shock cord from the ejection baffle (which is located between the lower 2 tubes) to the bulkhead or use kevlar from the baffle and tie elastic to it then connect that to the bulkhead.

Is this thing getting the overkill treatment?
 
The answer to your shock cord question (to me) would be a matter of preference, provided that your building techniques are robust.

For instance: Just be sure to use washers on both sides of the bulkplate on your eyebolts, and you can use a low-to-no stretch shock cord. Just make sure it's plenty long - I'd personally go with 10' - 12' on a zero stretch shock cord on a rocket this size.

You can cut that cord length in half (or more) if you use the kevlar only as a short harness to tie elastic to.

I would *not* recommend the zero-stretch shock cord if you were tying it directly to the plastic loop on a nose cone, especially if the cone had any nose weight in it. I've read on this board where folks have had a separation at ejection because the loop that is molded into the nose cone (that everything ties to) snapped, probably due to the zero-stretch shock cord. Again, if your attaching to metal eye-bolts that are well secured to lite-ply bulkplates that are attached to your rocket with good fillets (again, nothing overkill, just sound building techniques) you'll be fine.


As far as your 18" parachute: Since you have RockSim at your disposal, I'd use it. Build your rocket, then weigh it and balance it (without a parachute, motor, or wadding. But do include the shock cord in this.)

Then go back to your rocksim file and adjust the weight of your model so that the CG matches what you've actually got and it weighs the same. Usually a fella has to add weight to get the file to match the actual model. This can easily be done by adding a mass object, anywhere on the model. I say anywhere because you want to add it in a place that will also adjust your CG to actual.

Anyway, do that simple thing, then re-select your parachute. RockSim will tell you (on the parachute selection screen) the approximate descent rate for a given parachute size. I wouldn't want to go much (if at all) over 15 fps descent rate on a model like this one. Especially if you only intend to fly it on Estes 24mm BP engines (it sims to a max altitude of 900' on an E9-6 in the current configuration.) That said, I'd go with a 24" chute. But that's just me.
 
Originally posted by Fore Check
The answer to your shock cord question (to me) would be a matter of preference, provided that your building techniques are robust.

For instance: Just be sure to use washers on both sides of the bulkplate on your eyebolts, and you can use a low-to-no stretch shock cord. Just make sure it's plenty long - I'd personally go with 10' - 12' on a zero stretch shock cord on a rocket this size.

You can cut that cord length in half (or more) if you use the kevlar only as a short harness to tie elastic to.

I would *not* recommend the zero-stretch shock cord if you were tying it directly to the plastic loop on a nose cone, especially if the cone had any nose weight in it. I've read on this board where folks have had a separation at ejection because the loop that is molded into the nose cone (that everything ties to) snapped, probably due to the zero-stretch shock cord. Again, if your attaching to metal eye-bolts that are well secured to lite-ply bulkplates that are attached to your rocket with good fillets (again, nothing overkill, just sound building techniques) you'll be fine.


As far as your 18" parachute: Since you have RockSim at your disposal, I'd use it. Build your rocket, then weigh it and balance it (without a parachute, motor, or wadding. But do include the shock cord in this.)

Then go back to your rocksim file and adjust the weight of your model so that the CG matches what you've actually got and it weighs the same. Usually a fella has to add weight to get the file to match the actual model. This can easily be done by adding a mass object, anywhere on the model. I say anywhere because you want to add it in a place that will also adjust your CG to actual.

Anyway, do that simple thing, then re-select your parachute. RockSim will tell you (on the parachute selection screen) the approximate descent rate for a given parachute size. I wouldn't want to go much (if at all) over 15 fps descent rate on a model like this one. Especially if you only intend to fly it on Estes 24mm BP engines (it sims to a max altitude of 900' on an E9-6 in the current configuration.) That said, I'd go with a 24" chute. But that's just me.
Click to expand...

The elastic shock cord I mentioned is the kind used in sewing. It's flat with a fabric type weaving and elastic through it. I'll use 1/4" for this project. I think what I'll do is use the kevlar and go about 3" out of the main tube then tie a barrel swivel to that and tie elastic cord to it and...well...you know the rest. I plan on using a snap swivel on the chute shroud lines to try and keep them untangled.

As for the engines...should I add removeable nose weight to accommodate for the D - E transitions due to weight differences?

I hope this project flies....:rolleyes:

Edit: What do you think about the stability? Is 2.91 overstable bad?
 
annother tip,try to get cotton elastic not the polyester type, it's doesn't hold up to heat worth a darn .
 
Originally posted by bigone5500
The elastic shock cord I mentioned is the kind used in sewing. It's flat with a fabric type weaving and elastic through it. I'll use 1/4" for this project. I think what I'll do is use the kevlar and go about 3" out of the main tube then tie a barrel swivel to that and tie elastic cord to it and...well...you know the rest. I plan on using a snap swivel on the chute shroud lines to try and keep them untangled.

As for the engines...should I add removeable nose weight to accommodate for the D - E transitions due to weight differences?

I hope this project flies....:rolleyes:

Edit: What do you think about the stability? Is 2.91 overstable bad?
Click to expand...

I certainly would NOT add nose weight of any kind (removable or otherwise.) Adding nose weight to this design is completely un-necessary, and would only reduce performance.

2.91 overstable is ok. Might weathercock a bit into a nice breeze if launched under those conditions, but that margin isn't enough to cause any real concern that I can think of. If you were worried about the overstability, you could shave some off of your fin span (the tips of your fins) until you get it closer to 1.5 with a full load.

I'm sure your project will fly just fine!!
 
I have been thinking...I have a hommeade ejection gas baffle installed in this rocket and am wondering if I still need to use recovery wadding.
 
Its likely that you don't need any wadding,

if you pack in a ripstop nylon chute, do the first flight without and if you see some dark sooty marks on your chute afterwards, you'll need wadding...
...please do not try the first time with a plastic chute, you might end up having a parawad recovery...

Also, your design is not quite that overstable as shown, you gotta allow some weight on glue/epoxy you're using around fincan area, the weight depends on your building habits, could be as little as 0.5 oz that doesn't really make any diff, but if you like to overbuild, it'll move the CG further back thus making it less overstable. Not to worry thou, you've got plenty of margin to play with unless you go hog wild with the glue/epoxy...
 
Well it's done...!!!! YAY!

My first scratch build...does this look like a clone to any of you? What rocket does it look like the most?
 
looks like there might have been a richter recker in the mix
 
Well i got it done guys...!

Here's a pic of it launching. The only thing I had trouble with is the junky plastic chute. I used 1 square of wadding and it caused some warping of the plastic making the chute invert. The recovery was great though. It has a 4' shock cord and I think that helped it slow down on decent. I approximate the height on the E9-8 to be 1000' give or take. But overall for my first scratch build it is a success!

Thanks to all for your advice in aiding me to accomplish this task.
 
he said that he used a baffle too, though.

bigone5500 [snip] One thing I don't know if I should do is use kevlar shock cord from the ejection baffle (which is located between the lower 2 tubes) to the bulkhead or use kevlar from the baffle and tie elastic to it then connect that to the bulkhead.


something else I noticed, bigone5500:
roadkill [snip]...please do not try the first time with a plastic chute, you might end up having a parawad recovery...

either try a ripstop next time (per roadkill's suggestion) or use nomex cloth, or several sheets of wadding if you must use plastic...

I didn't catch this the first time, and I can't open the rsim file to be sure of the location, but if your baffle is too far aft, that would be a likely reason why you're still getting hot gas (particles) that are messing w/ ur plastic chutes. Baffles are supposed to be installed as far forward as possible, while still creating enough room for chute and nose cone shoulder...
 
i didn't have a nylon chute for it so i had to use what i had. i also didn't know that detail about the baffle. I used one square thinking i was safe but found out otherwise...

My Big Daddy had a bad first launch. It went up nicely but on ejection the chute got too hot and welded together at one small point. I didn't use enough shock cord either...the nosecone came back and damaged one of the fins. Small damage but to me any is unacceptable. It was a dent in the side of the leading edge. I'll use 6' of cord in it next time and will install kevlar for the tether (i guess that's what it's called - connects shock cord to rocket?)

i'm also going to get some of that nomex material. I think it will save time and headache...
 
I agree with your deductions. Lenghten the shock cord on the big daddy, and def. use some nomex in that airframe too. Packing (enough) wadding in something that large is NOT fun, with nomex, you haven't much too worry... Just make sure you use a large enough piece for the 3" airframe (something ~9" square would be my recommendation for the Big Daddy. You may also want to discover the "magic" of dog barf for other smaller dia. rockets. How much damage did your big daddy take to the fin? just a small amount where some FNF will patch it, or is a balsa patch in order?
 
Originally posted by TeenRocketNerd
I agree with your deductions. Lenghten the shock cord on the big daddy, and def. use some nomex in that airframe too. Packing (enough) wadding in something that large is NOT fun, with nomex, you haven't much too worry... Just make sure you use a large enough piece for the 3" airframe (something ~9" square would be my recommendation for the Big Daddy. You may also want to discover the "magic" of dog barf for other smaller dia. rockets. How much damage did your big daddy take to the fin? just a small amount where some FNF will patch it, or is a balsa patch in order?
Click to expand...

First off.....what in the world is dog barf???? LOL

The fin only had a spot about 3mm dia that looks like it was burned. I can sand and repaint that spot and be ok.

As with the nomex, do I have to use wadding in conjunction? I am going to order a nomex blanket to use with this one.

I have been looking on this site: www.unclemikesrocketshack.com and they have 2 nylon chutes. One is by Dynastar and the other is a Sunward brand. Which one would you reccommend for Big Daddy?

I am thinking that the nomex should be attached about 2 or 3 inches from the body with a knot. I am going to replace the shock cord as it was almost melted into. It is the polyester/elastic type 1/4" wide. I will replace that with some kevlar and connect that to more 1/4" elastic with a barrel swivel. I got a lotta work to do before my next launch....:rolleyes:
 
Originally posted by bigone5500
First off.....what in the world is dog barf???? LOL

The fin only had a spot about 3mm dia that looks like it was burned. I can sand and repaint that spot and be ok.

As with the nomex, do I have to use wadding in conjunction? I am going to order a nomex blanket to use with this one.

I have been looking on this site: www.unclemikesrocketshack.com and they have 2 nylon chutes. One is by Dynastar and the other is a Sunward brand. Which one would you reccommend for Big Daddy?

I am thinking that the nomex should be attached about 2 or 3 inches from the body with a knot. I am going to replace the shock cord as it was almost melted into. It is the polyester/elastic type 1/4" wide. I will replace that with some kevlar and connect that to more 1/4" elastic with a barrel swivel. I got a lotta work to do before my next launch....:rolleyes:
Click to expand...

dog barf: blow in insulation; comes in bales... Basically, it's shredded/pulverized newspaper, that is treated to resist burning... do a search, and you'll find plenty of info on it.

With nomex, you should not have to use wadding, unless you want to add some barf to "puff" out the sides of the blanket tight to the tube. (not necessary, though) Attach the nomex in one corner, and I would say your location would be ok.

For the replacement shock cord, I would recommend either 400# kevlar cord, or 500# flat nylon, both available at Uncle Mikes'. For the cord, make sure to anchor it shy of the forward end of the bt.

a chute? You could make your own easily out of a yard or so of ripstop and kevlar thread... after refreshing my memory with the selection at Uncle Mikes, I would recommend a sunward, reason being, dynastar only makes chutes that are WAY too big for a big daddy... SO, if you're going to order one of the chutes offered from Uncle MIkes', get yourself a sunward 18". Thrustline also carries ripstop chutes, as do a number of other vendors, and in a variety of different brands, too.

my 3 cents
 
i'm no seamstress so i will have to buy one if i want it to work right...:D

You say anchor it shy of the forward end of the body tube...what method do you reccommend?
 
For something this size, typing a loop in the kevlar cord (if that's what you're using) and then threading the elastic through it, looping it twice, if not three times around the loop, before tieing with your basic double knot (or triple) For attaching the kevlar to the bt or cr, their are many ways:

drill through both cr's and tie a knot in the kevlar and epoxy it, where it comes through the bottom cr

use a piece of bt-80 and slit it on one side. Tie the kevlar around it, then glue it inside th bt of the Airframe. MAKE SURE IT IS GLUED IN BELOW WHERE THE SHOULDER OF THE NC WILL SLIDE!!!!!

This is my favorite method...take non-corrugated cardboard, cut a piece about 1.5x 2.5 " long. Then, about a 1/4-3/8 of an inch from each long end, and use a finishing nail, or something of a similar diameter to poke one hole at each end, at the above specified distance in and centered. make the hole just big enough to get the kevlar through. Then, thread the kevlar through the two holes, and prior to gluing, making sure that the knot of the kevlar is facing you, and through the BOTTOM hole. Then, glue in place, below where the shoulder of the nc will contact the airframe. Then, attach the elastic as specified above.

suggestion: if you're going to use polyester elastic, use 3/8, not 1/4... it'll last longer.

for attaching the nomex, here is a thread on how to do it:
https://rocketryforum.com/showthread.php?s=&threadid=24656&highlight=nomex

hope this helps you.
 
here is a sketch of what I meant on the final way of kevlar attachment:

the black dots that represent the holes for the kevlar are exaggerated in size. You want the diameter of the hole to the kevlar to be much closer. I should also add that once the kevlar is looped through, it's good practice to spread a small amount of epoxy or atleast wood glue around the holes/kevlar, to secure it extra well. Do this, prior to installing the entire assembly.
 
Just catching up with this.

For Hobby-sized ripstop chutes,

https://www.thrustaero.com/rip-stop_nylon.htm

You simply *can't* go wrong with Thrustline ripstop chutes!

There are are a couple of Thrustline ripstop chutes that I have in the box that I fondly refer to as "Ol' Lucky." Both of 'em get the same nickname (I'm not that creative.) Good pricing for the product, and they are just great. I *highly* recommend them!
 
What do you guys think is better...using the spent casings to make a D engine adapter or use the yellow tube that comes with estes kits to insert the engine block in the engine tube? Either way it will be cut to a 1" length to accommodate a D engine.
 
a spent motor casing... The engine block spacer is not sufficient, IMO, to prevent the motor from pushing forward...not to mention it would be difficult to remove. A word to the wise, sand the adapter (casing) down a little, just take the outer layer of cardboard with print on it off. This makes it easier to get the adapter back out, when you want to fly E's again. Otherwise, I find the fit too tight, and difficult to remove...
 
I want to paint this rocket to sort of match the scheme that the V2 has. Like a checkerboard look. How would I go about doing this with a 3 fin design?
 
https://www.v2rocket.com/start/makeup/design.html

just lay it out like a normal v2 "checkerboard" theme. It's gonna look off w/ only three fins (and no boattail) no matter how you mask it ... I don't really understand what you are asking, as the number of fins can't change the way the design is layed out. just try it a couple different ways with your tape masking, and see what you like...
 
Originally posted by bigone5500
I want to paint this rocket to sort of match the scheme that the V2 has. Like a checkerboard look. How would I go about doing this with a 3 fin design?
Click to expand...

WIth 3 fins, devide your rocket, around the circumference, into 6 sections. You should then be fine and the pattern will look as though it belongs.

That should work out great
 
Originally posted by jflis
WIth 3 fins, devide your rocket, around the circumference, into 6 sections. You should then be fine and the pattern will look as though it belongs.

That should work out great
Click to expand...

Thanks....that's just what I'll do. I'm going to post a poll for the 2nd color. White being the 1st. Thanks again.
 
Originally posted by TeenRocketNerd
here is a sketch of what I meant on the final way of kevlar attachment:

the black dots that represent the holes for the kevlar are exaggerated in size. You want the diameter of the hole to the kevlar to be much closer. I should also add that once the kevlar is looped through, it's good practice to spread a small amount of epoxy or atleast wood glue around the holes/kevlar, to secure it extra well. Do this, prior to installing the entire assembly.
Click to expand...

Is the cardboard that comes on blister packages ok to use?
 
Originally posted by bigone5500
Is the cardboard that comes on blister packages ok to use?
Click to expand...

if it's glossy or has a label or is foil backed, I would say no. you want something that's somewhat rough, that will hold the glue, and stay in place. If you were to peel the label, and inner "foil" off of a piece of a pringles can, I should think that that would suffice, just make sure not to peel off more than is necessary to expose the brown cardboard. you want strong cardboard, so make sure, if you use a pringles can, to not use any part of it that contains a prevelent "seam" of cardboard. I would recommend using some 5 minute epoxy for re-enforcing around where the kevlar hooks into the cardboard around the holes), as well as at the joint where the whole assembly mounts onto the airframe.

for "double re-enforcement", once this assembly is dry, take a small amount of epoxy and run a fillet of sorts where the cardboard meets the airframe on the long sides (this step might be overkill, as the kevlar will likely fail before the epoxy gives)

btw, what # kevlar are you planning on using? 400# I hope.
 

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