Nose cone hitting body tube

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Fred

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I have a issue with the nose cones hitting the body tube at ejection. What is causing this? I don't like to fill and repaint every time I launch a rocket.


Thanks in advance, Fred
 
That is probably because you are an elastic shock cord. Whaen it ejects it gets pulled or stretched out and it sprigs back on itself, usualy pulling the nosecone back in slingshot fashion and hitting the rest of the rocket. You could use a longer cord or replace it with a long non elastic cord.
 
That is probably because you are an elastic shock cord. Whaen it ejects it gets pulled or stretched out and it sprigs back on itself, usualy pulling the nosecone back in slingshot fashion and hitting the rest of the rocket. You could use a longer cord or replace it with a long non elastic cord.

+1. I like to use sewing elastic (1/8" or 1/4") because it still stretches but doesn't snap back as sharply. I also like to sew the ends around the mounting loop in the nose cone, rather than tie it...That way you don't get a big blobby knot that could get jammed in the mouth of the tube when you put the nose on. Whatever you do, longer is generally better.
 
This problem used to be known as the "Estes dent". It's cause by elastic shock cords being too short on most kits. On my LPR rockets I fixed this by using non elastic shock cords at least 2.5X the rocket length.
 
+1. I like to use sewing elastic (1/8" or 1/4") because it still stretches but doesn't snap back as sharply. I also like to sew the ends around the mounting loop in the nose cone, rather than tie it...That way you don't get a big blobby knot that could get jammed in the mouth of the tube when you put the nose on. Whatever you do, longer is generally better.

I still have the elastic cords from my AT kits and I had my sister-in-law sew loops at the ends so I can attach them using a quick link. Kelvar is good, but pricey. I would use it as an anchor only and have either elastic or nylon to make up the majority of length for the shock cord
 
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That is probably because you are an elastic shock cord.

In the movie Pulp Fiction, at the end where the coffee shop is being held up, Pumpkin grabs the manager and starts giving him a hard time and asking him if he thinks he's a hero. The manager starts to talk but only gets out, "I am not a hero, I'm just a coffee shop...", and doesn't get to finish his sentence.

In the credits the actor is given credit as "Coffee Shop" instead of a character's name.
 
In the movie Pulp Fiction, at the end where the coffee shop is being held up, Pumpkin grabs the manager and starts giving him a hard time and asking him if he thinks he's a hero. The manager starts to talk but only gets out, "I am not a hero, I'm just a coffee shop...", and doesn't get to finish his sentence.

In the credits the actor is given credit as "Coffee Shop" instead of a character's name.



:rofl:

My Semroc Blue Bird Zero did the "Dent" on its second flight. Its fixable, but a PITA. I now try to make Shockcords of Kevlar when I can, and make them longer than I think they need to be.
 
All You kit builders: Save your selves a lot of heartache caused by the dreaded "ESTES DENT" by tossing the provided "Way To Short" Rubber band shockcords Estes provides in the scrap heap. Add 30-36" of 1/8" oval elastic cord as your shock cord. If you want to greatly increase the life of this Elastic shock-cord If tied around your motor mount. add a 12" braided Stainless Steel fishing leader or small diameter multi strand Stainless wire rope. or combine the Stainless Anchor, 70-100lb braided Kevlar and elastic.

I haven't burned off an Elastic Shock-cord or Kevlar shock-line since adding the aviation cable, Fishing leader or 49strand stainless Beading wire anchors to the mix. I can tell you guys I've actually transferred several of these combination shock-lines to other models when the bodies have worn out or imploded. All adds perhaps a buck to the entire model cost once you purchase a supply of the elastic, Kevlar and Stainless aviation cable.
If any are interested I will upload some photos with sizes and Cat numbers for these products.
 
Micromeister - I would be interested in how you tie these off (pictures) along with part numbers.


Sent from my iPhone using Rocketry Forum
 
This problem used to be known as the "Estes dent". It's cause by elastic shock cords being too short on most kits. On my LPR rockets I fixed this by using non elastic shock cords at least 2.5X the rocket length.

Upon completing my second rocket kit ever, a SEMROC "Iris", I noticed on my very first recovery an odd crescent shaped indentation on the balsa nose cone. I was surprised at this, and filled it and painted the spot again.

On the second launch, it was not observed, but on the third time it happened again.

Finally, an old hand at the club launch mentioned it was known as the "Estes Smile" and that a longer shock cord would solve that. As I didn't know the amount of weight the rocket could handle nor if it would even impact the flight, I did nothing, but just moved onto additional rockets. Most all have blown plastic nosecones, I have noticed, but not the quality of that original IRIS. I still like balsa nosecones, cause.... I dunno....they just seem more classy and substanial.

But I've never had an Estes Smile or Dent with a plastic nose cone yet.
 
Upon completing my second rocket kit ever, a SEMROC "Iris", I noticed on my very first recovery an odd crescent shaped indentation on the balsa nose cone. I was surprised at this, and filled it and painted the spot again.

On the second launch, it was not observed, but on the third time it happened again.

Finally, an old hand at the club launch mentioned it was known as the "Estes Smile" and that a longer shock cord would solve that. As I didn't know the amount of weight the rocket could handle nor if it would even impact the flight, I did nothing, but just moved onto additional rockets. Most all have blown plastic nosecones, I have noticed, but not the quality of that original IRIS. I still like balsa nosecones, cause.... I dunno....they just seem more classy and substanial.

But I've never had an Estes Smile or Dent with a plastic nose cone yet.

Well, I would hope not... any tube tough enough to take a bite out of the plastic nosecone would do some serious damage!
Longer shock cords DO help... another tip, ditch the rubber band material that comes with Estes kits and replace it with elastic or Kevlar. Wes from Dr. Zooch has commented that from his experience, he's found that most "Estes dents" to nosecones comes from the parachute opening too fast, and the rocket "flies into" the nosecone after ejection... he recommends a tighter packing of the parachute to delay the chute opening, to allow the entire rocket to slow down from air drag before the parachute physically opens...

Later! OL JR :)
Later! OL JR :)
 
Micromeister - I would be interested in how you tie these off (pictures) along with part numbers.


Sent from my iPhone using Rocketry Forum

Sure thing Martin:
Starts off anchoring our shock-Cord around the motor mount or adding a centering ring or piece of coupling that can be installed from the forward end of the model for retro-fit shock-cords. notch the centering ring or coupling with a round needle file to pass the Kevlar or Stainless Leader and secure with a series of half hitches with the knot on the inside of the ring or coupler. our Anchor should end an inch or two below the forward end of the model body to with either an overhand loop if Kevlar or braided or compression sleeve loop in Stainless fishing leader or small diameter Stainless steel wire rope.
Once the anchor ring or couple is epoxy installed or the motor mount is inserted the Shock Cord anchor is passed out the aft end of the motor mount. I always install motor mounts with the shock-cord or shock-cord anchor threaded back through the motor mount to keep it out of the way until the MMT is inserted and fixed in place with glue or epoxy.
After the internal mastic as cured it's time to tie on the Kevlar or Kevlar/Elastic extensions to our shock-cord anchor. I do this with either a series of 3 half hitches or a bowline know depending on the size of the model. Generally everything under 2lbs is down with half hitches.
WARNING!!! do NOT add glue to your knots.. it actually helps cut the Kevlar and/or elastic. Any properly tied knot will not loosen unless it's made to slip.
If using the Stainless/Kevlar/Elastic system you'll simply repeat the overhand loop/3 half-Hitch or SheetBend attachment done earlier.
After tying on all the lines thread them back through the motor mount and out the forward end of the model. Tie on the Nose Cone and tie a butterfly knot about 2/3rds of the way between the model body and NC for Recovery method attachment ( Chute or Streamer).
I have lots of different pic of these procedures, and materials I'll add as many as I can to help illustrate both new Constructions and Retro-fitting.

472p02b-sm_Baffle Shockcord Anchor_01-12-08.JPG

473p02a-sm_BT-50h-Bt70 MMT & Shock Anchor_01-15-08.JPG

473p02b-sm_Shockcord anchor-100lb Kevlar_01-15-08.JPG

451e8-sm_30in MB-Shockline 7pic pg_10-06-06.jpg

Shock-Cord Mount-h1_Retro mount 8pic pg1of2_09-28-06.jpg

Shock-Cord Mount-h2_Retro mount 6pic pg2of2_09-28-06.jpg
 
Kirk G:
It is perfectly OK to extend any LPR model's Shock-cord by adding 30 - 60'' of 1/8" oval elastic without worry about affecting the flight performance. I NEVER use the provided shock-lines in any KIT model replacing the Way TO Short Estes Rubber bands with as much as 6 feet of 1/8" oval elastic. The reason I stress Oval elastic is it holds up to the heat of ejection 10-to-1 over 1/8" Flat elastic. If you add the Kevlar or Stainless Anchor/Kevlar to the elastic shock-line system it will outlast the model;)
 
Kirk G:
It is perfectly OK to extend any LPR model's Shock-cord by adding 30 - 60'' of 1/8" oval elastic without worry about affecting the flight performance. I NEVER use the provided shock-lines in any KIT model replacing the Way TO Short Estes Rubber bands with as much as 6 feet of 1/8" oval elastic. The reason I stress Oval elastic is it holds up to the heat of ejection 10-to-1 over 1/8" Flat elastic. If you add the Kevlar or Stainless Anchor/Kevlar to the elastic shock-line system it will outlast the model;)

exactly!
 
I agree that Estes supplied "rubber" shock cords are a waste of time. They are usually way too short. They also become brittle far too fast and can easily separate at ejection. More cord length is almost always better. I typically go for the 3x length of the rocket ratio.

There are a couple of observations of mine I would like to share.

First off, the old tried and true Estes "Tri-fold" attachment works just fine. Use carpenter's glue and let it dry for 24-hoiurs... If your mount breaks, then you had some other issue causing your failure and the mount placement wouldn't have mattered anyway. Using this method, you don't need a steel or kevlar leader. It is also very unlikely to zipper a model with your shock cord mounted this way!

Flat sewing elastic works just fine as well. Use the proper amount of wadding/"dog barf" and you will have no issues. This flat elastic is also less likely to zipper a tube. When stretched, it will lay flat against the tube distributing its force over a larger area. Round elastic is a pin-point wire like saw. Kevlar even worse!


Jerome :)
 
Everyone has their "best" way to handle just about every issue out there. I personally use an idea from purchase of a Totally Tubular model. They had a length of kevlar thread and some elastic with instructions to mount the thread to the engine mount. Then tied the two together.

Another option is to simply use kevlar thread. You can get a bunch of it cheaply at The Thread Exchange (https://www.thethreadexchange.com/m...e=TTE&Category_Code=Kevlar-Thread-information). For a model rocket I would get at least 200 lb strength to ensure the 3 ounce rocket is held firm. Actually, I did get heavier thread than I needed so it would be thicker and easier to work with.


Kirk
 
I agree that Estes supplied "rubber" shock cords are a waste of time. They are usually way too short. They also become brittle far too fast and can easily separate at ejection. More cord length is almost always better. I typically go for the 3x length of the rocket ratio.

There are a couple of observations of mine I would like to share.

First off, the old tried and true Estes "Tri-fold" attachment works just fine. Use carpenter's glue and let it dry for 24-hoiurs... If your mount breaks, then you had some other issue causing your failure and the mount placement wouldn't have mattered anyway. Using this method, you don't need a steel or kevlar leader. It is also very unlikely to zipper a model with your shock cord mounted this way!

Flat sewing elastic works just fine as well. Use the proper amount of wadding/"dog barf" and you will have no issues. This flat elastic is also less likely to zipper a tube. When stretched, it will lay flat against the tube distributing its force over a larger area. Round elastic is a pin-point wire like saw. Kevlar even worse!


Jerome :)

I agree, especially about Kevlar... it will saw a tube in nothing flat. If you're gonna use Kevlar, better be SURE to put a few wraps of tape or something around it to distribute the force at deployment and "turnaround" (when the parachute deploys and the shock cord pulls out straight, and then "jerks the rocket around" from whatever direction it's still flying or tumbling or whatever when the shock cord pulls tight) to prevent zippered tubes... Never had it happen with any elastic, cord type or flat type, but Kevlar is something else altogether...

I've done the mounts both ways... I usually just use the good old "Estes teabag" style trifold mount... works and it's quick and easy to do. Dr. Zooch kits usually come with a long piece of Kevlar string and elastic, and the instructions recommend a "teabag" mount with the Kevlar and the elastic tied onto the end of the Kevlar and then to the nosecone screw eye. I've done the "loop round the motor mount" with the Kevlar, using it as a "leader" coming up the length of the rocket, with the elastic tied onto it and the nosecone. If you DO use Kevlar as a 'leader', be sure that you notch the centering ring on the OUTSIDE EDGE where the motor centering ring is glued to the inside wall of the main body tube, NOT the INSIDE EDGE of the centering ring where the motor tube is glued into the centering ring, to keep the Kevlar away from the heat and "hibachi effect" of residual hot gases and flame emanating from the motor case after ejection... Kevlar is HEAT RESISTANT, not HEAT PROOF, and the blast of ejection clay and flaming bits of BP WILL erode or damage the Kevlar or make it brittle over time... Keeping it to the side away from the heat and flame and blasted bits of clay will help its longevity...

Either method works... the steel leader, (STAINLESS I hope-- BP byproducts are very corrosive, so NO WAY would I use a NON-stainless steel leader!) which works as well, probably, as Micro says, VERY well, would certainly work too... but it's up to the individual builder... the stainless steel leader is kinda overkill for most projects IMHO, but that's a personal decision.

IF a "teabag" does the job, why bother??

One other tip on "trifold teabags"... If you can, clamp them up to dry using smooth jawed hemostats or whatever you favorite clamping method is... they come out MUCH thinner and smoother that way... Also, "pre-curl" them between your fingers to the contour of the inner wall of the rocket's body tube, and I stick them as far down as I can possibly get them (half the length to the motor mount if I can) so that the chute remains ABOVE them if at all possible. I know some people curse "teabag" mounts because they "snarl up the chute" and keep it from "exiting the tube cleanly" and stuff like that... If they're MADE THIN by clamping, and PRE-CURLED to TIGHTLY CONFORM to the inner wall of the tube, and DOWN LOW ENOUGH to put them just below the chute (but not below the wadding of course!) then there's NO PROBLEM with them whatsoever... it's all in the execution... the details make the difference...

Later! OL JR :)
 
Easiest Anti-Zipper attachment I've ever found is a 3/4" long piece of 1/2" plain masking tape doubled over 70-130lb Kevlar shock-line (See the Last photo in my earlier post). That little piece of double paper tape is all that's needed to prevent body tube zippering. You can also wick Water thin CA into the forward end of the tube but this step really isn't necessary.
Since adding this little item about an inch inside the forward end of the Shock-Cord I've yet to zipper a standard .013 or .021" Estes type body tube model. Believe it or not this tape tab anti-zipper works.

As for the Estes TeaBag mount I've always hated adding a blip to the inside of models. It is particularly bad on minimum diameter models BT-5, BT-20 and BT-50. But it does work ok on larger body model. I haven't used one since about 1973-4 whenever Dupont released Kevlar line;) The motor mount tie on just makes such an elegant and so much better sense shock-cord anchor to me.
 
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My kids have those nerf dart guns. The darts make excellent anti-zipper sleeves--fasten them to 300# Kevlar at the point it'd impact the airframe. Serves as a coushin as well as distributes the shock load across a wider area, effectively reducing the pressure at the impact point, reducing the likeliehood of a zipper.


Later!

--Coop
 
Flat sewing elastic works just fine as well. Use the proper amount of wadding/"dog barf" and you will have no issues. This flat elastic is also less likely to zipper a tube. When stretched, it will lay flat against the tube distributing its force over a larger area.


Jerome :)

But how do you determine what "the proper amount of wadding/'dog barf" is for each rocket? It seems that trial and error can be a particularly expensive proposition. A good friend of mine built a Xarconian Cruiser (Level 5!) and a "Long Tom" for his girlfriend. They went to the last club launch, and after preping the rocket, loading the parachute, and selecting a motor, they launched first her pink Long Tom...and saw it go up, but no exhaust or separation charge blow... eventually finding it lawn darted into a nearby field. A clever old hand lent a hand saw and shortened the crumpled tube up to be able to fly again someday... but it's not a "Long Tom" anymore...

The second launch was the silver Xarconian Cruiser, and again, it went up fast and was lost from sight. Eventually, it was spotted descending into the same adjacent field. No ejection charge apparent. This time, the various decorations and beautiful design work was all crumpled, and could not be easily salvaged.

The couple left the field somewhat discouraged. When I later asked them what happened, he just said "Recovery wadding" and "I'll talk to you later about it." With no further explanation, I'm puzzled as to what to tell him.
 
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Sounds like way too much wadding or too tight a nose cone fit. (Motor can make a difference too.) The amount of wadding depends on the diameter of the tube. For anything under 1.5" 1 piece should do. You just want to provide a barrier. This breadth, not depth. Crumpled up wadding that is 1/4 inch in height is just as effective as crumpled wadding that is 1"+ in height. (Although I'd check the nose cone fit first. Fit should loose, just enough to hold it in)
 
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