Align Mozzie fins? and fitting balsa nose cone (how snug)??

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Underdog

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Newbie questions on my first rocket (Madcow Mozzie)
1. How do I assure that the fins will be aligned correctly? I have 30 minute epoxy or yellow glue to attached the fins. I can't wrap my head around a guide or template that I could build out of foam core to assure that the fins get aligned correctly. The motor tube will have an Aerotech 29mm motor mount retainer. Probably fly on some Estes D12-3 on an adapter.

2. How snug should the nose cone be? I've sealed the balsa with spray polyurethane , filled the dents with carpenter's putty and primed and sanded in hopes of preventing the balsa from absorbing ambient moisture and swelling in the springtime. I can sand it some more and make it looser. Just don't know how loose a nose cone should be. Right now I have to really push to get the nose cone in.
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nose code.PNG
 
You should be able to hold the fully loaded rocket (incl. spent motor) by the nose, no more.

Print out two fin guides, but cut one from the outside instead of inside. Put a coupler or motor etc. in there to keep the aft guide aligned.
 
Does the nose cone's inserted section get left as bare balsa or does it get painted?
 
Payload Bay Fin Guide tool, it will produce a PDF fin guide, glue it to a piece of foam board (1/4" is what I use). Cut out the lines put the fins in and slide the guide over the tube and fins.

Easy peasy straight and easy!

https://www.payloadbay.com/page-Tools.html

MiniCowabunga2.jpgMiniCowabunga3.jpg

The paper for the guide has actually been peeled away in the two photos, but the fin guide is the result of the PDF.
 
Does the nose cone's inserted section get left as bare balsa or does it get painted?
The shoulder (what that's called) is not *usually* painted. I generally would not paint it, mainly because I would fear that the paint could eventually stick to the inside of the BT.
 
I primed the fins and tube (not yet glued in place). Should I sand them down to bare wood (the points of contact) before gluing. Or will the glue still form a strong bond with the primer there?
 
Sand the primer off the parts that join (and remember there will be fillets as well). You don’t want to glue to painted surfaces.

I usually mask off the mount points with thin strips of masking tape, but sanding it off after is fine if you do it carefully.
 
How snug does the retainer need to be for a "G" motor? The retainer slides easily on the motor tube with enough slack for one wrap of masking tape. Should I use masking tape to take up the slack or will the JB Weld fill that small gap well enough?
small retainer.JPG
 
How snug does the retainer need to be for a "G" motor? The retainer slides easily on the motor tube with enough slack for one wrap of masking tape. Should I use masking tape to take up the slack or will the JB Weld fill that small gap well enough?
View attachment 338952

JB Weld will fill the gap. If you wrap it with tape first, all the JB Weld can do is glue the retainer to the tape, not the motor mount tube. However, one hazard when fitting a retainer on an undersized MMT is getting it centered. Wrap a motor with tape so it’s a snug slip fit in the MMT. Then put the motor inside the retainer to hold the retainer centered to the MMT. If necessary put a wrap of tape around the thrust ring on the motor also.



Steve Shannon
 
what keeps this Estes motor from shooting out the topside (through the nose cone) during the launch? There's no thrust ring on these single use black powder motors
. motor.JPG
 
Make your own thrust ring by applying several wraps of masking tape around the tail of the motor.

That’s How It’s Done. (tm)
How many inches of the motor tail do you wrap? It would seem to me that this tape wrapping could interfere with the aluminum motor retainer. There's not room on the tail to wrap more than say 1/8" if the retainer is still going to screw all the way in on the threads.

tape.JPG
 
I had planned to start with Estes D motors (black powder) with an 24-29mm adapter. However, on closer examination it would appear that the Estes adapter does not have a thrust ring. Do I need to tape these adapters as well?

adapter.JPG
 
what keeps this Estes motor from shooting out the topside (through the nose cone) during the launch? There's no thrust ring on these single use black powder motors
. View attachment 338961

Ahh, but there is a thrust ring on that motor. Someone has added a masking tape thrust ring on the right side of the motor. True Estes BP motors dont have thrust rings but they are very easy to add, I use masking tape making several wraps then use a Xacto knife to trim off the extra. Has worked every time for me over the last 35 years.
 
It would appear that the orange Estes adapters do have a thrust ring! I must have been looking at the "mini adapters" previously.

adapter.JPG

adapter.JPG
 
Some of the orange Estes adapters appear to have a thrust ring and some do not. Do folks "tape on" thrust rings to these adapter sometimes?

Yes. The 24/29 adapters have the molded plastic ring, visible on the 2nd picture you attached. The 13/18 and 18/24 adapters do not have that feature so tape is the substitute. It just works. But my guess is that Estes figured most of these would be used with Estes rockets with motor hooks. Just some wild speculation on my part as to why smaller adapters don't have the molded ring. :)

[edit] Aha! Answered your own question before I finished typing.
 
Yes. The 24/29 adapters have the molded plastic ring, visible on the 2nd picture you attached. The 13/18 and 18/24 adapters do not have that feature so tape is the substitute. It just works. But my guess is that Estes figured most of these would be used with Estes rockets with motor hooks. Just some wild speculation on my part as to why smaller adapters don't have the molded ring. :)

[edit] Aha! Answered your own question before I finished typing.
Yes, but still not sure that the estes 24/29 orange plastic adapter will work with the Aeropack 29mm metal retainer. Is it safe to assume that all these are a universal fit? I have not epoxied the retainer in yet, so if I have to switch to the estes plastic retainer, I can still do so (I will just include that with the order for the adapter). thankyou.
 
Definitely order a 29mm retainer, cuz you never know when you'll want one.
I see no reason the orange adapter wouldn't work with the aerotech system. 29mm motor size should be universal.

As far as tape wraps, I like to do one wrap ~1/4" wide at the end, then a 1/2" overwrap. The seam makes it catch in the motor tube quite nicely, and it can be cinched down by the retainer.
 
Yes, but still not sure that the estes 24/29 orange plastic adapter will work with the Aeropack 29mm metal retainer. Is it safe to assume that all these are a universal fit? I have not epoxied the retainer in yet, so if I have to switch to the estes plastic retainer, I can still do so (I will just include that with the order for the adapter). thankyou.

The Estes adapter will work with the Aeropack retainer.

20180220_083209.png20180220_083446.png20180220_083652.png

The other dimension of interest is the thickness of the ring (the difference between the diameter of the thrust ring and the motor body) The molded lip on the Estes adapter is about 0.7 mm thick. The thrust rings on AT single use motors are about 1.5 mm thick. The thrust ring on my Hobbyline case measures about 1.7mm from the body.

FWIW, I have seen fliers use friction fit mounting (just wrapping tape around the body of the motor until it fits tightly in the motor tube) or just taping the motor overhang to the exposed end of the motor tube, with loads up to H impulse. Personally, I've taped 24mm BP motors and AT 24mm and 29mm single-use motors in with good results. (Don't try it with a reloadable, though; never mind losing the case, it would be a bad day if the ejected case came down on somebody's head.)

As for the question about how snug the nosecone should be. You want it to come off when the ejection charge blows, but you don't want the pressure difference between the air in the tube (which will be at about the pressure at launch altitude) and the lower pressure at altitude to remove it prematurely.

To see if it is snug enough, the method that was recommend to me by an experienced flier; load the parachute, hold the rocket upside down, and shake it. The nosecone should stay on.

To see if it is too snug, for a rocket with a small internal volume, you could try the puff test; blow into the back of the motor tube (no motor installed) and check that you can get the nose cone off without blowing out a lung. Wait until the paint and adhesives are dry and cured before you try this (less chance of asphyxiation, or glueing a rocket to your face). This won't be the way you test rockets much larger than the Mozzie.
 
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