Madow Hawk MIM-23B Questions and assistance

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sheepdog

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Have built several Mid-Power rockets and this is my first Madcow, but I am some what bewildered on a couple of things
and I hope you fellow rocketeers can educate me a little bit here.

#1 - It requires me to determine the CG/CP and add weight accordingly to the nose cone. Why do the majority of
other mid-power kits come with these parameters already calculated and I can just build, load and launch? But this model
I need to calculate this?

#2 - I am not understanding the nose cone instructions, it mentions to load metal/shot then Epoxy, then add screw and cut off.
Hmmmmm this one has me dumbfounded.

Has anyone here built this bird? and can you lend some support, sounds like I am about to learn something new.


Thanks

Kevin
 
Basically all their kits are the same. My first Bat ray did a corkscrew and torn a fin and other damage. I thought the CG and CP were calculated as well or maybe I didn't read the instructions? I went back and added weight to my Scooter kit to be on the safe side.

Yes you need to calculate the CG and CP. If you have a program like ROCKSIM or OPEN ROCKET they do it for you.

As far as the nose weight. Once you figure out how much you need. I always try to keep the CG ahead of the CP by 1.3 - 1.5 then add the mixture of BB's and epoxy. Not sure if your kit has a bulk head but that's what they may mean by add screw and cut off? Cut off meaning part of the nose cone shoulder.

Others who have built this kit will chime in.
 
I haven't built this kit but I have built similar LOC and PML models that use the same techmiques. I'll try to answer your questions.

Madcow is not requiring you to calculate the CP (although it will be a good skill to have going forward) and they don't assume you have a simulator program. They give you the CG for stable flight on the first page of the instuctions (22.5 inches from the tip of the nose). Because of the tailcone and some rocketeers tendancy to "build heavy", it's possible that a given model will balance further back (towards the tail) than this which would result in an unstable flight. So they specify lead shot in the "additional materials needed" section and give instruction for one method to anchor it in tip of the nose cone.

"Insert the largest motor you intend to fly (or simulate the weight with an substitute). Ensure the CG is forward of the recommended CG. The CG is measured from the tip of the nose cone. If the CG is behind the specified point, add weight inside the nose cone by pouring lead shot into the nose cone tip and adding some epoxy. IMPORTANT: Screw in a screw through the plastic nose cone into the lead to hold it in place. Grind or cut off the screw head before filling and applying the nose cone finish. The epoxy will not stick to the inside of the nose cone and if you do not anchor with a screw, the liftoff force will cause the weight to become dislodged causing an unstable model."

Here are some videos that might help illustrate the step:

John Coker is making several mods but the nose weight part starts at about 2:00 to 8:00 is the important parts:

[video=youtube;WDjgq0hfsgw]https://www.youtube.com/watch?v=WDjgq0hfsgw&feature=youtu.be[/video]



Tim Van Milligan from Apogee :

[video=youtube;A8bS6Dbdw9Y]https://www.youtube.com/watch?v=A8bS6Dbdw9Y#t=358[/video]


Both of these builders use cross pieces at the nose cone tip to anchor the weight where MadCow specifies a screw in the tip to provide some structure for the epoxy to grab.


Many mid and high power rockets use a plywood bulkhead glued into the nose cone shoulder. A design and strength consideration I guess.

Hope this helps.


<edit> The sim file for this model is available on the Madcow site: https://www.madcowrocketry.com/2-6-army-hawk-mim-23b/
Click on 'Product Description' and page down. :)
 
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I think that the least amount of nose weight I've used was for my super batray(used a big eye bolt), did the screws to hold the ballast with the patriot, bamboo skewers for the rest. it works better if you add the shot/bb's to the epoxy, then pour the mix into the nose, this helps to eliminate air pockets.
Rex
 
I would get some expanding foam to hold your BBs/epoxy mixture in the nosecone. It has worked for me without any shifting.
 
Hi Sam,

Holly crap, Thanks for the info, still somewhat confused on where I screw the screw into and then cut off the
head to make it flush. Instructions say nothing about drilling into the cone like Tim
did. Also when ever I mix my epoxy it does not pour like Tim's did, mine is usally thicker
and an applicator of some sort is needed.

Will go the Madcow website. Hopefully I can figure this out.....
 
Hi Sam,

Holly crap, Thanks for the info, still somewhat confused on where I screw the screw into and then cut off the
head to make it flush. Instructions say nothing about drilling into the cone like Tim
did. Also when ever I mix my epoxy it does not pour like Tim's did, mine is usally thicker
and an applicator of some sort is needed.

Will go the Madcow website. Hopefully I can figure this out.....

No worries Kevin, always something new to learn. I think the screw is used in a similar way as the skewers and rods that John and Tim use in the videos. Madcow instructions do leave a little to the imagination. The idea is you want some kind of structure at the tip to keep the shot and epoxy mixture from shaking loose over time. BTW, split shot from the Walmart fishing supply area is what I use.
The viscosity of epoxy varies from brand to brand and different formulas within brands. In general, the longer the "pot" life, the more "liquid" the epoxy; 5 minute is thicker than 30 minute is thicker than 60 minute... Also air temp affects the consistancy and cure time of epoxy. As you say, Keep Calm...
 
The big issue is that the plastic of the nosecone is such that epoxy doesn't stick to it well. So you need something to hold it in place.

MadCow' method is to run a screw into the weight and cut the head off and sand flush. Other drill holes and run a skewer for an anchor. Another option would be to use expanding foam to hold it in place.


Kirk
 
Here's how I just did my patriot nose cone today, can be applied to any cone..., I don't trust gluing to the cone either.

I doubled two 1/4" ply plates that fit forward of the shoulder of the cone(after cutting off the base of course) and drilled through the cone to secure the bulkhead to the cone with screws. I then mounted an eye bolt for recovery and a piece of allthread that goes all the way to the inside of the tip of the cone for adding weight. I can then thread washers or weights as needed, the recovery system is attached to the bulkhead/allthread and the cone is just along for the ride.

I also show how I modified the ply plate for the ebay madcow provides so it fits the 38mm missileworks sled...I just made one bulkhead for the bottom of the unit, and put four screws, two from the bottom and two from the top that fit into the holes in the sled, instead of using allthread...since I had the screws on hand. I simply slide the bulkhead upward so the screws go into the sled, and then tighten the nuts on the madcow provided allthread pieces to hold the ply tray and the missileworks sled in place.

Frank

Frank

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#1 - It requires me to determine the CG/CP and add weight accordingly to the nose cone. Why do the majority of
other mid-power kits come with these parameters already calculated and I can just build, load and launch? But this model
I need to calculate this?

It's something you should really do with every rocket. The safest way to do it is after the rocket is built, then you know exactly how heavy the rear end was built, and what motors are going to be used. Otherwise it's just guessing. Many rockets are designed to be very overstable, so you can get away with a wide variance in build techniques and it just eats into the stability. Since those rockets are overstable, there is plenty of room to eat into. When a rocket is going to need noseweight, it's best to balance it to the actual build weight.

There are many styles of building and flying. As you get up in size, you have more flight options, and less likelyhood that a "one size fits all" build plan is going to work. Instructions get vague to the point of being non-existant, and you rarely see two kits built the same way. You could build this kit as a simple mid-power, or you could change a few things up and fly it on I200W's.
 
I really want to thank everyone that has chimed in here. I am still learning but my number one priority
going forward based on feedback is to get Rocksim or open rocket and test each and every mid power
rocket I have built. So far the only issues I have had have been motor CATOs upon launch, or failed
seperation on my G-Force which from my research has always been an issue. So I guess I have been lucky.

Thanks again everyone for taking the time to respond....
 
For separation problems on the g-force, consider removing the cooling mesh (pull it out of the motor mount) and using a nomex. Mine's flown 4 times and separated fine, I would also check the coupler fit to make sure it's not too tight.
 
I really want to thank everyone that has chimed in here. I am still learning but my number one priority
going forward based on feedback is to get Rocksim or open rocket and test each and every mid power
rocket I have built. So far the only issues I have had have been motor CATOs upon launch, or failed
seperation on my G-Force which from my research has always been an issue. So I guess I have been lucky.

Thanks again everyone for taking the time to respond....

Sim software is a great resource, but not entirely needed. You should be able to get the CP online, or from the manufacturer.

The hawk's is listed here- https://www.rocketreviews.com/madcow-rocketry-hawk-mim-23a-7332.html

Then mark that spot on the rocket with a dot or decal. Always make sure the loaded center of gravity is one body diameter in front of that spot whenever you launch it. Fat stubby rockets can be less, but that's another discussion. When/if you get there, make another post and you'll get plenty of info on that phenomenon. (base drag adds to stability and you can go with .5 tube diameter, in short)
 
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