Madcow 4" fiberglass Super DX3 build thread

[Handeman]

to get the holes to line up perfectly every time, put the e-bay in the body tube and screw in all the shear pins to prevent the e-bay from moving.
dia. times dia. times length times 3.14 gives me 382.0752 cubic inches of air for the e-bay and 1/4" hole per 100 cubic inch. so I need 4 holes at 1/4"
since I'm drilling fiberglass and not want to just drill 1/4 inch hole I started with a smaller drill bit and worked my way up to the 1/4" drill bit

My first thought was that three 1/4" holes were too big for a av-bay on a 4" rocket. I realize you used the wrong formula for volume. Volume of a pipe is pi x R² x length (3.14 x 2 x 2 x length). A quick check would be a box that is 4" x 4" x 8" is only 128 cubic inches so a 4" dia. 8" long av-bay has to be less then that.

I actually like using the box dimensions to calculate the volume. It's a little more, but better having holes larger than needed then too small. I've heard the argument against too large of holes is to prevent wind gusts on the pad causing the altimeter to have a launch detect and firing the apogee charge. I guess that could happen, but I've never seen or heard of it.

Anyway, just wanted to get the formula right for the anyone following this. I have no doubt the 1/4" holes will work just fine.

 

[crossfire]

I was told many years ago by Tommy form Adept to never use a equal number of vent holes in av-bay. Use 1,3,or 5 holes. He says that you can avoid a cross wind from blowing though av-bay and setting off charges early. He has built altimeters for over 25 years so I think he knows what he is doing. I have followed his advice and never have had any problems.
GP

 

[Kehoes23]

My first thought was that three 1/4" holes were too big for a av-bay on a 4" rocket. I realize you used the wrong formula for volume. Volume of a pipe is pi x R² x length (3.14 x 2 x 2 x length). A quick check would be a box that is 4" x 4" x 8" is only 128 cubic inches so a 4" dia. 8" long av-bay has to be less then that.

I actually like using the box dimensions to calculate the volume. It's a little more, but better having holes larger than needed then too small. I've heard the argument against too large of holes is to prevent wind gusts on the pad causing the altimeter to have a launch detect and firing the apogee charge. I guess that could happen, but I've never seen or heard of it.


Anyway, just wanted to get the formula right for the anyone following this. I have no doubt the 1/4" holes will work just fine.

The formula that I used was from the instruction books that came with the altimiter, it looks like that I goofed up on the math

 

[kandsrockets]

Go here https://www.kandsrockets.com/tech.htm and download the VCT toolkit. It has a port sizing section that all you do input your e-bay size and it figures out your port size. It has a lot of other useful stuff too.

 

[stickershock23]

Kehoe, They are right you really should go with an odd number of vent holes.

It sounds crazy but 1 3 5 is best. I believe it has something to do with the way air flows through the tube. having two directly across from each other allows for odd readings to the alt. odd ones MAKE the pressure equalize across the tube and give you a better reading.

I also agree the 1/4" holes might be a little big. you could go down to 1/8" if you wanted to and be fine.

I think you already drilled them so I would not WORRY about them being to big. its not a huge problem but in the future just enough to equalize the pressure in the tube!

 

[Kehoes23]

Thanks for the advice guys

 

[Kehoes23]

Since my DX3 build is on hiatus for now, I went back to finish my Mega Der Red Max, I need to paint and throw on the decals. What would be the best way put on the big body wrap, it's a water slide decal and don't want to rip it when putting it on, I have never worked on such a big water decal before, any advice would be appreciated.

 

[Kehoes23]

this is the first coat of red going on the red max

 

[Kehoes23]

this is after 3 coats of paint, I'll let this cure for a few days in the heater room then I'll wet sand and put on a few more coats

 

[Kehoes23]

Just got word from Perfect Flight, they said with over sized port holes, I'll just get lots of "noise" on the flight curve data, and as for early or accidental ejection of the drogue chute they said no, so for now the port holes are not an issue for the strattologger, I'm still waiting to hear back from Missile Works about the RRC2 mini:wink:

 

[Kehoes23]

I had some time to work on the nos cone, I sanded with 120 grit, all the marks on the nose cone is for the pits, which would make it easy for me to fill in with bondo later. I also order aeropoxy so I can get the build back on track.

 

[Kehoes23]

I just got word from missile works, they said the 3 1/4" static holes should be no issue, they told me to set the Mach inhibitor, so it looks like the holes will not pose an issue. On a different build, the water slide decals that came with the Estes mega der red max are junk, next time I'll just order from sticker shock.

 

[Windeavor]

You mentioned earlier that your getting some Aeropoxy. If you decide to resize the holes smaller, stick a strip of electrical tape on the inside of the hole and fill the hole with Aeropoxy. Once epoxy has setup, repeat on the next hole. Sand Aeropoxy flush when it's fully cured and drill new smaller vent hole right in the middle of the old holes.

 

[Kehoes23]

You mentioned earlier that your getting some Aeropoxy. If you decide to resize the holes smaller, stick a strip of electrical tape on the inside of the hole and fill the hole with Aeropoxy. Once epoxy has setup, repeat on the next hole. Sand Aeropoxy flush when it's fully cured and drill new smaller vent hole right in the middle of the old holes.

I was thinking of doing just that and leave one 1/4" hole for altimiter switch and static port.
I also got word from both manufactures of the altimiters that I plan on using that the hole size will have no effect on early deployment of drogue or main parachute, just noise on the flight data.

 

[Kehoes23]

I'm using the RRC2 mini altimiter as a back up for the DX3, I do expect the rocket to go over Mach and plan on using the new K456DM motor, how long should I set the Mach inhibitor for? It can be set in one second increments

 

[Kehoes23]

Just got done ordering the motor retainer for the DX3 from aeropack, and I'm having the retainer engraved for the theam of the rocket, I also have aeropoxy on order as well, once I get them then my DX3 build can get back on track.

 

[csoechtig]

The 4" FG Super DX3 is an awesome flyer! Are you planning to add nose weight? I can't remember the exact analysis, but when I ran the SIMs, it looked like it would require a significant amount. I went a different route and ordered a 20" FG extension along with a FG coupler. It was an extra $60, but i was really happy with the results.

My first flight was on a J540R to 3,200 ft

My next flight was on a K550W to 5,004 ft





It literally came down 50 yards in front of my set up...



Next Saturday (weather permitting), I am putting it up on a K700W. O.R. predicts 6,993 ft. I'm hoping it will stretch another 7ft to reach 7,000

 

[Kehoes23]

I made the bulkhead removable, so if I need to I can add weight to the nose cone.
5004' on a K550? How much extra weight did the extended payload put on the Dx3?, how much does it weigh at the pad?
Curious that the K550 didn't take it higher.
That is a nice rocket, and if you were doing spot landing, you would win,50 yards from the pad, that's awesome

 

[csoechtig]

I made the bulkhead removable, so if I need to I can add weight to the nose cone.
5004' on a K550? How much extra weight did the extended payload put on the Dx3?, how much does it weigh at the pad?
Curious that the K550 didn't take it higher.
That is a nice rocket, and if you were doing spot landing, you would win,50 yards from the pad, that's awesome

I'm not sure exactly how much the extension and coupler weigh, but the entire rocket weighed about 15.5 lbs on the pad with a K550W. It was just under 15 lbs with the J540R.

As you know, G10 material is heavy. In fact, the FG MMT and Fins create substantial aft-end weight. With the relatively small fins on the DX3, it is a very different calibration than the cardboard/plywood version.

 

[Kehoes23]

So, I'm still waiting for the aeropoxy to be delivered, it's been almost 2 weeks, hopefully it will get here soon.
Did some more work on the nose cone, decided to use bondo spot putty, this stuff is to difficult to work with.
Pros: did not find any while using this stuff
Cons: this stuff smells horrible, even when using it outside, it has a 2 min. Pot life, had to make several batches due to pot life, very hard to work with.
I'll just stick with JB weld as my filler, long pot life, no smell and easy to work with. I'll post some pick when I get a chance.

 

[Kehoes23]

this was when I used bondo, this stuff smells horible and is hard to work with, I'll just stick with JB Weld as my filler.

 

[Kehoes23]

this was waiting for me when I got home, the rocket biuld can comence.

 

[rocketgeek101]

The 4" FG Super DX3 is an awesome flyer! Are you planning to add nose weight? I can't remember the exact analysis, but when I ran the SIMs, it looked like it would require a significant amount. I went a different route and ordered a 20" FG extension along with a FG coupler. It was an extra $60, but i was really happy with the results.

My first flight was on a J540R to 3,200 ft

My next flight was on a K550W to 5,004 ft

View attachment 117243

View attachment 117244

It literally came down 50 yards in front of my set up...

View attachment 117245

Next Saturday (weather permitting), I am putting it up on a K700W. O.R. predicts 6,993 ft. I'm hoping it will stretch another 7ft to reach 7,000

Nice looking bird you got there! I really like that paint scheme.

 

[new2hpr]

4-40 shear pins seem kind of overkill for just a 4" rocket. 2-56's would hold it fine. You're going to need a pretty hefty charge to blow them, relative to the #2's.

Otherwise, looking great!
-Ken

View attachment 113470View attachment 113471
here I use tape to hold the nose cone on the airframe, then I drilled all three holes for the 4-40 shear pins, the second photo shows the inside the nose cone, i glued in 4-40 T nuts so the shear pins can screw in to.

 

[Kehoes23]

got the MMT sanded and CR as well, I made a mark where I want the forward CR, then wraped the MMT with tape to hold the CR level and in place then tac the CR to the MMT with CA glue, I will add fillets later

 

[Kehoes23]

got the aeropac retainer with flange, I did get the retainer laser engraved, I will post pics of it when the rocket is done, has paint and decals.
I still have to drill out the holes and tap for the screws.

 

[Kehoes23]

4-40 shear pins seem kind of overkill for just a 4" rocket. 2-56's would hold it fine. You're going to need a pretty hefty charge to blow them, relative to the #2's.

Otherwise, looking great!
-Ken

thanks. I do not have a drill bit small enough for the 2-56, or money to buy one, but I do have the tools for the 4-40, I will ground test to see how much BP I will need, the space that has to be presserized is about 4"X13", so I'm thinking around 1.5 grams to start with and work from there.

 

[Kehoes23]

I'm using a 6-32 tap to thread the CR

 

[Kehoes23]

I'm using aeropoxy for the first time, its alot thicker then I thought it would be, which make it easy to work with, the fillets are done on the forward CR

 

[Kehoes23]

Got some work done on the DX3, got the motor mount epoxied in and the T nut for the aft rail button.
I also order a up scale of the Estes Ram Jet from KandS rockets, not to mention this is my all time favorite rocket kit.