Look at the HED on that one!

[bill2654]

Thought I would post this not for the rocket itself, but for the HED. It was inspired by a rocket I saw at last years Airfest built by Jason Griffith. As soon as I saw Jasons my first thought was "wow that looks fast". It's not quite minimum diameter but almost. The airfraim is 2.5" thin wall FG and the fins are .096 G10. I wish I would have beveled them but didn't. Motor mount 54mm with a slimline retainer.
Nose cone is Mad Cow and I added a 6" coupler for the shoulder/av-bay and vent band. The first picture is Jason's rocket.
View attachment 309813

Last year at Airfest I learned a hard lesson about venting airframes. For years Ive gotten away with not putting vent holes in my airframes but this time I flew a kick ass motor and my rocket separated at very high speed and luckily, I got it all back. So now I put vent holes in all my airframes and in this case the nose cone is acting as an airframe for the main so it gets a vent hole also.


Next is the HED system. I mounted my RRC3 on one side of the sled and tethered it to my MW GPS/Tx on the other side. MissleWorks screw switches for each and a Nanotech 300Mah 2s 7.4v Lipo for each. The 3D printed sled I got from Dan Pattel here on the forum. I'm going with two air sensor holes in my av-bay vent band. They are lined up with each one of my screw switches for access with a screw driver. Then I'm using two 2-56 nylon shear pins for the nose cone and two for the airframe.

 

[bill2654]

Still have some sanding and filling to do before the final paint. Haven't decided on a color yet, hey Jason how 'bout yellow?
I assembled the entire motor mount outside the airframe. Then when I cut my fin slots I extended the cut all the way to the bottom of the airframe then slide the MM into the airframe. Glued the fins to the motor mount with JB weld and the fillits are Aeropoxy. With the JBweld at the motor mount and big beefy outer fillits, I don't think my fins are going any where. I just wish I would have beveled them.

The last pic is of one of the av-bay bulkheads. I just wanted to show the new lifting eye I came across on fleebay. They have to be the smallest profile of any eye bolt I have seen. I want something that wouldn't stick up real high as it's a tight fit in the NC. _ have 15' of 1/4" tubular Kevlar and a 42" X Form chute in the nose cone for the main. I'm thinking about using a drogue on this (I usually go without) but haven't decided on that yet. This rocket comes in at 54 ounces, that's loaded with all electronics and recovery. I got a K1103X for this rocket but I may need to add nose weight for that beast. Sim says I have less then 1/2 a caliber with that motor in it so I need to figure that out.

 

[Buckeye]

I'm going with two air sensor holes in my av-bay vent band.

Usually an odd number of sensor holes (1 or 3) is recommended to prevent any cancelling out of symmetric pressure fluctuations. It may be an obsolete rule of thumb from the early days of finicky altimeters, but I still follow it.

Nice build.

 

[Swissyhawk]

Do you have to protect the antenna from the charge or is that not really an issue?

 

[bill2654]

Usually an odd number of sensor holes (1 or 3) is recommended to prevent any cancelling out of symmetric pressure fluctuations. It may be an obsolete rule of thumb from the early days of finicky altimeters, but I still follow it.

Nice build.

Thanks and yes this is my first time to go with two. I have them at 180 degrees from each other. I was thinking of another hole on the altimeter side of the sled but I don't know. I know of a guy that just uses one big one. I'll see how it does on it's shake down flights.

 

[bill2654]

Do you have to protect the antenna from the charge or is that not really an issue?

On all my previous HED flights I put my deployment charge in the tip of the nose cone. I got the idea from Jason who explained to me that he
wanted to make sure his laundry got ejected out of the nose cone instead of blasted further up in the NC. For my main ejection charge I use a finger tip from a latex glove and 1/2 gram
of BP wrapped a bit of masking tape. Put that in the very tip of the NC, a pinch of dog barf and then my Kevlar shock cord and then my chute burrito.

 

[ksaves2]

Question: Why not have the antenna face aft so it's in free air at apogee? Gives one their best chance of receiving information after deployment. There may be attenuation of the signal with the black nosecone even though it is not carbon fiber.
The carbon black used for coloring may have an effect on propagation. The Missileworks though puts out 250Mw Rf so that is on your side as far as blasting through the nosecone. I'm sure you do a range check before flying so that helps determine
the installation will work when flown.

As far as protecting the antenna from the charge, get a cardboard tube and slip fit it loosely over your antenna. Once the charge blows it will protect the antenna from the flash and who cares if the cardboard tube protector falls off?
Just get/make another one and consider it a consumable. I bet is will protect against the momentary heat flash and your antenna will be fine and last longer.

Addendum: I see you mention the charge is in the tip of the nosecone so perhaps the antenna is protected by the laundry. Kurt

 

[FerdBerful]

Sorry if this is a stupid question, but ...

What's a "HED system" (what does HED stand for?)

 

[rharshberger]

Sorry if this is a stupid question, but ...

What's a "HED system" (what does HED stand for?)

Head End Deployment. The main chute deploys from the nosecone.

 

[CzTeacherMan]

Head End Deployment. The main chute deploys from the nosecone.

Pioneered by Crazy Jim with the introduction of the Wildman Punisher.
...
Might have been done by others on scratch builds, but, to my knowledge, that was the first stock kit to feature HED.

 

[GRIFFIN]

Actually, it was really first brought out of Wildman's Area 51 from Greg Muri. CJ just spiced it up and added the switch band.

 

[GRIFFIN]

BTW,

I'm working on my replacement of this same rocket. My blue one never came down at Airfest. They kept saying all day long "we've never left one up there yet".......till mine.

Props to Mr. Justin Farrand for starting my build with some perfectly straight fins.

With most of my time getting ready to move, I hope to have the 2.0 BlackStar ready for Airfest 2017

 

[GRIFFIN]

BTW, who's this Jason GRIFFITH you speak of?

 

[mrwalsh85]

BTW, who's this Jason GRIFFITH you speak of?

Not you. :dark: