Rocksim file changes: Hydra VII

[gary7]

I am interested in increasing the length of only the main MMT in the Hydra VII (or the only MMT in the Hydra One) so that it protrudes into the main body air frame. Right now, the main air frame just sits on top of the cluster of MMTs. By increasing the length of the main MMT, one could place centering rings around it and within the main air frame tube, making the rocket much, much stronger. I have what I consider a very interesting idea with this rocket but need to make this change and need your help to do so. I can not get my idea to work in Rocksim.

[DanFrank]

When I built my Hydre 7, I thought about doing the same thing; this is a very good idea. Not only for added strength like you said but it would seal off all the tubes so ejection gases don't escape and not pop out the parachute. This is probably the biggest problem people have with this model, not making an airtight seal at this junction. Bad design in my opinion. All that would be needed is about 2-3 inches more on the main tube and one cr2060 centering ring. Not too expensive.
Daniel

[DanFrank]

Oops! I didn't answer your question. I have no idea about Rocsim but all that you would have to do is get a bit of BT20 coupler and extend the main body tube by 2-3 inches. If you are questioning the stability, don't worry about it, this addition is so far ahead of the fins that stability won't be affected. You will only be adding maybe .25 to .5 ounce to the rocket, way ahead of CG; CP will not be affected.
Hope this helps...
Daniel

[mack]

Has anyone tried something like what Daniel suggested? I too, have a Hydra VII that I haven't started building yet because I am not sure about the strength of this connection.

[DanFrank]

The strength of this connection on mine is good, but I did use epoxy and I applied fillets around all the "nose cone halves".
The 2 problems I saw at this connection are sealing it good so ejection gasses don't escape, and making sure that the BT60 is perfectly vertical and not attached at a slant.
Daniel

[gary7]

I could never get the central MMT to extend into the main air frame using Rocksim. So, I just added one in the main frame. This will at least help with Rocksim with regards to having it in there for weight, CP and CG calculations etc. But I definately plan to put the long tube in with two centering rings. That way, there will be no doubt that the main tube is straight and secure.

[KerryQuinn]

I would strongly recommend mods to improve the parachute blow portion of this rocket. I've built it twice: each time my first flight (both times on 7xC6-7s) each time I got all 7 engines to light (thanks to Q2G2 igniters which I also strongly recommend for this rocket) - both times all seven engines were fully retained for the entire flight up - including both (scary) ballistic returns after failing to blow off the nose cone. The rocket comes in with a whistling sound that can be heard at several hundred yards. Neither nose cone fit seemed over-tight (If anything the second one was loose). I only had the center and one of the side motor tube top ends open - the others were blocked.

I strongly suspect that I did not have a good airtight seal around the 6-half-nose cone-joint on the first flight. Not sure what happened on the second flight. I was suspicious that the volume of the rocket was just too large for the ejection charges to build up pressure (my 2nd version was a lengthened main body tube version of the stock design which may not have helped - I think that having a much longer center tube would help - by reducing the total volume inside the rocket rather than structurally. - I'm not sure that this rocket has a true structural difficiency.

-Kerry

(eventhough the flights ended poorly - it was REALLY fun to see it take off on 7 engines !)