Ok, another version of the bertha cam - DUAL STAGE!

[pinter75]

Hi,

Ok, now that I have successfully done normal images, video - it is time to try video with a twist. That twist is a new dual stage booster! This should get some cool video of the stages seperating in flight.

A question for all you dual stage pros.

Here is my current setup. The two stages form 1 fin area when together.

The motors currently a D12-0 and D12-3 are butted together. I need to know if I should:

A). Just butt the two stages together and hope for a good airstart.

B). Put some pressure vent holes to dissapate any pressure buildup that will result in the 1st stage seperating before the 2nd has ignited - bye bye camera!

C). Take out the 1st stages motor retention, tape the 2 motors together and insert with tape around them - like the Commanche 3.

There is a very small area that will fill up with hot gasses from the 1st stage, so a pressure pop before 2nd stage ignition is a possibility. Also when I say the motors are butted together, there is about 5mm sealed gap due to the 1st stages motor retention.

Hope I make sense - I wanna go and fly this later - just need to sort out this problem.

Thanks

Steve.

 

[Ryan S.]

I would definantly drill vent holes. Otherwise, as you stated the stages will seperate prematurely.

I dont butt my motors up agianst one another but leave a little space. I think butting them can also cause a premature seperation

 

[pinter75]

Thanks Ryan,

I do have 5mm space, I take it that is too little? I think I'll go the vent hole way, How big do vent holes have to be - plus will I need 2 (on opposing sides) or 4? The tube is 40mm.

Steve.

 

[Stymye]

..thats the reason for the wrap of celophane tape

.the tape holds the motors together long enough for the second motor to ignite, before it burns thru the tape

vent holes are for gap staging

 

[Stymye]

... The Handbook of model rocketry covers staging in detail...and than some.

 

[pinter75]

Read the whole chapter of the said book, but it still leaves the question open somewhat - tape 'em or de-pressurise the tube untill 2nd stage ignition.

I think I'll now go the cellophane route as this will ensure the second stage has ignited before the 1st stage has popped off. As the motors are butting together seperated by 5mm of closed space (the motor retention) - my guess is the pressure of the 1st stage gasses will push them apart before the 2nd stage starts. The vent holes will be nearly useless, as in order to vent pressure the motors will have to have speperated. Chances are they ain't gonna seperate a few mm, to vent - they are gonna seperate full stop!

The reason for my asking is that I have flown both a commanche3 (taped) - and a quest navaho agm (no vent holes) - both with successfull air starts. I just was interested to know what solution to apply to my home brew dual stager.

If it works the video will be here Any body seen a video camera looking down as the stages seperate in-flight?

Steve.

 

[cydermaster]

I've never flown a 2-stager (yet!), but from what Stine and others, say; a bit of Sellotape would be the answer.

I'm dying to see the results, Steve!

 

[sandman]

My take on second stage ignition is this.

Nozzle opening is probably the most critical aspect of upper stage ignition.

A D12 has a really nice big nozzle opening and so accepts the burning chunks of fuel from the first stage "break thru" much more redily than say a C6 nozzle.

So...in theory...a D12-0 to D12 stageing is much more reliable than a D12-0 to C6 stageing.

I don't really think you need to worry so much about it. As long as the stages are tight enough to hold the motors together long enough for ignition, you should be just fine.

I would use a D12-5 for the upper stage though.

Go for it!

sandman

 

[pinter75]

I am gonna go for it I am down to one D12-0 and one D12-3 in my supply box, but the weather has cleared so I am going to go and squeeze off a launch

I'll let you guys know what happens.

BTW here are some toatally amazing videos of some HPR's carrying DV cameras - not the little pencams I fly but expensive camcorders!

https://www.gbrocketry.com/movie_theater.htm

Steve.

 

[rkt2k1]

Steve,

Tape the two engines together with a little cellophane tape. Also to reduce the charring on the inside of the booster. Make some paper liners for the booster. Place a new liner in for each flight. This helps reduce any charring damage to the inside of the booster tube during ignition and seperation of the upper stage.

Good luck! Rocket looks great! Post a link to the video coverage if you can.

 

[Ryan S.]

cool videos here too

https://www.vahpr.com/Ts/ts47.html


if you go here

https://www.vahpr.com/gv.html

scrole all the way down and click three frames up on "onboard" this one is awsome because it shows flight data as it happens

 

[pinter75]

Ok,

Went out and flew this new creation, The stages were taped together and worked a treat, there is one problem tho'. I have LOST camera stage! The 2 boosters came back fine, it looks as though the chute failed on the camera stage as we saw it drifting back down... I looked for a while but gave up :-(

I suppose it is back to ebay to get a new camera and start building again.

Steve.

 

[cydermaster]

Originally posted by pinter75
I suppose it is back to ebay to get a new camera and start building again.

10/10 for attitude!

Keep at it Steve ..... you're on to a winner here! (+ its British ! )

 

[pinter75]

Thanks,

I suppose now I can get a 1.3 megapixel camera, and not do dual stages in the wind again! I may go and have an other look for it soon, but I think it is lost :-(

I will also fit a LOUD piezo beacon!

Steve.

 

[sandman]

Steve,

Go back out there tomorrow...I realize it's midnight there now.

Look again...you will be suprised when looking for a rocket...leave...come back and start looking from a different perspective, like the next day.

Suddenly...there it is!

How did it get there?

You'll find it

sandman

 

[sandman]

Get one of those cheap personal alarms.

They work really well.

And don't forget to put your name and address on it!

sandman

 

[pinter75]

Hi,

The problem is I am off on vacation for 4 days! I just had to get one off before i went

I will go back there when I return, but chances don't look too good. There is one place I need to look, the area under where the ejection charge went off. I think the ejection charge must have shredded the chute's kevlar cord (chute fell but not recovered) and the camera unit fell straight down. Hopefully it was unstable and tumbled down.

Failing that the project returned excellent still and video images and will probably rest in pieces

Don't worry as a new 1.3mp pencam is bidded on ebay The Bertha cam will return with vengance. Maybe I'll send it up to take arial photos of the search area

I have a loud PIEZO alarm ready built.

Steve.

 

[gerbs4me]

cool looking rocket
very nice job too
where did you get that pencam?