Two stage coast time

[Tbone]

Hi , I have two 2 stage rockets I am taking to XPRS.I am trying to decice on coast time. I was hoping some of you might look at some simulations and make comments regarding coast time. I am trying to get as much altitude possible but want to keep a straight flight.So here are the sim files to play with.Right now I have the heavier rocket set to coast 4.75seconds and the lighter rocket set to coast closer to 6.75 seconds.The lighter of the two rockets is the one I really want to push the limit on and am thinking 8 seconds coast time is what I really want on the lighter rocket if wind conditions permit.

The rocket names are "Carbon rocket" and "Painted rocket"
Both rockets are 100% scratch built carbon fiber ships. Dont let the names mislead you.
Trying to get imput from others that have launched two stage altitude ships.
Thanks , Terry

View attachment 4 inch 2 stage painted ship.rkt
View attachment 4 inch 2 stage with carbon.rkt

 

[TheAviator]

I'm only L1 certified, so I can't comment on something this big, but I have done delayed staging before. The key is to make sure that your rocket is still going at least 100fps (I would say 200fps to be safe) at staging. Make sure with the sims that you have the MEASURED weight and CG and make the program assume a Cd of .75. This will give you an underestimate of the performance to make sure that you don't boost the sustainer straight at the ground.

Best performance would be accomplished by accelerometric integration to find forward flight speed ONBOARD the rocket. When the rocket decelerated to 150fps or so, the computer would fire the upper stage. Unfortunately, I don't know of any flight computer that does this, so you either make it yourself or do your best guess on timing.

 

[bobkrech]

What did your sims predict?

Bob

 

[Adrian A]

I'm only L1 certified, so I can't comment on something this big, but I have done delayed staging before. The key is to make sure that your rocket is still going at least 100fps (I would say 200fps to be safe) at staging. Make sure with the sims that you have the MEASURED weight and CG and make the program assume a Cd of .75. This will give you an underestimate of the performance to make sure that you don't boost the sustainer straight at the ground.

Best performance would be accomplished by accelerometric integration to find forward flight speed ONBOARD the rocket. When the rocket decelerated to 150fps or so, the computer would fire the upper stage. Unfortunately, I don't know of any flight computer that does this, so you either make it yourself or do your best guess on timing.

The Parrot altimeter can be set up to ignite a sustainer when the altitude exceeds a user-defined value, the time is less than a user-defined value, and the pressure is decreasing. That way you can be sure that ignition won't happen unless the rocket is moving upward with close to predicted performance.

The Featherweight Raven altimeter (currently in beta test) also has deployment logic checks available for velocity < or > a user-defined threshold.

I'll be using both of these for a 3-stage, 38mm carbon flight at XPRS if I can pull everything together in time.

 

[highpowerrocket]

If you've input reasonable (slightly conservative if necessary) data into RockSim then it will give you good estimates of delay times versus performance. Remember that the longest delay time may not result in the highest peak altitude.

 

[quickburst]

My own preference, I'm not telling you how to fly your project.

Usually the safest bet is to light the sustainer just after burnout of the boster motor. I'm talking no more than a couple of seconds.

 

[Tbone]

Thanks for the input everyone.I realise this was a vague queston .

Below is how I have each rockets electronics set up right now :

Electronics on the heavier rocket Named "Phyllis" (35lbs empty)

- Booster to burn for 4.5sec
- Seperation to take place at 5 sec after lift off - When including time delay for gee switch of .25 sec [true seperation should be at "5.25 sec. after lift off ].(.75sec after booster burn out)
- Sustainer to ignite at 7 sec after lift off -When including time delay for gee switch of .25 and 2 sec for the sustainer to come up to pressure . [true sustainer ignition should be 9.25sec after lift off] .( this should allow 4.75-5sec. coast time)

Im going to allow more coast time on the lighter rocket to try to go for more altitude

Electronics on the lighter rocket named Gladys (30lbs empty)

- Booster to burn for 4.5 sec
- Seperation to take place at 5 sec. after lift off. When including time delay for gee switch of .25 secor [true seperation should be at 5.25sec. after lift off ] (.75 sec after booster burn out) .
- Sustainer to ignite at 9sec. after lift off. When including time delay for gee switchof .25sec and 2 seconds for sustainer to come to pressure[true sustainer ignition should be 11.25sec after lift off].(This should allow 6.75sec.of coast time)

Depending on how the weather is, I may try to add two more seconds coast time to the lighter rocket . What I really think I want is 8 seconds coast time.
Hopefully I layed these numbers out understandably so to here a little feed back. I want to let these babies coast but dont want to over do it. Ive been know to fly rockets horizontal

Oh ya , As far as electronics components , both rockets are set up the same but idependently
Booster : 1 rdas , one missile works rrc2 mini
Sustainer: 2 rdas units
Drogue : 2 -25gm Co2 cartrides
Nosecone : GPSFlight GPS system and Walston tracker
Booster : Walston Tracker

Velocity at Ignition wil be around 800fps

All these configurations will change depending on wind conditions.

Thanks ,Terry

 

[Tbone]

If I did this correctly , You should be able to "click on this picture" to see a bunch of mixed up build pics.If it doesnt work Ill try again. Im not the best at moving things around on computer
These are various pictures of different stages in the build of both rockets.Please let me no if it works
Terry

 

[Tbone]

The Parrot altimeter can be set up to ignite a sustainer when the altitude exceeds a user-defined value, the time is less than a user-defined value, and the pressure is decreasing. That way you can be sure that ignition won't happen unless the rocket is moving upward with close to predicted performance.

The Featherweight Raven altimeter (currently in beta test) also has deployment logic checks available for velocity < or > a user-defined threshold.

I'll be using both of these for a 3-stage, 38mm carbon flight at XPRS if I can pull everything together in time.

Adrian,
I think your Parrot would have been great for this attempt. By the time I learned of your product. I had already ordered all electronics.
Each rocket has 2-rdas in the sustainer, 1 rdas in the booster, 1 missile works rrc2mini in the booster, GPSflight GPS system in the nose. I will be trying out your product soon
Terry

 

[Tbone]

If you've input reasonable (slightly conservative if necessary) data into RockSim then it will give you good estimates of delay times versus performance. Remember that the longest delay time may not result in the highest peak altitude.

Hi,
I added a link to my rocksim files to see if some people might try to play around with simulations and add suggedtions. Im not sure if the link actually worked. It works on my end
Terry

 

[Tbone]

My own preference, I'm not telling you how to fly your project.

Usually the safest bet is to light the sustainer just after burnout of the boster motor. I'm talking no more than a couple of seconds.

Hi Dave ,
Usually I take the same approach but on these two flights Im going to try to pick a coast time that will allow for some extra altitude but not too long to the point it starts veering over. On a calm day I feel safe that these rockets will be able to coast for up to 8 seconds before actual take off of the sustainer.
Im shooting for an altitude of around 65000ft.with the heavier rocket and closer to 75000ft out of the lighter rocket.Or I may just come home with a couple piles of parts

 

[TheAviator]

Just a suggestions: do a range test on your Walston trackers. Carbon Fibre has a shielding effect on RF radiation, and can significantly attenuate the Walston's signals to the point where range is a small fraction of what it should be. If you find this to be the case, you will need to route the antennas outside the airframe for them to work.

 

[Tbone]

:Brian ,
Can you let me no if the link to a bunch of build pictures worked? If you click on the picture of the sheet of carbon material in an erlier post , the link should open.
As far as tracking devices. The booster has a Walston in it which is going to be tied to the recovery cord. So no I wont have good reception until the booster reaches apogee. I dont foresee a problem tracking the booster..
The sustainer will have a GPSflight GPS system in the fiberglass nose cone (no Carbon in the nose).The nosecone is made of a high temp epoxy and was post cured to 250degrees following a schedule. Then the nose was completely painted with contronics 500degree epoxy.
The nose will also have a Walston tracker in it so that when I am right on top of the rocket coordinates from the gps and still dont see the rocket, I will be able to do a quick track and load it up and take it home . I hope,
Terry

 

[gregzo]

Terry, beautiful work. I was wondering if you could describe how you are coupling the booster to the sustainer and how the two will be separated?
Thanks
Greg

 

[gkieley]

I was wondering if you could describe how you are coupling the booster to the sustainer and how the two will be separated?
Thanks
Greg

I am curious about this too.... for short delays on the sustainer... does drag separation have enough time before burning :hot::hot::hot:the booster when the sustainer lights??

 

[gregzo]

It looks like you will be using a piston to separate the booster from the sustainer? Is this the plan?
Thanks for any info.
Greg

 

[sandmantoy]

Pictures worked