M to N Two-Stager

[Andrej]

Here is a video of a two-stage rocket I flew last week. It's an all aluminum rocket flying M motor in the booster and N in the sustainer. Both motors are 100mm in diameter. Booster motor geometry is a 6-point star and the propellant is catalyzed with Ferrocene for fast burn rate. Sustainer motor is a simple core burner with a slow (10 second) burn. Both propellant grains are monolithic and case bonded. Sustainer motor igniter is a wire mesh basket loaded with B/KNO3 ignition pellets. Both sets of fins were canted 0,5° which gave a roll rate of about 300rpm at sustainer burnout. Flight went well until shortly after sustainer burnout, when the telemetry was lost. Exact cause of failure could not be determined, since no sustainer hardware was recovered.

 

[FredA]

Nice project! Too bad you didn't find the sustainer.
Thanks for posting.
That sustainer motor must have been really progressive - what was the ignition and burnout pressure targets?

 

[Andrej]

This motor is somewhat erosive at start due to high L/D ratio, so at the beggining the pressure is about 50bars (multiply by 14,5 to get psi), then it decreases to 35bars, before it steadily ramps up to 70bar.

 

[Rocket501]

Very nice! However, do you know if the motor did fully burn out before the telemetry was lost? Otherwise, it is possibly that you could have had a motor cato near the end of the motor's burn. Motors spinning that fast tend to have a higher burn rate than they will when ground tested, which could have possibly resulted in a motor failure.

I have some more questions as well. What sort of telemetry were you using? What was the predicted max altitude and velocity?

What sort of insulator did you use? Spin-cast EPDM?

Finally, do you have any build pictures or additional information on the fin system?

All in all, I am very impressed by your work and hope your next flight goes even better!

 

[Kip_Daugirdas]

@Andrej that was awesome! Thanks for sharing, I’m sorry you lost the sustainer - beautiful rocket. You are doing great work out there!

I have read that spin rates for our small diameter rockets need to be exceedingly high - on the order of 15-20 rotations per second similar to the Arcas roll rate. I know pitch roll coupling can otherwise become a problem with spinning too slow. I’m guessing many other factors come into play here like CP/CG location and fin size (the Arcas fins are pretty small). Anyways all these factors dissuaded me from trying to spin my rockets.

Good on you for trying it! I wish you had some data from the sustainer.

 

[Andrej]

Very nice! However, do you know if the motor did fully burn out before the telemetry was lost? Otherwise, it is possibly that you could have had a motor cato near the end of the motor's burn. Motors spinning that fast tend to have a higher burn rate than they will when ground tested, which could have possibly resulted in a motor failure.

I have some more questions as well. What sort of telemetry were you using? What was the predicted max altitude and velocity?

What sort of insulator did you use? Spin-cast EPDM?

Finally, do you have any build pictures or additional information on the fin system?

All in all, I am very impressed by your work and hope your next flight goes even better!

Yes, from the limited data that is available it seems that signal was lost about a second after burnout. Spinning does increase the burn rate, but nowhere near enough to produce so radical increase in chamber pressure. Casing is strong enough to handle twice the maximum expected operating pressure.
TeleMega from Altus Metrum was used as primary flight computer. If everything would work as predicted altitude would be about 20km and max. velocity mach 3.
EPDM rubber sheet (1mm thick) was used for insulation. First inside surface of the casing was sanded with honing tool, thoroughly cleaned, then a single layer of rubber was bonded to it. After adhesive cured, surface of the rubber was primed and painted with a layer of HTPB/MDI (small roller was used for this). With HTPB still wet, the propellant was poured in, around the styrofoam core (made with a CNC hot-wire cutter). When the propellant was cured, styrofoam core was dissolved with acetone/xylene mix.

 

[Andrej]

@Andrej that was awesome! Thanks for sharing, I’m sorry you lost the sustainer - beautiful rocket. You are doing great work out there!

I have read that spin rates for our small diameter rockets need to be exceedingly high - on the order of 15-20 rotations per second similar to the Arcas roll rate. I know pitch roll coupling can otherwise become a problem with spinning too slow. I’m guessing many other factors come into play here like CP/CG location and fin size (the Arcas fins are pretty small). Anyways all these factors dissuaded me from trying to spin my rockets.

Good on you for trying it! I wish you had some data from the sustainer.

Hi Kip
Yeah, spin stabilization is definitely not easy. There are a lot of things you must get right. I'm thinking that for the next flight I will definitely have to use some kind of dynamic balancing equipment in order to precisely balance the payload section.
Just out of curiosity. Were you at BALLS last year with a Subaru and a small trailer with a launch rail? If you were, then we meet at the away cells. My rocket flew right after yours.

 

[Kip_Daugirdas]

Oh yeah good point on balancing. Are you going to try to spin faster or just rebalance and keep it at 300 rpm on the next try?

Yep that was me and my total disaster of a flight. I plan to be back with a project in 2022. Right now, I’m working on experimental motors (which is new to me) so it feels a bit like starting from scratch. So many static tests this year...I’m getting tired of driving out to the desert to test!

 

[blackjack2564]

I have been spin stabilizing for awhile also. Building full scale Sparrow-Arcus.
Only sustainer spins. .5 degree also..... fun getting jig for that alignment!
Flown 1/3 scale and 1/2 scale ready to fly.

I use the magnetometer feature on Telemaga to determine spin rate. Since the sensor for tilt control only is good for 2000 degrees or 5.5 rps before lockout [2000/360=5.5]

1/3 scale booster on 4g 54 to sustainer 5g 29 . At separation spun up to 33rps instantly.[no spin when attached to booster, just like the original]
You can follow green line to see how spins up right after separation. [slow roll from booster] then after coast really hammers at sustainer ignition. [low point of green velocity line.
Motor burn out 1.7 separation. coast 5 sec. sustainer ignition

I was concerned more about how fast it would spin at apogee with possibility of twisted, tangled deployment, even damage to telemetry antenna. May have been part of your problem
Don't want to use de-spin on big one, thats another story.

But as u see it was down to only 2.5 rps.
Just blow up graph as seen and count peaks or valley between any 1 second division to obtain.
Link to all data/pics about that flight:
https://www.rocketryforum.com/threa...s-2-stage-sounding-rocket.132380/post-1653058

Went 17,000 ft and lands 900 from pads on windy day at Argonia....spin keeps it straight and recovery close.....er.

 

[FredA]

Why does sustainer ignition make it spin?
The fins don't know the motor is lit.....
What retards the spin before ignition????
Something's weird with this story.

 

[TimothyG]

Why does sustainer ignition make it spin?
The fins don't know the motor is lit.....
What retards the spin before ignition????
Something's weird with this story.

Spins related to mass flow of air across fins. At sustainer ignition you start to increase this rate by increasing velocity. At least this is how im understanding this.

 

[jderimig]

Why does sustainer ignition make it spin?
The fins don't know the motor is lit.....
What retards the spin before ignition????
Something's weird with this story.

BJ said the spin started after separation. My money is on the bet that the stack had a net lower fin cant.

 

[blackjack2564]

Why does sustainer ignition make it spin?
The fins don't know the motor is lit.....
What retards the spin before ignition????
Something's weird with this story.

It spins upon separation, then increases spin upon ignition 5 seconds later.
Original Sparrow Arcus functions the same, by design.
Booster has large fins uncanted.
Rather than re-inventing the wheel, I copied what has proven successful.
It came about by mating surplus air to air missile fincan/motors to Arcus sounding rockets.

Booster has fast burn time, gets sustainer up to spin velocity quickly.
When doing my research, I thought the same as u.....but it works. lol

First test flight proof of concept,no motor in sustainer. Just one slow revolution prior to separation. U can see negative spike from separation charge. then immediate full spin. "in god we trust, all others bring data" lol




,

 

[blackjack2564]

By the way i used a hard flat surface, with fins hanging over the edge to balance the sustainer. When finished I could set rocket in any position relating to 360 degrees and it would not roll. I added 3/4lb powdered lead to NC to increase mass and lower chances of wobble. [flywheel effect, read that somewhere during my 1.5 yrs of research prior]

My major concern was such high rate of spin [33 rps] may cause twisted recovery gear inside before ejection. Careful packing and no space left over insured tight fit and no movement during flight. 3 successful flights on 1/3 scale and confidence larger versions will function correctly. See link above and go through the posts to see how I did it.
Enough about me....this thread is dedicated to OP's flight

 

[FredA]

First test flight proof of concept,no motor in sustainer. Just one slow revolution prior to separation. U can see negative spike from separation charge. then immediate full spin. "in god we trust, all others bring data" lol

Why isn't the spin velocity dependent???? Your DATA seems to indicate the spin rate is constant.
Spin should increase as the sustainer burns and the velocity increases and mass decreases.
Thinning air could account for some of this, but your data is TOO linear.

 

[blackjack2564]

It is V dependent.... go back to post 9 and look at the actual 2 stage flight graph.
That one in post 13 does NOT have a motor in sustainer and is an expanded view of just a few seconds.
Actual raw graph is just a blur, u must view it expanded a few seconds at a time to see what going on.
The whole point of my post was to possibly show the OP how to harvest data from his flight next time.
If U wish to continue the discussion go to thread linked, start at beginning read the whole thing and post questions there. thx.

 

[steveh.jae]

It spins upon separation, then increases spin upon ignition 5 seconds later.
Original Sparrow Arcus functions the same, by design.
Booster has large fins uncanted.
Rather than re-inventing the wheel, I copied what has proven successful.
It came about by mating surplus air to air missile fincan/motors to Arcus sounding rockets.

Booster has fast burn time, gets sustainer up to spin velocity quickly.
When doing my research, I thought the same as u.....but it works. lol

First test flight proof of concept,no motor in sustainer. Just one slow revolution prior to separation. U can see negative spike from separation charge. then immediate full spin. "in god we trust, all others bring data" lol

View attachment 435731


,

Does this relate to the Loki Super Dart also?

 

[blackjack2564]

No the launcher makes it spin at lift off,the whole stack is spinning.

Mine has large straight fins on booster, tiny canted fins on sustainer. Starts spin at separation/motor burn out of booster .
Just like the real one.