Rockoon to 100km

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I don't think you will get much spin from canted fins launching at that altitude. There simply isn't enough air to exert the necessary force, unless your fins are huge and/or heavily canted, both of which will rob altitude.

saadzmirza said:
Yep... Hopefully will have an APRS beacon for recovery, no waiver (Class 1 and following 101.D balloons), spin stabilization with fin cant, insulated avbay, nozzle with enlarged exit cone for 25:1 pressure ratio (0.01 atm), Magnelite igniters for vacuum, and a little plug in the bottom of the motor nozzle to keep it pressurized, maybe clay or cork.
For recovery thinking confined BP charge.
Click to expand...
 
Boosted dart does not make any sense if you are launching it from a rockoon. All the benefits of a boosted dart are lost launching that high up!
 
saadzmirza said:
Yep... Hopefully will have an APRS beacon for recovery, no waiver (Class 1 and following 101.D balloons), spin stabilization with fin cant, insulated avbay, nozzle with enlarged exit cone for 25:1 pressure ratio (0.01 atm), Magnelite igniters for vacuum, and a little plug in the bottom of the motor nozzle to keep it pressurized, maybe clay or cork.
For recovery thinking confined BP charge.
Click to expand...

where are you flying? I'm thinking 100 miles should be a safe distance.....maybe...........
This project is way, way over your heads. I think the FAA would be interested in your little project, even though it's class I. Read ALL of 14 CFR 101.23. Anything like that falls under "Does not create a hazard to persons, property, or other aircraft" Once you hit where the zulu pathways are in your area, you are a hazard especially since you are launching from a balloon.
Further, 101.7 demands " No person may operate any moored balloon, kite, amateur rocket, or unmanned free balloon in a manner that creates a hazard to other persons,
or their property.
(a) No person may operate any

There's no way you can do this without a chat with our friends at the FAA.

THEY will ask you why you feel qualified to pull this off. Personally, I can think of some folk who could do this (or at least be qualified to try), but they are ALL VERY experienced level 3 flyers

This, in my humble opinion, is a failure of your mentor/advisor to reign this in to something that is safe and that you are qualified to do.

You guys sound like smart people but that's not what qualifies you to do this project. Your lack of capacity to take advice from those with WAY more experience proves that you are light years from being qualified. Gotta walk before you run.
 
saadzmirza said:
What are the benefits of a boosted dart? I thought it was mostly the mass loss, and also drag reduction...
Click to expand...

Mass loss works against you, which is why the dart is built to be extremely heavy. The basic premise of a boosted dart is to use a large motor to impart a tremendous amount of kinetic energy into a small, dense, aerodynamic second stage that coasts to apogee. The reason it wouldn't be as efficient at altitude is because the air density is reduced to the point where drag is less of a factor. Also, the dart stage of a G/H powered rocket would need to be very small in order to get much of an increase in performance over a minimum diameter single stage.
 
Thank you for your thoughtful response. We'll have to look into more research on boosted darts; you're probably right, it might be pointless.
 
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Lugs:
You can have a pop lug, since you're doing 2 stage in a much thinner atmosphere, having 45 degree angle cut lugs (trapezoid shaped) or wire arches (like the ones on a paper clip) on the booster should be sufficient and more reliable. That or you can get or make a pop lug.
If you are worried about rod flexing, use a launch rail. There are different sizes, but since I'm not familiar with the conditions at launch altitude, I won't try to recommend anything. With rails, there are rail buttons, rail guides, and pop guides, which are like pop lugs but for a launch rail.
Commercial pop lug:
https://www.fliskits.com/products/components/misc.htm
(listed as PL001, Competition 2inch pop lug)

Weight:
If you into getting every tenth of a gram squeezed out, custom fiberglass tubes are the way to go. The problem is fragility comes with thin walls, and thin walls come from light tubes. Also, get the electronics and electronics bay light, no threaded steel rods, for example. Shroudlines are heavy. Most chute material is heavy. 1/4 mil Mylar and lots of sewing thread would work in theory, but would problably break in practice. Although the air could be thin enough that there isn't much drag from the drouge chute and the rocket slows down much more gently. Fillets are heavy, paint is heavy, etc.

Spinning:
Spinning up the rocket to a certain rate should produce roughly the same drag at different altitudes. What changes is the angle or size of the fins. Think about it this way: To spin up the rocket, you need passing air to impart its energy into the side of the fin. The energy pushing the fin sideways depends on how much air hits it, if the speed is constant. So by increasing the fin area or canting the fin to catch the same amount of air should mean that the same amount of air is also pulling it back, e.g. Drag.

I missed something, right? Mindsim can't do Navier Stokes, Mindsim can't calculate wake currents, Mindsim can't even solve algebra well.


Are you defining Mach as Mach at altitude or Mach at ground level?

You'll need a small hole in each section of the rocket somair pressure won't pop the tubes apart.

If if you have any questions, post them and I will make sure to take a guess and present it as fact. Make sure to check everything I tell you, since I'm not perfect and I'm not paying you if the rocket fails resulting from my data. Think of it as a research lead, or something similar.
 
well, guess they show inexperience here again.
People who are serious about altitude don't use lugs or rail buttons because both are just drag and we know what that causes, right??

further, fins designed to spin the rocket also decreases the efficacy of the rocket to convert fuel into upward motion....that darn drag again.

So, why not peruse some of the books as to how to build a real altitude seeker?????

p.s. I'll give you a hint, length matters....
 
saadzmirza said:
Uh oh! Any suggestions? I really want to avoid spinning up a launch pad...
Openrocket says it will spin... but I question its accuracy over your experience. but, there should be SOME airflow by the time it hits Mach 3.5
Click to expand...

Why do we have these [folks] frequenting this forum?
 
Last edited by a moderator:
Incongruent said:
Lugs:
You can have a pop lug, since you're doing 2 stage in a much thinner atmosphere, having 45 degree angle cut lugs (trapezoid shaped) or wire arches (like the ones on a paper clip) on the booster should be sufficient and more reliable. That or you can get or make a pop lug.
If you are worried about rod flexing, use a launch rail. There are different sizes, but since I'm not familiar with the conditions at launch altitude, I won't try to recommend anything. With rails, there are rail buttons, rail guides, and pop guides, which are like pop lugs but for a launch rail.
Commercial pop lug:
https://www.fliskits.com/products/components/misc.htm
(listed as PL001, Competition 2inch pop lug)

Weight:
If you into getting every tenth of a gram squeezed out, custom fiberglass tubes are the way to go. The problem is fragility comes with thin walls, and thin walls come from light tubes. Also, get the electronics and electronics bay light, no threaded steel rods, for example. Shroudlines are heavy. Most chute material is heavy. 1/4 mil Mylar and lots of sewing thread would work in theory, but would problably break in practice. Although the air could be thin enough that there isn't much drag from the drouge chute and the rocket slows down much more gently. Fillets are heavy, paint is heavy, etc.

Spinning:
Spinning up the rocket to a certain rate should produce roughly the same drag at different altitudes. What changes is the angle or size of the fins. Think about it this way: To spin up the rocket, you need passing air to impart its energy into the side of the fin. The energy pushing the fin sideways depends on how much air hits it, if the speed is constant. So by increasing the fin area or canting the fin to catch the same amount of air should mean that the same amount of air is also pulling it back, e.g. Drag.

I missed something, right? Mindsim can't do Navier Stokes, Mindsim can't calculate wake currents, Mindsim can't even solve algebra well.


Are you defining Mach as Mach at altitude or Mach at ground level?

You'll need a small hole in each section of the rocket somair pressure won't pop the tubes apart.

If if you have any questions, post them and I will make sure to take a guess and present it as fact. Make sure to check everything I tell you, since I'm not perfect and I'm not paying you if the rocket fails resulting from my data. Think of it as a research lead, or something similar.
Click to expand...

Regarding the spin: I don't think it's desirable at all. One of the OP's goals stated a camera payload for capturing the event. Spinning the rocket up to a conservative 30 rev/s will degrade the footage from the camera package and it sounds like he doesn't have the weight to add in a despin for that section.

Regarding the lugs/rails/tower: This rocket has to endure a balloon flight to at least 80k. Have you calculated the expected forces that the ride will put on the lugs/rail buttons if you use them? My intuition says you would be far better off tower launching. It's a little extra weight for the balloon but it eliminates most of the carry risk. You will want to run the numbers to be sure.
 
NateLowrie said:
Regarding the spin: I don't think it's desirable at all. One of the OP's goals stated a camera payload for capturing the event. Spinning the rocket up to a conservative 30 rev/s will degrade the footage from the camera package and it sounds like he doesn't have the weight to add in a despin for that section.

Regarding the lugs/rails/tower: This rocket has to endure a balloon flight to at least 80k. Have you calculated the expected forces that the ride will put on the lugs/rail buttons if you use them? My intuition says you would be far better off tower launching. It's a little extra weight for the balloon but it eliminates most of the carry risk. You will want to run the numbers to be sure.
Click to expand...

After reconsidering, I definitely agree.
 
saadzmirza said:
Regarding a launch tower, that WOULD be ideal... but the FAA only allows a 6lb payload total under the balloon. We're awfully close right now - with a 6 ft carbon fiber rod. I imagine a rail, or a tower (could be constructed with 3 of the rods) would put us over.

Check out this launch some Stanford students did:
[video=youtube;H-AcSucRBbw]https://www.youtube.com/watch?v=H-AcSucRBbw[/video]

I don't think they used any spin, or even a rod/rail - and from the looks of it, it didn't seem to fly very straight.
Click to expand...

They used a rail, I think. There's protrusions on the side, it looks to me looks like a pair of conformal rail guides, but could be a lug. Probably not.

As for the flight path, it might be from rod or maybe rail whip, where the rod/rail swings around (normally happens with flexible rods, bit in this case the entire launch pad is moving so a rail will still move around.)

I don't tell whether they used spin from the video but the fins seem straight at 0:52

Couldn't they have just gone up further with just the balloon, though?
 
At that altitude you will need to spin the rocket before you launch it. Without spin or significant atmospheric drag forces at the initial low speeds when launched what is theory of angular stability of the rocket?
 
Can you show us the plans and data (weight, CP, CG, motor size, and materials if not included in the plans) for the rocket?
 
They definite could've, but it was a proof-of-concept.
I think that their fins were also too small.
@Incongruent
 
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saadzmirza said:
They definite could've, but it was a proof-of-concept.
I think that their fins were also too small.
@Incongruent
Click to expand...

Weathercocking maybe? It seemed stable after a while, so either it was flying into the wind or it was, as you said, unstable- until enough mass had been burned.

If you have access to a wind tunnel, that will be a great resource. Model rockets typically use static CP, as it is easier to compute, but dynamic CP is what acts on the rocket in flight. It changes, so unpredictable things can happen. Wind tunnels model dynamic CP.
 
some thoughts. the full scale rockoons launched through the balloon, the Stanford rocket bounced off the balloon. there is also the issue of reaching minimum effective airspeed for the fins to work. possible solutions, use of v-max or warp9 propellant in the first stage should help get the rocket up to minimum airspeed, and use 3 balloons so the rocket can go up in the center. my .02
Rex
 
saadzmirza said:
But all of that is irrelevant - we talked to the FAA Office of Commercial Space Transportation and the Air Traffic Organization - the federal ones. The local FSDO office didn't want to deal with us. We now need to be approved, even though it's a Class I rocket. And the coordinator said 'of 12 rockoon proposals, I'm proud to say that I've never approved one.'
Click to expand...

And there you have it. Probably won't get the chance here. Guess you'll have to make a road trip out of country
 
saadzmirza said:
In other news, I'm now building my L1 cert. It's a LOC IV. I'll probably use a CTI 38mm 1 grain to make sure it doesn't get too high.
Click to expand...

You cannot certify on a CTI 38mm 1 grain motor as they only go up to G-impulse and you need an H-impulse motor to certify L1.
 

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