Re: [UKHAS] Altitude control with valve

[Steve Aerospace]

Here is my Balloon Vent Valve 

http://www.youtube.com/watch?v=eahxgo7u5nI

Its not been flown yet - I got sidetracked onto other projects.  Maybe someday soon.

Yes I believe floating for a few hours or more at 20-30Km is possible with such a system.

Steve G8KHW

On 9 Apr 2013, at 23:23, John Couto wrote:

Hello!

I'm new here! I must say I'm impressed by all the work lots of you have been doing :)

Let me present myself: I'm an undergraduate student from Brazil. I'm studying Control and Automation Engineering and I'm going to get my degree at the end of the year. Until then, though, I need to work on a project and I've chose to design and assembly an embedded system for a HAB mission.

I've associated with a Professor in my University who wants to send to near-space an electronic system he have designed in order to study the effects of radiation on the circuit. To do so, he wants the balloon to stays 4 to 10 hours at high altitude (20-30km), so he can get relevant data. He suggested us (the team working on this project) to use a valve on the ballon and implement a control system to keep the balloon from early explosion.

We have searched throughout the internet for references about how this could be done. I tried to find missions that used this design. But I can't find information good enough. The best we have found was this article:

http://library.queensu.ca/ojs/index.php/PCEEA/article/view/3641

But it is still little information. I've searched even here in the group for missions or doubts related to altitude control but I couldn't find anything really relevant. That makes me think: is this type of control really possible?

Do you think I could keep a ballon on high altitude for 5-10 hours by controlling only its lift?

Do anybody have any other suggestions (cheap ones) on how I could accomplish this?

And, last but not least important: do you know about any mission, hobbyist or scientific paper that have done and described this type of system? Could you offer me some links to their work?

Thank you very much!

Best regards to all,

John

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Steve Randall

Random Engineering Ltd

st...@randomaerospace.com

+44 7802 242135

[Dan Bowen]

Hi John, 

There are several amateurs who have experimented with valving, and they have been accomplished successfully in the past by professional and amateur systems.  Mechanical valve systems are very tedious to make reliable on balloons, due to such varying severe cold temperatures.  If he's going for a reliable testbed for the circuit project, then I would recommend you try to purchase a ready-made zero pressure balloon.  

However, the most reliable, quick-to-obtain solution in your situation is to use a zero-pressure (equal pressure) polyethylene balloon.  ZPs use a passive one-way valve system, and reliably reach their target altitude by nature of their designed volume and payload weight alone, not requiring any active control of the venting.  They are very easy to fly normal payloads on for less than 24 hours of flight, but the flight will end when the sun sets.  A small amount of ballast (passive or active) should be included.

They are not as simple to launch as latex balloons, but can be done confidently by a crew of 2 or 3 that is familiar with latex balloons, as long as they're trained to deal with the very different ZP launch techniques required.

Also, the laws of countries in your flight path, and international laws, may put limits on various payload characteristics, and/or balloon size.  I am familiar with international law, but not yet Brazil law.

Here's a few useful links:

http://ravenaerostar.com/files/uploads/aerospace/Aerostar_small_zero_pressure_performance_curves.pdf

http://webserver.dmt.upm.es/~isidoro/ot1/Balloons.pdf

I'll find some more and get back to you.

Thanks,

Dan

[Steve Aerospace]

Hi John,

Its something I made myself out of PVC pipe and foam PVC sheet turned on a lathe. It uses a standard 5g micro RC servo.  

Your right - it gets cold up there - the servo is rated to work down to -30C which on its own isn't enough to work at 20Km - but I have a small heater which wraps round it and is designed to keep it at a snug -20C.  An alternative approach might be to keep moving the servo slightly throughout the flight to generate a little heat - this was something that I was going to flight test.

I'm not sure you will find a suitable valve off the shelf - one with a big enough vent and light enough to put on a latex balloon. But if you do I'd be very interested.  Mine weighs 60g all up.

Steve

On 11 Apr 2013, at 02:36, John Couto <johnl...@gmail.com> wrote:

Hey Steve, thank you for your feedback! This valve of yours is a mechanical one, activated by a servo-motor? Did you assembly it yourself?

My research until now have led me to believe I should use a electric, cryogenic solenoid valve, as they can work on very low temperatures. My problem is finding the right specifications to decide which one I should buy...

[Steve Aerospace]

Pic of the heater http://imagebin.org/253589

If you want any further detail please email me direct.

Steve

[Ed Moore]

Yes he is a UKHAS regular! I think this is your cue to chip in Ben :)

On Sat, Apr 20, 2013 at 4:24 AM, John Couto <johnl...@gmail.com> wrote:

Oh, I forgot to paste the link. Here it goes:

http://www.benoxley.com/b/altitude_controller_report.pdf

I have a feeling that some of you may know Ben, and maybe he is in this group, as he works with HAB projects too :)

[Steve Aerospace]

Oh yeah - I remember that now.

I like my design better :-)

A servo is probably the simplest way to go - although (like the report says) a standard servo offers a potential source of ignition if hydrogen is being vented.  My design would be relatively easy to change to solenoid operation - I didn't use one because of the higher power requirements.  A solenoid won't suffer cold problems either.

Steve

On 20 Apr 2013, at 04:24, John Couto <johnl...@gmail.com> wrote:

Oh, I forgot to paste the link. Here it goes:

http://www.benoxley.com/b/altitude_controller_report.pdf

I have a feeling that some of you may know Ben, and maybe he is in this group, as he works with HAB projects too :)

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[Mike Bessant]

Hi

The weight of any altitude control mechanism flown will be at the expense of payload. The long duration flights by the CNSP group, and more recently by our very own David Akerman, managed to obtain a reasonably stable float condition without active control. Maybe it 

would be better to try and refine this passive approach?

MikeB

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[Steve Aerospace]

The difference is that a valve will allow faster ascent rates - and then levelling off by release of gas.  The floats you mention have only been achieved have been at the expense of some very low ascent rates making launch difficult.  Anthony's recent flight (thats the one that was still transmitting the next day) only just cleared some trees 0.5km away - it was skin of teeth stuff - (a real worry with a huge bladder of hydrogen potentially not taking off and dragging across country).

I think your "weight of any altitude control mechanism flown will be at the expense of payload" is incorrect because the takeoff weight can be higher due to the increased amount of gas. And obviously the choice of altitude is under much more control and not set by the vagaries of weight/fill/envelope stretch.

In any event the aim is not necessarily to "float" - my interest was in controlling ascent to take advantage of winds at different altitudes (together with ballast release).

Steve

[Mike Bessant]

Steve,

Yes, all good points. Latex balloons would certainly become a much more useful research tools if a lightweight form of altitude control could be developed.

MikeB.

[navrac]

The other alternative is to use the sky anchor method. Someone did it a while back and it was apparently very successful but despite my googling attempts I can't find the site of the people who did it.

Basically they had one latex helium balloon and underneath another one with air in it - but used a net round the lower one to constrain its volume - so as it rose the density of the lower balloon kept the system in balance at a set altitude.

If you search for sky anchor there is stuff on the net - but mainly for superpressure balloons so the maths is a bit different.

Richard

[Steve Aerospace]

NSS in the US - Earthbreeze

http://www.qsl.net/nss/earthbreeze.html

Steve

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[Cresswell family]

That's the one - thanks Steve