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Old Aug 02, 2009, 08:03 PM
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Ballonets for Blimp

Hello:

Most of the big airships have front and aft ballonets to control Helium Pressure and Pitch Attitude. Some of the old ones even have pannier ballonets (left and right) to control roll.

Has anyone tried to built ballonets for RC blimps ? I am having a hard time visualizing how to build ballonets inside the envelop. Any suggestions or previous thread I can look into??

Thanks,
Harshad
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Old Aug 02, 2009, 09:24 PM
Marcus Franco
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USA, HI, Makawao
Joined Jul 2004
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I did used them and built them...
It is the pain os pains...
A Hassle with many problems...
Never more...
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Old Aug 02, 2009, 11:53 PM
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Hello there Harshad, as Guga stated it is a really complicated job as you have to find internal curves and seal seams within the built up envelope.
alternatively if you intend to build a medium size blimp around 24 feet, you could seal into the blimp envelope 3 mooring points and have spherical ballonets tied within the envelope with 1 inch light weight ducting leading from them to the outside of the envelope. Another question, how do you intend to ram air into the ballonets? Do you intend to fly the blimp with such a varying altitude/ barometric pressure?
Raejus
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Old Aug 03, 2009, 01:02 PM
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Quote:
Originally Posted by raejus
Hello there Harshad, as Guga stated it is a really complicated job as you have to find internal curves and seal seams within the built up envelope.
alternatively if you intend to build a medium size blimp around 24 feet, you could seal into the blimp envelope 3 mooring points and have spherical ballonets tied within the envelope with 1 inch light weight ducting leading from them to the outside of the envelope. Another question, how do you intend to ram air into the ballonets? Do you intend to fly the blimp with such a varying altitude/ barometric pressure?
Raejus
Thanks for the reply. My planned blimp is about 14 feet long and am doing this as a technical elective towards my degree. I have a sleek idea for ballonets, but I still need to test if they work. I bought Auto Inflate Digital Blood Pressure Monitor which measures pressure and also inflates and deflates the bag electronically. When I ripped it apart, its just a small gas bag with a tube attached to it for inflating and deflating. This is controlled by a small circuit which has a pressure transducer soldered to it. I am trying to control its circuit using arduinos. Hopefully, I will find a way to do this. But my biggest worry is sealing the blood pressure bag inside the Mylar hull.
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Old Aug 04, 2009, 12:32 AM
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I have built an (outdoor) blimp with ballonet. The blimp was 13 feet long of 1.25 cu mtrs. The single ballonet was spherical, stuck to the inside of the envelope at the lowest point. A hole was cut thru both membranes at that point, to connect a blower and valve to the ballonet. A bellows type switch controlled the blower. The glued seal between envelope and ballonet was satisfactory, but it started to peel with the stresses of inflating and packing up after deflating. I had to reinforce it by clamping between two plywood rings with thru bolts.

As Guga says, it was a pain to get working properly, and added quite some weight. I eventually discarded it and went back to just a plain envelope relying on a bit of extra pressure to prevent it going limp. All that was 15 years ago. However, with modern sensors, it may be more practical now.
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Old Aug 04, 2009, 09:50 AM
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Quote:
Originally Posted by Alan Sherwood
I have built an (outdoor) blimp with ballonet. The blimp was 13 feet long of 1.25 cu mtrs. The single ballonet was spherical, stuck to the inside of the envelope at the lowest point. A hole was cut thru both membranes at that point, to connect a blower and valve to the ballonet. A bellows type switch controlled the blower. The glued seal between envelope and ballonet was satisfactory, but it started to peel with the stresses of inflating and packing up after deflating. I had to reinforce it by clamping between two plywood rings with thru bolts.

As Guga says, it was a pain to get working properly, and added quite some weight. I eventually discarded it and went back to just a plain envelope relying on a bit of extra pressure to prevent it going limp. All that was 15 years ago. However, with modern sensors, it may be more practical now.
well, i dont think a lots changed in 15 years, as far as techniques go...lol. I will keep your comments in mind when i do this. Will keep posted if I ever go through with this..

thanks
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Old Aug 05, 2009, 10:51 AM
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hello we do almost all our outdoor rc blimp (from 7m) with central air ballonet
as we do use nylon ripstop fabric (not extensible) pressure can raise dramatically in hot weather alos one ready for storage we can deflate the ballonet and so the pressure and He loss is very low



for small blimps from 7 to 10 m we use a manual system above we do use a automatic system with barocontrol sensor and small blower.

take a look to our photos and you will see the airballonet
webiste minizepp.com)
cheers phil


Most of the big airships have front and aft ballonets to control Helium Pressure and Pitch Attitude. Some of the old ones even have pannier ballonets (left and right) to control roll.

Has anyone tried to built ballonets for RC blimps ? I am having a hard time visualizing how to build ballonets inside the envelop. Any suggestions or previous thread I can look into??

Thanks,
Harshad[/QUOTE]
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Old Oct 02, 2009, 04:31 PM
Mostly harmless
Nepal, Central Region, Dhulikhel
Joined Aug 2006
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Just wondering if a rubber band around the tail section of a 5-foot blimp envelope might provide some form of pressure control against temperature variations. I occasionally fly my 5-foot semi-rigid outdoors (the envelope has no ballonets due to it's small size), but temperature difference between outdoors and indoors always cause a bit of fiddling to get the envelope full enough for reasonable wind flying capability.
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Old Jun 09, 2013, 05:05 PM
Mostly harmless
Nepal, Central Region, Dhulikhel
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Air pumps?

Hmm... this thread seems to have been inactive for quite a some time. However, since it exists with the correct topic no less, I'll just post here instead of starting a new one.

Some of the folks here have been using ballonets in their larger outdoor blimps to allow for some pressure control. I was wondering how the ballonets are filled. Ram air from propellers is used in real-sised blimps, but does this apply to smaller blimps requiring more envelope pressure for the same rigidness?

I do have some plans to build a real outdoor-capable compact RC airship, but as my experience from the HB-8 prototype has shown, an active pressure control would be needed for outdoor flying. Temperature variations such as the blimp taken from indoor to outdoor can be countered with addition/release of gas while on the ground, but while flying during the day, sun going into/coming out from a cloud can cause some interesting changes in the flying characteristics if not countered.

While the semi-rigid models such as mine can fly with saggy envelope, there are a few unique characteristics: First of all, the gas can shift inside the envelope to an extent, also shifting the centre of lift along with it. Secondly, flying at high speeds or against wind is challenging due to rippling effect on the envelope. Finally, flying during daytime, sunshine can cause superheating in a saggy envelope, making it to expand, also increasing lift uncontrollably without any way to control the volume of the gas and thus ascent. That is unless the craft was flying tremendously overweight to start with, which is somewhat manageable with vectored thrust.

At any rate, I was wondering if some form of pressure control could be built for relatively small blimps also. Because of the small envelope area, a greater pressure is needed for it to achieve sufficient rigidness. Thus, ram air might not be enough, and an actual air pump would be needed. I gave this a bit of thought, and considered a membrane pump with reed valves for the task. The pump it self could be driven by a modified servo mechanics (constant rotation), which would probably be lighter than a solenoid drive. Stabilising the pressue would not be a problem due to availability of tiny barometric sensors these days, it is just the mechanics that might require some development work.

Also, any considerations on mounting a ballonet inside an envelope? I was thinking about an inner wall seamed to the lowest gores of the envelope. This would have to be done in the making phase, when it is still relatively easy to attach valves and fixtures to the unfinished envelope. However, I'm uncertain how much volume would such a ballonet need and whether or not it would be stable against pitching motion of the aircraft (when partially full, air might roll around the ballonet, changing the center of lift abruptly). What do you think?
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Old Jun 15, 2013, 07:33 PM
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As an update to my earlier post, I have since built another nonrigid with ballonet. This was described in AirshipModeler, which now seems to have finally died. So I shall reiterate:

It is a scale ZPG-3W, 1400 litres and 4 metres long. Again I used a spherical ballonet at the centre, attached to the envelope thru a bolting ring, and also a sting from the top of the ballonet to the nose and tail to stop it rolling fore/aft.

Inflation was from a blower adapted from a small battery vacuum cleaner (sold for vacuuming keyboards, now no longer available), running off 2.5 V (see first pic). A non-return valve fitted between blower and ballonet. Control was electronic, using an All Sensors solid state pressure sensor with op amps and FET. Blower switches on at 1.3 inches water, off at about 1.5. There is also a pressure valve on the ballonet that cracks at 1.7 inch, and the helium envelope valve cracks 2.0 inch. The ballonet valve is necessary, or else fluctuations in temperature, etc will cause the ballonet to keep inflating, while the helium valves off.

So far this ballonet control has worked quite successfully.
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Old Jun 23, 2013, 05:30 PM
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Nepal, Central Region, Dhulikhel
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Hi Alan!

What sort of valves were you using? As for the non-return I reckon using one of them balloon filler valves found on foil balloons, but these pressure release valves you write about seem somewhat obscure to me.

I've conducted some tests myself with an servo-operated bellow-type air pump. The micro servo in itself is very light yet provides quite some torque, certainly enough to pump a ballonet to sufficient pressure. Furthermore, the bellow structure consists of a thin bladder of balloon foil sandwiched between two hinged balsa wood frames. Foil balloon valves are used in both intake and outlet, so the structure, on paper at least, is extremely lightweight. I'd imagine reducing the weight for a next version down to 15 grams.

My next airship will probably have a volume of some 400 litres with internal ballonet for pressure regulation. The thing I don't know is how large the ballonet should be in contrast to the envelope itself. I'd imagine that depends on the desired mission altitude range among other things, while my aim is just to counter for temperature differentials occurring outdoors.
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Old Jun 25, 2013, 10:33 PM
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Melbourne, Australia
Joined May 2005
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The non-return valve is just a disc of ABS plastic sitting on an O-ring, with a cage to stop it flying off when open.
The ballonet pressure valve is also home made, similar but with a compression spring to set the cracking pressure.
The helium valve is a Halkey-Roberts valve I got as a free sample many years ago. I don't know how you'd get one now.
Both ballonet vlaves leak, but that's OK because its only air. The helium valve is good quality, and is totally leak free with a light coating of machine oil on the seal.

I use a 10% volume ballonet, which has always been sufficient to deal with temp changes and leaks (beyond 10% gas loss and it no longer lifts). I think a bellows type pump would be hard pressed to provide the flow rate needed, why I use a fan.
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Old Sep 04, 2013, 09:03 PM
PhoenixFlyer
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South Florida
Joined Dec 2006
219 Posts
Ballonets

May have mis-spelled above. I had plenty of time in LTA. ZW-1, Lakehurst, NJ.

2W's and the new 3W's. The 3W's did not last long, crashes. The ballonets in the ships were fore and aft, port and starboard. We could look thru the
plexi-glas in the vertical tube. Imagine a bat wing, with the semi curved edges, or Bat Man's cape. These were secured to the bag, which we would pump up when the bags were heavy, or deflate when we were light.
When the ballonets were inflated, this would compress the helium and make a lighter bag, deflate, the opposite.
This is a good forum, a lot of knowledge with the modelers of airships.
Vince
Hobe Sound, FL
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Old Mar 16, 2014, 05:56 PM
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I finally have a video of my ZPG-3W model. Please excuse the quality, I was holding the camera in one hand and the Tx in the other.
20140306182839 (1 min 21 sec)
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Old Mar 17, 2014, 05:39 PM
Warpquad: practice, practice!
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Quote:
Originally Posted by Alan Sherwood View Post
I finally have a video of my ZPG-3W model. Please excuse the quality, I was holding the camera in one hand and the Tx in the other.
Kudos, Alan. Your scale model of the ZPG-3W is stunning.

20140306182839 (1 min 21 sec)
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