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Old Oct 21, 2013, 04:22 AM
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Gabe_BigApple's Avatar
United States, NY, New York
Joined Jan 2013
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Question
Blimp / Aircraft Hybrid

I'm thinking of making something where one or more envelopes form part of the structure, while at the same time lightening the ready-fly-weight of the thing.

The idea is that I might be able to make something that's maybe 5ft long that can be flown indoors in a very nice 3D routine, but, due to the magical power of helium, it would weigh very little and it could perform it's routine in a very calm, low-energy manner (instead of the manner of more conventional 3D planes which are more like angry bumblebees).

I tried to take the easy way out already and tried "marrying" both a small quadcopter and a small helicopter (Blade Tandem) to balloons, but it's completely unworkable. Basically for both of these, the ratio of motor thrust used for maneuvering vs the thrust used to fight gravity is very low (the overwhelming percentage of the power goes towards fighting gravity) so what happens is that anytime you try to maneuver the craft, only a tiny bit of power goes towards steering it, while the majority will go towards making it go UP.

So anyway, I'm pretty much convinced that no super-simple solution exists, and that to get something workable I will have to envision and create a thing from scratch and that it will have more in common with airplanes than with helicopters.

So anyway, what would such a hybrid creation be called, and are there examples of good hybrids out there?

Cheers,
Gabe
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Old Oct 21, 2013, 11:23 PM
Go small or go home
ruzam's Avatar
Canada, SK, Regina
Joined Mar 2008
1,408 Posts
Instead of hanging props underneath, I think you need to get them off to the side and clear of the bag.

Why not use the bag like a landing pillow and attach the power to a framework hanging over the bag. Use a small micro quad like an FF120, but put the props on extended carbon fibre rods so the the frame extends out past the edge of the balloon. With the props hanging off the edges, it should 'rotate' pretty good, although you're probably still going to be hard pressed for good forward movement. You might get some interesting 'alternate' control if the booms are pulled down so the thrust pulls out more to the side than straight up and down.

Even with extended booms something like an FF120 should still be able to get airborne on it's own. The extra balloon lift will help it float like a butterfly instead of screaming like a bee.
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Old Oct 22, 2013, 01:08 AM
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Gabe_BigApple's Avatar
United States, NY, New York
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I tried a quad (not a 120, but a clone), and what happens is similar to what happens with the heli hybrid shown in the picture.

A normal quad, when it wants to pitch forward (it would work the same for any direction) in level flight, will have F / R thrust ratio of 80%F / 90%R (or something like that).

However, a blimp needs next to no thrust to support itself, so what you would need for a neutrally buoyant blimp is 0%F / 10%R or maybe even -5%F / +5%R, and this is not available from an unmodified quad controller board.

Similarly, in the case of the thing shown in the pictures, using the tandem heli, looking at yaw control (it's the simplest scenario because it eliminates the issues of swashplate mechanical linkages, etc), in order to yaw the thing, you would need to get something like:

(C= clockwise, CC=counterclockwise)

Front CC 5% (only one rotor turns forward, not both) / Rear C 5% (only one rotor turns in back)

and the thing will yaw just great (let's say).

However, what you get from the standard heli board will be something like

Front CC 90% + C 80% / Rear CC 90% + C80%

and the result is just too much vertical thrust in any and all cases, so that you end up going UP regardless of which way you want to go.

(Note that one could try to finesse the issue by limiting total throttle travel to 10%, so you get much greater resolution of control inputs in the 0-10% range of thrust, and this might work ok if all your rotors / props were equally pristine, and all the motors calibrated to match, etc, etc, but using toy-grade stuff that gets banged around, I figured that this would be a fool's errand.)

There is nothing wrong with the notion of having 4 small props projecting out the sides of a blimp -- that would work great, but they would have to be driven by a controller specially programmed for such a craft, not a "re-purposed" quadcopter controller.

Gabe
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Old Oct 24, 2013, 10:43 AM
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On a historical note, a full size hybrid like this was tried in real life. Four helicopters were rigged to the bottom of a large Navy blimp. It didn't work out so well:

Piasecki PA97 Helistat Accident Crash - helicopter helium blimp hybrid air vehicle heavy lift (2 min 12 sec)
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Old Oct 24, 2013, 06:02 PM
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Gabe_BigApple's Avatar
United States, NY, New York
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Quote:
Originally Posted by pyronaught View Post
On a historical note, a full size hybrid like this was tried in real life. Four helicopters were rigged to the bottom of a large Navy blimp. It didn't work out so well:

https://www.youtube.com/watch?v=_7jENWKgMPY

Thank you for the link, I had not seen it before.

However, it appears that they suffered structural failure, which is an engineering matter.

There was nothing in the video to show that the idea and the configuration was inherently flawed and unworkable.

I will try to see if more information is available about it to see if any other conclusions were drawn afterwards.

Cheers,
Gabe
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Old Oct 25, 2013, 10:38 AM
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Majortomski's Avatar
Oklahoma City OK USA Where fakts still exist even if they are ignored
Joined Aug 2000
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Gabe, your biggest problem will be containing a volume of helium that is large enough to offset all of your equipment.

As for a name you're building a rigid airship. Just that you are trying to build one that is far more maneuverable than current mental paradigms are used to.
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Old Oct 25, 2013, 02:06 PM
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Gabe_BigApple's Avatar
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Quote:
Originally Posted by Majortomski View Post
Gabe, your biggest problem will be containing a volume of helium that is large enough to offset all of your equipment.

As for a name you're building a rigid airship. Just that you are trying to build one that is far more maneuverable than current mental paradigms are used to.

The volume won't necessarily have to match. It doesn't HAVE to be LTA, and as a matter of fact, it may be BETTER if is NOT full LTA,. Actually I wrote the last sentence and was trying to decide in my head if it's true, or not but couldn't.

It would be great if it ends up at least a little like this:
Festo Air_ray (1 min 31 sec)

but this Ray IS fully LTA. You can tell because in the instances where nothing is flapping it keeps accelerating in a straight line in whatever direction and has no downwards bias. On the other hand, the ray in this video took actual work and a huge space, while I'm looking to make something that's small, quick and cheap, and I'm ok with only getting part-way to the end result (at least at the beginning).

Cheers,
Gabe
BTW, Festo has a bunch of other really cool things, floating / flapping around that are worth watching when you have time.
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