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My apologies as this question is not directly related to all that you guys (and gals) do here.

I am a helicopter pilot and in my job I carry equipment on a sling or long-line beneath the helicopter. Most things are not meant to fly between 60 and 90 Mph and most tend to oscillate or rotate. Best case scenario it just makes the ride uncomfortable sometimes, and worst case things can get ugly and dangerous.

Most ppl attach a cargo net or a fir tree to one end to make things fly better (well, fly worse, but travel better). My thought was to attach a small drouge chute or pilot chute to the item... something small yet effective to make the items behave better. I've been looking online and am wondering if these devices might help, or because of the questionable flight regime be a waste of time...

Any advise of any type (constructive, that is) would be appreciated.

 
I recall a paper that was presented at PIA a few years ago. It was basically a design for a droge shape. It was kind of the equivolent of a sigma 0 design for hot air balloons. Interesting math. Althoue they were focused on the mathmatics the purpous of the droge was to stablize long line cargos under helecopters if flight. And aparently it was very successfull. So yes it can be done and it can work. I recall the design but they never got into how it was attached to the load so every thing else here is guess work.

They were going totaly over board on their math matmatics. You don't need to worry about all that shit. On the other hand I don't think you can just attach any thing on the back of it and expect it to work. Hmmm I'm setting here thinking about what is involved. Stuff like your carying doesn't quite fit into ordenary aerodynamics. I recently read a paper were they were talking about vortex sheding around a cylinder. The short version is there are several diffrent modes it can behave in depending on the renalds numbers, lets just say speed. In a certin speed range you will shed vortecies off alternent sides of the load. I'm guessing that's when things get interesting and if you're even close to the natural frequence... The droges they used acted as a damper keeping the load from twisting and stoping osolation. You'd need a good drogue that was not it self prone to osolation. It would need to be big enough. But I think the most important thing is where it is located. The length of the bridal and where it is attached are probbable the biggest factors. I don't think you can just tie a pilot chute on a nine ft bridal to the back of your load and call it good. If it's inside of the burble behind your load I doubt it would have any effect at all. Eather the bridal needs to be long enough or it needs to be located out side the burble. Bridal length will also change the effectiveness of the damping of the ossolation. you might do better to locate the drogue slightly above the load where it would get clean air. You could do this with a much shorter bridle. But that wouldn't keep it from spinning. You might try a split bridal. A Y with one point above the load and the other point on the back of the load. The split in the Y needs to be wide enough and the lengths right so that you get load on both lines. Basicaly the upper line just lifts the bridal up so that the drogue rides above the burble from the cargo. It's not a great picture. It's rather exagerated. I think you could get by with a much smaller drogue that way and a shorter bridle.

Please note that I am totally talking out of my ass here but that's what I would try. but what you really need to do is talk to a pilot with expereance with them. Of course that would take some of the fun out of it.

OK, FINE NO FUCKING PICTURE. STUPID FUCKING PROGRAMS. GERRR


Lee

a few quick thoughts...

tandem drogues effectively stabilize "the load." they function at higher speeds than you mentioned.

the size and shape of the objects long-lined will greatly affect the results, and where you would attach a drogue.

a really large object might require a bridle longer than your standard tandem to keep it out of the burble (wake). the slower speed will lessen the burble size, but a wider object will increase it.

if the object is relatively symmetric (water bucket, bambi bucket, sand bags, etc.), then the drogue could be attached around the hook, or other convenient location. sure, the load might still spin, but it will still dampen oscillations.

if the object is NOT symmetric, like a tree, then it would be better to attach the drogue to the object itself. the drogue would then dampen rotation and oscillation.

think in terms of an unbalanced wheel. if it spins, it will wobble. attaching the drogue to the rigging does little to stop spinning. of course attaching the drogue to the object increases the duties of the ground crew and also the snag potential. it could greatly complicate logging, or even setting flood protection sand bags or other "dropped" objects (how will you recover the drogue?).

since your loads are likely far heavier than a tandem, and the speeds are less, you might need a far larger drogue.

at slow speeds, the drogue will be dancing around in your rotor wash. the bridle could be at risk of entangling with the load.

I think it would be fun to rig and test such a system.

Another battle with some equipment today... it's amazing what flies great and and what doesn't.

I can imagine the aerodynamic math that must be going on, but i'm just a dumb pilot... i was looking for a "one size fits all" sort of solution to a multitude of scenarios...

A 3'x4'x5' (H W L) basket with mesh side flies nicely empty at 400 lbs and 80 MPH and just as well full with all sorts of shit at 1800 lbs. and 60 MPH. A half a dozen 6"x6" beams of 1200 lbs stacked into a tidy rectangle oscillates and rotates counterclockwise for ever and any speed over 40 MPH. If a cargo net is attached to the trailing straps then they still oscillate but don't spin.

Instead of taking a net out of production, i was hoping to attach said drogue or chute to at least stop the rotation and if all things were perfect make the timber fly like a lawn dart (grandiose dreams to be sure!)

Ideally they could be easily attached but unlike what i've researched online only cost a few bucks each so each pilot/machine could have a few on hand for such jobs...

No questions here really... just a venting... and a hope for more valuable input. Thanks to those that have posted and PM'd.

 
Look, call up Strong Enterprises. Tell them what you're doing. I suggest you get a couple of their tandom drogues. Not cheap but they wont wear out. Start there and start expearamenting. Worst that will happen is it will stop rotating and ossolate less.

http://www.strongparachutes.com/pages/contacts.php

Lee

Consider NOT having your load evenly balanced. I used to rig loads in the Army, and more often than not, we used a nose-down attitude to help prevent oscillation. Every load will vary, but the concept is the same. I have sling-loaded everything from trucks and connexes, to water blivets, to a helicopter and even a small church. On your 6x6 load, try flying them with one end about a foot lower than the other (i'm assuming 12+ foot lengths) and see if that doesn't help your scenario.
As far as a drogue chute, the idea is intriguing, but you might be better served with something like they use in drag racing.
Also, it's really important to note that if you should lose this chute during flight, your oscillations could be very immediate and aggressive. For safety's sake, i'd quadruple the bridle.
Just some thoughts.
A.T.

Now with your rigging have you considered adding a swivel in there if the load is balanced and the orientation is irrelevant? Then the load twisting will be irrelevant... I don't know what your anchor points on the Helo look like nor the system used but that's my 2 cents of ideas.