|
|
| Doug
Peacock's H-500 Crash Doug Peacock's advice on Cargo Lifting How to build a Cargo Hook & Bambi Bucket Dave Neves offers his Cargo Hook Release Mechanism Mike Spinner offers a word of advice on Bambi Bucket Dipping |
|
|
(click the photo for
a larger image)
 |
That's N808FD, a Hughes 500E, during an attempt to retrieve water for a simulated fire fighting demonstration. For an undetermined caused, the helicopter momentarily became unstable and the pilot panicked. Pushing down on the collective rather than pulling up forced the aircraft to make contact with the water container. Severe damage was realized with the separation of the rear vertical stabilizer section, separation of landing gear, and major alterations to the control surfaces. No injuries were reported. (Equipment used: Century Hawk III, O.S. 32, Funkey H500E body, Diablo Helicopter Cargo Hook & Bambi Bucket accessories). -dP |
| Back To TOP | |
| How to lift cargo... from Doug Peacock "Look at that! Someone's long-lining over there!" Gasping in shock, amazement, and horror, a visiting full-size helicopter pilot had noticed a model helicopter doing something most full size helicopters rarely do... lifting an external load. Although soon after, my flight ended in tragic disaster (luckily, I have a great photo to prove it), the experience of flying with cargo was well worth the reward, and the challenge. And now, at Circumgyration 2003, there are official events for pilots with these advanced skills. When you're done flying in the pattern with your scale ship, here's the low down on the how-to for building a cargo hook on your model aircraft. First, let's talk about what it is, and what it isn't. A cargo hook is a remotely operated, self-releasing, mechanical connector mounted on the airframe intended for displacing or towing non-flying apparatus. Typically, you will find cargo hooks used when lifting air conditioners on top of buildings, taking trees out of forests, placing a HUM-V in Saddam's backyard, fighting fires, and towing banners. A slightly different configuration of a cargo hook on fixed-wing aircraft is used for towing gliders into the air. But, in all circumstances, a cargo hook is not designed to winch a person into the aircraft, or to tie down when parked on the ramp. In designing the mechanism, there are some very important factors to consider. First is the releasing mechanism. Bottom line, if the aircraft falls into an unusual attitude while under load, the safest thing to cut the cargo free. Nine times out of ten, the aircraft will come back to normal flying characteristics. The only loss will the be client's $10 Million air conditioner unit now in pieces on 5th Ave. But, at least you still have a helicopter! The second critical design point for the hook is placement. Airplanes have it easy, the hook goes on the back just above the tail wheel, wherever the plane goes, the banner follows. Helicopters have to be a bit more concerned. Anyone know a thing or two about balance or CG??? The hook must be placed directly on the vertical plane of rotation, which, in theory, should also be the Center of Gravity for the aircraft. For a typical single main rotor design, this point is directly below the main mast. Weight is the final item to consider. While a Sikorsky AirCrane might be able to lift more than three times its own weight, your little Hawk IV Sport won't. So don't even try. Trust me. Been there. Done that. Waiting for the T-Shirt. Varying types of configuration considered, you'll be lucky to be able to lift anything that weighs the same as the Pod and Boom mechanics alone. The maximum cargo load for my Hughes 500E, which had a ramp weight of 8 lbs, could lift no more than 4 extra pounds of dead weight. Now with all that in mind, let's get building. To begin with, you'll need some sort of latch. My own preference is to use those removable keychains, where you press a button on one side, and the thing splits in two. This is an outstanding design for our application as it permits release under any weight, any direction, and any amount of torque. This is all very, very important, because the one time you will want to release the hook, you will not be straight and level with the load stabilized! But if you want purism, actual cargo hooks are similar to nautical snap-shackles. The hook is hinged at some point, and the end of hook is held up by a pin or a latch. The pin is pulled, the hook flaps down, and bye bye birdie. A variation of this design, used by Dave Neves in his banner tow operations, includes two blocks of aluminum with a pin running between them. A servo then pulls the pin out to release the load. This also works well. So, for your shopping list: A servo, a removable keychain or snap-shackle. Now you'll need to attach this Mickey Mouse thing to your scale model. Since you'll be lifting no more than 10 lbs, you won't need heavy gage steel. But stay away from some of the softer aluminum too, the vibrations from the airframe can create stress breaks anywhere you've bent this metal. My own choice: 1/2" acrylic Plexi-Glass. Not only does it look cool, but the keychain probe fits perfectly through the acrylic, with just enough on the other end to use an E-ring to keep it in place. Mount the assembly to the bottom rails of the main airframe. This allows a clean installation, not noticeable when not slinging loads, and easy access. A temporary mount could be made to the skids, but might interfere when landing. Again, do not forget that the hook must be located directly under the main mast...no exceptions! Finally, attach the servo to the release mechanism. For the keychain design, a simple servo horn is used to push the button on the probe to release the load. If you don't like this idea, then you'll need clevises and cables and pullies and whatever else is takes to pull your release. Connect the servo to your last remaining free channel on your receiver, this is most likely the landing gear channel. Set the switch for however you feel like to can remember it, without thinking. Again, you will be very close to the ground, in a very unusual attitude when you want to release. This ain't the time to be lookin at no labels on the sticks, Clyde! So, on the Futaba radios, the Channel 7 switch is up and to the left of the cyclic control. Flying by the thumbs, I can rest my right pointer finger on the switch, and pull it towards me when its time to ditch. You might also use the momentary engine-kill switch (and stop the engine by some other means), or on the other side, the Gyro select or Idle Up switches. Wherever your fingers can go the fastest. Oh yeah, one other note.... No inverted flying while carrying external loads! Nuff' said. Now that the airframe side is working, change hats and become the load rigger. A net is a great way to lift up odd objects. Or, straps coming from the farthest points on a box also works. The length of cable from the load to the aircraft is allowed to vary. However, unlike the real thing, you'll be taking off with the load already attached, so you'll need enough line to become airborne and not interfere with the cargo. This is one reason for using an exceptionally heavy cargo line, like 1/8" steel cable. It lays flat and it won't move. Finally, fix the receptor for your cargo hook on the end of the cable. Good stuff, now lets go flying! You'll need reasonably good piloting skills to fly external loads. For the rotary winged pilots, this equals a precise Out of Ground Effect hover. Plus, with this added dimension, you will have to think about piloting just slightly differently. Let's take a look why: First, although horizontally the CG has not changed, the vertical CG has dramatically changed... Its now a whole lot lower! And gets lower the heavier the cargo is. When you first started flying, perhaps your instructor told you that the helo is like a pendulum, swinging and rotating around the rotor hub. Well, that hasn't changed. Only know, the pendulum is bigger, so you'll swing more. You will now discover that as you tilt the rotor disc forward, the fuselage will take longer to rotate forward, as it does, the load remains stationary. Then the fuselage and disc are parallel, but you won't go anywhere. Until the load gets going, and momentum carries all three of you speeding merrily away. Banked turns will become steeper, and you'll need to stop long before you get to the point where you want to finish at. This is all because of the added weight farther down the vertical CG. If you stop quickly, or suddenly change directions, your load, however, won't follow. Once it figures out the rest of the aircraft has changed direction, it'll do what pendulums do the best... Swing the opposite and equal distance in the other direction! Most of your flying will be spent trying to minimize this effect. So here's my advice: Get off to a good start. Always fly slow and steady. Big turns and shallow descents. Once the load begins to swing violently out of control, pull into a hover, then side slip in the opposite direction of the swing. But slipping away from the swinging weight at proportional distances, you will eventually regain a stable load. Takes some practice, but this "counter-swinging" is one of the best ways to control. Do not try to fly farther, faster, or steeper. Without pilot response, a swinging load will pull the aircraft with it. This can be highly dangerous, especially to observers on the ground. If control cannot be regained, then cut the load free, and land safely. Spend your time hovering with progressively larger and heavier loads until you get a feel for this pendulum effect. Once you've mastered that, you can move on to forward flight, and drag! Yes, its back, bigger than ever ladies and gentlemen. Like a kid pulling on his mother's arm, he's not going anywhere. You will mostly notice an increased drag mostly during a banner tow. So what, you say? I'll just give it more gas and more forward cyclic, right? Sure, that'll do it. But wait until you turn downwind. Without the full explanation of aerodynamics and translational lift, if you're flying into a 5 mile an hour headwind and want a slow ground speed for a parade pass, your airspeed is likely to be about 10 miles an hour (10 mph Air Speed - 5 mph Wind= 5 mph Ground Speed). To maintain that same ground speed (the speed apparent to you, the pilot watching from the ground), you'll essentially be at a hover to travel downwind (0 mph AS + 5 mph Wind= 5 mph GS). So, with all that gas and forward cyclic you just added, you now have to take away. Otherwise, you're new ground speed will much larger! (10 mpg AS + 5 mph Wind = 15 mph GS ....yikes!). The only way to compensate for this is to know its coming. When making your crosswind turn (upwind of show center), slow your airspeed down to a modest hover. Downwind, on the base turn, increase your speed so that when you turn into the wind, your airspeed is already up to par. There ya go. What takes pilots thousands of dollars to learn, I just told you in three pages! Aren't you lucky. Now go out there and go pick up something! |
|
| Back To TOP | |
Diablo Helicopters - Electronically Releasable Cargo Hook Accessory Design and photos copyright 2003 Diablo Helicopters/Douglas R. Peacock. Distributed only for informational and non-profit use. |
|
|
(click the photo for
a larger image)
 Hawk-Hook1 |
Somewhere in that jumble of wires contains one servo and one male end of the detachable keychain interface The unit is mounted on 1/2" Acrylic Plexi-glass in place of the Gyro tray on the Century Hawk III. The servo is controlled through Channel 7 of the receiver (located just aft of this installation, not visible). The servo arm rotates down and presses the release mechanism of the keychain. |
 Hawk-Hook2 |
Close-up view of
servo alignment. |
 H500E-Below |
The belly of the
Hughes 500E body with the cut-out for the cargo hook. Leaving ample
finger space and clear plastic lets the load rigger easily attach the
cargo. Note the E-Ring used to secure the male side of the keychain to
the airframe. |
 HAWK-Below |
Close-up view of the
receptor connected to the airframe. |
 Accessory-Jack |
This connector is
used to the activate the servo on the BAMBI Bucket for a controlled
water drop. |
 Disconnect |
The detachable
receptor easily slides off the keychain pin under nearly all strains. |
 BUCKET-Side |
The latest version
of dH's BAMBI Bucket uses orange plastic (from those infamous CalTrans
trash bags at the side of the freeways), a bit of black tubing, lots of
orange wire, and the filler top from a Traxxas R/C truck gas tank. |
 BUCKET-Top |
Looking down inside
the bucket, the servo (bottom) is enclosed in a rubber balloon to seal
out water. Wire is used to keep the dump flap closed. |
 BUCKET-Open |
With the original
spring removed, the top of an R/C truck gas tank is a ready-made
self-sealing flap. A length of wire pulls the flap up from the inside
to
close. The weight of the water forcing the rest of the bucket down
creates a water tight seal. |
 BANNER-Rig |
Flying flags and
banners with a cargo hook is one of the easiest tasks. Pilots prefer a
length of heavy cable as the load line. This added weight ensures
release of cargo when necessary, and can help the banners hang below
the
aircraft. |
 BANNER-Wire |
To help the banners
fly straight, a length of piano wire is installed on the top edge and
along the leading edge. In light winds, this support makes for a
better presentation. The bottom leading corner is then weighted with
approximately 1 pound of lead weight. |
| Back To TOP | |
Cargo Hook Release Mechanism by Dave Neves |
|
|
(click the photo for
a larger image)
 Cargo Hook Release Mechanism
(bottom view)
|
A simple mechanism to allow controlled release of a cargo hook is shown here. This mechanism is built to fit between the lower frame rails (an Excel Gasser in this example) and is actuated by a servo controlled "release" pin. When in use, the "cargo hook" is held in the slot by the pin connected to the servo. If it becomes necessary to "dump the load", the pin is withdrawn and the hook falls free. Dimensions are not critical, but links should be kept short and straight. This example is made from aluminum, but wood would also work. |
 Cargo Hook Release
Mechanism (edge view)
|
In this edge view,
the attachment blocks can be clearly seen. The slots in the two
rails clamp to the lower frame rails on the helicopter. Sizes are not critical and will vary to fit the mechanics chosen. The servo sits outside the frame while the "hook" is positioned under the center of gravity (CG, usually under the main-mast) of the helicopter. |
| Back To TOP | |
Words of wisdom on Bambi-Bucket Dipping from Mike Spinner |
|
 |
I just thought of something while on the site on the water bucket thing. I make a water source that I can land in if I have too. Its only deep enough to submerge the bucket but I can land right next to if I have to. Just something I thought I should bring up! |
| Back To TOP | |