Helicoptorial

EXTERNAL LOADS II
Let It All Hang Out Again!


External load operations are unique to helicopters. Last month, I discussed some highlights of important considerations while performing sling load operations. This month we will review an external load mission from planning to execution. This article is not for the squeamish so if you bore easily, have no interest in the excruciating details of external loads or your parents won't let you read about things like slings and harnesses, turn back now.

For demonstration purposes, I'll use a UH-1H (since the Army seems to be giving them to everyone and their brother). A quick background check reveals that the UH-1H has a maximum gross weight of 9500 pounds. It's cargo hook has a maximum capacity of 4000 pounds. With a full load of fuel and two people on board it will weigh in at about 7400 pounds. Fuel capacity is approximately 209 gallons of fuel with a full tank.

SITUATION

The local electric company has hired us to move a cement block from a road to a hill top. The cement block weighs 2500 pounds. It's a 45 minute flight from the home airport to the block on the road. The road is at 500 MSL and the hill top is at 2000 MSL. The distance between the road and the hill top is roughly 5 miles. Fortunately winds are expected to be light and the temperature cool.

PLANNING

Our goal is pretty straight forward. Get the cement block to the top of the hill. Before I accept the mission, I must decide if my aircraft is capable of performing this feat.

The Aircraft. Returning to the information discovered in our background check of the UH-1H, we see that the cargo hook is adequate for the load, however 7400 pounds plus 2500 pounds is greater than the maximum gross weight of 9500 pounds. (We'll assume that the environmental conditions will support the aircraft at 9500 pounds in an out-of-ground effect hover.)

The dilemma is easily solved by reducing my variable - fuel. A reduction of 400 pounds of fuel will give me my maximum gross weight of 9500. I've predicted that my burn rate will be 550 pounds and hour. At that rate, in the 45 minutes it will take me to get to the pick- up area, I will burn off about 410 pounds of fuel.

Using the math techniques that I learned in second grade, I compute that I will have approximately 900 pounds of fuel remaining when I arrive at the pick-up area. As long as my burn rate remains the same, I will have roughly 1 hour and 38 minutes of flight time. Subtracting 45 minutes for return time, and the 20 minutes for reserve, the mission can take no longer than 33 minutes. Hook up, travel time, and release I calculate at 15 minutes - 18 minutes to spare. As a contingency for fuel, I found a closer "ma and pa" airport that sells Jet A. It is only ten minutes away.

Recon. Next I'll want to look over the area to see if there are any unusual or special considerations for my flight.

The Pick up Area. When I get there I notice that the cement block is to the side of the road in a fairly dusty area. There are trees not too far from the load that are about fifty feet in height. Winds appear to be predominately coming from the south.

The Route. Along the route of flight to the hill top, I must cross a huge set of power lines. The terrain climbs rapidly and is devoid of any buildings.

The Landing Area. I get to the hill top and I see that the area for the block is sufficient. The hill top is not the highest peek in the area. In fact the hill is on a small ridge from a larger hill that is about 1000 feet higher. I notice also that the predominant winds might force me to make my approach to the southwest. This will put the larger hill out my right side as I approach the landing area.
The Load. The load looks like it should fly normally. There are no protruding edges. It looks like it has all the aerodynamic qualities of ... well ... a cement block. I check the load to ensure that it is rigged properly and that the harnesses will be strong enough to support the weight.

THE FLIGHT

I arrive at the pick-up area slightly ahead of schedule. I calculated my fuel burn rate to be 540 per hour. My fuel gauge indicates that I have slightly more than 900 pounds. Things are going to well so I'm a little on edge. I land by the load to begin a final inspection and hook-up.

Important Safety Tip Igon...
If I hook-up with the aircraft sitting on the ground, make sure the sling goes to the hook from the front of the aircraft. If I just go straight to the hook "over" the skids, I'll end up with an extremely lateral CG.

Hook-up complete, I get back in my aircraft to begin the lift.

First thing I do is cross check my fuel..is it below my maximum allowable that I computed for the mission?

Then I bring the aircraft to a hover and confirm that I have out-of-ground effect hover power prior to continuing my ascent. I do this facing into the wind if possible. I know when I landed that I had OGE power without the load, but now is it within acceptable limits if I add 2500 pounds? I slowly bring the aircraft to an OGE hover and continue to a point to where the line is tight. The weight is great enough that if I'm slow with my maneuvering I will center myself over the load. It is important to be centered over the load at lift off to minimize oscillations from the very beginning.

I note my power and my controllability as I carefully increase collective to bring the load off the ground. By controllability, I'm talking about cyclic and pedals. How is the CG? How much left pedal do I have remaining?

With the load now off the ground, I'm going to continue my ascent until the load is at least 25 feet above the obstacles in my takeoff path. I want this little extra cushion in case I lose any altitude going through effective translational lift.

Enroute, I make all control movements slow and positive, so as not to induce an oscillation. Turns will be very shallow. I also am very aware of my altitude so I ensure that my load clears all obstacles.

I make my approach as I had planned, using the hillside to the right of my landing area as a reference point. I select an area on the hill abeam my intended landing area to slowly come to a hover next to. I remember to lead my deceleration so the inertia of the cement block won't begin an oscillation and it will be much easier to place the load if it is not swinging.

As I come to a hover with the load, I'm am very aware of my power and controllability. I definitely do not want to droop the rotor RPM. I also don't want to run out of left pedal. Of course if I begin to occasionally bump the pedal stops all I really need to do is reduce power to regain control. This could be a problem if I descend too soon.

Gently I lower the load to the landing area and take some slack out of the line. I move slightly to the side of the load prior to opening my hook to release to sling. I do this out of habit. The sling falling on the cement block is probably not going to hurt the block, however a huge metal clevis falling on an air conditioner or something more fragile can cost everyone a lot of money.

The mission complete I check my fuel to ensure that I will have enough to return to my home plus a twenty minute reserve.

Planning, Planning, Planning. It helps you to prepare for a job so you have all the right tools prior to beginning. It also will help you understand your options if things start going your way.

Next Month: Evaluations

You can send your feedback and input to Chuck at chuckm@aero.com
Back * Home