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Subject: I spend most of my time flying over dense forest...need advice!
 
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FLYnLOUser is Offline

Posts:25

09/23/2012 11:42 PM  
Curious if any one has experience or training in how to deal with an autorotation into very densely populated forests. I spend most of my flight time over tall trees in the Appalachian Mountains. I understand the obvious, ie..find a clearing etc. but need some technical advice as how to survive in engine failure over such harsh terrain. My concern is if a come to a zero airspeed flare at the canopy tops it seems the 100+ ft drop would fatal. Thoughts? Thanking you in advance
carabeUser is Offline
JH Guru
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Posts:93

09/24/2012 2:22 PM  
What would happen if you didn't flair and slow your airspeed before you hit the trees? You will slam into the trees, the blades will fly off, down you go. Either way, you will still be dropping 100' to the ground! I'll take my chances on one potentially hard impact rather than the almost certainty of two! The trees may slow your descent. I believe the army teaches flaring and settling into the trees.
FH1100PilotUser is Offline
JH - Addicted!
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Posts:400

09/24/2012 3:14 PM  
I worked for a guy for five years who liked to fly low (meaning 500' agl). He gets real nervous if we get as high as 1,500'. We flew over south Alabama, which is heavily if not densely forested. Fortunately it is also fairly level. At first flying this low made me very uncomfortable. But what I came to realize was that there were tons of little clearings into which I could stuff the helicopter if push came to shove. The a/c would likely be a total, but I was fairly confident I could get it down okay. During the day.

But we also flew at night.

My philosophy may be wrong, but for going into the trees at night or where there is no definable clearing to shoot for here's what I think: Flare at the treetops and at the last instant pull aft cyclic to get the tail down as the ship drops through the trees. Let the tailboom and aft fuselage absorb the impact at the bottom. (Obviously get the fuel valve off to minimize the risk of fire.) This is better, I think, than having branches and stuff coming in through the bubble. This assumes that the helicopter settles backwards nicely and doesn't turn around. Like I say, I've never had to prove this theory in real life.

But more important than any specific autorotative technique is this: Have good maintenance, and make sure you have plenty of oil and fuel to feed that engine. Operate the engine conservatively and gently (don't overtorque and/or overtemp it). Turbine engines are marvelously reliable these days. I won't say they *don't* quit, but the chances of one blowing up or just signing-off are quite small. Having two of them would be the cat's meow.
Little BirdUser is Offline
JH Member
JH Member
Posts:10

09/24/2012 10:20 PM  
This is from the Army student handout, aptly named "How to crash a helicopter". There's more if you like, I can send it to you if you want. b. Tree Landings When a tree Landing is unavoidable or preferable, the pilot should select a touchdown spot based on the following considerations: (I) The height of a tree is less critical than the height above the ground where it begins to branch. Tall trees with thin tops allow too much free-fall height after the aircraft passes through the branches. (2) When dealing with young or short trees (twice helicopter height or less), the most densely and evenly wooded area should be chosen. This is an ideal situation in which the bottom of the aircraft as well as the main rotor provide a cushioning effect. (3) When dealing with large trees, resistance against the bottom aircraft structure should be avoided in such a manner that the fuselage and tail boom will settle between the tree tops before the main rotor engages the branches of the surrounding trees. In other words, the pilot should look for an area where the rotor disk meets equal resistance to tree top level with the "softest" spot for fuselage and tail boom to insure a tail-Low attitude at ground contact. The general implication is that, although their branches may overlap, tree trunks should provide a clearance of at least 1 1/2 times the rotor diameter. (4) If at all possible, main rotor contact with heavy trunks high above the ground should be avoided as it may result in loss of main rotor or transmission failure. If a retreating (metal) blade strikes very heavy lumber, the tendency of the transmission is to fail in the forward direction (with counter-clockwise rotor rotation,) The opposite is true when an advancing blade strikes a heavy obstacle, including the ground. (5) A landing in a sparsely wooded area may require more finesse than landing in a dense forest canopy since the few individual trees act as obstacles rather than energy absorbers. Under these circumstances, the terrain itself will probably be the main touchdown area and hitting an obstacle prior to touchdown often leads to loss of aircraft control and an uncontrolled crash. For example, if the left side of the rotor disk were to settle into trees while the right side met no resistance, the afrcrait would tend to strike the ground on its right side. (6) Brush-type Vegetation of less than helicopter height should be dealt with as if it were not there (7) Clearings in woods should be treated with caution as they may contain tree stumps and other obstacles that may penetrate the aircraft's bottom. (8) Dead trees are dangerous; they offer little energy absorption and tend to puncture the fuselage (9) A tree landing should be executed with zero or near-zero ground speed and in a tail-low attitude If for some reason the pilot is unable to reduce forward velocity to safe limits and tree contact is unavoidable, he should flare the aircraft Ii an extremely nose-high attitude against the densest growth and as close to the ground as possible. In this case, the pilot is using the trees to absorb energy of motion in the horizontal plane and the bottom of the aircraft becomes the main contact point as well as a protective shield. Even individual trees--preferably the smallest ones--can be used for this purpose if the center of the aircraft is aimed at the center of the tree crown. Uprooting a tree under these conditions adds to the impact attenuation process, as shown by accident experience- As far as less yielding obstacles and man-made obstructions are concerned, the same concepts apply: Avoid nose-first contact under all conditions and avoid destruction of the main rotor until the aircraft is close to the ground and/or the forward velocity is negligible.
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