EOL into wooded areas

[Mungo5]

An interesting discussion has erupted here, as a result of the very sad and unfortunate S300 crash in Massachusetts yesterday, so rather than invade that thread.

As someone who regularly flies a piston engine in the same area and equally wooded areas of the North Eastern US, I've often discussed what to do in the event of an engine failure over wooded areas.

The two schools of thought are generally accepted: Auto as normal to tree top height, looking for the densest part of woodland, then pull back in the cyclic so the tail goes in first and tries to cushion the fall. The other method up for consideration is to look for the sparsest woodland and try to auto as normal, chopping your way in with the blades.

Thoughts?

[Gordy]

Here is your answer taken from

DEPARTMENT OF FLYING SAFETY
THE UNITED STATES ARMY PRIMARY HELICOPTER CENTER
FORT WOLTERS, TEXAS
File No. 1-403-2
STUDENT HANDOUT
HELICOPTER ACCIDENT PREVENTION
"HOW TO CRASH A HELICOPTER"


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.


You can read the whole document Here (http://fireheli.com/Files/howtocrashahelicopter.pdf)

[biggles99]

My hat comes off to anyone who can remember any part of that excellent advice Gordy has dug out for when the engine quits for real over the woods.

For me, I think that I'd do everything I could to get the groundspeed back to zero and point the nose up as far as practical just before impact.

After that, it would be all luck -- either good or bad.

Big Ls

[Trans Lift]

Agreed. I have discussed it many times too as I fly in the same area, just south, of where the crash was. It is a very heavily wooded area. I think I would treat the tops of the trees as the ground and just do my best to flare back to zero airspeed, get an extremely nose high attitude and try and settle into the trees tail first.

Its a hard one to call though!

[Heli-Ice]

Thank you for this thread and thanks for the document Gordy.

I have often thought about how you guys look at this and I have to say that I admire your faith in your machines.

Up here in Iceland we don't have woods but we have very cold waters and we usually do not fly over them in single engined helicopters unless with our rubber boots on (Wellingtons for the Brits).

[Mungo5]

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.

There's food for thought right there. Even if you get down to a survivable drop, you've always got to consider the Tranny coming through the back of the canopy to struff you. I suppose the same applies when settling into water - roll over to the right so the advancing blade stops first.

Heli-Ice.. Mass, Maine and New Hamps are in the three most wooded States in the US.. Translift and I are often over those woods for most of our time in the air.

[Gordy]

biggles

My hat comes off to anyone who can remember any part of that excellent advice

I don't think I have it memorized but I do know the basics. It is better to at least read some ideas than be faced with the situation unprepared. For some it is our bread and butter....a vast majority of my time is spent 50 feet above the forest...then add fire and one has to have a plan for the worst case scenario. I discuss it with my crew probably every couple of months.

This was the recent, (last week), 8,000 acre jack pine crowning fire in Michigan where we lost a bunch of homes, as you can see---nowhere good to go if the engine quits---I am headed to the trees:

http://i76.photobucket.com/albums/j35/helokat/Rolla%202010/MeridianBoundaryfireMioMI5187.jpg

http://i76.photobucket.com/albums/j35/helokat/Rolla%202010/DSC00326.jpg

[Nigel Osborn]

Gordy

Suggest land upwind!:ok:

[SASless]

I had a Hughes 500D suffer an engine failure over a very large wooded place....called Alaska. It quit at 9800 feet above ground thus I had way too much time to think on the way down. After some highly concentrated observation, contemplation, and finally a decision....I gave up on making it to any kind of a clearing. There was one better place but no good places.

Being very late in the afternoon, I chose to put the Sun behind me...accepted the wind for whatever it was....and aimed for the one better place. After some waffling....I decided it was the trees for me.

I recalled something an old forestry pilot had told me many years before....and that was once one decided it was trees and not a clearing....then hold the collective all the way down....maintain lots of airspeed....and when there was no other choice...do a healthy flare....build all the rotor RPM possible...and just as you run out of airspeed/height/ideas.....aim for the best place you see in front of you. Use up all the rotor RPM and aim for the softest stuff possible...and aim to hit the big trees with all/both rotor blades at the same time.

It worked.....in fact I was able to do a cyclic climb and pop over some bigger trees and hit a very lovely hole in the trees....landed atop a very soft Pussy Willow thicket and walked away without a scratch on me or the aircraft.

Never arrive short with no Rotor RPM trying to make it to a clearing....always arrive with as much RPM as you can get.

Helicopter pilots live and die by Rotor RPM.

[kevin_mayes]

Sas
I was once on the UK run Robbo safety course, we talked about autos and energy in the rotors, I asked if it was better to overspeed the rotors at the last minute to gain energy near to the ground, would they fall off I asked, no but the tail will come off first... Apparenetly the R44 (which I was learning on then before the 47) only has one bearing half way down the tail, the shaft tends to "whip" about at speeds other than 100% RRPM and can whip about so much at higher speeds that it can detatch from the bearing and cut the tail boom off. I'm not too convinced my self, think I would still go for the highest RRPM to gain the most energy for the last few feet - after all in the woods a overspeed on the engine/gearbox is the least of your worries...

The examiner that did my initial LP Check on the 47 said much the same as the article above about landing in trees, "come down on the tail first, else the tail and engine will come down on you"

Kev.

[Heli-Ice]

Mungo5

Total respect :ok:

[Torquetalk]

and walked away without a scratch on me or the aircraft

As the bloke in Life of Brian said to the guy who fell out of the tower, got abducted by an alien spaceship, crash landed and then walked away unscathed: " you jammy b******" :ok:

[John R81]

Fascinating to read. I have absolutely no intention of ever trying this!


Still - I bet those who have started off like me