23 June 2005

Vertical Takeoff

Helicopters are the most amazing contraptions!

Just land in your back yard, and if necessary, you can take off vertically, right?

Nope. Not always.

In previous posts I said the Charley Model Hueys I flew in Viet Nam wouldn't hover, and we had to do "running takeoffs" to get them flying.

Here's a video of a pilot that is almost in that position. The video reportedly is from Sweden. The family of a 100 year old man bought him the helicopter ride to celebrate his birthday. Six people from his family join him on board the Russian MI-2 helicopter, so it's fairly heavy. The machine can hover close to the ground, but has trouble getting any higher.

The results are interesting:

http://svt.se/content/1/c6/40/98/01/helikopter2.asx

It's also reported the Birthday boy got two helicopter rides that day........the second in an EMS helicopter.

Happy Birthday, Grandpa!

UPDATE, 25 June:
Aviatrix, www.airplanepilot.blogspot.com , comments she would like a better explanation of what happened here.

Again, I need you to visualize for me...........
When a helicopter hovers near the ground, it draws air from above the rotor and forces it down. That "donut" of air around the main rotor then strikes the ground, moves outbound and upward, and is then re-accelerated through the rotor. It makes the rotor VERY inefficient in a hover, because the air the machine is using to support itself is already moving as it enters the rotor from above and needs to be accelerated again.

If you recall, I said once you begin forward movement with the helicopter and the rotor begins to move into un-accelerated air, the rotor becomes more efficient. That transition into clean air is called "translational lift".

A helicopter will actually fly at MUCH lower power settings than those it needs to hover. That's how we took off in Viet Nam with Gunships that were so heavy they wouldn't hover......we slid them forward on the ground, (a "running takeoff"), until the rotor was in clean air.

This pilot no doubt was trying to accelerate the helicopter through translational lift so it would have the necessary power to climb out from the tight space he was in.......and yes, that is the reason he slid sidewards and backed up before he started forward movement.........to give himself as much room as possible to accomplish that.

Unfortunately, once he started down the narrow street, he was pretty much fully committed to the takeoff run.

One more thing.......striking a few leaves will probably not damage the rotor. I suspect the rotor on this machine could have even eaten a few fairly small branches without a problem. What finally brought his effort to an end was striking a utility pole!

4 comments:

Rubberducky1.0 said...

I would laugh at the stupidity of the guy, but it scares me a little to much.

I'm sure the guys down at the airport will want to see this.

You have me worried now. When I thought noone was reading my blog, I figured it was safe to skip days. I'll be sure to stay on top of it, and check yours now and again for kicks and adivce when needed

Aviatrix said...

Can you give us non-rotary pilots more information on what seems to have happened here?

Was he initially backing up to get a bit of room in order to puck up horizontal speed and climb?

Did he misjudge the proximity of the trees or have some control difficulty that caused him to hit them. (I'm guessing that even a few leaves are not something you want to whack with your rotor blades).

Walk us through what seems to have occurred.

Aviatrix said...

Ahh, thank you. Excellent explanation. We didn't notice the utility pole hidden in the trees -- I guess neither did the pilot, until he hit it.

Do helicopter operating manuals have tables to calculate the amount of space you need to gain a certain amount of altitude, based on wind and weight and temperature and elevation, the way fixed wing ones do?

Greybeard said...

Aviatrix.....
The answer to your question is yes, BUT!
I think most of that stuff is now required by the FAA (CAA?) in order for an aircraft to be certified......
The MI-2 is old, and may not have had performance planning charts to fall back on.
We are also watching a video of a Russian aircraft in Sweden making this takeoff attempt, so FAA rules don't apply here anyway.
And of course there is always reality rearing its' ugly head.....
You land and pick up your clients. They are excited to get the ride under way. In this case, the pilot was dealing with a 100 year old passenger that may have been difficult to get aboard.
The charts, if there are any, are in the P.O.H. (Pilot/Operators Handbook). This document may be stored under the seat....difficult to grab and refer to, particularly if you are in a hurry.
Helicopter pilots more often than not use their "gut feeling" about takeoff power. When you have difficulty maintaining a hover, alarms should be going off, unless you are in an area with no obstacles.
This pilots' "alarm system" failed him.

I've always wondered about the charts anyway. For most helicopters, they are difficult to read, and when you do it correctly, require a certain amount of interpolation. Do they illustrate power that can be expected of a new machine, or one that has 1500 hours on the engine, bleed air leaks, and lots of bugs on the main rotor?
In the real world of helicopters they are nearly useless........I know of no pilot that ever REALLY refers to them!