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Helicopter question


Alpo
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If a helicopter can get off the ground, can it fly?

 

Movie. Yes I know it's Hollywood and they can do whatever the hell they want. The helicopter is loaded with gold. It is about 6 feet off the ground and they're complaining that it's too heavy.

 

Just seemed to me that if it was too overloaded to fly, it would not be able to get off the ground at all. If they could get it six feet off the ground, they could fly away. They might not get very high, but they could fly.

 

Anybody got any helicopter experience that might know an answer to that?

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There’s a phenomenon called ground effect where aerodynamic drag is reduced when operating very close to the ground. My experience with it is with fixed wings.
 

As I recall, an overloaded helicopter might be able to fly, but only within the GE regime which is roughly 10 feet above ground. 
 

Hopefully Charlie Harley will chime in. 

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Disclaimer: I was Huey mechanic/crew chief in the Army after high school, not a pilot.  That was a long time ago.  If I remember correctly, If we had a wide open space we could remain in ground effect while we gained airspeed.  More airspeed created more lift.  I'm sure a helicopter pilot could explain it better.

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Read Robert Mason's "Chickenhawk."  ;)

 

 

         51IFx69HwvL._SY291_BO1,204,203,200_QL40_FMwebp_.jpg

 

 

 

 

 

 

 

Edited by Hardpan Curmudgeon SASS #8967
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297120876_IMG_20210917_2238314962.thumb.jpg.275ced18631872ef2f925e6c50fca4d1.jpg

 

You see all the boxes that are stacked in the back of the cargo area? They're full of gold. So that is as high as the overloaded bird can get off the ground.

 

Oh no. We are too heavy.

 

They pitch out the hostage. They pitch out the pilot - the bad guy is going to fly it himself. Then he throws out his assistant. Have to make it lighter so he can fly away.

 

They seem to be about 10, maybe 12 feet off the roof.

 

In case anyone's interested, the assistant caught hold of a skid, then started shooting into the bottom of the bird with her Uzi. Blowed a hole in the bottom and the gold started falling out. The bad guy let go of the controls to try to save his gold. That was a mistake.

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Yes and no…depends how heavy.  As mentioned there is an “in ground effect” where the air coming through the blades hits the ground and creates a cushion like effect.  The problem becomes moving through effective translational lift or ETL where you are out of ground and on your own gaining some lift through forward movement.

 

Now if you had a 100 mile long highway to follow you could probably bounce it down it all day long or until enough fuel burnt off to lighten it.  If you want to clear trees or obstacles it would get a lot riskier.  
 

Overloaded enough to get off ground you could possibly finesse it enough to get through ETL with enough room is the bottom line.  You would have to worry about some flight conditions as well that could impact you such as PA\DA, temperature, winds etc.  It would be possible to lose control or if you tried to land you may not be able to stop your descent.  
 

 

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They are attempting to take off from the roof of a three-story building. As I said in my last post, they are about 12 feet above the roof.

 

Would they be outside of ground effect, and actually flying at that height? If at that low altitude, they were to fly over the wall, so now instead of being 12 feet above the surface they are 45 feet above the surface. Would they still be flying or would they suddenly lose it and crash to the ground?

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"Yes" is not a nice answer to an either/or question. My father used to do that all the time. I never did like it. He thought it was funny.

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Reread the question. I asked if, once he flew off of the building and was no longer twelve feet above the surface but was now fifty feet above the surface, would he continue to fly or would he crash. Either/or. The answer, apparently, is that he would crash.

 

 

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I’d say it depends…likely at the height in the pic i would say some benefit from ground, and once over the edge would lose that…likely would be a drop but I can’t say how much.   If pilot was able to gain some forward airspeed once over the side, likely while dropping it could in theory make it.   It could also not have enough power to arrest a descent if started and could crash.

 

A vertical take off would use the most power once out of ground effect.   That might be safer to try to find out where you are…

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I was told that helicopters don’t actually fly.  The explanation was that they beat the air into submission!!

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19 hours ago, Abilene Slim SASS 81783 said:

Hopefully Charlie Harley will chime in. 

 

19 hours ago, Chuckwagon McTaggart said:

I'm sure a helicopter pilot could explain it better.


This is me on both accounts. And I have to say that most of the answers are pretty close to accurate. 
 

Bottom line:  If a helicopter can hover, it can most likely fly away. 
 

If the aircraft can pull to a 6’ or so hover, it is still “in ground effect” or IGE.  Basically, the air that is pushed down by the rotor wash hits the ground and creates a cushion that helps keep it off the ground. 
 

Above about 10’ or flying off the top of a building, the ground is too far away to create that cushion. At this point, the aircraft is Out of Ground Effect or OGE. An OGE hover takes a lot more engine power and is one of the harder maneuvers to execute. 
 

The second phenomena in play here is Effective Transitional Lift or ETL. When a helicopter is in hover, whether IGE or OGE, a large part of the rotor was hits the fuselage’s top. Obviously, this makes it hard to hover when it’s own rotor wash is pushing down on the frame.  
 

As the helicopter starts moving forward, the rotor wash starts moving to the rear. Around 10-20 knots of speed,  the rotor wash is no longer hitting the fuselage and the aircraft gains lift. It actually is a neat feeling when piloting a helicopter to go through ETL and suddenly you have lift without adding power. 
 

Back to Alpo, the bad guys are hovering, so if they can gain airspeed and go through ETL, they can fly away with all the gold. 
 

They’re on a building so they do t have much space to reach ETL, but when they fly off the side and start dropping, they’ll gain airspeed and maybe reach ETL, or maybe hit the ground first. 
 

And in truth, this scenario is not far-fetched. It is the exact scenario faced by helicopter pilots when they picked up people in tight places in the mountains of Afghanistan.  Sometimes they literally flew off the side of a mountain to gain air speed so they can eventually fly away with wounded. Real world.

Edited by Charlie Harley, #14153
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In one of the Charlie Castillo books he is going to take off in a Blackhawk from an aircraft carrier. He has never taken off from an aircraft carrier before. So he puts it in a hover six or eight feet above the deck, and let the carrier sail out from under him.

 

Now if I am understanding your response correctly, he could hover 8 feet off the deck nicely, but when the deck was no longer underneath him, and it's 80 feet or so down to the water, he's likely to get wet?

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20 hours ago, Alpo said:

If a helicopter can get off the ground, can it fly?

 

Movie. Yes I know it's Hollywood and they can do whatever the hell they want. The helicopter is loaded with gold. It is about 6 feet off the ground and they're complaining that it's too heavy.

 

Just seemed to me that if it was too overloaded to fly, it would not be able to get off the ground at all. If they could get it six feet off the ground, they could fly away. They might not get very high, but they could fly.

 

Anybody got any helicopter experience that might know an answer to that?

Short answer: Yes, if it can hover, even if overloaded...it can stay in ground effect until it picks up speed (like an airplane), then it can climb.

of course if it is not too over loaded.

By the same token, if he gets it flying and has a problem, same rule applies, he has to land like an airplane or risk stalling the blades and crashing.

Edited by Savvy Jack
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As long as not overloaded won’t get wet.  You typically have weight and balance checks done combined with weather conditions to know your situation before you take off.

 

Directional airspeed is your friend.  Yes, you can sit and hover at 2,000 feet but it’s the most unnatural feeling ever and I did not like it.  I would take a high speed low altitude autorotation at tree level any day over a stationary hover autorotation.  There is some strange comfort in being closer to the ground.

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My experience, was Trees are your friend.  Altitude was not your friend over a hot LZ or SAR, especially the rescue part.  With some altitude, you quickly become a Slow Aerial Target.  Trust me, that is NOT fun.  Exciting, but NOT fun.

 

Autorotation, regardless of altitude is NEVER fun.  For as long as I was Air Crew, I was in complete agreement with Blackwater's information.  The Helicopter just beats the atmosphere into submission and when that loud thing overhead gets quiet, homesick rock.

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I hopped ona Huey that was leaving our firebase in Cambodia. It was a cool rainy day. As I sat there wet and miserable a few guys headed to R&R climbed in. Then a scout dog handler and his pooch. Then they loaded a pile of captured weapons and the outgoing mail. Then a couple of Kit Carson scouts. Eventually we were chock full and the pilot pulled pitch.


We lifted up about 8 feet or so. I was sitting  jammed behind the pilot as he and the copilot were looking at the gauges. A couple of them seemed to be in the red zone. The drivers looked at each other and shrugged. The nose dipped and we started moving forward. The tree line was about 3-400 meters away. We raced toward it. I waited for us to get some height. We didn’t. Just kept speeding faster toward those bigass trees. I tried to remember the Hail Mary thing but being a pagan I had to improvise. I decided that if we were going to hit the trees I would shoot the pilot at the last second. :angry: 

Then, miraculously, we suddenly started to pull up. We cleared the triple canopy by 10 or 15 feet. The copilot looked back at me and winked!

I considered shooting him.

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Way back I worked for Digital Equipment Corp.  The company believed that putting the right people face to face led to better products.  DEC had an Air Force, many helicopters and a few fixed wing craft. When we were designing some terminals we would book a chopper flight to have a meet with the hardware types, etc. could also use a chopper to get to an airport.  DEC had a gate at Logan airport and at Manchester in NH.

 

nothing quite like flying over Storrow drive at 120mph while the evening traffic is bumper to bumper at 40. To and from an airport, I’d be invited to sit in the left seat up front, always a thrill.  Whenever the company planned a building, a helipad would be included as well as a pond for the fire department to draw from if needed.

 

I was told that a candidate needed 5000 hours of helicopter experience before being considered for employment. The number seems incredible now but we were told that Viet Nam vets had that many hours.

 

we had Bell Jets, sorry but I don’t have more info.

 

So, IIRC in Spring ‘83, in Merrimack, NH, I was having lunch in the caf as a chopper took off from the helipad. We had all seen this many times. But there was a problem and it came down into the pond, the term is auto rotated. The water was not deep, maybe two feet over the bottom of the chopper bubble.  The passengers got into the water and walked ashore. The pilot remained with his ship.

 

The pilot was the most senior pilot in the company and was the one who gave autorotation tests to the other pilots.

 

I had a neighbor who was also a DEC chopper pilot. Some time after the event I commented to him about the incident. He told me that the pilot quit flying after the incident, he had never had such a terrifying incident before and he couldn’t swim.

 

 

Edited by Marshal Mo Hare, SASS #45984
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Alpo, you over-think and over-analyze and ask lots of odd questions about books you're reading (how many books a day do you read, anyway?) or movies you watch, but BY GUM!!!! do you generate some fine and fun discussions with those questions!

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40 minutes ago, Subdeacon Joe said:

Alpo, you over-think and over-analyze and ask lots of odd questions about books you're reading (how many books a day do you read, anyway?) or movies you watch, but BY GUM!!!! do you generate some fine and fun discussions with those questions!

Damn! He’s gonna need a bigger hat!

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One problem with jet engines is their power output is proportional to mass flow.  Mass flow is a function of intake air temperature, pressure & humidity.  An issue with jet engine powered helicopters is close to the ground in a hover is the HOT exhaust gas mixes with the rotor air which is deflected upward by the ground.  Some of the heated air will be ingested into the engine air intake.  The hotter intake air reduces the mass flow through the engine; therefore the max. shaft power is less than when not hovering.

 

P.S. The only way to counteract the loss of max. power would be if there is a water supply to humidify the combustion air (cools intake air by evaporation & increases mass flow).  This and/or air conditioning the intake air of gas turbine powered utility power generators are employed to maximize revenue during peak electricity demand periods.

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Just because a helicopter can hover and move forward, does not mean it can get out of ground effect and fly.

 

I actually witnessed this back in the 80's.

 

There was one of our regular summer fires in the mountains down here in southern Arizona.  Hueys were used to transport Firefighters to the fires.  One typical 100 degree June afternoon they loaded up, got into a hover, taxied to the runway, went screaming down the runway for at least a mile, could not get out of ground effect.  Turned around, tried again, no luck.

 

They taxied back, two guys got out, they went out again, and down about a mile, just barely got out of ground effect and flew off.  Took quite awhile to get any altitude.  Density altitude was probably close to 10K.

 

I don't fly them, but been fixing them since '82.

 

 

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