Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
Soku39
Topic Author
Posts: 1731
Joined: Fri Nov 03, 2000 7:16 am

Flying Stationary/backwards Relative To The Ground

Fri Apr 21, 2006 5:05 pm

Today I got in an intensely heated argument about flying stationary (for all intents and purposes a ground speed of 0 ) with my friend. I explained over and over how the relative wind can equal my airspeed, and that having that wind still going over the wings will generate sufficient lift to keep the airplane up even if I'm not moving relative to the ground. It seems though that he can not grasp the concept that the air is not attached to the ground, and that the ground has absolutely nothing to do with the speed of the airplane during flight as it is part of the air mass.
Does anyone have an easier less technical way of putting it, because 45 minutes of explaining and examples seemed to have failed.
The Ohio Player
 
3MilesToWRO
Posts: 264
Joined: Sun Mar 12, 2006 2:08 am

RE: Flying Stationary/backwards Relative To The Ground

Fri Apr 21, 2006 5:19 pm

A kite? You stand and keep the kite's cord - what's lifting the kite if not wind? (Remind your friend that you don't need to run with the kite all the time, you usually do a short takeoff run only  Wink
 
MrChips
Posts: 933
Joined: Wed Mar 30, 2005 2:56 pm

RE: Flying Stationary/backwards Relative To The Ground

Fri Apr 21, 2006 5:20 pm

Tell your friend to think about a boat in a river. If the current is 5 mph and you are paddling upstream but you aren't moving anywhere relative to the shore, your speed relative to the water is 5 mph. If you are paddling downstream at 5 mph relative to the water, then your speed along the shore is 10 mph in the opposite direction. It is exactly the same principle, just explained in a less abstract way.
Time...to un-pimp...ze auto!
 
3MilesToWRO
Posts: 264
Joined: Sun Mar 12, 2006 2:08 am

RE: Flying Stationary/backwards Relative To The Ground

Fri Apr 21, 2006 5:26 pm

The boat example has one, but serious incompatibility: the boat won't sink, whatever her speed would be. So the friend can easily reject this example as Completly Different Thing (R)  Smile
 
viv
Posts: 2953
Joined: Tue May 31, 2005 5:17 pm

RE: Flying Stationary/backwards Relative To The Ground

Fri Apr 21, 2006 8:39 pm

The difference between aiir speed and ground speed.

You can demonstrate the effect with a flying model aircraft - or a kite.
Nikon D700, Nikkor 80-400, Fuji X Pro 1, Fujinon 35 f/1.4, Fujinon 18 f/2
 
okelleynyc
Posts: 205
Joined: Fri Feb 24, 2006 10:26 pm

RE: Flying Stationary/backwards Relative To The Ground

Fri Apr 21, 2006 11:44 pm

Or, you could take him to see paragliders stupid enough to fly in 20+ mph winds. My neutral trim speed on my Ozone is about 22MPH. I've flown in conditions where the winds aloft were significantly stronger than at launch and encountered a very disturbing sensation - flying backwards and climbing albeit not very much!

With a glide ratio of only 8:1, you don't get very far in these conditions and really need to have a good bailout landing site. We have a gizmo called a speed bar that we use with our feet to change the angle of attack on the leading edge of the wing to help "drive" through the headwind or to increase our speed. The only problem is that if you're too agressive and encounter turbulent air, you can get a frontal collapse of the wing and then you're in a world of hurt.

My understanding of gliding is that you're always coming down. It's just that the column of air you're in is rising faster than your decent rate. So the net effect is you're able to maintain your altitude or climb.

I don't think that increasing the horizontal air flow over my glider would appreciably increase it's lift. I could be wrong, but that's why we're always in search of thermals. Upward moving columns of air. Maybe this is just a factor for paragliders aircraft?

Now I'm confused!


 Confused
Just give me my Vario, my Ozone Mojo and a gorgeous day of soaring.
 
aogdesk
Posts: 748
Joined: Wed Jun 09, 2004 2:26 am

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 12:44 am

Demonstrate like this: With your right hand raised, make a flat surface high above your head. Now, in one quick swooping motion, bring your hand down across your friends face, making firm contact. You've already done your best to explain verbally, hopefully my method of demonstration will drive the point home.
 
User avatar
Starlionblue
Posts: 19879
Joined: Fri Feb 27, 2004 9:54 pm

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 1:24 am

Quoting Okelleynyc (Reply 5):
My understanding of gliding is that you're always coming down. It's just that the column of air you're in is rising faster than your decent rate. So the net effect is you're able to maintain your altitude or climb.

I like the explanation.

Quoting Aogdesk (Reply 6):
Demonstrate like this: With your right hand raised, make a flat surface high above your head. Now, in one quick swooping motion, bring your hand down across your friends face, making firm contact. You've already done your best to explain verbally, hopefully my method of demonstration will drive the point home.

LOL!


It always amazes me how some people fail to think analytically, but are stuck in old preconceptions. Evaluate the evidence, always.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
474218
Posts: 4510
Joined: Mon Oct 10, 2005 12:27 pm

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 1:37 am

STOL aircraft work on the principal that if they can lower the stall speed to a point where the the headwind is greater, you can takeoff and land in a very short distance. I saw a Helio Courier (USAF U-10) land during an Edwards AFB airshow in the 1960's. The pilot flew into a 35mph headwind lowered the flaps increased the angle of attack and flew backwards a short distance and then landed, with no perceptible roll-out. After sitting on the ground for a short time the pilot throttled up and became airborne with no perceptible takeoff roll. The U-10 stall speed was about 30mph and the 35mph headwind was enough to create the lift required.
 
bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 2:04 am

It's not too easy to grasp unless you have a basic understanding of how lift is produced by the wing.

In very simple terms, a Cessna 172 needs the air to be passing over the wings to be around 50 mph say ... that is the speed of the air - nothing else. If there is no relative wind, then you can achieve this by moving 50mph forward into the wind. If the relative wind is already a 50mph headwind, then you already have the required speed of the air over the wings to produce lift...and in theory can stand still, or take-off vertically.

You have to keep explaining that it's the speed of the AIR over the wings that's make a plane fly (in simple terms again).

Maybe a wind tunnel example might help. Engineers test how the plane flies by 'blowing' wind over it - the plane is fixed and doesn't move. This is equivalent to just haveing a strong headwind.


Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
Tod
Posts: 1716
Joined: Sat Aug 28, 2004 6:51 am

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 2:57 am

Quoting Bond007 (Reply 9):
If the relative wind is already a 50mph headwind, then you already have the required speed of the air over the wings to produce lift...and in theory can stand still, or take-off vertically

This was accomplished from the top of Mt. Rainier in the mid-1950s.

Tod
 
Skyslave
Posts: 44
Joined: Sat Oct 22, 2005 12:52 pm

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 3:04 am

I've got another one... a bird! I've seen a bird ride the wind and actually start to move backwards.

I my self have put down full flaps and pointed my cessna 150 into a 40kt headwind. I started to slowly move backwards, it was a trip.
 
David L
Posts: 8551
Joined: Tue May 18, 1999 2:26 am

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 3:19 am

Quoting MrChips (Reply 2):
Tell your friend to think about a boat in a river.



Quoting 3MilesToWRO (Reply 3):
the boat won't sink, whatever her speed would be. So the friend can easily reject this example as Completly Different Thing

If your friend doesn't like the boat example, next time you get the opportunity, push him into a fast moving river and see if he can swim upstream at his usual speed (assuming his usual speed doesn't include a vertical component)!
 
Soku39
Topic Author
Posts: 1731
Joined: Fri Nov 03, 2000 7:16 am

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 3:27 am

Ha I like all of these especialy Aogdesk's. Thing is he just doesn't get that its the wind over the wings, not the motion in any direction. As much as I explain the more he argues back. So for now I'll let him coninute thinking the Earth is flat till this summer when I can take him up during some 35+ knot winds aloft. The cost of the flight will be the bet.  Smile
The Ohio Player
 
Skyslave
Posts: 44
Joined: Sat Oct 22, 2005 12:52 pm

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 3:33 am

Quoting Soku39 (Reply 13):
Ha I like all of these especialy Aogdesk's. Thing is he just doesn't get that its the wind over the wings, not the motion in any direction. As much as I explain the more he argues back. So for now I'll let him coninute thinking the Earth is flat till this summer when I can take him up during some 35+ knot winds aloft. The cost of the flight will be the bet.

Just dont tell him that the sun doesnt revolve around the earth, his skull may explode. Is he reading this thread with you, or are you just going to relay the posts?
 
User avatar
Starlionblue
Posts: 19879
Joined: Fri Feb 27, 2004 9:54 pm

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 3:34 am

Then again, if the runway were a conveyor belt.  stirthepot 
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
vikkyvik
Posts: 12567
Joined: Thu Jul 31, 2003 1:58 pm

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 3:49 am

So since we're using birds, in theory our chickenwire airplane is STOL. That ought to attract customers.

Quoting Starlionblue (Reply 15):
Then again, if the runway were a conveyor belt.

Dammit, look what you started.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
David L
Posts: 8551
Joined: Tue May 18, 1999 2:26 am

RE: Flying Stationary/backwards Relative To The Ground

Sat Apr 22, 2006 4:28 am

Quoting Starlionblue (Reply 15):
Then again, if the runway were a conveyor belt.



Quoting Vikkyvik (Reply 16):
in theory our chickenwire airplane is STOL.

And... goodnight!  crazy 
 
User avatar
litz
Posts: 2365
Joined: Wed Dec 24, 2003 6:01 am

RE: Flying Stationary/backwards Relative To The Ground

Wed Apr 26, 2006 10:27 pm

Back to seriousness (yes I know, not allowed), why don't you just take him up one nice gusty day and do some hovering?

Nothing's better than his own eyeballs looking at the ground not moving ...

- litz
 
oly720man
Posts: 5813
Joined: Fri May 21, 2004 7:13 am

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 12:02 am

Do you have any birds like seagulls that he can see hovering or flying backwards on a windy day?

Tell him to walk up the down escalator, or down the up escalator. Same idea.

Aircraft travel relative to the wind, he travels relative to the escalator.

Get him to throw paper planes on a windy day.
wheat and dairy can screw up your brain
 
User avatar
Starlionblue
Posts: 19879
Joined: Fri Feb 27, 2004 9:54 pm

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 1:06 am

Quoting Oly720man (Reply 19):
Do you have any birds like seagulls that he can see hovering or flying backwards on a windy day?

Tell him to walk up the down escalator, or down the up escalator. Same idea.

Aircraft travel relative to the wind, he travels relative to the escalator.

Get him to throw paper planes on a windy day.

Yes but he'll say "it's not the same thing". For some people physics varies per device.  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
cancidas
Posts: 3985
Joined: Thu Jul 03, 2003 7:34 am

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 2:37 am

did it only one, on a day with 50kt winds aloft. slowed the airplane down in slow flight until it stopped moving. an interesting experience for sure. we didn't go backwards, only sustained a C-172 in a "hover" for about 30 seconds.

would a 172's wing create lift in reverse or would it tumble from the sky?
"...cannot the kingdom of salvation take me home."
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 2:50 am

Quoting Cancidas (Reply 21):
did it only one, on a day with 50kt winds aloft.

You've got me beat. Despite a few thousand hours in good STOL airplanes (Helio Courier, DeHavilland Beaver to name two) and even helicopters I've never had the opportunity to do this. I've landed the Helio in a skydiving target, a sawdust pit about forty feet across. I've averaged 35 mph in the Beaver for more than three hundred miles, but I've never backed a fixed-wing aircraft up.

A good friend of mine once got a Beaver in a killer ridge wave and had it stationary for two and a half hours. He flew three and a half hours on about six gallons of gas. Not bad for an R-985. A dozen times he reached for the mixture to shut the engine down, but didn't want to take the chance. (You do get more cautious when you might have to pay for the airplane.)

Yes, absolutely, positively, a fixed-wing airplane can back up when conditions are right. I've seen it done at airshows a dozen times. I saw the late Captain Dick Schramm hover his J-3 into the wind at a height of a foot or two, then throw out a parachute tied to the tailwheel. The plane landed going backwards.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
planemad
Posts: 510
Joined: Tue Oct 07, 2003 9:35 pm

RE: Flying Stationary/backwards Relative To The Gr

Thu Apr 27, 2006 4:57 am

I found it easy to explain if I think of the air like a moving runway above the ground and the plane is going along that moving runway. The direction the runway is moving is the wind direction and its speed is the wind speed. The planes' speed therefore is varied depending on that moving runway.

Sam  Smile
 
prebennorholm
Posts: 7055
Joined: Tue Mar 21, 2000 6:25 am

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 5:21 am

Tell him that a plane is flying in a sea of air. Same way as a ship is sailing in water, or maybe even better a submarine.

A ship making 10 knots upstream a river streaming at 12 knots will never make it. It obviously ends up in the sea.

Flying in the air, then the ground is no more than a distant body which creates gravity. And airspeed is what created the lift to counter the gravity.

How the ground moves underneath, relative to the air, has no effect on the plane. Just like it has no effect on the flight that the whole thing - planet earth, its atmosphere and the airplane - is rotating around the sun at 18 miles per second. And the sun - positioned in a spiral arm of our galaxy - is rotating.... - while our galaxy group.... etc. etc.
Always keep your number of landings equal to your number of take-offs
 
Fly2HMO
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 5:37 am

I got an idea!!!

Fire flightsim up, load the 747, put a 160kt steady (no gusts, no turbulence) wind aligned with a runway, and just hover your way out of the airport. Show him the groundspeed. Then, make a 180 deg. turn to make it a direct tailwind, and show him the groundspeed again, which should be double, assuming you keep a constant AS of 160kt.

If that doesn't change his mind, I recommend you find smarter friends  Yeah sure
 
User avatar
Starlionblue
Posts: 19879
Joined: Fri Feb 27, 2004 9:54 pm

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 7:28 am

Quoting FLY2HMO (Reply 25):
If that doesn't change his mind, I recommend you find smarter friends

Lol! Concur!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
litz
Posts: 2365
Joined: Wed Dec 24, 2003 6:01 am

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 11:49 am

Was it a Dale Brown novel where the guy landed the 727 on the aircraft carrier in the middle of a tropical storm or hurricane?

Same principle, though - throw out anything on the wing you can for lift, and then push a TON of air at the plane from the nose, and you pretty much eliminate ground speed.

In his novel, they hovered the 727 right onto the fantail of an aircraft carrier.

Fanciful fiction yes, but boy would that have been a sight to see !

- litz
 
USAFHummer
Posts: 10261
Joined: Thu May 18, 2000 12:22 pm

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 12:34 pm

Quoting Litz (Reply 27):
Was it a Dale Brown novel where the guy landed the 727 on the aircraft carrier in the middle of a tropical storm or hurricane?

I believe it was in John Nance's "Medusa's Child"...

Greg
Chief A.net college football stadium self-pic guru
 
viv
Posts: 2953
Joined: Tue May 31, 2005 5:17 pm

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 5:45 pm

Take the example of a model aircraft in a wind tunnel. The aircraft is rigidly fixed in one position.

When the tunnel fans are switched off, the model aircraft has a ground speed of zero mph and an air speed of zero mph.

When the fans are switched on, they propel the air through the tunnel at, say, 100 mph.

The model aircraft now has a ground speed of zero mph, and an air speed of 100 mph.
Nikon D700, Nikkor 80-400, Fuji X Pro 1, Fujinon 35 f/1.4, Fujinon 18 f/2
 
speedracer1407
Posts: 330
Joined: Fri Dec 24, 2004 4:19 pm

RE: Flying Stationary/backwards Relative To The Ground

Thu Apr 27, 2006 6:45 pm

If your friend still needs convincing, here are some videos. You can explain the reasons for these takeoffs and landings at nearly 0 kt groundspeed, and suggest what would happen with another 15 kts of headwind.

http://www.alexisparkinn.com/photogallery/Videos/SuperCub18ftTO.mpg

http://www.alexisparkinn.com/photogallery/Videos/SuperCubLand.mpg
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
 
Soku39
Topic Author
Posts: 1731
Joined: Fri Nov 03, 2000 7:16 am

RE: Flying Stationary/backwards Relative To The Ground

Fri Apr 28, 2006 12:24 am

Ah thanks for all the replies and help. If he doesn't get it now, I will truly be shocked, though I'd like him to spend 120 bucks just to prove a point. That would be great.
The Ohio Player
 
rolfen
Posts: 1539
Joined: Tue Jan 17, 2006 6:03 am

RE: Flying Stationary/backwards Relative To The Ground

Mon May 01, 2006 6:36 pm

Maybe if you bring up the example of a treadmill
rolf
 
bri2k1
Posts: 952
Joined: Sun Dec 19, 2004 4:13 am

RE: Flying Stationary/backwards Relative To The Ground

Mon May 01, 2006 9:37 pm

I think the kite is a much better example than the treadmill, for the same reason that abomination of a thread about a conveyor belt runway went on forever. Airplanes are powered through the air, not against the ground. A treadmill runner pushes against the moving belt, not the air. They're both valid; I just personally believe the kite is a better example.
Position and hold

Who is online

Users browsing this forum: StTim and 8 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos