posted
Apparently, there's a rumor that a postage stamp placed on the rotor of a helicopter can throw off the delicate balance of the blades and cause it to crash. This one's false. I just saw it on the new mythbusters with the Diet Coke/Mentos experiments. But has anyone heard it before?
-------------------- I like to go down to the playground and watch the kids run and jump and scream, because they don't know I'm only using blanks. Posts: 942 | From: Illinois | Registered: Jan 2004
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Not I. Now something stuck to the rotors can affect if it is heavy or bulky enough or if the rotors are damaged so the concept is sound but the stamp just doesn't have enough mass/bulk.
But I do wonder why it took so long for the mentos/diet coke explosion to become a phenemeon. But then I have never had a mentos before then tried to drink diet coke while the candy was still in my mouth. Hey I think I figured out the most plausible reason someone figured out the mentos would have that reaction with the diet coke.
Now onto the methane soap bubble fire effect. That does have a very logical reason namely the methane gets into the soap bubbles when they are forming and lifts them up. Methane is flamable. Hence a huge flaming pillar. I certaintly would have used a remote lighter say one of those model rocket ignition switches instead of throwing a match at it.
Now the smoke bomb is quite easy to get a handle on since salt peter isn't as expensive/hard to get a hold of as the methane.
I have done the dry ice 2 liter soft drink bottle before. When you got a quarter of the bottle filled with water or even half the explosion occurs a lot quicker with a smaller piece of dry ice. As for sharpnel the bottle disintegrates when you do it like that but you would still want it far away from you. The trick is you put the dry ice then fastly tighten it then throw the bottle. It is fairly loud so loud after three or four you will have cops patrolling the neighborhood. Scares the poop out of any neighborhood dog too.
Now dry ice you can find at certain small markets/convenice stores. They also don't care what age you are if you look like a teenager.
Posts: 320 | From: Birmingham, Alabama | Registered: Jul 2006
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posted
That is so weird that this is on now. I just finished watching the mythbusters where they busted it.
Posts: 59 | From: Nampa, ID | Registered: Jun 2006
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PrincessLeia
I'll Be Home for After Christmas Sales
posted
I didn't see this Mythbusters episode, so I am not sure how they carried out said methane bubbles demo, but at my school, we put the bubbles on our hands or on someone's shaved head before lighting.
Posts: 185 | From: British Columbia, Canada | Registered: Jul 2005
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posted
They had a bucket filled with soapy water with a garden hose pumping in the methane. They got a five foot pillar of methane filled soap bubbles. Trust me you wouldn't light that close to you. It would burn off your face as well as ignite your clothes, body hair.
Posts: 320 | From: Birmingham, Alabama | Registered: Jul 2006
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quote:Apparently, there's a rumor that a postage stamp placed on the rotor of a helicopter can throw off the delicate balance of the blades and cause it to crash. This one's false. I just saw it on the new mythbusters with the Diet Coke/Mentos experiments. But has anyone heard it before?
Totally bullshit. I've seen rotor blades that has accidentally cut off tree tops as thich as my wrist, and the helicopter could still land.
The Mi-28 attack helicopter is designed to take a 30mm round to a rotor blade and keep flying. It just blows a neat hole, things will shake a bit, but it will get home.
The main rotor is fairly robust, it has to be to withstand the load, at speed and in wind. The tail rotor is more vulnerable, but can still take some damage.
Edit: If someone is interested in how a rotor blade is constructed, I have two pieces on the wall, one from a Bell 205/UH1, one from an AS350. They are cut in such a way that you clearly see the construction, and it would be easy for me to snap a few pictures.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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Those are military not civilian rotors. Numerous helicopter accidents in the states have been caused by the rotors slamming into telephone wires, trees etc.
Military helicopters have had decades of being shot down by rotor hits btw. Modern military helicopters are the result of a lot of research/development so they could survive a few hits there. A blast at the rotors is still one of the best ways to bring a helicopter down besides hitting the guys in the cockpit.
Posts: 320 | From: Birmingham, Alabama | Registered: Jul 2006
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posted
Considering that rotor repair is often done with "speed tape", there's no way a postage stamp will cause enough imbalance to cause the aircraft to crash.
Rotor RPM is, I think, on the order of only 500rpm. For a Huey with a 48ft rotor diameter, a 100mg postage stamp would put about half a pound of force on the rotor if placed at the rotor tip.
The problem of putting anything substantial on the rotor would be that I think most adhesives would let go during spinup long before the aircraft could take off.
I've got a couple of pictures of Apaches that took 20mm fire during Operation Iraqi Freedom. The rotors are pretty much in shreds, but they still managed to get back to their forward refueling point. Rotor strikes are a bit of a different issue. Since they invariably happen close to the ground and involve alot of energy and momentum transfer, the possibility of a crash is high, even if the aircraft would still have been flyable after the impact damage.
-------------------- "My neighbor asked why anyone would need a car that can go 190 mph. If the answer isn't obvious, and explaination won't help." - Csabe Csere Posts: 1225 | From: Wichita, Kansas | Registered: Nov 2003
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The Bell 205 is both military and civilian, and the blade part I have is from a civilian craft. The leading edge of that blade is a solid metal bar, approx 30 mm diameter (although it's more D shaped), followed by a sturdy box made of approx 5 mm aluminium, followed by aluminium honeycomb filling, all covered by sheet metal.
The AS350 is purely civilian (it might be used by some military, but not in combat operations). That blade has a sheet metal leading edge, with a solid composite bar behind it, followed by a composite box and filled with some kind of hard foam. The surface is hard composite material.
quote:Numerous helicopter accidents in the states have been caused by the rotors slamming into telephone wires, trees etc.
Of course, that has happened all too frequently here as well. It all depends on how it hits and what it hits, as well as how the pilot handles it. My point is that it's possible for a helicopter to survive fairly hard hits to the main rotor, such as a tree top. A stamp will do nothing to something that can survive that.
Think about it for a while. The rotor blades are quite flexible (look at the rotor disk the next time you are flying in one, you'll see how it constantly flexes to absorb vertical and horizontal movements). They move a lot, especially in rough weather. The blade travelling forwards is moving faster through the air, so that also creates some imbalance. You are basically hanging several tons off the rotor blades. All that together is much more than the weight of a stamp.
quote:Military helicopters have had decades of being shot down by rotor hits btw. Modern military helicopters are the result of a lot of research/development so they could survive a few hits there. A blast at the rotors is still one of the best ways to bring a helicopter down besides hitting the guys in the cockpit.
Yep, rotor hits tend to bring them down, and the Mi-28 is more or less unique in its ability to withstand hits.
That said, aiming at the rotor is pretty useless, as an hit is unlikely. Remember, only a tiny bit of that rotor disk is actually a rotor blade at any given time, and even if you hit the blade, you need to hit some part that gives it structural integrity, and hit it so badly that it breaks. A hole straight through it will not down the helicopter, it has to break that leading edge reenforcement.
If you are trying to take down a helicopter using small arms fire, aim for the crew or engine if it's a civilian helicopter. If it is military, hide until it goes away, as the vulnerable spots are small and very difficult to hit.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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quote:Originally posted by Troberg: If it is military, hide until it goes away, as the vulnerable spots are small and very difficult to hit.
That and they're usually armed and rarely travel alone.
-------------------- "My neighbor asked why anyone would need a car that can go 190 mph. If the answer isn't obvious, and explaination won't help." - Csabe Csere Posts: 1225 | From: Wichita, Kansas | Registered: Nov 2003
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posted
On a related note, I had heard a story of a helicopter that got a bullet hole thru one of the rotors and couldn't take off. The pilot shot a hole thru the other rotos and taped over the holes with duct tape, and was then able to take off. But after seeing the stamp episode and reading these comments, I start to doubt whether the original hole would have been that much of a problem.
Posts: 439 | From: Redondo Beach, CA | Registered: Sep 2005
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quote:Originally posted by Troberg: Edit: If someone is interested in how a rotor blade is constructed, I have two pieces on the wall, one from a Bell 205/UH1, one from an AS350. They are cut in such a way that you clearly see the construction, and it would be easy for me to snap a few pictures.
I'd be fascinated! I've seen cross-sections of old wooden propellers -- aviation-themed bars tend to have shortened antique prop-hubs on the wall as part of the decor, but these are usually carven wood. I've never seen a cross section of a modern prop, either fixed-wing or 'copter.
Thanks!
Silas
Posts: 16801 | From: San Diego, CA | Registered: Sep 2000
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quote:CW3 Robert Carpenter, who during a combat aerial reconnaissance mission in Iraq, received hostile fire to his OH-58D which caused significant damage to the main rotor. CW3 Carpenter reacted to significant control vibrations and executed a landing without further incident. Postflight inspections revealed that one of the rotor blades was missing a 3-foot section of its leading edge.
Ovbiously, if helicopters can sustain that kind of damage and still be in flyable condition (albeit with control vibration), then a postage stamp isn't going to cause it to crash.
-------------------- "My neighbor asked why anyone would need a car that can go 190 mph. If the answer isn't obvious, and explaination won't help." - Csabe Csere Posts: 1225 | From: Wichita, Kansas | Registered: Nov 2003
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posted
Maybe it's not the weight or drag of the postage stamp that causes a crash- but the cost for postage nowadays is more than enough to unbalance a blade. LOL
Posts: 479 | From: Owosso, MI | Registered: Jun 2003
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quote:On a related note, I had heard a story of a helicopter that got a bullet hole thru one of the rotors and couldn't take off. The pilot shot a hole thru the other rotos and taped over the holes with duct tape, and was then able to take off. But after seeing the stamp episode and reading these comments, I start to doubt whether the original hole would have been that much of a problem.
I believe that he wouldn't take of, but not that he couldn't. If you are in the air when it happens, you don't have any choice but to keep flying, but if you are on the ground, you don't take the risk of there being structural damage. The rest of the story (shooting the opposite blade) sounds like bullshit, if nothing else because those blades cost more than a car.
quote:I'd be fascinated! I've seen cross-sections of old wooden propellers -- aviation-themed bars tend to have shortened antique prop-hubs on the wall as part of the decor, but these are usually carven wood. I've never seen a cross section of a modern prop, either fixed-wing or 'copter.
I'm off to work now, I'll snap some pics in the next 10-12 hours or so.
quote:CW3 Robert Carpenter, who during a combat aerial reconnaissance mission in Iraq, received hostile fire to his OH-58D which caused significant damage to the main rotor. CW3 Carpenter reacted to significant control vibrations and executed a landing without further incident. Postflight inspections revealed that one of the rotor blades was missing a 3-foot section of its leading edge.
He was lucky, I knew one pilot who didn't make it after loosing one meter of a blade to a wire supporting a telecommunications mast, on a helicopter of similar size.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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As I don't own a weapon, I had no bullet to use for size reference, so I used an AA battery instead.
The large blade is a Bell 205 ( http://en.wikipedia.org/wiki/Bell_205 ), the smaller is a As 350 ( http://www.airliners.net/info/stats.main?id=202 ). The large wing rib beneath them is from an older glider (the exact model is written on the side facing the wall, and I don't remember which model it is now), and is a good example of how aircraft used to be built.
I tried to get a shot of the trailing end of the Bell 205 where some of the covering metal is cut away so you can see the aliminium honeycomb structure, but it's a bit dark, so you may have to increase the brightness on your monitor a bit. I was in a bit of a hurry, so I didn't have time to go for another snap with an external flash.
As you can see, in most places, a bullet would just punch straight through with very little damage. You can also see the size of the blade and imagine how little difference the slight change in geometrics from the edges of the exit hole would make.
The Bell 205 construction is all metal. I believe the cover on the leading edge is steel and the rest is aluminium, apart from the main support behind the leading edge. I have no idea what metal that is, it looks a bit like bronze, but it doesn't make sense to use bronze there, so it's probably some other alloy.
The As 350 construction is all plastic and composites (apart from a bit of sheet steel over the leading edge) and represents the current generation of rotor construction.
Worth noting is also that the Bell 205 blade is much larger. This is not only because it's a bigger aircraft, it's also because it had a two blade rotor. This makes the construction of the rotor head simpler, but makes the rotor larger and gives it a much heavier thump-thump noise. The trend now is to use more rotor blades, which makes the rotor disk smaller (needs less landing space) and gives less annoying noise levels (less sound and more of a constant drone than the classic thump-thump). Sound levels are very important for civilian use. A smaller rotor disk also lessens the problems associated with the forward moving blade generating more lift than the backward moving blade, as well as the speed limits imposed on the aircraft by the tip of the forward moving blade approaching the speed of sound (it is a bad thing if it gets too near the sound barrier).
It's a sturdy construction, but one must remember that it has to be capable of lifting 2 tons of cargo and 2.5 tons of helicopter, plus fuel, all hanging from that rotor and rotor head/mast, even in choppy conditions which causes much higher peak loads. A stamp will not make any difference at all.
If I recall correctly, ordinary metal washers are used to balance the blades (this probably varies between models). Look at the ends of the blades the next time you have an opportunity to get close to a helicopter. When the best resolution you can get on that is one washer, you also see that a stamp could not make much difference.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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quote:I've seen cross-sections of old wooden propellers -- aviation-themed bars tend to have shortened antique prop-hubs on the wall as part of the decor, but these are usually carven wood. I've never seen a cross section of a modern prop, either fixed-wing or 'copter.
Propellers for fixed wing aircraft are solid. They may be wood, aluminium or composites, but they are solid. Wood is still in use, as it has some nice properties the other materials lack, which makes it sensible in some applications.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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quote:Originally posted by Troberg: Forgot to answer this one:
quote:I've seen cross-sections of old wooden propellers -- aviation-themed bars tend to have shortened antique prop-hubs on the wall as part of the decor, but these are usually carven wood. I've never seen a cross section of a modern prop, either fixed-wing or 'copter.
Propellers for fixed wing aircraft are solid. They may be wood, aluminium or composites, but they are solid. Wood is still in use, as it has some nice properties the other materials lack, which makes it sensible in some applications.
Out of curiosity, what would those properties be? I can't seem to think of any property wood possesses that wouldn't be outstripped by another material, such as aluminum (which you mentioned), or a composite (which you also mentioned). Admittedly, I'm no expert, so I'm assuming I'm missing something.
Posts: 121 | From: Illinois | Registered: Jul 2005
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quote:Out of curiosity, what would those properties be?
Well, the most well known is used on the Yak-50 and the Yak-52, where the wheels do not fully retract into the wing so that it can make a belly landing without getting destroyed. The propeller is too large to survive that, though, so it's designed to break at a certain length, then there are markings on it which you can use to saw all blades to the same length, which will be enough to fly home (this is probably another nail in the coffin for the stamp myth). Wood splinters in a way that makes this possible, but composites and aluminium would be destroyed.
Wood is also less likely to break unexpectedly, as it's less likely to have microscopic cracks that are not visible to the naked eye but which can make it fail. Both aluminium and most composites are also prone to cracking and breaking if struck by something, such as debris on the runway or another aircraft (for instance, if failing to fly in formation). Wood can also do that, but if you're lucky it will just chip.
I suspect (although I have little proof of it) that more aircraft would use wooden props if there were more skilled people that could make them.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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posted
Troberg: thanks! That's nifty. I love the various weight-saving techniques: the honeycombing, the hollow section, etc. Also, good points about wooden propellers and the differences in natural properties of wood and metal.
I will add that both wood and metal flex a little under stress -- airplanes' wings are designed to flap up and down, a little, under lift or load -- but that wood recovers from distortion with less permanent alteration than metal does. Metal fatigues under repeated stress, whereas wood, being more spongy, springs back to its old shape without being permanently weakened.
Wood, however, is bulky: you can't cut it as thin as you can cut metal and have it retain its strength. Also, pieces of wood must be shaped individually, whereas metal parts can be stamped out in cookie-cutter processes, so (as always!) economics is a big determiner of materials.
quote:Originally posted by Silas Sparkhammer: ... Also, pieces of wood must be shaped individually, whereas metal parts can be stamped out in cookie-cutter processes, so (as always!) economics is a big determiner of materials.
Silas (cranium of oak, manhood of tin)
Wood can, and usually is, carved by automatic machines. A modern high speed CNC controlled router can probably turn out a wood prop as fast as it could be cast in metal. (I don't think you could "stamp" a prop from metal, the shapes is much to complex.)
Given the value of a prop, and the critical nature of its job, I wouldn't think that the economics of the material or the method of manufacture enter into it all that much. It is not like you are trying to stamp out a bazillion widgets that are going to sold for $1 a piece. Somebody's life depends on that hunk of wood or metal. Can you imagine what the insurance costs are for a company that manufactures props? Wouldn't surprise me if the insurance cost per prop didn't approach the cost to manufacture the prop.
Posts: 629 | From: Greenwood, IN | Registered: Dec 2005
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quote:Originally posted by Troberg: Worth noting is also that the Bell 205 blade is much larger. This is not only because it's a bigger aircraft, it's also because it had a two blade rotor. This makes the construction of the rotor head simpler, but makes the rotor larger and gives it a much heavier thump-thump noise.
I grew up around UH-1 Hueys and AH-1 Cobras with their two-bladed rotors and distinctive "Whop-Whop-Whop-Whop" sound. At one point I lived virtually across the street from the airfield with the rotating airfield beacon shining through my bedroom window at night. That sound is still near and dear to me!
-------------------- "My neighbor asked why anyone would need a car that can go 190 mph. If the answer isn't obvious, and explaination won't help." - Csabe Csere Posts: 1225 | From: Wichita, Kansas | Registered: Nov 2003
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quote:I will add that both wood and metal flex a little under stress -- airplanes' wings are designed to flap up and down, a little, under lift or load
Yep, that flex is needed for the construction to work. It's much like a fishing rod, which would snap under load if it was rigid, but the flexibility allows it to bend instead.
quote:Wood can, and usually is, carved by automatic machines. A modern high speed CNC controlled router can probably turn out a wood prop as fast as it could be cast in metal.
Yep, but it still takes a very experienced human professional to pick out the right piece of wood for such a critical application. Metal and composites are pretty much solid ang homogeneous quality, while wood requires you to find the right piece and determine where in it you'll find your propeller.
quote:Can you imagine what the insurance costs are for a company that manufactures props? Wouldn't surprise me if the insurance cost per prop didn't approach the cost to manufacture the prop.
I doubt it. Insurance cost is not based only on the cost of a failure, but also the frequency of failure. With all the regulations regarding service and technical maintenance, failure is _very_ uncommon. If there is a fault, it is discovered before it becomes a problem almost every time, and becomes an ordinary warranty issue (if the part is new enough).
quote:I grew up around UH-1 Hueys and AH-1 Cobras with their two-bladed rotors and distinctive "Whop-Whop-Whop-Whop" sound. At one point I lived virtually across the street from the airfield with the rotating airfield beacon shining through my bedroom window at night. That sound is still near and dear to me!
You and my parents' dogs should have a talk to Pavlov.
When they lived in Stockholm, the dogs got happy whenever they heard the distinctive sound of the helicopters my father used to fly, as they knew it meant that he would be home soon. After he died, they became sad and confused after hearing a helicopter and he wasn't showing up.
Btw, the UH-1/Bell 205 and the AH-1 share the same engine, driveline and rotor systems, so I'm not surprised if the sound is similar. My father had an idea (although never made anything out of it) to buy some surplus Cobras and convert them for lift jobs. They can carry as much as the Bell 205, but with a bubble canopy you have a good field of vision down towards the hook, and it's much faster which cuts down on ferry times and overhead. As most of the profitable helicopter jobs are lifting (mostly for the forest industry and the power companies), it would make a good machine for profits.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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The AA battery used for size reference in my photos is actually a pretty good choice of size reference. I brought out the calipers, and it's very close in caliber to a .50 bullet.
Just imagine how much damage that battery would do ig it punched straight through the blade, leaving a neat hole. Jacketed bullets leave neat holes in this thin aluminium (I worked a couple of summers changing lamps in streetlights, and outside populated areas, hunters sometimes get bored and shoot the lights). Almost no material is lost, just stretched into a funnel like shape. Apart from a few critical points (leading edge, back of "box"), a hit would do next to nothing.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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When I'm talking about AA battery for size reference, I'm talking about the kind of device used to power flashlights, not anti-aircraft artillery groups. Just wanted to make it clear, as there is a certain logic in both in this case.
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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quote:Originally posted by Troberg: Btw, the UH-1/Bell 205 and the AH-1 share the same engine, driveline and rotor systems, so I'm not surprised if the sound is similar.
Yup. That's why the Cobra was initally called the HueyCobra. The Army needed a gunship and the Hueys with bolt-on ordinance weren't quite cutting it. So Bell designed a new body tight around the Huey's driveline. The new AH-1Z has a 4-bladed rotor, tho.
quote:Originally posted by Troberg: Just imagine how much damage that battery would do ig it punched straight through the blade, leaving a neat hole. Jacketed bullets leave neat holes in this thin aluminium (I worked a couple of summers changing lamps in streetlights, and outside populated areas, hunters sometimes get bored and shoot the lights). Almost no material is lost, just stretched into a funnel like shape. Apart from a few critical points (leading edge, back of "box"), a hit would do next to nothing.
My dad once took a 7.62mm round clean through the aluminum drive shaft to the tail rotor on a OH-6. It somehow passed through without imbalancing the shaft.
quote:Originally posted by Troberg: Another small clarification:
When I'm talking about AA battery for size reference, I'm talking about the kind of device used to power flashlights, not anti-aircraft artillery groups. Just wanted to make it clear, as there is a certain logic in both in this case.
This is what a AAA Battery does to an Apache rotor blade. And it flew back to the FARP that way!
-------------------- "My neighbor asked why anyone would need a car that can go 190 mph. If the answer isn't obvious, and explaination won't help." - Csabe Csere Posts: 1225 | From: Wichita, Kansas | Registered: Nov 2003
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posted
I don't think any of you has proved the point. Not one of you has come up with a single instance in which a postage stamp was placed on a rotor and the pilot lived to tell the tale.
Posts: 4922 | From: Kyoto, Japan | Registered: Sep 2005
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quote:I don't think any of you has proved the point. Not one of you has come up with a single instance in which a postage stamp was placed on a rotor and the pilot lived to tell the tale.
If they can take losing big chunks of metal like that, I think we are pretty safe from mail man terrorists...
-------------------- /Troberg Posts: 4360 | From: Borlänge, Sweden | Registered: Nov 2005
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posted
The person posting the helicopter didn't remember to stamp: "Fragile: handle with care" on the side. The postmen can't be blamed for anything that happened to it in transit. Posts: 457 | From: Sacramento, CA | Registered: Jan 2006
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