Bryan Wood

Bryan Wood

Well Known Member
For those interested next Wednesday at 9:00p.m. eastern the Mythbusters on the Discovery channel will be building and testing "Concrete Gliders" to see if it is possible to make such contraptions. Any predictions? :cool:

Best,
 
Concrete boat - Confirmed. Concrete Glider - Busted! Even if they think to use the foamed concrete used at the end of some commercial runways.

I did like the paper crossbow last night though - never would have thought it could work...
 
Yea Myth Busters, What's a good Aviation Myth to Bust?

bsacks05 said:
I want to see them do the "airplane takeoff from a treadmill runway" myth/theory.
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They will never do that since there is no myth or mystery, it's a riddle or trick word problem, easily solved with basics physics if you read the scenario carefully.

It's like asking what is heavier a pound of feathers or pound of lead?

The answer, a tread mill running in the equal but opposite direction proportional to the aircraft's (air)speed, makes no difference. The only difference is the tire speed (rotation) will be twice the airspeed at takeoff. Takeoff distance may be slightly longer due to increased wheel bearing friction. Now if you are in a car and the driving on a tread mill, opposite to wheel speed, than you'll not go anywhere, like running on a tread mill. However an airplane gains its thrust thru its prop not tires. :( :rolleyes: :eek: Sorry to ruin your myth.

Regardless its not likely anyone will takeoff on a treadmill, ever. :D


I would like more "Myth Buster" plane myths. We should write in with some suggestions.

ANY ONE KNOW OF ANY GOOD AIRPLANE MYTH'S TO SUBMIT?

PS: on TV Discovery, Friday's, there's a new series on aircraft dog fights, recreating famous aerial dog fights and battles, including bombing, with advance computer animation. I guess this is a spin off of the hour long special they did on 4 of the greatest dog fights, one from WWI, WWII, Korea and Vietnam a year ago.
 
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favorite

was when they shot a bird through a GA windesheild ..sometimes thos two arent as smart as they would have you beleive. or when they burried the hat guy in a coffin. you gotta admit that was a challenge. never wouldve gotten me to try it. makes me sweat thinking about it.
 
"Sorry to ruin your myth."

Don't be sorry, George. It's not my myth. It does, however, spark impassioned debate and would be great to see someone demonstrate it. :D :p :eek:
 
My contribution!

A friend of mine, a retired engineer that flew Mustangs in the War, asked me these questions:

1) An airplane in flight has a bird setting in a seat, clearly the weight of the bird is being lofted by the airplane. Now take that same scenario and now the bird is flying INSIDE the airplane, is the weight of the bird carried by the airplane? I have my opinions, but it's an interesting question.

2) If you are flying (or running or driving) in a rain storm, do you get wetter by going faster or slower or is there any difference?

Also why is Octoberfest in September.......why is West Palm Beach on the east coast of Florida.................................I digress!

My silly contribution!
 
1) - Easy, a simple physics question. The example I heard was a fly in a jar sitting on a scale, but the physics is the same - the scale will show the same weight (or the airframe as it were). The fly or bird has to displace a downward force on the air column equal to or greater than its weight.

2) Mythbusters did the running vs walking, but I cannot remember the outcome. (on edit - william remembered)
 
I've tried a few times on their forum to lobby for this one:

Grinding steel and aluminum on the same wheel will create thermite and explode.

I think I read about that around here, but I don't believe it. At least not for the light grinding that we do.
 
Davepar said:
I've tried a few times on their forum to lobby for this one:

Grinding steel and aluminum on the same wheel will create thermite and explode.

I think I read about that around here, but I don't believe it. At least not for the light grinding that we do.
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Interesting. I never heard of the whole thermite reaction thing.

A regular grinding wheel, though, can and does load up with aluminum and that could certainly cause the wheel to crack. At the speeds they turn, it may as well be an explosion. VERY dangerous.
 
Grinding steel and aluminum on the same wheel will create thermite and explode. I think I read about that around here, but I don't believe it. At least not for the light grinding that we do.
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Asked an uncle who is experienced in machine-tool stuff about this. The danger isn't the formation of thermite (which doesn't really explode anyway - ask me how I know) - it's that the wheel will load up with aluminum and eventually crack and fly apart. I'm not sure what makes it crack - perhaps the thermal expansion of the loaded aluminum filings? Don't know.

As for the rain question, it seems to me:

1. If standing still, your 'wettable area' is the top of your head and shoulders.

2. When moving, the larger frontal portion of your body is colliding with raindrops, making you accumulate more water per unit of time, but

3. You arrive at your destination sooner so that needs to be accounted for somehow.

I'll bet that for each rain situation, body top/frontal area and distance, there is a chartable ideal speed to minimize wetness.

Edited to add: And once you're saturated, who cares? At that point you can't get wetter, so speed becomes most important - to get you to your destination to change out of the wet clothes.
 
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Confirmed, Drier if you run in rain!

Baja_Traveler said:
2) Mythbusters did the running vs walking, but I cannot remember the outcome. (on edit - william remembered)
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Kai Wikipedia to the rescue.

It was in session 1, episode 1:(Wikipedia)

"You end up drier running in the rain than walking?" Busted (was retested and results reversed later)


However it was revisited, reversing the original result and confirmed in Episode 38, season 3: (Wikipedia)

"You end up drier running in the rain than walking. (From "Who Gets Wetter?", Season 1, episode 1)" Confirmed

"When retrying the test in actual rain it was conclusively proven that the running test subject got less wet than the walking test subject. The use of artificial rain in the original test led to a false negative."

I think it is just a time thing mostly. Its all in fun with a dash of silly. So the results are not as important to me, but there was one of importance to us and aviation.

It was the "Chicken Gun" Myth that caught my attention. When testing windscreens for large aircraft (with thick windows) they use a large air cannon that shoots a chicken at the window to determine if it can withstand a bird strike. That part I know is true. The urban legend occurred while testing windows for the FAA, when an engineer used a frozen chicken instead of a thawed one and destroyed the window. The Mythbusters wanted to see if a frozen or thawed chicken made a difference, regardless if it ever happened (which is doubtful). In some cases the Airforce opts to use frozen to simulate a "tense" bird about to get creamed. Now they use simulated birds to make the animal right folks happy. (sesson 1, episode 9) The original effort used the front of a Piper Cherokee. They found both thawed and frozen birds went thru the Piper's thin windscreens (they used several) like a hot knife in butter. It even went across the adjacent field!!! So they assumed it made no difference. Of course the thin windshield was no match to a bird going ++100 mph, frozen or not. It was revised with a thick windshield and found it made a little difference (sesson 2, episode 14).

Bottom line, the insight from the first effort was our windscreens are not a match for much. Anything at our speed is going thru the windscreen. We are in deep trouble if a bird strikes the windscreen, because it will be in our face. As fast as we go it could be real bad news. So wearing those cool shades may save your vision if you do cook a goose in flight.
 
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Grinding wheel exploding due to aluminum build-up... that does sound like a more likely cause. In either case, they love blowing stuff up. They should make thermite and load up a grinding wheel with aluminum. :eek:
 
If I'm remembering correctly...wasn't it Lindberg that came up with the question about the fly? While he was crossing, he found a fly in the airplane and wanted it out because of the extra weight he was carrying. Then he thought about the fly flying. Did the weight dissappear? I think we've talked about this before... :confused:
 
pussy cat in the cockpit

If you are flying with a cat, and lose all your gyros while sold IMC in the clouds, can you stand the cat up on your lap or the seat next to you and see if the cat is leaning to tell if your wings are level? :rolleyes: What does it mean if the cat is standing in the roof or top of the canopy? :eek:
 
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gmcjetpilot said:
If you are flying with a cat, and loose all your gyros while sold IMC in the clouds, can you stand the cat up on your lap or on the seat next to you and see if the cat is leaning to tell if your wings are level? :rolleyes: What does it mean if the cat is standing in the roof or top of the canopy? :eek:
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Funny. If I remember properly, they recently found some prehistoric winged animal fossils around the peak of a mountain. Apparently, animals aren't much better at avoiding cumulous granite than humans when they're in the soup with no instruments... :)
 
That's what ducks are for. No self-respecting duck will fly in IMC, they will find the ground and stay on it. Throw the duck out the window and follow him down.
 
gmcjetpilot said:
If you are flying with a cat, and loose all your gyros while sold IMC in the clouds, can you stand the cat up on your lap or the seat next to you and see if the cat is leaning to tell if your wings are level? :rolleyes: What does it mean if the cat is standing in the roof or top of the canopy? :eek:
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Don't forget the duck! Can a reasonably skilled private pilot follow a duck in dense haze to find the ground?
 
Better yet...

Through the cat out the window. We all know that the cat will land on it feet unhurt. Just see which way the cat points if feet after throughing it out the window. :rolleyes:
 
Now about the rain

A thought experiment:
With a constant rain source stand still until reaching saturation. Record time Y.
Now change close and lay on your back in the same rain. Record time X.
(if anyone wants to do this experiment for real and give me the actual times that would be great). :)
Now the least amount of time to spend in the rain will be the minimum distance to the hypotmus of the right angle formed by time Y and time X. This is the same as is used to find crosswind componet. I can't remember the correct formula, but it involves the sin or cos or both.

Kent

Is this were we get the term "wetted area"? :rolleyes:
 
Bryan Wood said:
For those interested next Wednesday at 9:00p.m. eastern the Mythbusters on the Discovery channel will be building and testing "Concrete Gliders" to see if it is possible to make such contraptions. Any predictions? :cool:

Best,
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I'm cringing as I watch this. I have often been impressed by the Mythbusters' ingenuity, but these guys are so friggin clueless about aerodynamics...
 
dan said:
I'm cringing as I watch this. I have often been impressed by the Mythbusters' ingenuity, but these guys are so friggin clueless about aerodynamics...
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I can't help but think they'll have to revisit this one due to letters from viewers....in the final trial (in the old Moffet Field blimp hangar), Adam sure looked to be pulling his along like a kite - even after releasing it from the launching string - and that had to account for (at least some of) his "incredible" glide ratio!

Paul
 
Yea it was too crude

Ironflight said:
I can't help but think they'll have to revisit this one due to letters from viewers....in the final trial (in the old Moffet Field blimp hangar), Adam sure looked to be pulling his along like a kite - even after releasing it from the launching string - and that had to account for (at least some of) his "incredible" glide ratio! Paul
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I guess if a house, cow or barn door can fly (ref: The move - Wizard of Oz) than I guess a concrete glider can fly?

Adam claimed a 4 to 1 ratio using the ZIP line launch. At least he recognize the thing had to be moving fast to get any lift, even barn door lift. It did seem to pitch up have a trajectory shallower than ballistic, but not much. They should have repeated the test with a brick of the same weight. So it seemed to "fly" for one second, but the drag was so great the velocity dropped than it stalled, so really that is not flying any more than your hand flys hanging out your car window while driving down the road. Fortunately it was close to the ground and when it crashed it did not break apart.

Jamie's was lighter and seemed more promising, but his decision to hand launch off a balcony was the kiss of death. I suspect if the aerodynamics where close and he used the zip line launched like Adam, at a faster speed, he may potentially have got a little more than the 4 to 1 Adam claimed. Of course it just nose over and went stright in like a lawn dart. Was the CG right? What airfoil did he use and wing area?

I agree the aerodynamics, airfoil, CG, control surfaces where crude at best. The foam test glider Adam used an eye-ball airfoil that had a cartoon profile with a gigantic leading edge and camber. It may have had lift but the drag was huge. I agree it was a kite and unstable kite. However his final design was completely different? I think they threw this episode together and needed footage.


A concrete glider with a 4 to 1 glide ratio for 9 feet, but than it will stall and crash. I would have liked to see what Adams glider would do from an elevation. I suspect it would just go like it did for 9 feet like a ballistic projectile, than stall/tumble and flutter to the ground.
 
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If the issue was "can Adam and Jamie build a concrete glider?", I'd say no. On the other hand, I bet that space Dr. at Moffet would have little trouble.
 
Baja_Traveler said:
1) - Easy, a simple physics question. The example I heard was a fly in a jar sitting on a scale, but the physics is the same - the scale will show the same weight (or the airframe as it were). The fly or bird has to displace a downward force on the air column equal to or greater than its weight.
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By the same logic, wouldn't the low pressure zone above the fly offset the high pressure zone below it?

And I also cringed watching this episode. Adam's test glider was "cartoonish" (as another put it) at best, and his final design would have flown great had it been made out of wooden sticks and a sheet of paper like it was supposed to be.

Jamie's design was MUCH better, though he dropped the ball in a few places. For the speeds these things were going, I would have to think that a sweptwing design would not be the most effecient. (And what's with basing your design off of models of fast-flying powered aircraft anyways? No one thought to take a look at why a sailplane looks the way it does?)

That aside, he was right it trying to get more weight up front before his test, but he grossly overcompensated for it. I don't know how he came at that being the balence point, but it was cleary wrong. More pre flight testing would have done him a lot of good, also considering he appeared to have adjustable elvators in the rear.

I think you would definately be able to design and fly a glider made of concrete if yuou used Jamie's construction techniques.
 
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gmcjetpilot said:
ANY ONE KNOW OF ANY GOOD AIRPLANE MYTH'S TO SUBMIT?
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How about we let them settle the primer war once and for all?

Now Buster gets to sit in a tank of salt water wearing aluminum jockey shorts. Man, that dude gets no respect.
:)
 
How about the one that says that if you fly from A to B against a headwind, and if the same wind is present when flying the return trip back to A, it will all average out.
 
Whizwheel test

You can work this one out on your favorite E6B - you do still have one, right ? :D

If your 'wheel' is temporarily lost, the bottom line is that since your ground speed is slow in the headwind and fast in the tailwind, you'll spend more time in the headwind and less in the tailwind so they can't average out.
 
Aviation myth they got wrong

A couple of years back the Myth busters tried to see if jet blast could blow a car over and decided that "That myth is busted." In fairness though they could only get access to a small corporate jet and nothing worked out for them. As I was watching it my mind kept going back to a training video put out by my employer to show the danger of the ramps. This plane was a 767 with one engine running at greatly reduced power. The Truck was an old panel or box truck like a public works department or a plumber would drive with the engine and trans removed to prevent a cleanup afterwards. It will become pretty apparent why they did this when you see the video. The SF Bay is on the top of the list by environmentalists as fragile. Somehow this video made it onto the net but is shown as if it is a 747. Funny, as I'm writing this I'm second guessing my memory, but pretty sure it was a 767. Anyway, it was being pulled by another vehicle on a very long line behind the running jet and was, well you can see for yourself. Keep this in mind if you taxi behind one of these beasts at a class c airport. It could ruin your day.



http://www.zippyvideos.com/3710428786264296/aviation_-__dont_walk_behind_a_boeing_747-200/

Best,
 
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