h a l f b a k e r y
Loading tagline ....
idea:
add, search, annotate, link, view, overview, recent, by name, best, random
meta:
news, help, about, links, report a problem
account:
Browse anonymously,
or get an account
and write.
Login
Create account.
|
|
|
Sprinkler like power can raise person in air. Hose goes down to lake. Just enough to hover (say 5 to 10 meters up), and win the manpowered helicopter prize.
Prior art: patent number 4,274,591 for toy, and Halfbakery idea: [[Flying Toy]] here on HB by [KCSolutions123].
Water propelled hover device
http://www.google.c...AAAAEBAJ&dq=4274591
on Google Patent Search [baconbrain, May 18 2008]
Flying Toy
Flying_20Toy
Non-descriptive name, derivative idea. [baconbrain, May 18 2008]
Decavitator Human-Powered Hydrofoil
http://lancet.mit.edu/decavitator/
These guys had every opportunity to drive their watercraft with a water jet, or an underwater propellor, but chose an air propellor. Seems relevant to me. [baconbrain, May 20 2008]
Steamboatwilly
http://steamboatwil...vercraft/about.html
Strewth ! A human powered hovercraft that works ! [8th of 7, May 20 2008]
For [baconbrain]
http://en.wikipedia.org/wiki/Tipjets
Tipjets do work, just not particularly well... [neutrinos_shadow, May 21 2008]
[link]
|
| |
If you used the water jets to power very large rotors by reaction, still no. |
|
| |
Direct mechanical drive just barely works in human-powered helicopters. The weight of the water would be a bad thing. |
|
| |
"A high power-to-weight ratio is needed, such aircraft must be light and must have efficient rotors." |
|
| |
So a human powered water rocket? |
|
| |
The thrust of the (water) spray seems to be much more effective than air thrust from a helicopters propeller. |
|
| |
Maybe if you pedaled for about a day and
a half to compress air into a tank to push
the water. |
|
| |
The spinning spray would not, i repeat NOT, be able to lift the weight of a human. |
|
| |
It's the old reaction mass problem. You're describing an Newtonian reaction drive. The problem is that along with the ship and its payload you have to lift all the reaction mass as well. |
|
| |
An airscrew uses the surrounding air as its reaction mass (working fluid), therefore only fuel is needed. |
|
| |
And, even though this design gets water out of the lake, it still has a boatload in the copter at any one time. Plus it has to lift all the water up the stated 10 meters, which is a lot of work. |
|
| |
The pilot's going to be - for the sake of argument - 80 Kg. With composites and light alloys, the airframe and mechanism (pumps, pipes and nozzles) might come in at about another 20 - 30 Kg (a racing bike is 10Kg or a bit less). |
|
| |
Add to that the suction hose - 50mm internal diameter and 10m long - that's about 20 litres (so 20 kilos) plus the water in the nozles, pump and pipework. |
|
| |
Now, kiddes, what is the specific impulse required to keep 120 Kg hovering ? Assume g is 10 m s-2. Write on both sides of the paper. Close cover before striking. The altitude of water copters can go down as well as up. |
|
| |
physics says "NO!", but I like it... |
|
| |
The hose can be thin, the pump can be floating (so outside the weight of the heli!!) and there is rotor movement at the same time. |
|
| |
Last but not least: Your not considering the energy released by the evaporating (spray) water, and the extra large volume of air displaced by the spray, which would need a lot of material if it was wings. Since this mass is NOT attached to the helicopter anymore, its just causing elevation without weighing down the helicopter. |
|
| |
So this is extra surge power from your body via pedals/levers to the air. |
|
| |
In any case it would win the Flugentag, because everyone around it will get wet. |
|
| |
And thanks to 8th I have an extra HalfOvendea: The floating part can have a spray creating intake, so that I get spray not water in the pipes. |
|
| |
(Besides disagreeing with 8ths 30kg airframe, I don't need a bike, just the propeller and a harness. No chain either, just hydraulics, 9 mm in 3 lightweight pipes, 10 m is 10k mm, so thats 90k mm2, or 1 Liter, weight: 1 KG. |
|
| |
//Your not considering the energy released by the evaporating (spray) water// Of course we're not, because there is absolutely *NO* energy being released by evaporating water in this case. |
|
| |
(The only way the water would be "evaporating" is if you operated this in Hell's bottommost basement, and even then, it would be absorbing the energy, not releasing it. Unless you're positing a magical, zero-mass, high-pressure, anti-thermodynamic boiler system placed just below the pilot...?) |
|
| |
This is ignoring basic hydraulics/hydrodynamics. If the pipes are really narrow, the volume of water is decreased, yes, but the resistance to flow is increased. That is so obvious to some folks that they haven't bothered to mention it, but it evidently isn't known to others, and needs to be pointed out. |
|
| |
It takes effort to push water through pipes, and MUCH more effort is needed as the pipes get skinnier. Skinnier pipes need faster flow for the same volume, and everything goes to hell, quick. |
|
| |
The description isn't real clear. Is the plan to make a helicopter rotor crossed with a lawn sprinkler, so the reaction from the horizontal water jets makes the rotor blades turn, and the rotor does the lifting? Or is it more of a water rocket, with the jets vertical, the reaction supporting the craft directly, with no rotor needed? Or is it some halfway thing? |
|
| |
I think this is supposed to be something like taping rotor blades to the arms of a spinning-type lawn sprinkler. But that still won't work, as I said in the first anno. |
|
| |
Throwing the water out in a jet is pushing against the inertia of the water--you have to move a little very fast, or a lot somewhat slower. Putting the water into a hydraulic motor, say, is pushing against metal attached to the structure of what you are trying to move. |
|
| |
Another way to look at this is to imagine the simplest HP helicopter possible. Get your pedaler person to lie on their side, with their feet against a drum on the hub of the rotor blade. Tell them to push the drum around with their feet. That's as direct as it can get--their feet push the blade around. If you were to stop the rotor somehow, the pedaller would notice it. |
|
| |
Now, make another copter with pedals, a pump, hoses and water jets. The feet push a pump, which pushes water through pipes, and pushes water out in a jet that pushes the rotor blade around through reaction. That's needlessly otiose, and rather heavy. And, if the blade was stopped, the pedaller would never notice--his work is not going directly into the rotor. |
|
| |
Also notice that reaction-driven helicopter rotors have been thought of, but almost never used. One of the common scams of the internet is selling plans for little helicopters driven by ramjets, tipjets or pressure jets. They don't work. |
|
| |
Reaction waterjets aren't used anywhere but in the lawn sprinklers and little toys like that cited, for good reason. The rule of thumb for jets is much like that for pipes--the littler the nozzle, the greater the needed speed and the worse the efficiency--for much the same reasons. |
|
| |
Google doesn't like Flugentag. |
|
| |
Flugtag is the Red Bull contest where people run funny vehicles off a pier to see how far they fly. |
|
| |
[baconbrain] - see link about tipjets (although I agree, the cheap ones advertised at the back of science magazines and such are crap). |
|
| |
Tipjets can work, yes, which is what I meant when I said "that reaction-driven helicopter rotors have been thought of, but almost never used". |
|
| |
Tipjets are very tricky, but they are one of those "magical technology" icons that folks think will get a poorly-designed, poorly-built POS off the ground. |
|
| |
Those crap designs are bogus, they are what "don't work". |
|
| |