will it take off?

[Egon]

Hey I'm still posting!!

 

[patrick_g]

Lets see if we can do a philosophical merge of the two topics, Eddie's pond and the will it fly.

How about a sea plane in Eddie's pond and a large prop in the water to create a counter current to move the water backwards past the plane as fast as the plane moves forward with respect to the dirt. OR, have the prop move the water past the plane as fast as is required to make the plane stand still (to cover both versions of the problem statement.)

Pat

 

[tallyho8]

I think Eddies going to need a larfer pond.

 

[MossRoad]

Lets see if we can do a philosophical merge of the two topics, Eddie's pond and the will it fly.

How about a sea plane in Eddie's pond and a large prop in the water to create a counter current to move the water backwards past the plane as fast as the plane moves forward with respect to the dirt. OR, have the prop move the water past the plane as fast as is required to make the plane stand still (to cover both versions of the problem statement.)

Pat

Make sure it is a magic prop and I'm all for it!

 

[TomOfTarsus]

I think Eddies going to need a larfer pond.

I think at this rate TommyOf Tarsus is going to need some prescription migraine medications.

 

[patrick_g]

Make sure it is a magic prop and I'm all for it!

Moss, buddy, problem statement #2 which has the prop moving the water backwards past the plane as fast as is required to stop the plane's forward motion, is in fact a "Magic Prop" per se in that it is the analog to the conveyor with the same capacity.

It should be well within most reader's visualization capacity to see that finite and probably achievable water velocities generated by a large prop in the water powered by a large engine could in fact prevent a float plane from making any forward progress with respect to the frame of reference defined by the land. I assert that for many folks it is easier to visualize a variable speed "river" acting to push the float plane backwards enough to stop the plane's forward motion than it is to do the same with a rapidly accelerating conveyor stopping the plane through the reactioin of storing energy in the rotating wheels, friction of sliding tires, etc.

All that is required to hold the plane motionless (not just ****** its forward speed below take off speed) is for the speed of the water moving toward the plane to generate sufficient hydrodynamic drag in the float to equal the thrust of the prop. Even allowing for the fact that at some speed the float will "get up on the step" (begin to hydroplane and exhibit a considerable reduction in drag) and leave the speed regime where displacement hull speed restrictions are so great. This will require the immersed prop to really speed up to move the water fast enough to generate the requisite drag on the float while planing to keep the float plane standing still with respect to the pond's banks.

Since the plane will not be permitted to move forward due to the moving water, the size of the pond is not an issue since it is clearly large enough to easily contain a float plane. The potential down side for Eddie is the terrific current set up by the submerged prop will muddy us the pond but it will settle out a gain after the experiment is finished.

Eddie will get bragging rights and the snobability of installing a commemorative plaque and statue on shore next to the site of the experiment and undoubtedly a newspaper writeup and TV interviews.

Pat

 

[turnkey4099]

But when I have proven it won't take off and go to anchor, will the level in te pond go up or down when I toss out the anchor?

Harry K

 

[patrick_g]

But when I have proven it won't take off and go to anchor, will the level in te pond go up or down when I toss out the anchor?

Harry K

The pond level will go down when you deploy the anchor assuming:

1. You had the anchor on board during the trial.
2. The anchor is made of metal (or heavier than water material.)
3. The pond is not full and overflowing.

When on board the plane the anchor causes the plane to sink deeper into the water until a volume of water equal to the weight of the anchor is displaced making the pond rise a little.

When the anchor is tossed over the side and allowed to be supported by the bottom of the pond the water displaced is equal to the volume of the anchor, not its weight. Since the anchor is more dense than water (or it wouldn't sink) the displaced water when deployed is significantly less than when supported by the plane.

Pat

 

[Egon]

Forget the pond! Just head for a fast flowing river!

 

[Egon]

On second thought, forget the river, head to Jimmy Angel Falls and try and take off going up the falls!

 

[patrick_g]

Egon, To fit the conditions, the fast flowing river would have to have easily controlled speed and a max speed fast enough to generate enough hydrodynamic drag to equal the plane's thrust. Perhaps a river on the downstream side of a dam with a huge impoundment that could be released to make a tremendous current.

Nah, I think Eddie's pond and a carefully selected prop with proper engine would be more fitting.

Pat

 

[Egon]

That's why I changed to Jimmy Angel Falls!

 

[Brad_Blazer]

If I may jump in,
As the water speed goes up, the contact patch required to support the weight of the plane will get smaller and smaller until a layer of air is finally forced between the hull and the water. At this point the drag will be less than or equal to that of a wheel on a conveyor.
I don't know? THIRD BASE!

 

[Egon]

The pond level will definitely go up when you toss the anchor and it is in the air!

 

[patrick_g]

If I may jump in,
As the water speed goes up, the contact patch required to support the weight of the plane will get smaller and smaller until a layer of air is finally forced between the hull and the water. At this point the drag will be less than or equal to that of a wheel on a conveyor.
I don't know? THIRD BASE!

Brad, In my previous post I allowed as how the float would eventually get up on the step and hydroplane with a resultant loss of hydrodynamic drag that would necessitate an increased water speed to compensate. At this point the plane has effectively zero air speed and thus no lift. Simply passing water under the float with no air speed will not "pack" air under the float in sufficient quantity to eliminate hydrodynamic drag.

The problem as stated is NOT equivalent to having a boat (or float plane) run across the surface of the water where the float or boat would have a relative wind (air speed) as well as a speed through (or across) the water. In the case of the boat or plane going across the surface the relative wind (airspeed would indeed tend to pack air under the float. A properly designed hydroplane hull form is shaped to generate and encourage "foam" under the hull to reduce skin friction.

Now, back to the case at hand where the plane is not moving through the air so no air is being packed under the float(s). Not having specified the type of flotation we must allow for a flying boat where the fuselage is boat-like or there may be a pair of pontoons where the wheels of the landing gear would be in a land plane. The design of the flotation not having been specified, there may in fact be no hydroplane step, just a couple of canoe shaped floats, not conducive to having air directed below them to make friction reducing foam.

As regards "contact patch" area. This assumes that the hull form will induce hydroplaning. If it doesn't and the float(s) remain in the displacement mode drag will increase dramatically when the speed of the water past the flotation devices exceeds approximately 1.3 times the square root of the length of the floats at their water line. The phenomenon of bow-stern wave trap will lower the floats deeper and deeper into the water as the water speed increases until ultimately they are submerged. As a matter of practicality they would be sheared off (if the plane had sufficient thrust) but if we can have a "magic" submerged prop and motor to run it why not magically strong floats and their connection to the plane too.

Anyway, even with hydroplaning since the air speed is essentially zero or a very low value there is no packing of high pressure air under the flotation devices as would be the case in say a racing hydroplane which has both water and air speed.

Thanks for your interest and input but sorry, no pantella.

Pat

 

[patrick_g]

The pond level will definitely go up when you toss the anchor and it is in the air!

Actually Egon the pond level goes down while the anchor is in th air as the float plane is not displacing a volume of water equal to the weight of the anchor since it is in the air. The pond level comes up a tad when the anchor goes in but not as high as it was when the float supported it by displacing a volume of ware equal to the weight of the anchor.

Come on Egon, think like a Greek (Archimedes.)

Pat

 

[Egon]

Well gee, two choices and it's early in the morning, That's what I meant, go down!

 

[Iplayfarmer]

Actually Egon the pond level goes down while the anchor is in th air as the float plane is not displacing a volume of water equal to the weight of the anchor since it is in the air. The pond level comes up a tad when the anchor goes in but not as high as it was when the float supported it by displacing a volume of ware equal to the weight of the anchor.

Come on Egon, think like a Greek (Archimedes.)

Pat

This is assuming that the anchor is in the air long enough for the plane to recover from the "recoil" from the force of tossing it into the air. (Newton's third law). Initially, the pond will rise a fraction as force is applied between the plane and the anchor forcing the anchor up into the air and the plane deeper into the water.

Of course if you just drop the anchor without throwing it that isn't any fun, and the pond will go down as Pat stated.

 

[patrick_g]

Of course if you just drop the anchor without throwing it that isn't any fun, and the pond will go down as Pat stated.

Silly me, I assumed you wouldn't want to startle the fish any more, the ones that weren't run through the magic prop and were already nearly at max nervousness. So you just drop, or lower the anchor. Of course if you toss it out in a parabolic trajectory starting with a finite upward vertical component there will be an oscillation of the level of the pond but the central tendency will be as I previously described and of course the final result will not change assuming the anchor ends up in the water.

I overlooked the case where the anchor is tossed onto the shore and that will result in the water going down even more by the volume of water that the anchor would have displaced had it gone into the water.

A friend of mine at SEE (Santee airport near San Diego) had (and may still have) a 1948 Lake Amphibian ( 4 person flying boat.) If there is a ground swell of enthusiasm to run the full scale experiment I can contact him to see if we passed the hat and got enough response he might be interested in supplying the plane. I have flown with him in various craft and would be pleased to be his relief pilot in helping ferry the plane to the site or taking charge and delivering it myself. With its terrific short landing capability there should be no problem getting it safely down at Eddie's (it has regular landing gear as well as a boat type fuselage for water landings.)

Pat

 

[tallyho8]

Well, I'm willing to make a small donation to the cause, but maybe we better check with Eddie first. He may not want his fish traumatized.