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Leaptech Aviation

03/22/2015 12:11 AM

http://www.jobyaviation.com/LEAPTech/

I couple weeks ago someone asked a question about small props and a plane.

Found this today and would like to know what you think.

Seems we still have ways to go in technology. Here it looks like small and more is not the same as big and less.

Or is it?

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#1

Re: Leaptech Aviation

03/22/2015 1:18 AM

It's called "blowing". Really.

Using many small engines/props to blow air across the wing adding lift.

I'm not ready to invest, just yet.

But, advancing technology (graphene?) may let this fly someday.

My biggest concern is that the wing won't fly if the motors die.

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#2

Re: Leaptech Aviation

03/22/2015 11:04 AM

The wing provides lift by deflecting the air stream momentum downward. The velocity of the air stream is generally provided by the foreward motion of the aircraft. "Blowing" the wing with multiple small propellers allows the wing to generate lift at a slower foreward velocity of the aircraft. Using multiple small motors is simpler to implement with electric propulsion.

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#4
In reply to #2

Re: Leaptech Aviation

03/22/2015 1:09 PM

Yes, but..................................we're not talking slower forward velocity. We're talking added lift without wing area, and the drag it produces.

It's the narrow wing that I don't like.

Wing loading on the Leap Tech wing is 266 kg/m2.

Wing loading on Sirius TL 2000 is 55.5 kg/m2.

Without power, the Leap Tech becomes a rock.

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#9
In reply to #4

Re: Leaptech Aviation

03/22/2015 4:49 PM

I have to agree with you. Lift is partly derived from the power plant. It would be interesting to see the difference between power on and power off stall speed. When the fans* stop, the pilot has enough to worry about finding a large flat place to put down. It could be really serious in this case.

I would think it should at least have flaps to be extended in case of loss of power to compensate for loss of lift.

* The purpose of the big fan on the front of an airplane is to keep the pilot cool. When it stops, he starts to sweat.

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#10
In reply to #4

Re: Leaptech Aviation

03/22/2015 11:39 PM

A pilot friend of mine described it to me once as "having the glide ratio of a Brick".

He was referring to a Lockheed F-104 Starfighter

Once upon a time there was a thread here about putting a plane on a conveyor belt with a cast iron bath as an anchor to keep it safely on the ground.

BAB

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#20
In reply to #4

Re: Leaptech Aviation

03/24/2015 4:05 PM

Gotcha covered Lyn


I know I don't have to tell you, but others here may need to realize that as a pilot, the moment you start your take off roll, you need to start picking a spot to park, in case of failure, that includes hot air balloons too.

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#22
In reply to #20

Re: Leaptech Aviation

03/24/2015 4:40 PM

Yep, I'd have one of those, just to be safe.

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#6
In reply to #2

Re: Leaptech Aviation

03/22/2015 2:01 PM

There is a little error in what you wrote. The portance is not generated by a flow deflection but by a pressure difference generated by the air flow between upper (less) and bottom (more) sides of the wing. This is generated by the difference in flow path and the wing section profile.

The traditional way is to move the plane and thus generate the flow. The presented method makes usage of the propellers to generate the flow and those are so numerous in order to generate an almost uniform flow along the wing.

If propellers stop the plane has the trend to fall down but this will generate a relative movement with respect to air and generate a portance as the classical system does so that the plane will be able to come smoothly down. Of course it is not as simple as I write but it will not fall down as a stone.

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#7
In reply to #6

Re: Leaptech Aviation

03/22/2015 2:30 PM

There are two statements you make that need response.

First, you are referring to asymmetric wings that are found on most aircraft and your assumption that only a velocity and pressure differential over the wings produces wing lift. Bernoulli's Principal contributes to lift, but is not the only factor.

Many aerobatic planes have perfectly asymmetrical wings and they seem to fly quite well.

Most importantly, if you look at the relative wing area and wing loading of Leap Tech's wing and a typical small aircraft wing, you will see that it will fall out of the sky if the fans quit turning.

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#11
In reply to #7

Re: Leaptech Aviation

03/23/2015 5:05 AM

It will fall out of the sky, but it will fall forwards. Leaptech wing loading 266 kg/m2, Boeing 747 wing loading about 730 kg/m2. The Boeing 747 has a glide ration of 17:1, so the Leaptech should do better, albeit at high speed for a small plane.

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#12
In reply to #7

Re: Leaptech Aviation

03/23/2015 5:22 AM

You said; Many aerobatic planes have perfectly asymmetrical wings and they seem to fly quite well.
Did you mean symmetrical wings?
Jim

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#13
In reply to #7

Re: Leaptech Aviation

03/24/2015 7:41 AM

Many aerobatic planes have perfectly asymmetrical wings and they seem to fly quite well.Thank you for supporting my suggestion. It is exactly what I wrote the asymmetrical wing profile leads to the force generation.As for the wing area we do not know (and one made already the remark) if the wing cannot be in case of need extended. If you look at the planes from the window you see how before take off and landing the wing profile is modified in order to obtain a higher portance.In such situations the flaps make a "flow deviation" action but not during flight. This action is used in order to obtain at low speed a higher vertical force and same time an increase in drag.In one design the deflected air flow was used as important factor this is the planes with ground effect (one example being the Caspian monster).The "jet" is used as portance generator in short take off landing designs the first such plane being designed by engineers in the UK and the US took over and developed further the plane combining the main jet with a powerful fan.If you look at gliders their wings are also "narrow", "slim" and as I mentioned if the "fans" do partially stop the plane will start a descend and this relative movement to the environmental air will generate a portance force.

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#14
In reply to #13

Re: Leaptech Aviation

03/24/2015 10:00 AM

I meant to say symmetrical. As in exactly the same profile top and bottom.

Aerobatic planes have SYMMETRICAL wings.

I stand by everything I said about this plane dropping like a rock without power.

Your arguments are weak, if not misinformed.

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#15
In reply to #14

Re: Leaptech Aviation

03/24/2015 10:50 AM

Why the fixation on dropping like a rock? The NASA Space Shuttle has a wing loading of nearly 600 kg/m2, yet it still can be piloted to a controlled landing.

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#16
In reply to #14

Re: Leaptech Aviation

03/24/2015 12:59 PM

Yes BUT they have an attack angle which generates on the upper side a turbulence and a lower pressure. Of course an angle will generate a supporting force BUT there is a need for a higher speed since the impulse force is quite small. This is the reason why such planes have a stall speed higher than the classical curved profile. We do not discuss a performing plane which will have to flight upside down but a NORMAL plane thought for normal flights.

Of course I may be wrong since I only had a look at the pictures and I only analysed a possible situation by logical analysis, I am aware that my knowledge is limited and that I can make an error so that I do not consider that I detain the TRUTH.

I am surprised by your aggressiveness and your way to maintain a position with no knowledge foundation. You do not know more than the others if you were not member of the development team. As for the weakness of my arguments it seems that other too have doubts about the validity of yours.

Of course in fact I should apologize to defend an opinion different from yours since I am only from time to time present on this discussion and not giving an answer to every OP which ever the subject is. In general I participate when I have a personal (not only Wikipedia) knowledge of the subject. Of course I can also be wrong but I remember that some time ago you wrote that I would give sure a better answer than yours. Times did change.

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#17
In reply to #16

Re: Leaptech Aviation

03/24/2015 1:15 PM

Regardless of your expertness, the wing loading is VERY high compared to a normal general aviation aircraft.

The expression, "drop like a rock" is not an absolute statement that the plane will fall directly out of the sky, but will drop much more quickly than a GA aircraft.

This may only cause concern on final approach or the turn to final approach.

While I do not claim to be an aviation expert, I have actually flown an aerobatic airplane up-side-down while performing mock dog fights.

I'll withdraw my responses if it satisfies your sensibilities.

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#19
In reply to #17

Re: Leaptech Aviation

03/24/2015 4:00 PM

You are completely wrong there is no problem of sensibilities. We ALL know NOTHING about this plane so that we imagine according to each one experience a "probable" behavior. This is the reason we should be in doubt and not claim that only one opinion is the true one. That's all.

I never was a pilot but I did a lot of experiments and analysis of flows (hydraulics and pneumatics) and I based my comment on what I know, what I saw when flows were visualized by ink injection for instance or smoke which of course can be not totally applicable in this case.

This the so called "scientific doubt" which brings us further.

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#21
In reply to #19

Re: Leaptech Aviation

03/24/2015 4:24 PM

"I never was a pilot but I did a lot of experiments ...." Until you experience an engine or any other mechanical failure as a PIC, you really can't related to the experience trying to pick a spot to land, hopefully in one piece. There is nothing more frighting than hearing nothing but the sound of air going over the wings instead of the roar of the propeller. I would highly recommend spending a few dollars, take an introductory flight and experience the feeling.

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#23
In reply to #21

Re: Leaptech Aviation

03/24/2015 5:49 PM

That's why I like gliders. They are much quieter than powered aircraft and you learn to manage quite nicely without an engine.

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#24
In reply to #21

Re: Leaptech Aviation

03/25/2015 8:14 AM

I am sincerely sorry but the question was not if you are afraid or not when the engine stops but only if in case of the plane could glide. This has nothing to do with pilot experience but only with aerodynamics and flow behavior.

Or may be I am wrong and flow behaves according to degree of fear. It could be a subjective influence of flow via brain waves.

I deeply doubt that all people who did research in wing design have been pilots.

A last comment since you are a glide pilot do such planes not have slim wings ? Do they have symmetrical or asymmetrical wing profiles ? I only once was a passenger not a pilot on a glider and very much enjoyed the feeling to be a bird!

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#25
In reply to #24

Re: Leaptech Aviation

03/25/2015 11:20 AM

It is not a question of if the plane will glide. Every plane will glide. The real question is the lowest airspeed at which it will glide, and at what rate of descent/attack angle with respect to the ground terrain. A landing with an attack angle of anything more than 15 degrees nose down, and a stall speed of 150 mph is not necessarily going to end well at the point of landing.

Every landing is a more or less controlled crash, especially landings on a flight deck. The ones you can walk away from are considered to be successful.

From what I can see of this prototype plane, I would guess an unpowered stall speed of around 200 mph, with an attack angle to dirt of at least 30 degrees. Sorry, it better have a deployable parachute, or option for the pilot and all passengers to bail out.

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#26
In reply to #25

Re: Leaptech Aviation

03/25/2015 12:50 PM

May be they have who knows ?

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#27
In reply to #26

Re: Leaptech Aviation

03/25/2015 1:41 PM

Supposedly all new private A/C were to be fitted with parachutes to limit crash velocity to survivable values.

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#28
In reply to #25

Re: Leaptech Aviation

03/25/2015 2:29 PM

I understand the point you are trying to make, but I cannot see that the figures you quote are derived from anything better than the Mk.1 eyeball. The correct term for your "rate of descent/attack angle" is the glide ratio, numerically equal to the lift/drag ratio. A Boeing 747 has a glide ratio of 17 (distance along) to 1 (distance down) with a wing loading of 730 kg/m2. Its stalling speed is quite low, at about 100 knots. The Space shuttle glide ratio is only 4.5 to 1, with a wing loading of 600 kg/m2. Concorde in landing mode also had a glide ratio of around 4.5. All these are/were capable of controlled landings.
We are a bit short on data for the Leaptech, but the wing loading is given as 266 kg/m2. This is much higher than a general aviation plane, but is still half that of the Boeing. This is relevant to the landing speed. The aspect ratio of 17.4 is quite high, which helps to improve the L/D ratio. Your 30 degrees translates to a glide ratio of 1.7. I see no justification for that, nor for the stalling speed being as high as 200 mph.

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#30
In reply to #28

Re: Leaptech Aviation

03/25/2015 3:11 PM

Probably so on the Mk.1 assessment. I can see that this plane is fairly lightweight, and if the proplets are all electric powered, and based on the new electric power plant recently publicized, surely they would not generally fail simultaneously?

All I ask is that you go first.

Do you agree, by the way, that heavy lifters generally have better glide capability simply because they have to produce so much lift to be functional at all? A 747 looks a lot more like a "long-range bomber" than this little 6 seater with its tiny wing.

Some more of my Mk.1 eyeball stuff, huh.

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#31
In reply to #30

Re: Leaptech Aviation

03/25/2015 6:40 PM

heavy lifters generally have better glide capability Not exactly. A given aircraft has a given glide ratio, whether laden or unladen. The only difference is that the heavily laden aircraft follows the same glide path rather more rapidly to the ground than its unladen brother.
Between aircraft it is not the weight that is definitive. I could rank, in increasing order of weight, my open-cockpit training glider, a high performance sailplane (about 3 times the weight) and the 747 (vastly heavier). The glide ratios of the open cockpit and the 747 are almost the same, while modern sailplanes can have glide ratios of over 50 to 1.

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#32
In reply to #31

Re: Leaptech Aviation

03/26/2015 8:30 AM

I understand that, but what I was attempting to say is that planes designed for heavy lifting should be designed (1)with substantial wing area, and (2) have a suitable glide path ratio commensurate with lifting efficiency, i.e. high lift to drag ratio, and high lift to empty weight ratio. I am aware that gliders and sail planes are inherently good lifters because thrust = zero.

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#41
In reply to #6

Re: Leaptech Aviation

03/28/2015 3:03 PM

The difference in pressures (Bernoulli) and the air deflection (Newton's 3rd law) are both correct. They are just looking at two different stages of the same process.

There has been a lot of contention over how aircraft wings actually work. Here is a useful explanation.

http://amasci.com/wing/airfoil.html

The shape of the wing and its angle of attack deflect the air and the change in direction (momentum) of the airflow has a reaction force on the wing (lift). The reaction force is transmitted from the fluid (air) to the wing by a difference in pressure. The change in the air's momentum per unit time equals the reaction force against the wing (lift + drag).

When all is said and done, airplanes stay up by pushing air down.

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#3

Re: Leaptech Aviation

03/22/2015 12:55 PM

Doing preflight power checks might be a nightmare with a "blown wing". Airborne in the run up area?

I, myself, still prefer cable and pulleys over fly by wire

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#5
In reply to #3

Re: Leaptech Aviation

03/22/2015 1:20 PM

I don't think a pre-flight run-up is necessary with an electric motor.

No carb heat, mixture, mag, oil pressure, very few gauges, other than battery.

Now, let me be clear. I'm just guessing here.

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#8

Re: Leaptech Aviation

03/22/2015 4:42 PM

I always like to think of a plane as a glider first, and the power just enhances the experience....The design reminds me of this thing....↓ For some reason...

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#18

Re: Leaptech Aviation

03/24/2015 3:20 PM

Thought this was cool until I saw electric range of 200 nm. Last time I checked standard units, nm is nanometers not "nautical miles". At least the stall speed is only 61 knots. The plane is pretty light-weight, so that helps...how is it supposed to handle, maneuver?

Hope this will not also earn the moniker of "widow-maker".

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#33
In reply to #18

Re: Leaptech Aviation

03/26/2015 4:12 PM

Nanometer is: nM not nm.

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#36
In reply to #33

Re: Leaptech Aviation

03/27/2015 9:01 AM

Not in my world. Who told you that? I have never, ever seen nM written in any of the spectroscopic journals, but I have seen paper after paper, and any number of analytical protocols where nm is used for the wavelength of light.

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#37
In reply to #36

Re: Leaptech Aviation

03/27/2015 10:51 AM

I always thought that the multiplier was in lower case and the unit in upper case, such as kW, mHz, kJ, kV etc. Maybe the unit is only capitalized if it is/was a persons name (makes sense), as in those examples. As there was no Mr. Meter, then it is not capitalized. Will have to swat up. Meanwhile, please accept my apologies.

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#38
In reply to #37

Re: Leaptech Aviation

03/27/2015 2:51 PM

In a nasty mood of late, due to my wife (witch) hitting me over shoulder with her broom last night. I wish some days she would get on it and ride off into oblivion.

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#39
In reply to #38

Re: Leaptech Aviation

03/27/2015 3:08 PM

Funny you should say that - I have the same problem.

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#40
In reply to #37

Re: Leaptech Aviation

03/28/2015 5:44 AM

Not exactly. The prefix m- means milli-, while the prefix M- is for Mega. Other capitalised multipliers include G-, T-, E- Z- and Y-. The suggestion that units named after people should be capitalised is correct, though it was actually Mr. Volta and Mr. Faraday rather than Volt and Farad.

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#29

Re: Leaptech Aviation

03/25/2015 2:54 PM

So that we're all clear, there is no aircraft of this design flying.

There is one set of prototype wings at Edwards AFB in California, but don't quote me on that, I may be wrong there, too.

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#34

Re: Leaptech Aviation

03/26/2015 4:22 PM

There have been many, many experimental blown wing aircraft in the past, with varying degrees of success. Going into a steep glide following power failure is common to all of them, just as it is with normal aircraft. Can't see what all the fuss is about - electric, jet, piston engine, rubber band - what does it matter?

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#35
In reply to #34

Re: Leaptech Aviation

03/26/2015 5:12 PM

I guess it only matters when the houses are getting REALLY big.

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#42

Re: Leaptech Aviation

03/30/2015 11:48 PM

More on blown wings.

"while AFC technology could lead to a 17% reduction in tail size, which would reduce drag and weight".

757 EcoDemo Focuses On Laminar And Active Flow

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#43
In reply to #42

Re: Leaptech Aviation

03/31/2015 9:06 AM

They should try some of the non-stick coating Obama uses, or the one used by Hillary Clinton - nothing seems to stick to either one of them.

As to the Kreuger flaps - sounds like something out of a horror movie, but if they work by putting the bug strikes away from the actual leading edge, that is a good thing.

That is what I do not get about all these fans right in front of the smallish wing on the plane in question. How does this not exponentially increase turbulent flow and drag? Is there some nonlinear critical dynamic at play here that we are not aware of?

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#44
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Re: Leaptech Aviation

03/31/2015 10:58 AM

The propellers chop the bugs up finer so that they do not stick to the wing and so laminar flow is preserved.

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#45
In reply to #44

Re: Leaptech Aviation

03/31/2015 11:13 AM

LOL. I was talking about the props causing more turbulent flow over the wings...is that not expected? Untrue? More drag? I don't know, just speculating with oversized Mk. 1 eyeball, other one is lazy, and taking a rest.

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#46
In reply to #45

Re: Leaptech Aviation

03/31/2015 11:17 AM

In that design adjacent propellers rotate in opposite directions and the tips of the propellers overlap slightly. In the picture this appears to straighten out the flow considerably.

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