X Prize Clean Aviation: $10 million

[mheslep]

You asked for it. I scanned this in from one of my references. The mB notation refers to the mth harmonic/mode and B is the number of blades. The rest should be somewhat decipherable.

Thanks Fred!

 

[FredGarvin]

BTW...This all stems from the basic wave equation. I sat through many a proofs showing this stuff and it is amazing to see just how much can be pulled from such a seemingly unimposing equation. You may want to look up Ffowcs Williams for a reference.

 

[Cyrus]

Bessel function, wave equations? Eeeeuccccwkkkk!

Quick, something more pleasing to the ear: Laplace transforms, Bode Diagrams, Nyquist plots, PSD, Autocorrelations...ahhhhhhhhhhh. I can breathe again, whew.

 

[Cyrus]

I'll tell you what, if you guys want to formulate a list of questions, I can email them to Dr. Moore and report back his answer. I'd prefer to keep the list short, so think of good ones.

 

[FredGarvin]

Quick, something more pleasing to the ear: Laplace transforms, Bode Diagrams, Nyquist plots, PSD, Autocorrelations...

:zzz: :zzz::zzz: huh...wha?...hmmm...:zzz: :zzz::zzz:

 

[mheslep]

So do the lithium batteries most of them use for power.

A good Li Ion is ~95% efficient on discharge at room temperature (unlike lead acid), so Cyrus's RC battery would shed 55W of heat on take off, probably 5W cruise. In a small package w/ no thermal path, yes I imagine that gets very hot. If so, RC'ers might consider measures to cool them, as running a Li Ion hot will degrade its lifetime.

 

[FredGarvin]

All of the ones I have used and seen have no external means for cooling other than some form of exposure to the outside air.

 

[mheslep]

You asked for it. I scanned this in from one of my references. The mB notation refers to the mth harmonic/mode and B is the number of blades. The rest should be somewhat decipherable.

Think I have it all except for theta, the 'retarded radiation angle'? I would expect the SPL is not isotropic, so maybe this is addresses the acoustic pattern?

 

[mheslep]

I'll tell you what, if you guys want to formulate a list of questions, I can email them to Dr. Moore and report back his answer. I'd prefer to keep the list short, so think of good ones.

On the subject of prop/fan noise, I expect that his answer would concur w/ the article which he probably informed:

At up to 95 percent efficiency, electric motors are far more efficient than internal combustion engines, which only rate some 18 to 23 percent. This means electric aircraft are much quieter than regular planes—at some 150 meters, it is as loud as 50 decibels, or roughly the volume of a conversation, making it roughly 10 times quieter than current low-noise helicopters.

You gents suggested otherwise upthread, so first I want to run the numbers from Fred's Propeller and Fan Noise reference; then we can ask a more informed question.

 

[FredGarvin]

That is not a proper statement. It should read that the ENGINE noise is lower, not the overall aircraft noise. You can not change the acoustic performance of a prop by changing the thing that drives it. The prop noise will still be there.

 

[mheslep]

That is not a proper statement. It should read that the ENGINE noise is lower, not the overall aircraft noise. You can not change the acoustic performance of a prop by changing the thing that drives it. The prop noise will still be there.

Right, the implication of the SIAM statement is that engine noise dominates in a helicopter w/ combustion engine. That's why I'm running down the prop noise alone. SIAM says its 50dbL at 150 M, a number that can be calculated (if I can define the terms )

Assumptions per prop:
B (blades) = 4
y = sideline distance = 450 ft
D = 6 ft
T = thrust = 300 lbs takeoff
W = shaft power = 30 HP
c0 = 1000 ft/s
zeff = 0.8

I want worse case, so I'm bypassing all the modal analysis and setting the sincx and Bessel functions to one.

Edit:Still need help on defining theta? It can't be zero or the SPL is zero.

 

[Cyrus]

That is not a proper statement. It should read that the ENGINE noise is lower, not the overall aircraft noise. You can not change the acoustic performance of a prop by changing the thing that drives it. The prop noise will still be there.

According to the article, they made rotors with lower tip speeds to reduce noise as well.

 

[Cyrus]

Oh man, I just read that the battery power will only allow it to hover for 6 mins before they are drained.

 

[mheslep]

Oh man, I just read that the battery power will only allow it to hover for 6 mins before they are drained.

For comparison, the total flight time of those novelty http://en.wikipedia.org/wiki/Jet_pack" is about 9 minutes. Total flight time (not hover) of this VTOL appears to be about 20 minutes (80 km / 240 km/h), with today's batteries. I expect a good idea would be to equip the VTOL with a small but very high density primary battery as a one-time emergency backup, maybe 2 minutes worth of flight time. The military might go with an all-primary, throw away battery set which would triple the flight and hover times immediately.

 

[Cyrus]

Why would add a backup battery (more weight) that adds 1/10th more flight time, when you could just make the original batter a 1/10th bigger?

I would hold of on any extrapolations as to what the military may or may not due until this thing is actually built.

As I said in my blog though, all of this still comes off as pie in the sky concepts with little to no calculations or experiments to validate the technology. That's leaving out the fact that NASA hasn't been supporting this idea either.

The electric airplane will come into fruition once a battery with sufficient energy density has been developed. Now is not that time.

 

[mheslep]

Why would add a backup battery (more weight) that adds 1/10th more flight time, when you could just make the original batter a 1/10th bigger?

Because as I indicated above the best primary (non-rechargeable) batteries have 3-4X the energy density of the best rechargeable ones. So to add 10% emergency flight time, add only 2.5% more battery by weight.

I would hold of on any extrapolations as to what the military may or may not due until this thing is actually built.

More generally I was pointing out that if the VTOL user had the resources to throw the battery away after every flight, the hover and flight time is much more reasonable using today's technology, i.e. 1 hour, 250 km range.

The electric airplane will come into fruition once a battery with sufficient energy density has been developed. Now is not that time.

Maybe, but this thread at its root is about the feasibility of one particular event: a coast to coast aviation speed contest using electric aircraft, the outcome of which will help demonstrate just what is actually possible.

 

[Cyrus]

Because as I indicated above the best primary (non-rechargeable) batteries have 3-4X the energy density of the best rechargeable ones. So to add 10% emergency flight time, add only 2.5% more battery by weight.

Since this battery is one time use, I have to ask: what is the shelf life and cost of this thing going to be? If I have to replace a several thousand dollar battery every few months because it goes bad from not being used, that's not a very attractive backup option.

More generally I was pointing out that if the VTOL user had the resources to throw the battery away after every flight, the hover and flight time is much more reasonable using today's technology, i.e. 1 hour, 250 km range.

That's not very practical, from an operational or budgetary standpoint, you'd agree?

Maybe, but this thread at its root is about the feasibility of one particular event: a coast to coast aviation speed contest using electric aircraft, the outcome of which will help demonstrate just what is actually possible.

How will it demonstrate what is actually possible if it uses one shot, expensive batteries though? I'm still not seeing why this is a good challenge. Why not just make a 'long life' battery challenge?

 

[mheslep]

Since this battery is one time use, I have to ask: what is the shelf life and cost of this thing going to be? If I have to replace a several thousand dollar battery every few months because it goes bad from not being used, that's not a very attractive backup option.

http://www.all-battery.com/alarmsecurityandmeter.aspx" appears to be the current top performer, 10 years. Used in alarm systems, remote metering systems, etc.

That's not very practical, from an operational or budgetary standpoint, you'd agree?

Again I'm not talking about the common 'flying car' zaniness. For the military, it depends on the alternatives. Might be a very reasonable cost to transport a couple of Special Operations folks quietly in, and then out again, of a tight spot.

How will it demonstrate what is actually possible if it uses one shot, expensive batteries though? I'm still not seeing why this is a good challenge. Why not just make a 'long life' battery challenge?

Because the effectiveness or the economics of the aircraft is not simply f(battery energy density), though I grant that's a big part. There are many other important factors:

• efficiency of the electric drive system
• electric propulsion means the power source (battery) and the propulsion (e-motor/prop) can be separated and distributed over the aircraft, unlike a standard turbo prop or turbo fan engine which are (far as I know) mechanically coupled along an axis. This may open up some possibilities for aircraft design.
• noise (yes that's still an open issue). Quiet aircraft will be allowed in many places louder ones are not.
• pollution
• 're-energize', take-off, land time. That is, if the aircraft could land, re-energize, and take off again in very, very short time perhaps maybe short range is not an issue in some scenarios
• cost of electricity + amortized battery cost versus the cost of fuel for the same distance traveled.
  and so on

 

[Cyrus]

http://www.all-battery.com/alarmsecurityandmeter.aspx" appears to be the current top performer, 10 years. Used in alarm systems, remote metering systems, etc.

Does this battery technology also work in the high power regime for VTOL flight?

Again I'm not talking about the common 'flying car' zaniness. For the military, it depends on the alternatives. Might be a very reasonable cost to transport a couple of Special Operations folks quietly in, and then out again, of a tight spot.

Are you referring to the X-prize, or the NASA puffin here?


Going back, let's assume your numbers of 95-98% efficiency. Then the puffin is looking between 1.2-3HP of losses that will be converted into heat (yes, I've been sloppy using HP here, but we can think of it as the rate of energy per hour). That's a good deal of energy to dissipate. Without an air scoop, the only means of heat transfer is conduction to the skin of the nacelle, and then convection of the aircraft skin to the boundary layer. Thats not a good way of dissipating heat. If you have an air scoop, you have nice turbulent air going over the motor and batteries (turbulent air is an order of magnitude better for convective heat transfer than laminar). You could probably even get away with a low drag http://en.wikipedia.org/wiki/NACA_duct" .

 

[FredGarvin]

There is nothing wrong with using HP for energy losses. We use it all the time.

 

[RonL]

You guys seem to be having a hard time getting out of the box :)
An idea or two if you will allow.

First, consider your batteries built into a ring around the props (5 or more blades?) acting as a flywheel, with lots of air flow to keep them cool.

Props would consist of tractor and pusher design giving counter rotation, which gives options of dual power application to the two motor parts (housing and armature).

Current technology (PWM) feeds motors in pulses, so a generating action, (also in pulses) and maybe 4 or more times the motor voltage, might offset a lot of battery weight.

Ground power to the point of being airborne, battery power to altitude and top speed, then at top speed wind energy allows power applied and generated to be cycled as needed. This can happen because of speed of the plane and flywheel action of the props.

The almost instant reaction times between power used and power generated is much like the chicken and egg question,( Which one needs to be first ?).
If a speed of 300 knots is assumed, in one instant your plowing through the air and in the next instant your sitting in a windmill with a 300 knot wind blowing past it.

The main question in all this is, can the duration of batteries be extended by any worthwhile amount ??
I just hope everyone interested, will not dismiss these thoughts too quickly.

Ron

 

[OmCheeto]

You guys seem to be having a hard time getting out of the box :)
An idea or two if you will allow.

um. Ron. There's thinking outside of the box, and then there's jumping out of the box at an altitude of 30,000 feet without a parachute.

First, consider your batteries built into a ring around the props (5 or more blades?) acting as a flywheel, with lots of air flow to keep them cool.

I believe mheslep mentioned that they'd weigh 11 tons. I don't think it would be desirable to have 11 tons of anything spinning.

Props would consist of tractor and pusher design giving counter rotation, which gives options of dual power application to the two motor parts (housing and armature).

Current technology (PWM) feeds motors in pulses, so a generating action, (also in pulses) and maybe 4 or more times the motor voltage, might offset a lot of battery weight.

Increased voltage <> increased energy density.

Ground power to the point of being airborne, battery power to altitude and top speed, then at top speed wind energy allows power applied and generated to be cycled as needed. This can happen because of speed of the plane and flywheel action of the props.

There are locations on the trip where there will be excess lift due to thermals, but I doubt your flywheels will be practical to store this energy.

The almost instant reaction times between power used and power generated is much like the chicken and egg question,( Which one needs to be first ?).
If a speed of 300 knots is assumed, in one instant your plowing through the air and in the next instant your sitting in a windmill with a 300 knot wind blowing past it.

I think the trip is 2600 miles, which in 24 hours, yields an average speed of about 110mph. I'd say that should be the target speed. Unless of course we can reach a high enough altitude where the wind resistance is less.

The main question in all this is, can the duration of batteries be extended by any worthwhile amount ??
I just hope everyone interested, will not dismiss these thoughts too quickly.

Ron

Your ideas are either:

a. completely unthought out mind spinning(which I can totally relate to)

or

b. so far advanced as to be technologically unfeasible in this or the next century.

Though your flywheel battery pack did remind me of Cort Nozzles, which makes me wonder how much more efficient we could make props with such a device. I mean, when was the last time anyone saw an open framed turbine?

Ah ha! http://en.wikipedia.org/wiki/Ducted_fan" . Just what we were looking for.

Uh. Oh.

Turbofan engines are used on nearly all airliners, fighters, and bombers.

Did I mention that I know almost nothing about airplanes?

 

[mheslep]

Does this battery technology also work in the high power regime for VTOL flight?

No, not that particular chemistry I happened to grab off the shelf - it doesn't have great power density, not as much as its rechargeable cousin Li Ion. I'd have to look some more.

Are you referring to the X-prize, or the NASA puffin here?

Puffin.

Going back, let's assume your numbers of 95-98% efficiency. Then the puffin is looking between 1.2-3HP of losses that will be converted into heat (yes, I've been sloppy using HP here, but we can think of it as the rate of energy per hour). That's a good deal of energy to dissipate. Without an air scoop, the only means of heat transfer is conduction to the skin of the nacelle, and then convection of the aircraft skin to the boundary layer. Thats not a good way of dissipating heat. ...

A good way is whatever is good enough. For comparison, a big tower case home computer dissipates a HP of heat, which it seems to do without an air scoop.

 

[mheslep]

I believe mheslep mentioned that they'd weigh 11 tons. I don't think it would be desirable to have 11 tons of anything spinning.

This is my fault - bringing both the X prize and the small Puffin into this thread. 11 tons of battery was of course for the 850 mi leg of the X prize in semi-large aircraft. The two (Puffin/prize) really should be separated into different threads. Ron was talking about the Puffin I believe.

 

[RonL]

um. Ron. There's thinking outside of the box, and then there's jumping out of the box at an altitude of 30,000 feet without a parachute.

I believe mheslep mentioned that they'd weigh 11 tons. I don't think it would be desirable to have 11 tons of anything spinning.

Increased voltage <> increased energy density.

There are locations on the trip where there will be excess lift due to thermals, but I doubt your flywheels will be practical to store this energy.

I think the trip is 2600 miles, which in 24 hours, yields an average speed of about 110mph. I'd say that should be the target speed. Unless of course we can reach a high enough altitude where the wind resistance is less.


Your ideas are either:

a. completely unthought out mind spinning(which I can totally relate to)

or

b. so far advanced as to be technologically unfeasible in this or the next century.

Though your flywheel battery pack did remind me of Cort Nozzles, which makes me wonder how much more efficient we could make props with such a device. I mean, when was the last time anyone saw an open framed turbine?

Ah ha! http://en.wikipedia.org/wiki/Ducted_fan" . Just what we were looking for.

Uh. Oh.

Did I mention that I know almost nothing about airplanes?

Hi Om,
Nothing really advanced, It's just a matter of putting things in motion that are normally bolted down and in a static condition.
Manage air flow, it can be more than just a barrier to push through.

I started to try and explain things, but there is just too much interaction that must be blended together.

Speed and air flow are key to making use of a generator that can replace a large amount of battery weight.

My thoughts are geared more to a conventional airplane design.

Ron

 

[RonL]

This is my fault - bringing both the X prize and the small Puffin into this thread. 11 tons of battery was of course for the 850 mi leg of the X prize in semi-large aircraft. The two (Puffin/prize) really should be separated into different threads. Ron was talking about the Puffin I believe.

mheslep,
While the Puffin is pretty neat, I was thinking of a more conventional plane, not too big and most likely a twin motor design.

Ron

 

[OmCheeto]

My thoughts are geared more to a conventional airplane design.

Ron

My opinion is that this is going to be a non-conventional design.

The first airplane was made by a couple of bicycle mechanics with a very rudimentary ICE at best.

Now that we have laptops that exceed the capabilities of supercomputers from just 30 years ago, superconductors that did not exist 40 years ago, composite materials that are improving daily, I'd say we are in for something very..., um, I'm going to go for cheating.

 

[RonL]

My opinion is that this is going to be a non-conventional design.

The first airplane was made by a couple of bicycle mechanics with a very rudimentary ICE at best.

Now that we have laptops that exceed the capabilities of supercomputers from just 30 years ago, superconductors that did not exist 40 years ago, composite materials that are improving daily, I'd say we are in for something very..., um, I'm going to go for cheating.

The dream weaver always makes it sound easy and simple, a fact I'm aware of.

Consider a cesna 310, just as an example, remove the big bulky ICE's and replace with the two electric power tubes.
These power tubes might be placed over or under the wing, and based on motor size will likely be less than 12" in dia. and long enough to hold a tractor prop in front and a pusher prop behind the wing, one on each side of the fuselage. The motors/generators in series inside the tubes.

The props (say six blades) have a composit ring of proper thickness and width, secured to each of the six tips, with batteries secured inside or, on the outside of the ring.

As I said before, it seems to me that thrust load and RPM of the props can be much greater, but this may in fact be false, being as I am not an engineer, finding the answers will be very hard for me if at all I can.

Ideas have to start somewhere, right? Lots of ring products in the market, I have not seen one on a real airplane.

Ron

 

[OmCheeto]

The dream weaver always makes it sound easy and simple, a fact I'm aware of.

Consider a cesna 310

A Cessna? Talk about thinking inside the box...

I was thinking more on the line of meshing and morphing the technologies of the desired attributes of existing electric vehicles:

Speed:

105 mph. Batteries not included.

Altitude:

96,863 feet

Range: Lots of range on most vehicles. Though there are none that have both range and speed.

, just as an example, remove the big bulky ICE's and replace with the two electric power tubes.
These power tubes might be placed over or under the wing, and based on motor size will likely be less than 12" in dia. and long enough to hold a tractor prop in front and a pusher prop behind the wing, one on each side of the fuselage. The motors/generators in series inside the tubes.

The props (say six blades) have a composit ring of proper thickness and width, secured to each of the six tips, with batteries secured inside or, on the outside of the ring.

As I said before, it seems to me that thrust load and RPM of the props can be much greater, but this may in fact be false, being as I am not an engineer, finding the answers will be very hard for me if at all I can.

Ideas have to start somewhere, right? Lots of ring products in the market, I have not seen one on a real airplane.

Ron

Rings? This one has lots of rings:

But seriously, I would imagine, based on the the Nuna and Helios examples above, that the most efficient and likely candidate to win the race would be some sort of flying wing.

Kind of like this little fella:

Only not quite so thick. I don't think we need to be carrying around 40,000 lbs of bombs.

 

[mheslep]

...

But seriously, I would imagine, based on the the Nuna and Helios examples above, that the most efficient and likely candidate to win the race would be some sort of flying wing...

I doubt it. This is a speed contest, not a stay-aloft-a-long-time contest. Adding a bunch of wing adds a bunch of drag.

On any kind of aircraft at all I doubt if solar panels help for this one time, one trip contest. Panels might provide 8 kWh (10 M^2 x 200W/M^2 x 4 hours ), which is provided by 53 kg of rechargeable Li Ion batteries (150 Wh/kg), or 16kg of non rechargeable batteries. Dump the panels, go with extra batteries.