Hydrogen powered flight

[Count Steer]

an interesting test bed setup. that can produce 4500ish SHP but that prop will be fixed pitch at quite a low power setting.



https://www.linkedin.com/pulse/zeroavia ... g-largest/

If that's the hydrogen-electric version, it's supposed to produce 2,700hp...which is quite a bit of oomph.

(Should get that truck moving quite quickly )

Aren't those big Tu-95 bears something like 15000shp per engine?

Probably...I think these are aimed at 18-20 seaters though, rather than carrying enough bombs to flatten a few villages.

[Mussels]

Bit odd they didn't just fit electric pitch control....

Honestly though, I'm not sure if you need variable pitch on an electric engine. You don't need to run at constant speed anything like as much and motors are generally far more tolerant to a wide range of speeds/powers. Similar to why electric cars usually only have one gear.

Maybe you can just ditch the weight and cost of a variable pitch prop?

The propeller tip speed matters a lot, apart from the damage dust can do at high speed the shockwaves when they go supersonic aren't helpful.

[Cousin Jack]

IIRC the US experimented with supersonic props. Allegedly the Thunderscreetch could be heard 20 miles away on takeoff. It was not a succesful experiment.

[Count Steer]

Bit odd they didn't just fit electric pitch control....

Honestly though, I'm not sure if you need variable pitch on an electric engine. You don't need to run at constant speed anything like as much and motors are generally far more tolerant to a wide range of speeds/powers. Similar to why electric cars usually only have one gear.

Maybe you can just ditch the weight and cost of a variable pitch prop?

The propeller tip speed matters a lot, apart from the damage dust can do at high speed the shockwaves when they go supersonic aren't helpful.

If something is moving fast enough even rain can do damage. Back in my warmongering days I worked on novel materials/fabrication for the pointy end (radome) on missiles. The silica ones wouldn't let you start a war in the rain as they eroded too quickly. (They get quite hot).

In an aside...in order to test materials the USA attached them to a rocket sled on a long track and fired it through water droplets. In the UK they fired water droplets at a static piece of hot material in the lab.

(Did stuff on body armour and bullet 'proof' structures for helicopter seats too so it wasn't just about blowing stuff up ).

[Bigjawa]

Tu-95/142 has supersonic props , contrarotating too.

[Bigjawa]

Bit odd they didn't just fit electric pitch control....

Honestly though, I'm not sure if you need variable pitch on an electric engine. You don't need to run at constant speed anything like as much and motors are generally far more tolerant to a wide range of speeds/powers. Similar to why electric cars usually only have one gear.

Maybe you can just ditch the weight and cost of a variable pitch prop?

The propeller tip speed matters a lot, apart from the damage dust can do at high speed the shockwaves when they go supersonic aren't helpful.

If something is moving fast enough even rain can do damage. Back in my warmongering days I worked on novel materials/fabrication for the pointy end (radome) on missiles. The silica ones wouldn't let you start a war in the rain as they eroded too quickly. (They get quite hot).

In an aside...in order to test materials the USA attached them to a rocket sled on a long track and fired it through water droplets. In the UK they fired water droplets at a static piece of hot material in the lab.

(Did stuff on body armour and bullet 'proof' structures for helicopter seats too so it wasn't just about blowing stuff up ).

IIRC the shuttle couldn't be launched in rain because the tiles were so fragile. If a bad storm was forecast, they'd roll it back indoors.

[Count Steer]

IIRC the shuttle couldn't be launched in rain because the tiles were so fragile. If a bad storm was forecast, they'd roll it back indoors.

I'm pretty sure that's right. They are sort of clever though. On re-entry the surface glazes and wears away but the heat pulse makes them foam at a certain depth which makes them more insulating. Of course that meant they had to strip them off each time and get the vac students to stick another set on.

[Yambo]

Hydrogen is about three times as energy dense as oil based fuels, weight for weight. That's why its such a compelling choice for rockets and very attractive for aircraft too.

It's just pretty low energy density by volume so you need a big tank, albeit one carrying not much weight.

Maybe they should consider using a trailer.

[Mr. Dazzle]

That's pretty much what rockets do innit, then unhitch it when empty.

[Taff]

Bit odd they didn't just fit electric pitch control....

Honestly though, I'm not sure if you need variable pitch on an electric engine. You don't need to run at constant speed anything like as much and motors are generally far more tolerant to a wide range of speeds/powers. Similar to why electric cars usually only have one gear.

Maybe you can just ditch the weight and cost of a variable pitch prop?

I asked about this in work, and there's a few reasons why fixed pitch works for low power and doesn't work for higher power applications, like noise (increases with tip speed), tip speed restricts power available from a prop that is a compromise for all running speeds, and one of the biggies is that in the event of an engine failure, the prop needs to be able to turn to be in line with the airflow so that it isn't creating huge amounts of drag, or turning itself into a windmill which can over speed and risk throwing a blade.

[Mr. Dazzle]

My question gets down into the subtleties of electric motor power characteristics though...they have completely different "power bands" and the like. Variable pitch first came about for the same reason cars have gearboxes, but most electric cars are single speed transmissions....IYSWIM. Big topic!

May interest you to know that regen is a real thing with EV planes, using the props as windmills as you descend. If you just cut all the control and let it spin in the breeze it'll generate it's own "back torque" which self limits the speed. The problem then becomes the motor cooking itself

[Mussels]

My question gets down into the subtleties of electric motor power characteristics though...they have completely different "power bands" and the like. Variable pitch first came about for the same reason cars have gearboxes, but most electric cars are single speed transmissions....IYSWIM. Big topic!

May interest you to know that regen is a real thing with EV planes, using the props as windmills as you descend.

Don't electric motors have a sweet spot for speed/efficiency just the same as ICE engines?
EVs don't need a gearbox because motors work effectively from no revs but that doesn't mean they won't benefit from one.

[Mr. Dazzle]

The sweet spot is fucking wide though, it's more of a "sweet region". You're also talking about the difference between "90% efficient" and "87% efficient" sort of thing, so the extra losses from a complicated gearbox overwhelm the advantage of being able to change gear.

There are very few electric cars with a gearbox, the only ones I am aware of (and this might well have changed back recently) are the Porsche Taycan and top levels of Tesla, both of which have a 2 speed box. One of the vehicles I'm working on started out 2 speed and has now gone back to single because we managed to get more out of the motor.

EDIT: Aston Martin actually did/do an EV conversion on the DB4/5/6 shaped cars. The original prototype retained the 4 speed box of the standard car. When the press came to drive it they all ask "which gear should I be in?" to which the answer is "it makes no difference" Such is the difference with the way EVs make torque.

[Taff]

My question gets down into the subtleties of electric motor power characteristics though...they have completely different "power bands" and the like. Variable pitch first came about for the same reason cars have gearboxes, but most electric cars are single speed transmissions....IYSWIM. Big topic!

May interest you to know that regen is a real thing with EV planes, using the props as windmills as you descend.

not really, gearboxes came about so that the wheels can be turned faster with a limited engine rev range, variable pitch came about for efficiency, the engine speed is stepped down quite a lot for the prop and the prop doesn't care what is driving it, it only knows how fast it is going and how much torque it is creating against the airflow, this explains why variable pitch much betterer than I can https://www.centennialofflight.net/essa ... or%20them.

regen, yes, I've been in discussions about this, Windmilling is a high drag condition that slows the aircraft's airspeed so there are challenges with how much energy you can extract without causing too much drag and slowing the aircraft down too much. very fine control of the prop is needed because the pitch will be heading towards reverse thrust setting, a lower pitch than would currently be available. And then the question is, is it worth it for 4 minutes of regen?

[Mr. Dazzle]

Yeah not denying that variable pitch is a thing and that aircraft speed makes a big difference, just musing on the cost/benefit.

To contextualise it a bit this a topic I've been tangentially involved with already on the motor side. Mostly waiting for customers to decide if and how they want variable pitch . Or even if they want a gearbox vs. direct drive.

S'also part of the reason you see these concepts with loads of little motors/props instead of 2 big ones.

[Taff]

Yeah not denying that variable pitch is a thing and that aircraft speed makes a big difference, just musing on the cost/benefit.

To contextualise it a bit this a topic I've been tangentially involved with already on the motor side. Mostly waiting for customers to decide if and how they want variable pitch . Or even if they want a gearbox vs. direct drive.

S'also part of the reason you see these concepts with loads of little motors/props instead of 2 big ones.

we're in the same position on the prop side, as the phot above shows, they are using our props for testing already. I assume they're just trying to work out the effect of constant speeding the prop on the motor control rather tan asking you to control pitch?

[Mr. Dazzle]

I suspect it's more complicated than that, 'cause the very need for constant speed is different. You have much more freedom on the motor side to run at different rpm and maintain the same efficiency, unlike an ICE. This is probably helpful because it unties your hands on the motor side and lets you play with both rpm and pitch to maintain a certain condition (e.g. AoA) on the propeller blade. So for example you can have much less pitch variation for the same performance envelope.

[Taff]

[Mr. Dazzle]

That truck is never gonna fly! Surely not.

[Taff]

That truck is never gonna fly! Surely not.

them wheels are way too heavy