BLOODY FOREIGNERS COMING OVER HERE ON JETPACKS

I wonder how fuel efficent a flying board is compared to other flying transport. Is it better than an ultra light or a back pack helicopter?

My intial instict is, it isn't because it looks wholely unaerodynamics, but it also has a lot less weight.

>>19853
The gliding capability of ultralights probably makes a large difference in fuel used overall. It needs a push to get up but then it can continue a long way without burning. Something like this or a mini-helicopter needs continual burn to not fall out of the sky.

>>19852

A story like that must feel like a wet dream to ARE Nige.

>>19855

A Gryphon system will still be your contraption of choice though, because due to the lift under its wings, it has been proven to be able to glide/fly 200 miles on a single fill up of kerosene. Despite having four, more powerful jet engines.

>>19858
That's surprising, it doesn't look particularly aerodynamic except in a Hollywood sort of way.

>>19859

I would guess that a Gryphon also has a bigger fuel tank than a "flyboard".

Really a fascinating piece of kit. But I think it's difficult to launch from the ground, normally when you see people flying them, they have to drop out of airplanes at considerable altitude.

Rumour has it that the U.S. military has been looking into creating a military version for years, the obvious advantage being its small form factor, at least compared to jet fighter planes, and the ability to have airborne troops penetrate deep into enemy territory without jeopardising the safety of the airplane they drop from. Retail price for the civilian version is said to be around £250K per unit, which is small change both compared to the U.S. military's annual budget and the replacement value of an airdrop-capable airplane.

>>19861
>they have to drop out of airplanes at considerable altitude.
That seems like cheating. If you're weighing them against each other equally then the fuel requirement of getting them up like that should be taken into account too.

>>19862

indeed, otherwise a glider is obviously the most fuel efficient plane there is having an infinite miles to gallon and range.

>>19863
Is there no way to launch a glider with a massive catapult?

>>19859

Well it does have 4 fucking jet engines, doesn't take off from the ground and is less efficent MPG per passanger than any plane I can think of that isn't an intercepter.

>>19864

That is how they are mostly launched, but that obviously requires energy, and therefore calling that not fuel because it isn't petrol and on board is a bit intellectually dishonest.

>>19866

You could pull it back with a large system of gears attached to a bicycle contraption of some sort.
There's also this
https://twitter.com/XHscitech/status/1156493788149374978

>>19864

Funnily enough, that's pretty much the standard way of launching a glider, albeit with a big winch and half a mile of cable.

https://en.wikipedia.org/wiki/Gliding#Winch_launching

>>19868
It would take a while to winch half a mile of cable by hand even if you used some fancy gears to do it but if you're refilling on peaches at 60p for a pound it's still probably cheaper than aviation fuel.

>>19869

Just don't let monkeys steal your peach.

>>19870


This is singularly the most surreal reply I've ever read here, I don't know what is going on

>>19871

So you read my post on 60p a pound peaches, but you failed to also take a closer look at the picture I posted with it.


This is why people voted Leave, you know.

>>19869

Avgas is about £1.90 ish per litre at the moment, while Jet A1 is about 90p per litre. The latter weighs close enough to a gram per millilitre so if my maths is right - it likely isn't - then jet fuel is cheaper than peaches.

>>19872

>but you failed to also take a closer look at the picture I posted with it

Clearly I must have, pic related.

>>19872
That was someone else.

>>19873
Jet fuel might be cheaper than peaches by weight but that's irrelevant if we're talking about the price of energy output.

>>19865

Jet engines are surprisingly efficient at low loads. While huge airliners need tonnes of kerosene to fly, the tank on that thing can't be much bigger than a very small car tank. I'm not saying it's the most efficient thing in the world, but better than a car, probably.

>>19875

I have to assume 400 odd ml of jet fuel has more potential energy than a pound of peaches.

>>19877

What if the peaches were used in a cold fusion reactor?

>>19878

You shouldn't keep your peaches cold, apparently.

>>19879

I don't even like peaches very much.

>>19880
If I had my little way, I'd eat peaches everyday.

>>19881

Just don't let ninjas steal your peach.

>>19876

>Jet engines are surprisingly efficient at low loads.

"low load" is a relative term here though. I think what they use on the Gryphon kits are beefed up model airplane turbines. Model jets don't normally weigh more than around 30 or 40 lbs, so if you've got four of those modified model jet engines under your wings, then maybe they produce enough thrust for 200 to 250 lbs of total weight. Jet fuel has a density of about 800 grams per litre, so with a 25-litre kerosene tank on your back, that's another 20 kg of weight to consider.

Of course if you strap an engine out of an F-15 on your back, then we're really talking low load.

>>19884

>Jet fuel has a density of about 800 grams per litre

Does it really? Interesting. I only ever work with it in terms of tonnes, but I'm sure I've heard pilots use weights and litres interchangeably like you would water. This is mildly concerning but I'm sure its fine.

>>19885

Grams per litre or per cubic centimetre is one of the scientifically correct ways to specify the density of something.


Wikipedia kind of leads you to believe that fuel is measured in gallons in aviation, I wouldnt know, but for example the Boeing 747-8 is listed with a fuel capacity of 63,034 US gal.

https://en.wikipedia.org/wiki/Boeing_747#Specifications

Tonnes kind of sounds like you hear it more often though, I agree.

>>19886

Certainly in the UK, for commercial airliners at least, it's measured in kilograms. A standard fuel order would be spoken or written as 12.8 tonnes (Or is it tons? The kilogram one) or 12800 kg.

Perhaps I'm just second guessing myself at this point, but I swear I've heard people ask for x thousand litres too, I'm sure that's where I made my assumption on the density of the fuel. I worry now that a captain has told me he had 6k litres on board and I've calculated for 6 tonnes. That sort of variance could put a smaller plane out of trim entirely.

I think I've just had a severe lack of sleep and am imagining the litres thing. I hope so anyway. Enjoy your flight, otherlad, it's probably fine.

>>19887

Hydrocarbon fuels are almost invariably lighter than water though. That's common knowledge, as well as water having a density of 1.

I've made similar calculations for air conditioning refrigerant, except R134a has a density of around 4.25 g per cubic centimetre. It is measured in grams or kilograms when you buy it wholesale, while a shop that I went to here said they would charge me per 100 millilitres to have the AC in my car serviced. One of their mechanics told me, "Ah, grams, millilitres, it's all the same." Which is a bit of a scam, because if my system in my car needs 700 grams of R134a, then that's 164 millilitres of refrigerant, and not 700 millilitres that they said they would charge me for when I asked for a quote.

>>19888
That sounded like a very high density for R134a - https://www.engineeringtoolbox.com/r134a-properties-d_1682.html has it at 1225.5 kg/m^3 , 1.2g/cc

I use this stuff, https://www.solvay.com/en/brands/galden-pfpe and it's weird enough at 1.8 g/cc
4.25 would be fun, Mercury's 13.5g/cc, but that stuff's odd.

>>19889

You're right and I got it wrong. 1,1,1,2-tetrafluorethane, a.k.a. R134a, has a gas density of 0.00425 g/cc, that's 4.25g per cubic metre in SI, not 4.25 g per cubic centimetre.

So then as you said it's got an SI density of roughly 1.2 g/cc in liquid form, meaning if my system needs 700 grams, that's 583 millilitres of liquid R134a. Not quite the scam I thought it was.

Might be time to top it up regardless, because the place I went to said it is going to be phased out and the price will artificially be driven up because it's a potent greenhouse gas, a few orders of magnitude more potent than CO2.

>>19888

>Hydrocarbon fuels are almost invariably lighter than water though. That's common knowledge

I really don't think that's common knowledge. I'd concede that many (most?) people would know that oil floats on water, but most wouldn't necessarily link that to the applied density of fuel.

I also know that 1ml of water being 1g is a miraculous revelation to many I've told.

>>19886
>the Boeing 747-8 is listed with a fuel capacity of 63,034 US gal.
That would make sense, as it's the volume of the tank, independent of the density of the fuel that goes inside.

>>19891

I never really thought about it before but that mean when they recalibrate against the international kilo the size of a litter changes too or is there a different ability measure for volume and it is just by old convention that the 2 match up and they technically don't now.

>>19893

One litre is always defined as 1000 cc, regardless of units of weight measurement. Water having a density of approximately 1 is just a coincidence.

Also, it's more a rule of thumb that water's density is 1. It's accurate enough for most calculations by and large, but the real figure for water at standard atmospheric conditions is closer to around 0.997 g/cc. And the litre as a unit of volume was not derived from the volume of 1 kg of water, but from the metre's definition of being the precise distance that a beam of light travels in a vacuum in 1/299 792 458 of a second (originally it was assumed to be one ten-millionth the distance from the Equator to the North Pole).

It gets slightly more complicated when you also factor in that water's density on Earth is only what it is because of the specific mix of protium and deuterium hydrogen atoms contained in it. It might be different on other planets where the protium-deuterium relation in the local water is different. Deuterium-enriched water here on Earth is known as heavy water, with a density of around 1.107 g/cc, and it's what is used in some reactor designs of nuclear power stations.

>>19895 Isn't water literally the basis for the metric system? It's not coincidence at all.

>>19895
>Water having a density of approximately 1 is just a coincidence.
No, it was by definition. The small difference is a combination of better control of standard conditions and the drift in the IPK.

>>19926

The original definition was based on the volume of a kilogram of water, but the current definition is fixed at 1000 cm^3 and has no relation to water.

>>19929
Yes. You see that "was" in the past tense, right? You know what that means, yeah?