Hi power electric ducted fans

[Jeremy Harris]

what happens if you have controller failure on hoverbike?

Death or serious injury, I expect. Something like this has no redundancy or fail safe capability, plus if you're "flying" it (assuming it works, which I doubt) low then something like a ballistic recovery 'chute wouldn't have time to deploy and bring you down relatively safely. I think this thing was really just a triumph of over-active imagination over practical reality, TBH.

 

[Arlo1]

what happens if you have controller failure on hoverbike?

Death or serious injury, I expect. Something like this has no redundancy or fail safe capability, plus if you're "flying" it (assuming it works, which I doubt) low then something like a ballistic recovery 'chute wouldn't have time to deploy and bring you down relatively safely. I think this thing was really just a triumph of over-active imagination over practical reality, TBH.

Yeh the plan with my "JET WING" was to build it in such a way I could fly it like a hang glider so I could coast in for a landing if anything were to happen. I expected to be working on this by now but....

 

[voicecoils]

what happens if you have controller failure on hoverbike?

Death or serious injury, I expect. Something like this has no redundancy or fail safe capability, plus if you're "flying" it (assuming it works, which I doubt) low then something like a ballistic recovery 'chute wouldn't have time to deploy and bring you down relatively safely. I think this thing was really just a triumph of over-active imagination over practical reality, TBH.

Parachute is what you're expected to use, though you'd need to be high enough as Jeremy mentions.

The hoverbike I linked to above is a working prototype, I watched it do a tethered flight in person a while back.

A scale model can also be seen making an untethered flight :lol:
[youtube]CbV4rMWiuYQ[/youtube]

 

[Jeremy Harris]

The safety problem is serious, though, as the vast majority of aircraft and helicopter accidents occur when operating near the ground, often during take off and landing. That's the very part of the flight regime where a parachute system, ballistic or otherwise, provides very little protection. At least helicopters can autorotate if anything other than the rotors fails and powered aircraft can glide just fine with power off. Even the multi-rotor aircraft are reasonably safe, as they have some redundancy. I remember talking to a chap that had flown the Japanese GEN H4 multi-engine one man helicopter (not electric, see : http://www.gen-corp.jp/ ) a few years ago, and that got around the safety issue by connecting all the engines to a common rotor via the normal one-way clutches all helicopters use. This allowed one or two engines to fail with the thing still having enough power to bring the craft down to a controlled landing. If going electric then I reckon the same sort of configuration is the way to go.

 

[whatever]

a bit off topic but in italy alot of research has been put into what they call a 'prandtl-plane',
Apparantly the guy Prandtl made quite a few discoveries, one of which is that a box wing configuration will give maximum lift per area of wing.
Anyhow seems quite alot of time and effort has been put into this with a view for future planes. I guess main positive is less width of plane for max lift.
I think it has potential ( quite different to biplanes ).

 

[Hillhater]

Is there a premise here that ducted fans are more efficient / effective than conventional heli' rotors for vertical lift??
What is the "science" vs practical results experience on this ?
I can see come "pro's" for DF's .. vectoring, safety, size , etc... but i cant help thinking that in practice there are few DF systems used for vertical power.
And one step further along the "realistic" thought train... the power required and the energy density of current battery systems, would seem to confine electric powered VTO strictly to the model scale.?

 

[Jeremy Harris]

Is there a premise here that ducted fans are more efficient / effective than conventional heli' rotors for vertical lift??
What is the "science" vs practical results experience on this ?
I can see come "pro's" for DF's .. vectoring, safety, size , etc... but i cant help thinking that in practice there are few DF systems used for vertical power.
And one step further along the "realistic" thought train... the power required and the energy density of current battery systems, would seem to confine electric powered VTO strictly to the model scale.?

Ducted fans are far less efficient than a big, relatively slow turning, rotor for lift, by a big margin. In general it always more efficient to move a large mass of air slowly to get a given thrust than it is to move a small mass of air quickly, as the losses are proportional to the square of velocity. The benefits ducted fans give is in being able to get a high level of thrust from a small diameter unit, plus some safety benefit from not having a large rotor whirling around.

I think you're right about the power and energy density limits restricting electric craft like this to model scale, or just very short endurance demonstration projects. One company has been supposedly developing a ducted fan vehicle powered by four Wankel rotary engines for years, and despite having several hundred hp it still hasn't really demonstrated very successful flight or any worthwhile endurance (http://www.flyingcarreviews.com/portfolio-view/moller-skycar/). That may be because it's been suggested that the Moller Skycar is an investment scam, though, as may some of these other weird and wonderful new forms of aircraft. It seems that some people will flock to give you money to develop stuff like this, for some reason.

 

[Hillhater]

Thanks for confirming my suspicions Jeremy.. ( i was too lazy to do the research )
So why do these "projects" keep trying to use a low efficiency thrust device (DF), when they know the power/weight factor is borderline !
If the "flying Bike / Car were even remotely viable, the Military would be using them already.

 

[SlyCayer]

http://www.ebay.com/itm/Leopard-L90...Control_Parts_Accessories&hash=item3cc7d708d8

4.3KG of thrust at 37.5V and 73A?

 

[Jeremy Harris]

Thanks for confirming my suspicions Jeremy.. ( i was too lazy to do the research )
So why do these "projects" keep trying to use a low efficiency thrust device (DF), when they know the power/weight factor is borderline !
If the "flying Bike / Car were even remotely viable, the Military would be using them already.

The reason is simply style, I believe. A lot of people want to believe that you can defy physics and power limits and have something that looks like a renegade from an SF film.

The military have looked at flying cars and bikes occasionally, usually using more conventional lift systems though, like rotors or folding wings. A former colleague even helped evaluate a powered parachute for military covert insertion about 20 years ago, the idea being to drop the guys out the back of a C130 some way from their target and have them fly to it low level under their own power. The US military looked at using rocket packs for a long time, for similar purposes, I believe.There are just too many downsides to personal thrust-borne flying to make it viable with today's technology.

http://www.ebay.com/itm/Leopard-L90...Control_Parts_Accessories&hash=item3cc7d708d8

4.3KG of thrust at 37.5V and 73A?

Not very good efficiency though. It's using 2.7 kW to lift just 4.3 kg. A model aircraft that weighs 4.3 kg would need less than 1 kW to fly, and even a model helicopter of this weight could do a straight lift on around 1 kW with a fairly big rotor.

Edited to add:
Just done some digging around to see how efficient a big rotor might get at producing thrust. The Gamera II human powered quadcopter produces around 96 kgf of static thrust from 460 W of input power. This works out at about 4.8 W per kgf of static thrust. By comparison, the Leopard ducted fan unit above needs about 628 W per kgf of static thrust.

If we rated the Gamera II at an arbitrary 100 %, then the ducted fan unit would come out at just under 0.8 % efficient............................

 

[biohazardman]

I really like the sound and looks of the big 4" units so, bought one from Hobbyking. Going to put it on the back of my 3220 mid-drive to drown out the RC sound when I pass some special folks. Will make it look like a real turbine just so they don't think I am passing them under my own power like it looks now. ;^) Looking forward to some fun in the next few months.

 

[whatever]

just an add on to the Gamera II, a brief search shows the Sikorsky Prize is still open I think ( $250,000), you only have to reach 3m and be aloft for 60secs,
how hard can it be? lol

 

[Hillhater]

, you only have to reach 3m and be aloft for 60secs,
how hard can it be? lol

Obviously harder than those people who have tried thought it would be !!

 

[lpbman]

I wonder what one of these http://www.hobbyking.com/hobbyking/store/__19634__High_Torque_EDF_Ducted_Fan_Unit_5Blade_90mm_w_1600W_Outrunner_Motor.html

would do to a fuel injected honda cbr250r with a separate 6s battery if placed on the intake.

Anyone care to hazard a guess?

 

[lpbman]

Err, besides melt the motor... I just divided the kv with the max rpm. I see it's a 3-4s design.

so... ~12v is easier...

Could slap a pair of hobbyking 4s 8.4ah lifepo4's and the fan and still be lighter than lead.

 

[Jeremy Harris]

I wonder what one of these http://www.hobbyking.com/hobbyking/store/__19634__High_Torque_EDF_Ducted_Fan_Unit_5Blade_90mm_w_1600W_Outrunner_Motor.html

would do to a fuel injected honda cbr250r with a separate 6s battery if placed on the intake.

Anyone care to hazard a guess?

Very little. The pressure increase would be tiny, so tiny as to provide very little boost. These fans are designed to shift large volumes of air at low dynamic pressure, and will stall if run into a closed duct with a lot of resistance, like an engine intake. Turbocharger compressors are designed to deliver air at high dynamic pressure, with a relatively modest flow rate. They use radial or centrifugal compressors to get the high pressure ratio needed, not axial flow fans.

 

[lpbman]

I wonder what one of these http://www.hobbyking.com/hobbyking/store/__19634__High_Torque_EDF_Ducted_Fan_Unit_5Blade_90mm_w_1600W_Outrunner_Motor.html

would do to a fuel injected honda cbr250r with a separate 6s battery if placed on the intake.

Anyone care to hazard a guess?

Very little. The pressure increase would be tiny, so tiny as to provide very little boost. These fans are designed to shift large volumes of air at low dynamic pressure, and will stall if run into a closed duct with a lot of resistance, like an engine intake. Turbocharger compressors are designed to deliver air at high dynamic pressure, with a relatively modest flow rate. They use radial or centrifugal compressors to get the high pressure ratio needed, not axial flow fans.

We're talking about a ~20hp engine, You really don't think adding 2 hp worth of ram air would increase the top end of a thumper a noticeable amount?

 

[amberwolf]

Doesn't matter how many HP you throw at it, if the air isn't compressed enough to force it into the engine.

Try an experiment, and take a ducted fan and pipe it into a nearly enclosed space, and measure the pressure differential on each side. It probably will have little more than you'd get out of a typical box fan in the same setup, at a guess.

But if you use a fan designed to compress the air (like those in turbochargers or jet engines), you can get many times the pressure differential even into a nearly enclosed space.

 

[lpbman]

This could be done with an axial fan though, it just needs blades designed for the job, yes?

 

[Jeremy Harris]

We're talking about a ~20hp engine, You really don't think adding 2 hp worth of ram air would increase the top end of a thumper a noticeable amount?

You'll just be throwing more than 90% of that electrical power you're using away. As I've already said, and as AW has reiterated, you need increased intake pressure to make more power, and these ducted fans only produce a tiny pressure increase.

 

[lpbman]

I know I'm hijacking, but the idea is that these bikes are cheap, and no one wants to spend a 1500+ dollars for a proper turbo... but if you could get 2-3 psi out of a 150 dollar "axial flow compressor" then you might have something.

 

[Arlo1]

I origanly wanted to try that but Luke has already tried it and he said he got some absurd number like . 5psi boost so thats ~ 3% increase in power but thats if everything else is 100% which its not because the air is now hotter. So you can maybe expect 1% increse for all the time and money and the risk of shit breaking and sucking into your motor. So 1% x 20 hp = .2hp.... Do you think you will feel it???

 

[lpbman]

I origanly wanted to try that but Luke has already tried it and he said he got some absurd number like . 5psi boost so thats ~ 3% increase in power but thats if everything else is 100% which its not because the air is now hotter. So you can maybe expect 1% increse for all the time and money and the risk of shit breaking and sucking into your motor. So 1% x 20 hp = .2hp.... Do you think you will feel it???

Awesome. numbers...

So assuming he used an off the shelf fan and got 3% increase in power, I would bet a redesign of the blades could double that, and proper sizing of the motor would negate most of the heat dump (150 watts over 100cfm?). Couple that with a thumper being starved of air in the top end and you would definitely feel a 5% power increase with something like 500w at WOT. Electrical system mods would be minimal and you could put the fan before the air filter for catastrophic failure protection... though I don't know if that defeats the purpose.

I'm guessing you get the power lost from sucking in air + a tiny bit extra... so whatever that comes out to on these pocket rockets.

 

[Jeremy Harris]

I know I'm hijacking, but the idea is that these bikes are cheap, and no one wants to spend a 1500+ dollars for a proper turbo... but if you could get 2-3 psi out of a 150 dollar "axial flow compressor" then you might have something.

The pressure rise will be a heck of a lot less than 3 psi, more like 0.3 psi if you're lucky..............

I've just done some quick calculations. This fan delivers around 0.58 psi when running in free stream with no obstructions. As soon as you start to obstruct the flow with an intake that is smaller than the fan diameter of 90mm the pressure will drop as the fan flow conditions change and the mass flow rate drops, so I think I was being optimistic with my 0.3 psi guess above. If you have an intake diameter of, say, 40mm (pretty big for a small bike), then you will be obstructing around 80% of the fan. My guess is that this will cause partial or full stall and the pressure will drop to maybe 0.1 psi if you're lucky.

 

[lpbman]

I know I'm hijacking, but the idea is that these bikes are cheap, and no one wants to spend a 1500+ dollars for a proper turbo... but if you could get 2-3 psi out of a 150 dollar "axial flow compressor" then you might have something.

The pressure rise will be a heck of a lot less than 3 psi, more like 0.3 psi if you're lucky..............

I've just done some quick calculations. This fan delivers around 0.58 psi when running in free stream with no obstructions. As soon as you start to obstruct the flow with an intake that is smaller than the fan diameter of 90mm the pressure will drop as the fan flow conditions change and the mass flow rate drops, so I think I was being optimistic with my 0.3 psi guess above. If you have an intake diameter of, say, 40mm (pretty big for a small bike), then you will be obstructing around 80% of the fan. My guess is that this will cause partial or full stall and the pressure will drop to maybe 0.1 psi if you're lucky.

How much of that is because that's not what the fan blades were designed for, and how much is because it's a single stage axial fan? Not expecting you to do my "homework" for me,

I just look at the basics of it and think there is quite a bit of energy lost to the engine having to suck air in at high rpm, and this would "replace" that energy even if little positive pressure is achieved. Maybe I'm overestimating how much energy it takes to fill the cylinder or perhaps the pressure diff. is too low to transfer that energy to the engine...?

Thanks for the responses regardless... this has been buzzing in my head for sometime and it's nice to have feedback.