Help please, Lightweight motor for Hovercraft

[Tiberius]

wouldn't a second small 5kW gas engine be a simpler, cheaper and more efficient solution ?

To answer, that and Frxdy's point. Yes it would and some craft do that, not sure about cheaper and more efficient though. The lowest power craft in normal use are 25 hp and this can be for instance one 25 hp engine doing it all, or a 20 hp for thrust and a 5 hp for lift.

I quite like the idea of a single engine though. And there are attractions to an electrical transmission. It makes sense to be able to vary the proportion of power split between lift and thrust, and it is useful to be able to maintain lift irrespective of thrust. Both these are difficult with mechanical drives. OK, the second problem is solved with a separate engine, but with the downside of weight, noise, reliability and the fact that you never seem to be able to get an engine of exactly the right power.

Nick

 

[Lock]

Hi Nick

Ya definitely want to get up close with the ePPG folks! Did you see the "E-Pac" that Yuneec International is offering (claims to offer?):
http://yuneeccouk.site.securepod.com/paramotor_products.htm
From that page:
"Powerful, Ultra Smooth and Very Easy to use, E-Pac features a new Direct Drive Sensor Controlled motor, Sensor Speed Controller and Lithium Polymer batteries all built into a practical, strong, ergonomic moulded body unit. These key features, together with a 4 piece 'aerofoil profile' propeller cage, a 1.2m 'Quiet' prop and E-Pac's featherweight 'easy grip' handcontroller with integral LCD flight data display, combine to create one of the most advanced and futuristic paramotor power units available today."

E-Pac Outline Specification (specification and design subject to change)

Power Unit Yuneec 'Power Drive' 160 Power Source: Plug and Play Battery Packs
Type: Direct Drive Type: Lithium Polymer
Diameter: 160mm Total Voltage: 55.5v
Control: Internal Sensor Packs/ No. Cells 6x Packs (15 Cell per Pack, Total 90 Cells)
Voltage: 55.5v (Constant) Total Amperage: 30Ah (Supplied) 60Ah (6+6 Pack Option)
Weight (6 Packs): 10Kg (30A)

Propeller Yuneec 'Q-Prop' Charger: Yuneec E-Charge
Size: 1.2m 2 Blade System: Full individual cell monitoring/balancing
Specification: Carbon with quick release system No. of Packs: 3 Packs at a time
Charging Time: Approx 1.5hr per 3 Packs

Motor/Prop Output Flying Time
Thrust: 50Kg (55.5V) With Supplied Pack: 25~35mins (At variable power settings)
(Using 6 pack standard configuration)

Speed Controller Yuneec 'Power Block' Statistics
Voltage: 75v (Max) Weight inc. Batteries: 22~25Kg (Ready to fly - no wing)
Amperage: 250A (Max) Body Types: Moulded Plastic/Fibreglass/Carbon
Audible Alarms: Power On / Start / Tempreture Propeller Frame: Profiled Aluminium
Start Protection: 5 sec Slow start (Initial activation) Frame Diameter: 1.25m

Internal Cooling Upgradeability
Motor and Controller: Motor Integral Fan Pressure System Power Packs Additional battery packs can be added
internally and externally ot a maximum 60A

Hand Controller Optional Items
Functions: Start, Stop, Throttle, Cruise. Batteries: Battery Pack 5Ah (Each),
Display 600x400 pixel LCD display Battery Pack 30Ah (Tri Pack)
Data Information: Rpm, Amperage, Voltage, Motor/Controller Tempretures
Data storage: All relevant E-PAC data Pricing To be announced Spring 2008

Please note: Due to continual development the above specifications are subject to change. All estimated flying times are given from current testing and must be considered approximate. Times will vary depending on pilot weight, wing used and other varying conditions.

Roll yer own, or maybe just buy off the shelf:

http://www.hovpod.com/index.html

cheers

lOcK

 

[curious]

Is that throttle control the same PWM signal used for servo positions in RC; I am at least familiar with that scheme?

Yes.

 

[olaf-lampe]

I see one problem with the generator . When you throttle down the engine, the generator will drop voltage and available current. The "governor"mode of a RC-ESC can not keep the lift-RPM constant at that moment without a second powersource like a small battery. Maybe a bunch of supercaps can help too.
Did you ever thought about a hydraulic-pump/motor for the lift? Most of the hydraulic systems come with an oiltank that can keep the pressure up long enough to corner the hovercraft.

only my 2 cents
-Olaf

 

[Tiberius]

Hi Olaf,

Generally, you would not want to throttle the motor all the way down. With a mechanical drive and single engine, we have got used to keeping the revs above about 75% max. If an electric drive could extend the range to 60-100% or 50-100% then it would be an improvement. OK, yes, to go much further than that would need a battery at some stage.

There is a guy here in England who has built one with a hydraulic drive, but I think it is a fixed ratio system.

Oh, and BTW, one of the funny things about hovercraft is that you don't power down for corners - that is usually when you want maximum thrust, and quite often you will want to apply the thrust before actually reaching the corner.

Nick

 

[1clue]

Tiberius,

Bob Windt did a small one-man pointed hovercraft that was completely electric. He used a couple BLDC outrunners and 3 12-volt car batteries. It worked with his nephew, Bill Zang on it. It had about 10 minutes worth of run time.

He used some crappy Chinese motors, supposedly 8 kW each, but throttled them down to 2 kW or under. It was a proof of concept thing.

I think the motor-generator idea is a very good one. I want to do that on my UH-18sp as well. The Yuneec 20 kW seems just the thing, one for the motor and one for the generator.

With the lift system, we'll have to have extra provision for cooling. I was thinking to put a vent hole in the lift fan, and let lift air blow through the hub to the low pressure side. We'll need something similar on the engine, there's no way an aircraft motor will cool itself in that protected space.

 

[1clue]

I see one problem with the generator . When you throttle down the engine, the generator will drop voltage and available current. The "governor"mode of a RC-ESC can not keep the lift-RPM constant at that moment without a second powersource like a small battery. Maybe a bunch of supercaps can help too.
Did you ever thought about a hydraulic-pump/motor for the lift? Most of the hydraulic systems come with an oiltank that can keep the pressure up long enough to corner the hovercraft.

only my 2 cents
-Olaf

What you're describing is not really a problem in any on-the-river use case. It might be an issue moving it around in the garage, but IMO you could make a plug-in power supply for that, so you don't have to start the engine at all.

My current hovercraft (a UH-18sp from http://www.hovercraft.com) uses a belt drive from the automotive engine for lift, only it runs through a variator. This is sort of like a snowmobile clutch, it offers a change of ratio based on how you move a lever. So the lift is already dependent on the thrust setting, only more so than what an electric transmission would have.

The UK guys I've talked to who use hydraulic use a pair of gear pumps. There is no variable lift, it is directly linked to thrust speed.