Electric motor pre-rotator

[ironcowboy]

Is there such a thing?

[dusty wallace]

I haven't researched it yet. But to add to his question. If there is electric pre-rotator is any one using them as a generator to charge the batteries? Like old farm machinery that used the same unit to start the machine and once it started it would run as a generator. Or would it create to much drag on the rotor?

[Joe Pires]

Yes there very common, they use starter motors from small cars, I think toyota is pretty popular.
They are only engaged via bendix for a very short time so no I dont think anyone is trying to charge a battery with them.

[Aviomania]

yes here is one which is the lightest prerotator you can have. Electric car starters are heavy but are also used.

http://www.aviomania.com/booster-prerotator.htm

You can watch the videos for detailed information on performance, installation and operation.

Now.... using it as a generator from the rotor..... that is a really a No, No!!!!!

it is much more efficient for the generator / alternator to be driven directly from the engine. If for example the generator requires 2 HP to charge the battery that is almost what it will draw from the engine. If on the other hand you connect the generator to the rotor that means that the rotor will require much more than 2 HP from the engine to provide power to the generator because turning the rotor from pushing it through the air is not the most efficient way.

[dusty wallace]

Nicolas, thanks
that makes sense I was just curious.

[danmcgee]

When you got your plans from Martin did he not include the new mechanincal prerot plans with the set he sent you? If not here sent me a copy and I would be glad to convert it to a PDF and send it to you. This was designed for the sportster

[jcarleto]

Drag on the rotor is a bad thing. There have been accidents caused or at least contributed to by bendix gears that have engaged or failed to disengage. The amount of drag caused by a motor with the power to spin up rotors used as a generator would be significant and probably dangerous.

Best to find your power elsewhere. There are many other options. Worst case...go get a bicycle generator and put a little model airplane prop on it. Gyroplanes are draggy anyway, it couldn't cost much speed. I've seen light FW aircraft with that setup.

[GrantR]

Ag planes use a prop driven spray pump. Of coarse they are flying a lot faster and the little prop on the pump is in the prop blast.

[ironcowboy]

Dan,

I have plans for a mechanical pre-rotator for my HA-2M but I got to wondering about the weight and, got to thinking about an electric motor. Seemed like it’d be easier to install and maintain, and might be lighter in weight… so I thought I’d ask. I try to follow the KISS principal.

[jcarleto]

Aviomania's solution is sweet. It is lightweight and effective. It solves one of the problems electronically that plagues electric motor pre-rotators. That is, "soft-start."

Most electric motors that have the ability to get a set of rotors up have so much torque that they can twist a mast right off. The ole' standby solution when using an automotive starter was to have two start circuits (using two soleniods). One connected normally, and a "soft-start" circuit that basically has a dead-short resistor...usually made from a piece of copper wire...perhaps with a half-hearted coil...across the leads to the starter. The "coil" heats up and becomes an effective resistor, reducing the current to the starter. Once the rotors are spinning a little, you release the "soft-start" circuit and engage the normal circuit. Effective..but brutal. Five or six successive spin-ups equal a dead battery.

[PW_Plack]

Deriving charging current from the rotor could have useful applications and be safe, but not backwards through a geared-up flex shaft. (A Bendix wouldn't stay engaged in that mode anyway - it only stays engaged while providing torque, and retracts if receiving it.)

It would be really inefficient to expect the rotor to provide any meaningful contribution to charging the main system battery, but using it to keep your avionics alive in an engine failure would be a useful thing to do, especially if flying at night.

For example, an MGL Enigma panel uses only 1.5 amps at 14 volts, which works out to less than one-tenth of a horsepower. Probably less than a rotor brake left on by mistake, and we know that's possible. Or, so I'm told. ;)

Using rotor power in concert with a small backup battery for the avionics, with a little reserve for 30 seconds of operation of a landing light, would be very doable.

Such a backup could be configured to draw power from the rotor alternator only when the main electrical system failed, so it wouldn't affect efficiency in normal operation. The backup would only work while the rotors were turning, but if you're faced with a dead-stick landing at night, the emergency is over once the rotors slow down, one way or another!

[Timchick]

Dan,

I have plans for a mechanical pre-rotator for my HA-2M but I got to wondering about the weight and, got to thinking about an electric motor. Seemed like it’d be easier to install and maintain, and might be lighter in weight… so I thought I’d ask. I try to follow the KISS principal.

With a choice between electric or mechanical I'd go with mechanical. A properly maintained mechanical system is pretty reliable.

[Aviomania]

With a choice between electric or mechanical I'd go with mechanical. A properly maintained mechanical system is pretty reliable.

Tim is right. A mechanical is simpler to maintain (most people understand mechanical more than electrical equipment). you also do not have to worry if you have a flat battery. Yes you can start the engine and charge the batteries enough to prerotate (10-15) minutes but the mechanical... if your engine works then you can prerotate.

The benefits i see on our electric are:

1. it is the lightest,
2. it is a clean installation (less drug) with out any feedback on the rotor system (change in trim or stiffer stick because you need to flex the shaft of the mechanical one)
3. it performs as good as the mechanical.
4. it is very gentle on the rotor system and must (no shocks when the bendix engages and acceleration is softer)

Now if i get those 4 benefits on a mechanical system then i would choose the mechanical.

there is not such a mechanical system yet.. but we are working on it.

and if weigh is not a big issue then the existing mechanical systems are pretty good.

[Timchick]

Just to be clear, I wasn't saying mechanical prerotators are the only way to go. Some engine/redrive setups make a mechanical prerotator difficult to install. Electric prerotators are a nice solution.

Nicolas has a nice electric setup. His has a nice soft start which a lot of the electric setups don't.

[Aviomania]

Tim, It is Ok..... I know.

I just like to say things as they are and when i find the time to finish the mechanical set up as i want it then this will be my first choice. The other type i am fond of is the small engine driven one.

All kinds have there uses and benefits. Each one of us should choose what He or She needs and works better for them.

[Vance]

I have an electric pre-rotator on the Predator that uses a Toyota starter.

I cannot hear the control tower when I am pre-rotating. This means I cannot position and hold because I cannot hear the take off clearance unless I leave the rotor still and then I am slow to get off.

When flying at un-towered airports I cannot hear the radio when I am in a critical position on the runway.

I have a small battery so if I am doing pattern work at a place that requires a taxi back I am limited to about five takeoffs.

My starter is not designed for the duty cycle I am subjecting it to and it gets hot. The starter that is on there now has about 500 flight hours on it and shows no sign of failure.

In my opinion running a large, 4 gage power wire to the starter motor up the mast is not good practice in case of an electrical challenge. I have a fusible link but it still makes a lot of heat before the fusible link fails. I run the prerotator motor through the main power relay. The Lycoming will continue to run with a complete electrical failure but most automotive conversations will not. I have a ground wire straight to the starter but if it fails I am running a lot of amps through my rotor head bearing. I feel is a flight critical part that is easily damaged by that sort of operation.

I like Martins prerotator design and it probably weighs less than my starter, ring gear and wiring which weighs about 12 pounds.

I have the minimum size battery to start my Lycoming IO-320 so I am not counting my 14 pound battery. I could save about 22 pounds if I got rid of the starter, alternator and battery and all that large wire. I am too lazy to hand prop her although we have when I had a starter problem.

I engage the prerotator as I am crossing the hold short line and usually see 100 rpm on my 30 foot rotor by the time I get to the centerline of our 150 foot wide runway. At that point I can go half back. I can go full back at 120 rpm so my take off is usually about 300 feet after I get to the centerline. It takes even longer on a hot day with a passenger and full fuel. In a 35kt gusting wind I would like a stronger prerotator because the blades want to sail away at low rotor rpm and I would like to get through that more quickly. If the wind is steady it makes for a nice short takeoff.

The gyroplane I am going to build will have a hydraulic prerotator.

Thank you, Vance

[Aviomania]

Vance,
Brushed type motors (car starters) generate "spikes" which makes radio interference and draw very high amps (150-200A) at start up... that is why you can not use your radio.

The brush less motors i am using do not have this problem and the wire needed to drive them is 12 Gage. the controllers have short circuit protection and cut out. wile spinning up ( accelerating) the Amps are low 10-20A.

The system is also designed to use airspeed through the rotors to promote higher prerotation speeds. For example.... 25 feet untwisted blades give 145 RPM at 0 airspeed. if there is 5mph wind then they go to 160 RRPM, with 10mph wind the prerotation is at 180 RRPM, at 20 mph wind the prerotation is 230 RPM and the take off run is only 15 -20 feet.

[Vance]

I did not mean to denigrate your system Nicolas, only report on mine on the Predator as a way to answer Courtland’s query.

The automotive starter is very easy to fabricate and in my opinion has some significant drawbacks.

Thank you, Vance

[Jetrock]

Has anyone looked into these ?
CRYSTALYTE HUB MOTORS from Electric rider electric transportation

[Aviomania]

I did not mean to denigrate your system Nicolas, only report on mine on the Predator as a way to answer Courtland’s query.

The automotive starter is very easy to fabricate and in my opinion has some significant drawbacks.

Thank you, Vance

Vance I know. In this Forum we are all learning.. i just stated the reasons, observations and ideas behind the electric prerotator with the intention of sharing my experience with people that are interested in knowing why and how.

It has nothing to do with defending the system. In fact.. i have encouraged people on going with a mechanical one after we have discussed, there needs.

[Aviomania]

Has anyone looked into these ?
CRYSTALYTE HUB MOTORS from Electric rider electric transportation

yes i did but the brush less small motors after winding them specially for high torque are very good.

[Brent_Brown]

Take a look at this motor /Batt pack

If you don't know I work with new equipment for the some of the Military units. I was a diver with them before I got out.

This system is high end but I'm sure it can spin some blades up to speed at that weight use both motors.

http://www.jetboots.com/JDPS/J-DPS.html