use of pre-rotators hints and tips

[SandL]

I have been reading threads on prerotation, take off distances, electric power needed, Birdy taking off with it still engaged etc.
So I thought about my use and experiences.
Generally I start my engine (pull start) pat my drangon wings just 2 or 3 times to get over inertia, climb in to the pod and strap in.
increase engine rpm to about 2,500-3,000 and give a quick 2-3 second squeeze on the pre lever, to engage the wunderlick wheel. then release just to put a bit of engergy into the blades. (and prove all is working)
from this point I am taxiing with stick forward and every now and then just for a few seconds engage the pre rotator to stiffen the blades , so they are spinning and stiff, not drooping. Some, I know engage the rubber wheel hard some gently, I am a gentle user, some say I'm wrong as the wheel skids on the drum. I am a "skidder" as a hard engagement seems to add lots of stress (cable, load on engine and flex tube). I think about what we are asking the kit to do, (try hand patting where the pre rotator cog is and it's a lot of weight/inertia due to moment.)
so I taxi with stiff blades, I am told that it's best to have stiff turning blades when you taxi over rough ground as it produces less stress on the head.
I then let the engine warm up and sit pointing into wind with a few more prolonged dabs on the pre rotator and as the rotor speed builds I use the pre rotator less and less and let the wind do the work gently easing the stick fully back as the rotor speed permits.
When I have the max RRPM that the wind will give me (with stick fully back now) I line up, apply wheel brakes open the throttle and engage pre rotator and gradually opening the throttle more untill the brakes can not hold me.
I then release the brakes and after a few yards release the pre rotator, as the blades blur and become a solid disk I am able to go to full throttle.
I believe I am gentle on the pre-rotator and head.
this all deppends on the wind, in flat calm I pre-rotate for longer and at a higher engine and rotor RPM, this results in a much faster ground speed when I take off. I never go full throttle with pre rotator engaged as even in nil wind conditions I can build up ground / air speed and so rotor speed to sufficiently to lift off and have enough runway left to land on if the motor stops. (500 yard grass strip.)
I realise this is not possible nor taught in the modern gyros.
many modern gyros have an interlock between stick and pre-rotator so the prerotator can only be operated when the stick is fully forward.
I also appreciate that Birdy seems to have his fully engaged until just after lift off.
I guess the guy that uses an electric drill, that gets discarded before take off roll commences also has no option.
I believe the genesis electric motor will only handle low speeds to get the blades turning.
I need to use a prerotator, I have tried patting up dragon wings to a speed where I can move the stick back with out flapping , but I failed to get enough RRPM.

so how do you use your prerotator ?, what can I learn from your experience ?
what have you had fail ? and why ? what components have you lost through the prop that I need to make sure are tie wrapped down ? Am I right to skid the rubber wheel ?

 

[Hardy]

I never taxi with the blades turning, I only prerotate when taking the active runway.

 

[All_In]

I never taxi with the blades turning, I only prerotate when taking the active runway.

Hi Hardy
That is a good tip.
However I'm wondering what to do when I sitting at LAX waiting my turn.

Shouldn't I prerotate at the holding line so the incoming traffic doesn't have to wait?

I'm using LAX as an extreme however one day I will land and take of from there just to do it! I've done it in a Cherokee Archer, and Turbo Arrow and I did have business with an FBO on the field.

However there are many airport I will be using that have a great deal of traffic and they would hate me for waiting. Their favorite word is expedite.

 

[Hardy]

Yes you should John we never want to hold up the flow of traffic but how long does it take to spin up your rotor blades, at 170 rpm I bring the stick back and start my take-off roll.

 

[All_In]

Yes you should John we never want to hold up the flow of traffic but how long does it take to spin up your rotor blades, at 170 rpm I bring the stick back and start my take-off roll.

Thank you I really don't have the experience to know I've never timed it and I think only once I had traffic of one FW landing.
But watching videos I know it's long enough for me to get board and fast forward to just before they release the barks.

You bring up a great point. I will have to do it both ways and see and ask the tower which they would prefer I guess I'm really not sure?

 

[Vance]

Some thoughts on Pre-rotators.

Some thoughts on Pre-rotators.

The Predator uses a Toyota starter, a small battery and an 8.5 inch chord 30 foot Sport Copter rotor.

Typical duty cycle for an automobile starter is less than eight seconds so anything over that and I am building up a lot of heat.

I am on my third starter and I have 800 hours on this one. The second starter lasted about 550 hours. The Predator has about 3,590 takeoffs on her since I started flying her.

I taxi to the centerline with the prerotator engaged and the disk flat. About the time I get to the centerline (150 foot wide runway) I am at 100 rrpm and I bring the cyclic half back. At 120 rpm I bring the cyclic full back and at 150 rrpm I let go of the button. It takes about 15 to 20 seconds.

Around 180 rotor rpm the nose wheel lifts and I begin to bring the cyclic forward to balance on the mains. At somewhere around 290 rrpm she waddles into the air at around 50kts IAS.

I can’t hear the tower with the pre-rotator engaged so I can’t line up and wait or wait with the rotor rotating behind the hold short line.

The tower at SMX will often launch me with an aircraft on a three mile final because I get off faster than most fixed wings and I can side step the runway if things get close.

I timed the Cavalon (Puff) and it took 15 seconds to get from zero to 200 rrpm at a dead stop and use the POH take off protocol. Because it was mechanical I could hear the tower while engaging the prerotator. I experimented with pre-rotating behind the hold short line and I was not able to launch in less time doing it the taxi and stop in the middle of the runway system. This surprised me and if I had practiced more I might have been able to launch quicker by a few seconds by starting behind the hold short line.

 

[All_In]

PS:
I'm not sure if you mean the Aviomaina Genesis pre-rotator or some Genssis motor for a pre-rotator.

But I'm willing to put in a shameless plug for the worlds lightest pre-rotator.

With the Nicolas's prerotator https://aviomania.com/booster-prerotator.htm you turn a rheostat to increase the RRPM's until it hits about 125 RRPM's they you increase the throttle let off the braks and leave it at full power letting the realivite wind help increase the RRPM and under power until the bendix pop out.

I have not flown one yet so if this is wrong I hope Nicolas will correct the mistakes.

https://www.bing.com/videos/search?...54ACDD5B4AE060F8B43554ACDD5B4AE060&FORM=VIRE7

 

[anthom]

The Predator uses a Toyota starter, a small battery and an 8.5 inch chord 30 foot Sport Copter rotor.

Hi Vance, that seems like a real powerful starter for such large blades. could you please give me the specs/part number of this starter? Thanks a lot.

 

[Vance]

I suspect it is nothing special.

I suspect it is nothing special.

Hi Vance, that seems like a real powerful starter for such large blades. could you please give me the specs/part number of this starter? Thanks a lot.

My recollection is that it fits a Toyota 4runner Antony.

It is a typical small Denso starter with a reduction drive and I suspect it is nothing special.

I handed them the dead one and most of a hundred dollars and they handed me the rebuilt one.

Beyond that I know nothing about it.

I don’t see any NAPA numbers on it.

It appears to me to have a shorter motor than some of the geared Denso starters so I suspect it is not the most powerful one.

The best thing I did was to use welding cable going directly from the main solenoid to the starter and from the starter motor to the negative terminal on the battery. This helped the performance a lot and stopped the broken cable.

I feel bigger battery would help although it might just burn the starter down quicker.

The Predator uses an Odyssey dry cell battery PC680.
Pulse (5-second) Hot Cranking Amps (PHCA): 520
Cold Cranking Amps (CCA): 170
20Hr Nominal Capacity (Ah): 16
Reserve Capacity Minutes: 24
Dimensions L x W x H (in): 7.15 x 3.00 x 6.65
Metric Dimensions L x W x H (mm): 181.5 x 76.3 x 167.8
Weight (lbs.): 15.4

I copied this from Aircraft Spruce and I don’t know what most of it means.

I liked it because it is little and I can lay it down. They make a mount for it and that made things easy. It was much smaller and lighter than the Gill battery The Predator came with. I am on my second battery and I suspect soon to be my third in seven years.

I am on my third alternator and fourth starter.

 

[anthom]

Thank you very much, Vance. Also for the photos. I feel that a simple electric prerotator system seems to be the most practical and cost effective.

 

[All_In]

Thank you very much Bro!
I learned from that!!!

 

[Vance]

Your welcome Antony.

Your welcome Antony.

Thank you very much, Vance. Also for the photos. I feel that a simple electric prerotator system seems to be the most practical and cost effective.

I am sorry I didn’t have more information for you.

I was in the hangar and a picture was easier than trying to describe the starter.

A car starter would not be my first choice for a pre-rotator on a gyroplane with a 30 foot rotor.

I may not have said it clearly enough; I can only get the rotor up to around 100 rotor rpm in still air and not moving. From 100 rpm to 150 rpm is wind assisted. I suspect it could do a little better with a bigger reduction ration but that would cause other problems.

I asked Tilton who makes race car starters to build me a custom high performance starter for a pre-rotator and when I told him it needed to work for 20 second he refused to even try.

I feel 100 rotor rpm isn’t enough for gusting conditions. The last time I took off in gusting conditions (18kts gusting to 28kts) I started to flap the blades twice. It was probably my fault and I found myself starting over.

As my battery gets weaker I see less rotor rpm in still air and have to work harder at getting the blades up to speed with the wind.

There is no soft start on The Predator and that is hard on everything. I expect to start losing ring gear teeth before too long, it puts a big twisting load on the mast and moves the cyclic around quite a bit unless I have it forward and right. I feel this and the need to nurse the blades up to speed adds complexity to the training process in The Predator.

Not being able to use the radio during pre-rotation is troubling at a pilot controlled field and a small challenge at a towered field.

I feel an engine driven pre-rotator with a real clutch (not a slipping belt), a drive shaft and a Bendix is the best setup.

The RAF setup with the flexible shaft worked well except it was always cooking the clutch because its use was not explained well. I could probably have eventually learned how to use it. I feel a multi plate clutch out of a small motorcycle would work a lot better.

In the starters and the electrical systems defense I gave 45 rides in one day at El Mirage and that is a lot of pre-rotating. I never imagined it would hold up and I am still using that starter and ring gear four years later.

The idea of using an electric motor with a longer duty cycle and a system with more voltage appeals to me. I don’t like the big wire needed to get 12 volts to work. The big wire is heavy and prone to failure from the constant movement of the rotor head.

I like the idea of a drive shaft rather than hanging the motor on the rotor head.

Some kind of soft start appeals to me.

 

[Waddles]

G'day All,

Interesting to note the different techniques used by the individual posters on this thread. Here's my technique.

I operate a heavily modified RAF but still use most of the original pre-rotator. The drive system has been replaced by a belt driven right angle gearbox fitted with the original RAF clutch. The flex cable was cut down to fit the new installation. 1300 hours and no sign of the clutch burning out at all. Rotors are 29' twisted/tapered composite blades from a local manufacturer.

Now the technique. Pre rotate to 60 RPM, lined up for take off or not. I usually taxy with the blades spun up to 80-90 RPM, but still start off with only 60. Standing still into a 10 kt headwind, the blades come up to around 130 RPM and a 20 kt headwind gives something towards 180 RPM. Power needed in this case to stop the gyro backing up. At about 175 RPM the blades "disc' or "blur" and shortly thereafter, the nose "pops". Forward cyclic to balance and full power over about 3 secs. Lift off around 50 kts with rapid acceleration once off the ground. At gross weight of 600 kgs (about 1320 lbs), nil wind and 30*C, take off roll is less than 275 m (900' I think).

My students with light single place gyros are taught the old "Armstrong" method of pre rotation, whether they have a pre rotator or not, as are the new generation gyro pilots. In most cases with the NGs, it is necessary to pre rotate to around 60 due to the configurations, but from there a safe take off is possible provided one is patient.

In general, we are not permitted in controlled airspace so the difficulties with a tower operator don't exist for us. The nature of our airstrips is such that it is wise to taxy with something towards 100 RRPM to lessen hub-bar stresses.

Waddles.

 

[blw2]

this is interesting to me. Not a gyro pilot, but a single engine GA pilot dreaming about gyros....

the you-tube vids I have seen all seem to show taxi into position and wait operations..... and wait, and wait, while the prerotator does its thing.

I've wondered why they don't prerotate at least a bit if not most of the way up before taking the runway.

 

[Rick E]

I believe at busy airfields it's common courtesy to enter the active runway with blades spinning. With my prerotator engaged and my engine on idle it is quite simple to maintain 100 RRPM which then allows for a quick departure once lined up and rolling, just do it carefully!!!!!