I have a question.

On the Wallis which is a pusher, has a cyclic control head, and a pre-rotor spin up, direction are to set the blade pitch to zero degrees. It was suggested that the blades could be set slightly positive and should improve lift.

I started at 2 degrees positive and went up to 5 degrees positive. I didn't plan on the 5 degrees positive. It was due to a field adjustment after a bad landing and I didn't know it until I returned to the shop and checked the blades with a heli pitch indicator that I had positive 5 degrees.

Anyhow, even a slight positive pitch on the blades really adversely affects control. It will attempt to roll over on the ground during takeoff and anything over about 10% throttle the nose pitches up violently and is almost incapable of making left turns.

With zero pitch on the blades it's very stable but anything even slightly positive it handles terrible.

Any explanation?

Thanks, Phil

Rotor speed is too low. It probably won't maintain autorotation for long at that high of
an angle. Until you have enough RPM for the flybar to be gyroscopically stable and
have enough airflow for the paddles to work, the rotor just goes where it wants to.

Hi,

Mickey, thanks for the response and you may be right.

Did you put a cyclic control head on the PT Gyro?

Phil

I put a cyclic head on a GWS stearman.
Flies great.

Mickey, what did you use for a helicopter head and what servos would you recommend? I would like to try with a PT Gyro.

thanks,

Phil

I'm very interested you trying this. I'd be willing to help if
you need it.

I used the GWS dragonfly head, modified to take Aerobalsa blades.
I think the PT is a little bigger and heavier. I'd suggest the TREX 450X head.
It's collective pitch but easy to lock down at a fixed pitch setting.
What's especially nice is the parts are really inexpensive.
I can photo my TREX head if you want a look.

You can use any servo. I'm using the $14 (9 grams) GWS picos.
For the TREX head any of the micros will do, HS55's,
pico's, MX30's, etc.
My TREX running > 2000 RPM is using MPI MX50's ($19 each)
with no problems at all.

It seems that you've been bitten by the cyclic pitch bug.
They fly really well don't they?
mickey

Mickey, thanks for the info.

Yes, I'm very interested in the cyclic control and I have the Wallis flying really well and I don't know how much is due to the Wallis configuration or because it has cyclic control.

If I put cyclic on something like the PT Gyro, I should be able to determine if it's everything that it seems to be.

Even if it didn't control better, one real big advantage is the ability to control flight with small light servos that let the flybars do the work. With a flapping DC control head, the servos really get a work-out, especially the pitch control. One small tip-over and boom, there goes even a metal geared servo. I know that the HiTec HS-85MG has a least one plastic gear and over $30 at our local hobby shop.

There are real advantages to cyclic control, and only two blades to break and probably other advantages that I haven't thought of.

Thanks,

Phil

What is a "servo workout"? Lots of movement or overstress or what? The servos don't know if they are installed in a gyrocopter or quicky 500. We used plastic geared servos with absolutely no in-flight problems. They don't strip out in flight so I'm sure they aren't 'overstressed'. IF anything gets a "workout", it might be the battery. In the PTGyro we typically got 3ea 10 minute flights on a 270ma battery pack. After switching to a 720 ma NiMH battery, we can fly approx 1 hour before field charging. So I don't think that is a problem either.

You are correct though about stripping servo gears on a tip over, IF the servo has plastic gears. After switching to metal gears in a early 'proof of concept' engineering prototype, we have accumulated over 16 hours of flight time in our PT Gyro demonstrator with metal geared servos on pitch and roll. There have been many intentional (and unintentional) tip overs during testing and normal flying with not a single servo gear replacement or broken blade. A metal gear set for the HS-85 is $12.50 at ServoCity.

There are now 50 PT Gyro's all over the world and we have not sold a single replacement blade.

All of this information is assuming factory parts as supplied with the PT Gyro kit. In a post dated 1-11-2005 titled "Modified PT Gyro" you stated that you had replaced the stock Aerobalsa blades with homemade carbon fiber blades weighing 30 grams ea. This could easily contribute to your stripped gears. Twice the weight of the Aerobalsa blades (16 grams) at 30 grams each is a lot of inertia during a sudden stoppage. Factory testing was only accomplished with the Aerobalsa blades and the shear bolt system.

As far as breaking 'only' 2 blades, there will probably be some expensive plastic helicopter parts to replace too if the model hits hard enough to break blades. I also fly R/C helicopters so I know how expensive some of those parts can cost. I just don't know how much simpler and durable a great flying model gyrocopter can get than using the DC control system.


Regards,
PTGyro team
www.flyingbalsa.com

Hi,

I guess I must be the exception on breaking blades. I break lots of them. Of course I fly the PT Gyro with a .15 engine and do things that they are not designed for. I locked up two blades together yesterday in a combination loop & roll during a 20 mph wind. That's why I like the PT Gyro. It's small and fun to do all the things that I would not attempt with a larger more expensive gyro. It came down straight down and sustained only slight damage.

One set of blades that came with the PT Gyro averaged 26 g and the other set averaged 29 g. My new carbon fiber blades average about 24 g and probably several times stronger and a lot stiffer torsionally. ( I think think that's a word) Plus I can put lots of different colored sparkles in the resin and it looks great in the air.

I don't disagree, a cyclic control head is going to be more complicated but I still maintain that the servos will have less strain, less battery drain, and less prone to damage during a crash. What the real benefits are to control still remains to be seen.

Anyhow, the PT gyro is great for it's size and provides a nice platform for experimentations. Hope you guys don't object.

Phil

PTGyro Team,
It seems like you guys think we are picking on the PT Gyro, but I for one am not.
We are discussing the relative characteritics of two kinds of heads.
The servo torque required for a DC head is fairly easy to estimate.
There is a diagram here and a table of about what you can expect for a
1 and 3 pound model.
http://www.rcgroups.com/forums/showthread.php?t=362020
Although blade weight may have some effect on the servo
during an impact the in flight control load is also related to flapping
offset and model weight. The coning angle is a function of
blade weight, blade spanwise CG, model weight and RPM so this does
add to the equation also.

Maybe relative frame of reference is a problem.
The HS85MGBB servo is 49 ounces inches and $31.
Two of them weigh 1.7 ounces.
Compared to a 100 ounce inch $100 digital servo this is
actually a small inexpensive servo. No arguments.

But my cyclic pitch controlled
models fly well and don't strip gears with the 11 ounce inch
$14 GWS pico servos with tiny plastic gears. Two of them
weigh .38 ounces. This is a one pound model that will roll, loop and hover.
Compared to GWS picos, an HS85MGBB is a substantial servo at 4 times the
torque, twice the $ and 4 times the weight.

It's just simple fact that the DC controlled heads will take
more servo power than a cyclic pitch controlled head, all
other things being equal.
Yes DC heads are simple.
Yes DC heads are durable.
Yes well designed DC heads (like yours) fly well.
No arguments here.



Please allow us room to discuss a head design that may be addressing a different interest.
You are marketing your PT gyro as a Primary Trainer where simplicity and durabilty are
important. It's a great design, and I wish everyone would start with one of your kits to
get some air time in gyros.

Cyclic pitch heads address a different need, they have different stablity characteristics.
With a flybar you can run two blades easily, run a low mast height and don't need
a horizontal stab. The controllability is excellent at all speeds.
Cyclic pitch adds a new element, different performance and is not necessarily for the
rank beginner. It does take much less servo load than DC heads.
Collective pitch adds yet another element beyond cyclic. If I manage to fly inverted
you can bet that someone else will want to try it too!! But appropriate for a beginner,
of course not.
I would expect that at some point you may want to offer a cyclic head for your kit as
an additional option especially if Prolific Phil prototypes it for us so we can copy him....

There's room for all of us in the hobby.
regards
mickey
p.s. and yes, I have flown a PT Gyro.

Hi Phil and Mickey,

I never even considered it. The only reason I responded to this thread is because of the misinformation that may confuse someone not familiar with the DC head.

This is absolutely untrue and wrong.

I absolutely encourage discussion. I would even join in if I had time.

This is in my opinion, a Ford vs. Chevy debate.
There are pros and cons of both DC heads and swash plate/cyclic pitch heads cannibalized from a helicopter.

We can save that debate for the next fly-in we attend together.

If you are offering or planning to offer a gyrocopter kit I did not know.
I wish you all the luck in the world. We need more gyrocopters in the hobby!
I hope to see you in Muncie.

Take care,
John

Phil,
Here's the parts you need to make a TREX head.
You can get them from www.like90.com (Indianlatic FL).
Flybar Paddle $6.95
Flybar Rod $3.95
Flybar seesaw holder $7.95
Main Blade Holder $9.95
Main rotor housing set $3.85
Main shaft $6.95
Feathering shaft $6.95
swashplate set $10.95
You'll probably want to get some
linkage balls and short ball links too.

You can use their bearings, or find some of you own.

The assembly manual is here :
http://www.align.com.tw/html/en/asse...x450xen_2.html
You don't need the washout unit because you are not
going to do collective pitch.
You will just have to make straight pushrods to replace the washout links
and this will hold the swashplate in the correct vertical position.
mickey

Mickey, Thanks for partts list. I had started researching for parts but you saved me a lot of time.

They are on order.

Phil

Let me know if you want detailed photos on the TREX head.
mickey

Hi to all,

I'm getting a little bit confused on the coning angle issue.
how do you determine the coning angle of a flapping hinge rotor?
what value would you recommend as the best compromise between stability and manoeuvrability?
The project I'm working on, is a gimbal rotorhead with fixed coning angle (see picture, of course not scale), which I hope will act like dihedral on plane wings, to provide additional rotor stability.
Did anyone experiment this configuration?

Coning angle does NOT act like dihedral.
Coning angle is a negative thing that you try to
minimize. More than 9 degrees is supposed to
create control problems.

Start with your gyro weight, say 3 pounds.
You want about 1.25 ounces/square foot/per blade, so
you need about 13 square feet. This is about a
4 foot diameter ( 2 foot radius).
The blades need to be about 10:1 length to chord
so you need about 2.5 inch blades, 24 inches long.

Divide the total gyro weight by the number of blades, say 3.
Then you need 1 pound of lift per blade.
The blades are 24*2.5/144 = .4 square feet.
The tip speed to make enough lift to fly is
between
v = 50 * sqrt( lift per blade(lb) / area per blade (ft^2))
= 78 feet per second, = 78/radius/2/pi*60 = 372 RPM
and
v = 71 * sqrt( lift per blade(lb) / area per blade (ft^2))
= 112 feet per second, = 112/radius/2/pi*60 = 535 RPM

The blades should weigh about 3 ounces.
The centrifugal force on 3 ounces is
= ( blade weight(lbs) * O * O * K)/32.2
O = rpm in radians per second = RPM*2*pi/60 = 39 - 56 radians/sec
K = radius of gyration = sqrt(blade length * blade length / 3)
= 1.2 for 2 foot blades.

so the centrifugal force per blade is between
CF = 3/16 * 56 * 56 *1.2 / 32.2 = 22 pounds.
and 3/16 * 39 * 39 * 1.2 / 32.2 = 10 pounds
The lift per blade is 1 pound.
The coning angle is between 1/22 (radians) or about 3 degrees.
and 1/10(radians) or about 6 degrees.
You will get slightly more than this due to blade flexing.
Note that the "apparent" fore and aft coning angle will seem higher due
to blade flap as a result of forward flight.

If you try to force a coning angle other than this you will be creating
extra stresses in the blades. And there are aerodynamic disadvantages
to higher coning angles anyway.

mickey

Hi,

thanks for taking the time to give me a full comprehensive answer.
It seems that I have to overwork the design of my homebuilt head, alas.
What do you think about 0 offset hinge(on a 6 lb DC pusher)?
I know I could take an ARF and avoid most of these questions, but I'm having more fun with designing than with the flight itself, so forgive the bore.

best regards

Thierry

Zero offset heads have some challenges:
1) Low control power
2) Stability

Start here:
http://www.rcgroups.com/forums/showthread.php?t=324822
more later
mickey

I have the TREX head mounted on the PT Gyro and it was ready to go. However, I have been unable to get the blades to spin up. I can't get the head spinning fast enough to allow the fly-bars to start controlling. The head just wants to till side to side. The Wallis has a pre-rotor that spins the head until the fly-bars take over. I tried using an electrric drill on the Wallis but I still couldn't get the head going fast enough.

Mickey, what's the secret to getting the blades spinning and keep them from flopping side to side?

Phil

Lock the blades down so they are very difficult to move.
Then put them perfectly straight.
A little hand flip and it will all straighten out.
If it doesn't the flybar or something is out of balance.
Make sure you have enough negative so that when you start to
taxi, it spins up.
Going away for the weekend. good luck.
Will check back sunday.

Mickey,

Before I got your message I have already modified it. I have removed everything and connected the swashplate directly to pitch arms. It now spins up good and it seems to control. What do you think it will do? I have uploaded a picture.

Phil

Likely that that roll and pitch rate will be so high that it will roll over immediately.
The flybar's function is to slow everything down to where a human can control it.

Hi Mickey

Can the parts from TREX be used on the BEGI or G3PO are they too heavy?

The TREX head seems to have very good quality.

Wahid

Too heavy for G3PO.
The hummingbird elite parts would work or the 3D Pro parts.
So would piccolo pro, etc.
The fixed pitch parts work fine.
I am having the metal blade straps made so putting a head
together should get easier.
The will be $8/set of 4 when they come in.
I'll be able to ship kits when they get here also.

Phil,
It looks like your up and down elevator is going to give you up and down collective
pitch. Is this your intention? I'd like to hear your thinking if it is.
mickey