Jbolt

Is there a general rule of thumb for hub dimensions and shaft sizes? Say a 48" to 52" 3-blade? How about construction materials?

Thanks,

Jay

Spindizzy

Take a look at www.autogyro.com or www.gyronuts .com

Both sites have considerable information on hub materials and design.

Personally speaking I find polypropylene hinges are fine on models up to 32" in diameter using a shaft of 3/32 piano wire. Some folks like to use Klett landing gear axles as shafts.

Sean

tintrax

Hello Jay - Maybe this will help. Below is a sketch of the rotor hub that I use. It requires no engineering, being made of 1/8th plywood with quite thin polypropylene sheet sandwiched between. The inner section (2 pieces- one above the polysheet, one below) extends to the hinge lines only, the poly sheet of course extends all the way, and then there are six smaller pieces beyond the hinge lines. Putting something simple into words makes it seem confusing!
It`s held together with contact glue, reinforced with nuts & bolts. See photo on my website
http://www.geocities.com/tintrax/page7.html
Size - My autogyros range from 44 inch disc diameter to 56 inch, the last being .40 power.
Distance from rotor shaft (which is 1/8th wire in all cases) to hinge line is one inch.
The hubs have three more pieces of ply, these are the platforms where the rotor blades sit.
From wire shaft to end of blade is 1 1/2 inches in the biggest plane, a little less in the others.
Hope this helps. Regards, Colin

tintrax

Problem - Image failed, try again, Colin

Jbolt

Colin,

Thanks so much. That helps a lot. I tend to over engineer things myself.

I notice you use a single bolt on the blade. Are these tight or snug to let the blades seek there own lead/lag?


Thanks again,

Jay

tintrax

Hi Jay - Single bolt is kept quite tight, ignore lead/lag. Keep at 120 degrees between blades, I use a length of dowel with a notch at one end that fits into the squared off blade tip, and have a mark near the other end of the dowel to indicate where the adjoining blade tip should be. Takes a bit of fiddling to get the blades set right! Sandpaper is used, glued to both the bottom of the blade and to the blade mounting platform, where they make contact, to give friction to resist movement, but if the blade happens to whack the ground it should fold back thereby avoiding damage (well, that`s the theory and it has worked sometimes).
The plywood hub is nice and light, I hate weight!
Regards, Colin

Spindizzy

Well if its show and tell time

This is a poly hub. I designed this one myself though of course the real credit goes to Jim Baxter who came up with the original idea. I tried to make it even simpler by making it from an easy to shape piece of triangular poly. I only uses single mounting bolts just tight enough to hold the blades and it all folds up if you whack the ground. This one has straight tangs but I now always use tangs with the hinge line offset by 15 degrees.

The shaft is 3/32 piano wire and the hub tube is just commercialy available brass with two small model car bearings inside.

Sean

Jbolt

Colin,

what sze servos are you using for the pitch & roll controls?

Thanks,

Jay

tintrax

Jay - You ask what size servos I am using for pitch & roll. Well, nothing special, my largest aircraft uses Futaba FP-S3001 servos, these have an output torque of 42 oz/in. This I understand is not powerful - but they do the job fine with rapid response to control input (me waggling the sticks!). My planes are fairly light, the largest of 56 inch disc diameter (OS FP40 motor) weighs 3lb 12oz which gives a disc loading of 3 1/2 oz./ sq ft. Maybe this enables servos of modest power to be satisfactory.
Perhaps others reading this might like to give their comments on the subject of adequate servo power. Also - there was comment a while back on size of batteries, the thought being that constantly the pitch servo is working, fighting against aerodynamic forces trying to tilt the rotor back, and thus draining the battery. I am using ordinary 600 mah battery, no problems but I generally do not fly for extended periods of time at a session. Any comments anybody?
Colin

Spindizzy

Tintrax

I just use an offset gimbal, get it right and it virtually unloads your servos completely. I use SD 250's in my 32" model which are basic micro servos. Pack is a 550 mah AAA nimh. Tx always goes flat before the rx even thinks about giving up.
I don't want to tell anyone how to suck eggs but for those of you who love egg gobstoppers here is an offset gimbal.

Mind you, I don't fly the huge gyros some folks do on here so maybe the offset gimbal just doesnt work with repect to models over a certain size ??

Sean

iwadmin

spindizzy,

Where do you have the fore and aft servo attached to the gimbal? On the front side or back side of the gimbal?

Thanks

Spindizzy

It doesn't matter where you put it.

On my Kellerva model its on the back and on my Huff and Puff pusher model its on the front (images attached).

On the brown coloured hub (Kellerva) you can see the small amount of offset. Works really well and in fact I had to use a stronger servo on the roll control compared to the one on the fore & aft tilt.

Sean

iwadmin

You gat a full picture of your Kellerva somewhere on the net? I like the way you finished out your gimbal. looks real good!

I'm going to use (sence I am a Futaba guy) s3004 ballbearing servos for both rotor controls. They have 44.4 oz/inch torque. I figure sence my rotor span is going to be 62" I had better go with a good servo.

I was thinking about using poly to hinge the gimbals tilt action. Is that what you did?

Spindizzy

John

Yes I did use poly for the roll hinge. I think the diameter of the kellerva rotor was about 42". I used Futaba s148 servos. Thats the biggest gyro I have ever built so I don't really know if a 3004 will do it......give it a try!

Kellerva was just a little experiment and seemed to fly ok. The double control rods were used because 1 tended to flex too much when pushing.

Sean

Hal deBolt

Hi ya'll,
First do believe rotor size and model weight plus flying speed all effect
the airstream force the rotor sees.
Believe the the larger any of those items are the greater the ASF! and the amount can increase dramatically with minor increases.
There seems to be a simple answer to all rotor control needs at least up
to 60" rotors. FMA direct has a jewel of a standard size servo with 120 in oz and at a reasonable cost. Model # PS905MBB
Learned the hard way> with a 5 to 6 lb craft with a 54" rotor you will need at least 1200 mah batteries!
Good luck!

Hal deBolt

tintrax

Like regular aircraft autogyros vary a lot with regard to speed, rotor disc loading, and the type of performance that the flier wants. My personal aim is gentle flying, with much low speed hovering and low level slow flight. However many others will want lively performance and use powerful motors and have higher disc loadings. Maybe its because of light weight and gentle flying I am able to get away with low power servos for rotor tilt and pitch, (full DC gyro) and I also confess to using only a 600 mah battery. Hal mentions 54 inch rotor and weight of 5 to 6 pounds. My largest autogyro has 56 inch rotor diameter and weighs 3 pounds 12 ounces, giving a disc loading of 3.5 oz sq ft. I guess this is lighter than most and maybe explains how I can use what seems to be minimal equipment. So it all depends on what you want, and how you go about it. Incidently my Gyrace Two was flying backwards relative to the ground nicely yesterday, (moderate breeze), until the unreliable old motor cut.
Colin