The Atom Special

[Max Z]

Posted by David P Williams on 07/01/2015 20:47:29:

I'm a bit baffled by this 'rods in compression if at the rear' business. Now, almost all my autogyro experience is with full size machines, specifically the MTo Sport, Calidus and Cavalon. The head geometry is very similar to the HK C30 head that we're using for the Atom, but reversed, i.e. the gimbal block with the pitch and roll pivots is at the front, the rotor pivot behind that, and the control arms at the rear.

David,

Who am I to debate this with someone who has full size autogyro experience, but I will try to make some points anyway.

Firstly, you are remarking that the HK head is the reverse of many full size AG's, but if you look closely you will see that the rotor pivot is directly above the gimbal, not in front or behind. Now, if you delve into the rotor theory you will see that there is a tendency to pitch up when the forward speed increases, as a result from the difference in lift between advancing and retreating blades which plays out as a forward/aft force moment. This force moment would result in the rotor tilting back uncontrollably if it were not to be held back by the the forward control rods, which are thus under tension.

So your entire plane is pitching up now, not just the rotor. When you push your stick forward to correct, the result is not a neutralization of the rotor pitch-up moment, but merely changing the rotor pitch angle resulting in a new balance of forces acting on your plane so you are resuming level flight.

When you observe full size AG's, notably Ken Wallis' AG, you will see that the rotor pivot is offset aft from the gimbal. This results in a compensating force moment for the rotor pitch-up due the lift force exerted by the rotor being offset from the gimbal. This offset can only be correct for one forward speed, given a fixed CofG postion or vice versa. So I am guessing that the pneumatic (?) cylinder you are talking about is either a means of changing the offset to redress the balance, or a variable spring to compensate for the control linkage forces.

Max.

Edited By Max Z on 08/01/2015 11:31:35

[Richard Harris]

Posted by David P Williams on 08/01/2015 10:24:08:

I'm thinking of enlarging the whole thing by about 10% - do you think that will work?

David

David,

Absolutely, the Atom flies really well at its current size and I am sure the old saying ' bigger flies better' will be true in this case with the added bonus there is more to see!

I will be attempting a larger version for my mass build project, just need to finish off what was supposed to be a quick christmas build!

Rich

[Gyrocopter]

Still working on this. It has removable U/C  mast and tail boom assy, blade loading 3oz /sq. ft and 18 deg hang so should fly well. Blades spin up very well without any shims. (AJ blades)  I'm not happy with the tail boom as its a bit floppy so have ordered some carbon rectangular section to try. Can't wait to fly it!!

 

Chas.

 

Edited By Gyrocopter on 08/01/2015 16:16:58

[Max Z]

Posted by Max Z on 08/01/2015 11:28:00:

.......This force moment would result in the rotor tilting back uncontrollably if it were not to be held back by the the forward control rods, which are thus under tension.

My choice of words here may be confusing. What I meant to say is that the rotor tries to tilt backwards, but is held in position (relative to the plane) by the front-mounted control rods pulling it forward. Reversely, rear-mounted control rods would have to push it forward and would be in compression, possibly giving way if they are not stiff enough.

Max.

[BILL PETTIT]

Chas:

Many of the Atoms shown here and my own have the spreader piece between the boom rods up tight to the rear of the fuselage, this might take some of that flexing out of you booms. Just a thought. I like the thought of a larger Atom maybe you could call it the Molecule lol I crack myself up some times.

Bill

[BILL PETTIT]

oops double post,,fat fingers.

Bill

Edited By BILL PETTIT on 08/01/2015 17:05:32

[Gyrocopter]

Molecule sounds good Bill or mighty Atom?? I might have a go at another spreader or better still I like your idea of using foam for the tail.

Chas

[David P Williams]

Max - thanks for the response. Just because I used to work as an engineer on full size gyros doesn't mean that I understand any of the aerodynamics!

I thought I was saying that the HK C30 head itself is very similar to the full size layout, just that in the Atom design (and other models it seems) it is fitted in reverse. On the examples of the HK head that I have, the main rotor pivot is about 4mm behind the pitch pivot, with the control arm connection a further 40mmm or so further back. There is a definite separation of the two pivot points, they are not directly in line as you state.

I understand your explanation of the rotor disc tilt back forces, and that the offset on the head will allow the overall lift forces to help counter them. Why does this only work for one speed? Doesn't an increase in lift cause an increase in the tilting force and vice versa, or is this a non-linear relationship?

The pneumatic cylinder that I refered to is for pitch trim. The pilot moves the control column to alter the rotor disc angle to give level flight at the chosen speed/power setting. The trim is then adjusted to take any load off the column. My point is that the air pressure to the cylinder is always in a direction to tilt the rotor back, i.e. a downwards pull on the rear of the head. Trimming the rotor forward is done by releasing pressure. Maybe the full size geometry is such that the total lift force is always greater than the 'tilt back' force?

I know that the gimbal/rotor axis relationship is quite critical. During the certification process for the Calidus a problem arose when approaching its designed Vne of 120mph. A pitch oscillation started which increased until the speed was reduced (an undamped phugoid). This took a while to resolve, meaning that the early Calidus machines were only certified with a Vne of 90mph. I remember various solutions being tried, including the fitting of a damper (like those for motorbike steering) to the head, and many test flights where we shimmed the head to change the gimbal/rotor axis distance in 0.1mm increments.

David

[Max Z]

 

 

Posted by David P Williams on 08/01/2015 18:03:47:

On the examples of the HK head that I have, the main rotor pivot is about 4mm behind the pitch pivot, with the control arm connection a further 40mmm or so further back. There is a definite separation of the two pivot points, they are not directly in line as you state.

I have to admit that I do not have an actual example of the HK head at hand (impatiently awaiting their arrival since early December ), so far I had to make do with a home grown example. I do not know how much the 4 mm will influence the control force, but it could potentially neutralize or reverse them.

 

 

Posted by David P Williams on 08/01/2015 18:03:47:

I understand your explanation of the rotor disc tilt back forces, and that the offset on the head will allow the overall lift forces to help counter them. Why does this only work for one speed? Doesn't an increase in lift cause an increase in the tilting force and vice versa, or is this a non-linear relationship?

My reasoning was that, when talking about level flight, the weight of the craft remains the same and so does the lift force. And in turn the force moment created by the head offset. However, the pitch-up moment due to the advancing blade effect increases with speed.

 

Posted by David P Williams on 08/01/2015 18:03:47:

Maybe the full size geometry is such that the total lift force is always greater than the 'tilt back' force?

I think so. The pneumatic cylinder you are describing is effectively my "variable spring" pulling down the back end of the head, with the spring pull controlled by the air pressure in upper and lower chambers.

Posted by David P Williams on 08/01/2015 18:03:47:

..and many test flights where we shimmed the head to change the gimbal/rotor axis distance in 0.1mm increments.

Sounds like a very sensitive balance, David.

Please remember that my actual experience with this type of autogyro is only one, Richard's Atom! Maybe he or one of the other gyronuts can share more of their experiences relating to this.

Max.

Edited By Max Z on 08/01/2015 19:59:18

[Richard Harris]

Chas,

Now that is a big Atom, great work. What is the span? 60"? it will be a floater that is for sure, cant wait to see it in the flesh

I have been thinking of the booms and thought they would be ok doubled, I know you have ordered carbon but I wonder whether a 3rd tail boom at the top(creating a triangle) would add a little more rigidity to it? it would certainly look different.

Rich

[Terry Whiting 1]

Hi Bill,

Depron is a material I have been using of late, and I have found the 6mm thick can take heat shrink film.. Although I have one of those digital readout irons I can not remember off hand what temperature I used.

I have made a balsa tailplane for my Atom (not fitted as yet) and was about to replicate it by making one of 6mm Depron.

Terry

[BILL PETTIT]

Terry my tailplane is made from blue fan fold building insulation maybe 3/16" thick and very light, cheap as chips to replace when needed.

Bill

I also have pink fan fold it is thicker.

Why do the pictures come out in the wrong order?

Edited By BILL PETTIT on 08/01/2015 21:05:19

Edited By BILL PETTIT on 08/01/2015 21:07:46

Edited By BILL PETTIT on 08/01/2015 21:11:29

[Terry Whiting 1]

Bill, we can get the pink up to 5" thick as an insulation board, but Depron has a finished outer skin which I have found is cyno safe which I find as a great alternative to balsa..

[BILL PETTIT]

Terry:

I use a hot melt glue stick gun ( on low heat) .

Bill

[Baz Lewis]

Posted by Phil Winks on 07/01/2015 19:49:41:

think I might just dig out those m3 rods then

I have used M2 clevises and ball ends....using dia.2mm carbon rods x 3 in a triangular bunch and then a tube of heat shrink wrap to squeeze em tight....just pour cyno down the tube to make solid

[Grasshopper]

My Atom build is well on after the (sadly!) obligatory Xmas break.

I am using AJ blades and about to glue the 4mm wide shims to the lower plate. I know that Rich had said that these should be 0.4mm thick but note that Steve Jones 2 said (page 50) that he had gone for 0.8mm as this gave a fast spin up but reduced lift. He had found that with 0.4mm the take off was at 60 degrees whereas with 0.8mm spin up was faster and take off perfect.

What do we all think - 0.4 or 0.8mm?.

Peter

[Richard Harris]

Peter,

0.4mm thick for AJ blades, I believe Steve is not using AJ's but blades based on the PDF which produce more lift.

Rich

[Steve Jones 2]

I was wrong on my first with 0.4mm , hence the change to 0.8.

Second Atom was build with 0.8mm shims from the start and flew perfectly

Yes the blades were made by me to Rich pdf.... 

Steve

Edited By Steve Jones 2 on 11/01/2015 13:29:56

[Gary Manuel]

Just in time.

I was about to ask for clarification of shim thickness for AJ blades as this is my next job.

This clears it up thanks.

Gary

[Tomas Dunker]

Does anyone know if there is an autogyro that works with RealFlight 7?

[Richard Harris]

Tomas,

I'm sorry but I have no idea, I am not into SIM's but someone is sure to chip in with info on the subject.

Rich

[Baz Lewis]

Posted by Tomas Dunker on 11/01/2015 16:47:55:

Does anyone know if there is an autogyro that works with RealFlight 7?

**LINK**

[Stephen Jones]

Hi ,

I have bought two new batteries to try , a 3s 1600mah @ 30-40c and a 3s 2550mah @40-50c .

1st i tested the 2550mah @40c on my Sipa 200 now i am pulling 273W

2nd i test the 1600mah on my Atom now i am pulling 150W - 15amp.

So yes it does confirm i need new batteries .

Steve .

[Terry Whiting 1]

Steve,

15amp =150w means you battery was only 10v, so were these test figures with batteries straight out of the box uncharged?

[Martin McIntosh]

Now just about finished my mk2 version with a few mods, so have two to crash when the conditions improve.

I shall attempt to get the text and pics in order but forgive me if it does not work out.

Firstly, my idea of a molecule.

The bearings on this head are from old motors.

 

 

 

The tail wheel linkage makes Heath Robinson look professional.

The u/c clamp was made full width this time round.

 

 

A smaller park fly Rx has been installed this time.

 

A more powerful motor.

 

Fin and rudder area has been increased a little.

 

Actuating bar thingy has been shortened to take into account the shorter servo arms.

 

 

Lovely sharply focussed pic.

I have a problem with one of the MG90S servos which seems to have an iffy motor and am awaiting some hopefully better ones (Corona). Also ordered a couple more Vigors which have proved to be reliable in the past and could be very suitable for a model like this since they are screwed in from the bottom (i.e. through the front or rear former. They are very slim and have metal gears).

Not sure about the angle of dangle and have not properly measured it yet with the 2200`s but have ordered some Zippy Compact 1300`s which will be adequate for a decent flight time.

Lots of other things I should be doing now but I have always been facsinated with very small models and have lots of surplus indoor gear so if these are successful I may just try a `particle` version.

Wish me luck because I shall need it.

 

 

Edited By Martin McIntosh on 13/01/2015 21:16:43