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p901
07-19-2007, 11:50 PM
Helicopter dynamics...

Okay, progress. Took the three blade damper rubbers and slid them over a dowel pin which was installed in the milling machine. Spun the dampers in the machine and applied a cutting block to skim a light cut on the rubbers.
Quite interesting to see the amount that the rubbers were out of concentric and how much they were different in concentric dimension from one another. All other factors being equal this out of concentric with the stock rubbers would have made it nearly impossible to get good tracking.
Removed .010" from the overall diameter which still left .010" in excess of the internal diameter of the blade grip. Instead of .020 compression, (rubber very hard), the .010 setting allows for a slight increase in the coning angle with a little less initial compression of the damper rubber in the blade grip.
A bit more pitch to hold back the headspeed a little and the hover is very nice. Stable, controllable, predictable with plenty of cyclic authority.

[Question, a certain amount of coning in the hover is necessary? or desirable?
How much coning in relation to relative factors before the onset or shift to
completely undesirable conditions in other phases of flight?]

Fairly new, first helicopter, Hirobo Schweizer converted to electric, three blade head.
(See Hirobo Conversion post if you wish)
Cyclic has tight response with MS 515CF and a bit quicker with
Rotortech 515CF, (less chord, higher loading, slightly higher headspeed).

Question, if I increase pitch and lower the headspeed will this increase the coning angle?
I understand that an excess of coning will cause the onset of problems in forward flight and increased instability in windy or gusty conditions.
Servo arm throw is a bit stronger with the Futaba arms versus the previous JR arms but this only served to reduce the amount of stick throw back at the transmitter, hover sensitivity still the same.
Headspeed with MS 515CF is 1650 in OGE hover, Rotortech 515CF is 1700.
Recommended headspeed with stock wood blades for this machine is 1450-1650.
Any information/ discussion on hover stability will be helpful.


Thanks, andrew

HX3D014
07-26-2007, 01:35 PM
Helicopter dynamics...

Question, a certain amount of coning in the hover is necessary? or desirable?
How much in relation to relative factors before the onset or shift to
completely undesirable conditions in other phases of flight?

Fairly new, first helicopter, Hirobo Schweizer converted to electric.
(See Hirobo Conversion post if you wish)
Cyclic has tight response with MS 515CF and a bit quicker with
Rotortech 515CF, (less chord, higher loading, slightly higher headspeed).

Question, if I increase pitch and lower the headspeed will this increase the coning angle?
I understand that an excess of coning will cause the onset of problems in forward flight and increased instability in windy or gusty conditions.
I would like to find a way to set the coning angle on the bench during setup that would produce an increased stability in the hover balanced against fair speed in forward flight/windy conditions.
Three blade head, (no flybar stabilization assist)
I see where there are stiffer blade grip damper rubbers to enhance and quicken the cyclic response.
If I was to lower headspeed and reduce the damper stiffness this combination would increase coning and then slightly improve the hover stability without going to far and making forward flight unmanageable.
Servo arm throw is a bit stronger with the Futaba arms versus the previous JR arms but this only served to reduce the amount of stick throw back at the transmitter, hover sensitivity still the same.
Headspeed with MS 515CF is 1650 in OGE hover, Rotortech 515CF is 1700.
Recommended headspeed with stock wood blades for this machine is 1450-1650.
Any information/ discussion on hover stability will be helpful.


Thanks, andrew
Try Wiki. they are a great source of Info. It would take a long time to completly cover your first question. But basicly. it depends on what you are useing the heli for. (Blade cone is a result of weight (Disk loading) and is a good thing when you think of Delta ofset, delta ofset is good for forward flight and the reduction of flapback and other flaping phenomenon)

Question, if I increase pitch and lower the headspeed will this increase the coning angle?
the cone angel is increased slightly by this due to lack of centrifugal forces holding the blades level. Ultimatly. cone angle is a direct result of Load and resistance to the load. (RC heli have resistance by way of either blade fles or rubber gromets) Check out "Coriolis effect at Wiki" deals with the down side of to much cone angle. Also check out Blade Sailing.

Oh. just reading the rest of your post now.

Seem you know the answer alredy. but, what is the craft you are useing. what do you want to do with it.

I'm thinking scale :ws:
what . Lama. Squirel. 500. schwizer. >>>???

p901
07-26-2007, 10:18 PM
Hello HX3D014,

Yes, this is a scale Hirobo Schwiezer so I would like to get the machine to lift off into a nice smooth hover and then transition easily into forward flight. Any maneuvers or aerobatics will come far into the future.
One article I read on RCUniverse got into all the math which would be helpful when I take the time to "get the head around" all the information but I was looking for someone who might have had personal experience in modification of the rotorhead to change coning for a particular application.
I do appreciate the response since it does give me a more specific perspective.
I`m thinking that I`m going to need to set a couple of conditions and then change one variable at a time. For example I will leave the pitch/headspeed the same and change the damper rubbers. To do this I will need to make a test rig that will measure the amount of force relative to the angle of the blade. This might mean I would see 1,000 grams, ( 1/3 the copter weight with three blade head), on the weight scale with a blade deflection of 1 degree of coning. Then go fly, see how it handles come back to the shop and modify again with 2 degrees of cone with the same amount of upward weight or pull applied to the blades. At some point I would think I would find the balance between more stable hover and uncommanded roll tendencies in forward flight due to excessive coning.
This is going to take a little time but I already have a setup where I can precisely tune the outer diameter of the damper rubbers and thereby set the amount of compression applied to the feathering shaft. Took .010 inch off the dampers last night, looking forward to reassembling the head to see the results.
Empirical data...
Thanks for the response !
andrew

p901
07-26-2007, 10:20 PM
Oh, a PS.

By "Wiki" you mean the Wikipedia?
Not familiar with the site but did you say to a search for coriolis effect?
Tx a

HX3D014
07-29-2007, 07:50 AM
Oh, a PS.

By "Wiki" you mean the Wikipedia?
Not familiar with the site but did you say to a search for coriolis effect?
Tx a
http://en.wikipedia.org/wiki/Angular_momentum#Conservation_of_angular_momentum
the term is Properly known as Conservation Of Angular Momentum. (Some heli Pilots know the difference when used in context to either weither or Blade talk.

Coriolis is more comonly known as The effects due to Earth rotation.

Principlay similar on a Heli setup

p901
07-29-2007, 02:09 PM
I have heard that term before, have a bit of an idea what it means.
Apparently this will take further study.
Trying to find out what effect the coning angle has on hover stability.
Can`t seem to find out whether or not the coning angle will have a direct effect on the that stability.
It seems as if the attraction for the 3D type of flight, (higher headspeed, with more "angular momentum", [less coning]), suggests that coning is a negative in the achievement of the 3D goal, ie; less stability = more maneuverability.
I am amazed at what a 3D heli can do, never thought it was possible out of such a machine until I witnessed this action.
Since I am new to helicopter flight I was hoping to modify the machine just so slightly to improve the hover stability while I work my way into the subsequent flight regimes. Add to that, I am kind of leaning toward scale machines and that type of flying, (Hirobo Schweizer 300 on floats) any increase in stability when the machine is a distance away, especially over water, could be beneficial.
I have a NASA manual on helicopter aerodynamics but it is all math, (rather like reading Greek). Discovered in the text portion, (between all the math), this morning that coning will be inherent in any design but is generally found to be best controlled at less than 9 degrees before problems arise.
Still, however, no direct answer as to whether slightly increased coning will aid in hover stability, (apparently I need to brush up on my understanding of mathematical symbology).
The search continues...
Thank you for your feedback, I will investigate your suggestions !
P901
andrew

HX3D014
07-30-2007, 08:56 AM
Try Wiki. they are a great source of Info. It would take a long time to completly cover your first question. But basicly. it depends on what you are useing the heli for. (Blade cone is a result of weight (Disk loading) and is a good thing when you think of Delta ofset, delta ofset is good for forward flight and the reduction of flapback and other flaping phenomenon)

Question, if I increase pitch and lower the headspeed will this increase the coning angle?

the cone angel is increased slightly by this due to lack of centrifugal forces holding the blades level and an increase of AoA to provide the same lift. Ultimatly. cone angle is a direct result of blade Load and resistance to the load. (other resistance methods particularly in RC heli is by way of rubber gromets < this is actualy a form of semi-Rigid construction in that the blade is not free to flap without resistance> <Real Heli of Semi Rigid Construction use Flexing parts that absorb Lead lag but are free to Flap by way of a teeter where one blade flap up causes the other blade to come down-they are conected and can not flap individualy-thus the cone angle dose not increase at a flap hinge. just from blade flex or the pre set cone angle-) Check out "Coriolis effect at Wiki" deals with the down side of to much cone angle. Also check out Blade Sailing.


the text in red. I am Second Guessing (Actualy Revising from this book (http://www.amazon.com/Principles-Helicopter-Flight-W-Wagtendonk/dp/1560276495)) and I am Now not confident in these parts. will get back to you.. PS what book do you have ?

The Text in Green Is just further Explanation and or rewrite for clearer explanation.

How are you geting your cone angle.

p901
07-30-2007, 05:50 PM
Hello HX3,

Good to hear from you.
Yes, what you are saying is somewhat familiar to me, I have run into discussions regarding the Delta offset, still need to read more.
Also what you say regarding your description of a "semi-rigid" head meshes directly with what I am reading out of my reference manual.
The book I am working with is Rotary Wing Aerodynamics by Stepniewski and Keys, solid math with little text, not an easy read but "endevour to persevere" as they say.
The odd thing for me is to try to deduce from the math the effect that coning has during the hover. If the text would simply say, more coning makes a stable hover but too much, (over 9 degrees they do say), will cause "aerodynamic interference"....
Then I could be confident in moving forward with my modification to the damper rubbers until I reached a point where the hover was stable enough and forward flight had not been too negatively impacted.
Still cannot find that statement being made anywhere??
Oddly enough, taking your suggestion I did begin to dig a bit deeper yesterday and ended up at a university website where the Masters students were defining the parameters for a design limitation for hover stability by a robotic helicopter. The helicopter would hover in a stable condition with minimal input from the controls or the softward.
Again, no straight statement was to be found that would simply say, more coning in the hover increases stability.
I am working with a Hirobo 3 blade head so I do not have the assistance of the gyroscopic aid of the flybar. ( You can see my machine in this forum under Hirobo Conversion ).
It appears as if I will need to do an ongoing experiment by making changes to numerous sets of damper rubbers and headspeed until I can start to see changes in the coning angle during hover and the results therefrom.

Thanks for the reply, if you run across any sites that make the statement that coning increases hover stability please let me know !
andrew