Homebuilt Coaxial Helicopter: Ben Dixey, SW UK

[btd1982]

Part 6

Something I'm wondering and can't quite understand. The tilting of the rotors while spinning close to lift off but still on the ground is hard to move via cyclic stick. Probably twice as hard than in the air, if the tilting of the rotors is 98% areodynamic 2% weight shift why is there such a difference in control force from on the ground to in the air? Do standard blade feathering helicopters experience the same thing ? Is the same thing true with gyros ?

 

[wolfy]

No difference with a conventional heli whether airborne or not, or a gyro. Very interesting.

wolfy

 

[FlintHelo]

A REAL project! I admire all the effort and skills involved in making this machine. Wish you great further success.
Also, with a few added components, you'll be ready to spray the gardens!

 

[WaspAir]

Something I'm wondering and can't quite understand. The tilting of the rotors while spinning close to lift off but still on the ground is hard to move via cyclic stick. Probably twice as hard than in the air, if the tilting of the rotors is 98% areodynamic 2% weight shift why is there such a difference in control force from on the ground to in the air?

Are you perhaps working against those big outriggers still in ground contact? Once airborne they would offer no resistance.

 

[btd1982]

Are you perhaps working against those big outriggers still in ground contact? Once airborne they would offer no resistance.

It's the same with or without the outriggers. The only conclusion I can come to is it's more weight shift than originally thought. ??

 

[btd1982]

A REAL project! I admire all the effort and skills involved in making this machine. Wish you great further success.
Also, with a few added components, you'll be ready to spray the gardens!

Thank you.
Crop spraying yes.

 

[Aerofoam]

I am thinking that on the ground, you are fighting the gyroscopic stability completely, as soon as you lift off, the freedom of the undercarriage to pendulum put's some slack in the system and the "Weight shift" is an easier motion to overcome for the initiation of the movement....

 

[btd1982]

I am thinking that on the ground, you are fighting the gyroscopic stability completely, as soon as you lift off, the freedom of the undercarriage to pendulum put's some slack in the system and the "Weight shift" is an easier motion to overcome for the initiation of the movement....

It seems that way to me but helicopters and gyros would have to be the same for that to be true. If they aren't the same then then I'm confused again.

 

[WaspAir]

Using "stability" and "helicopter" in the same sentence always leaves me waiting for the punchline.

 

[All_In]

Using "stability" and "helicopter" in the same sentence always leaves me waiting for the punchline.

Now that's funny.

 

[Mayfield]

Something I'm wondering and can't quite understand. The tilting of the rotors while spinning close to lift off but still on the ground is hard to move via cyclic stick.

Does your machine have an over running (sprag) clutch in the rotor system?

Feel/measure the pressure required to move the cylic some distance in some time. 1 CM per 1 second is a good goal. Do this at near flight rpm then repeat just as throttle is reduced but before significant RRPM decay. Are the forces the same?

 

[Aerofoam]

It seems that way to me but helicopters and gyros would have to be the same for that to be true. If they aren't the same then then I'm confused again.

So, another thing to consider is that you are trying to tilt 2 opposing gyroscopes and the top one had to move a significant lateral distance.
As soon as you lift off, the undercarriage can move to other direction allowing the tilt to happen more freely.
When the rotor is perpendicular to the longitudinal axis, you are trying to tilt the entire disk.
On a single rotor, when it is parallel to the longitudinal axis, you are aerodynamically changing the AOA, which causes it to rise and fall 90deg behind the initial input, so it tilts. With 2 rotors, they may not be aligned longitudinally, so you are always trying to move the entire disk, which is easier if the undercarriage can initially slide out from under it....
Hope that makes sense, I'm looking for another dark beer right about now.....

 

[btd1982]

Does your machine have an over running (sprag) clutch in the rotor system?

Feel/measure the pressure required to move the cylic some distance in some time. 1 CM per 1 second is a good goal. Do this at near flight rpm then repeat just as throttle is reduced but before significant RRPM decay. Are the forces the same?

It doesn't have an overrun clutch now. However I can still do some investigations, i will do some testing and report back.

 

[btd1982]

So, another thing to consider is that you are trying to tilt 2 opposing gyroscopes and the top one had to move a significant lateral distance.
As soon as you lift off, the undercarriage can move to other direction allowing the tilt to happen more freely.
When the rotor is perpendicular to the longitudinal axis, you are trying to tilt the entire disk.
On a single rotor, when it is parallel to the longitudinal axis, you are aerodynamically changing the AOA, which causes it to rise and fall 90deg behind the initial input, so it tilts. With 2 rotors, they may not be aligned longitudinally, so you are always trying to move the entire disk, which is easier if the undercarriage can initially slide out from under it....
Hope that makes sense, I'm looking for another dark beer right about now.....

The top rotor having to move a lateral distance could be the answer, this is how mine is different to a helicopter or gyro. In the air the machine pitches and rolls about its CG on the ground only the rotor tilts about its hinge.

 

[Asker]

This guy uses the front door to abandon ship in case of an emergency. Expensive stuff, nothing like pocket money.

 

[btd1982]

This guy uses the front door to abandon ship in case of an emergency. Expensive stuff, nothing like pocket money.

That's pretty different. Looks like a flying portaloo. What's the name of this machine ? Like the rotor design though.

 

[Aerofoam]

This guy uses the front door to abandon ship in case of an emergency. Expensive stuff, nothing like pocket money.

I only see a broken photo link......

 

[Asker]

I didn't want to distract the thread but here is the link.

https://www.flynow-aviation.com/

 

[Aerofoam]

I didn't want to distract the thread but here is the link.

https://www.flynow-aviation.com/

So it's a 10" model designed as a flying porta-potti?

 

[Asker]

So it's a 10" model designed as a flying porta-potti?

Exactly,

And it is a little bulky too.