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HelicopterMain Discussion › New twin rotor machine
06-02-2004 11:31 PM  13 years agoPost 1
Dave P

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England,UK

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Hi guys
I have just test flown my new toy.
it's made up from two Morley Maverick heli's with my own chassis joining them together.
My question is, are any of you guys familiar with twin rotor flying ?
as I am having problems with the fore & aft cyclic stability.
hovering in a steady wind the heli is stable in roll, yaw & collective but fore & aft is a little touchy.
gusts of wind really upset it in the fore & aft plane giving me the impression that the heli is going to fall over backwards.

have any of you guys experienced this problem & if so how did you cure it ?

(more pictures in my gallery)

Do a Hover - it avoids G

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06-02-2004 11:37 PM  13 years agoPost 2
Roger Hamilton

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Surrey, England

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Dave, Skyline have recently taken delivery of the MS CH46 twin rotor. It uses a very clever mixer board with 2 gyros and this seems to work very well, the model is very stable in all axis, suggest you contact them

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06-02-2004 11:44 PM  13 years agoPost 3
G-DAVE

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Tyne and Wear , England

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Flew the Hirobo Chinook for a couple of years - always a challenge in any wind , but this was mainly due to being Flybarless.As yours is home built I cannot see how the fore and aft is worked.
The most sensible way is for only one swashplate to do the work - for eg. just have the collective increase and decrease on the rear mast this will give you the fore and aft movement .
Dave d

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06-02-2004 11:49 PM  13 years agoPost 4
jag01

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Pennsylvania

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hmmmm just a guess but it might have to do with rotors r not both virtical on a real one that helps make it stable.

keep them blades turning !

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06-02-2004 11:54 PM  13 years agoPost 5
Dave P

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England,UK

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Hi G Dave
I have 3 servo ccpm on both rotors.
I am mixing fore & aft cyclic on the front rotor with diferential collective on the front & rear rotors. (the same setup that hirobo use on the vertol)

forward stick gives ....front swash tips forward & collective is reduced while rear collective is increased.

back stick gives .... front swash tips back & collective increases while rear collective is reduced.

is this correct ?

Do a Hover - it avoids G

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06-03-2004 12:07 AM  13 years agoPost 6
ScareCrow_Delta

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Sebastian, FL

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Maybe if you give less movement on the opposite you'll get better stability. I mean, If you give it fore, front sp goes just a little or goes back to 0 pitch but the aft sp gives more pitch. Can you work with the ratio of the sp mixing? i.e. 30 deg movement in aft sp but only 5 deg in fore. Just a thought,,,,

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06-03-2004 12:09 AM  13 years agoPost 7
G-DAVE

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Tyne and Wear , England

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Yes that sounds correct - the hirobo when making a decent for a arrival had the habit of putting it's back down - this was alarming but consistant and could be anticipated and allowed for . I found the more I flew it the better I became at 2nd guessing what it would do next.
I tried a gyro on the fore and aft axis and this did help.On yours though this may be a problem as ccpm is involved.
Dave

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06-03-2004 12:23 AM  13 years agoPost 8
Dave P

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England,UK

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This is the second twin I have made & the first one had the same problem but only as you say on the approach for a landing.
I too managed to get used to this bad habit (well a little bit)
but this machine is doing it much more severely & in the hover.
I have the ability to fit a gyro on the rear collective or front swash or both
if this might help.

there are a few pics of the MK l on my website
.

Do a Hover - it avoids G

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06-03-2004 02:21 AM  13 years agoPost 9
Taipan

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Sydney, Australia

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Have you tried a gyro on elevator? I believe the new Hirobo tandem ccpm servo control box has gyros on all three axes!

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06-03-2004 04:28 AM  13 years agoPost 10
mikefoy6

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Thief River Falls, MN

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just a quick question about 2 rotor helis....

how do you controll the yaw movements?

mike

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06-03-2004 05:00 AM  13 years agoPost 11
Joe P

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Morristown, NJ

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just a guess about the yaw, for yaw right, wouldn't that be cyclic right in the front and cyclic left in the rear? good luck with the project

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06-03-2004 05:15 AM  13 years agoPost 12
vaportrail OLD

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Anchorage, Alaska

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Just a thought on the approach problem: in forward descending flight, the aft rotor is flying through the front rotor's downwash which reduces its efficiency. I didn't deduce this myself, read it somewhere, but it makes sense. Full size twin rotors fly a little sideways on approach. I've seen this myself as I used to work around Chinooks. Just never gave it thought back then.


The real point of terrorism is not the act itself, but our reaction to the act.

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06-03-2004 08:43 PM  13 years agoPost 13
Eyal M.

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Israel

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Dave P

I'm doing a similar project. I use electronic mixer TH-1 from http://www.tech-mp.com with a special SW they made for me to fully control the two CCPM servos.
The project is built and working, just having some problems to get a long belt (80" perimeter measure).
How did you connect your helis, is it by a belt or a long shaft? if you use a long belt, where can i get one?
What size of engine do you use? what size of blades?
Thanks.

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06-03-2004 09:50 PM  13 years agoPost 14
Dave P

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England,UK

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update

I have now made a modification that appears to help.
I have raised the rear rotor, (they were level with each other to start with)only 22mm but in the brief flying session I had today the heli didn't rear up in the hover.
It does however rear up when flying slowly forward (higher airspeed) so must be the rotor wash from the front rotor disturbing the rear one.
it is a great improvement so i will try raising it a little more & report back.
thanks for the input guys

Do a Hover - it avoids G

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06-10-2004 03:46 AM  13 years agoPost 15
arbrnedaddy

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Camp Humphreys, Korea

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Tandem Rotor helis

Vaportrail,

The sideways landing chinooks you saw were holding a wind correction on approach. Also someone mentioned the rotor systems not being vertical. This is to provide forward thrust during ground taxi. There is actually no traditional forward or aft cyclic in a chinook. Pitch attitude is controlled through DCP (Differential Collective Pitch), wherein with a forward cyclic input, the rear head collective increases and aft head collective decreases. There is also a computer controlled system called LCT(longitudinal cyclic trim) that provides a very small forward or aft cyclic input to trim the aircraft into a more natural level attitude during different modes of flight. They trim aft for hovering and forward for flight. This is also to reduce strains on the aft head due to the turbulence created by the forward head. Without this system the Chinook would hover about 20 degrees nose high as did the older models that did not yet have it, and airspeed would be limited.If anyone has questions about tandem helicopter control, The Army manual 1-216 gives a thorough explanation.

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06-12-2004 06:33 PM  13 years agoPost 16
Dave P

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England,UK

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arbrnedaddy

you mention an army manual 1-216 that might have some information useful to me, could you point me to a copy of this manual please.

you describe your occupation as Hook Driver
does this mean you are a chinook pilot?
.

Do a Hover - it avoids G

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06-12-2004 07:43 PM  13 years agoPost 17
arbrnedaddy

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Camp Humphreys, Korea

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Sorry Dave, I had my manuals confused, it is actually FM 1-203 (Fundamentals of Flight). It is a public domain publication and should be easy to obtain or at least view as a PDF. You may also try http://www.chinook-helicopter.com. Lot's of neat stuff there. And yes I am a Chinook pilot here in South Korea.

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06-13-2004 10:22 PM  13 years agoPost 18
badbradbreece88

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Northwest Ohio

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always liked twins

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