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01-23-2007 12:51 PM  10 years agoPost 1
Jag001

rrNovice

australia

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Hi all,

New poster here so be gentle with me

I have a Hawk Sport with some minor upgrades, 50 engine & 14T gear, long tail boom, constant drive tail and solid shaft, 4mm flybar and upgraded flybar supports, anti-rotation bracket. I am running red dampers on the teeter.

I am having a problem with the heli being very pitch sensitive in forward flight. Firstly let me say that the CG is neutral when supported by the flybar. I have trimmed the heli for a stable and level hover however when progressing to forward flight it seems I need to hold in lots of down elevator to prevent it from ballooning nose quite severely.

I would appreciate any ideas on what could be the cause of this.

cheers,

Jeff

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01-23-2007 01:03 PM  10 years agoPost 2
PbThumbs

rrApprentice

Katy, Tx USA

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Ok , I'll try,, Loose linkage or a weak servo ,,,Lets see maybe paddles not aligned correctly

Maybe change cg slighty fore and aft to try to correct

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01-23-2007 02:28 PM  10 years agoPost 3
Jag001

rrNovice

australia

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Willing to listen to anything!

Thank for the reply,

I am willing to listen to all options as this problem really bugging me. All servo's are recently new. All linkages have been up-graded recently to ball bearings.

I will try different Cg's on the weekend and see how I go, however I would like to go to the feild armed with a few options to try.

Cheers,

Jeff

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01-23-2007 02:37 PM  10 years agoPost 4
PbThumbs

rrApprentice

Katy, Tx USA

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Don't forget the paddles , perfect alignment ,with each other and the head

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01-23-2007 03:51 PM  10 years agoPost 5
ZXXflyer

rrKey Veteran

stone mountain, georgia, US

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I second the paddles. They need to be alighned perfectly parallel with each other WHILE the swash is LEVEL.

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01-23-2007 03:55 PM  10 years agoPost 6
SteveH

rrProfessor

Texas

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Jeff,

One thing you did not mention is the paddles...you upgraded the flybar to 4 mm, did you change the paddles, and if so, what paddles are you using?

The government cannot give you anything without first taking it from someone else.

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01-23-2007 07:01 PM  10 years agoPost 7
MikeInMobile

rrElite Veteran

Mobile, Alabama

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Setup the Hawk so that it is slightly nose heavy. This characteristic is quite common in Hawks, and is easily remedied by shifting the CG foward slightly.

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01-23-2007 08:42 PM  10 years agoPost 8
heliguy

rrVeteran

Boulder, CO

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The basic problem as I remember it with the Hawk Sport is that the elevator bellcrank is mounted on the pitch arms but the elevator servo is fixed to the frame.

This means that as the pitch arm moves up and down the elevator linkage will push or pull on the elevator giving it either foreward or backward elevator.

The only way I remember to correct this is to mix some pitch into elevator to keep the swashplate level through the entire pitch range.

Al

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01-23-2007 09:05 PM  10 years agoPost 9
SteveH

rrProfessor

Texas

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Al,

The error in the Hawk system is a little more complex than that. Because the aileron bellcranks are also mounted on the same shaft, in theory they would cancel the input to the elevator point on the swash with collective movement. However, the servo output balls are at different levels to prevent interference, the rod lengths are different, and that is what causes the elevator input with collective. But then, with the system set up correctly, with positive pitch input, it gets a hair of down elevator, which is usually good for foward flight. The real problem is, with negative collective, it also gets down elevator, which pushes the nose up when inverted. That is the characteristic of the Hawk system that I always found most disturbing...being an old airplane flyer, I always found it impossible to hold up elevator when the model was inverted. I always used a mix, collective to elevator, on the negative collective side, that would mix up elevator in, but did not use it on the positive collective side, but that is just what worked for me.

The government cannot give you anything without first taking it from someone else.

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01-23-2007 09:17 PM  10 years agoPost 10
SteveH

rrProfessor

Texas

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Jeff,

In an effort to try to help you with your problem, I would suggest you go over your setup. Going back to square one on the control system, check to make sure when you are at 0 degrees pitch, and no cyclic input, the servo arms are perpendicular to the output rods. Then at that point, check to make sure your bellcranks, elevator and both aileron are perpendicular to the mainshaft. Then at the same point, adjust the rods from the aileron bellcranks to the swash to level it, if you need to. If you get the basic setup, servos to swash, done correctly, the Hawks are great flyers.

The government cannot give you anything without first taking it from someone else.

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01-23-2007 11:18 PM  10 years agoPost 11
beavis1

rrKey Veteran

New York state

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Ya baby !

I found the best cure for the pitching is the raven head. The plastic head with 50 power was very pitchy for me with 570 blades.
The raven head got rid of the pitching. It takes only a little give to catch air and make the pitch initiate. Once it initiates then the forward movement just compounds the flex and pitch.

I was doing a hurricane one day and when I turned into the wind the head pitched from flex as it cought the wind and it was almost as violent as a snap roll on a plank. It did what it wanted and I was a spectator for a sec there. Just the nature of trying to get too much from a head block intended for far less .

What Stevo said on the inverted. A mix is a must. As a planker from way back holding the elevator opposite of my past natural norm is definitly un-nerving and makes for sloppy inverted. With the mix as Steve states it is a fantastic.

with a stiff set up like the red dampners more of an issue with light blades and fast paddles with sharp edges also.

what flybar paddles they are a big factor here and could be key to your answer.

I also go a little for CG on mine and it tamed the pitching but then it did not roll axil. But it tamed some pitching befor the head swap

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01-23-2007 11:29 PM  10 years agoPost 12
Jag001

rrNovice

australia

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Something To work with

Hi All,

Thanks for the all the replies, I really appreciate the advice. Least it gives me something to work with. Since I am in the process of reassembling the hawk at the moment (after a nasty engine cut when inverted at low altitude last weekend). I check all linkage lengths and basic setup up details when doing so.

I did experience the having to feed in down elevator when inverted problem and appreciate the explanation for what causes this.

I assume that a conversion to CCPM would solve this problem? Perhaps that maybe worth looking into for the future. Has anyone done this modification to their hawk sport and if so what were the results?

Again thanks to all who replied I really do appreciate it.

cheers,

Jeff

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01-24-2007 01:14 AM  10 years agoPost 13
oldfart

rrProfessor

Vancouver, Canada

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Something you also may want to check (specically if you have ever crashed and had to replace the Elevator A-Arm bellcrank. Be sure you replaced it with the proper length unit (H13032C and not the A).

But I agree with Steve and Beav - probably your flybar paddles if they are not stock ones.

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01-24-2007 04:54 AM  10 years agoPost 14
Jag001

rrNovice

australia

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Me Again

Hi again all,

OK paddles are interesting. I am not exactly sure what paddles they are! they look a lot like the light weight 3d paddles however they are not the fluro colour they are grey. I do know they are thin in section, sharp leading edge and relatively light.

I cannot find any identifying marks on them so I am tempted to discard them and go for a known paddle. So now for my next question what paddles are recomended? I am an intermediate flyer with some 3d skills. My preference is to have the set up pretty twitchy and reactive.

Again any thoughts are appreciated !

cheers,

Jeff

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01-24-2007 05:02 AM  10 years agoPost 15
cassat

rrVeteran

Alberta,Canada

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The grey paddles are most likely the stock Raven paddles from Century.

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01-24-2007 06:24 PM  10 years agoPost 16
oldfart

rrProfessor

Vancouver, Canada

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IF they are the stock paddles, then I would suspect the rotor blades are of a type that "lead" excessively. What mainblades are they?

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01-24-2007 06:35 PM  10 years agoPost 17
automan

rrApprentice

Topeka, Ks - USA

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Jag001,
I assume that a conversion to CCPM would solve this problem? Perhaps that maybe worth looking into for the future. Has anyone done this modification to their hawk sport and if so what were the results?
Another alternative to eCCPM that you might consider is the "Peregrine" conversion (do a search here on the Century forum).

Dan

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01-24-2007 10:21 PM  10 years agoPost 18
Jag001

rrNovice

australia

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Main Blades

old fart,

the blades at the time were standard century 600mm woodies.

Cheers,

Jeff

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