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Hawk Sport not enough lift

Old 05-06-2007, 09:15 PM
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carguy1994ca
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Default Hawk Sport not enough lift

Hi everyone. I'm new to RC helis but been flying airplanes for some years. I got myself a slightly used Hawk Sport and tried it this morning. Here is the set up: On normal mode, low throtle stick is - 2 degree of pitch, 50% stick is 0 degree, 75% stick is 6 degrees, and 100% is 10 degrees, measured with a robart pitch meter.

Engine is OS 32 SX-H well tuned, radio is Spektrum 2,4 Ghz DX7. Blades that came with the heli are wood, symetrical, 543 mm long (total lenght), CSM heading lock gyro, heli-max training gear. Fuel is 20% oil, 15% nitro heli.

Everything is running smooth, blade tracking is OK, no vibration. Problem: Heli is trying to lift but even at full throtle can barely get off the ground. I put the hovering pitch trim at full and still would not get off the ground. I went into pitch curve on normal mode and adjusted all the points up to get more pitch. Now it lifts off the ground with some wind to help it but still has not much power.

The clutch is not slipping (at idle i feel the blades want to move strongly as soon as i move throtle sick up). The engine seems to be revving too much, like its not working hard if i dont put the hover pitch trim full up.

What could be wrong? I feel it doent have enough pitch.... Thanks in advance guys !
Old 05-06-2007, 09:38 PM
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Default RE: Hawk Sport not enough lift

What are your throttle curves, sounds like they are to low at mid stick and your engine doesn't have enough momentum to move up to full throttle. I am running almost 70% throttle at mid stick. Pitch at full stick is 11.5 inches. That is with an os 37 though
Old 05-06-2007, 09:53 PM
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carguy1994ca
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Default RE: Hawk Sport not enough lift

Wow that was fast reply Cambo ! Here is the throtle curve: 25 % stick = 17% throtle
50% stick = 38% throtle (0 degree pitch)
75% stick = 50% throtle (6 degrees pitch)
100% stick = 90% throtle (10 + degrees of pitch)

I dont use 100% throtle because there is a cyclic to throtle mix and i dont want to override the throtle end points. At 50 % throtle ( mid stick) i feel the engine is reving too uch, althoug i dont have a heli tach to verify head speed.

Thanks
Old 05-06-2007, 10:15 PM
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Default RE: Hawk Sport not enough lift

Your throttle curves are to low. When i first started the heli thing i was scared of this thing to. I always thaught i was overspeeding the blades. But 38% throttle is WAAY out of its power band. You are never going to get to full throttle from 38% throttle. Bump up that HS

50% stick should be at least 50% throttle ( i like 70%)
75% stick should be at least 75% throttle (i run 85%)
Full pitch should have full throttle
Old 05-07-2007, 09:48 AM
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carguy1994ca
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Default RE: Hawk Sport not enough lift

Wow this seems a lot but it makes sense since i had to add a lot of pitch to get in the air at hover. So you think it will not over speed at 50 % stick if i boost throtle to 50 or 60 %? Is your pitch setting at mid stick 0 degree too ? I must say im afraid to throw a blade if it overspeed, read some scary things about blade acccident. The reason I have this throtle curve is I used Ray's helitech DVD to make my setup but he has a raptor 50 so maybe he needs less throtle to get in the air (OS hyper 50).

BTW, i saw that i have to buy a special tach to know the heli head speed, one that can tach the blades from afar. How much is it and what do you suggest i should buy ?



Thanks again for your answers !
Old 05-07-2007, 07:19 PM
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Default RE: Hawk Sport not enough lift

I am running 65% at the moment with the os 37 (reportadley a big power boost over the os 32). So i wouldn't worry about it to much.
I am going to be upgrading the head soon, and buying a new muffler. I am going to try to bump up the speed even more. (use nicer blades when doing this)
Old 05-07-2007, 07:46 PM
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Default RE: Hawk Sport not enough lift

Thanks again cambo. Did you tach ur head to see what rpm your running? I see some figures in the magasine but dont know if I absolutely have to tach the head and target a certain RPM.

So much questions, I hope its not too much...LOL! BTW, is it hot in Arizona this time of year? here in Canada we are just beginning the season and it is still cold, about 10-12 celsius.

Old 05-07-2007, 10:37 PM
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Default RE: Hawk Sport not enough lift

Your head speed is to low, its a heli not a plank. At mid stick your carb should be at a high half throttle, the engine should sound like its balls to the wall. More pitch only loads up the head, which slow the blades down and no lift.
Old 05-07-2007, 11:07 PM
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Default RE: Hawk Sport not enough lift

ORIGINAL: carguy1994ca

Thanks again cambo. Did you tach ur head to see what rpm your running? I see some figures in the magasine but dont know if I absolutely have to tach the head and target a certain RPM.

So much questions, I hope its not too much...LOL! BTW, is it hot in Arizona this time of year? here in Canada we are just beginning the season and it is still cold, about 10-12 celsius.

I have not tached it yet and i sure as heke am not going to try it. That blade is big and powerful [X(]. I would predict my HS is around 1700. Flying season is year round here in Arizona . It does get hot during the summer though, like 105 degrees.
Old 05-07-2007, 11:14 PM
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Default RE: Hawk Sport not enough lift

I want you to hear this t-rex 600 at mid stick, especially when it hits idle up
http://www.thetrex600forum.com/index.php?topic=1260.0
Old 05-08-2007, 01:21 PM
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carguy1994ca
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Default RE: Hawk Sport not enough lift

Hard to say for sure but when mine is at zero degree pitch and 50% throtle seems to be reving like theres no blades attach, it takes a lot of pitch to make the engine seems like its working harder. Of course i wont need the power that Alan Szabo needs...

I'll try your set up this weekend and will tell you how it goes. The manual says to hover at 50 % throttle and 5 degrees of pitch but it doesnt work for me.
Old 05-10-2007, 05:13 PM
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carguy1994ca
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Default RE: Hawk Sport not enough lift

Hi, I found on century's website and on this forum information about washers being reversed on the feathering shaft. With the centrifugal force when the head is at hover speed, the bearing in the blade grip is forced against the washer and this jams the bearing, preventing the servo to move the blade grip and limiting the pitch available.

I checked the head on my hawk and the washers were indeed reversed. I replaced them in the proper order and I hope it will cure my problem. Will try it this week end, can't wait !! Why isn't it already saturday...???

Will tell if its OK,

Happy flying
Old 05-13-2007, 06:05 PM
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syclic
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Default RE: Hawk Sport not enough lift

I would bet that you are not getting the same pitch in the air (when the rotor is spinning up at flight speed) as you are getting on the bench. If the mainrotor blade grips are not properly attached to the feathering spindle this can happen.

Check the Hawk Sport manual here:

http://centuryheli.com/support/manua...ksport_man.htm

Then look at page 6 and check out the assembly is step 4. Note that, just inboard of the retaining locknut, are two washers. One is a 4 x 12mm one and the other is a 4 x 10mm one. The 4 x 10 should be inboard against the bearing and the 4 x 12 should be outboard, between the 4 x 10 washer and the locknut. If these are assembled in reverse order, this will cause the bearing to bind against the 4 x 12 washer under the centrifigal loads of rotation, and your collective servo will not have the power to move to the pitch setting you have set on the bench.
Old 05-14-2007, 11:50 AM
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carguy1994ca
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Default RE: Hawk Sport not enough lift

Hi Syclic, I e-mailed you something about this but maybe you never received it. You responded to a post of mine when I bought the Heli and I found you had good knowledge of these heli, thats why I sent you some questions.

As for my problem not getting enough lift, it was indeed the washers on the feathering shaft that were reversed that cause the problem. I flew the heli last weekend with the same set up for pitch and throttle as described above and I had more than enough power to hover at 75% throthle stick.

Noe I have to trim the heli but it was windy and I will have to wait to finalize the trimming. One thing that bothers me is with the gyro. It is a CSM heading lock gyro and when on the ground the servo arm is slowly moving out of neutral. This seems to be a normal operating condition of the gyro. What happens is when I try to take off, the tail rotor servo is not centered and the heli turns on itself about 1/4 turn very fast befor the gyro centers it. When in rate mode, I don't have this problem as the rudder servo arm is centered at lift off.

What should I do ?

Thanks all for your insight
Old 05-16-2007, 03:20 PM
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syclic
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Default RE: Hawk Sport not enough lift

Try leaving it in the standard yaw rate switch setting until you are just ready for take-off - then just before take off, switch to HH.

If that does not work check out this article on gyros:

http://www.leisuretech.ca/hints_gyro.html
Old 05-16-2007, 04:38 PM
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carguy1994ca
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Default RE: Hawk Sport not enough lift

Syclic youy do know your heli stuff. Thanks cery nice article. I have another question for you: I noticed while flying my hawk sport that the tail moves a little in flight. I can see the tail fin moving a little left to right, like the boom shaft pivot either at the pod attachement or its the transmission case that is moving.

I dissassembled the rear rotor transmission and found that it is made with a little slop. The two parts forming the transmission case are keyed but it moves a little (very little). Is this normal or could I suffer tail rotor failure and then budget failure.

Thank You.

BTW, you can see my hawk photo with its training gear in the heli section on RCU ! Cool !

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