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Home✈️Aircraft🚁HelicopterCentury Radikal G20-30 N640 Hawk Predator › severe elevator interaction during inverted climbouts
05-21-2007 02:07 PM  13 years ago
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flyboy0413

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Brookfield, CT

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severe elevator interaction during inverted climbouts
I have a helimax kinetic 50, which is made by century and has the exact same control system as a hawk or falcon. I'm aware of the collective-elevator interaction due to the MCCPM geometry and have mixed it out in the radio so that the swash stays level through the entire collective range.

Problem is, even w/ the mix in place, the nose still rises pretty strongly during inverted climbouts and needs a lot of back elevator to hold it level. I checked the CG and the heli balances perfectly level when picked up from the flybar.

I tried to alter the mix % so that the heli does climb out level while inverted. It took about 35-40% collective to elevator to finally do it, however it looks totally screwed up on the bench and it makes other manuevers such as tic tocs feel all screwed up.

I'm at a loss. What am I missing.
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05-21-2007 06:53 PM  13 years ago
flyboy0413

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Brookfield, CT

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anybody??
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05-21-2007 08:57 PM  13 years ago
marked23

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Lynnwood, WA

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> anybody??

Ok, I'll be anybody.

On inverted climbouts the blades are grabing 'dirty air' coming across the boom... resulting in less lift on the back of the heli. (I'm not sure I believe this myself. I'm just making stuff up.)

Really, is there that much interaction in the Hawk/Falcon mechanics that you need to mix it out? I wonder if doing a more precise setup would yield different results.

There are flying quirks to every heli, I'd guess. And pulling back on an inverted climbout might be something you simply need to do when flying this one.

-Mark
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05-21-2007 09:04 PM  13 years ago
jackheli

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Vancouver - Canada

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Yes. This mechanical interaction is a characteristic of the Falcon/Hawk mCCPM setup, but first make sure your swashplate is levelled at 0 degrees and that there is no binding.

What I do is start mixing 5% of up elevator for negative collective only, on idle up. Then go up high and see how the bird responds. If necessary, increase/decrease the mixing and try again until you feel the heli flies neutral.

Are you using a slipper? make sure the elevator bellcrank does not hit the slipper collar. I had to trim some of the arm off.

Are you using woodies? They tend to increase the problem somewhat.

The Raven has a much better feeling in that regards...
It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.
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05-21-2007 09:14 PM  13 years ago
flyboy0413

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Brookfield, CT

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What I do is start mixing 5% of up elevator for negative collective only, on idle up. Then go up high and see how the bird responds. If necessary, increase/decrease the mixing and try again until you feel the heli flies neutral.
From what I can remember, it took about 10% mixing to keep the swash level on the bench, but once it got in the air, it took 40% to keep it level during the full negative climbout. That's a HUGE amount. I can't figure out what's causing it. Initially, I said, screw it, leave it at 40%, but then when I tried doing some nose up tic-tocs, the elevator felt all screwed up because the mix was mixing out my down elevator command during the negative pitch portion of the manuever.

I don't have a slipper and I'm using carbon blades at 1850rpm. Other than this interaction issue, the heli flies great! Fast and lots of power.

Actually, at first I thought it was the large horizontal fin causing this. This was proved wrong when I removed the horizontal fin and pitching interaction was still exactly the same.

Maybe, I'll try adding a little weight to the nose to see if it does anything. I doubt it, but it's easy to try.

I've flown shuttles, t-rexes, xcells, raptors, logos, and a bunch of other helis and this is the first one I've seen that exhibits this problem. It really annoys me!!!

Jackheli: What is your mix percentage at full negative pitch? How much negative pitch are you running?
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05-22-2007 01:57 AM  13 years ago
BC Don

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Calgary, AB Canada

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From what I've seen, you need nose weight. When I was flying the Hawk Pro, I had to keep forward cyclic in and when inverted the tail dropped. Putting a sub C Rx pack fixe it for me.Got Money? Send it to me, I'm a Heli Addict.
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05-22-2007 03:03 AM  13 years ago
beavis1

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New York state

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Both
First make sure you have a balanced machine on the flybar

Then You definitly need a mix to get rid of the interaction. It is a mechanical flaw in the geometry of this heli. It is not a huge deal you just need a p-mix of pitch to elevator and dial in enough to level the swash in full negative. You will be very happy after that.

You wont need to hold in inverted flight also !
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05-22-2007 03:04 PM  13 years ago
flyboy0413

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Brookfield, CT

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beavis1

Machine IS balanced on the flybar and I had created a mix that keeps the swash level on the bench. However, if you read my post above, it stilll pitches down pretty strongly during full negative climbouts.
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05-22-2007 06:39 PM  13 years ago
jackheli

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Vancouver - Canada

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Jackheli: What is your mix percentage at full negative pitch? How much negative pitch are you running?
I am sorry. I don't have my Falcon setup for 3D anymore. From what I recall I didn't need more than 10% @ +/- 10degrees, and was able to do all the stunts in the book with it, no problem.

What brand blades are you using?
It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.
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05-22-2007 08:13 PM  13 years ago
flyboy0413

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Brookfield, CT

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I've tried both the stock woodies and some helimax carbon 600s. Both exhibit the exact same problem.
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05-22-2007 08:46 PM  13 years ago
jackheli

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Vancouver - Canada

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Ok.

Unfortunately both blades seem to display the same aerodynamic characteristics. Do a search here on RR for what people are saying about the Helimax blades. They are cheap but you get what you pay for.

Woodies are woodies. There is only so much you can get out them, and perfect tic-tocs are not in the list.

Would it be possible to ask a buddy to lend you a set of quality blades, just to see if they attenuate the problem you are experiencing?
It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.
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05-22-2007 09:13 PM  13 years ago
flyboy0413

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Brookfield, CT

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Yeah, I'll have to try that.

Thanks for the help
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05-22-2007 09:51 PM  13 years ago
steve9534

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yakima, wa.

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Balance
You might try and check your flybar paddles to ensure they are aligned properly. Beyond that, I've found the proper balance for flying is not always right on the mainshaft. Even though the balance should be OK there, you might try moving the balance point forward to see if it helps the situation. The correct balance point will be where the heli flies neutral and for me this usually is a little ahead of the main shaft. Hope this helps. steve.
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