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HelicopterMain Discussion › Zero pitch - conflicting messages!
08-04-2013 04:22 PM  4 years agoPost 1
raybans

rrApprentice

Northern Ireland

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Guys,

got some of the new JR adjustable servo arms and the quickUK delrin ball links. So just re-doing the head set-up and now at the stage where i am looking for zero pitch on both blades at mid-stick.

Normally I 'zero' the pitch gauge somewhere on the heli frame, set "neutral test" in the Tx, then adjust the threaded rod between the swash and the blade grip to zero in one blade. Then I use the v-bar method to align the blades. Set the heli on its side, rotate both blades 90 degrees in each grip and adjust the other link rod so the blades perfectly align.

All done ... or so i think. Set heli back up vertical and rotate blades back to their normal positions. But the blade I adjusted when the heli was on its side dose not look at zero degrees. Sure enough, put a hex driver into the blade grip bolt hole and it confirms 2/3 degrees of pitch! How come? Swash is perfectly level, head axle not bent.

Where is the error creeping in? Appreciate any ideas/advice.

Thanks.

"Not everything that can be counted counts, and not everything that counts can be counted"

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08-04-2013 04:36 PM  4 years agoPost 2
unclejane

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santa fe, NM, USA

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Perhaps the mast isn't perfectly perpendicular to the hanging blades?

But you've already discovered the better method anyway when double-checking your result, the hex driver though the blade bolt hole trick. This will get you just about on the gnat's a$$, as you can already see. You don't have the weight of the blades being possibly not quite 90 to the mast which can throw things off and it's easy to do....

LS

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08-04-2013 04:37 PM  4 years agoPost 3
RCHSF

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NC

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Not sure, but I usely just get one blade grip 0 pitch with the link. Then pop that link off, and use it to measure the other one, tip to tip, hole to hole, with the other link. I usely end up with perfect 0 on both blades.

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08-04-2013 04:40 PM  4 years agoPost 4
pH7

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Sterling Heights, MI - USA

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Turning the blades 90 degrees and aligning them only works if both link rods are exactly the same length. I don't use this method to size the link rod, I use it to find zero pitch on my stick to zero my digital pitch gauge. The test with a wrench through the blade grips, aligning with the main mast is very accurate.

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08-04-2013 05:54 PM  4 years agoPost 5
rcflyerheli

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Granbury, TX USA

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One reason that I don't try to get the blade tips even is due to inherent "slop" in the system. As much as we would like to be able to say there isn't any, we just can't do it.

In this situation, is the hex driver loose in the grip hole? I could never find a perfect size driver for a 90/700 sized grip hole. However, I did discover that the rod and cones from a Dubro or True spin prop balancer will insure that the rod is centered in the grip holes. I've completely changed over to using that instead of a hex driver.

Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

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08-04-2013 06:08 PM  4 years agoPost 6
D.Magee

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kansas city mo.

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I still use a pitch gage. I have never been able to get it right buy putting the blades together on it's side.

Teameagles@HaveFun

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08-04-2013 07:30 PM  4 years agoPost 7
Flyin for Jesus

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Dana Point, Ca. 92629

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I set the heli on my table and shim the skids to get the heli mainshaft perpendicular to the ground. ( I pull of the top domed piece and put a small level in the head., keep rotating it and shimming until it is level in every direction )
Once I do this... everything else is easy. I can easily lever the swashplate with the same little bubble level and then set the pitch on both blades with the pitch gauge.
I don't setup helis everyday but the last one I did... the blades were tracking great right out of the gate.

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08-04-2013 09:50 PM  4 years agoPost 8
RogerRabbit62

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Thuerigen germany

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+1

basic necessary step. Omitting that makes errors.

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08-04-2013 10:16 PM  4 years agoPost 9
Rick_H

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Boulder City, Nevada

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Was the FBL Unit still in setup mode when you made the last check?

Just a thought

Rick

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08-04-2013 11:09 PM  4 years agoPost 10
Jeff polisena

rrElite Veteran

westpalmbeachflorida usa

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Get it close ,make opposite links the same .Check for binding and correct direction of swash . Hover and check for tracking and pay attention to where stick is when Heli lifts ,if you are close to 1 hash mark past 1/2 stick on your TX your close . After tracking and tuning and safe to fly do climb outs rite side up and inverted to make sure you have same climb outs both directions . This works for me with no headache .

I stole it ,flew it and gave it back ;)

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08-04-2013 11:21 PM  4 years agoPost 11
raybans

rrApprentice

Northern Ireland

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Guys,

thanks for taking time to reply. Learning plenty from your posts.

See photo of the swash level tool i use. I am pretty sure i got it nearly perfect. Certainly any imperfection would not account for the magnitude of pitch that i am seeing. It is also constant throughout the whole rotation of the head.

Some of your questions ...

Rick_H - tried it in both setup (in the swash basic menu) and non-set-up mode. Have I understood your question correctly? No difference that i can see.

rcflyerheli - definitely not a perfect fit. Its the Thorp 3mm driver in the picture but it seems to seat very well. Granted there is slop there.

I just cannot get my head around how both blades can be anything other than 0 degrees when they perfectly align when rotated through 90 degrees. The swash is static, the threaded rods are static. The blades are (in theory) just being rotated in exactly the same plane. Yet at 180 degrees to each other they not aligned, but parallel to each other they appear perfect.

rcflyerheli ... like the idea of using the kit from the dubro tru-spin to ensure a snug fit in the blade grip bolt hole.

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08-05-2013 12:24 AM  4 years agoPost 12
unclejane

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santa fe, NM, USA

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Try switching the blades to the other grips - could be that one of them is warped or the faces at the root are out of alignment on it?

If everything else is square and even, could just be a bum blade?

LS

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08-05-2013 02:28 AM  4 years agoPost 13
Dr.Ben

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Richmond, VA, USA

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You do understand that that swash level, even when used to perfection, does not mean your swashplate is level, right?

Ben Minor

Team Synergy Team Futaba Team Kontronik USA
Progressive RC

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08-05-2013 09:43 AM  4 years agoPost 14
raybans

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Northern Ireland

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Ben

No I did not! If not perfect, then thought it would be at least sufficiently accurate.

Is there something about this particular model of swash level?

Would the resultant error account for what i am seeing?

Ray

"Not everything that can be counted counts, and not everything that counts can be counted"

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08-05-2013 02:20 PM  4 years agoPost 15
rcflyerheli

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Granbury, TX USA

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You do understand that that swash level, even when used to perfection, does not mean your swashplate is level, right?
I'm not sure if you were making a joke. Level is only a reference to whether the swash is perpendicular to the main shaft. I suppose there is some machining tolerance in a swash gauge, but for it to be out that much, it would be visible to the eye.

Raybans: is there any chance this is happening with the power off to the radio. If your swash is sufficiently tight, as you rotate the head, the blades will drive the swash out of level as it rotates.

Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

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08-05-2013 02:31 PM  4 years agoPost 16
rcflyerheli

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Granbury, TX USA

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Also, just taking a closer look at your photos, in the first photo of the hex driver inserted in the grip hole, the grip arms are not parallel (or symmetrical). The one on the back grip is angled down (it's the right one in the photo). On the second photo of the hex driver, it appears that you have rotated the head 180 degrees, and now is is the front one and is on the left with its angle still being down.

Adjust that side back up to bring the hex driver parallel to the main shaft. If your swash is level, then it should stay level when you rotate the head 190 degrees.

It just doesn't appear to me that it is level in your initial photo.

I know I use this procedure on every head setup I do, and I have never had a situation happen like this. I have not ever had a blade tracking problem with this setup method.

Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

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08-05-2013 11:21 PM  4 years agoPost 17
raybans

rrApprentice

Northern Ireland

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Guys,

ok ... used the du-bro truspin parts through the grip bolt-hole to assist with the alignment.

Got both grips as near zero as my skill level allows.

Bolted in a set of different blades just in case the last set were not perfectly straight.

At 180 degrees they look pretty good.

But rotate through 90 degrees where blades are both parallel the blade tips do not align.

I was in swash basic mode (GCY750) when doing these tests. Gyro's in normal mode. So i should not be getting any swash movement / compensation.

I do NOT get it. How can it be?

Lets suppose the blade grips are not machined identically. The slot where the blade root is inserted is somehow not exactly parallel to the spindle shaft. So, the blades are at 180 degrees in their flight ready position and are both at zero degrees pitch. But as the rotor disc spins one blade tip is riding higher than the other. That can't be good, can it??

Anyway, a bit lost. Now happy that both blades are at zero pitch in their flight ready configuration, but i cannot account for or explain what causes the blades to not align when rotated through 90 degrees in exactly the same plane!!

"Not everything that can be counted counts, and not everything that counts can be counted"

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08-05-2013 11:45 PM  4 years agoPost 18
JKos

rrProfessor

Redondo Beach, CA

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What does the "du-bro truspin parts" test show with the head rotated 90 degs from the pictures above?

- John

RR rules!

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08-05-2013 11:47 PM  4 years agoPost 19
unclejane

rrElite Veteran

santa fe, NM, USA

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Did you check the alignment with the prop balancer with the grip axis longitudinally oriented? That is, rotated 90 degs from what's pictured, feathering shaft parallel to the centerline of the machine?

Or better yet, does the alignment stay the same, and I mean dead, slap don't-move-at-all the same, while rotating the head through all 360 degs?

If the swash isn't "level" (perpendicular to the mast) in the AIL axis, that could cause the pitch to be off in that orientation, which is what the head is in when you're doing the check with the blades.

Otherwise, it can only be off everywhere, which would indicate the interior surfaces of one of the grips or both are off. which is unlikely?

LS

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08-05-2013 11:49 PM  4 years agoPost 20
barely can fly

rrApprentice

oxford ga. usa

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In either of your first two pictures is the guage in line with the main shaft.
First picture is a 1/4 to 1/2 turn off and second picture is almost a full turn off.
Start at the head button in relation to the sides of the guage that is above the button and look close,sight down from the top, the two shafts are not parallel.
I also mean the pictures just above this post not the ones at the top off the page.

ATLRC wrecking crew / NCRC

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HelicopterMain Discussion › Zero pitch - conflicting messages!
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