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Elevator pulsation

 
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Kellym



Joined: 10 Jan 2006
Posts: 1598
Location: Sun Lakes AZ

PostPosted: Fri Apr 26, 2019 5:41 am    Post subject: Elevator pulsation Reply with quote

Has anyone else experienced vibration/pulsation in the elevator? Most
noticeable on runup, and in cruise on autopilot. Vibration goes away
when power is reduced for descent. The only play I have found so far in
the control system is the elevator trim tab cables allow about 1/16" up
and down movement of the tabs at the trailing edge. I can't think such
vibration is good for the health of the mechanicals, and can only think
it is induced by prop power pulses hitting the elevator.
Kelly


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Kelly McMullen
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Lenny Iszak



Joined: 23 Mar 2008
Posts: 252

PostPosted: Fri Apr 26, 2019 6:37 am    Post subject: Elevator pulsation Reply with quote

Mine does it too. I machined a new trim bellcrank with pressed in ball bearings to take out all the slop I can from the elevator trim. The cable still allows some slop though. Pulsing is still there. I took a slo-mo video of the stick in flight to determine the pulse rate and it was about 2Hz. Prop blade pulses are RPM/2.
I was thinking maybe it’s an elevator balance problem. Those were the first things I painted, and it took a few tries Smile so they may have ended up too heavy.

Lenny
Quote:
On Apr 26, 2019, at 9:41 AM, Kelly McMullen <kellym(at)aviating.com> wrote:



Has anyone else experienced vibration/pulsation in the elevator? Most noticeable on runup, and in cruise on autopilot. Vibration goes away when power is reduced for descent. The only play I have found so far in the control system is the elevator trim tab cables allow about 1/16" up and down movement of the tabs at the trailing edge. I can't think such vibration is good for the health of the mechanicals, and can only think it is induced by prop power pulses hitting the elevator.
Kelly





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Lenny Iszak
Palm City, FL
2014 RV-10, N311LZ - 500 hrs
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Kellym



Joined: 10 Jan 2006
Posts: 1598
Location: Sun Lakes AZ

PostPosted: Fri Apr 26, 2019 6:51 am    Post subject: Elevator pulsation Reply with quote

Glad (I guess) to hear it isn't just my aircraft. I don't know the pulse
rate for mine, but I have 3 bladed MT prop, so I assume it would be in
the 700-800 rate. I have no paint, so balance is per construction plans.
Haven't had elevator off yet to see how close it is to the specs you get
with finish kit. My elevator counterbalance fairings don't match as well
as I think they should, but haven't tried to get leading edge fairing to
match up better with elevator horns.

On 4/26/2019 7:26 AM, Lenny Iszak wrote:
Quote:


Mine does it too. I machined a new trim bellcrank with pressed in ball bearings to take out all the slop I can from the elevator trim. The cable still allows some slop though. Pulsing is still there. I took a slo-mo video of the stick in flight to determine the pulse rate and it was about 2Hz. Prop blade pulses are RPM/2.
I was thinking maybe it’s an elevator balance problem. Those were the first things I painted, and it took a few tries Smile so they may have ended up too heavy.

Lenny


> On Apr 26, 2019, at 9:41 AM, Kelly McMullen <kellym(at)aviating.com> wrote:
>
>
>
> Has anyone else experienced vibration/pulsation in the elevator? Most noticeable on runup, and in cruise on autopilot. Vibration goes away when power is reduced for descent. The only play I have found so far in the control system is the elevator trim tab cables allow about 1/16" up and down movement of the tabs at the trailing edge. I can't think such vibration is good for the health of the mechanicals, and can only think it is induced by prop power pulses hitting the elevator.
> Kelly
>







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Kelly McMullen
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Lenny Iszak



Joined: 23 Mar 2008
Posts: 252

PostPosted: Fri Apr 26, 2019 7:17 am    Post subject: Elevator pulsation Reply with quote

Good point. My counterbalance fairings don’t match very well either.

Lenny

Quote:
On Apr 26, 2019, at 10:50 AM, Kelly McMullen <kellym(at)aviating.com> wrote:



Glad (I guess) to hear it isn't just my aircraft. I don't know the pulse rate for mine, but I have 3 bladed MT prop, so I assume it would be in the 700-800 rate. I have no paint, so balance is per construction plans. Haven't had elevator off yet to see how close it is to the specs you get with finish kit. My elevator counterbalance fairings don't match as well as I think they should, but haven't tried to get leading edge fairing to match up better with elevator horns.

On 4/26/2019 7:26 AM, Lenny Iszak wrote:
>
> Mine does it too. I machined a new trim bellcrank with pressed in ball bearings to take out all the slop I can from the elevator trim. The cable still allows some slop though. Pulsing is still there. I took a slo-mo video of the stick in flight to determine the pulse rate and it was about 2Hz. Prop blade pulses are RPM/2.
> I was thinking maybe it’s an elevator balance problem. Those were the first things I painted, and it took a few tries Smile so they may have ended up too heavy.
> Lenny
>> On Apr 26, 2019, at 9:41 AM, Kelly McMullen <kellym(at)aviating.com> wrote:
>>
>>
>>
>> Has anyone else experienced vibration/pulsation in the elevator? Most noticeable on runup, and in cruise on autopilot. Vibration goes away when power is reduced for descent. The only play I have found so far in the control system is the elevator trim tab cables allow about 1/16" up and down movement of the tabs at the trailing edge. I can't think such vibration is good for the health of the mechanicals, and can only think it is induced by prop power pulses hitting the elevator.
>> Kelly
>>
>>
>>





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Lenny Iszak
Palm City, FL
2014 RV-10, N311LZ - 500 hrs
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bill.peyton



Joined: 19 Sep 2010
Posts: 192
Location: St. Louis, MO

PostPosted: Fri Apr 26, 2019 8:07 am    Post subject: Re: Elevator pulsation Reply with quote

I have never noticed the vibration, but I did not like all of the slop in the current trim actuation design. I redesigned the trim bell crank pivot point to reduce the slop, and I use #10 castellated nuts to hold the cable ends in lieu of the pins. I have little to no play now.

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Bill
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Aviation Partners, LLC
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Mauledriver(at)nc.rr.com
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PostPosted: Fri Apr 26, 2019 8:45 am    Post subject: Elevator pulsation Reply with quote

Kelly, FWIW I haven't never experienced any elevator pulsation (my
Miata's stick shift pulsates but that's a different matter).  I think my
elevator counterweight to stabilizer fitting is relatively tight if a
bit crudely finished.

Bill in Durham NC

On 4/26/2019 9:41 AM, Kelly McMullen wrote:
Quote:


Has anyone else experienced vibration/pulsation in the elevator? Most
noticeable on runup, and in cruise on autopilot. Vibration goes away
when power is reduced for descent.  The only play I have found so far
in the control system is the elevator trim tab cables allow about
1/16" up and down movement of the tabs at the trailing edge. I can't
think such vibration is good for the health of the mechanicals, and
can only think it is induced by prop power pulses hitting the elevator.
Kelly




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Greg McFarlane



Joined: 12 Apr 2012
Posts: 45
Location: Albany Western Australia

PostPosted: Sat Apr 27, 2019 1:07 am    Post subject: Re: Elevator pulsation Reply with quote

JFI, ... For sure the whole horizontal tail plane shakes and buffets with high power run ups on the ground, I think the solution to that is to keep that sort of operation to the minimum required and if possible with the aircraft moving especially for prop cycling. Regarding in flight, when on AP, our RV10 and AP (TruTrac) is particularly sensitive to out of pitch trim and close attention to trim is needed (or auto trim) otherwise the AP will cycle up and down to correct the out of trim situation, in our case very easy to recognise because the aircraft starts a little nodding motion. As far as elevator pulsation is concerned generally when in flight, I’m pretty sure that a lot of that is from turbulence in and around the elevator horns and the lightening holes in the outer horizontal rib, and that will vary depending on W&B. Others have found a marked difference if those lightening holes are taped over or otherwise blocked. From day one our RV10 (now flown 400hrs) has had all those holes blanked off with tight fitting auto rubber blanking plugs that are securely contact glued in. We’ve never experienced any elevator pulsation. Cheers from Western Australia.

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Bob Turner



Joined: 03 Jan 2009
Posts: 841
Location: Castro Valley, CA

PostPosted: Sat Apr 27, 2019 7:48 am    Post subject: Re: Elevator pulsation Reply with quote

I seem to recall that Tim Olsen reported elevator pulsing on his -14?? He noted that the fiberglass fairing on the elevator horn was thicker (vertical dimension) than the matching piece on the stabilizer. He fixed that, the pulsation went away. That is, if I remember correctly.

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Tim Olson



Joined: 25 Jan 2007
Posts: 2776

PostPosted: Sat Apr 27, 2019 11:21 am    Post subject: Elevator pulsation Reply with quote

That’s not too far off, Bob, as far as Internet thread memory goes. Smile It was somebody else with an RV 14 that had a pulsing. I just had occasional brief periods when leveling out two crews trim that the plane would change trim just slightly but very quickly.The other person that you were referring to did indeed widen or I should say heighten his stabilizer tips so that they more completely shielded the elevator from airflow. That fixed it for him. Mine are just slightly smaller than the elevator horns. I think it is a definite case that you should try to make sure that the stabilizer tips are as big or slightly bigger than the elevator horn’s in height, but mine are not quite like that, unfortunately. But it is a fairly occasional thing for me, and you have to be paying attention to notice it. Mine is not currently fixed. Mainly because after having it painted and having those tips fiberglass in over the rivet lines, the only way to fix it is probably to tear the tips off and then repaint the stabilizer. That’s probably not going to happen. At least not for something that is barely noticeable and only occasional.But mine does not pulse up and down. It’s more like you can feel a difference when the elevator horn hits the air flow versus when it’s not As far into the airflow.

Anyway, yeah, that’s on the -14, but I think the parts are basically very similar.
Tim

Quote:
On Apr 27, 2019, at 10:48 AM, Bob Turner <bobturner(at)alum.rpi.edu> wrote:



I seem to recall that Tim Olsen reported elevator pulsing on his -14?? He noted that the fiberglass fairing on the elevator horn was thicker (vertical dimension) than the matching piece on the stabilizer. He fixed that, the pulsation went away. That is, if I remember correctly.

--------
Bob Turner
RV-10 QB




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