Hi All,
Just some further observation on pitch change.
The pitch change action is usually in three stages. The first is the easy take
up of any slack in the cable until noticeable resistance is felt. The second is
the continued pulling of the lever with some effort (but without pulling the
lever very far!). The third is relaxing the the pressure on the lever.
We have found that the process can vary quite a bit between props on the same
aircraft depending on how the prop is configured after overhaul or resetting.
We have also found that in addition to RPM, AIS is significant. eg the prop
current not wanting to go into cruise pitch at 60-65kt but readily going in at
55-60kts at the same RPM. The current prop also has a much great difference
between the fine and course settings requiring a significantly greater AIS for
efficiency in course.
Jarek, that there is an even clearance between the pitch plate and the two
pitch change bearings was previously mentioned. You can make an easy visual
check on this from the right hand side of the motor. Just look to see that the
clearances look to be the same as this is very important as any even load
applied will cause premature wear on the mechanism and worse, especially if
you have been a little over boisterous in operating the lever.
We have found the change usually works best at 2200 RPM. From P31 of the H36
manual...
Hoffmann
4
H 36 DIMONA
NormalProcedures
4.10 Cruise:
To changepropeller position from Take—Off to Cruise the RPM must be between
2000 and2200. Pull and release the propeller control. A 500 RPM drop should
occurwithout throttle adjustment. The throttle can then be opened for Cruise
power(2500 - 3000 RPM) as required.
Best Regards
Laurie
On Monday, 15 October 2018, 6:09:32 am AEDT, Jarek Steliga
<[email protected]> wrote:
Michael,
That convinces me further that my "pull" was ridiculously inadequate. I am
beggining to hope that my troubles are soon going to be over, but can't be sure
of course before trying to do it the way it is demonstrated in your clip.
RegardsJarek
niedz., 14 paź 2018 o 20:58 Michael Stockhill <[email protected]> napisał(a):
In my case, when on the ground before takeoff, I start with flat pitch at 1500
rpm, A fairly easy pull of an inch or so drops the rpm to 1200. A second more
aggressive pull returns the rpm to 1500 rpm. I have noted over the last
fifteen years that in flight the required force has progressively increased. I
have mitigated that by dropping the rpm at pitch change. I am now probably
closer to 1800 rpm than 2200. There is some evident wear on the pitch change
rods, likely creating some binding due to greater centrifugal force at
increased rpm. Not to suggest that this is yet an airworthiness issue.
M
On Sun, Oct 14, 2018, 12:38 PM <[email protected]> wrote:
Hi Jarek,
With our newish prop (280 hours, also with aSN that starts with A), we shift
into cruise at about 1800-2000 rpm, and find that when in flight (as opposed to
pitch changes on the ground during run-up), the pull requires a bit more force,
but the lever should only come out about 2-4 cm. I would describe the pull as
steady but not sharp and not particularly slow. Kristn just uploaded a short
video of me this https://m.youtube.com/watch?v=VyYbV802UAM
Tom
Sent from my Windows 10 device
From: Jarek Steliga
Sent: Sunday, October 14, 2018 13:57
To: [email protected]
Subject: Re: [DOG mailing list] Hoffman propeller HO-V62-R / Issues
withchanging positon to cruise
Tom and Nigel,
Perhaps that's where the shoe pinches? Perhaps the manner I pull the pitch
change handle needs to be looked into before other reasons are examined (shaft
runout or two bearings not touching the driven plate simultaneously). It is
unlikely that serious mechanical malfancions occur just a year since that
particular prop had been released by Hoffman from overhaul, with the time of
actual use not exceeding 20 hours.
I have to admit that I always pulled the handle all the way and only now
having read your remarks realize that perhaps that was completely wrong. Can
the handle be pulled slowly untill the drop of RPM occurs or does it have to be
a shorter but energetic jerk?
Is the jury out on the RPMs at which the pitch change should be made? Is it
2200 or between 1800 and 1900 or what? Which works best for you?
Regards
Jarek
niedz., 14 paź 2018 o 14:03 Nigel Baker <[email protected]> napisał(a):
Hi Jarek I checked the Hoffman Prop manual and indeed you are correct.
However all on this list will say 2200 RPM I think.
Expect a drop of 200 rpm for cruise so aim for a drop of 250 momentarily. The
idea is to provide enough clearance for the slide to move into place in the
Centre stem nut shoulder without the RPM dropping so far that the centrifugal
force drops so much the slide will not stay out in the cruise position.
It is a balancing act between RPM and hand force on pull handle.
As Tom says if you pull the change handle far enough back it will rumble like
hell as the blades are stalling due to too high an angle of attack. It won’t do
any damage but is unnerving.
This takes a little finesse but once mastered you will find it easy enough.
Nige.
From: [email protected] <[email protected]> On Behalf Of Tom
Preisser
Sent: Sunday, October 14, 2018 8:19 AM
To: [email protected]
Subject: Re: [DOG mailing list] Hoffman propeller HO-V62-R / Issues with
changing positon to cruise
Perhaps you are pulling the handle too far out ? Just pull it a little, because
if you pull it too far the prop will rumble, the rpm will fall too much, and no
change to cruise will happen.
Let us all know what you discover.
On Friday, October 12, 2018, Rob Thompson <[email protected]> wrote:
> 1- Normally the RPM on change should be 2200 to go into cruise.
> 2 - Sounds like the pitch change/feather plate on the rear of the prop is not
> running true or alternatively the two bearings that contact it are not
> touching at the same time.
> Use a finger dial guage to check if the plate is true.
> regards
> Rob
> Rob Thompson
> 0429 493 828
> (Please note that my new email address is [email protected])
>
> On Sat, Oct 13, 2018 at 6:53 AM Jarek Steliga <[email protected]> wrote:
>>
>>
>> Hello,
>> I am quite new here (have owned Dimona for only 3 months).
>> Despite scrupulously folliowing the instructions regarding the required
>> RPM-s of between 1800 to 1900 at which the propeller pitch is changed from
>> START to CRUISE in midair, I have only succeedded twice despite numerous
>> attempts. Also pulling the pitch lever in the cockpit results in scary
>> vibrations which discourages me from continuing my trial and error methods.
>> Can someone please help?
>>
>> Best regards
>> Jarek
>>
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