914 vibrations

[rhtrudder]

Had a wheels up landing in my Sabre, mechanical failure, broken prop, gearbox checked out by Wal , all good, borrowed another prop from a mate, Kaspar, had to change the pitch as it was over reving, now have a bad vibration as is throttles back past 4000 revs , only noticed this as I was flying to deni to get some panel work done, could it be caused by a miss match in the pitch of the blades , cruise and idle it is good , got a mercury balance plate fitted. 

[Blueadventures]

54 minutes ago, rhtrudder said:

Had a wheels up landing in my Sabre, mechanical failure, broken prop, gearbox checked out by Wal , all good, borrowed another prop from a mate, Kaspar, had to change the pitch as it was over reving, now have a bad vibration as is throttles back past 4000 revs , only noticed this as I was flying to deni to get some panel work done, could it be caused by a miss match in the pitch of the blades , cruise and idle it is good , got a mercury balance plate fitted. 

One early check I would do is observe the movement of throttle levers / cables; any binding or hesitation in the movement from full to idle on one of the carbs compared to the other.

Edited October 18, 2020 by Blueadventures

[skippydiesel]

Hi Rhrudder- dont have a 914 (wish I had)but do have a 912 ULS so may be able to contribute a little or could be all fake news

 

In my application I took a great deal of time & trouble to static balance, pitch and then dynamic balance my 2 blade Fiti prop. Ran like a sowing machine from the static balance/pitch onward, so noticed little change with the dynamic balance. I guess I am going the long way about suggesting you may have been a tad hasty in your temporary re propping.

 

I would also second Blueadventures suggestion again you can only benefit from aa precise as possible pneumatic balance of the carburettors.

 

One other point - check out your engine mount & rubbers for nil damage/security

[rhtrudder]

All good suggestions, thanks for the advice 

[rhtrudder]

1 hour ago, skippydiesel said:

Hi Rhrudder- dont have a 914 (wish I had)but do have a 912 ULS so may be able to contribute a little or could be all fake news

 

In my application I took a great deal of time & trouble to static balance, pitch and then dynamic balance my 2 blade Fiti prop. Ran like a sowing machine from the static balance/pitch onward, so noticed little change with the dynamic balance. I guess I am going the long way about suggesting you may have been a tad hasty in your temporary re propping.

 

I would also second Blueadventures suggestion again you can only benefit from aa precise as possible pneumatic balance of the carburettors.

 

One other point - check out your engine mount & rubbers for nil damage/security

If the pitch is not set the same for each blade could that make it vibrate when throttle is retarded, only set the pitch on each blade with a bubble type pitch gauge, took a few goes started off to fine then to course , struggled to reach 5000 on take off, so I split  the difference, I was surprised  how little movement made the difference , since found out you can use the inclinometer on a phone to check it, 

[skippydiesel]

Cause I'm anal, I use several different devices to check/adjust pitch:

 

Alan key, spanners, accurate torque wrench to loosen/tighten hub fittings

 

Tin of  Carnauba wax polish 

• Lubricate blade hub socket (only need to be applied at first adjustment)

Masking tape

• Wrapped around blade at approximate measuring radial (dont forget to remove befor engine start)

Steel metre rule

• Used to make accurate measurements from, pre scribed,  centre of hub to recommended measuring location on each blade. I make two measurements/blade - hub centre to leading edge and to trailing edge.

Sharp pencil & short strait edge

• For marking a strait measuring line/location, between above marked points,  on masking tap

Nice builders level

• Set the hub/blades to exactly vertical for each measurement. I do all my measurements on the left side of aircraft so blades must be rotated 180 degrees

Digital protractor

• Have fitted with straight edge that can be clamped exactly to blade measuring point/line. Protractors (both) are "zeroed" against vertical face of hub before each measurement/adjustment

Warprive bubble protractor

• Rough check/adjustment befor using digital protractor

Home made wooden "clamp" (2 pieces of  wooden strip, hinge at one end)

• Clamped (hand grip)around blade to give leverage & additional control in making fine rotational adjustments of blade

With all of the above I am able to make accurate adjustments down to better than  .5 of a degree

[rhtrudder]

Hell, at that rate mine will be out for sure , I did notice when I tightened the clamp bolts it would change the angle a bit , plane is at lame in deni , I am hoping this is my problem as it is bad enough to not fly it as I said good at cruise but bad when throttling back

[rhtrudder]

Thinking of replacing the prop studs and the flange bushes are they available from floods or the propellor mob

[skippydiesel]

1 hour ago, rhtrudder said:

Thinking of replacing the prop studs and the flange bushes are they available from floods or the propellor mob

Dont know what your prop flange system looks like but mine has separate blade "root" /hub socket clamping to the flange securing bolts. This means that I can clamp the blades in the selected pitch without fear of making an inadvertent change when I tighten the 6 x 8 mm flange bolts. I always tighten progressively, using an accurate torque wrench, to minimise the chance of distortion. 

 

Your LAIME should be able to advise on what needs replacing. If your prop was a hollow composite, there may be little if any damage to the hub & "studs"/bolts.

 

My aircraft uses "off the shelf " Allan key " head, 8mm HT bolts and lock nuts - much cheaper than buying from BF

[Blueadventures]

If not serious consider 1 change at a time to identify the fix.  Also check the carb rubber flanges for cracking as may have cracked with the landing jolt.

[cscotthendry]

Also check blade tracking. Getting the pitch the same on all blades is only half the job.
Chock the aircraft against movement.
Put a chair or a ladder near the prop, but where the prop can be turned without hitting the chair.
Turn the prop bringing each blad near the chair and measure the distance.
There are specs (RA Aus tech manual?) for prop blade runout, radially and axially.
The above is easier to do if you remove 1 spark plug from all cylinders.

But as Mike said, pneumatic synching of the carbs is a major cause of RPM related vibrations.

Edited October 18, 2020 by cscotthendry

[skippydiesel]

1 hour ago, cscotthendry said:

Also check blade tracking. Getting the pitch the same on all blades is only half the job.
Chock the aircraft against movement.
Put a chair or a ladder near the prop, but where the prop can be turned without hitting the chair.
Turn the prop bringing each blad near the chair and measure the distance.
There are specs (RA Aus tech manual?) for prop blade runout, radially and axially.
The above is easier to do if you remove 1 spark plug from all cylinders.

But as Mike said, pneumatic synching of the carbs is a major cause of RPM related vibrations.

Agreed - one one point I would differ slightly - I do my tracking check against a pointer (small piece of wood/plastic/even stiff cardboard), taped securely to the nose wheel fairing.

Rotate prop so tip of one blade nearest point to nose wheel.

Move pointer to within known distance from prop tip. Secure pointer with tape.

Rotate prop & observe each blade tip clearance to pointer.

By using a part of the airframe, there is little concern that aircraft movement might influence the test.

[rhtrudder]

After trial and error with the Kašpar worked out the thrust  bearings are shot , to much side play and if tightened up they become notchy, got them a bit better , ok at cruise,  big trouble trying to get new prop shipped , so I thought of replacing with a ground adjustable until it turns up but apparently it can’t be done without factory approval which makes it hard because the Sabre mob went into liquidation years ago, the new crowd, skyleader, can’t help, is there anyway around this or should I just fit another prop and get back in the air 

[skippydiesel]

Rhtrudder - May I ask what brand & type of CS/In flight Adjust  propeller is fitted to your aircraft ?

[rhtrudder]

It’s a 3 blade in flight adjustable Kaspar 1620mm ,  made by kasparaero cz

 

[skippydiesel]

Thanks Rhtrudder - I am trying to get information on CS/IFA propeller suppliers/producst - see my conversation in Prop Selection

[skippydiesel]

Sorry had to attuned to Grandpa duties- I would be interested in the following:

 

RPM & estimated fuel consumption at:

 

100 knots

110 knots

120 knots

 

The Sabre's stall speed, max load (600 kg?) and your  ground role, climb/speed, comfortable cruise & top speed as experienced by you.

The manufactures POH stall , cruise and max speed.

 

Your comments on your propeller performance (befor the accident)

 

[rhtrudder]

Happy with the Kašpar , quiet, full fine 5800, about 100 m roll out , cruise 120 at about 5400 and 35 on the map gauge 18 lts , stall about 35, wheels and flaps up climb maybe 1200 at 70 kns. Just clocked up 1700 hrs ,bought 

at 470 hrs about 10 years ago , 3rd owner, been a great plane , factory certified to 544

[skippydiesel]

That's great! My Thanks.

 

Have just written to the factory, seeking costed recommendations for Rotax 912 ULS powered ATEC Zephyr.

 

My home strip is marginal to say the least, so ground adjustable prop set for advantage TO/Climb Out. 

 

I wish to preserve the ground role (sub 100 M on grass) climb out (1500 f/mint + @ 60 -70 knots) but improve on cruise.

 

Existing  cruise is 100-110 knots  @ 500-5200 rpm for a fuel burn of -13 L/h to -14 L/h. I flight plan at a conservative 14L/hr. I have seen just under 120 knots @ 5500 RPM at 500 ft (beach run). POH has a max speed of 124 knots.

 

With a CS/Inflight adjust I would hope to have an econamy cruise of 115-120 knots.

 

Do you think this is possible with the right Kaspar AND what is the factory like to deal with AND which Kaspar & control system do you have ????

[rhtrudder]

A inflight adjustable will extract more useful power from your engine , I reckon, factory is good to deal with, look them up, I think they make three sizes in 2 and 3 blade , right and left , tractor and pusher, also wheels and brakes that are fitted to my plane , the controller in mine is a standard vernier type , all available from them , pricey though, your fuel burn looks  a bit better than mine , if I hammer mine it will make 130 but burns closer to 25 

I think I might bolt on a duc prop and pitch it for cruise, my strip is 800 m heading south , should be ok , 

[skippydiesel]

My home paddock/strip is 400 m from the stock yards to the base of tall trees and on the side of a hill. Stockyard(west) end has low trees & power line. East end has a lot of tall trees  - no landing area for about 2 km.  Creek line at base of hill can reduce over all length by 1/3. This is why I must preserve my TO performance but have always hankered after a CS or IFA to maximise cruise.

 

I have no experience but Kyle of Kyle Communications  (on this Forum) is agent for E-Prop. He speaks very highly of its performance and he sounds like a good guy. 

[skippydiesel]

Been checking out the Kaspar catalogue - which of the several propeller control systems do you use??