Vibration when leveling off

[Flyphilly]

Anyone ever experience a shimmy or vibration when leveling off?

My O2 recently started producing a shimmy at the top of the climb through the level off. It subsides once the aircraft settles into it’s level pitch attitude - lasts no more than a few seconds.
 

It feels like very light chop or riding a boat through another’s dying wake on an otherwise flat lake.

The prop was overhauled at annual about 6 months ago, I thought maybe prop needs to be balanced but then why wouldn’t it give me the same vibration in other situations. 
 

Any insight?

[carusoam]

Fp,

What prop do you have on your O2?

When leveling out there is probably a change of AOA on the prop...  and some adjustment that it goes through automatically...

 

Lets ask the prop guy if he sees this behavior anywhere...

@Cody Stallings (prop vibration at top of climb, during leveling..?)

Best regards,

-a-

[Flyphilly]

It’s a 3 bladed hartzell - are you saying it would naturally adjust pitch based on aoa change with no change in RPM?

 

[carusoam]

1 hour ago, Flyphilly said:

It’s a 3 bladed hartzell - are you saying it would naturally adjust pitch based on aoa change with no change in RPM?

 

That’s the magic of the constant speed prop...

Blade angles get adjusted continuously... when the plane goes from climb to cruise... it changes again...

Another period of change occurs as the plane accelerates....

None of this would cause the vibration you described... if everything is working well...

But, it does give some insight if something is not working so well....

Have you had any prop maintenance lately?

PP thoughts only, not a mechanic...

Best regards,

-a-

[StevenL757]

2 hours ago, Flyphilly said:

Anyone ever experience a shimmy or vibration when leveling off?

My O2 recently started producing a shimmy at the top of the climb through the level off. It subsides once the aircraft settles into it’s level pitch attitude - lasts no more than a few seconds.

It feels like very light chop or riding a boat through another’s dying wake on an otherwise flat lake.

The prop was overhauled at annual about 6 months ago, I thought maybe prop needs to be balanced but then why wouldn’t it give me the same vibration in other situations.

Any insight?

Could use some more detail here, such as…

• What altitude(s) does this occur?
• What are your MP and RPM settings when it occurs?
• Any engine and/or airframe work done recently; and if so, what?

Steve

[Ragsf15e]

Probably not much help since I’ve got a 68 F, but yeah, mine does exactly what you described.  I even had the cowl flaps tightened up with new hardware because I thought they might be part of it.  No change.

I thought about the prop balance too but had the same questions as you.

[Cody Stallings]

Anthony is speaking the truth.

you have a very large blade angle increase as you transition from climb to cruise. 
 

Did the issue start after the propeller came back from O/H?

Little trouble shooting for ya.

Pull propeller control all the way out(engine off) an have yourself an 2 of the beefier ramp rats you can find an manually move all 3 blade together to High pitch. While doing so be mindful of any catches or rough spots in the actuation.

If the Blade Preload is to tight on 1 or 2 blades, then you will have a bit of a blade tracking issue for a couple seconds till the larger adjustment is made. Once the big addition bit of blade angle is achieved then the smaller adjustments your Governor makes really aren’t detectable.

In the photo you will see Round plates with a smiley face on the butts of the blades. Those are the pre-load place that are adjusted individually between the blades. If one is to tight it will allow the other two blades to move more freely yielding a slight blade angle issue for just a second. Once the angle is adjusted then the blades wind themselves back in sync 

Edited May 19, 2021 by Cody Stallings

[Flyphilly]

@Cody Stallings This is very helpful- I will fool with it and provide feedback. Getting an oil change this week so I can have the guys at the shop help me with this.

I acquired the plane in December and it received a heavy prebuy/annual. 
 

Prop was overhauled but no other engine or airframe work. The engine got new hoses but I don’t see how that would be relevant.

the issue occurs at 2500rpm and the manifold pressure depends on the altitude at which I level off - I climb at 25 square until unachievable. Level off is anywhere from 4000 to 12000 and altitude has no impact on this phenomenon. 
 

What Cody is describing is most plausible. When this occurs, what is required to correct it, and is it causing faster wear or deterioration? Or does it not matter? I can live with it if it isn’t going to reduce prop life and would be costly or time consuming to resolve.

thanks again-

[A64Pilot]

Also take a chair and put it so it’s  just touching a blade and double check mags off and rotate the prop. all blades should just touch the chair. It’s a shade tree way of checking blade tracking.

‘Anytime there is an airspeed change in the aircraft, there will be a pitch change in the prop, assuming it’s not against any stops, which it shouldn’t be in normal flight.

‘If you don’t find anything you may want to get an A&P or a prop shop to use a prop protractor and check prop pitch of all three blades, but if one is slightly off it usually gives a constant vibe.

That yellow line on the back side of the blades purpose is to give a identical point of all blades to check pitch as the blades of course have a twist. 

Edited May 19, 2021 by A64Pilot

[Ibra]

On the ground once you are done recycling prop, do you get any of those vibrations when you keep recycling very slowly from fine pitch to higher pitch? is it smooth? or it also vibrates?

- If yes, probably one of blades is slightly behind when prop pitch changes (picture above is worth 1000 words)

- If no, it's probably prop balancing or random vibration on specific regimes Power/RPM/ASI

If the latter you can check on various climb & level off speeds or RPM/ASI

If greasing & balancing does not sort it, it will take a while to debug... 

 

[Mark89114]

A very experienced MSC mentioned the "mooney rumble".....i sometimes hear something but no indication on flight instruments, controls or engine gauges....i just shrug and go on.

[Flyphilly]

I have treated it as such so far but it is strange. I have though perhaps a gear door is held slightly open and vibrates itself closed once pitch decreases.. but the blade tracking described above makes way more sense.

 

will Investigate all of the tips above and see where this leads. Thank you for sharing your experiences. Much appreciated!

[Hank]

And here I thought it was because he climbs out at reduced power rather than WOT / 2700 like the rest of us . . . . 

[Flyphilly]

I take it easy on the old girl  I am just a lone SOB must days  never short climb rate.

love this plane.

Edited May 20, 2021 by Flyphilly

[carusoam]

Fp,

See if you can capture a video of the level-off / vibration...

Max power climbs to altitude are awesome...  if you have the FF to maintain CHTs all the way up...

Some Os are physically limited to 2500rpm... 

It also helps to have to have a prop balance done...

PP thoughts only... not a mechanic...

Best regards,

-a-

[Flyphilly]

I can try but it’s subtle. I am not sure the video would show anything.

What CHT’s are you guys comfortable with on the climb? I do what I can to keep them under 400- is that too conservative?

[A64Pilot]

If you can’t keep it well below 400, something’s wrong. Higher power and increased airspeed sometimes can be cooler than lower power and slower.

What is your takeoff fuel flow? What engine? Shade tree answer, but I like to see just under 10 GPH per 100 HP, so 19 or so for a 200 HP, and 28 or so for 300.

NA motors, turbos are different.

[ilovecornfields]

If your fuel flow is good and your climb rates are reasonable you should have no problem keeping the CHTs under 380 at WOT/2550 RPM. It’s a lot less work this way than to keep having to add an inch of MP every 1000’ and the higher climb airspeed (from the higher power setting) will cool your cylinders.

I didn’t believe it until I tried it and it’s a little counterintuitive but you actually get cooler CHTs at higher power settings sometimes. 

[Flyphilly]

8 hours ago, ilovecornfields said:

If your fuel flow is good and your climb rates are reasonable you should have no problem keeping the CHTs under 380 at WOT/2550 RPM. It’s a lot less work this way than to keep having to add an inch of MP every 1000’ and the higher climb airspeed (from the higher power setting) will cool your cylinders.

I didn’t believe it until I tried it and it’s a little counterintuitive but you actually get cooler CHTs at higher power settings sometimes. 

This is helpful - I’ll give that a shot. I do have the 310hp increase and I typically climb at constant speed of 115, or 120 if CHT’s start creeping up.

The scream of WOT/2700 rpm is just too jarring to sustain for a long period to me. I feel like something is going to shoot out of the cowling at any moment. But then again, I come from a Diamond with io360

Do a lot of you fly WOT/2700 all the way up? Do any of you fly 2700 in cruise?

[LANCECASPER]

On 5/19/2021 at 8:58 PM, Flyphilly said:

I can try but it’s subtle. I am not sure the video would show anything.

What CHT’s are you guys comfortable with on the climb? I do what I can to keep them under 400- is that too conservative?

How are your baffle seals? If they are bending back letting the air escape out the back, then the air is not pushing down over the cooling fins and keeping your cylinders cool. The baffles seals that they used at Mooney back then were good for about a year or two, then they would bend back.

[ilovecornfields]

1 hour ago, Flyphilly said:

This is helpful - I’ll give that a shot. I do have the 310hp increase and I typically climb at constant speed of 115, or 120 if CHT’s start creeping up.

The scream of WOT/2700 rpm is just too jarring to sustain for a long period to me. I feel like something is going to shoot out of the cowling at any moment. But then again, I come from a Diamond with io360

Do a lot of you fly WOT/2700 all the way up? Do any of you fly 2700 in cruise?

I really only use 2700 RPM for the first 1000’, then bring it back to 2550. The only exception is if I’m trying to climb through an icing layer in which case I’ll climb at 120 KTS (minimum icing speed), 2700 RPM/WOT.

I usually climb at 120-130 KTS which may explain our differences in CHT. I have a 225 AP so I can’t directly set the speed, but I’ll set it to 1000 FPM to start then slowly dial it down as the speed drops off until I get to my cruise altitude or 500 FPM.

Savvy tells me I cruise at lower power settings than my peers. I usually cruise around 50-55% power (around 18”/2300 RPM). It’s nice and smooth, temperature are good and it only uses about 12 gph at this setting. I wanted the big engine for takeoff and climb performance, not necessarily to go fast.

[carusoam]

WOT and Max rpm all the way up is possible...

Initial climb rate will be around 2kfpm...

CHTs will be try to climb...

FF required to keep CHT control will be around 29gph...

120kias is a typical selection for improved air cooling in a cruise climb

The extra 200rpm and Max FF... is a personal choice...   

Prop efficiency and climbing out at 2550 also cuts back a lot of sound....

 

Kind of have to be ultra attentive while doing this... things are changing so fast as you climb...

Your scan rate has to be really quick to process the data....

Things change again as OAT rises... summer is coming...

 

Keep collecting data of what works for you... and try to repeat it...

Some things repeat very easily once you have your procedures down...

PP thoughts only, not a CFI...

Best regards,

-a-

[Ibra]

 

On 5/21/2021 at 2:05 PM, Flyphilly said:

Do a lot of you fly WOT/2700 all the way up? Do any of you fly 2700 in cruise?

It does not make sense unless you are climbing nasty weather (at 110ias) or terrain/obstacles (at 80ias), if you want to keep 100% power climbs at 20kts faster will not hurt your rate of climb (or climb gradient) but it helps finishing the trip quickly and keep CHT in good range 

On cruise max recommended power is 260HP (about 83%), the engine won’t deliver more than that at high altitudes, so you can go 2700rpm & WOT above 8kft, it’s the only way to climb past 10kft 

It will be odd to cruise any Mooney at 2700rpm & WOT bellow 4000ft, it will be the same efficiency MPG & GPH as Cirrus and Bonanzas “just” 15kts faster 

Edited May 24, 2021 by Ibra

[PT20J]

Three things affect CHT: Power, Mixture, Airflow. There are multiple combinations to achieve the same result.

[Ibra]

2 minutes ago, PT20J said:

Three things affect CHT: Power, Mixture, Airflow. There are multiple combinations to achieve the same result.

For Power, do different values of MPxRPM make any difference to CHT on same power % as long as mixture & airflow remain the same? 

Is there way to get proxy table for CHT vs (Power, FF & ASI) in standard ISA conditions? how much is left to correct in non-standard conditions?