Engine Droop - M20J with the A3B6D Engine and Hartzell prop

[StevenF]

I wanted to see if anyone had a view on the rather strange angle we seem to have on our M20J engine.  My co-owner and I were standing looking at her yesterday and it suddenly occurred to me that our prop wasn't aligned to the cowling, and appears to have about an inch of droop.  The cowling doesn't appear to be obviously misaligned at the firewall end.  My immediate suspicion is that the engine-mounts have sagged or are not set correctly somehow?  We've been noticing our speed has been deteriorating over a period of years and put that down to a tired engine that's approaching TBO, but perhaps that isn't the case after all?  

We also then had a good look over and noted that our ailerons both appear (when centred) to be "low" by about 1/2" against the tips, but roughly in line with the flaps.  If one is centred, the other is approximately 1 inch below the natural location on the tip fairing.  Also, when the end of the aileron is aligned to the tip fairing, it sits about 3/4 inch above the flap?  Is it possible we're rigged wrongly?  Being in the UK the shops see very few Mooney's so I wanted to see what wisdom the crowd could offer on this before discussing it with our maintenance organisation

Is it possible our thrust line is quite a few degrees out, and our ailerons are increasing camber and drag unnecessarily, and that and would that have a material speed difference? 

We reckon we should see closer to 160kt, but we're getting about 145kt TAS at 6,000'.  We've just had her polished which might give us back a few knots but could engine alignment and flaps dragging cause a 10kt type of loss?  Pictures attached.

Thanks for anyone's input on this.  We'd like our speed back :-)

[JModelDave]

I agree with the previous post. Engine Lord mounts may be deteriorating or simply need to be shimmed. Control surfaces certainly appear to be out of rig.

[RoundTwo]

Your mounts are shot. I replaced mine this summer and it’s pretty easy as long as you have an engine hoist. I’d imagine you have several points of contact between the engine and your lower cowl too. Mine were original to the plane, 1987, and some had ruptured the internal gel sacks.

[EricJ]

There are two things that cause that "droop" between the cowl and the prop.   One is the engine angle, which can be corrected by moving the shims around in the engine mounts (basically move the washers to bring the prop up).   That's covered in the article linked above.      The other is that the cowl naturally wants to move up due to the aero pressure.   When I put my cowl on it initially lines up very nicely with the prop, but then once it gets flown once or twice the cowl creeps up and makes it look like the prop is droopy.    Yours looks like you probably have some of both going on.

Does your airplane fly straight?   There are some easy tests to tell whether the rigging is off symmetry.   It can be off and still fly straight, but if it doesn't fly straight it's a reasonable sign that it needs attention.    Travel boards make it easier to rig, but it can be done without them if your local maintainers don't have access to boards.  That's often a problem.

This article has some good techniques for determining whether the rigging needs adjustment from a flight perspective:

https://www.knr-inc.com/shoptalk-articles.html?view=article&id=75&catid=25

[Fly Boomer]

6 hours ago, StevenF said:

My co-owner and I were standing looking at her yesterday and it suddenly occurred to me that our prop wasn't aligned to the cowling, and appears to have about an inch of droop.

Not sure how useful they are, but this version still has some of the pictures attached:

https://web.archive.org/web/20031226052837/http://www.donmaxwell.com/ALIGNING_YOUR_ENGINE.HTM

 

[PT20J]

As @EricJ outlined, there are two possible issues.

1. If the spinner is out of alignment when the cowling is removed and then replaced, it is likely that the engine mounts are the issue. Old mounts may sag. The mounts are properly shimmed at the factory and shims should not need to be adjusted when the mounts are replaced. But what sometimes happens is that some unaware maintainer lets them fall out when replacing the mounts and they don't get back in their original locations. So, if the mounts are old and saggy, I would assume that the shims are correct and replace them as removed (which is what the service manual describes). If there is still an alignment issue, then you will have to mess with them.

2. If the cowling and spinner are in alignment when the cowling is removed and then replaced, the alignment issue is caused by the cowling moving due to air pressure. Mine has done this since I purchased it in 2018 and this year at annual inspection I decided to investigate more carefully why this would be so. The cowling is held in place on my M20J by camlocs. The bottom cowling has two camlocs that attach it to a small shelf at the bottom of the firewall. I discovered that each side has a crack that allows this shelf to flex forward allowing the cowling to rock back. I'm going to have that fixed and then see if that solves the problem. 

Skip

Edited December 3, 2023 by PT20J
Added pictures

[PT20J]

26 minutes ago, bluehighwayflyer said:

If I am not badly mistaken, there is also a service bulletin out there somewhere to replace some of the cowling camlocks with machine screws and nut plates to address the cowling rise issue.  It might be worth researching, especially if you have an older J model.  It was probably incorporated into production at some point.

I heard that LASAR once had some mod for this, but Corrine told me that it was just something they did in the shop. Not sure of the details. Perhaps @SheryLoewen remembers.

[Rick Junkin]

Joe at Hawk Aircraft Services has done this mod recently. Give him a call for info.

Cheers,
Rick

[1980Mooney]

10 hours ago, StevenF said:

I wanted to see if anyone had a view on the rather strange angle we seem to have on our M20J engine.  My co-owner and I were standing looking at her yesterday and it suddenly occurred to me that our prop wasn't aligned to the cowling, and appears to have about an inch of droop.  The cowling doesn't appear to be obviously misaligned at the firewall end.  My immediate suspicion is that the engine-mounts have sagged or are not set correctly somehow?  We've been noticing our speed has been deteriorating over a period of years and put that down to a tired engine that's approaching TBO, but perhaps that isn't the case after all?  

We also then had a good look over and noted that our ailerons both appear (when centred) to be "low" by about 1/2" against the tips, but roughly in line with the flaps.  If one is centred, the other is approximately 1 inch below the natural location on the tip fairing.  Also, when the end of the aileron is aligned to the tip fairing, it sits about 3/4 inch above the flap?  Is it possible we're rigged wrongly?  Being in the UK the shops see very few Mooney's so I wanted to see what wisdom the crowd could offer on this before discussing it with our maintenance organisation

Is it possible our thrust line is quite a few degrees out, and our ailerons are increasing camber and drag unnecessarily, and that and would that have a material speed difference? 

We reckon we should see closer to 160kt, but we're getting about 145kt TAS at 6,000'.  We've just had her polished which might give us back a few knots but could engine alignment and flaps dragging cause a 10kt type of loss?  Pictures attached.

Thanks for anyone's input on this.  We'd like our speed back :-)

The second half of your post is about rigging.  1/2 inch alerion droop on each side is common.  Spec is 0 to 2 degree droop on the travel boards,   With the gap tolerances in the rod ends they tend to ride up higher in flight and generally a little above the flaps..But the 1 inch difference in flight is not normal. 

However do not mess with the rigging until you fix the engine droop/alignment first.   You will just be chasing your tail.

There is static rigging and dynamic rigging.  Since you are in the UK here are 2 excellent KNR Shoptalk articles that are clear and pragmatic.  Also see the discussion in Mooney Flyer on page 8.

As Clarence (MSC in Ontario) advised:

1. Flight control rigging is not too hard. Locate and replace all worn and sloppy rod end bearings.
2. All are essentially the same, lock the two yokes together with a straight edge across the control wheels.
3. Adjust the lower center bell crank under the floor with the off set per the manual or install the rig pin per the manual.
4. Adjust the left and right wing bell cranks per the manual by use of the wing push rod..
5. Adjust the left and right aileron short rods from the bell crank to the aileron for up to two degrees of droop in the static position, generally more droop for faster planes.
6. Adjust the left and right flap up stop bolts to zero degrees as measured with the correct travel board.
7. Test fly the plane.
   1. You should end up with aileron and flap trailing edges aligned at cruise speed with the ball centered.
   2. If not you will have to make small adjustments. (this is the "dynamic rigging" and may include adjusting {bending} the aileron tabs carefully)
8. I never bend the aileron trailing edges with wide vice grips as shown in the manual. I use two long boards clamped to the trailing edge with many clamps so I end up bending the entire edge a very small amount and never end up with waves caused by vice grips.

Clarence

https://knr-inc.com/shoptalk-articles.html?view=article&id=75&catid=25

https://knr-inc.com/shoptalk-articles.html?view=article&id=106&catid=25

https://themooneyflyer.com/issues/2017-OctTMF.pdf

Edited December 3, 2023 by 1980Mooney

[Alan Maurer]

Hello Steven, I just had the exact same prop sag problem.....You need a new set of engine mounts. And you will go faster.....Ailerons ,I cannot tell but the low sitting prop is an engine mount problem. 

[Aerodon]

So I had this problem on a C172 180hp upgrade I did recently.  Followed the manual exactly and had a bit of spinner backplate rubbing in flight.  I replaced all the cowl mounts, as well as trimmed the front engine baffle that was pulling the cowl forward.  But the real problem - I looked at the old engine and found a set of 'double' washers in the engine box with the old engine.  Apparently it is quite common to have two of the 0.125 washers on the lower mounts.  This makes about 3/8" difference upwards at the spinner.

So the lesson is look carefully before you remove your old engine mounts, and don't be shy to put extra washers on the bottom mounts.

 

Aerodon

[EricJ]

3 minutes ago, Aerodon said:

So I had this problem on a C172 180hp upgrade I did recently.  Filled the manual exactly and had a bit of spinner backplate rubbing in flight.  I replaced all the cowl mounts, as well as trimmed the front engine baffle that was pulling the cowl forward.  But the real problem - I looked at the old engine and found a set of 'double' washers in the engine box with the old engine.  Apparently it is quite common to have two of the 0.125 washers on the lower mounts.  This makes about 3/8" difference upwards at the spinner.

So the lesson is look carefully before you remove your old engine mounts, and don't be shy to put extra washers on the bottom mounts.

Aerodon

Yes, Maxwells told me they did this to my airplane to get it back where it should be.   They also said it's shimmed as far as one can expect to get away with, so if it sags more it'll need new mounts.    It hasn't moved noticeably in six years.

[StevenF]

Thanks everyone!  Most enlightening and helpful.

We now have a basis to have a talk to our Maintenance Organisation.

Cheers!

[StevenF]

11 hours ago, 1980Mooney said:

The second half of your post is about rigging.  1/2 inch alerion droop on each side is common.  Spec is 0 to 2 degree droop on the travel boards,   With the gap tolerances in the rod ends they tend to ride up higher in flight and generally a little above the flaps..But the 1 inch difference in flight is not normal. 

However do not mess with the rigging until you fix the engine droop/alignment first.   You will just be chasing your tail.

There is static rigging and dynamic rigging.  Since you are in the UK here are 2 excellent KNR Shoptalk articles that are clear and pragmatic.  Also see the discussion in Mooney Flyer on page 8.

As Clarence (MSC in Ontario) advised:

1. Flight control rigging is not too hard. Locate and replace all worn and sloppy rod end bearings.
2. All are essentially the same, lock the two yokes together with a straight edge across the control wheels.
3. Adjust the lower center bell crank under the floor with the off set per the manual or install the rig pin per the manual.
4. Adjust the left and right wing bell cranks per the manual by use of the wing push rod..
5. Adjust the left and right aileron short rods from the bell crank to the aileron for up to two degrees of droop in the static position, generally more droop for faster planes.
6. Adjust the left and right flap up stop bolts to zero degrees as measured with the correct travel board.
7. Test fly the plane.
   1. You should end up with aileron and flap trailing edges aligned at cruise speed with the ball centered.
   2. If not you will have to make small adjustments. (this is the "dynamic rigging" and may include adjusting {bending} the aileron tabs carefully)
8. I never bend the aileron trailing edges with wide vice grips as shown in the manual. I use two long boards clamped to the trailing edge with many clamps so I end up bending the entire edge a very small amount and never end up with waves caused by vice grips.

Clarence

https://knr-inc.com/shoptalk-articles.html?view=article&id=75&catid=25

https://knr-inc.com/shoptalk-articles.html?view=article&id=106&catid=25

https://themooneyflyer.com/issues/2017-OctTMF.pdf

Really helpful information, thanks for this.  I would hope our shop knows, but it's worth checking.  Appreciate it.

[EricJ]

9 hours ago, StevenF said:

Really helpful information, thanks for this.  I would hope our shop knows, but it's worth checking.  Appreciate it.

Let us know how it goes!  

[StevenF]

Bit of feedback just to let everyone who helpfully suggested know.  The mounts were shot and replaced at the annual, and testing indicates with ceramic polish and the engine pointing the right way we have gained 7 or 8 knots at high speed cruise.  We're still down a few on where we think it should be, but we have a Hartzel prop that is end of life and we think that's costing us 5 knots, and has been disappointing since it was fitted years ago.  We are considering replacing with either the original spec McCauley, or possibly the MT 3 blade which we've heard good things about.  Anyone got any thoughts to share on MT versus the standard Mac?  We have a healthy debate going on that Mooney would have fitted whatever was best at the time, however things have moved on in the last 40 years, and we've heard amazing stories about performance with the MT fitted to a J.

[redbaron1982]

1 hour ago, StevenF said:

Bit of feedback just to let everyone who helpfully suggested know.  The mounts were shot and replaced at the annual, and testing indicates with ceramic polish and the engine pointing the right way we have gained 7 or 8 knots at high speed cruise.  We're still down a few on where we think it should be, but we have a Hartzel prop that is end of life and we think that's costing us 5 knots, and has been disappointing since it was fitted years ago.  We are considering replacing with either the original spec McCauley, or possibly the MT 3 blade which we've heard good things about.  Anyone got any thoughts to share on MT versus the standard Mac?  We have a healthy debate going on that Mooney would have fitted whatever was best at the time, however things have moved on in the last 40 years, and we've heard amazing stories about performance with the MT fitted to a J.

Cruise speed wise, the MT 3 Blades runs a few knots slower than the original prop. You do get better climb performance though. 

I have a MT and the only negative thing I see is that the paint is piling off at the tip of the blades. I will have to have it refinished soon. 

[Ragsf15e]

4 hours ago, StevenF said:

Bit of feedback just to let everyone who helpfully suggested know.  The mounts were shot and replaced at the annual, and testing indicates with ceramic polish and the engine pointing the right way we have gained 7 or 8 knots at high speed cruise.  We're still down a few on where we think it should be, but we have a Hartzel prop that is end of life and we think that's costing us 5 knots, and has been disappointing since it was fitted years ago.  We are considering replacing with either the original spec McCauley, or possibly the MT 3 blade which we've heard good things about.  Anyone got any thoughts to share on MT versus the standard Mac?  We have a healthy debate going on that Mooney would have fitted whatever was best at the time, however things have moved on in the last 40 years, and we've heard amazing stories about performance with the MT fitted to a J.

Consensus here has been that any 3 blade costs you a few knots.  That being said, 5 seems high.  Were they able to check the rigging carefully and make sure the flaps come all the way up?  Rigging costs more speed than most people think.  Gear not fully retracting (worn gear parts or not set up right) could also be an issue.  Here’s how my gear looks when up.

[EricJ]

1 hour ago, Ragsf15e said:

Consensus here has been that any 3 blade costs you a few knots.  That being said, 5 seems high.  Were they able to check the rigging carefully and make sure the flaps come all the way up?  Rigging costs more speed than most people think.  Gear not fully retracting (worn gear parts or not set up right) could also be an issue.  Here’s how my gear looks when up.

You could rotate your brakes, you know.   That's, like, six knots right there.   

[EricJ]

5 hours ago, StevenF said:

Bit of feedback just to let everyone who helpfully suggested know.  The mounts were shot and replaced at the annual, and testing indicates with ceramic polish and the engine pointing the right way we have gained 7 or 8 knots at high speed cruise.  We're still down a few on where we think it should be, but we have a Hartzel prop that is end of life and we think that's costing us 5 knots, and has been disappointing since it was fitted years ago.  We are considering replacing with either the original spec McCauley, or possibly the MT 3 blade which we've heard good things about.  Anyone got any thoughts to share on MT versus the standard Mac?  We have a healthy debate going on that Mooney would have fitted whatever was best at the time, however things have moved on in the last 40 years, and we've heard amazing stories about performance with the MT fitted to a J.

The Hartzell two-blade top prop isn't slower than the McCauley or any other prop.   It's a little heavier, but not much, and supposedly quieter.    It's highly unlikely to be costing you any speed unless there's something wrong with it.

[201Mooniac]

When I installed the MT 3 blade, I found it about 1 kt slower.  Also, the more recent ones seem to have addressed the paint peeling issue which was a problem for early ones.  I've had no issues at all with mine and like the weight savings, the smaller prop diameter, and the looks.