Prop indexing / install

[Scott MacMoyle]

I have a Grumman Tiger with a McCauley Prop which has a 200 hour dye pen AD against it. I did it and it passed but I want to do a prop balance to make it as smooth as possible. Eventually upgrade but not for a year. Anyway, When installing the prop the clock angle given by the book is as viewed by the pilot seat correct ? Or viewed by the guy installing it ? I was always taught everything is as viewed by the pilot seat. Also. Isnt indexing for ease of hand propping or is it something else ?

 

[Clip4]

I am sure an FAA certified mechanic would know the answer.

 

[Scott MacMoyle]

Ouch ! I have beeen an FAA certified mechanic/IA for over 30 years but my expertise is not in General Aviation. I only do GA as a hobby so I covet advise from guys who specialize in this area

 

[Doc Holliday]

Ouch ! I have beeen an FAA certified mechanic/IA for over 30 years but my expertise is not in General Aviation. I only do GA as a hobby so I covet advise from guys who specialize in this area

There are several Grumman gurus on the board, I'm sure one will chime in. I don't have any manuals on the Grumman or Lycoming/McCauley here.

FWIW, when I have installed props I always marked everything before removing to make sure it went back the way it came off. Also, after installing I would note the tip position and swing the other blade around to see how close the track was. If the track was off, I would move a bolt hole over and try it again. Blades out of track will cause vibration.

I use to do dynamic prop balancing using an ACES 2020 probalancer.

 

[Scott MacMoyle]

Thanks, Its an overhauled engine so all marks on the starter gear are gone but I did check the track and is good. I have an old Chadwick Helmuth 177M from back in the day. Its was used to track and balance helicopter main and tail rotor blades. It will work on a prop as well as its really similar to a tail rotor when it comes to balance. I think I am all good. I was just wondering about it. I use to do alot of helicopter maintenance when I was younger.

 

[Doc Holliday]

Thanks, Its an overhauled engine so all marks on the starter gear are gone but I did check the track and is good. I have an old Chadwick Helmuth 177M from back in the day. Its was used to track and balance helicopter main and tail rotor blades. It will work on a prop as well as its really similar to a tail rotor when it comes to balance. I think I am all good. I was just wondering about it. I use to do alot of helicopter maintenance when I was younger.

Good deal, and you're correct on the track and balance. I only used a Chadwick a few times years ago. Old tech, but effective. The ACES was very simple to use.

 

[Salty]

The prop flange and hub should be indexed so there’s only one way to install it, unless you removed the indexing.

 

[Salty]

Note the shorter bushing and the hub bolt with no space for the bushing.

 

[Bell206]

When installing the prop the clock angle given by the book is as viewed by the pilot seat correct ?

Don't know Grummans much but I thought it was more a bushing/serial number type index than a clock position as shown above. As for the 177 for balance, used it on props for a number of years until wasn't worth fixing then went to the 2020 also. And regardless which method you use to balance the prop be sure to index the backplate/spinner/prop as an assembly. I used to print out a decal that stated these items were an assembly and attached a decal to each item after I completed the balancing. But it sounds like you have everything else in order. Good luck.

 

[bkspero]

Here is a link to a posting on the Grumman Gang by the late Bob Steward in which he goes through clocking a prop. It is about as close to gospel as anything there gets. The original poster was asking about his Cheetah, but the guidance holds for Tigers, too.

http://grumman.net/archive/2009/msg01420.html

The net result, if I read it correctly, is that, when the engine is stopped by pulling the mixture the prop will stop with a blade in the 1-2 o'clock position when viewed from the cabin. And that this results in both lowest vibration and easiest hand propping.

 

[Doc Holliday]

Great info.

 

[Scott MacMoyle]

Yes, Great info indeed. Thanks so much. I agree. #1 at TDC and blade at 1 oclock as viewed from cabin. I also have a punched out spinner back plate. This is why I am going into overkill on this issue. Lots of people have messed up installing the prop which makes me think the prop AD came about due to poor installation rather than a bad prop design. I tape the back plate to the cowl and make sure all bolts can be screwed down by hand before putting a torque wrench to them.

 

[Dan Thomas]

Note the shorter bushing and the hub bolt with no space for the bushing. View attachment 80556 View attachment 80558

That's for a constant-speed propeller installation. The Tiger has a fixed-pitch prop. The Tiger's prop flange won't look like that.

 

[Dan Thomas]

Yes, Great info indeed. Thanks so much. I agree. #1 at TDC and blade at 1 oclock as viewed from cabin. I also have a punched out spinner back plate. This is why I am going into overkill on this issue. Lots of people have messed up installing the prop which makes me think the prop AD came about due to poor installation rather than a bad prop design. I tape the back plate to the cowl and make sure all bolts can be screwed down by hand before putting a torque wrench to them.

The installation instructions in the manual are for the mechanic, who is not in the pilot's seat when he installs the prop. Cessna will tell you to set the crank so that #1 is at TDC, then hold the prop vertical and rotate it to the right, or clockwise (as seen by the mechanic) until the bolt holes line up with the crank flange holes. That'll put the prop at about 2:00 - 8:00 as seen by the mechanic, which is where we want it for hand-propping. The impulse mag clicks at about TDC, so you want that downgoing blade at around 7:30 or 8 o'clock when it does that. Anywhere else makes hand-propping awkward and dangerous.

 

[Dan Thomas]

Here is a link to a posting on the Grumman Gang by the late Bob Steward in which he goes through clocking a prop. It is about as close to gospel as anything there gets. The original poster was asking about his Cheetah, but the guidance holds for Tigers, too.

http://grumman.net/archive/2009/msg01420.html

The net result, if I read it correctly, is that, when the engine is stopped by pulling the mixture the prop will stop with a blade in the 1-2 o'clock position when viewed from the cabin. And that this results in both lowest vibration and easiest hand propping.

That isn't the TDC position, though. If you clock it there with the crank at TDC, it will stop at a position about 90° to that. The natural place for an engine to stop is with one piston halfway up its compression stroke and another halfway down its power stroke (unfired, of course), balancing each other, and that's 90° to TDC.

 

[bkspero]

That isn't the TDC position, though. If you clock it there with the crank at TDC, it will stop at a position about 90° to that. The natural place for an engine to stop is with one piston halfway up its compression stroke and another halfway down its power stroke (unfired, of course), balancing each other, and that's 90° to TDC.

I think that is what Bob's note says (or maybe I was reading into it based on other postings there<G>). At TDC the prop is installed at the 10-11 o'clock position when viewed from the cabin (1-2 o'clock when viewed from the front looking towards the rear). As a result the prop stops at the 1-2 o'clock position viewed from the cabin (10-11 o'clock when viewed from the front) when the mixture is pulled (consistent with your guidance that it stops at about 90 degrees to the TDC install location).

 

[1RTK1]

This is from Gary Vogt a Grumman guru his words are golden. I asked him the question on where the prop should stop on shut down. Mine has a Sensenich.


Depends on the plane and the prop.
sitting in the plane and looking at the prop
Tiger w/Sensenich: It should be at the 10 o’clock position.

 

[Dan Thomas]

I think that is what Bob's note says (or maybe I was reading into it based on other postings there<G>). At TDC the prop is installed at the 10-11 o'clock position when viewed from the cabin (1-2 o'clock when viewed from the front looking towards the rear). As a result the prop stops at the 1-2 o'clock position viewed from the cabin (10-11 o'clock when viewed from the front) when the mixture is pulled (consistent with your guidance that it stops at about 90 degrees to the TDC install location).

Yup.

 

[Dan Thomas]

This is from Gary Vogt a Grumman guru his words are golden. I asked him the question on where the prop should stop on shut down. Mine has a Sensenich.


Depends on the plane and the prop.
sitting in the plane and looking at the prop
Tiger w/Sensenich: It should be at the 10 o’clock position.

The authority here is not me or any Grumman guru or SGOTI. The authority is the maintenance manual for that make and model of airplane. The manual is written by the people (engineers) who designed that airplane and tested it, and the manual is FAA-approved. One deviates from it at his own risk.

There is a LOT of folklore passed around the GA community, and some of it can result in bad maintenance practices. I've had to repair a lot of stuff because of that sort of advice. I've also been dismayed by the lack of relevant manuals in some shops, in direct contravention of the regulations that state that maintenance shall be done to the latest version of the manufacturer's recommendations.

 

[1RTK1]

Agreed, although the engineers that designed the tiger said one thing and later it was changed, assuming McCauley prop.

 

[Dan Thomas]

Agreed, although the engineers that designed the tiger said one thing and later it was changed, assuming McCauley prop.

Quite possible. Different props have different vibrational modes, and the indexing position can influence some of that and possibly result in more vibration that fatigues the prop. The TCDS for the airplane, for instance, will list the minimum diameter of the particular prop installed to avoid such destructive vibration or blade flutter. Some airplanes have a yellow arc on the tachometer where cruising is prohibited; one can pass through that arc on acceleration or deceleration, but not stay there. That's a prop vibration problem range. For instance, we see in the Piper PA-28 TCDS this paragraph:

[Note 10]
All PA-28 models with Lycoming O-360-A3A engine and Sensenich propeller Model M76EMM-0, M76EMMS-0, 76EM8S5-0, or 76EM8-0 must avoid continuous operation between 2150 and 2350 r.p.m. Placards must be installed in accordance with Piper Service Letter No. 526, and Airplane Flight Manual Supplement No. 1, dated April 22, 1969.

Piper's Service Letter 526 is based on Sensenich's Service Bulletin R-13, here:
https://www.sensenich.com/wp-content/uploads/2018/01/Service_Bulletins_R-13_1263314519.pdf

 

[1RTK1]

Yep, the tiger has a yellow range with the McCauley prop, but with the sensenich it is removed.

 

[Bell206]

the manual is FAA-approved.

Just a minor point. The manual is only acceptable data except if there is a Airworthiness Limits/Life Limits manual section which is FAA approved.

the regulations that state that maintenance shall be done to the latest version of the manufacturer's recommendations.

FYI: There are actually 3 options to perform maintenance from per 43.13. While the MM is preferred it is not the only option. And technically it states "current" manual version which as defined by FAA guidance means "current" at the aircraft time of manufacture not what is current today. This was a hot topic when Cessna slipped in a repetitive eddy current inspection into the Airworthiness Limitations section on a 210. It took a few months to fix but the FAA head shed and Legal hammered the ACO that approved the ALS revision and issued an LOI defining current meant at time of mfgr so no older 210s were required to perform the inspection but new ones would be. It's also partly due to the APA Act where OEMs can't legislate new rules on aircraft owners.

 

[JAWS]

I've also been dismayed by the lack of relevant manuals in some shops, in direct contravention of the regulations that state that maintenance shall be done to the latest version of the manufacturer's

That is a Canadian requirement. As bell206 pointed out, current has been defined by the FAA as at the time of manufacture. Canada used "the most recent", which leaves little wiggle room during an audit.

 

[bkspero]

This is from Gary Vogt a Grumman guru his words are golden. I asked him the question on where the prop should stop on shut down. Mine has a Sensenich.


Depends on the plane and the prop.
sitting in the plane and looking at the prop
Tiger w/Sensenich: It should be at the 10 o’clock position.

My experience with him is different. My Tiger had been maintained by Gary prior to my purchase and he installed its Sensenich prop after its engine overhaul. That prop stops at 1-2 o'clock when viewed from the airplane cabin. You can also see the 1-2 o'clock from the cabin orientation in some photos on his AuCountry.com website. I've attached one for reference.

 

[1RTK1]

That’s a quandary

 

[Dan Thomas]

View attachment 80593

My experience with him is different. My Tiger had been maintained by Gary prior to my purchase and he installed its Sensenich prop after its engine overhaul. That prop stops at 1-2 o'clock when viewed from the airplane cabin. You can also see the 1-2 o'clock from the cabin orientation in some photos on his AuCountry.com website. I've attached one for reference.

That's where it should stop for most installations. It will have been installed at the 10-11 o'clock position as seen from the cabin, or the 1-2 o'clock as seen by the installer, when the crank was at TDC. If a maintenance manual specifies otherwise, they have good reason for it, and vibration might be a big factor.

There's a lot of stuff in maintenance manuals that is mistakenly taken across by mechanics to other airplanes where that procedure, specification or advice does not apply. Prop position is only one area that a mechanic might think that if a 172's prop gets installed this way, then a Tiger's does, too. Even between various models of the 172 I have found that mechanics will have been using the wrong lubricant on electric flap actuators, for instance. The old airplanes used a molybdenum disulfide grease on the jackscrew, so some mechanics just kept using it as the screw technology changed. They didn't check the relevant manuals. There were three different actuators used, and they required different lubes. Since about 1969(?) they used a recirculating-ball jackscrew that required a bit of No. 10 non-paraffinic oil to be wiped on it with a clean rag, just to dampen it, but I had to remove several actuators to clean out the moly grease, which will gum up those newer actuators. Could flat-spot the balls and so on. As bad are the guys that spritz LPS all over it, which drips into the microswitches and gums them up and fouls their contacts so that one day the flaps either won't extend or won''t retract.

 

[3393RP]

That's for a constant-speed propeller installation. The Tiger has a fixed-pitch prop. The Tiger's prop flange won't look like that.

Sometimes Google doesn't have all the answers.