IO550G =>IO550N

[ronr]

I am about to have my IO550G-AP (310 HP modification from Midwest) overhauled.

Replacing the G cylinders with N cylinders has been recommended (and makes sense to me given the lighter weight and consequent moving of the CG a bit more aft).  Also recommended by the overhaul shop, who indicates he had done a number of these in the past.

But reading through the verbiage of the engine and propeller STC's, I don't see where that is an allowed modification.

The Propeller STC clearly states that it (the Propeller STC) is valid for either a G or an N engine, but I can't seem to locate anything that directly allows the replacement with N cylinders. 

And the TCDS calls for one of several IO550G's.

What am I missing?

Thanks

[carusoam]

ron,

I went with the (N) engine via STC for the 310HP...

Solely for the weight savings...

Some Brand Ci owners have experienced cylinder cracks... on their (N)s...

I have had no issues...

Read up on max FF setting... and keeping CHTs in check...

In the STC for the 310HP... they list the engines...

It probably requires interpretation to change the (G) to the (N)...

90% changing cylinders... 9% changing govenor... 1% changing tach graphics...

 

Lets invite @StevenL757 to the conversation... He knows many of the details and where to find the pen that wrote the details...   

Best regards,

-a-

[StevenL757]

23 hours ago, ronr said:

I am about to have my IO550G-AP (310 HP modification from Midwest) overhauled.

Replacing the G cylinders with N cylinders has been recommended (and makes sense to me given the lighter weight and consequent moving of the CG a bit more aft).  Also recommended by the overhaul shop, who indicates he had done a number of these in the past.

But reading through the verbiage of the engine and propeller STC's, I don't see where that is an allowed modification.

The Propeller STC clearly states that it (the Propeller STC) is valid for either a G or an N engine, but I can't seem to locate anything that directly allows the replacement with N cylinders. 

And the TCDS calls for one of several IO550G's.

What am I missing?

Thanks

Ron, given you already have approval for the 310HP STC on your airplane, CMI (via Service Bulletin M75-6R1 - attached below) allows install of "N" cylinders on the "G" engine (within the same "engine family"), so long as all other related components are replaced as well.  Some of the differences are (your shop should be able to speak to these.  If not, I can provide more context)...

• Intake & fuel system differences.  For example, the "N" engine has a venturi insert on the valve side, whereas the "G" is straight.  The "N" generates about 1.5 to 2% more power over the "G".
• You'll need three pieces of aluminum sheet metal (two on the front of the engine, one on the rear) fabricated into small "wedges" to plug the gaps between the baffles and the cylinder fins.  Mooney has these listed as parts, but they are very easily-made if your OH folks are good with sheet metal.  Bob Minnis - with whom I worked in 2014 for my "N" engine replacement - sent me my three pieces, but has no more on hand.  He sent me the drawings, so I'll dig these out and forward them to you a bit later.  It will save you from having to call Mooney.
• Your engine placard will be modified to indicate "-C -N" to show the conversion.

STC# SA03024CH does allow for you to install the -F7498 (the Acclaim Type-S) model prop to your Ovation.

Steve

M75-6R1.pdf

[ronr]

Steve,

Thanks for that.

In doing some more research I also note that there has been a change in STC SA02193CH.

The STC with my paperwork is ONLY for the installation of the 3-Blade Hartzell prop on the engine.

The current STC verbiage is and, instead of being just for the prop install, is described as being for a power increase by virtue of installation of the prop and either a modified io550G or an IO550N.

I guess that plus the continental SB pretty well nails down the legality.

Ron

[ronr]

10 hours ago, carusoam said:

ron,

I went with the (N) engine via STC for the 310HP...

Solely for the weight savings...

-a-

The overhaul facility felt that he hadn't seen any more cracks in N vs G cylinders.  The Heads are the same.  So I've not been too concerned about that.
He also thought that he had heard that with less weight on the nose there would be a speed increase.  Kind of makes sense theoretically as, with the cg further aft, less down-force needed on the elevator which should equate to less drag. (Whether it is significant or not is beyond me to calculate).

Thanks for your thoughts.

Ron

[ronr]

@StevenL757 or @carusoam  Overhauled engine/prop etc finally back and being re-installed.  It has the N cylinders.

Neither I nor my IA have been able to locate online guidance regarding weight and balance computation.  From what I've read, the N is either 18 or 18.3 lbs lighter than then G, but I haven't found anything official about re-computing the W&B when modifying an Ovation with this change.

What did you all do?

Thanks.

Ron

[GeeBee]

Personally, I reweigh my airplane every 5 years. You might be surprised at the outcome. Continuing re-calculations rarely work out and if you are careful with the fueling for the weighing, you can pick up a little payload.

[Scottknoll]

Curious how close the reweigh is to the math? I know 135 requires it every 3 years, so a fed somewhere thought it was worth someone else’s expense…

Not advocating one way or the other. I’m just not aware of any actual data showing the difference between the calculations and a proper scale weight after X number of years.

Personally, I avoid the scale. I already know I take in more calories than I use. Don’t need a scale tell me that. Lol

[StevenL757]

8 hours ago, ronr said:

@StevenL757 or @carusoam  Overhauled engine/prop etc finally back and being re-installed.  It has the N cylinders.

Neither I nor my IA have been able to locate online guidance regarding weight and balance computation.  From what I've read, the N is either 18 or 18.3 lbs lighter than then G, but I haven't found anything official about re-computing the W&B when modifying an Ovation with this change.

What did you all do?

Thanks.

Ron

Glad to hear you got everything back and progress is being made.  Been awhile since we talked, and I know you’ve been waiting awhile.

When mine was done in 2014, I know we weighed everything (engine, old hoses, etc.) that came out, and also everything that went in, but I’d have to look at the books to see what we did.  I do know the weight savings was fairly decent (about 15 pounds loss from the “G” engine).  I just got back from the hangar, but will be there in the morning.  I’ll also chat with my IA in Texas who did the work and get you a better answer.

[ronr]

20 hours ago, GeeBee said:

Personally, I reweigh my airplane every 5 years. You might be surprised at the outcome. Continuing re-calculations rarely work out and if you are careful with the fueling for the weighing, you can pick up a little payload.

I weighed a previous Mooney (an M20E) once, about 30 or so years after it came out of the factory. We did it because my IA just got a set of scales and wanted to try them out.  I lost about 70-80 lbs useful load!  Hence my reluctance. 

[ronr]

20 hours ago, Scottknoll said:

Curious how close the reweigh is to the math? I know 135 requires it every 3 years, so a fed somewhere thought it was worth someone else’s expense…

Not advocating one way or the other. I’m just not aware of any actual data showing the difference between the calculations and a proper scale weight after X number of years.

Personally, I avoid the scale. I already know I take in more calories than I use. Don’t need a scale tell me that. Lol

I think in older airplanes, that have mods done over the years, certain things (old cables, conduits, etc) may not get removed, and contribute to inaccuracies in the calculations.

[ronr]

19 hours ago, StevenL757 said:

Glad to hear you got everything back and progress is being made.  Been awhile since we talked, and I know you’ve been waiting awhile.

When mine was done in 2014, I know we weighed everything (engine, old hoses, etc.) that came out, and also everything that went in, but I’d have to look at the books to see what we did.  I do know the weight savings was fairly decent (about 15 pounds loss from the “G” engine).  I just got back from the hangar, but will be there in the morning.  I’ll also chat with my IA in Texas who did the work and get you a better answer.

I look forward to it. 

First one hr flight today with new engine.  Everything seemed nominal except idle speed too high.  But that'll be adjusted when they uncowl for the post flight inspection.  Seems to be running well. And I'll be looking at the download from my JPI later on.

[GeeBee]

The trick is to make sure you know where the "full mark" actually is on your tank and weigh it tanks full with not a drop more (ahem!), then subtract the fuel. You can usually do well.