Monroy Fuel Conversion

[JD.O2]

I recently purchased a 20J Missile with the Monroy Conversion (w/ speedbrakes), but it looks like the flight manual supplement is missing. Does anyone out there have a fuel conversion table?

Edited April 30, 2023 by JD.O2

[Fly Boomer]

2 hours ago, JD.O2 said:

I recently purchased a 20J Missile with the Monroy Conversion (w/ speedbrakes), but it looks like the flight manual supplement is missing. Does anyone out there have a fuel conversion table?

Welcome to MooneySpace!  If you have been hanging out, you may already know we have several Missile owners here.  I'm sure someone will be along shortly.

[1980Mooney]

8 hours ago, JD.O2 said:

I recently purchased a 20J Missile with the Monroy Conversion (w/ speedbrakes), but it looks like the flight manual supplement is missing. Does anyone out there have a fuel conversion table?

I had Monroy auxiliary tanks installed in my J more than 20 years ago.  I have all the paperwork including the full installation manual and drawings. 

If you are looking in the Supplement for a conversion table for your panel gauges, there isn't any.  The Supplement does have a table for you to manually stick measure the auxiliary tanks. 

The auxiliary tank drains into the main tank through a single line.  The auxiliary tanks sit outboard and slightly higher than the main tank.  Since you have speed brakes the Monroy auxiliary tanks hold only 14.5 gal.  (vs. 17 gal. for those without speed brakes). 

When the main tank is half full the panel fuel gauge reads accurately.  When it says "16" gallons on your plane then that is what you have.  When it says "Full" then you have 46.5 gallons on that wing. So the first half spans 16 gallons and the last half spans 30.5 gallons.  I don't think it is linear.  I have 98 gallons total capacity.  If I am at 98 (49 gal per side) or at 80 total (40 gal per side) the panel gauge reads about the same - i.e. "Full".

The line between the auxiliary tank and the main tank has AN-6D fittings.  I think that is 3/8 OD pipe and only about 0.3 inch ID.  The point being that the gravity flow between the tanks is slow.  If your main tanks are below 1/2 (16 gal) and you fill them full to the lip your panel fuel gauge will read full.  Wait about 10 minutes and 8-10 gallons a side will flow into each auxiliary tank.  Your panel fuel gauges will read about 2/3 to 3/4 full (24 gallons on your gauges).  

I use the Fuel Totalizer to keep tabs on the fuel when I am above 1/2 tank.. Between 1/2 and Full, the panel gauges just give me a rough idea of fuel on board.   However I do know when my panel reads 1/2 full I know I have 16 gallons left in the tank.

 

 

Here is the Supplement for your plane with speed brakes:

[Pinecone]

The flight manual supplement table on fuel based on inches.  It would work if it were a true aux tank.  But as the level in the Monroy changes, so does the level in the main tank section, so you can’t say I have 2.0 inches in the aux, meaning 8 gallons and X in the mains, so I have X+8.

When I calibrated some dipsticks for my plane, even putting in the last gallon in the aux, I could hear more air bubbling out of the main and the aux level dropped a bit after 5 - 10 minutes

 

[JD.O2]

On 4/30/2023 at 10:28 PM, 1980Mooney said:

I had Monroy auxiliary tanks installed in my J more than 20 years ago.  I have all the paperwork including the full installation manual and drawings. 

If you are looking in the Supplement for a conversion table for your panel gauges, there isn't any.  The Supplement does have a table for you to manually stick measure the auxiliary tanks. 

The auxiliary tank drains into the main tank through a single line.  The auxiliary tanks sit outboard and slightly higher than the main tank.  Since you have speed brakes the Monroy auxiliary tanks hold only 14.5 gal.  (vs. 17 gal. for those without speed brakes). 

When the main tank is half full the panel fuel gauge reads accurately.  When it says "16" gallons on your plane then that is what you have.  When it says "Full" then you have 46.5 gallons on that wing. So the first half spans 16 gallons and the last half spans 30.5 gallons.  I don't think it is linear.  I have 98 gallons total capacity.  If I am at 98 (49 gal per side) or at 80 total (40 gal per side) the panel gauge reads about the same - i.e. "Full".

The line between the auxiliary tank and the main tank has AN-6D fittings.  I think that is 3/8 OD pipe and only about 0.3 inch ID.  The point being that the gravity flow between the tanks is slow.  If your main tanks are below 1/2 (16 gal) and you fill them full to the lip your panel fuel gauge will read full.  Wait about 10 minutes and 8-10 gallons a side will flow into each auxiliary tank.  Your panel fuel gauges will read about 2/3 to 3/4 full (24 gallons on your gauges).  

I use the Fuel Totalizer to keep tabs on the fuel when I am above 1/2 tank.. Between 1/2 and Full, the panel gauges just give me a rough idea of fuel on board.   However I do know when my panel reads 1/2 full I know I have 16 gallons left in the tank.

 

 

Here is the Supplement for your plane with speed brakes:

Thank you! This is exactly what I was looking for. I’m not sure how or why this was left out of my AFM, but I need to get to get to work and update the supplemental section.