Aux Tank option in M20J. How much fuel in Main before Crossover?

[Missile=Awesome]

Our M20J/Missile 300 has 32 Gallons each side and a 17 Aux Bay tank option installed.  Anybody (paging Jose) know at WHAT AMOUNT of fuel in main does crossover into AUX tank begin?  I have heard 10,15,25,tabs.  What is the EXACT amount?  Anybody KNOW?  Please no guessing as I already have a LOT of that.  The wing gauges show what is in main with further panel reading on quantity.  Thanks for knowledgeable replies and experience.  This is NOT a cue for Cies senders (thank you for NOT going there)

 

[carusoam]

Seeing if @Gagarin is around today... (tech question regarding fuel tank, fuel level, and extended tanks...)

Best regards,

-a-

[anthonydesmet]

Jose has not been around for quite some time.  Talked to Edison at WetWing last year, Jose had been at the airport a couple times.  For your answer I would also try and give Edison at WetWingologists, Paul at Weep or Don Maxwell.  Those three have seen it all and probably have documentation.

[wpbarnar]

The cross over from the mains into the aux begins at approximately 50% capacity of your main tanks, at least that was the case in my Encore. (37.5 main & 15 aux)
If I filled my mains and added nothing to the aux,  given time the mains would equalize into the aux  and the main tank level would decrease indicating about 18 gallons.    The fuel level gauge would remain there until the aux was empty.

I suspect there is minor differences from airplane to airplane depending on the installation.  You  can determine your crossover point by  very slowly adding fuel to the main and observing the aux for the first indication of fuel in the bottom inboard side of aux.    I emphasized slowly as I could easily fill my mains up with very little going into the aux until they sat for a few minutes.

Knowing the actual amount per side was a challenge while flying.  If the indicated amount was above 18 gallons, then that wing contained the indicated amount plus some quantity in the aux.   When potentially starting out with 52 gallons per wing,  only when the indicated amount drops below the cross over point does the fuel gauge actually become representative is the downside of the Monroy system.   An accurate fuel totalizer can be very beneficial.

Bill

Edited August 10, 2020 by wpbarnar
Typo

[Missile=Awesome]

1 hour ago, wpbarnar said:

The cross over from the mains into the aux begins at approximately 50% capacity of your main tanks, at least that was the case in my Encore. (37.5 main & 15 aux)
If I filled my mains and added nothing to the aux,  given time the mains would equalize into the aux  and the main tank level would decrease indicating about 18 gallons.    The fuel level gauge would remain there until the aux was empty.

I suspect there is minor differences from airplane to airplane depending on the installation.  You  can determine your crossover point by  very slowly adding fuel to the main and observing the aux for the first indication of fuel in the bottom inboard side of aux.    I emphasized slowly as I could easily fill my mains up with very little going into the aux until they sat for a few minutes.

Knowing the actual amount per side was a challenge while flying.  If the indicated amount was above 18 gallons, then that wing contained the indicated amount plus some quantity in the aux.   When potentially starting out with 52 gallons per wing,  only when the indicated amount drops below the cross over point does the fuel gauge actually become representative is the downside of the Monroy system.   An accurate fuel totalizer can be very beneficial.

Bill

Thanks Bill.  Very helpful.  Hoping someone that flies a J with the Monroy tanks can also lend some input to “Their” experience as your tank totals are different than my J.  Of course agree there will be some minor variance depending on the install/airframe.  Anybody have the 32 Main plus 17 AUX set up that cares to comment?  I will FILL the mains now that we have the tanks resealed and observe the level next day AND when the gauges start to move in future.  Just trying to be knowledgeable as I can...Hoping others have cracked “the code” like you have.

 

[carusoam]

@Gagarin / José / Piloto / Mr. Monroy is still around here...

Some health issues along the way haven’t slowed him too much.... 
 

Using WD40 as a speed mod may get him banned for a couple of days.... but nothing longer... 

Best regards,

-a-

[N56394]

I have a Missile 1983/2001 with speed brakes and am also interested in this discussion. As any Missile owner knows we are constantly flirting with the forward edge of the envelope. I have been trying to determine how adding these tanks affects the CG arm during the fuel burn. only data I can find so far is the 10-12 lbs @ 71 inches for the install weight and 15 gal per wing if speed brakes installed. If anyone can reveal the fuel arm for the Monroy aux tank it would be great. I have had the Missile for almost 20 years without the tanks, but am seriously considering the mod now as my flight mission is changing to visit kids far away.

[Missile=Awesome]

21 minutes ago, N56394 said:

I have a Missile 1983/2001 with speed brakes and am also interested in this discussion. As any Missile owner knows we are constantly flirting with the forward edge of the envelope. I have been trying to determine how adding these tanks affects the CG arm during the fuel burn. only data I can find so far is the 10-12 lbs @ 71 inches for the install weight and 15 gal per wing if speed brakes installed. If anyone can reveal the fuel arm for the Monroy aux tank it would be great. I have had the Missile for almost 20 years without the tanks, but am seriously considering the mod now as my flight mission is changing to visit kids far away.

Here is WnB Pro Ap with my common loadout (passengers and baggage and increasing fuel to 90 gallons.  Hope this helps.  It appears that the cross-over is right around 15-17 gallons into AUX.  With ten gallons in main AUX is dry.  With 15-17 gallons in main when you rock the plane you see a little fuel (more a stain showing than actual fuel in tank) in AUX.  My guess is that the tanks will begin functioning when you have 90lbs remaining in Mains.  Call it 15 gallons.  That is an hour of flight in a Missile or two hours when both fuel gauges begin to function.

[Missile=Awesome]

Jose @Gagarin has been non-responsive to this thread to date...

[N56394]

Thank you for that, so you are using the same arm for the aux tank as the main tank? I thought the aux was aft of the spar and the main was forward of the spar? My basic empty weight is 2206 lbs and arm is 42.2 so with that loading I would be over gross of 62 lbs and forward of the envelope corner at 45. Man, I need to lighten my plane, lol. I just looked at my records and found the ARM for the AUX fuel - look at the attached W&B from Rocket engineering - the AUX fuel is at ARM 71. Recomputing your loading with 64 gal mains and 26 gal aux would put me at an arm of 46 which would be within limits. ( I still need to shed 62 lbs though) Following your logic of half of the mains are used before the aux tank begins to feed that would be even better 32 gal mains and 26 gal aux would be an arm of 45.9 which is almost no change in arm. So this I think puts the mystery to bed. Just make sure you are using the arm of 71 instead of 48.43 for the fuel.

[Missile=Awesome]

52 minutes ago, N56394 said:

Thank you for that, so you are using the same arm for the aux tank as the main tank? I thought the aux was aft of the spar and the main was forward of the spar? My basic empty weight is 2206 lbs and arm is 42.2 so with that loading I would be over gross of 62 lbs and forward of the envelope corner at 45. Man, I need to lighten my plane, lol. I just looked at my records and found the ARM for the AUX fuel - look at the attached W&B from Rocket engineering - the AUX fuel is at ARM 71. Recomputing your loading with 64 gal mains and 26 gal aux would put me at an arm of 46 which would be within limits. ( I still need to shed 62 lbs though) Following your logic of half of the mains are used before the aux tank begins to feed that would be even better 32 gal mains and 26 gal aux would be an arm of 45.9 which is almost no change in arm. So this I think puts the mystery to bed. Just make sure you are using the arm of 71 instead of 48.43 for the fuel.

VERY interesting.  My max fuel is lowered to 75 with a VERY forward CG on takeoff.  Thanks for this.

[N56394]

FYI - When I did my training flight with Rocket Engineering back in 2001 the test pilot had me set my trim a bit nose up from take-off. This has worked well - the bottom of the black indicator is aligned with the top of the take off trim window. After I lug the beast at rotation, and gear goes up the yoke forces are light and flaps up and a final trim tweak to 115 kts and I'm off.

[PJClark]

Chiming in with a Rocket input.

This is a pic of what I look like empty: my Rocket CG is almost right on top of the fuel station smack in the middle of the envelope.  Matter of fact, before my avionics work took the KFC200 and standby vac etc out of the avionics Bay, empty CG was exactly 48 inches...same as fuel.

I have 19 lb of lead charlie weights in the tail which probably accounts for this (installed by some previous owner, I take no credit).  Point is if you have a Missile and you're  fighting forward CG all the time, the 19 lb sacrifice in UL (3 gal of gas) might be worthwhile.

My aux tank station is the same as mains.  I get about the same bleedover as reported above from mains to aux.

Second photo: me, my wife, 85 gallons, and 40 lb baggage

In flight the fuel burn-CG line is almost vertical...trends just slightly forward with no baggage in back

[Missile=Awesome]

So, We have the two batteries on the shelf in the Missile.  I had zero idea that I needed to use 71 in the fuel with Aux tanks...I only have one fuel input available.  Seems weird to use 71 vs. 46...Makes a huge difference on CG station...

[Missile=Awesome]

35 minutes ago, Missile=Awesome said:

VERY interesting.  My max fuel is lowered to 75 with a VERY forward CG on takeoff.  Thanks for this.

Kind of questioning the change with Aux...I have plenty of trim available at take off...

[N56394]

Great info and yes the 19 lbs. in the tail would probably be of huge benefit.

Truth be told, I have an old battery (no acid, just water) loaded into the original Mooney battery box - at 27.5 lbs and an arm of 110 that helps set me back a bit - I can remove if needed.

[N56394]

Did you find your loading sheet from Rocket Engineering? Mine is in the 3 ring binder - there are about 4 loading examples - if the aux tanks were there before the Missile STC it should be there for the station 71...see this wing fuel tank layout for the LR tank - its aft of the spar... https://www.emapa.aero/Monroy-Mooney-Fuel-Increase-Upgrade-p/mooney-fuel-increase-upgrade.htm

 

[Missile=Awesome]

28 minutes ago, N56394 said:

Did you find your loading sheet from Rocket Engineering? Mine is in the 3 ring binder - there are about 4 loading examples - if the aux tanks were there before the Missile STC it should be there for the station 71...see this wing fuel tank layout for the LR tank - its aft of the spar... https://www.emapa.aero/Monroy-Mooney-Fuel-Increase-Upgrade-p/mooney-fuel-increase-upgrade.htm

 

We have a tabbed “soft cover” Three ring binder titled “Missile 300 STC & Gross Wt Increase conversion paperwork package.  The Weight and Balance are in our POH in the plane.  Ours had the STC for the Monroy Long Range Tanks at time of conversion, but I had/have nothing on the station 71?  The Ap I have has only “one” fuel station.  Doesn’t include the AUX.  Are using the main AND aux in your W&B calculations or JUST the station 71?

[Missile=Awesome]

33 minutes ago, N56394 said:

Did you find your loading sheet from Rocket Engineering? Mine is in the 3 ring binder - there are about 4 loading examples - if the aux tanks were there before the Missile STC it should be there for the station 71...see this wing fuel tank layout for the LR tank - its aft of the spar... https://www.emapa.aero/Monroy-Mooney-Fuel-Increase-Upgrade-p/mooney-fuel-increase-upgrade.htm

 

Is the page as you have shown above in this thread?  If no please take a photo and post on here.  Thanks.

[PJClark]

Uhhh...maybe the 201/J stations are different.  If you look at my station chart above, 71 would be in the middle of the rear seats.  If your J has main tanks at about 48", then those are the same.  I don't think there's any wing at station 71 to put fuel into...

Just saying, I could be missing something.

[Missile=Awesome]

Just now, PJClark said:

Uhhh...maybe the 201/J stations are different.  If you look at my station chart above, 71 would be in the middle of the baggage compartment.  If your J has main tanks at about 48", then those are the same.  I don't think there's any wing at station 71 to put fuel into...

Just saying, I could be missing something.

Ya, I am completely confused by this to be honest...

[Missile=Awesome]

The Aux is “EVEN” (forward and back) and outboard of the Mains in the J...

[PJClark]

Just now, Missile=Awesome said:

The Aux is “EVEN” (forward and back) and outboard of the Mains in the J...

Yep.  My two fuel caps are in line also.  I'm not sure fuel as far aft in the wing at 71, even if there's enough wing there, would be able to flow downhill into the mains to begin with.

Something's wacky...

[N56394]

I agree totally. Do you have the POH for the aux tank? It should show any loading changes...  the 71 came from my Missile loading table from Rocket - since I don't have the aux tank it shows up as zero. If you have those charts from Rocket, it should clear up the issue... You have the aux I don't - but this photo of a Missile  shows the cap aft of the wing spar. 

[N56394]

I'm convinced that the 71 arm is correct for the aux tank for the missile if the tank cap is just aft of the spar. I went out to the airplane and taped the main and from the diagram in my link from emapa I taped the aux tank. I estimated where the 48 arm would be for the main tank and then put a 2 foot level to see about where the 71 arm would be - yes it turns out to be at where I would guess the CG of the aux tank would be. I would double check your records to be certain. It is possible you all have different tanks, but can't hurt to double check.