Monroy fuel tanks

[highflyer77]

Dear Mooniacs, 

I just got my aircraft newly painted. As standard procedere the aircraft´s w&b was done new. Unfortunately, they choose to do the w&b with the "full fuel method"... :-((( .

As I have installed the monroy l/r-fuel STC: where do I find the arm for the rear tanks ? Standard tanks are 122 cm (48 inch). I found something inofficial that reads 168 cm (66 inch) for the rearward tanks, but I don´t know where to get the "official" numbers to forward to the maintenance facility...

Thanks for your help ! 

[Fly Boomer]

22 minutes ago, highflyer77 said:

Dear Mooniacs, 

I just got my aircraft newly painted. As standard procedere the aircraft´s w&b was done new. Unfortunately, they choose to do the w&b with the "full fuel method"... :-((( .

As I have installed the monroy l/r-fuel STC: where do I find the arm for the rear tanks ? Standard tanks are 122 cm (48 inch). I found something inofficial that reads 168 cm (66 inch) for the rearward tanks, but I don´t know where to get the "official" numbers to forward to the maintenance facility...

Thanks for your help ! 

Should be in your installation document.  Mine says:

Center of gravity (M20C, M20E) . . . . . 66.0 inches
Center of gravity (M20F thru M20K) . . . 71.0 inches

 

[philiplane]

1 hour ago, highflyer77 said:

Dear Mooniacs, 

I just got my aircraft newly painted. As standard procedere the aircraft´s w&b was done new. Unfortunately, they choose to do the w&b with the "full fuel method"... :-((( .

As I have installed the monroy l/r-fuel STC: where do I find the arm for the rear tanks ? Standard tanks are 122 cm (48 inch). I found something inofficial that reads 168 cm (66 inch) for the rearward tanks, but I don´t know where to get the "official" numbers to forward to the maintenance facility...

Thanks for your help ! 

They need to drain the system and weigh the aircraft empty. This arrangement is hard enough to fuel, there is no way they can be certain how much fuel is "full fuel".

Drain it.

[highflyer77]

Absolutely my opinion. They also did the mistake not having the airframe in the position required when doing the weighing (spirit level on the row of rivets on the fuselage). They just put it on the scales on the workshop floor, I assume. This falsifies the weight reading in such a way, that the CG shifts rearward by 1,5 inches (IIRC, the wrong weighing procedure shifts about 30 kgs. from nose gear to the main gear...). When I bought the plane, the CG sheet showed an empty CG of 48.05 inches. I reweighed everything myself (unofficial) - weight was correct, but the CG moved forward to 46.7 inches. This gives you a lot of possible weight in the rear seats and baggage compartment, compared to 48.05 inches...

As the plane was stripped and paint, the offer also included a new w&b (done by a different company than the paint shop). The paint shop did a perfect job. But it´s a PIA when you expect to get a new, correct w&b after repainting the aircraft (I even sent them the instructions for determining the correct values...) , and then it´s just useless... Theis just said: No, we don´t do the "empty plane method" - it´s too much work do drain the fuel. And I am quite sure that they have not nivelled the fuselage by means of using a spirit level. Grrrrrhmpfff... 

But what do you think - isn´t she a beauty ??? I´ll just do a new w&b sheet with my A&P/maintenance facility !

[1980Mooney]

5 hours ago, philiplane said:

They need to drain the system and weigh the aircraft empty. This arrangement is hard enough to fuel, there is no way they can be certain how much fuel is "full fuel".

Drain it.

Absolutely correct.  @highflyer77 there was a recent topic about Monroy tanks and @Pinecone commented:

"If you fill main with aux empty, fuel starts moving into aux.  So when you stop filling main and put on the cap, the level in the main is still going down.  So you fill the aux, but the main is not full, so the level in the aux goes down and leaves you short of full.

Filling aux first means fuel is moving from aux to main.  Then you fill the main, which reduces flow from aux to main.  So you then top the aux after doing the same to the other side and you are much closer to full."

The shop that did the W&B had no way to accurately know how much fuel that you had in the tanks to start with - and they had no way of knowing if they actually filled the Monroy and Mains all the way to "Full Fuel".

[highflyer77]

I had a thorough conversation & recheck of the new w&b with the maintenance shop doing it now. Weight seems to be correct (I had the plane weighed last year at "my" first own annual (all tanks propperly drained by my A&P and me), and compared to that weight, the aircraft got about 18 lbs. heavier. Seems to be realistic, as the new design has more layers of different colours, and 2x clear paint coating. They also used a water spirit, so the measured weights are correct. 

When I checked with my old w&b, it came out they used wrong arms (please correct me, but we measured the following: nose gear is -2cm, main gear is +167cm from STA 0). They used -3cm and +172cm for the calculation and got a empty CG position of 121,77 cm. 

I don´t know, where they got their measurements... When the recalculation was done with the the shorter arms (they where measured by my A&P as well as they were used a few years ago in an old w&b, so I am sure they are correct !), it turned out that empty CG position is 117,33 cm.

Quite a shift, if you take into consideration, how small the changing in arms for calculation is ! But this makes the plane much more usable (otherwise, I would barely have been able to take baggage with me, and only small children on the rear seats) !

w&b sheet finally is  issued new by the maintenance facility, and everything happy now ;-) !

As allways: thanks for all of your input´s !

[FlyingDude]

13 hours ago, highflyer77 said:

 

Arm lengths and the datum are clearly explained in the maintenance manual. My coarse guess is that some previous mechanic took the nose wheel hub as the datum whereas it's actually a couple inches (3-4cm) aft of it. 

[highflyer77]

FlyingDude, have you got the arms for a 1964 M20E at hand (I assume the arms might be the same than for your plane, as there never were changings on this at the M20E) ? I just have the arms from a older w&b at the moment... 

[FlyingDude]

13 hours ago, highflyer77 said:

arms for a 1964 M20E at hand

No. I have the measurements for my 1967 m20e. Not exactly the same as your plane I assume.