M20C 48 gallon tanks usable fuel

[markazzarito]

My 1963 M20C Mark 21 has 24 gallon tanks. Im curious as to whether or not the entire 24 gallons are usable in each tank. It seems like most 1960's era c models have the 52 gallon tanks. Does anyone have info/experience with the 48 gallon tanks?

[Guest]

Here's what the type certificate say,

Serial No. 1852, 1940, through 2622 - 48 gals. (Two integral tanks in wings at +48.4) Serial No. 2623 and up - 52 gals. (Two integral tanks in wings at +48.4) See NOTE 1 for data on unusable fuel. 

Current weight and balance report, including list of equipment included in certificate empty weight and loading instructions when necessary, must be in each aircraft at the time of original certification and at all times thereafter (except in the case of air carrier operators having an approved weight control system.) The certificated empty weight and the corresponding center of gravity location must include unusable fuel (not included in fuel capacity) as follows: 4 lbs. (+47.6) for the M20 and M20A; 3.4 lbs. (+48.4) for the M20B, M20C, M20D, M20E, and M20G; 15.0 lb. (+48.4) for the M20F and M20J; 48.0 lbs. (+48.59) for the M20K (S/N 25-0001 thru 25-0446); 18 lbs. (+48.59) for the M20K (S/N 25-0447 and ON); 36 lbs. (+48.43) for the M20L (S/N 26-0001 and ON); 36 lbs. (+49.23) for the M20M (S/N 27-0001 and ON) and M20R (S/N 29-0001 and ON) and M20S (S/N 30- 0001 and ON); 36 lbs. (+49.23) for the M20TN (S/N 31-0001 and ON) 

Clarence

[carusoam]

So, knowing what the useable fuel is supposed to be is one thing...

You will find there are many discussions on how to verify the fact that the useable fuel is actually useable....

With a Mooney it is a normal procedure to run a fuel tank out in flight at altitude.  Fill it back up on the ground two gallons at a time use a stick and a sharpie marker to make a calibrated fuel stick.  Repeat on the other side. Leave nothing to chance

Now you have three good things...

1) Known useful tank volume on both sides.

2) Known calibrated stick to partially fill the tanks.

3) Known procedures for filling the tank and switching tanks in flight.

next up...

4) known fuel burn rates for all stages of flight...  T/O, Cruise, Descent, Start and taxi....

 

How does that sound?

 

All stuff that I have learned on MS, I am only a PP...

Best regards,

-a-

[markazzarito]

Can anyone elaborate on the procedure for running a tank dry and then restarting? I've read about the procedure both in the POH and on this forum. I'm just hesitant to deliberately run a tank dry to the point of the engine quitting at altitude.

What is the restart procedure for the M20C? 

In an emergent situation i would 

- switch to tank with fuel

- ensure mags are on both

- engine should start back up

not sure i want to test this if i dont have to.. 

 

[mooniac15u]

If you just want to run it dry for capacity measurements you could run in very low in the air and then finish it off on the ground. That way you could avoid the stress related to doing it in the air. 

[carusoam]

At altitude, the engine will start showing lower fuel pressures followed by stumbling before quitting.

At speed, the engine doesn't actually quit rotating.  Restoring the fuel flow (properly) restores the power quickly.

Once you have a feel for the procedure to change tanks, it isn't a big deal to run one tank dry first before changing.

use caution to follow the procedure.   Restoring FF with FT may overspeed the prop or something similar...

It takes a handful of seconds to restart FF if the tank has run dry.  The fuel pick-up is (?) near the back of the tank.  Good for T/O and climb but will show a different challenge when descending

If unsure of the execution of the procedure, use a CFI to fly right seat with you while picking up the experience...

The latest POH for the M20C was written in 1976.  Every year it got better and more complete.  Copies are available, get one...

i am only a PP, not a CFI...

Best regards,

-a-

[gsxrpilot]

Still waiting for Chuck Noe to go up with me when I run a tank dry. He's done this successfully in his J, and I'd like to have that experience in the cockpit when I do it.

[Bob_Belville]

An alternative method for draining a tank: we disconnected the fuel line downstream of the electric boost pump and used it to run fuel into a 5 gallon (Harbor Freight) gas container a few weeks ago to drain a tank in order to pull the level sensor. As I recall that pump is good for 30 gph or more pumping against zero head so it only took a few minutes to drain about 10 gallons.  (That was not my first bright idea but it was the best one.)

[carusoam]

The POH should have the detail that you want, in the proper order. It's been five years since I last flew a C...

Having the throttle full open when fuel gets delivered may not be best for engine health.  The mechanical systems take seconds to equilabrate.  Seconds can be too long of a time for some things...

expect the procedure to include running the auxiliary fuel pump prior to switching tanks.

Not trying to be hard.  I just don't have that much memory.  

Look to see if somebody posted a POH.  There were a couple here in the downloads section.

Best regards,

-a-

[Hank]

I haven't run a tank completely dry, but did once make it surge and burp. Just threw the selector and she smoothed right out. It gets your attention when it happens, but the first burble I didn't realize what was happening, too busy sightseeing, looking at my intended destination to see why it was closed as I headed one county over (replacing the runway! Good things happen sometimes.).

[carusoam]

Consider this...

Before landing, you select the tank that is most full...  

1) If you run both tanks down, the accuracy of the gauges may be misleading.

2) On final approach, when you lower the nose, fuel runs forward away from the pick-up.

3) The Power setting is just about zero.  It may be hard to notice the engine is no longer running.  Air is entering the fuel lines.

4) The go around usually happens with fuel flowing and power on full...

5) If the fan has gone quiet, it may be 10 seconds before the air has been run out and fuel starts flowing again with the fuel pump on and valve switched.

6) I selected the tank that was indicated as most full.  Apparently, It had less fuel than the other... I had been performing maintenance flights around the traffic pattern with it...

7) the next plane got four fuel level indicators and FF with a totalizer.

8) some day it will get those nifty digital FL indicators when the coffers get a little more full...

This, essentially, is the logic I use to not empty a tank completely as a regular procedure.  Just too many things to goof up for me, as a PP...

Best regards,

-a-

[cnoe]

If you just want to run it dry for capacity measurements you could run in very low in the air and then finish it off on the ground. That way you could avoid the stress related to doing it in the air. 

I might suggest that it would be much less detrimental to one's plane running the tank dry in flight rather than on the ground. Even if you landed with only a couple gallons of usable fuel left in a tank it would take a long time ground-running with poor/uneven cooling to run the tank dry. That is not good for your engine.

Instead... 1) confirm that your fuel selector is functional, 2) put a few thousand feet between you and the ground, 3) go fly somewhere scenic until the engine starts to miss and sputter, 4) RETARD your throttle position to ~1/4 throttle, 5) switch leisurely to the fuller tank (the prop will continue to spin briskly unless you slow the plane down A LOT). The engine will quickly resume running at the lower power setting so all you have to do now is smoothly advance the throttle and fly home.

With that being said I'd advise against doing this with a nervous spouse in the right seat. Other than that it's not that big of deal.

Disclaimer: Perform at your own risk. I'm only stating what works for me and is in keeping with the manufacturer's procedures.

Sent from my iPad using Tapatalk

[carusoam]

Find CNOE's writing regarding using your Mooney as a glider.  It's an interesting read.

Best regards,

-a-

[mooniac15u]

54 minutes ago, cnoe said:

I might suggest that it would be much less detrimental to one's plane running the tank dry in flight rather than on the ground. Even if you landed with only a couple gallons of usable fuel left in a tank it would take a long time ground-running with poor/uneven cooling to run the tank dry. That is not good for your engine.

Instead... 1) confirm that your fuel selector is functional, 2) put a few thousand feet between you and the ground, 3) go fly somewhere scenic until the engine starts to miss and sputter, 4) RETARD your throttle position to ~1/4 throttle, 5) switch leisurely to the fuller tank (the prop will continue to spin briskly unless you slow the plane down A LOT). The engine will quickly resume running at the lower power setting so all you have to do now is smoothly advance the throttle and fly home.

With that being said I'd advise against doing this with a nervous spouse in the right seat. Other than that it's not that big of deal.

Disclaimer: Perform at your own risk. I'm only stating what works for me and is in keeping with the manufacturer's procedures.

Sent from my iPad using Tapatalk

Running your plane on the ground at low power for 15 minutes (half of which is taxiing back to your hangar) is hardly going to be detrimental to your engine. 

Do what you are comfortable with in your plane but I don't personally feel like it's a good idea to encourage another pilot to take a risk that makes them uncomfortable. Especially when there are other options available. 

[Andy95W]

For the carbureted models at least, the procedure is actually in the POH to run the tank dry:

 

[StinkBug]

I was about to mention the POH fuel strategy. I've used it many times. In fact I ran one dry a couple days ago somewhat unintentionally. It's really a non-event. Switch tanks, wait a couple seconds, everything goes back to normal. I generally only do it on very long legs where I'm planning to land with just my reserves (I always like to have 10 gallons on board). Personally I'd far rather have one tank with 10 gallons in it, than 2 with 5 gallons each. 5 gallons sloshing around is a little too close to sucking air for my comfort, and since we don't have a "both" position on the fuel selector I'll put all my reserves in one tank where I know the pickup will stay well submerged. 

[mooniac15u]

8 hours ago, N1395W said:

For the carbureted models at least, the procedure is actually in the POH to run the tank dry:

 

 

The POH for my M20D said the same thing.  I'm pretty sure it was the same for the M20E so I don't think carb vs fuel injection had anything to do with it.  As I recall the POH also told me that the normal operating range for CHT was 300-450 deg F.  Your mileage may vary.

It is interesting that the POHs for newer Mooneys don't contain a recommendation to run a tank dry.  In the POH for my M20J the in-flight engine restart procedure is in the Emergency Procedures section.  One strategy I use as part of my risk evaluation is to ask myself what it would feel like to have to explain what I was doing to an FAA inspector following an incident.  I don't think I would want to explain why I intentionally put my plane in a fuel starvation scenario while planning to rely on an emergency procedure for the safe conclusion of my flight.

Each of us should do what we are comfortable with based upon our own risk assessments and POH guidance.  If the OP isn't comfortable with running a tank dry in flight then he shouldn't do it.

[mooniac15u]

6 hours ago, StinkBug said:

I was about to mention the POH fuel strategy. I've used it many times. In fact I ran one dry a couple days ago somewhat unintentionally. It's really a non-event. Switch tanks, wait a couple seconds, everything goes back to normal. I generally only do it on very long legs where I'm planning to land with just my reserves (I always like to have 10 gallons on board). Personally I'd far rather have one tank with 10 gallons in it, than 2 with 5 gallons each. 5 gallons sloshing around is a little too close to sucking air for my comfort, and since we don't have a "both" position on the fuel selector I'll put all my reserves in one tank where I know the pickup will stay well submerged. 

How about switching tanks with ~1 gallon left?  Then you would have 10 gallons in one tank and 1 gallon in the other.  How much would that impact your range?

[Bob_Belville]

16 minutes ago, mooniac15u said:

How about switching tanks with ~1 gallon left?  Then you would have 10 gallons in one tank and 1 gallon in the other.  How much would that impact your range?

And you'd determine that there was 1 gallon left by...? 

[mooniac15u]

Just now, Bob_Belville said:

And you'd determine that there was 1 gallon left by...? 

By knowing how much fuel I started with and monitoring my fuel burn with my engine monitor and fuel gauges.  The M20J also has low fuel warning lights for each tank.  I actually try to leave a few gallons in the tank in case I need to switch back to it in an emergency.  I just flight plan with a little more reserve and then I never have to run one dry.

If you aren't sure when you are down around a gallon left then how sure are you that you have 10 remaining in the other tank?

[mooniac15u]

I'm not saying you shouldn't run a tank low and keep your reserves in the other tank.  Splitting your reserves is a bad idea.  With modern fuel flow measurement technology and good preflight planning I just don't see the value in actually letting one run completely dry.

[cnoe]

9 hours ago, mooniac15u said:

Running your plane on the ground at low power for 15 minutes (half of which is taxiing back to your hangar) is hardly going to be detrimental to your engine. 

Do what you are comfortable with in your plane but I don't personally feel like it's a good idea to encourage another pilot to take a risk that makes them uncomfortable. Especially when there are other options available. 

You are right; I do not mean to encourage anybody to take a risk that makes them uncomfortable. I only intended to point out that IMO purposely running a tank dry in flight presents very low risk compared to many of the things we do while flying these small airplanes through the sky. The list of things that I consider to be more risky include: take-offs, flying over large expanses of forest or rough terrain, landing with a 15 kt crosswind component, executing a missed approach, flying at night, etc.

I am not trying to be a smart aleck, and I do realize that not everyone is comfortable with hearing their engine stop making power. But I'd rather do this a few times on purpose under controlled circumstances than unexpectedly encounter it for the first time stumbling through the recovery process. Just like few people enjoy practicing "stalls" (which is also more risky IMO) we're encouraged to go out occasionally and pull back on the yoke 'til our plane drops a wing.

Bob has a good point above too; my fuel gauges don't give me much resolution, and my totalizer only tells me what's in the tanks "combined". His suggestion to utilize the fuel pump to drain the tank may be an adequate alternative for anybody uncomfortable with the in-air tank switch but I don't believe that's as accurate of method due to the plane's attitude on the ground. And my Dukes boost pump is not rated for continuous duty so I use it sparingly.

I only intend to explain my thought process and procedure. It is not my intention to encourage anybody to do anything they're not comfortable with. I apologize for any other appearances.

[orionflt]

I have a 1962 C with the same tanks, I have run my tanks dry to check what my unusable fuel is and I found that on my plane I was down to about 1 gallon total. I later reverified this accidentally while doing a cross country flight. it was to a destination I had traveled to several times before and always landed with plenty of reserve, but this time the head winds were stronger and my fuel burn was in higer then I estimated (no engine monitor at the time). to top it off one of my fuel gauges failed between a1/4 and 1/8 tank making me believe my timing and fuel calculations were correct . just before entering the pattern at my destination the tank I was on started to run dry (planned), I swapped over to my other tank for landing as planned estimated (6 gallons), as i got abeam of the departure end of the runway my fuel pressure started fluxing, I called an emergency and turned into the runway. the engine quit.... I swapped tanks and set up for landing, the engine refired for a few minutes then quit again on short final. I rolled out safely, refired the engine and taxied to the fuel pumps.....i took 48 gallons. I definitely do not recommend verifying your useable fuel this way, but running one tank down until the pressure fluctuations will give you a good idea of your usable fuel per tank. since that adventure I have added an engine monitor, replaced my gauges and sender (part of the new monitor). I also use 2 gallons as my unusable fuel number just to give me some leeway.

 

Brian

[Bob_Belville]

Just now, cnoe said:

Bob has a good point above too; my fuel gauges don't give me much resolution, and my totalizer only tells me what's in the tanks "combined". His suggestion to utilize the fuel pump to drain the tank may be an adequate alternative for anybody uncomfortable with the in-air tank switch but I don't believe that's as accurate of method due to the plane's attitude on the ground. And my Dukes boost pump is not rated for continuous duty so I use it sparingly.

I only intend to explain my thought process and procedure. It is not my intention to encourage anybody to do anything they're not comfortable with. I apologize for any other appearances.

Chuck, my boost pump is rated for continuous operation though I am not happy with myself when I discover 10 minutes into a flight that I failed to turn it off after t.o.

True, the "used" info from the ff accumulator does not distinguish between tanks directly but when I'm on a longer trip I write down how much I've used out of each tank when I switch tanks.

The fuel line from the tank is close to the rear of the tank and sitting in the hanger the plane might be a little more nose up than in level flight. OTOH, descent and flair are probably on either side of that attitude. And of course flying downwind, base, final involves banking... if you're flying left hand pattern with very little fuel in the right tank rolling out level on final might get interesting.  

[Bob_Belville]

4 minutes ago, orionflt said:

I have a 1962 C with the same tanks, I have run my tanks dry to check what my unusable fuel is and I found that on my plane I was down to about 1 gallon total. I later reverified this accidentally while doing a cross country flight. it was to a destination I had traveled to several times before and always landed with plenty of reserve, but this time the head winds were stronger and my fuel burn was in higer then I estimated (no engine monitor at the time). to top it off one of my fuel gauges failed between a1/4 and 1/8 tank making me believe my timing and fuel calculations were correct . just before entering the pattern at my destination the tank I was on started to run dry (planned), I swapped over to my other tank for landing as planned estimated (6 gallons), as i got abeam of the departure end of the runway my fuel pressure started fluxing, I called an emergency and turned into the runway. the engine quit.... I swapped tanks and set up for landing, the engine refired for a few minutes then quit again on short final. I rolled out safely, refired the engine and taxied to the fuel pumps.....i took 48 gallons. I definitely do not recommend verifying your useable fuel this way, but running one tank down until the pressure fluctuations will give you a good idea of your usable fuel per tank. since that adventure I have added an engine monitor, replaced my gauges and sender (part of the new monitor). I also use 2 gallons as my unusable fuel number just to give me some leeway.

 

Brian

That's tops my dubious record of putting 50.2 in a 52 usable rental Mooney G.