JimD

Diminishing Useful Load

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I've been shopping for my first airplane over the past couple of months.  I can't realistically afford anything beyond the J and K models so that's where my focus has been.  The Js were spec'd at just under 1100lbs useful load and the Ks were spec'd right at 1100lbs.  I fully understand that some minor fluctuations are going to occur from aircraft to aircraft.  I recently saw a K model for sale that listed only 830lbs as the useful load.  What do some folks do to their airplanes that bring the load down that much??  If I buy an airplane like this, can most of these "mods" be reversed??

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In most cases you will probably find that the lower useful load numbers are real, airplane put on the scales recently, numbers.  The higher useful load numbers are calculations upon calculations since the airplane was new, last real weight and balance being many years ago.  And those “negligible weight change” logbook entries for each small mod completed, rather than doing a proper w&b and equipment list, add up.

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20 minutes ago, JimD said:

I've been shopping for my first airplane over the past couple of months.  I can't realistically afford anything beyond the J and K models so that's where my focus has been.  The Js were spec'd at just under 1100lbs useful load and the Ks were spec'd right at 1100lbs.  I fully understand that some minor fluctuations are going to occur from aircraft to aircraft.  I recently saw a K model for sale that listed only 830lbs as the useful load.  What do some folks do to their airplanes that bring the load down that much??  If I buy an airplane like this, can most of these "mods" be reversed??

Typically it's because I cant push myself away from the table.....  realistically I would look at the record of W&B changes over the life of the plane - I for one have all the documentation of things added / subtracted with the associated W&B  - that said I've never weighed the plane to validate the claim as its not required. And the I've not had any issues with performance when I've been at the calculated MTOW. 

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4 minutes ago, Culver LFA said:

In most cases you will probably find that the lower useful load numbers are real, airplane put on the scales recently, numbers.  The higher useful load numbers are calculations upon calculations since the airplane was new, last real weight and balance being many years ago.  And those “negligible weight change” logbook entries for each small mod completed, rather than doing a proper w&b and equipment list, add up.

But only the legal useful load is what matters. Obviously any errors in past calculations should corrected after a thorough review but a number of insignificant less than a pound changes without an update are not going to make large difference or create a safety of flight issue. Nor is re-weighing the aircraft considered a accurate error free method to re-establish empty weight. Frankly that is a much more error prone process that updating the weight balance with correct station and weight numbers.  Mooney's are quite capable handling their full max gross takeoff weight and quite easily with significant margin. But the difference between lightly loaded and max gross weight can be significant; especially as we move up the Mooney models to the longbody with considerations for a takeoff max weight that exceeds max landing weight. But I would put much more emphasis on the need for the pilot transitioning to a new Mooney to work up to max gross weight learning how the heavier airframe handles along way so as to not be hugely surprised; especially at higher density altitudes.  

In the end, anyone purchasing the new aircraft is going to seek an airframe with as much useful load as they can. 

But getting to the OPs expectation for 1100 useful load, that is way too optimistic. A good useful load on a K is closer to 900 lbs, many are less than 900. A J can be a bit higher but I'll let some J owners give a realistic number. My 252 after converting to an Encore and going all glass panel is now 1127 pounds - but that is very rare. 

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I think most of the heavy weights that you’re looking at came that way from the factory. Most were optioned in such a way that they never had a useful load that approached anything close to the “standard” 1100lbs. The older machines are more pedestrian but tend to have higher useful loads ( I have a 67F model with 1060lbs useful). The conventional wisdom is that airplanes get heavier with age. That maybe true, but I would submit that it really should be the opposite. These days, charging systems are lighter as are solid state digital electronics.   All other things being equal aircraft should be getting lighter. The reason they don’t is because of available equipment. There are now 50-year-old Mooneys flying around with more redundancy and situational awareness than a 767 had just 20 years ago. You can have a simple, IFR certified, XC aircraft with good useful load or you can get something very well equipped with less useful load.  Keep looking until you find the right balance.

Edited by Shadrach
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Useful loads for M20J's seem to run generally in the 850-950 lbs range with typical equipment, not because of modifications or unnecessary equipment.  IIRC, some of the older J's had a lower maximum gross weight that could be increased through paperwork?

There are some people out there who have J's with useful loads >1050 lbs, but that is through a concerted effort to shed weight and sheer force of will.

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1 hour ago, kortopates said:

Nor is re-weighing the aircraft considered a accurate error free method to re-establish empty weight. Frankly that is a much more error prone process that updating the weight balance with correct station and weight numbers.

I honestly have not heard this before.  The scales don’t lie and the weighing procedure in the manual really isn’t very complicated,  how could it not be more accurate if done correctly? 

How many installations include the weight and stations of the components but not include the 18’ of coax or 50’ of 20 gauge wire?  And my point about the ‘negligibles’ is that they all add up to more than the weight we save on lightweight starters, alternators, prop governors, etc.  I have all these items on my airplane now and it’s still 70#’s heavier on the scales than it was when last calculated in 2002.

I’m not disagreeing with you, I’m asking so that I understand.

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52 minutes ago, jaylw314 said:

Useful loads for M20J's seem to run generally in the 850-950 lbs range with typical equipment, not because of modifications or unnecessary equipment.  IIRC, some of the older J's had a lower maximum gross weight that could be increased through paperwork?

There are some people out there who have J's with useful loads >1050 lbs, but that is through a concerted effort to shed weight and sheer force of will.

The vast majority of Js are not eligible for the GW increase. It is serial# dependent and only available on models built after 1988 or 1989if memory serves. My f has the same 2740 MGW as most Js, I could probably get close to 1100 if I went all glass and got rid of my generator. Especially if I swapped my Hartzell for an MT prop.

Edited by Shadrach
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The models with the best useful load are:

  • M20F
  • Encore (a 252 can be converted to an Encore)
  • Eagle

I've heard... most 252 owners, fly them using Encore W&B data.

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19 minutes ago, Culver LFA said:

I honestly have not heard this before.  The scales don’t lie and the weighing procedure in the manual really isn’t very complicated,  how could it not be more accurate if done correctly? 

How many installations include the weight and stations of the components but not include the 18’ of coax or 50’ of 20 gauge wire?  And my point about the ‘negligibles’ is that they all add up to more than the weight we save on lightweight starters, alternators, prop governors, etc.  I have all these items on my airplane now and it’s still 70#’s heavier on the scales than it was when last calculated in 2002.

I’m not disagreeing with you, I’m asking so that I understand.

The scales can actually lie, very accurate scales are expensive and need calibrations like torque wrenches. But the real problem is the plane has to be leveled accurately per the manual when placed on scales and then we find many tech are terrible at math and make lots of errors. But an accurate weigh in requires the plane to be  drained of fuel and then add back in the unusable and fill other liquids (oil, O2). Many take shortcuts following the procedure, rather than draining fuel, they may fill the tanks and subtract off the fuel. Lots of error there since they really don't know how many gallons they have nor don't use the proper weight/gal for 100LL; perhap use 6 lbs/gal.

Years ago a shop offered to weight my plane, and I thought great way to see how close it comes out - when they were done due to calculation errors it was a few 100 pounds off! Admittedly it was with new scales and little experience. 

100' feet of 20 gauge wire weights only a few ounces. Enough coax can add up, but we're often replacing coax unless its the first GPS installed or the like.

Honestly, I would never advise anyone to weight their plane except for informational purposes only - not for a legal weight - unless it was your only recourse or you had reason not to trust the official empty weight. Then I would seek someone with experience and good scales simply because its too easy to botch.

Edited by kortopates
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I honestly have not heard this before.  The scales don’t lie and the weighing procedure in the manual really isn’t very complicated,  how could it not be more accurate if done correctly? 

How many installations include the weight and stations of the components but not include the 18’ of coax or 50’ of 20 gauge wire?  And my point about the ‘negligibles’ is that they all add up to more than the weight we save on lightweight starters, alternators, prop governors, etc.  I have all these items on my airplane now and it’s still 70#’s heavier on the scales than it was when last calculated in 2002.

I’m not disagreeing with you, I’m asking so that I understand.

50’ of 20 gauge wire is about 1/8 lb, that’s the definition of negligible.

I bet if you took your plane to 3 APs to weigh, you would get a range of values of 100lbs.

They do not empty the fuel tanks, they will either fill them and subtract full tank specified in the POH, or use the fuel gauges and calculate the weight of the fuel.

Edit: my 78J UL is 997, when I bought it was 938.

 

Tom

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I recently had SWTA weigh my 252. The number they came up with was 32 lbs lighter than what was in my log book. So we wrote up the new one and put it in the log.

The empty weight of my 252 is 2058 and gross 2900, which gives me a UL of 842. The Encore conversion will raise the gross to 3100, I believe. 

A friend once told me that they fly just fine at 3100 gross. 

 

BTW... SWTA drained all the fuel, then added back the unusable amount, carefully measured. We had a fresh oil change. And the plane was carefully leveled. The scales used are the expensive one's but I can't say when they were calibrated.

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The process isn’t really that complicated as Paul points out.  As with all things there is the human being involved and hence some mistakes.

Clarence

4CE51E9E-52AD-4997-ACD6-E2BF9C9F4549.jpeg

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Sorry for the thread drift but this is really interesting to me.

Sure, I can understand if the workshop procedure is not followed then the results will not be accurate. But this should not be the norm, if the procedure is followed as it should be then the results should be absolutely accurate.  

Now if 3 mechanics get wildly varying results using the same equipment and procedure on the same airplane, the equipment or procedure is not the problem (unless the instructions are overly complex or poorly written, which in this cause they are not).

 

 

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43 minutes ago, M20Doc said:

The process isn’t really that complicated as Paul points out.  As with all things there is the human being involved and hence some mistakes.

Clarence

....

FWIW, Clarence is one of the few A&P's I would trust to do a good job with a result that would be repeatable. But he's way above the norm or average of the person that you might get at the typical shop. PLus I expect Clarence would be pretty anal about measuring the distances called out in which error can have a big impact. Again if you really need to do it, go to someone hopefully you know that you can trust that is going to use the proper procedure and be anal about the process.

Clarence, I hope you don't mind your attentions to detail being referred to "anal" - its in a good way!

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1 hour ago, Culver LFA said:

Sorry for the thread drift but this is really interesting to me.

Sure, I can understand if the workshop procedure is not followed then the results will not be accurate. But this should not be the norm, if the procedure is followed as it should be then the results should be absolutely accurate.  

Now if 3 mechanics get wildly varying results using the same equipment and procedure on the same airplane, the equipment or procedure is not the problem (unless the instructions are overly complex or poorly written, which in this cause they are not).

 

 

human factors are THE problem in 80% of problems (based on no data at all) :P

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1 hour ago, jaylw314 said:

human factors are THE problem in 80% of problems (based on no data at all) :P

So true, no different than us fallible pilots !! 

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5 hours ago, JimD said:

I've been shopping for my first airplane over the past couple of months.  I can't realistically afford anything beyond the J and K models so that's where my focus has been.  The Js were spec'd at just under 1100lbs useful load and the Ks were spec'd right at 1100lbs.  I fully understand that some minor fluctuations are going to occur from aircraft to aircraft.  I recently saw a K model for sale that listed only 830lbs as the useful load.  What do some folks do to their airplanes that bring the load down that much??  If I buy an airplane like this, can most of these "mods" be reversed??

Jim,

That 1100 pounds is usually for a basic airplane with few if any radios.  By the time you add a couple radios, a transponder, intercomm, ELT, and an autopilot along with all the required antennas you are probably down closer to 1000 lbs.

Then some people add thicker glass to make the plane quieter, articulating seats, storm scope, speed brakes, long range tanks, second battery or alternator, nicer upholstery and interior, three blade prop, etc.  Five pounds here and 10 pounds there and pretty soon you are looking at a useful load down around 900 lbs.

FWIW, our J is currently at 992 UL (no oil) so practically speaking around 980 lbs.  But that's before we finish swapping out our KFC200 for a GFC500.  I'm hoping for a bit over 1000 lbs by the time we are done.

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37 minutes ago, Bob - S50 said:

Jim,

That 1100 pounds is usually for a basic airplane with few if any radios.  By the time you add a couple radios, a transponder, intercomm, ELT, and an autopilot along with all the required antennas you are probably down closer to 1000 lbs.

Then some people add thicker glass to make the plane quieter, articulating seats, storm scope, speed brakes, long range tanks, second battery or alternator, nicer upholstery and interior, three blade prop, etc.  Five pounds here and 10 pounds there and pretty soon you are looking at a useful load down around 900 lbs.

FWIW, our J is currently at 992 UL (no oil) so practically speaking around 980 lbs.  But that's before we finish swapping out our KFC200 for a GFC500.  I'm hoping for a bit over 1000 lbs by the time we are done.

Per the manual excerpt above your J should have been weighed with full oil.

Clarence

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Welcome aboard JimD!

You have come upon an interesting situation...

Some Mooneys began life as a stripper model... and stayed lean and fit their entire lives...

The benefit of being Stripped of all content... Great useful load... 1,100 LBs is a lot for a Mooney... 

The challenge of being Stripped of all content... Many things have been left out...

 

Other Mooneys started life in the SE category... special edition...they are so loaded with factory goodies that their UL is affected by its bulging waistline...

 

You want to determine a few things about your typical mission... how far you want to go, and how many people you are going to bring with you...

A K model is one of the most developed airframes on the planet... some got...

  • Six cylinder engine with a turbo...
  • intercooler..
  • Automated pressure controller... 
  • anti-ice equipment...
  • installed O2 system...
  • weather radar...

With all that capability, the UL is a bit affected...

Some Mooneys are intended to fly 1knms, non-stop, solo...

Other Mooneys intend to bring a family of four, an hour away to see Pop-Pop...

Select a mission, and then select a Mooney around that mission...

If you intend to fly 1knm with a family of four... Expect to take a stop in the middle, or every hour depending on your family...

Selecting a Mooney 101 kind of stuff... we have a few threads around here that cover this idea pretty well.

Best regards,

-a-

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3 hours ago, M20Doc said:

Per the manual excerpt above your J should have been weighed with full oil.

Clarence

Not for our '78J.  Step 3 in our POH says to drain the oil sump.  Oil is located at station -11.5".

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21 minutes ago, Bob - S50 said:
3 hours ago, M20Doc said:

Per the manual excerpt above your J should have been weighed with full oil.

Clarence

Not for our '78J.  Step 3 in our POH says to drain the oil sump.  Oil is located at station -11.5".

M20 was originally certified under CAR 3 which defines empty weight as not including oil. At some point, Mooney switched to the GAMA definition of basic empty weight which includes full oil. FAR Part 23 which supercedes CAR 3 also includes oil in empty weight. Practically speaking, you can do it either way so long as you document it clearly.

Skip

 

 

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Last year we put in an EDM900 in our M20C and took out a bunch of redundant stuff.   Items removed included: Garwin instrument cluster, MP/FP gage, tach, carb temp gage, EGT gauge and switch.  We went through the wiring and removed a pound or so of disused wiring and connectors.   The Hartzell prop gov was replaced with the compact and lighter PCU5000.  I was certain that in the process of all this change/modernization we would gain useful load.   My A&P Dave (RIP) was pretty certain not.   No wager was placed, but I would have lost if a wager were made.

The a/c w&b logs gave the accumulated/calculated useful load of 986 lb.  We drained the tanks by removing the sump valves.  Then we carefully leveled the a/c according to the Service & Maintenance Manual.  The recently purchased digital scales were double checked.   The result said that the UL was 945 lb after subtracting out the weight of the oil.   Leaving in 8 qts of oil, the UL is 931 lb.   As a card carrying engineer, I verified the level and performed the moment calcs following the procedure in the SMM.

Why was the a/c 41lb heavier?  A discussion ensued around the shop about the difference.  Maybe we left a few lb of gas in the tanks when we pulled the sump drains.  The sump drains are located so that when the plane is sitting at normal ground angle  they are very near the bottom of the tanks, so we probably left no more than maybe 1/2 gal per side. So that's maybe 6 lb gained back.  Looking at the logs, when the a/c was painted in 2004 they stripped the paint off the removable cowl parts and rough sanded the rest before repainting.   The paint that they left on could easily weigh 20-30 lb, maybe a bit more depending on thickness.  Also, I had put on Michelin tires that are about 1 lb each heavier than the originals.   An a/c will gain 1/2 oz of weight per year by accumulated grease, dust, residue, mud dobber nests (e.g.

Since weighing I've excised 0.5 to 1 lb of mud-dobber nests discovered since then.   That gain can add up to a few pounds over 50+ years of "if a little grease is good, a lot is better".

Paint.  Tires.  Mud dobbers.  It all adds up.

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5 hours ago, Bob - S50 said:

Not for our '78J.  Step 3 in our POH says to drain the oil sump.  Oil is located at station -11.5".

I stand corrected, interesting that there is a difference between PoH and maintenance manual weighing procedures.

Clarence

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16 hours ago, kortopates said:

Clarence, I hope you don't mind your attentions to detail being referred to "anal" - its in a good way!

I'll have to remember that one.  "I'm not anal, I'm attentive to detail":D

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