MTOW?

[Lood]

On what grounds is the MTOW of a specific airplane calculated or determined? A friend of mine brought this up and it got me wondering.

He flies an M20E and seeing that we share the same engine and wing, wanted know why the F has a higher gross weight?

In turn, I would like to know how the later model M20J's had their gross weight increased to 2900lbs? Apart from the aerodynamic improvements, the J is basically the same airplane as the F in terms of power, wing, fuselage, etc.

The question that arises here is, if the F can fly at 2740lbs, why can't the E do the same and if the J can fly at 2900lbs, why can the F do that as well?

We don't have any intention to overload, or even try this out, but would just like to know out of interest.

[stevesm20b]

I'm still wondering why the B only has a gross wt of 2450 and the C is 2575? Same airframe, same engine.

[AndyFromCB]

On a Mooney, it's mostly an issue of landing gear and tubular structure differences like the M20J 2900lb example.The landing gear has always been the weak point in Mooney design. The rest of the airframe apparently does not care if you overload it. Imagine a redesigned landing gear, VGs to lower the stall speed and 310hp in a Mooney airframe. At 13lb/hp a horsepower, we could have a 4000MTOW aircraft, a true full fuel, full people, full luggage aircraft. One can dream ;-) Or buy a TNed A36.

[Jerry 5TJ]

On a Mooney, it's mostly an issue of landing gear and tubular structure differences like the M20J 2900lb example.The landing gear has always been the weak point in Mooney design. The rest of the airframe apparently does not care if you overload it. Imagine a redesigned landing gear, VGs to lower the stall speed and 310hp in a Mooney airframe. At 13lb/hp a horsepower, we could have a 4000MTOW aircraft, a true full fuel, full people, full luggage aircraft. One can dream ;-) Or buy a TNed A36.

Perhaps the landing gear is perfectly designed --- for a 2400 pound airplane -- but not much 'growth factor' was designed in. I don't think of the manual landing gear as particularly weak on the 2575 pound gross "C" or "E" models.

Likewise the wing may be optimized for flight at about 1.2 ton gross weight and below 10,000' or so. For a higher-flying, 2.1 ton airplane (I have in mind the PA46) Piper elected to use a 43 foot span with an aspect ratio similar to a Mooney's wing.

You can fly a "C" at 2800 or 3000 pounds, but it won't perform as intended, and it won't have the required strength margins.

You could put a 700 shp PT6A in an M20M, but that would not make it into a TBM700. I don't think the resulting machine would be a very useful airplane. It sure would climb well, though.

[AndyFromCB]

Perhaps the landing gear is perfectly designed --- for a 2400 pound airplane -- but not much 'growth factor' was designed in. I don't think of the manual landing gear as particularly weak on the 2575 pound gross "C" or "E" models.

Likewise the wing may be optimized for flight at about 1.2 ton gross weight and below 10,000' or so. For a higher-flying, 2.1 ton airplane (I have in mind the PA46) Piper elected to use a 43 foot span with an aspect ratio similar to a Mooney's wing.

You can fly a "C" at 2800 or 3000 pounds, but it won't perform as intended, and it won't have the required strength margins.

You could put a 700 shp PT6A in an M20M, but that would not make it into a TBM700. I don't think the resulting machine would be a very useful airplane. It sure would climb well, though.

Actually, I find the Mooney wing to be highly optimized for flight between 16,000 and FL250 ;-) Much better wing for flying high than a Tornado Alley A36 or a Cirrus SR22.

The airframe/wing have strength to spare, even at 4000lb a Mooney wing exceeds the 5.7 ultimate load factor by about another 4Gs.

And lord knows the climb rate is not an issue, my Bravo routinely climbs out at 1100fpm even when accidentally overloaded by about 160lb which to be honest is what happens most of the time heading west if taking off from near sea level airport. I do however religiously obey the 3200lb landing weight.

You are correct in stating that the landing gear for designed for lighter airframe. So were the brakes. I find the brakes on my M20M to be just barely adequate for the weight.

However, back to the originally question. If you look at all the gross weight increases over the years and various retrofit kits, they all involve either landing gear components or tube thickness used in the roll cage.

[aerobat95]

So are you saying that the landing gear on a 1980's J is different from my 1974 F? I know they had inner gear doors but besides that I thought they were basically the same??

[stevesm20b]

I don't believe they changed anything on the gear between the B,C,D,E,F or G.

[sreid]

I don't believe they changed anything on the gear between the B,C,D,E,F or G.

Do you know what changes were made after the G?

Steve

[stevesm20b]

Not sure of the changes made to the J and later models.

[AndyFromCB]

So are you saying that the landing gear on a 1980's J is different from my 1974 F? I know they had inner gear doors but besides that I thought they were basically the same??

In case of the later model J with 2900 gross weight, no landing gear component changes were made, but the tubular cage is made from thicker walled steel.

Andy

[marks]

We all know that the MSE in 1991 was delivered with the 2,900 lbs. gross weight increase and that the increase can be retroactively applied back to '89 model serial number 24-1686. I am the owner of 24-1686. This aircraft was the very first Mooney Advanced Trainer, N900AT. My understanding from the previous owner (another Mooniac whose name I don't remember) told me that the front portion of the landing gear was beefed-up along with a couple of small alterations to help guard against students twanging the gear and to protect somewhat against over-steering the gear during ground operations. The AT model is generally considered an inferior model, but from useful load to the beefed up gear, she's been a winner for me. Once the adjustments were made, the improvements to the AT model were carried through to the last Allegra model built.

[Z W]

I've been told that marketing departments based MGTOW numbers on the length of runway they wanted the planes to be able to use. The later models generally use a lot more runway at gross than the earlier models at gross, so perhaps there's something to it. Or maybe it's an old wive's tale.

The logic goes something like this:

We want our plane to be able to clear a 50' obstacle at the end of a 2000 ft runway on a hot day, so that people based at 2000 ft runways will buy it. For a C model to do that, we know from flight testing it needs to weigh XX pounds. Therefore, we certify it to XX pounds.

As time went on, runways got longer, and marketing departments quit caring so much if a plane couldn't be sold to people based at 2000 ft runways as a true 4-place (or 3-place, or 2-place) plane.

If anybody has a better explanation I'd like to hear it, though. I'm not by any means convinced this is correct.

[Jeff_S]

We all know that the MSE in 1991 was delivered with the 2,900 lbs. gross weight increase and that the increase can be retroactively applied back to '89 model serial number 24-1686. I am the owner of 24-1686. This aircraft was the very first Mooney Advanced Trainer, N900AT. My understanding from the previous owner (another Mooniac whose name I don't remember) told me that the front portion of the landing gear was beefed-up along with a couple of small alterations to help guard against students twanging the gear and to protect somewhat against over-steering the gear during ground operations. The AT model is generally considered an inferior model, but from useful load to the beefed up gear, she's been a winner for me. Once the adjustments were made, the improvements to the AT model were carried through to the last Allegra model built.

I own 24-1692-14, another AT. It's true they came out of the factory somewhat stripped down with no A/P, but they were well IFR equipped to teach complex IFR operations by at Flight Safety, etc. Mine has been pretty souped up with interior, avionics and the like over the years, and about the only thing separating it from an MSE are speed brakes and the gross weight increase. And I could even get that if I wanted to pay for the STC and the modified airspeed indicator. Since I don't need to carry the weight I haven't bothered, but it's nice to know I could if necessary.

[marks]

Jeff - I'm surprised that your AT didn't have speed brakes. I have read several times that the AT model was noteworthy for the fact that factory speed brakes were standard equipment on all AT models. I have met two other owners and each had this feature just like mine. I just found this fact again in both the Feb. 2001 and the May 2004 editions of Aviation Consumer. Perhaps your plane was a special order in some way. Did you ever see the plane painted in the striped red and white pattern?

[marks]

My understanding is that colors could be ordered without additional cost (they could have been school colors someplace) and that sometimes they were ordered with school symbols and patterns that didn't have the slanted stripes at all. I've seen a few without the stripes in advertisements in the past.

[Parker_Woodruff]

My 1990 M20J-AT did not have speed brakes. After the max weight increase, the useful load was 1035 lb, IIRC.

One nice feature was the cowl flaps were not electric (one less motor to break).

[fantom]

When I looked at factory new ATs they most certainly didn't have either standard or optional speed brakes. The option list, as I recall, was only about 6 or 7 items.

[marks]

Obviously, Aviation Consumer was wrong about speed brakes. I'm glad I have 'em but apparently they weren't standard. It looks like my AT being the very first one and having speed brakes, gave the impression that the speed brakes would be standard equipment. I also have manual cowl flaps, no head rests or arm rest.

[Jeff_S]

I have never once found myself wishing I had speed brakes. Of course, since I've never had them I may not know what I'm missing, but I have learned that a good forward slip can drop the bird down at over 1000' fpm if needed. As to other's questions, I have only ever seen photos of my plane since it's prior owner. I know he did some touch-up paint but didn't paint the whole thing, so I suspect this might be the original paint scheme. There's nothing in the logs about paint color numbers, because I tried to find that last year when trying to match the blue for a new inner-gear door.

[marks]

I frequently make use of aggressive forward slips too, but in IMC the speed brakes allow good forward speed to the FAF and then when deployed allow a quicker process to slow the plane to the desired speed. I frequently tuck them back in as soon as I get the gear down. In a strong headwind in IMC I might not use them at all.

[Alan Fox]

On a Mooney, it's mostly an issue of landing gear and tubular structure differences like the M20J 2900lb example.The landing gear has always been the weak point in Mooney design. The rest of the airframe apparently does not care if you overload it. Imagine a redesigned landing gear, VGs to lower the stall speed and 310hp in a Mooney airframe. At 13lb/hp a horsepower, we could have a 4000MTOW aircraft, a true full fuel, full people, full luggage aircraft. One can dream ;-) Or buy a TNed A36.

Yea but as the GW increases , so does the runway needed to get off the ground....

[RJBrown]

My old 231 did not have speed brakes and I never thought about them. After it was converted to a Rocket I found I really needed them. Had them and long range tanks installed when it was painted. A Rocket really needs both. My current J does not have or need speed brakes. I consider them a waste of money on a J but worth their weight in gold on a Rocket.

After spending 800 hour in a Rocket a 4000# Mooney is not impossible. They will lift more than the gear will land for sure. Problem is it will gain weight somewhere to gain the structure needed to certify.

But a Bonanza is so Slow.........

[WardHolbrook]

I've been told that marketing departments based MGTOW numbers on the length of runway they wanted the planes to be able to use. The later models generally use a lot more runway at gross than the earlier models at gross, so perhaps there's something to it. Or maybe it's an old wive's tale.

The logic goes something like this:

We want our plane to be able to clear a 50' obstacle at the end of a 2000 ft runway on a hot day, so that people based at 2000 ft runways will buy it. For a C model to do that, we know from flight testing it needs to weigh XX pounds. Therefore, we certify it to XX pounds.

As time went on, runways got longer, and marketing departments quit caring so much if a plane couldn't be sold to people based at 2000 ft runways as a true 4-place (or 3-place, or 2-place) plane.

If anybody has a better explanation I'd like to hear it, though. I'm not by any means convinced this is correct.

Good, don't be.

It's not all that simple. Modern light aircraft are certified to Part 23 requirements, prior to 1965 they were certified under the old CAR Part 3 rules. These certification rules establish all of the many parameters that must be met - structural loading, airframe, performance, stability, controllability and many others. As far as addressing whether or not the idea you heard has any merit... Think about it, if the reason for the particular MGTOW was purely a self-imposed marketing department limitation, wouldn't some enterprising individual have gone out and developed an STC to allow operations at the higher weight? Not everybody needs their airplane to be able to clear a 50' obstacle at the end of a 2000' runway. If you need to do that, they give you performance charts that will tell you what the weight limitation would be to allow that to happen.

Now what did happen back in the 1970's was some IRS involvement in the maximum certification weights of some light aircraft. Back then they had federal excise taxes based upon certain arbitrary aircraft weights and manufacturers would manipulate the MGTOW to keep the aircraft out of the higher FET bracket. Nowadays you see this same thing too. Take the King Air 200 for example . Civilian versions are limited to 12,500 pounds for no other reason than the requirement that anything over 12,500 requires a type rating. The military flies their "off the shelf" King Airs at much higher weights.

[Alan Fox]

My old 231 did not have speed brakes and I never thought about them. After it was converted to a Rocket I found I really needed them. Had them and long range tanks installed when it was painted. A Rocket really needs both. My current J does not have or need speed brakes. I consider them a waste of money on a J but worth their weight in gold on a Rocket.

After spending 800 hour in a Rocket a 4000# Mooney is not impossible. They will lift more than the gear will land for sure. Problem is it will gain weight somewhere to gain the structure needed to certify.

But a Bonanza is so Slow.........

You wish LOL

[Lood]

Affirm on the extra runway needed. I took of right at MAUW yesterday morning and I had my work cut out. Only a few degrees warmer OR just a little more weight on board, and we would not have been airborne in time.

The conditions were a 2820 ft grass runway with concrete for the first 900 ft, 5300 ft elevation and the temperature was about 15 deg Celsius. It rained quite a bit the previous afternoon and evening and the grass was still a bit damp. I got off the ground with about 600 ft to spare and I must admit that although I knew it would fly, the poor acceleration really got my attention.

The wind was 90 deg from the side at around 8 kts and density altitude was around 6200 ft. A turbo would have been very welcome yesterday...