MTOW that mythical number

[red750]

Interesting subject.

 

I noticed when completing the Aircraft profiles, some listings quote Gross Weight, and some MTOW. A few quote both.

 

It appears that with GA aircraft, the Gross slightly exceeds MTOW, which I have assumed allows for fuel consumed in runup and taxying - I could be wrong, please correct me if that is so.

 

With Military aircraft, MTOW usually exceeds Gross by a good amount. Again, I assume that Gross is just the fully equipped plane, while MTOW includes ordnance.

 

 

[facthunter]

MTOW is weight at beginning of take off roll. Taxi fuel can be deducted. It takes account of Aircraft configuration, runway length, obstacle clearance, density altitude etc. These are performance related factors, not structural ones. Nev

[Bruce Tuncks]

Please tell us more djpacro. I have been looking on google for the upgust which determines rough air, alas to no avail. I sure got the 40 knot figure from somewhere, just as I got the 15 knot upgust for " smooth air". In the case of the 15 knot figure, it came from a top glider pilot who worked at WRE in Salisbury sa.

Again, it is a hard figure to check out...  maybe there are different upgusts for different planes?  That would explain why you just get double-talk when you try and look it up. It makes no sense to me if there are indeed different figures to define "rough air".

 

[djpacro]

6 hours ago, APenNameAndThatA said:

If Va increases with increased weight, then so will Vno, I expect. Both are counter intuitive. I suppose that the reason is that the engine mounts are designed to break before the wing spar.

Design cruise speed Vc, from which Vno is derived, does increase with weight because whoever wrote the regulations decided that. The ASTM for LSA is quite similar to FAR 23 in this respect. This Advisory Circular explains considerations of design airspeeds (see page 26 etc) https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23-19A.pdf

 

I know of one airplane where the engine mount is definitely not stronger than the wing. At lighter weights the load factor due to a gust increases (aeroplane flying at the same airspeed, Vno does not vary with weight) so there is more load on the engine mount than at the higher weight where the wing stresses are higher.

[APenNameAndThatA]

2 hours ago, Bruce Tuncks said:

Please tell us more djpacro. I have been looking on google for the upgust which determines rough air, alas to no avail. I sure got the 40 knot figure from somewhere, just as I got the 15 knot upgust for " smooth air". In the case of the 15 knot figure, it came from a top glider pilot who worked at WRE in Salisbury sa.

Again, it is a hard figure to check out...  maybe there are different upgusts for different planes?  That would explain why you just get double-talk when you try and look it up. It makes no sense to me if there are indeed different figures to define "rough air".

 

The stronger the updraft, the steeper the angle of attack. That means that if a wing stalls with an updraft of, say 15 kt (1500 fpm) updraft, it will be able to cope with an updraft above that because the wing will be already stalled. You need to organise it so you are slow enough so that the wing stalls before there is an updraft strong enough to damage it. The slower the aircraft the slower the updraft will have to be to stall the aircraft. The intensity of the updraft does not have to specified because you just need to make sure the wing does not break. The intensity of the acceleration is specified, though. Its bout +4 and -2 G's for some things, IIRC, and there are design limits, safety factors and ultimate limits and etc. 

[djpacro]

4 hours ago, Bruce Tuncks said:

Please tell us more djpacro. I have been looking on google for the upgust which determines rough air, alas to no avail. I sure got the 40 knot figure from somewhere ..

This may explain https://airfactsjournal.com/2020/12/understanding-vb-turbulence-penetration-speed/

 

That is for transport category aircraft and does not apply to small aircraft.

 

 

[spacesailor]

red750

In your profile albums, how many of them specify " wing loading ", 

With all the talk of ' upjust ' isn,t the G actor the test for wing strength !.

+ 6 & - 6 seems quite strong. It will stall, but  the Reno air racer rules are 6 G + or minus.

Few winga detach at their meetings. ( BeeGee modle R  )

spacesailor

 

Edited March 22, 2022 by spacesailor
Spelling

[Bruce Tuncks]

Thanks dj, the 4000fpm is indeed 40 knots, but the advice "to slow down " is correct of course. And I didn't know that the 40 knots did not apply to Jabirus etc.

I still reckon that the thing has been hijacked by bureaucrats who have a one in a billion   problem if they do the realistic thing, so of course they err on the side of caution.

There is a story about how Willy Messerschmidt told Hitler that he could build a world-beating fighter plane if he was only free from bureaucrats. Well in 1938, the Me 109 was a world-beater.

[Bruce Tuncks]

Space, my son has a Lancair which can come with wing-extensions removable for Reno racing.

[spacesailor]

Bruce,

So too the Hummel Bird.

BUT

A lot !, l mean A BIG lot cheaper.

6G + or minus without wing extensions.   LoL

140 mph VNE  wouldn't win many races.

Unlike " STRAGA "A very modified mustang.   500 mph, the media quote.

spacesailor

[djpacro]

7 hours ago, red750 said:

I noticed when completing the Aircraft profiles, some listings quote Gross Weight, and some MTOW. A few quote both.

 

It appears that with GA aircraft, the Gross slightly exceeds MTOW, which I have assumed allows for fuel consumed in runup and taxying - I could be wrong, please correct me if that is so.

 

Depends on the certification. These days I only fly small FAR 23 certified airplanes where

Sec. 23.25 — Weight limits.

(a) Maximum weight. The maximum weight is the highest weight at which compliance with each applicable requirement of this part (other than those complied with at the design landing weight) is shown. 
 

The POH for a FAR 23 airplane simply states the maximum weight i.e. cannot have more than that when one starts the engine.

 

More complex types may specify a MTOW and an associated max ramp weight.

 

Australian pilot theory seems to me is a hangover from when Australia had its own certification requirements and unique flight manuals which generally used the term MTOW. (There were also MTOW limits depending on the density altitude for even simple types like a Cessna 150.) Pilots naturally assumed they could make a very generous allowance for additional taxi fuel in the absence of a specified max ramp weight.

 

The term “maximum weight” is simply that.

[djpacro]

11 hours ago, djpacro said:

Depends on the certification. These days I only fly small FAR 23 certified airplanes where

The POH for a FAR 23 airplane simply states the maximum weight i.e. cannot have more than that when one starts the engine.

and how it was done, I should've added. I see that PA-28 and Cessna 172, even the 152 have a MTOW and max ramp weight defined in the POH. The Decathlon AFM simply has maximum weight. Pitts POH has both maximum gross weight and maximum takeoff weight - the same number.

 

The ASTM for LSA has slightly different terminology again "maximum takeoff or maximum design weight". My copy of a Jabiru POH specifies maximum takeoff weight in one section, gross weight in another section (same number 600 kg)

[Bruce Tuncks]

Correct djp, my poh also states the bit about being stressed to 700 kg. This is only allowable if flown vh.

 

[Bruce Tuncks]

Space, that hummelbird has a good top speed. I reckon it would win a race if they had a class for efficiency...  for example, if your speed was handicapped by the engine size.

 

[spacesailor]

Perhaps a ' half engine ' caturgory

Not too many in that category! .LoL.

spacesailor

[walrus]

Bump. 

[spacesailor]

Pity those super fast " B D J " planes.

Will win every race !.

How about fuel efficiency? .

61 mpg, 3 l/ 100.

Thats dam good. 

spacesailor

[spacesailor]

Correction 

Pity !.

Those B D J ---.

It's a Grammer thing.. l missed the comma .

spacesailor