SINNERS COME TO CHURCH AGAIN - "WHO HAS NEVER FLOWN OVERWEIGHT" - THESE ARE MY EXAMPLES IN REAL LIFE.

[RFguy]

Walrus

I appreciate the caution. !

I do not intend on going beyond the POH CoG limit, nor any steep pitch ups.

 

I've been reading various aircraft flight test guides, manuals etc, and the classifications for utility or aerobatic attitudes, states and   recovery. What I have read is enough to scare me a little.

 

There's a good reason the same  aircraft in aerobatic category (compared used to utility category ) has tighter CoG  limits. Get the thing pointing straight up and 2% extra of CoG aft may prevent a recovery.... It's that tight ! 

 

Just like in electronics, and other systems that are not unconditionally stable, systems can still be stable but oscillatory behaviour increases, although the system will still return to equilibrium in a rather ugly fashion. Apparently same with aircraft - with pitch control inputs, the tests of negative, neutral or positive stability in that axis  and CoG. As the aft CoG limit is approached, the response to a step input  will show deteriorating behaviour returning back to equilibrium.

 

This reading  and study I have done drives home the importance of not exceeding the POH aft CoG limit at all, there may be zero margin , you don't know whether the mfr was optimistic on the margin or conservative on the margin. Test configurations and aircraft condition and configuration vary , which is enough to assume you have no margin. I think anyway.......

 

-glen

 

 

 

 

Edited October 19, 2020 by RFguy

[SSCBD]

RF - you must remember theses aircraft (RAA LSA)  are not tested to the degree of absolutes. Nor are the specs and quoted figures can be relied on by some manufactures in this sector. 

As we have seen Boeing stuffs up a lot and they have thousands of qualified engineer's that still get it wrong.     

 

Don't try to push the envelope as it might bite you with SSCBD = Stall - Spin - Crash -Burn -Die! 

[RFguy]

agreed.

anyway, back to the topic I guess.

spill your overweight sins ...  I dont have any, so far. 

 

 

 

 

[SSCBD]

RF -  Do you know the way bush pilots check single engine C of G?  This is a real question? 

 

[RFguy]

putting aside the obvious (knowing various pre computed or weighed scenarios which can cover most likelihoods : ) 

ahhh tricycle : ummm check how easy it to tip the plane on its mains, -  by pulling down on the tail tiedown point , nose wheel off the ground ?

ahh tailwheel - hmm dunno.  maybe check how heavy the tail is by same way - pick up the tail ?

-glen

 

 

 

Edited October 20, 2020 by RFguy

[Old Koreelah]

5 hours ago, RFguy said:

... check how easy it to tip the plane on its mains, -  by pulling down on the tail tiedown point , nose wheel off the ground ?

ahh tailwheel - hmm dunno.  maybe check how heavy the tail is by same way - pick up the tail ?

It amazes me that some bright spark hasn’t produced a reliable cockpit aid that uses pressure on undercarriage to compute actual CoG. 

[IBob]

15 minutes ago, Old Koreelah said:

It amazes me that some bright spark hasn’t produced a reliable cockpit aid that uses pressure on undercarriage to compute actual CoG. 

It's a great idea, O K, but probably near impossible to get certified:

Even assuming the loadcell arrangement could be designed to remain sufficiently accurate, the thing would then have to be correctly configured for the layout of the aircraft. I would have added 'and used only on a horizontal flat surface' but we have the technology nowadays to correct for lean...though that's all more stuff to go wrong.

[facthunter]

The idea has been around for ages. You could have a weighbridge in a part of the taxiway. or adjourning bay  An accelerometer to measure how you are actually accelerating along the runway would be helpful also and easier to design.  It doesn't stop you using a runway that's too short for you by mistake either.

  Rearward C of G will probably go unnoticed until you get slow enough for the tailplane to stall with stick forward . That's where you will naturally put it to stop the tail dropping  and probably ending your days.. The mainplanes will stall as a result and you can't recover unless somehow you can get the speed high enough for the horizontal stab to function and control pitch attitude and AoA once more. Nev

[M61A1]

6 hours ago, RFguy said:

putting aside the obvious (knowing various pre computed or weighed scenarios which can cover most likelihoods : ) 

ahhh tricycle : ummm check how easy it to tip the plane on its mains, -  by pulling down on the tail tiedown point , nose wheel off the ground ?

ahh tailwheel - hmm dunno.  maybe check how heavy the tail is by same way - pick up the tail ?

-glen

 

 

 

Hahaha.....Nosewheel.......🤣

 

42 minutes ago, Old Koreelah said:

It amazes me that some bright spark hasn’t produced a reliable cockpit aid that uses pressure on undercarriage to compute actual CoG. 

OzRunways has section in the aircraft library where you can create your own W&B envelope and load different configurations. I have set up several configs and find it really helpful.

[RFguy]

I have read and watched instances of loss of control due to excessive aft CoG in a stall, at altitude,  tail goes down.... and by the time the aircraft is lucky enough to tumble and  to get into a recoverable attitude, it has likely reached a high velocity, and you might rip the control and lift surfaces off with a sudden movement. It's an undesired aircraft state alright.

 

 

[IBob]

49 minutes ago, M61A1 said:

Hahaha.....Nosewheel.......🤣

 

OzRunways has section in the aircraft library where you can create your own W&B envelope and load different configurations. I have set up several configs and find it really helpful.

Funny you should mention that, M61A1. This thread prompted me today to do what I've been meaning to do for a while now: set up a spreadsheet and button in a whole range of W & B scenarios for my aircraft.

[RFguy]

this is an excellent treatment on W&B

 

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/faa-h-8083-1.pdf

 

 

[Thruster88]

32 minutes ago, IBob said:

Funny you should mention that, M61A1. This thread prompted me today to do what I've been meaning to do for a while now: set up a spreadsheet and button in a whole range of W & B scenarios for my aircraft.

That is what I did for my Beech Musketeer when I got it many moons ago. Back seat and a big baggage 140lb was al new to me. It will only get out of CG if one did something really silly. 

[RFguy]

I have found an excellent two page paper  on effects of aft CoG and forward CoG

It's written for homebuilders evaluating their aircraft.  (1962 )

 

Why is this one so good? (IMO)

 

The author attempts to explain concepts several different ways, and one of them you will understand...

 

 

CG_limits_and_longitudinal_stability.pdf

Edited October 20, 2020 by RFguy

[facthunter]

I think you will find better if you continue looking. Can't say I was over the moon with it. The difference in mainplane and horizontal tail AoA is often referred to as longtitudinal dihedral. The average aircraft we fly has the nose held up by a download on the tail. This force has to be resisted by the "extra" lift of the wings so creates extra drag.  so you don't want  to be excessively nose heavy for efficiency as well as flaring for landing. As you speed up the nose should rise if you touch nothing. so you trim nose down as you go faster. and the aircraft flies more nose down as the lift required is constant so less angle of attack on same wing.

   The comment on  flat spinning is not well made. Weight at extremes both forward and rearwards count more than C of G position in flat spinning. Rearwards CofG makes stall recovery much more difficult and you do have to unstall to exit a spin. IF the rear horizontal surfaces carry  positive flight loads the efficiency can be greater and this is done on seaplanes to counter high thrust lines of the engines.. Done to excess the plane is unstable as speed increase makes the nose lower which makes you go even faster. Area and distance from the C of G affect the pitch control force (moment) available from the tail feathers.

  I also consider prop wash helps  make them more effective where the engine centre is near the fore and aft axis alignment. I couldn't make any sense of the comment in this regard in the article.

  If the mainplanes stall first the nose drops and you recover and it will continue to do that until something changes. If the horizontal tail stalls there's  no self recovery and no procedure generally to cope with that as the aeroplane is unairworthy and unsafe . Maybe some one can devise something but it would be beyond most pilots capability to fly it so like high voltage wires  and crocodile infested creeks, don't go there. Nev

[RFguy]

good comments Nev.

While I have gone way deep into it, I've been looking for something to post that goes into it, but not too far into it, so not  to lose the reader in depth or length.  In RAaus and GA circles, there is I think amongst a good proportion regularly flouting of rear aft CoG limit and being simultaneously overweight, without understanding the implications.  In W&B in RAaus the syllabus says "dont do it" without going much  into the implications.  I think good instructors will supplement the syllabus with greater detail and information.

Edited October 21, 2020 by RFguy

[facthunter]

This phenomenon has been the cause of many prangs since planes first got into the sky. Lack of pitch control is  usually fatal. That's been known since before powered flight. E/C and F/E/C should cover it. A planes design should include sufficient duplication of pitch control to have an acceptable redundancy function.

   There should be a placard... Note This vehicle is NOT a CAR it's an AEROPLANE . If you don't know how to "THINK" aeroplane, don't touch  anything.. 

   Some people will never learn. It's a pity they take innocent others with them when they get involved in aviation when they are unsuitable. RAAus has encouraged the "anyone can fly a plane" misconception for commercial reasons. Don't allow low flying to be taught except for mustering. Propagate the idea you can have a  Certificate in 20 hours.etc.   IF students don't get the basics well understood because of inadequacies in the syllabus, learning process, follow up, testing  and ongoing information guidance scene it's close to negligence. Nev

[Yenn]

In the operating handbooks I have written I put in worked examples of several weight and balance conditions.

For the RV 4 I had Max weight with max luggage at rear posn, Max wt with max fuel and also min fuel, plus others. The most dangerous loading was max weight with min fuel, which would put you out of safe C of G quite easily.

I am surprised at the apparent lack of knowledge of a lot of RAAus pilots and how they seem surprised to find that they can easily load the plane into a dangerous situation.

[facthunter]

In several type endorsements I've done W & B and fuel management had a pass mark of 100% required. That's how seriously it is regarded in some quarters. Nev

[RFguy]

Hi Yenn. seems to be a pretty common thing for the low wing LSA (minimum fuel CoG hazard) . 

Low wing LSA - (Min fuel CoG hazard) , as fuel tanks are often in wing  forward of the wing spar, and a long way forward of the seats and baggage.

High wing MAY have  a different issue at min fuel - MAY be nose heavy IF  the wing(+fuel) is behind the front seats.....and only pax no bags. (J230)

 

GA low wing normal and utility  aircraft I see the wing is often further back to promote better baggage +  load capability I guess. spar under the seat..

 

Where's the fuel in the RV4 wing ?

 

 

Edited October 21, 2020 by RFguy

[facthunter]

Most hi wing have fuel tanks in the in board part of the wing which has the extra benefit of fuel fed by gravity (and little Co G change). Wing tanks reduce structural wing loads also.. In some planes the MAX permitted weight must include fuel above a certain figure. Nev

[kasper]

And the reason people do not openly talk about overweight flight in RAAus aircraft is ... the heft of the bricks that can be thrown at you if you admit to it and who can throw those bricks.

 

If you are overweight your aircraft immediately falls outside the exemption allowing RAAus to issues registration and pilots certifciates for legal operation... and your RAAus insurance coverage for third party damage immediately ceases so be extra careful not to hit anything expensive while breaking the CAO exemptions.

 

So if you are flying overweight for the CAO exemption you are immedaitely flying an unregistered aircraft in breach of the Act and Regs and unless you hold a valid PPL you are in addition an unlicenced pilot flying that unregistered aircraft ... but if you are a PPL holder you are in trouble under that licence for flying an unregistered aircraft - you are in double breach of aircraft and pilots requirements no matter what ... and the only people who can throw bricks at you are CASA and they are enforced by courts.

 

The worst that RAAus can do to you in response is to suspend your pilots certificate and/or cancel your membership ... slap in the face with limp lettuce compared to CASA.

 

I'd love to talk openly about unusual operations eg. T500 thrusters can take off so long as the doors can be forced closed but I have a PPL and RAAus pilots entitlements I'd rather keep so sorry but this topic is very dangerous given it is a public forum and we do not know who is trawling through ... a UK board had a similar thread years ago and CAA enforement were watching and did act on what they read.

 

 

Edited October 21, 2020 by kasper

[pmccarthy]

The classic problem is an RAA reg aircraft which is weight limited but would have a higher legal weight in GA. You are about to cross Bass Strait. Do you limit your fuel load to the RAA amount, or do you fill to the technical safe limit of the aircraft? Obviously the latter is the responsible decision. You will be legal about one hour into the flight once the excess fuel has burned off. If you then have an incident on arrival, can insurance be refused because you must have departed overweight?

[kasper]

1 hour ago, pmccarthy said:

The classic problem is an RAA reg aircraft which is weight limited but would have a higher legal weight in GA. You are about to cross Bass Strait. Do you limit your fuel load to the RAA amount, or do you fill to the technical safe limit of the aircraft? Obviously the latter is the responsible decision. You will be legal about one hour into the flight once the excess fuel has burned off. If you then have an incident on arrival, can insurance be refused because you must have departed overweight?

You will not get insurance coverage as the fact is you took off overweight.  And your own flight plans and fuel plans will clearly prove it as would a backwards call of take off weight based on what they can see.  It’s insurance - they will deny coverage and you will be put to shouting and showing in court how you were not.  Not likely to be well received if you try claiming I was under and the 912 only burned 4lph for the flight as might be required to have legal take off weight.  

[RFguy]

how about :

"got a  tow from a glider  tow aircraft for the first 90 nm  and engine was shutdown the whole time "

" on departure, had a unusually strong 2000 fpm updraft up to 28,000 feet, passed out, engine stopped. aircraft maintained trim somehow and was close to best glide. regained consciousness at 8,000 ft over the Tasmanian coast  and successfully restarted and landed immediately. "

"only used 1 gph  using the ultra lean of peak  burn kit on my Jab "

" a 747 came up in front of me and I got sucked along in the  low pressure area behind the 747 - I was shutdown for the whole hour as I didnt want to run into the back of it "