Heron flightplanning

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SkippyBing
Concorde
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Joined: 30 Aug 2006, 18:21

Re: Heron flightplanning

Post by SkippyBing »

Worth bearing in mind that the datum is a completly arbitrary point, on a lot of aircraft it's in front of the nose which handily means you don't have to bother with positive and negative arms when you're doing your maths. You don't particularly need the datum point marked on the aircraft as you already know the moment arms to all the places you're going to put stuff, it would only really be of use if you wanted to load something in an unusual position and you needed to measure it but even then it wouldn't be vital as you could measure reference a known point.
Regarding units, you can have any combination of weight and distance units as long as you're consistent. For instance if you were in a metric country flying an aircraft designed in imperial units it wouldn't be out of the question to weigh everything in kilos but still use inches for the measurements as long as you had the CoG chart in KG which would be relatively easy to do by just converting the units on the weight axis. This has the advantage of only doing the conversion once rather than for every passenger. Having said that a lot of aircraft have a metric and imperial CoG chart.
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Anders Samuelsson
Meteor
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Joined: 03 Jan 2013, 12:57

Re: Heron flightplanning

Post by Anders Samuelsson »

Thank you for all input, it's been quite a learning curve since I never bothered with the complexity of CoG before in my flightsim career :)
take-care
Andy

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dfarrow
Vulcan
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Joined: 16 May 2005, 13:01
Location: N Dorset

Re: Heron flightplanning

Post by dfarrow »

Andy , might be a bit late , but here goes...
an example of a real load sheet For a Piper Cherokee Warrior , the 1st is the blank sheet , maybe you can copy , print 'n practice . The variables of fuel , pilot , passengers , baggage are all added to the loadsheet when information is available .

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The basic empty weight and basic arm [ index ] are aircraft specific [ even within a common fleet ] .
Here is a copy from PA28 operating handbook , which states where datum is ......

'' The datum used is 78.4 inches ahead of the wing leading
edge at the inboard intersection of the straight and tapered section.''

In practice we just use the blank sheet as a skeleton and just fill it in . One of the co-pilots duties whilst en-route is to prepare the loadsheet for filling in on arrival . That's one reason a final check in time is used . So that final pax , cargo , baggage figures can be entered and the loadsheet finalised and signed by the Skipper before departure . [ hopefully on time ]

Finished example .
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This 2nd one , I've filled in with a guessed but representative set of figures , all the explanations are on it , but a few back ups . Sketchy's spot on with datum info and also that the figures have to be changed to one set of units . In example I've got 1 pax in Kg and changed it to lbs , and the other 2 are changed from stone to lbs .
We're making sure a/c weighs less than Max Gross Structural weight ... 2300 is less than 2325 ... that's ok .
We're making sure that a/c is within the allowable trim limits ..... 88.8 is ok .
If trim is less than 83 .. ie all weight at nose ; the elevators may not generate enough force to lift the nose at rotation . Likewise if all weight is at the back ie trim greater than 93 ; then a/c will probably autorotate on takeoff , and elevators may not generate enough force to lower the nose thus leading to an unrecoverable stall . [ perhaps like the freighter 747 in Afghan when perhaps all the tanks on board rapidly moved to the rear on take off ].
This loading philosophy is the same for all a/c , so a Cherokee example is similar to an Heron or even a 747 . [slight difference is that swept wings introduce different moments for fuel in wing tanks ] .
For airlines an aft trim [ within limits ] is preferable . In the cruise less trim is used and thus less drag is generated = less fuel burn .
Some a/c have a more narrow envelope in which to load .. on ATPs , the 1st 20 pax had to sit in the back , if less than 20 pax total ; we had to load ballast in 25kg bags of shingle !
Nowadays most loadsheets are computer generated , but was still doing the odd manual one on Tristar [ 393 pax ] up to 2000 . For big a/c standard weights are used , male, female , child , infant . [ they were increased several years ago ! ] . Smaller ones like Islanders might still have scales at check in !
Check in times can now be reduced as approximate figures are used to prepare the loadsheet by the Dispatcher [ Redcap ] . After a/c pushes back final figures are sent by Data link or radio . If they within limits a/c takes off straight away . If outside pre set limits , then you can't take off until figures are finalised .... very often you'll here crews saying they are staying on the ground ''awaiting final figures ''

hope this explanation is not too longwinded .

Brgd Dave f .

Anders Samuelsson
Meteor
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Posts: 90
Joined: 03 Jan 2013, 12:57

Re: Heron flightplanning

Post by Anders Samuelsson »

Hi,

Very interesting and a good post, very nice to see a filled in loadsheet. I think I am starting to get a hang of the ideas a little bit at least.

In the sim it is interesting, I did a flight from EGQK to EGQL in the heron and I did all the planning, all weights and CG stuff and even calculated the required lenght of the runway, and then when I was done I realised that I had a 20 wind crosswind component (gusting to 34 I think) so the flight couldn't be flown (since it was the sim, I did it anyway, interesting landing in that kind of crosswind (it was pretty much the same at EGQL)) :)
take-care
Andy

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