View Full Version : Computerised RTOGs?
APPYMAN
16th Jan 2004, 04:55
Anybody know if there is any PC-based software available for solving Regulated Take-off Graphs?
john_tullamarine
16th Jan 2004, 05:52
(a) most of the major manufacturers will provide such software to their customers
(b) there are commercial providers of such services who have done the work and will provide RTOW tables for clients at a dollar (or many)
(c) you could do the thing the long way and start with a flight manual, do the regressions or set up lookup tables (according to preference), and generate your own software .. nothing too difficult with this but be prepared for some investment in time ... not to mention the odd numerical analysis problem in achieving appropriate levels of accuracy ...
Mad (Flt) Scientist
17th Jan 2004, 01:35
Plus, if you choose option (c) and do it yourself you should be very careful to validate your results when all is done.
After all, you're essentially substituting an unapproved method (the PC program you have developed) for the manufacturer's approved charts. If you drop a zero inadvertently and go careering off the end of a runway somewhere, I'd imagine there might be some raised eyebrows.
APPYMAN,
What type of aircraft are you talking about???
J_T,
not to mention the odd numerical analysis problem in achieving appropriate levels of accuracy ...
You might be surprised at how inaccurate the present systems are! Considering that there is only one AFM for an aircraft, boeing offers 3 computerized systems for takeoff analysis on the B744. Their latest uses the first principle method of calculations rather than the older model tables. They believed that the increased takeoff weight of this "program" was worth $250k per tailnumber, as if offered 8000 kgs more takeoff weight out of hot and high airports.
Doesnt say a lot about the accuracy of their older programs... :):)
Mutt.
john_tullamarine
17th Jan 2004, 05:33
Following on from the previous posts, the main problems with DIY simulation approaches lie with the following ..
(a) the AFM is the legal document against which your simulation would be tested at law after an accident or serious incident ... the lawyers can be presumed to have the time and resources to obtain antipathetic expert opinion designed to demolish the integrity of your simulation .. so, beware.
(b) the simulation must reproduce the printed carpet lines so that the values are conservative. However, any conservatism costs the operator money so we endeavour to minimise conservatism and produce numbers which are on the centreline of the printed line to a suitable level of accuracy. What is a suitable accuracy ? I suggest that a magnified scan should plot the calculated point close to, and slightly conservative with respect to, the observed centreline. Does this involve a moderate investment in time resources ? .. sure does ...
(c) having done (b) we have a good picture of the ACTUAL printed lines. However, we rarely need to calculate data which is right on the lines .. now comes the interesting part wherein one has to come up with an interpolation technique which will stand up in court.
Interpolation in a "normal" carpet is comparatively straightforward. Where there are a few discontinuities (as routinely is the case) the task gets a bit tedious. Running up interpolation routines which can handle regions where the chart carpet folds back on itself can be more than a little difficult when it comes to putting hand on heart for the validation process.
One needs a reasonable knowledge of the capabilities and limitations associated with various numerical modelling techniques. Generally speaking, 3D techniques are pretty useless as the detail simulation accuracy is just not there in the outcome ... so it is usually a case of coming up with sets of very tedious 2D simulations .. and there are various ways of approaching this problem....
About the nitty gritty detail which goes into this part of the exercise I will remain mute as the likes of Mutt and I derive a dollar from doing this sort of work ....
Is the simulation work a pain in the neck ? Absolutely ... one needs to be quite painstaking in detail while working up the simulation and similarly in validating the simulation against the printed AFM data.
Is it fun ? .. yes, in the same way that stopping after bashing your head against a brick wall is fun ...