Performance Charts (rolling your own).

[Garfly]

In the absence of P-charts in my POH and, in any case, wanting to establish real world actual numbers for my particular aeroplane - numbers that could be extrapolated to cover all scenarios - I've been looking for some kind of iPad app that could help with this, but without much success.

 

The nearest thing I can find is this one from Gyronimo - but it's specifically for the C150

 

Gyronimo aircraft performance apps - iPad Pilot News

 

Of course, if I could wait for a standard day at sea-level and load my plane to its precise MTOW and take-off by specified method in nil wind on a hard surfaced perfectly level runway, I could establish perfect base-line figures from which to extrapolate - according to generally accepted factors. (For example: for each 1000' increase in DA add 10% to take-off distance.)

 

But, short of that perfect day and perfect place I suppose there could be an app that allowed observed data from any given set of take-off conditions which would be a valid base from which to calculate any other set. That is, similar to the Gyronimo idea but tailored to your own real world aircraft.

 

Any ideas?

 

 

[djpacro]

Back when the DoT (before CASA) used to produce ‘P’ charts to go in the Australian-specific flight manuals they used some straightforward software to correct measured distances to ISA SL and MTOW. It then printed out those ‘P’ Charts. A camera was used and distances/heights measured off the printed photo to get distance to/from 50 ft to the ground. People standing beside the runway marked ground distances,

 

Some years ago I ran a Uni Course which did that as a student project using some more modern tools. I might still have those notes on how to do it (consistent with FAA AC 23-8 FAR 23 Flight Test Guide).

 

Perhaps I should develop an app and retire on the profits from sales?

 

CASA has similar info with details at https://www.casa.gov.au/file/122726/download?token=NFLC3fMe with a further reference to FAA AC 23-15.

 

 

[Garfly]

Perfect! That's a really interesting CASA document I'd never seen before.

 

If you read the comments below that iPad Pilot News article I quoted above

 

(Gyronimo aircraft performance apps - iPad Pilot News) you can see that there might be a good market out there for an app for all types!

 

But really, tips about the best ways to establish your real world baseline numbers realistically would be handy.

 

Even if we have to nut out the calculations by hand.

 

I guess any app is going to be, first and foremost, a learning tool.

 

I'm pretty sure that old hands get by quite well by applying common rules-of-thumb as far as performance goes.

 

The main thing, I guess, is not to forget any of the relevant factors and to take take-off performance quite seriously (especially in summertime in the high country).

 

 

[Oscar]

Back when the DoT (before CASA) used to produce ‘P’ charts to go in the Australian-specific flight manuals they used some straightforward software to correct measured distances to ISA SL and MTOW. It then printed out those ‘P’ Charts. A camera was used and distances/heights measured off the printed photo to get distance to/from 50 ft to the ground. People standing beside the runway marked ground distances,Some years ago I ran a Uni Course which did that as a student project using some more modern tools. I might still have those notes on how to do it (consistent with FAA AC 23-8 FAR 23 Flight Test Guide).

Perhaps I should develop an app and retire on the profits from sales?

 

CASA has similar info with details at https://www.casa.gov.au/file/122726/download?token=NFLC3fMe with a further reference to FAA AC 23-15.

Having been one of 'the people standing beside the runway', (at Hoxton Park!) for the Australian Twin Otter performance chart figures, I have to say DJP's commentary is spot-on. Mind you, when Randy Green landed the bloody thing on full beta thrust and ended up his roll-out traveling backwards, it made a nonsense of the thing ( but beta thrust was not allowed for the official P charts). But it was farging awesome to watch! I reckon he could have put it down in the SCG and ended up at the nearest crease.

 

However, for determining proper POH figures, a bit more than just recording what appears on the ASI is necessary. To do it properly, you need a calibrated, free-swinging (in both vertical and horizontal planes) pitot probe that is NOT influenced by position error - and those are few and far between. That provides the correction table between true airspeed (TAS) and ASI reported airspeed (AIS). And TAS vs. the figures one sees in manufacturer's blurbs for stall, VNE etc. can become very sobering.

 

To produce a POH for a manufactured aircraft that will withstand audit, requires test-pilot skills. Certification authorities do NOT hand those out as a cut-out-the coupon on Cornflakes packets. Ask Keith Englesman.

 

PS: in earlier days, test pilots used to throw eggs out of the cockpit downwards to record lift-off, touch-down etc. points. No doubt many proto-chickens died - but probably, very few pilots!

 

 

[Oscar]

Oh, the curse of fat fingers and poor glasses: Indicated Airspeed is, of course, IAS - Not AIS... and is what you get on the ASI arcs..

 

 

[Garfly]

And I suppose with our less stringent amateur build rules the whole POH principle doesn't apply since every 19 construction, is likely to be an entity unto itself.

 

And if and when it's actually put to the test any aeroplane might turn out a weaker performer than it's 'supposed' to be. Sure, most of us operate most of the time under non-critical performance regimes. But sooner or later we'll be in a situation where we'll really want to know whether our safety cushion is about to be rudely sat upon.

 

Whenever in doubt, I'd probably err on the side of caution: flying out in the cool hours or making a second trip to retrieve the camping gear or decanting fuel or, heck, just leaving the pax to walk home! (Any other suggestions? ;-)

 

But best of all would be to know exactly what to expect from any situation (while still leaving a healthy margin for error).

 

 

[Yenn]

I have done this for two aircraft. Both of which I built and test flew.

 

Getting the figures takes time and because I used an experimental engine in the RV4 I had to do 40 hours of test flying. I thought this would be more than i needed, but it turned out that I could have done more to get all the info I needed.

 

Test flying can be demanding, especially when there is thermal activity, but you can come up with some good figures with perseverence.

 

The changing temperatures and pressures can be allowed for theoreticly, but unless you are really pushing for the last bit of performance they will not make much difference.

 

Some of the modern instrumentation can make life easier, such as getting a readout of ascent and descent directly, rather than having to use time and altimeter indication.

 

I am sure that if you just keep flying and following test procedures, you will eventually get the numbers you need. Remember even the numbers from the professional manufacturer only represent the best his test pilot could get at the time.