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.

 

 

[Garfly]

 

 

 

[Area-51]

Its a challenging task, but everybody knows (especially the medua), that in general, if the kitchen bench hobby plane is found in pieces upon the ground it has probably exceeded its performance parameters... However one can still search for a similar power weight style certified aircraft POH and get a ball park impression of the AF's performance across a mixture of various environment factors.

[Garfly]

In the video, Jason Miller urges against trusting your life to book figures at all - even your own POH's ones. 

He says add at least 20% to the book figure (after all other factors in "Notes" have been accounted for). 

Plus, as a back up, he pushes the 70% of rotation speed by 50% of runway length rule.

 

It's too bad DJP never got around to building that app.

 

On 11/12/2017 at 2:31 PM, djpacro said:

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.

 

 

Unfortunately, that CASA link doesn't seem to be working any more.   

[Thruster88]

Not the first pilot to prevent a C172 from taking off by adopting a stupid nose high attitude. The performance charts are null and void if the aircraft is not operated correctly. I agree with Jason's points however this is not a good example accident for the point he is making IMHO.

 

[facthunter]

You can't just make up your own rules and figures. Caution is fine. Have a lift off and climb, No go point and Pace it Out, before hand. Density  altitude is what will kill you.  IF she's not ready to take to the AIR then stop, where you have room to do it and unload or wait till Conditions change. Nev

[Garfly]

36 minutes ago, facthunter said:

You can't just make up your own rules and figures. 

No ... but it can't hurt to do your own reality check on your aircraft's book figures - assuming you even have P-charts for your plane.

 

 

"I’ve personally had the miserable experience of beginning a takeoff roll in a type-certificated light plane and not being sure that I’d have enough of a climb rate to stay safe in the initial climb. I was pretty sure, but I was flying a very old airplane with a very thin POH, and I didn’t have any way to be certain. This is an experience that I never want to repeat ...  "  Jared Yates, Kitplanes.

 

 

 

Predicting Performance

WWW.KITPLANES.COM

---

John T. Lowry's Bootstrap approach makes it easy to create performance charts for your pilot's operating handbook. By Jared Yates.

 

[djpacro]

3 hours ago, Garfly said:

 

It's too bad DJP never got around to building that app.

 

Unfortunately, that CASA link doesn't seem to be working any more.   

CASA has this sensible new AC:

[Freizeitpilot]

One of the critical risks I see is that a TODR or LDR calculation is simply not performed because of a ‘she’ll be right’ attitude or a couldn’t be bothered thumbing through the POH.
 

There is an unsophisticated, quick and dirty app available that can be used at your own risk. This app utilises your POH figures (rightly or wrongly), is very simple to use once set up for your aircraft, and can spit out a reasonable estimate based on prevailing conditions. The sliding scale function serves to indicate the influence of the individual factors on the TODR or LDR result.

 

Do I rely on an unverified random app I found on the internet ? Nope ! Do I use it as a rough estimate of what I may expect on a particular day at a particular ALA - Yep!

Before the keyboard warriors get hot under the collar, I have cross-referenced the app outputs with my POH table.

 

So far my POH figures are a tad optimistic, but I suspect that is most likely due to the PIC (me). The key figure for me is always the distance to 50’ as I’ve got trees to clear, and there have been days when I’ve stayed on the ground.

Use the app for entertainment value only, like I do.

 

Available in the App Store :  Take-off. (distance calculator)

Don’t know if there is an android version.

 

I have no affiliation with the app developer.

 

 

[Garfly]

2 hours ago, djpacro said:

CASA has this sensible new AC:

Yes, thanks DJP.  Here it is as .pdf:

 

advisory-circular-91-02-guidelines-for-aeroplanes-with-mtow-not-exceeding-5700-kg-suitable-places-to-take-off-and-land_0.pdf

[Freizeitpilot]

I forgot the screenshot, for those that are interested.

[Garfly]

 

The(US) Air Safety Institute rolls its own:

 

 

 

 

[facthunter]

So much NOT mentioned there. At least it advises Caution.. Nev

[Freizeitpilot]

Yes - grass is such a different animal to bitumen, amongst other things.

[Garfly]

6 hours ago, facthunter said:

So much NOT mentioned there. At least it advises Caution.. Nev

 

4 hours ago, Freizeitpilot said:

Yes - grass is such a different animal to bitumen, amongst other things.

 

Of course it is, but how does one come away from that video imagining its authors simply missed that most basic fact (among others) ?

Clearly, the film's starting point is that as pilots we KNOW that Density Altitude can kill; likewise a heavy load, a tail-wind, an up-slope and, to be sure, a draggy, clingy surface.  (Before we even get to our own skill level and our own aeroplane's declining vigour.) 

 

The point of the Air Safety Institute video (far beyond just preaching "caution") is that, added to all that, your POH can also kill, if you put unwarranted faith in its P-chart claims.

 

The experiments that the video team took pains to do turned up the shocking results that book take-off figures were, in the real world, fully 30% "optimistic" (in 2 common GA types).

 

Yes, of course, they did these experiments on bitumen but the whole point of P-charts/Tables or Take-Off Calculator apps is that a good set of numbers from any given situation can (by extrapolation/interpolation and known factors) yield rough results for most others.  With, of course, an added margin for safety.

 

But that unaccounted-for 30% error stretches 'rough' to its very limits - and in quite the wrong direction.

 

Which is probably why AOPA/ASI recommends adding 50% to book figures and urges us to "Go fly and test this for yourself!"

 

 

 

 

 

Edited March 15 by Garfly

[facthunter]

 Using better technique would have produces better figures. For short landing distances you must not be fast and must touch down early and not float. Get the nosewheel on the ground  and Mabe flaps up for extra braking effect.

  Take off use all of the runway start right at the end . Have tire pressure correct. Take full power on the Brakes and release quickly or do rolling start from the taxiway. Do not hold the stick back during the take off roll as there's more drag. Select flap or no flap to suit each particular situation. Stay in ground effect for best speed build up. Do not do an underspeed climb unless it's of short duration to clear a fence or a Tree stump ditch etc, Check you are getting FULL Power early in the process and carb heat cold. Watch for adverse wind shear if you have any downwind.. Pace out a point on the runway where you must  be  able to rotate and climb or STOP and abort the take off safely in the distance remaining.