Flight Sim’s Obsession with POH Numbers

[Los 416]

This is geared more towards the GA side of simming and meant only as food for thought,

I am not anti-modding and I both enjoy and appreciate the efforts of the modders in the community. (I particularly enjoy Robert Young’s turbonormalized Bonanza mod, for instance).

Seeing that the default GA aircraft in MSFS for the most part appear to be underpowered and most of the mods are geared towards correcting that, I wondered if we are too obsessed with the POH numbers and getting the aircraft to match, when in reality this would not necessarily be the case.

For example, this quote from the Aviation Safety Magazine, regarding real world operations:

“The performance figures in your airplane’s POH are another of aviation’s takes on “Heads I win, tails you lose.” Maximizing performance—especially takeoff performance—requires precise adherence to book procedures. But even with perfect execution, you can’t expect book results.

Both facts are consequences of manufacturers’ flight-test procedures as leavened by marketing pressure. The numbers arise from multiple trials by factory test pilots flying new airplanes, perfectly rigged, with fresh engines. They get repeated chances to perfect their technique, and missing the laser beam by six inches satisfies the 50-foot clearance test. Better numbers are presumably better for sales, which is to say that when the POH cites 1850 feet to clear that 50-foot obstacle, it means that despite all their advantages, the factory pilots couldn’t consistently do it in less. Most of us, on the other hand, can’t do that at all.”

https://www.aviationsafetymagazine.com/features/real-world-takeoff-performance/

So, maybe the lower performance experienced is more representative of what might be experienced in real life and the lower performance, wait for it... more realistic?!?!?

I know we all like to go fast in the sim, we can’t wait to see it we’re going to butter or botch that landing, but the same can be accomplished with the fantasy aircraft that have been in flight sim since forever. You know, the “experimental” planes out there from the flying brick, literally, to the hyper sonic thing that lands at 40 knots... so speed can be had, all be it totally unrealistically.

Like I said just food for thought and a little conversation.

Regards,

‘Los

Edited November 11, 2020 by Cmcollazo71

[SUNDR1V3R 72]

I guess 90% of the new simmers don’t even know what a POH means.. They just want to fly the 787 thru Eiffel Tower or stuff like that..

For the other 10% POH means a lot in terms of performance..

So let’s say I want to fly in from BIG BEAR to Henderson in summer time at noon full of pax and luggage.. I’m i gonna be able to do that..? Let’s see the POH.. 

Thats what you expect at least from a Simulator to simulate the aircraft.. Of course never is gonna be like the real thing but at least something close..

[ahsmatt7 1,213]

Flight sim enthusiasts have long forgotten that POH numbers should be approached as ball park figures. 
 

secondly, flight sim enthusiasts have forgotten that a desk top flight sim should be approached as a ball park idea.

thirdly, I would wager that the obsession comes from the fact hat flight sim enthusiasts are an anal bunch who if it’s not exactly right in ones eyes, then it’s all wrong. Not only that, they will do anything emulate flight because they can’t fly themselves...or just don’t know how to manage money well enough to get a PPL. It’s kind of foolish to be honest. 

[SUNDR1V3R 72]

9 minutes ago, ahsmatt7 said:

Flight sim enthusiasts have long forgotten that POH numbers should be approached as ball park figures. 
 

secondly, flight sim enthusiasts have forgotten that a desk top flight sim should be approached as a ball park idea.

thirdly, I would wager that the obsession comes from the fact hat flight sim enthusiasts are an anal bunch who if it’s not exactly right in ones eyes, then it’s all wrong. Not only that, they will do anything emulate flight because they can’t fly themselves...or just don’t know how to manage money well enough to get a PPL. It’s kind of foolish to be honest. 

What the hell is an Anal Bunch..?

I have a CPL and still love the sim.. Stop writing nonsense word not allowed..

[ryanbatc 13,125]

POH data is the only starting point.  If we have no POH we can't confirm what should be.  

Sure, engines wear out over time and we can't get book values anymore in real life.  But in sim world we want to recreate numbers that are at least very close.  So we use the POH.

[Janov 2,383]

Most POH numbers are to be taken with a grain of salt - as those are considered "sales fliers" for the aircraft and most aircraft don´t quite achieve the numbers mentioned there. Plus a lot of these values where achieved by test pilots, often taking several attempts (like to achieve a very short landing distance)...

Most airliners have an option in the FMC to set a "performance factor" that actually improves prediction accuracy - I have mostly seen it in the 2-3% range on our aircraft. Which means the aircraft peforms 2% worse than the manual says.

So yeah, I wouldn´t look twice if my C-172 performed 5% worse than the POH states. But 10%...I would start to frown.

That being said, 10% of a 500fpm climb rate is only 50fpm - one could still consider that quite accurate, definitely more accurate than just "ballpark".

It´s maybe just me - but I want to face the same performance challenges when flying a desktop simulator that I would face flying the real aircraft. If the difference is in the 10% range, so be it - but anything gross would take the challenge (and fun) out of it for me.

Cheers, Jan

[Los 416]

5 minutes ago, ryanbatcund said:

But in sim world we want to recreate numbers that are at least very close.  So we use the POH.

True, but would not allowing for a margin of error just as realistic?

[Los 416]

5 minutes ago, Janov said:

If the difference is in the 10% range, so be it - but anything gross would take the challenge (and fun) out of it for me.

How about 30%? This is what this AOPA video found. Granted the sample size is too small to be significant, but at least for these aircraft (well maintained with experience pilots as the video notes) found that much variance and suggested a 50% allowance in day to day flying.

 

[bobcat999 8,546]

19 minutes ago, SUNDR1V3R said:

What the hell is an Anal Bunch..?

Here...

[PICTURE DELETED]

Edit:  Huh!  The picture isn't showing!

Edited November 11, 2020 by bobcat999

[mtr75 653]

As a licensed pilot, I can tell you, POH numbers are a guide at best. The general rule of thumb for pilots who want to get old is to add 50% to the book numbers. In other words, if the book says to expect a 1,000-foot takeoff roll, plan for it to take 1,500. (Just a round number example). Many a pilot has wound up in the trees expecting book numbers. 

As my instructor always points out, POH numbers are with a test pilot and a brand new airplane.  

So the idea of modding planes so they achieve book numbers is actually unrealistic rather than realistic. 

Edited November 11, 2020 by mtr75

[2reds2whites 827]

This doesn't hold particularly true in a lot of ways. Yes over time the efficiency of an engine can slip, and yes there can be an increase in drag as panels move and paint fades etc.

That said, RPM is RPM and a prop is a prop. An engine producing a given RPM with a prop creates the same thrust regardless of how hard the engine has to work.

The POH is the only starting point. If you want to diverge from there then so be it, but for the most part Asobo haven't even got to the basics yet.

And then you have to ask - if it's not POH, then what the hell is it?

Edited November 11, 2020 by 2reds2whites

[James Callan 66]

Despite the validity of the various points of view, it’s disappointing if you’ve ever actually flown Cessna’s to even deal with mixture settings below 3-5k ft., except to kill the engine at the ramp post-flight. Seems an unfortunate own goal, no.

[marsman2020 1,310]

We can control a lot of the variables that cause the large variation in the video above, in sim.  Set 'Clear Skies' and the atmosphere exactly matches the ISA atmosphere.  Turn off all wind.  There is no wear and tear on the engine in the sim. 

So in my mind, we should get closer to POH values in sim then you can in reality.

I agree it's unlikely to be right-on for every value, but I'd expect within 5-10% for most items, on a Clear Skies day at a sea level field.  Personally for GA I care more about things like cruise speed and range of the aircraft, rotating at the right speed, and flying approaches at the right speeds, those are the things I'd like to see within 5%.  If the exact power settings needed to get those speeds are a little different from the real world, so be it, if the takeoff/landing distances are 10 % off, fine.

Asobo isn't even close for a lot of things (range off by 30%, cruise speeds off by 20%, etc).

Obviously once you turn on Live Weather, there will be a greater variation.

Edited November 11, 2020 by marsman2020

[mtr75 653]

21 minutes ago, 2reds2whites said:

This doesn't hold particularly true in a lot of ways. Yes over time the efficiency of an engine can slip, and yes there can be an increase in drag as panels move and paint fades etc.

That said, RPM is RPM and a prop is a prop. An engine producing a given RPM with a prop creates the same thrust regardless of how hard the engine has to work.

The POH is the only starting point. If you want to diverge from there then so be it, but for the most part Asobo haven't even got to the basics yet.

And then you have to ask - if it's not POH, then what the hell is it?

A 45-year old engine that's been overhauled twice and has 900 hours on it does not produce rated HP, period. Same is true for a prop that's been overhauled and has 1,000 hours on it. 

Then you've got a ham-fisted private pilot with 180 hours total time, and no, you aren't going to get the book numbers that the professional test pilot got with a new plane. 

Ask any GA pilot and they will tell you the same. 

[Los 416]

25 minutes ago, mtr75 said:

The general rule of thumb for pilots who want to get old is to add 50% to the book numbers.

Thanks for your insight, this matches the recommendation of the AOPA video embedded above!

 

26 minutes ago, mtr75 said:

So the idea of modding planes  so they achieve book numbers is actually unrealistic rather than realistic. 

And I guess this is what I was getting at with this post... I’m not a real world pilot and so information like this is fascinating to me.