Density altitude should be fixed

[motoadve 49]

I can take the Cherokee or 172 at 15,000 ft and still climbs at 500fpm and have 2,500 rpms, totally unrealistic.

[Murmur 3,940]

Density altitude is correctly modeled in standard conditions. The problem seems to be in engine modeling: it still outputs about 100 hp at 15.000 (vs 150 hp at sea level), maybe it's too much for an aspirated engine at that altitude.

 

Report it as a bug to Austin: Austin@x-plane.com

 

Give a brief and concise explanation, e.g. :

 

"In X-Plane, the C172, at 15.000 ft, is still able to climb at 500 fpm and have 2.500 rpms. That is not correct. Maybe the engine loss of power with density altitude is not correctly modeled."

[jcomm 5,882]

Even if we set power decay starting at, say 10,000', like in this picture, taken from an edit of the default C172 in Plane-Maker, we get 124hp at 15,000', while it is rated at 180.00 hp @ SL (ISA). I don't know if this reduction is realistic, I don't even know what altitude we should put there for a C172 P ... I used 10,000' but I may be completely wrong (?) BTW: default value is 0.0, and gives me more consistent power output results with SL ~150 hp, while at 10,000' I get around 116 after leaning, and at 15,000' around 98 after leaning (leaning rich of peak)

Edited August 7, 2013 by firehawk44
3 Images removed. Exceed 1600W limits

[motoadve 49]

X plane 10 is meant to be the latest most realistic flight simulator.

As a real pilot I can tell you density altitude is a very important part of flying.

Surprised not many people care about it.

[LAdamson 240]

 

X plane 10 is meant to be the latest most realistic flight simulator.

As a real pilot I can tell you density altitude is a very important part of flying.

Surprised not many people care about it.

  

I certainly would agree. I'm one of those pilots with plenty of experience in milking out the last bit of climb in small Cessnas & Cherokees....... in mountainous areas. Some days, it was tough to get the Piper Archer (180 HP) above 11,000' msl, with just me on board. Another time, it climbed to 12,500' to get over a ridge, with three of us in it. I don't like having to deal on the edges of performance, when it comes to density altitude. That's why I built the RV6 with a 180 HP & constant speed prop. Being much lighter, it could climb three times the rate of a Cessna or Piper. Getting to 17,999' wasn't a big deal. I had a two place oxygen system, but no instrument rating, and therefor didn't go higher, although it's service ceiling was 24,000'.

 

As to X-Plane, I haven't explored the limits of density altitude or engine performance. It's use has been more for topography data-bases.

[LAdamson 240]

A quick refresher course for density altitude..

 

Think about leaning at 3000' msl

 

You will use more runway, at higher altitude airports & strips. It's the reason that a lot of higher

altitude airports make it a point to have longer runways.

 

You'll cover more ground in the pattern, for the same indicated airspeed. Adjust the pattern distances if needed.

 

Don't be a fool with performance charts. Read and know what they're saying. It's not a good idea to guess, or just think it's your lucky day. Usually it won't be.

 

And as a personal note. I carried an oxymeter. One of those you put on a finger. With density altitude, your body might be noticing a lack of oxygen, even though you're at lower altitudes, than the FAA guidelines.

[motoadve 49]

4 days ago a friend of mine was killed while trying a mountain pass at 16,000 ft in the peruvian Andes.

Plane was a 180HP Diamond DA 40.

They tried to climb makin S turns when the plane just wasnt climbing anymore and plane stalled.

A tragedy and in my opinion ithis is pushing the limits, with a plane that has 16,400ft ceiling.

 

I tried to duplicate the flight first with the Xplane 172 then with the Carenado Cherokee.

I was at 16,000 climbing at 2500 rpms and 500fpm.

Totally unrealistic

[Murmur 3,940]

4 days ago a friend of mine was killed while trying a mountain pass at 16,000 ft in the peruvian Andes.

Plane was a 180HP Diamond DA 40.

They tried to climb makin S turns when the plane just wasnt climbing anymore and plane stalled.

A tragedy and in my opinion ithis is pushing the limits, with a plane that has 16,400ft ceiling.

 

I tried to duplicate the flight first with the Xplane 172 then with the Carenado Cherokee.

I was at 16,000 climbing at 2500 rpms and 500fpm.

Totally unrealistic

 

Have you reported this bug to Austin as per my former advice? I even wrote the text for you.

[GoranM 3,762]

I hope Austin doesn't change it.  I just tested the Saab using the details in this thread and it works perfectly.

Further proves my theory that it's likely the flight model and NOT the sim itself.

[Murmur 3,940]

Good news Goran!

[motoadve 49]

Yes I reported this to Austin.

The Saab is a turbo prop, much more efficient at altitude than a single piston 180hp engine

[GoranM 3,762]

Yes I reported this to Austin.

The Saab is a turbo prop, much more efficient at altitude than a single piston 180hp engine

Fair enough.

I just took the Beech Duchess up for a test. Twin engine recip engine.

Again, no issues. I set the altitude to 35000 feet (a little lower this time) on the local map, exited the local map and back to the cockpit, engines died instantly and couldn't get them started.

[motoadve 49]

Try the default 172 at 16,000 ft.

Let me know the results.

[GoranM 3,762]

My point wasn't about the default C172. It may very well do what you are describing and I have no reason to not believe you.

My point was that if there is an issue, it likely lies in the flight model and not the sim itself, seeing as I tested 2 other add ons (mine) and both did exactly as expected.

There are many areas in the engine specs that can affect an engines performance at altitude. Not just the critical altitude. We just spent a good 6 weeks, 6-7 days a week, in the Saab, tuning the engines to make them work properly at all altitudes. And this was done by working on a lot more than the critical altitude (That's the obvious one).

[LAdamson 240]

What's really counts here, is what the airframe is still able to do ( or not do) at specific altitudes, as in the original post. For instance, my RV engine, which is the same as a Cessna 180 HP SP,(but with a carb instead of fuel injection), will still be running with an ability to climb, far past the limits of the Cessna, 180 HP Piper Archer, or the Diamond DA40. The charts can be looked at, to compare altitude to manifold pressure, and output of engine expressed in percentages.