Modify drag

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zuentec
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Modify drag

Post by zuentec »

Dear experts,
compared to real aircraft drag in full flaps config feels too low at C172 modell.

I have compared it during approach at my home airfield. In real life I have to maintain 2100 rpm @ 65 kts. In simulation only idle is needed...

That does not match at all. The rest works excellent.

Is it possible to finetune it a bit?

Regards from EDMJ

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Oracle427
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Re: Modify drag

Post by Oracle427 »

To try and compare anything objectively...

What was the density altitude? Need temp, altitude, baro, altitude, aircraft weight at that time. Model of aircraft... Any STCs such as an upgraded engine? Are the flaps 40 degree or 30 degree?

Last night I flew 4 instrument approaches in a 172S (180hp) beginning with the first which was an ILS with full fuel tanks at takeoff only 10 minutes after takeoff. I was able to maintain 90 KIAS at 1900RPM with 10 degrees of flaps in a 500fpm descent. Temp was about 19C, baro was 30.20in hg, altitude was 3000 feet MSL. Weight ~2400lbs.

When trying to remain level I am using 2400rpm to maintain the same airspeed in the same configuration.

Is your peformance comparison when trying to remain level or in a descent? What was the descent rate if descending? I can easily reach 80 knots during approach with full flaps at idle power if descending for example.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

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DHenriques_
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Re: Modify drag

Post by DHenriques_ »

Oracle427 wrote: 23 May 2019, 15:14 To try and compare anything objectively...

What was the density altitude? Need temp, altitude, baro, altitude, aircraft weight at that time. Model of aircraft... Any STCs such as an upgraded engine? Are the flaps 40 degree or 30 degree?

Last night I flew 4 instrument approaches in a 172S (180hp) beginning with the first which was an ILS with full fuel tanks at takeoff only 10 minutes after takeoff. I was able to maintain 90 KIAS at 1900RPM with 10 degrees of flaps in a 500fpm descent. Temp was about 19C, baro was 30.20in hg, altitude was 3000 feet MSL. Weight ~2400lbs.

When trying to remain level I am using 2400rpm to maintain the same airspeed in the same configuration.

Is your peformance comparison when trying to remain level or in a descent? What was the descent rate if descending? I can easily reach 80 knots during approach with full flaps at idle power if descending for example.
What I don't see mentioned in this discussion in the initial post is pitch attitude.
DH

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zuentec
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Re: Modify drag

Post by zuentec »

Indeed many factors can influence that significantly but in this case I have used the same airfield and the same weather conditions (EDDM 171820Z 07006KT CAVOK 17/06 Q1005 NOSIG).
Even the engine is the same.

To avoid other influence I exactly followed the traffic pattern.

In current simulator condition it is really hard to land by the book with stall speed (airfield is only 1300ft and approch is quite steep due to terrain)

The question I have is how to find the right entry for drag in the specific config file ;-)

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zuentec
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Re: Modify drag

Post by zuentec »

[/quote]

What I don't see mentioned in this discussion in the initial post is pitch attitude.
DH
[/quote]

This is also strange: In real life nose down is the typical answer of a C172 during full flaps extension. In sim the effect doesn't feel realistic to me...

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DHenriques_
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Re: Modify drag

Post by DHenriques_ »

zuentec wrote: 23 May 2019, 16:08
What I don't see mentioned in this discussion in the initial post is pitch attitude.
DH
[/quote]
This is also strange: In real life nose down is the typical answer of a C172 during full flaps extension. In sim the effect doesn't feel realistic to me...
Not really. In the 172, as in most all high wing airplanes, flap extension over aprox 20 degrees causes a NOSE UP pitch moment due to downwash on the horizontal stabilizer, then as airspeed decreases, the nose should trend down requiring a re-trim.
In low wing aircraft there is a usually a definite nose down pitch moment as flaps are applied.
As far as I can remember, when we did the 172, we were very careful to replicate this properly.
Dudley Henriques

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Oracle427
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Re: Modify drag

Post by Oracle427 »

There is still insufficient information here. What was the descent rate and which engine are you running? The A2A model has two engne options.

What 172 model are you Flying and how many degrees of flaps?
What was your weight?

I think the only valid comparison would be in straight and level flight at constant airspeed, power and config. Too many variables to go by feel.

I use the A2A sim for IFR proficiency and it flys perfectly by the numbers for me so let’s get a little more data to compare notes.

I have been surprised about what I learned about the real aircraft performance when comparing it to A2A. Landing on a 1300’ field at 65KIAS is also too fast. 60 is the short field approach speed and you are close to the limits of aircraft performance here if you come in fast like this.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

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DHenriques_
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Re: Modify drag

Post by DHenriques_ »

Oracle427 wrote: 23 May 2019, 16:57 There is still insufficient information here. What was the descent rate and which engine are you running? The A2A model has two engne options.

What 172 model are you Flying and how many degrees of flaps?
What was your weight?

..................................and did you stay at a Holiday Inn Express last night?
DH

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Oracle427
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Re: Modify drag

Post by Oracle427 »

Lol Dudley, I surely did not, so just my .02. :mrgreen:
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DHenriques_
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Re: Modify drag

Post by DHenriques_ »

Oracle427 wrote: 23 May 2019, 17:03 Lol Dudley, I surely did not, so just my .02. :mrgreen:
LOL :-))))))))

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Oracle427
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Re: Modify drag

Post by Oracle427 »

In fact, according to the POH for the 172R you are not able to land without being a test pilot in 1300 feet in those conditions at EDDM when at max gross using short field technique.

To answer the question about modifying drag with A2A aircraft. You can’t because they rely on proprietary code to model the aircraft behavior. Modifying files will not generate the expected results and will cause weird behavior.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

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DHenriques_
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Re: Modify drag

Post by DHenriques_ »

Oracle427 wrote: 23 May 2019, 17:08 In fact, according to the POH for the 172R you are not able to land without being a test pilot in 1300 feet in those conditions at EDDM when at max gross using short field technique.

To answer the question about modifying drag with A2A aircraft. You can’t because they rely on proprietary code to model the aircraft behavior. Modifying files will not generate the expected results and will cause weird behavior.
That's true. Accusim operates outside the regular sim files and as such is "unique" unto itself.
I would add to this pointing to our aerodynamics that Scott took actual numbers from the real 172 when we set up the code for lift coefficients vs drag index as flaps were deployed. The numbers should be an exact match for the A2A 172 vs the performance of the actual 172.
I can attest personally that when I tested our 172 it all felt normal to me.
DH

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Oracle427
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Re: Modify drag

Post by Oracle427 »

I saw in the first post that the airfield in EDMJ. Found some videos on youtube of landings at the field. I see there are no obstructions or terrain in the approach and the technique seems to be to come in low and flat and touch down as close as possible to the threshold. In this case, I can see that the landing performance is well within the limits of the POH provided that the pilot is on their game. It definitely is not going to be the easiest field to land at!

Unfortunately, my FSX places a zillion trees about 10 feet from the threshold, so I end up having to ignore and fly through them to make the landing. :)

Still, the next time I fly the 172, I'll take notes about performance with flaps fully extended, straight and level flight at constant airspeed and power and see how many RPMs I am turning at 65KIAS. I am going to guess very close to 2400 RPM.
Flight Simmer since 1983. PP ASEL IR Tailwheel
N28021 1979 Super Viking 17-30A

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DHenriques_
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Re: Modify drag

Post by DHenriques_ »

Oracle427 wrote: 24 May 2019, 17:40

Unfortunately, my FSX places a zillion trees about 10 feet from the threshold, so I end up having to ignore and fly through them to make the landing. :)
It pays to have friends. :-)))))

During the FSX Beta Microsoft sent me an update one afternoon for testing. I fly out of KILG constantly and the ILS runway there is runway 1. During the test on approach I noticed that Microsoft had put a 50 ft tree in the middle of the approach lights. Needless to say I got an email off immediately to the Aces Team telling them to PLEASE get rid of that tree. Next day I got another update. The tree was gone!
I've always wondered about how disappointed I would have been had I NOT been advising Microsoft on FSX and had the ability to get that damn tree out of there.
Had I simply been a normal purchaser and bought the sim I would have as a natural course set up to fly from KILG as I had in the real world almost every day. Having that tree there in the middle of the ILS on 1 would have spoiled my entire FSX experience.
As I said.............it pays to have friends. :-))))))))))

Dudley Henriques

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Nick - A2A
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Re: Modify drag

Post by Nick - A2A »

Oracle427 wrote: 24 May 2019, 17:40 Unfortunately, my FSX places a zillion trees about 10 feet from the threshold (...)
I must admit I've never used it, but I believe this bit of software is designed to address the rather hazardous abundance of trees on some of the default runway approaches in FSX. I don't know if it does anything about the fact that all the trees seem to be oddly oversized, but I suspect not.

https://flyawaysimulation.com/downloads ... k-scenery/

Cheers,
Nick

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