Help with modifying Flight Models

[Ace_Hyflyer]

Hi all,

I'm trying to whip a little twin engine piston aircraft into shape, as the original Flight Model, while coming fairly close to the performance specs was crazily out of whack.

5000lbs too heavy, engines had about 800 extra HP, dimensions were all wrong, etc, etc, etc...

So, I set out to see if I could fix up the flight model. Here's what I've done.

Converted nosewheel to castoring
Modified Weight and Balance with correct empty and max gross weights
Adjusted Empty_weight_yaw_MOI as it was a bit high
Adjusted fuel amount (lowered to 90 gallons)
Increased parasite_drag_scalar and induced_drag_scalar by 0.05
Increased yaw_stability by 0.5
Adjusted airplane_geometry with as much accurate data as I could gather from the manufacturers website
Adjusted piston_engine with correct engine details for the Continental IO-360ES4
Decreased max_rated_rpm to 2800 and max_rated_hp to 210
Adjusted power scalar so engine produces 210HP at sea level
Decreased propeller_diameter to 6.0

That's pretty much it.

Here are my two questions, and bear in mind that I am brand new at this, and all changes this far have been mostly guess work.

1. (Most important) V_ne for this bird is 130-135KIAS, depending on where you look. Research has indicated that at sea level this bird can do 145KIAS flat out. With the adjustments I have made, the bird in FS will hit 148KIAS at sea level. However, performance drops off too quickly at altitude.

The real plane can sustain 127KIAS at 5,000 feet at 75 percent power. I used Sparks excellent flight test gauges and adjusted MP and RPM to get 75 percent of the horsepower reached at 5,000 feet, and the FS bird would only do 115KIAS. However, it did burn the correct 19.5 GPH total for both engines

At 9,700 ft at similar settings burning 16GPH, the real plane can maintain 120KIAS, whereas the FS plane was barely managing 94KIAS. And the service ceiling of this plane is still 7,000 feet higher.

So, what I'm asking is if there is a way to boost altitude performance without increasing sea level performance?

2. (Not quite so important) The real plane is equipped with reversable pitch propellers. I attempted to model this by setting up the prop_reverse_available and minimum_reverse_beta, but it didn't produce enough thrust. I read a post here in the Flight Dynamics board by Sparky, but I didn't understand it properly. Is there a way to model reverse thrust for piston engines?

Thanks very much for any help!

Chris

[errmail]

Hi all,

I'm trying to whip a little twin engine piston aircraft into shape, as the original Flight Model, while coming fairly close to the performance specs was crazily out of whack.

5000lbs too heavy, engines had about 800 extra HP, dimensions were all wrong, etc, etc, etc...

So, I set out to see if I could fix up the flight model. Here's what I've done.

Converted nosewheel to castoring
Modified Weight and Balance with correct empty and max gross weights
Adjusted Empty_weight_yaw_MOI as it was a bit high
Adjusted fuel amount (lowered to 90 gallons)
Increased parasite_drag_scalar and induced_drag_scalar by 0.05
Increased yaw_stability by 0.5
Adjusted airplane_geometry with as much accurate data as I could gather from the manufacturers website
Adjusted piston_engine with correct engine details for the Continental IO-360ES4
Decreased max_rated_rpm to 2800 and max_rated_hp to 210
Adjusted power scalar so engine produces 210HP at sea level
Decreased propeller_diameter to 6.0

That's pretty much it.

Here are my two questions, and bear in mind that I am brand new at this, and all changes this far have been mostly guess work.

What kind of plane is this? That always helps.

1. (Most important) V_ne for this bird is 130-135KIAS, depending on where you look. Research has indicated that at sea level this bird can do 145KIAS flat out. With the adjustments I have made, the bird in FS will hit 148KIAS at sea level. However, performance drops off too quickly at altitude.

The real plane can sustain 127KIAS at 5,000 feet at 75 percent power. I used Sparks excellent flight test gauges and adjusted MP and RPM to get 75 percent of the horsepower reached at 5,000 feet, and the FS bird would only do 115KIAS. However, it did burn the correct 19.5 GPH total for both engines

At 9,700 ft at similar settings burning 16GPH, the real plane can maintain 120KIAS, whereas the FS plane was barely managing 94KIAS. And the service ceiling of this plane is still 7,000 feet higher.

So, what I'm asking is if there is a way to boost altitude performance without increasing sea level performance?

Absolutely, but it is not something you can adjust or correct by modifying a few scalars. There are many tables and entries in the .air file that have to be painstakingly adjusted over a period of time to achieve the correct result. Also, your engine model must be set up properly before starting this process. And are you sure your mixture is set correctly? You can get very good results with careful mixture adjustment but in general, you want to perform your basic setup with automixture turned on to avoid any problems with consistency.

2. (Not quite so important) The real plane is equipped with reversable pitch propellers. I attempted to model this by setting up the prop_reverse_available and minimum_reverse_beta, but it didn't produce enough thrust. I read a post here in the Flight Dynamics board by Sparky, but I didn't understand it properly. Is there a way to model reverse thrust for piston engines?

Yes, this can be done with great authenticity but is not a simple process. Again, it involves specific modifications to the .air file rather than any entries into the aircraft.cfg file. What you will need to do is carefully examine aircraft that exhibit the properties you are trying to duplicate and find a way to reproduce this in your own work. To get your plane flying the way you want would be a matter of but a few hours for someone who is familiar with the process, but to describe it here is far beyond the scope of this forum.

Thanks very much for any help!

Chris

I don't know how much help this was, but at least you know it can be done. Now it is a matter of finding out how and making it happen. That takes a great deal of time and effort but there isn't any other way...:banghead:

[Ace_Hyflyer]

Hiya Errmail,

Sorry I should have mentioned the plane. It's the Beriev BE-103.

Unfortunately, there is a lack of specific data, such as the reverse range of the props, etc.

What I've been doing with the mixture is leaning to peak fuel flow. Is that the correct approach?

Thanks for the info, I'll try and see if I can dig up a piston plane which has reverse thrust.

Chris

[errmail]

Hiya Errmail,

Sorry I should have mentioned the plane. It's the Beriev BE-103.

Unfortunately, there is a lack of specific data, such as the reverse range of the props, etc.

What I've been doing with the mixture is leaning to peak fuel flow. Is that the correct approach?

Thanks for the info, I'll try and see if I can dig up a piston plane which has reverse thrust.

Chris

Good luck! Discovery is all part of the fun.

[fliger747]

ACE:

A note on the airspeeds: The manual will almost always quote True Airspeed, while you were quoting a tested IAS at 5000'. I think you will find that TAS in your test is quite close to the desired value.

I use the AFSD popup program by Herve Sors to measure all sorts of test values, more than can fit into Jerry's panel.

I'm not sure there is an ability to reverse thrust with PISTON engines in FS, though it is possible with turboprops.

Tools:

Ya need at least Aired to be able to open and edit air files. Also usefull is AIRFILEMANAGER, which allows visual editing of the graphs resulting from the hex tables and the now defunct aircraft container manager which is greatfor the geometry etc.

Jerry's Airwrench has some limitations, but is a great tool to get ya started and worth every penny. His Excell workbook is a terrific tool as well.

Good Luck!

[Ace_Hyflyer]

You may be right, Fliger. Unfortunately I'm not able to work from a manual, but rather from whatever aopa articles and manufacturers specs I can find. All the other values were quoted in KIAS, but it's possible that the cruise speeds are quoted in KTAS. It is not clear, but I'll have to see if I can ferret it out :d

Chris

[Ace_Hyflyer]

Well, testing KTAS instead of KIAS it comes a lot closer to factory specs. Performance still seems to fall off a little too quickly, but not nearly as much as if the cruise is quoted as KIAS.

Chris

[errmail]

ACE:

A note on the airspeeds: The manual will almost always quote True Airspeed, while you were quoting a tested IAS at 5000'. I think you will find that TAS in your test is quite close to the desired value.

I use the AFSD popup program by Herve Sors to measure all sorts of test values, more than can fit into Jerry's panel.

I'm not sure there is an ability to reverse thrust with PISTON engines in FS, though it is possible with turboprops.

Tools:

Ya need at least Aired to be able to open and edit air files. Also usefull is AIRFILEMANAGER, which allows visual editing of the graphs resulting from the hex tables and the now defunct aircraft container manager which is greatfor the geometry etc.

Jerry's Airwrench has some limitations, but is a great tool to get ya started and worth every penny. His Excell workbook is a terrific tool as well.

Good Luck!

There is indeed a way to reverse with piston engines and quite convincingly.:engel016:

See this thread for reference...

http://www.sim-outhouse.com/sohforums/showthread.php?t=21331

[Ace_Hyflyer]

Well, I've got prop reverse working, somewhat, but I've noticed something which is very annoying.

If I have reverse thrust set up so that I can gently move the plane backwards (values for that line start at -0.05 and get more negative), then there is no way to have idle RPM. Is that right, or am I missing something?

In other words, as soon as I start the engine and move the throttle even slightly, the RPM jumps straight up to the redline!

Chris