Adjusting DAT to fit with real performances

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DavideV
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Adjusting DAT to fit with real performances

Post by DavideV » Tue Sep 13, 2011 9:24 pm

Hello people,

I'm on the final to release my first model built entirely from scratch - actually my 2nd, the 1st is the MB339 that I stopped for some reason I'll explain later when there will be a chance. Since the unpainted model is 98% I'm now focusing on adjusting the DAT so to match the real performances, and these are some major facts I found on the internet

Two propellers of 400/420 HP each
600ft takeoff distance, 250 landing distance (yes, it's a STOL airplane)
47 KTAS stall speed (47*1.4 = 66 KTAS, this is the speed I set as "fully manueverable")
1,700 ft/min climbing rate
167 KTAS cruising speed
21,000 ft ceiling (I set 18,000 as cruising altitude)
2150Kg clean weight
with some calculations, I guessed roughly 900kg of fuel and then another 900 of max payload
31m^2 of wing area

Now, I tried to put these datas as they are in the DAT file but I'm not having what I expected, expecially for the takeoff. With 75% fuel loaded, it accelerates very fast and becomes airborne like in less then 200ft. I tried to put the HP down to 500 but no way, always too fast, and bringing it down more just doesn't give me enough power to achieve a 1,700 ft/m climbing rate. For now, I have an acceptable climbing rate by putting 600HP and 0.90% throttle setting for cruising speed... but the takeoff distance is still way too short, and without flaps! If I put down the flaps it goes up even faster...

For the landing speed I don't really have any clue, I just know that it has some problem decelerating when descending, even at idle... and that's really not that aerodynamic... :roll:

Is there anyone who can give me advices or even make some test? I'll greatly appreciate that (and put in the credits, if tested ;) )

Thanks,
Davide.

PS. Oh, the airplane is the GAF Nomad N22.
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Re: Adjusting DAT to fit with real performances

Post by waspe414 » Tue Sep 13, 2011 9:30 pm

There are a lot of little things that you'd think aren't connected to anything that end up having a massive impact on the performance. Landing throttle setting, for example, sets how much the flight vector "sticks" to the crosshairs.

Upload it here and I'll take a look.
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Re: Adjusting DAT to fit with real performances

Post by Dragon029 » Wed Sep 14, 2011 5:11 am

I might be able to do up a .dat with those specs if I get the time - otherwise you should try yourself - editing a .dat is extremely easy for the basic things.

For example, for the engines, instead of maxthrust, etc, replace it with:

PROPELLR 840HP

and for the cruising speed, etc, just put those into the cruise settings.

In other words - find the .dat of another plane that uses propellors and just edit that .dat to suit the MB339 - look for the Down In Flames, Wic Works, etc packs for aircraft with propellors.
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Re: Adjusting DAT to fit with real performances

Post by DavideV » Wed Sep 14, 2011 7:45 am

Dragon029 wrote:I might be able to do up a .dat with those specs if I get the time - otherwise you should try yourself - editing a .dat is extremely easy for the basic things.

For example, for the engines, instead of maxthrust, etc, replace it with:

PROPELLR 840HP

and for the cruising speed, etc, just put those into the cruise settings.

In other words - find the .dat of another plane that uses propellors and just edit that .dat to suit the MB339 - look for the Down In Flames, Wic Works, etc packs for aircraft with propellors.
I think you should read carefully my first post...

1) I already did what you suggested
2) this is not for the MB339 (which is a jet), but for an N22

;)
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Re: Adjusting DAT to fit with real performances

Post by Dragon029 » Wed Sep 14, 2011 9:51 am

Try reducing your wing area, or playing with the landing conditions.
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Re: Adjusting DAT to fit with real performances

Post by Flake » Thu Sep 15, 2011 12:48 am

I am going to say: Ignore these guys.

Sorry guys.

Here's what I reccomend. Adjust your cruise condition throttle to be much higher, reduce the distance required to stop, and increase the drag ratios of your gear/flaps.

This provides a "slow acceleration" at gear down, higher more realistic acceleration and high speed AFTER take-off.

To have realistic turn drag, you need to adjust the landing conditions, mostly angle of attack and throttle setting.

Think of this: If you set the landing AOA to the maximum pitch rate, the speed to the corner velocity, and the throttle to the ammount of throttle required to maintain speed during that turn, then you will neither lose nor gain speed while performing a 30degree wing alpha turn at corner speed, with the throttle at that setting. It's hard to graps so let's explain with variables:

Landing distance: 400m
Landing AOA: 40deg
Landing speed: 400KIAS
Landing Throttle Setting: 0.8

so now ignore the "landing". you have defined in the .dat that when the aircraft is at 400KIAS, if it were to pull a 40degree wing alpha turn, throttle hsould be at 80% to maintain that speed.

I used this to set a realistic turn/drag ratio for my hornets. ;)

My own custom Realistic F/A-18A .dat :

Code: Select all

IDENTIFY "F/A-18A USN BLUE ANGEL #1 [LBG]"
CATEGORY AEROBATIC
AFTBURNR TRUE                 #HAVE AFTERBURNER?
THRAFTBN 10.5t                #THRUST WITH AFTERBURNER
THRMILIT  6.5t                #THRUST AT MILITARY POWER
WEIGHCLN  10.34t                #WEIGHT CLEAN
WEIGFUEL  4.93t                #WEIGHT OF FUEL
FUELABRN 8.5kg                #FUEL CONSUMPTION WHEN USING AFTERBURNER
FUELMILI 0.45kg               #FUEL CONSUMPTION AT MILITARY POWER

INSTPANL user/luckybeargod/Hornet.ist

COCKPITP  0.0m  1.37m 3.86m  #COCKPIT POSITION
EXCAMERA "HUDLESS" 0.0m  1.37m   3.86m 0DEG 0DEG 0DEG INSIDE
EXCAMERA "HUDLESS_L" 0.0m  1.37m   3.86m -45DEG 0DEG 0DEG INSIDE
EXCAMERA "HUDLESS_R" 0.0m  1.37m   3.86m  45DEG 0DEG 0DEG INSIDE
EXCAMERA "HUD_HI" 0.0m  1.37m   4.05m 0DEG 20DEG 0DEG INSIDE
EXCAMERA "PORTRAIT" 0.0m  1.37m   4.5m 180DEG 0DEG 0DEG INSIDE
EXCAMERA "NOSEGEAR" 0.0m  -1.37m   1m 0DEG -10DEG 0DEG INSIDE
EXCAMERA "BELLY" 0.0m  -1.37m   1m 180DEG -10DEG 0DEG INSIDE
EXCAMERA "BELLY_R" -2m  -1.37m   -1m 105DEG 0DEG 0DEG INSIDE
EXCAMERA "BELLY_L" 2m  -1.37m   -1m -105DEG 0DEG 0DEG INSIDE
EXCAMERA "ROOF" 0m  2m   -1m 0DEG 0DEG 0DEG INSIDE
EXCAMERA "ROOF_R" 0m  2m   -1m 105DEG 0DEG 0DEG INSIDE
EXCAMERA "ROOF_L" 0m  2m   -1m -105DEG 0DEG 0DEG INSIDE
EXCAMERA "NUMBER_R" 3.5m  1.75m   -5.25m 90DEG 0DEG 0DEG INSIDE
EXCAMERA "NUMBER_L" -3.5m  1.75m   -5.25m -90DEG 0DEG 0DEG INSIDE
LEFTGEAR -1.55m -1.6m -2.24m  #LEFT LANDING GEAR POSITION
RIGHGEAR  1.55m -1.6m -2.24m  #RIGHT LANDING GEAR POSITION
WHELGEAR  0.0m -1.57m  3.30m  #WHEEL POSITION
ARRESTER  0.0m -1.62m -7.81m #Arresting hook position
SMOKEGEN  -0.48m 0.35m -8.12m  #SMOKE GENERATOR POSITION
VAPORPO0  5.94m  0.15m -3.25m  #VAPOR POSITION (Wings Swept Back or no-VGW)
VAPORPO1  5.94m  0.15m -3.25m  #VAPOR POSITION (Wings Spread)
HTRADIUS 10.0m                #OUTSIDE SPHERE RADIUS

SMOKEOIL 100.0kg
WEAPONCH SMK

STRENGTH 10

CRITAOAP  45deg               #CRITICAL AOA POSITIVE
CRITAOAM -15deg               #CRITICAL AOA NEGATIVE

CRITSPED 0.9MACH              #CRITICAL SPEED
MAXSPEED 1.8MACH              #MAXIMUM SPEED

HASSPOIL TRUE                 #HAS SPOILER?
RETRGEAR TRUE                 #HAS RETRACTABLE LANDING GEAR?
VARGEOMW FALSE                #HAS VARIABLE GEOMETRY WING?

VGWSPED1 300kt
VGWSPED2 300kt

CLVARGEO 0.0                  #EFFECT OF VARIAcBLE GEOMETRY WING FOR Cl
CDVARGEO 0.0                  #EFFECT OF VARIABLE GEOMETRY WING FOR Cd
CLBYFLAP 0.2                  #EFFECT OF FLAP FOR Cl
CDBYFLAP 2.6                  #EFFECT OF FLAP FOR Cd
CDBYGEAR 1.5                  #EFFECT OF GEAR FOR Cd
CDSPOILR 1.5                  #EFFECT OF SPOILER FOR Cd

WINGAREA 37.16m^2                #WING AREA

MXIPTAOA 23.0deg              #MAX INPUT AOA
MXIPTSSA 5.0deg               #MAX INPUT SSA
MXIPTROL 220.0deg             #MAX INPUT ROLL

REM CPITMANE corresponds to Spring Constant K
REM CPITSTAB corresponds to Damper Constant B
REM To be critically damped, B=2*sqrt(K)
REM 2% Settling Time=??

MANESPD1 40kt                 #MINIMUM MANEUVABLE SPEED
MANESPD2 100kt                 #FULLY MANEUVABLE SPEED
CPITMANE 8.0                 #PITCH MANEUVERBILITY CONSTANT
CPITSTAB 2                  #PITCH STABILITY CONSTANT
CYAWMANE 5.0                  #YAW MANEUVABILITY CONSTANT
CYAWSTAB 3.0                  #YAW STABILITY CONSTANT
CROLLMAN 3.0                  #ROLL MANEUVABILITY CONSTANT

CTLLDGEA TRUE                 #CONTROL LANDINGGEAR
CTLBRAKE FALSE                #CONTROL BRAKE
CTLSPOIL 0.0                  #CONTROL SPOILER
CTLABRNR FALSE                #CONTROL AFTERBURNER
CTLTHROT 0.0                  #CONTROL THRUST
CTLIFLAP 0.0                  #CONTROL FLAP
CTLINVGW 0.0                  #CONTROL VARIABLE GEOMETRY WING
CTLATVGW FALSE                #CONTROL AUTO VARIABLE GEOMETRY WING

POSITION 0m 3ft 0m           #POSITION
ATTITUDE 45deg 0deg 0deg      #ATTITUDE
INITFUEL 75%                  #INITIAL FUEL
INITLOAD 0.0t                 #INITIAL PAYLOAD
INITSPED 0.0MACH              #INITIAL SPEED

LMTBYHDP TRUE                 #Limit Max Num Weapon by Hardpoint
GUNPOWER 1
INITIGUN 0                    #INITIAL GUN

REM ClZero,CdZero is fixed by Cruising condition
REFVCRUS 0.8MACH              #CRUISING SPEED
REFACRUS 20000ft              #CRUISING ALTITUDE
REFTCRUS 0.3                  #CRUISING THROTTLE SETTING

REM ClSlope,CdConst is fixed by Landing condition
REFVLAND 134kt                #LANDING SPEED
REFAOALD 10.5deg                 #LANDING AOA
REFLNRWY 2700m                #RUNWAY REQUIRED TO STOP
REFTHRLD 0.3                 #LANDING THROTTLE SETTING

AUTOCALC

REM copyright 2007 by S.C
In this .dat, the aircraft will need 30% power to maintain 134KIAS while the wing alpha is 10.5 degrees. (which is very low, and thus the poewr to maintain a higher speed and turn rate is also low-ish, and not above 100% throttle)
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Re: Adjusting DAT to fit with real performances

Post by DavideV » Mon Oct 03, 2011 8:21 pm

Hi Flake, first of all thanks for your response and sorry for my very late one... I don't understand: why are you talking about turn rate when the AOA shows the angle between the wing chord and the direction of the airflow that goes toward the wing?
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Re: Adjusting DAT to fit with real performances

Post by Dragon029 » Tue Oct 04, 2011 5:30 am

Because AoA controls how much lifting surface is presented to the airflow; an AoA of 45 degrees generates more deflection than an angle of 15 degrees. Of course, when this happens, to make sure that AoA converts to turn rate, you need to have an appropriate wing area - small wing areas allow you to pitch your nose without changing your vector much; large wing areas generate high changes in vector direction when an AoA is applied. Also weight - a high weight will impede your chances at changing vector due to the extra inertia / momentum you're trying to battle.

So what he's saying is that by changing the landing conditions in the .dat, he can make the aircraft sustain a decent AoA of 10.5 degrees at 134 knots and with only 30% of military power. His wing area for the Hornet is a little low at 37m^2, but he doesn't have it that heavy. (Overall it's a pretty realistic .dat).
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Re: Adjusting DAT to fit with real performances

Post by DavideV » Tue Oct 04, 2011 7:09 am

Oh, I see... thank you very much, guys!
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