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martinlest2

Editing Aircraft Performance - advice please

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Hi. I have one or two a/c (a Dash 7 for example) which at level cruise altitude will not fly anywhere near the real-world max cruise speed, even with throttles flat out (I can't get the Dash 7 past about 180 knots). How do I change things so that I can get faster cruise speeds (that is to say, more realistic - I don't want the a/c to go any faster than they should of course!)? I thought I could edit the aircraft.cfg file's Performance section (after making sure editable=0 is changed to "1"), but it doesn't seem to help. I changed this (no mention of speeds):

 

performance=Range: 1,170 nm\nCargo: 11,310 lb\nPassengers: 50

 

to this:

 

performance=Max Cruise Speed\t235 kts\nMaximum Range\t1,312 nm\nService Ceiling\t21,000 ft\nCargo: 11,310 lb\nPassengers: 50

 

but as I say, the a/c still maxes out at around 180 knots in level flight. Even the speed indicator in the cockpit has the 'barber pole' at about 230 knots (which seems about right for the real a/c I think): the speeds section looks like this:

 

[Reference Speeds]

flaps_up_stall_speed=103.000

full_flaps_stall_speed=60.000

cruise_speed=223 //at 10,000'

max_indicated_speed=280.000000

max_mach=0.500000

 

I downloaded FSEDIT, but the ref speeds in the aircraft.cfg file look fine already, so will it help?....

 

Thanks,

 

Martin


Martin Stebbing, EGLF (UK)

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Hi

 

I'm by no means an expert in altering aircraft performance but I don't think that what you have altered will have any effect as you have already said.

 

Now I fly Flight1's Cessna 172 and have altered its performance by changing certain data in the aircraft.cfg file as shown below (alterations are where you can see the double backslashes):

 

[piston_engine]

power_scalar = 1

cylinder_displacement = 90

compression_ratio = 10 //8.5

number_of_cylinders = 4

max_rated_rpm = 2500 //2360

max_rated_hp = 200 //160

fuel_metering_type = 0

cooling_type = 0

normalized_starter_torque = 0.32

turbocharged = 1 //0

max_design_mp = 35 //30

min_design_mp = 1 //9

critical_altitude = 12000 //1000

emergency_boost_type = 0

emergency_boost_mp_offset = 0

emergency_boost_gain_offset = 0

fuel_air_auto_mixture = 0

auto_ignition = 0

emergency_boost_duration = 360

max_rpm_mechanical_efficiency_scalar = 1

idle_rpm_mechanical_efficiency_scalar = 1

max_rpm_friction_scalar = 1

idle_rpm_friction_scalar = 1

 

I don't know if this will help you but it does at least show how I have managed to alter performance.

 

David

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There are many flight dynamics variables, atmospheric etc, beside whats in the aircraft.cfg that will cause your aircraft to not achieve its max. designed cruise airspeed! Like HEAD WIND. Those numbers are absolute maximums under ideal conditions. like TAIL WIND. If you believ its needed. Whats more than likely slowing you down in a model is the induced and parasitic drag settings. The lower the number the less drag. Editing can cause ill effects elsewhere also!

 

Example:

 

[flight_tuning]

parasite_drag_scalar = 1.0

induced_drag_scalar = 1.0

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Hi, Martin,

 

Several thoughts:

 

First, you need to distinguish between Indicated Airspeed (IAS), True Airspeed (TAS), and Groundspeed (GS). Indicated Airspeed becomes lower and lower as your altitude goes higher and higher, as compared to TAS. So you might be moving at the appropriate TAS with a much lower IAS, depending on altitude. Check your GS (assuming no or minimal wind). You need to check in Aircraft>Realism to see if you are reading IAS or TAS.

 

Second, are you starting with the default fuel load? Often FS starts with max fuel, which puts you over the maximum gross weight. This can slow you down and also prevent you from reaching cruise altitude.

 

Third, it isn't true that a headwind will decrease your IAS or TAS, unless there is a sudden wind change. IAS and TAS indicate speed relative to the air. Only GS is affected by wind speed. (With a sharp wind speed or direction change your IAS and TAS will change, so you might be better off experimenting with the default weather rather than RW weather).

 

I don't think the "performance= " parameter has any effect on actual performance. These numbers are for your information. You probably can crank up horsepower or thrust as David suggested, but I would suggest you look into some of the above ideas first, since usually (but not always) aircraft modellers know what they are doing.

 

I hope this helps!

Mike


 

                    bUmq4nJ.jpg?2

 

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Martin,

 

If you're talking about the Milton Shupe Dash-7, you can expect the performance numbers to be correct. The "Performance=" section of the aircraft.cfg contains specs for the aircraft. These can be edited, but will have no effect on the simulation.

 

Most of the values in the [Reference Speeds] section are supposed to be KTAS, not KIAS. The exception is the value for Max Indicated.

 

At any altitude above sea level, your True Airspeed will be higher than your Indicated Airspeed. While cruising at 180 KIAS, your True Airspeed could be as much as 220 KTAS or higher depending on the cruise altitude. Also, max cruise speed will usually increase at lighter weights.

 

Regards,

JerryH

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Hi, thanks for the replies - looks like I will just have to experiment at different altitudes and weights (yes, the Dash7 is the Milton Shupe one). But I should be able to get the cruise speed up to somewhere near the barber pole I would have thought, no? As it is, my max cruise speed in the Dash 7 is way short of it (and flying from SCCI to ROTH, as I am at the moment, is taking for ever!).

 

Insofar as the aircraft.cfg file is concerned, have a look at the paragraphs headed [General] Section and [Reference_Speeds] section and the descriptions in AircraftContainerSDKFS2004.doc. According to the latter, changes should be effective, at least if implememented with FSEdit (see note about that in the latter section).

 

My engine data look s like this, I could try increasing the static thrust value, but I don't really want to increase power across the board, so that the a/c runs away at idle on taxi.

 

[TurbineEngineData]

fuel_flow_gain=0.014 //Gain on fuel flow

inlet_area=1.18 //Square Feet, engine nacelle inlet area

rated_N2_rpm=29920.000 //RPM, second stage compressor rated value

static_thrust=158.000 //Lbs, max rated static thrust at Sea Level

afterburner_available=0

reverser_available=1

 

The other 'problem' is that BAS (British Antarctic Survey) use the Dash 7 to run from Punta Arenas to Rothera Station, but my FS a/c runs out of fuel en route, even with 100% in all tanks at SCCI. I tried to increase the range in the aircraft.cfg, as above, but this also seems to have no effect. I could increase the fuel tank capacity, but this would throw Milton Shupe's a/c balance out, I am sure, so I hesitate... Any ideas here?

 

Thanks again,

 

Martin


Martin Stebbing, EGLF (UK)

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Hi Martin,

 

As the others have said , you need to be aware of the difference in the various airspeeds quoted.

 

As Mike777 said ..... " First, you need to distinguish between Indicated Airspeed (IAS), True Airspeed (TAS), and Groundspeed (GS). Indicated Airspeed becomes lower and lower as your altitude goes higher and higher, as compared to TAS. ....."

 

You mentioned ..... " I should be able to get the cruise speed up to somewhere near the barber pole "

 

The Barber Pole indicates Maximum Speed which may or may not be obtainable in level flight, it's usually only in a dive on most aircraft. So that's not really a cruise speed indication. Depends on the type of aircraft you're flying.

 

Collectively there's enough people here to help you through these issues.

 

Pete.

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Hi again, Martin,

 

I found this page with technical information on the Dash-7.

http://members.aon.at/~slenz/dash7.html#dash7_techdat

 

It shows a maximum cruise speed of 227 knots at 15000 ft.

 

At standard pressure (29.92), I found the following (using the stock FS9 737, but the particular aircraft doesn't matter for this):

 

At 15000 ft 190 indicated (IAS) gives a true air speed (TAS) of 220

 

At 18000 feet 183 indicated (IAS) gives a true air speed (TAS) of 223.

 

You can check TAS on the stock GPS or by tuning a VOR straight in front of you or straight behind you.

 

Another page shows the maximum range as 700 nm.

http://www.flugzeuginfo.net/acdata_php/acdata_dhc7_en.php

 

So if SCCI to Rothera Station is more than that (with a contingency safety margin), then their aircraft certainly have an extra tank or two.

 

You can add an extra tank but try to get the coordinates right at the center of gravity so it doesn't throw the aircraft out of balance. You will need to look through the FS SDK and your aircraft.cfg file to find this parameter and the parameters for a new fuel tank. If you do add one, you still need to stay under maximum gross weight. Look for "empty_weight_CG_position = " in the aircraft.cfg file.

 

Both the above pages appear to have a good deal of information on Dash-7 performance.

 

Best of luck!

Mike


 

                    bUmq4nJ.jpg?2

 

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Thanks again for the replies.

 

"The Barber Pole indicates Maximum Speed which may or may not be obtainable in level flight, it's usually only in a dive on most aircraft. So that's not really a cruise speed indication. Depends on the type of aircraft you're flying." The barber pole moves up and down (or around) the speed indicator according to altitude, weight etc. Its position should indicate the maximum speed at that moment. As you descend, the pole moves higher, so whereas at, say, 20,000' max speed may be 'only' 240 knots, at 5,000' it may be 290... But do correct me if I am wrong of course in so far as the Dash 7 is concerned! :unsure:

 

According to the documentation I have, the maximum range of the Dash 7 with reserves is 1313 miles (Commercial Aircraft handbook). Whatever, I will check information above and see what I can do. May try adding another fuel tank (can I not just increase the capacities of the existing ones?) - the speed issue is not crucial, but I would like to be able to get from Punta Areana to Rothera (as they do in the real-world) without having to 'cheat' by adding fuel via the FS9 menu!

 

Martin


Martin Stebbing, EGLF (UK)

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Hi, Martin,

 

Increasing the capacity of the existing fuel tanks might work, or it might throw the plane out of balance, depending on where the tanks are located relative to the center of gravity. If I were you, I would just try it and see what happens when you fly with full or nearly full tanks. Be sure to back up your aircraft.cfg file if you haven't already.

 

I am not knowledgeable about Dash-7s -- I think I used to have one and tried it out on Courchevel approaches with mixed results (this is an air field with a short runway that goes uphill from the side of a cliff in the French Alps). It is quite possible that there are several versions with different fuel capacities and ranges, and you might have to increase fuel capacity to match the range of some of them. Another thing to consider is that I think the Dash-7 has constant speed/variable pitch propellers. If you don't use them properly during cruise, you may burn too much fuel. Unlike a jet, you can't just use the throttle to set the thrust to maintain a given speed. You also have to adjust prop speed and pitch (as well as mixture).

 

Regarding the barber pole, it should move down as your altitude increases, as your maximum IAS decreases even if your maximum TAS remains the same. Pete is correct that the barber pole indicates maximum safe airspeed, not the target cruise speed. Its indications don't necessarily mean that you are able to reach that speed in all or most circumstances. My understanding is that you don't want to fly right at the barber pole as then you have no margin of safety -- if you descend or encounter an increased headwind, your air speed may go over the maximum safe air speed. RW pilots worry about this a lot!

 

Looking at Dash-7 performance on the web pages I found, it seems to me that it just doesn't go all that fast. That's what "simulation rate" is for on long trips over water (some purists may shudder :rolleyes:)!

 

Mike


 

                    bUmq4nJ.jpg?2

 

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Hi....

 

Re, barber pole - in all other a/c I can fly close up to the speed it shows (not TOO close, I agree) at any given altitude, but in the Dash7 I can't get anywhere close, except in a descent. Yes, the pole indicates maximum safe airspeed, I know, not cruising speed; but as I say, it should not be the case that I cannot fly faster than about 65-70% of that indicated max safe speed, unless the Dash 7 is some special case - I have no such issue with the Dash 8s or ATRs I fly...

 

I did notice that the fuel on the last flight seemed to be consumed very fast, so maybe I do not have propeller settings right - or the setting is not modelled. How do I use them 'correctly' in practice, in level flight?

 

I have increased the capacity of the fuel tanks, by 25% each: in the FS9 fuel & payload menu, the a/c looks well-balanced and the increased fuel weight registers too. Haven't flown it like this yet.. will try a little later today.

 

Martin


Martin Stebbing, EGLF (UK)

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At standard pressure (29.92), I found the following (using the stock FS9 737, but the particular aircraft doesn't matter for this):

 

At 15000 ft 190 indicated (IAS) gives a true air speed (TAS) of 220

 

At 18000 feet 183 indicated (IAS) gives a true air speed (TAS) of 223.

 

You can check TAS on the stock GPS or by tuning a VOR straight in front of you or straight behind you.

 

 

In a standard ISA conditions, (+15°C @sea level), using an aviation computer the results are even better.

 

At 15000', -15°C; 190kt IAS = 238kt TAS: at 18000', -21°C; 183kt = 242kt TAS.

 

Your method for TAS using VOR etc. would only give a true indication of GS and an approximation of TAS if you set sea level temp to +15°C and absolutely no wind at upper levels.

 

If those indicated speeds are representative of the Dash 7, then they match the performance quoted in the original post.

 

Colin B

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There are two versions of the Dash 7, the 100 and 150. The 150 series features much larger fuel capacities.

 

From Airliners.net Dash 7 Specifications:

 

Max cruising speed 428km/h (230kt), long range cruising speed 400km/h (215kt). Service ceiling 21,000ft. STOL takeoff distance at 18,600kg (41,000lb) TO weight 670m (2260ft). Range with 50 passengers and reserves 1270km (690nm), range with standard fuel and three tonne payload 2168km (1170nm). 150 - Range with 50 passengers at max cruising speed 2110km (1140nm), with max fuel 4670km (2525nm).

 

So your TAS doesn't need to be faster than 230 knots, and your range of the original version (which I assume this is?) is only 690 nm with a full load. If you are trying to simulate the 150 version, you probably need to add more fuel:

 

"The only major development of the Dash 7 was the Series 150, which featured a higher max takeoff weight and greater fuel capacity, boosting range."

 

From this site:

 

http://members.aon.a...lenz/dash7.html

Maximum Fuel Capacity (Jet-A) 4.5t 9.926lb. (16.000lb. for -150 conversion)

 

Since JetA is 6.7 lbs per gallon, that works out to:

 

1481 gallons (100)

2388 gallons (150)

 

So what capacity did the original model have?

 

Hope this helps,

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I believe Milton's version was the -100 not the -150.


Ed Wilson

Mindstar Aviation
My Playland - I69

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Hi. Thanks again for the input.

 

I am still not sure why the Dash7 (yes, it is the 100 version) is the only a/c I have in FS9 that will not cruise even close to the barber pole (in spite of all the numbers), but no matter. More important is the fuel 'problem'. I have changed the capacity, as I said, and although this may not be totally 'realistic', I can now fly to my preferred destinations as if this were a Dash7-150. It's a really nice plane to fly (great sound package!) .. makes a really nice change from the Airbuses and Boeings I tend to load up most days!

 

Martin


Martin Stebbing, EGLF (UK)

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