Default 172: Ground Steering and Max Power

[dirtydog1006]

I am building up time in the default 172, and I must say the more I fly it the better I like it. But, two simple questions:

1) I have no time in a real 172, but I am forming the impression that while driving around the ramp, the default model responds to steers way too fast and eager. I have seen some discussion of this on the Net, so it's probably one of those things that everyone but me knows about. If true, is there an easy fix to tone down the ground-steering response?

2) The tach has a redline at about 2700. I never seem to get that many revs, maxing out at about 24-2500. I have tried Tom's trick of exercising SHOW TRUE AIRSPEED, but that does not seem to help.


3) And the third of my two questions, not specifically about the 172:
Why the heck are the stall speeds in the AIRCRAFT file of so many models annotated as TRUE AIRSPEED? This makes no sense to me, as neither plane nor pilot give a rip about true AS: It's the indicated airspeed that counts (dynamic pressure and all that). So why specify these speeds as TAS???

[Ed Burke]

Go to the C172 aircraft.cfg file and scroll down to this line:-

[contact_points]
point.0 = 1, 0.90, 0.00, -4.09, 1500, 0, 0.5, 22.0, 0.25,2.5, 0.7, 0.0, 0.0, 0

The 22.0 is the steer angle. Reduce this value (and save) until you are happy with the ground handling. A much too high value is a fault in many a/c. Try 11.0 for starters. It is wise to note the original when altering such values, eg. ------ //steer was 22.0 ------ at the end of the relevant line.

Ed

[flaminghotsauce]

All my hours are in 172s. I find the default airplane to be pretty wild compared to the real thing. Too sensitive to roll and pitch, ground steering is bad, etc. I bought the Carenado 172 for FSX and it's everything I was hoping the default airplanes would be.

I have downloaded two different versions of the 172 for FS9 that are more "real as it gets" or whatever. One is the Real Air version of the default 172 and you can really side slip it.

www.realairsimulations.com/list_box.php?page=downloads

I like it way better than the default. There's another one I got from some training site but it's shut down. It's called the PCTrainer172A. I have a zip file somewhere on a thumbdrive, so I can't help you with that one. I can't remember if Tom's webpage has 172 FD's but if he's done them, they'll be way better.

The ground steering problem I never did whip. I tried messing with my pedal settings, but that messed with all the airplanes. I think there's a setting in the .cfg to mess with to make it steer less sensitively, but I don't recall off the top of my head. ~edit~ Read above, I type too slow! ;D ~end edit~

As far as the redline, are you talking about the takeoff run? That won't get to the red line until the airspeed is full up.

The stall speed in the 172 won't be much different from IAS to TAS as it's a slow aircraft.

Hope this helps.

[louross]

I hope this info will help you:
1) Haven't flown a 172 in years. Last time was around 1972. Many times in the 60's and this was also at rather high airports- Aspen, etc. I never saw the RPM gauge near max, except it would build up if I added power in a steep descent. (Adding power in a steep descent??? Let's not digress!)

2) Stall speeds are always given in TAS. As I remember, it was because at such low airspeeds and disturbances of airflow with so many different configurations, IAS was not reliable. Various flap settings, gear position, and attitude affect IAS to the point it is not reliable. That reason is basically it, but the tech aspetcs of the explanation are probably "off".
By the way, all performance speeds are also listed as TAS. There could be an exception or two I've forgotten about.
lr.

[Tom Goodrick]

Sorry,Lou but DD is right. Stall speeds should always be in IAS in FS. In reality Cessna gives them in CAS which is IAS corrected for low-speed, high angle of attack effects. But a pilot can never see CAS so we always worked out an IAS that would keep us out of trouble. The sim does have a deviation at low speed that is added as an error to IAS to make CAS. But, again you cannot see CAS and you have to use something you cna see to stay safe. IAS works.

MS is wrong to give stall speeds in TAS. Flaming is right in that the 172 nevr gets high enough to show a big difference between IAS and TASA. But your career will not be spent entirely low and slow in a 172 so learn to use IAS to avoid stall.

In any airplane where you don't know the stall speed, load it up to max gross and run some tests. Stall speed is independent of altitude so pick a reasonable altitude and fly gently slower in a slight climb until it stall (the vertical speed suddenly picks up negaitvely). Not that KIAS. Test clean and with full flaps. In actual flight with less than gross weight, you will still be safe using that stall speed though the actual stall speed is will be slightly lower. Being safe is the whole point.

If you have the rudder activated with pedals, then reducing the wheel turn will help the steering problem. But that usually applies when the value is up to 45 or 60 degrees. 22 is already a decent value. If you are steering with the joystick, which also runs the ailerons, I don't know what the solution is. You might try reucing your stick's roll sensitivity on the calibration. Maybe reducing a sensitivity scalar in the tuning section might help.

On a fixed-pitch aircraft like the 172, the max achievable rpm can be increased by decreasing the blade pitch angle. But be careful. Do it in small increments.

On my page there is a good set of FD for the C172. It clears up a number of things. It also allows for spins as I remember. (I did that for both the 172 and the 182, I think.)

I don't like the "Real Aircraft' model. They bent the rulles of physics badly to get a spin. They changed the MOI's so they are in the wrong ratios to each other. That messes up all other responses involving roll, pitch and yaw. (What else is there?) I had a knock-down, drag out fight with them the last time I said that. But I am always ready for that fight. I achieve spins with the correct MOI's but with altered stability derivatives which is the proper way to do it. If you check many aircraft on my site like the 182, Bravo, Baron, Piper Cub and many others, you'll find they spin fairly well. (But some, like the Baron and the A36 Bonanza, will prove difficult to recover after 1.5 revs. You'll dig a hole.)

On any aircraft, check the MOI's to see if they have the proper proportion. MOI Z (yaw) > MOI Y (pitch) > MOI X (roll). (If there are 4 engines, roll can be close to pitch.)

[flaminghotsauce]

Tom I don't ever do spins, but that Real Air 172 will slip like crazy. I was very joyously sliding in sideways to lose altitude, great fun! But I suppose that's probably physically impossible based on your observations?

[louross]

Jeeze. Okay. We can all admit the FS does whatever it does to do whatever it tries to mimic. I thought it was pretty obvious I was talking real world. Some who use FS actually like, and want that, real world, I'm talkng.
lr.

[Tom Goodrick]

Slips do not need to be done, normally, in aircraft such as the 172 with flaps. Flaps offer a better and safer way to get down steeply when too high on approach - provided you have managed airspeed reasonably well. There are some aircraft like the Piper Cub and Aeronca that do not have flaps and need to slip to make steeper approaches. When you fly these aircraft you are taught how to do slips. If you keep the nose low they are reasonably safe. On aircraft with flaps deflected, slips can be deadly.

FS aircraft will usually do mild slips but the value of CYbeta must be high enough to generate a significant sideforce when held at a sideslip angle beta. i don't usually look at that but I have in a few cases and any plane I've seen can generally use a little boost in Cybeta to slip nicely. But the slip is an invitation to a spin if the airspeed is not watched carefully.

My 172 owners' manual says spins are ok when the plane is in the utility category. I think every one should do spins - in aircraft that can easily recover from spins - becaues it provides an extra measure of competance in dealing with unusual situations that can occur. I learned in the Piper Cub as a kid. I never did spins in the 172 when I took formal lessons and got my private ticket because the FAA had decided that doing real spins was unsafe. To me that was dumb. At least FS allows you to do spins and walk away no matter how badly you mess up the recovery. But I checked my 172R's spin and did not like it. In fact I got too deep in the spin and it went flat. I need to touch that up a bit.

Lou, it is all right to talk about FS flight in comparison to real flight. FS flight should be, and is a very accurate representation of real flight. I grant you it is not very good in many of the detail operations a pilot has to know. That comes with the low cost of the sim and the lack of a physical cockpit. But if a real plane does a certain thing in rsponse to a particular condition, the FS model should be expected to do it. In most cases, if it does not respond realistically, we can make it do so.

FS "mimics" flight by using the equations aeronautical engineers have developed for calculating aerodynamic forces and moments at one instant, moving the aircraft through a short time like .001 seconds in response to those forces and moments, and then recalulating at the new condition. When this is repeated with proper care for numerical complications, the sim gives very accurate results. There are parameters like weight, geometry and MOI's that fit into those equations. If they are not chosen well, strange results will occur.

Microsoft has long had the idea that it is best to make aircraft appear to be invulnerable to troubles that might make them fall out of the sky. But we all know that can happen in real life if a pilot is at least a little bit stupid. So I have adjusted many FD files so that the pilot can get in trouble in deep stalls or casually accelerated turns that can lead to stall/spins. But I only make a plane dangerous if it has a reputation for being dangerous in a deep stall. The Bravo and the Baron are two that fit into that category. Both are know to go into a non-recoverable flat spin. My FS versions will do that.

[louross]

I'll go with just about everything you've said here, but I must stress "just about". The part "...is a very accurate representarion of real flight..." I have to take with a grain of salt. That comes from my actual experience in the real world. The best FDE's you're going to find in MSFS are the Dreamfleet 727 and the most complex programing you're going to find is the PMDG 744. Will these programs teach you how to fly the airplane? No. Too many things can not be represented- too many situations. You can learn the systems, procedures, and numbers, but those things are really learned in the a/c manuals. If anyone cares to differ, that's okay with me.
There is no real point in getting involved in a debate, as, with most ideas in life, a person is going to believe whatever he wants, regardless of facts or opinions. I've had discussions about flying concepts in the real world with less experienced pilots, but these were discussions done in a vain of learning, and all worked out well, even tho the less experienced pilot had a misunderstanding or insufficient knowledge. I find in FS that the FS crowd, including most commercial interests, don't want to discuss, but want to fight about the point at hand. That's too bad for those who really want to learn. I've really seen very little disagreement among experienced pilots concerning concepts. Maybe a procedural or even a technique difference, but those are actually minor.
One simple example. The engineers, light plane pilots, and GA flight instructors all know the basic theory of how to shoot an approach, flare, and land. That's all great. IF you are flying a light plane, and in this case we're talking anything at less than about 9,000 lbs. That info doesn't work for heavy stuff. Know of many a GA pilot who checked out (right seat) in a 727, 732, Beech 1900, etc, and had all kinds of problems in that realm of flight. The Captain easily straighened out the problems with a simple explanation that the "theory" doesn't work for heavy stuff. Once in a while you'll see in a forum some guy in FS explains he is very competent in the GA planes, but now is trying to fly a - some jet airliner - but can't land it. Invariably, a pilot who actually flies that a/c in real life for a real company will explain the real technique, and you can't believe the flaming he gets from all the FSer's,light plane CFI's, engineers, and etc. But see, here is a real pilot, who actually flies the real airplane, trying to help by giving the real world techniques (which also work in FS) and he gets flamed by some people who do video games, and those who know nothing about heavy a/c. I've seen many different examples. You'll also find- partially for that reason- that many airline and former airline pilots who enjoy FS don't get involved in forums. There is an FS forum that tends to have an exception, as there are former airline/military pilots that contribute.
Anyhow,
lr.

[dirtydog1006]

As usual, an excellent and wide-ranging discussion. Thanks for all the info, I will try the mod for the steering angle.

But, I have a follow-up question re RPMs.

In the default 172, because I cannot get to redline RPM, unless I do a power dive, how do I know what percent power I;m using?

Plenty of folks have advised me to cruise at 75%, climb at 85%, etc. Call me simple-minded, but I cannot figure the basis for the percent. I was assuming it would be percent of the redline (about 2700). But given that I cannot get that many revs, it seems wrong to think of 2700 as 100% power.

Stright and level in still air, the revs seem to max out at about 2490 or so. Is that figure what I should use to estimate revs for 75%?

I had this, apparently, idiot idea I would modify someone's digital tach to show percent, by having the gauge divide the RPM parameter by the redline value (of 27, in this case{cancelling the hundreds}). Perhaps I now understand why there seems a dearth of guages giving percent power for fixed-pitch recips like the 172.

[louross]

First- you're specific questions, I can not really answer. I flew 172's, 182's, lots of twins, Twin Otters, and other stuff for a short period in the 60's, thru the Colo Rockies, but that was a long time ago. There are folks here who can give you the specifics. It seems to me typical RPM in the 172 was around 2400, or maybe 2200, or maybe, something else at cruise. However, climb in the real 172 was at full throttle, as was the take-off. Reduced throttle (RPM in this case) was at cruise.
I could understand you're tinkering with certain FDE's, like turning radius, if you really think it's necessary, but why do you want to add imaginary gauges to any panel, since the real airplane doesn't have them? For the real (172), push the throttle all the way forward, and on every take-off note the RPM setting and keep an eye on the oil pressure. Then in the future, if the RPM is lower, or excessively high, you'll know that there could very well be some type of problem and you may want to abort the take-off. Your eye on the oil pressure gauge should be obvious, but it is surprising to me how many GA pilots hardly ever look at it on take-off.
How about a little FS info? Opinion? Okay. You will find those using FS that want to do it as real as possible, and those who could care less about reality. So you decide where you yourself want to be. You will find those who want a panel and systems as real and complete as possibe, and those who are more than happy with anything. You'll find those flying a heavy 4-engine jet with a panel of a twin jet and a 747 with the sound package of a Lear. And of course all those somewhere in between. So you decide where you want to be.
It seems very apparent you are new to FS and you aren't a private pilot. I'd suggest you go thru the FS private, instrument and commercial courses for a good base. Or, you could go purchase the Jeppesen Private Ground School Course and do that part. You will learn that TAS is very important to a pilot (point 3 of your first post).
lr.

[Tom Goodrick]

The 172 is seldom flown at poer levels above 2500 rpm. My Cessna owners manual does show 2700 rpm in the table. I was told to fly it at full throttle for climb and 2350 in cruise.

There is no point in using a Power Gauge with a fixed-pitch prop because your only power indication of engine performance is the rpm. You can adjust the "fixed-pitch beta" shown as 20 in this list:

[propeller]
thrust_scalar = 1.05 //Propeller thrust scalar
propeller_type= 1 //0=Constant Speed, 1=Fixed Pitch
propeller_diameter= 6.3 //Propeller Diameter, (feet)
propeller_blades= 2 //Number of propeller blades
propeller_moi= 5.0 //Propeller moment of inertia
beta_max= 0 //Maximum blade pitch angle for constant speed prop, (degrees)
beta_min= 0 //Minimum blade pitch angle for constant speed prop, (degrees)
min_gov_rpm= 0 //Miminum governed RPM
prop_tc= 0 //Prop time-constant
gear_reduction_ratio= 1.0 //Propeller gear reduction ratio
fixed_pitch_beta= 20 //Fixed pitch angle of fixed pitch prop, (degrees)

This is from the C172R. Try 18 and you might get 2500 rpm on takeoff and initial climb.

Glad to see you are back in good spirits, Lou! TAS means nothing to a pilot except when he'll be home for lunch. IAS keeps you in the sky.

DD was referring to my "Proper Turn Gauge" which shows TAS as well as the actual turn rate and the turn rate if obeying the Laws of Physics. Turn rate does depends on bank angle and the ture airspeed. That's about the only tim TAS matters to a pilot except for navigation. Today you can let the nav computer on your panel (like the "Garmin 500" in FS9) do the navigating. It will tell you when you will arrive based on measured ground speed.

It's a new world, Lou. But he was right in his first paragraph about TAS and IAS. At any altitude, IAS determines the forces and moments acting on all parts of the airplane. The wrong IAS can break the plane or cause it to stall, at any altitude. Remember dynamic pressure and Bernouli's Law? That's what the airspeed indicator measures and shows you as IAS. By the way, I checked my 172 Manual on the difference between CAS and IAS. There is no difference from 70 IAS up.

[louross]

Howdy, Tom. I clicked on your listed music site- very interesting- didn't know you were a professional player! What do you think of Boots Randolph?

TAS?. Nope disagree totally.
Q): Should a pilot know how to shoot an NDB approach?
A): Depends on where he's flying. Couple of AF pilots wiped out a bunch of people in a 737 flying some State Department figure into Bosnia or someplace there abouts during the Clinton admin because they couldn't fly an NDB approach
Should a pilot know how to shoot a VOR approach? I say yes. Same with the import of TAS.
Want to fly jets (real)? You better have a real good understanding of TAS.
lr.

[Tom Goodrick]

I have liked Boots Randolph for a long time. My style on tenor sax is similar to his. I chose my mouthpiece to get close to his sound. He has an amazing range that I can't touch. Hope you liked the music. The Sound Click audience gives me more "hits" when I play the soprano sax, so that is what I have been playing most the time.

I agree that someone flying with an ATP must be able to do NDB and VOR approaches even though these are being phased out in the US.

For pilots flying piston and turboprop aircraft below 25,000 ft, TAS has very little to do with anything except when estimating groundspeed and then you need a good estimate of windspeed. A GPS-based nav computer gives you directly measured groundspeed which is best of all for estimating the flight time remaining. Our Garmin 500 in FS9 gives us that. I have also made available wind component calculations which are available from the real Garmin 530 but not in the FS version. These estimates can be used in selecting the best altitude for a particular flight.

TAS is, of course used whenever anyone mentions cruise speed of any aircraft. This is normally done for bragging rights but obviously has an effect on long trips. A downonside to this is that the high cruise speeds shown for turbocharged piston aircraft like the Bravo look very good on paper and attract buyers. But then they find that taking the time to get up to and down from those altitues is imractical and having all pax wear oxygen masks is a big negative. Slow descent to avoid ear pain is another big negative. Many such aircraft are never flown as fast as their published cruise speeds. FS pilots should fly the Bravo using a 500 fpm decsnt rate and noting they are wearing an oxygen mask whenever above 12,000 ft (lower for smokers).

When I test-fly FS aircraft on which I am adjusting the FD file to meet published specs, I fly at gross in calm air at the altitude prescribed in the spec and read TAS from my Turn Performance Gauge. (Which I also check to be sure I have not cranked up the daw damping too much.)

Again, TAS has a direct effect on turn rate, especially notable at cruise speed and altitude. This is important to know so a pilot does not crank up the bank angle excessively to match the turn rate he sees at low altitude. That can get him into big trouble fast in some planes which are not too far above stall speed when they reach cruise altitude.

But IAS is used when a pilot wants to avoid stall or avoid breaking the aircraft. All "V speeds" are given in KIAS. VS (stall) , VA (max maneuvering or safe turbulence speed), Vno (max structural cruising) and VNE (Never Exceed speed) are all in KIAS. This fact as designated by the FAA. I will cite the AOPA as a source confirming this.

Specs Published for the Mooney Bravo (AOPA PILOT, Jan 1998):
Cruise Speed: @25,000 ft 214 KTAS ( 20.5 gph)
@10,000 ft 188 KTAS (20.4 gph)
VX (best climb angle) 85 KIAS
VY (best climb rate) 105 KIAS
VA (design maneuvering) 127 KIAS
VFE (max flap extended) 110 KIAS
VLE (max gear operating) 165 KIAS
VLO (max gear operating) extend 140 KIAS retract 106 KIAS
VNO (max structural cruising) 174 KIAS
VNE ( never exceed) 195 KIAS
VSI (stall, clean) 67 KIAS
VSO (stall, landing config) 59 KIAS

The Bravo is turbocharged but not pressurized.

I did a little demo for myself this morning. I had the Piper Malibu (pressurized) cruising at 16,000 ft and decided to reduce the power and watch it stall while the autopilot tried to hold alttitude. This is a good measure of stall speed if you are careful not to slow down too quickly. It stalled at 66 KIAS and 91 KTAS. At a lower altitude, it would still stall, clean as I had it loaded, at 66 KIAS but the TAS would have been close to the IAS. The point is IAS shows you when a stall is iminent, regardless of altitude.

In jets, TAS does, indeed, become important to a pilot, but, more importantly and directly, Mach becomes very important. TAS is only important as it relates to Mach but you should go by Mach because a significant Mach number depends not only on TAS but also on OAT. The OAT is such that a given Mach number is reached at a lower TAS when in cold air at high altitude. Generally, jets use a Mach limit for climb performance above 30,000 ft. That's where they catch Mach 0.7 which is often used.

Jet Mach effects pertain to stability and control so they are not ignored.

But the famous 'Coffin Corner" for jets is where, after a climb, the IAS is down close enough to stall speed so that a large bank can induce a stall. For example, many small jets like the Citations are down to about 180 KIAS when they make it to 41,000 ft if pushed hard in the climb. Clean stall is about 100 KIAS. Multiply this by the factor for a 45 degree bank and things can get dicy. Barry Schiff, among others, has discussed this in published articles.

There is one area where TAS figures in. That is in cockpit noise. The frequency of turbulence of wind around the cockpit windows depends on TAS. This means the sound of the relative wind becomes louder and will change frequency in some way at higher true airspeeds. For a few years I used a special airspeed indicator in testing that utilized this prinicple. The reason was I needed an indicator that worked accurately down to a few ft per second.

[louross]

I'll go with most of that to keep it simple. The specs you've given on jets, tho, I don't know where they came from, or maybe you are specific to a particular corp-jet. We climbed 727's at Mach .8 and cruised at .84 . Don't remember in the mini-pig, but it was a slower airplane. Also, Mach changeover starts around FL240, or bit higher, not 300. Talking about slower, French Caravelle was a slow airplane too, and a real gas hog.
As far as speed goes, probably all companies now fly slower than in the 70's because of the fuel cost. What's the typical cruise speed of a 767? There is none. Depends on the company. Typically programed anywhere form .74 to .78 .
"Coffin Corner" for jets is a term that was perverted to jets by somebody way back when, it really is a gross misnomer. Coffin Corner is an idea used for small planes when turning from (base to final) and the pilot slows the a/c and stalls it in. (I think it was base to final, I'm getting up into the ozone layer at the moment). Relating "CC" to jets is like the guy on the corner who talks about the infamous "air pocket". Okay- relating coffin corner to jets is the equivalent of relating "critical engine" to jets. Simply put, it doesn't exist.

By the way, I like a lot of Rod McKuen's older stuff, too, like Stanyan Street, but that's a different story.
lr.