Mach, mock, squawk

srgalahad

srgalahad

Charter Member 2022
Due to the nature of the PacRim event a lot of people are discovering the realm of Mach numbers for the first time. Others have been there but trusted the simple view that there are 'dependable' numbers that can be used to measure Mach and related performance.

First, here's a link to a specific reply I made to a query about a Duenna.
http://www.sim-outhouse.com/sohforums/showthread.php?t=35447&p=402137&viewfull=1#post402137

There has also been a lot of discussion about "subsonic/supersonic" aircraft. It was allowed in the PacRim that an aircraft would be deemed OK if it could be tested and flown and unable to exceed Mach 1.00 in level flight.
Assuming that everyone complied with 'standard' test procedures for this - Wx set to "Clear skies", aircraft tested at multiple altitudes from Sea Level to near service ceiling, - we have done the tests on pilot's honour and allowed numerous aircraft that have not complied with the "old rule" of a .cfg file with a listed Mmo of "less than M 1.00 We have demonstrated reliably the principle that the Mmo (Max. Operating Mach Number) is just that.. an aerodynamic MAXIMUM, not what the aircraft can maintain in level flight. (ie. ' It won't go that fast unless you dive it and then prepare to get hurt if you exceed the Mmo'). Now, the next question is whether we trust each other to do the testing properly. I'm beginning to wonder if we do... but that is a different can of worms.

However, it must be remembered that "Mach" is a variable. The empirical test shows the speed of sound (Mach 1.0) is 661 Kts at Sea Level in International Standard Atmosphere (ISA = 29.92"Hg and 15*Celsius) or roughly equivalent to MSFS "Clear Skies"). The link I posted in the above thread is repeated here:
http://www.militaryfactory.com/aircraft/mach.asp
and I am sure you can find many more references and tables.

What is critical for us is that we don't fly in ISA - we use Real World Weather. Temperature varies, pressure varies, winds vary. No single Duenna data point will conclusively show what is happening. Duenna produces:

  • A max GS -but GS is dependent on winds vs airspeed - so it does not show pure AIRSPEED and only indicative of speed over the ground - not though the air.
  • A Max IAS - but that is a) transient moment-by-moment; b)affected by temp. , pressure, rate of climb/descent so it is not a measure of level flight speed either
  • Duenna does not show atmospheric data at each reporting point so there is no way to know what the IAS/Mach relationship is at any given moment.
Certainly, an acceptable (M 0.99 or less in level flight) aircraft might well exceed Mach 1 in a dive (which is allowed) but consider the mechanics of it... Most aircraft I have tested require a significant dive (in excess of 5000 ft/min) to exceed M 1.0 so even a dive from 35000 ft will not be of much advantage and besides, the Race speed is NOT calculated from a Mach number or IAS but from Distance /Time so a few minutes of 700 Kts IAS are not going to have an impact over a race of 20+ hours! Additionally, ALL of you can test the limits of the aircraft if you are willing to take the chance on any leg.

As for the "apparent excessive speeds" you may see in a Duenna snapshot, look at these screenshots (remembering that old bit about 661 Kts at Sea Level)

1. Test flight at Darwin descending from 5000 Ft in "Clear Wx" note the Mach # and IAS
2. Same test in Real World weather at Darwin...
3. AFSD showing atmospheric data moments after the previous picture - note temp and pressure values -NOT ISA to be sure!
4. In an effort to put this together quickly, the test pilots pushed the envelope. Photo shows nose gear damage from a "too high" extension speed on approach. Repair bills are being sent to the PacRim participants.

In summary, the whole issue of "transonic" flight is a lot more complex that a few numbers in a snapshot view - just ask the guys who supported aircraft like the X-1. No simple rule and no simple look at the MSFS flight envelope is going to give a perfect answer. For all practical purposes, and over the long term, as long as an aircraft can be shown to be incapable of reaching/maintaining/exceeding Mach 1.00 IN LEVEL FLIGHT IN ISA conditions, it should be good enough.

As for the odd, temporary anomaly, perhaps we should look at rules that require a 24-72 hour maintenance period (even better, a slow-speed ferry flight to a maintenance base) for any reported overspeed or exceeding a "G" limit in flight or on landing (real-world commercial aircraft have sensors in the gear to show the latter and it requires logbook entries and an inspection). Ya Think????
The Committee in this event wanted simplicity to satisfy a request from pilots. The mystery is then why pilots want to nitpick the application of those rules - which can only result in tougher, tighter, more complex rules to "fix" the perceived unfairness or misuse.
 
A Clarification or expansion of my earlier comments:
Duenna produces:

  • A max GS -but GS is dependent on winds vs airspeed - so it does not show pure AIRSPEED and only indicative of speed over the ground - not though the air.
  • A Max IAS - but that is a) transient moment-by-moment; b)affected by temp. , pressure, rate of climb/descent so it is not a measure of level flight speed either
  • Duenna does not show atmospheric data at each reporting point so there is no way to know what the IAS/Mach relationship is at any given moment.
Click to expand...
Groundspeed must be viewed in conjunction with the simultaneous wind and still is not part of a race standard or rule.
Duenna does show interval data of IAS, but there is no relative Mach #shown. Even so, the issue is still "sustained" level flight at greater than M 0.99. The sustained speed would show up if prolonged, but to calculate the Mach # you would need the actual atmospheric data for the same period of time.
In addition, a wind shift can increase/decrease IAS on a transient basis but again it is not a 'sustained level flight' event. As the Mach number is a relationship between the object and the air around it, if the motion of the air changes, so will the Mach # and approximately so will the IAS. Instruments like an airspeed indicator have errors (hence the development of Calibrated Instrument AirSpeed obtained by test instrumentation and then calculated) and a small, but effective degree of lag as the instrument reacts to change in the airmass.

In the absence of an observer with tracking equipment and/or in a place to hear the not-modeled 'sonic boom' there is no empirical way in Flight Sim to state that an aircraft has reached and exceeded Mach 1 from the data currently available in the Duenna report. Could it be included? perhaps, but then it is one more factor to be regularly evaluated and checked during an event. Then we have to ask "what is the borderline between transient and sustained?"

Besides, other than to comply with an arbitrary rule that may not impact the event, who cares if it is a transient event?

Rob
 
The MAX speed of the A-4C (according to http://a4skyhawk.org/2c/techdata.htm) is A-4C/L = 649 MPH, which converts to '649 mile/hour (mph) = 0.852 593 258 69 mach', a FAR cry from M.98. (an example of one of this years participants) Can you post evidence that +/- 10 C. would effect the reported airspeed by M.13 ?

I know it's all relative as the rules said nothing about a model being an accurate representation of reality, it just has to be subsonic.

I DO enjoy our sparring, but ultimately I will bow to your expertise in aeronautical engineering and gift of gab (as usual).
 
that is a great website it confirms the FS Aircraft is modeled fairly close to the real world plane.

Maximum Level Speed (mph)
A-4A = 664
A-4B = 661
A-4C/L = 649
A-4E/F/M = 673
TA-4F = 675
A4D-1 BuNo 137820, LT Gordon Gray USN - 500 kilometer closed course world speed record 695.163 MPH, 15OCT1955, Edwards Air Force Base.

The Skyhawk can exceed the speed of sound in a dive, but it is not a recommended activity.

A Skyhawk's roll rate is 720 degrees per second with a limitation of 2 rolls before the front and back of the airplane switch positions uncontrollably do to a dynamic called "roll coupling".
Click to expand...
I say that because it is likely that the safe operating speed is 649 mph (assuming sea level) This safe operating speed in the real world will not be Full throttle.

It is very possible that pushing the throttle full forward will yield a .98 mach number or certainly a whole lot faster than .85.

This is ultimately a race so I expect that everyone one is running with the Throttle full forward.

If we look at cruise speed numbers for all of these aircraft that are being flown we will find non of us are with in the allowed real world numbers.
 
MaddogK said:
Where does it say 'safe' ?
Click to expand...

It doesn't its open to interpretation

The number is published as the "Maximum Level Speed" but they don't list a V-speed with it so its hard to tell just what they mean by Maximum Level Speed.

It could be VH or it could be VNo

If its Vno that should mean there is Vh above it followed by a Vne followed by splat.

But for the purposes of Flight Simulator Vh does not exists in was never built into the sim. If it would have been then a lot of things would have been easier.

The fact still is you are going to reach that Maximum Level Speed V(whatever) well short of full throttle.
 
In the end Flight Simulator is flawed dig deep enough and not a model made is accurate.

One of the things we have to ask ourselves is how do we know the information published on a site is accurate. Where did they get it. There are no sources listed.

Maximum speed 685 mph ( 595.24 knot) is this Vh, Vne, or Vmo?
Cruising speed 540 mph (469.24 knot) Assuming Vno?
Range 1,200 miles (1,042.77 nm)

Those numbers are a far cry off of your model. Either they are wrong or your aircraft is poorly modeled.

Aircraft-Reference: Vne=670KIAS, Vcruise=450KTAS, Mmo=M1.000
Autopilot/Autothrottle: 1 / 1
Max./Avg. Groundspeed: 595.0 kts / 549.5 kts
Max. IAS: 477.7 kts
Average IAS: 372.9 kts
Average Head/Tailwind: +3.4 kts

Summary:
Direct distance: 1108.2 nm
Flight time: 02:00:40
Baton time: 02:00:41
Average GS: 549.5 kts
Valid: VALIDATEDLooks like you exceeded the distance that your aircraft is listed to be able to fly. It must have a poorly modeled fuel burn.

Looks like you exceeded your Vno by about 88 kts if we adjust for tail wind.

This model falls into the class of most others.

Close we might say .13 close.

I suggest the next race we all fly the same poorly modeled aircraft.

Sound good.:kilroy:
 
Dangerousdave26 said:
They are the F-86 could exceed M1.0 in a dive.

That information came from fliger747 in the forums shortly after the sectionF8 model was released.
Click to expand...

Seems someones A-4 broke the sound barrier in level flight when the wind shifted- supposedly only achievable in a dive, a steep dive i remember someone saying.

So how does one travel 1400 miles (of the MAX documented 1800 nm range) on less than 50% of the max fuel the A/C has been documented to be able to carry, and call it 'reasonably close to' realistic ?
Summary:
Direct distance: 1108.2 nm
Flight time: 02:00:40
Baton time: 02:00:41
Average GS: 549.5 kts
Valid: VALIDATEDLooks like you exceeded the distance that your aircraft is listed to be able to fly. It must have a poorly modeled fuel burn.
Click to expand...

Yes, I had less than 10% of my fuel capacity left in the tanks when I landed, I also have a nice chart of the 'dead engine' glide distances expected- like to see the 100 mile expected range from 30k on the chart ?
 
All I know is that the T-33 Max Mach is 0.92. The fastest I've gotten it to go is about 0.83 in a 3000fpm dive for the airport.
 
If anyone thinks that the numbers in the .CFG file or in the a/c data and docs are a relevant measure, have a beer on me.. have several... and when you sober up spend some time reading these:
http://en.wikipedia.org/wiki/Critical_Mach_number
http://adg.stanford.edu/aa241/structures/placard.html
http://www.airliners.net/aviation-forums/tech_ops/read.main/261450/

then, using the A4D only as an example:
The Skyhawk has a remarkably low gross weight of 18,311 pounds but can deliver a weapons load of 2,040 pounds at a mission radius of 680 miles with two 300-gallon external tanks; unrefueled ferry range is 2130 miles. Maximum speed of the aircraft is 673 miles per hour (Mach 0.88) at sea level, and cruising speed is 498 miles per hour. Ceiling is just over 40 000 feet.
http://www.globalsecurity.org/military/systems/aircraft/a-4.htm
but if you go to the same source, another page...


Maximum speed: 586 knots (with a 4,000 pound bomb load)
and further down the same page...
Max level speed 561 knots
and further...
Max Speed: 660.00 Mph 1062.00 Km/H 574.05 Kthttp://www.globalsecurity.org/military/systems/aircraft/a-4-specs.htm

So, what applies to what? and then look at another site and see if you can find a comparison.

Of all the above values, which definition of Maximum speed is used for each? Did the posted data come from test flying or some PR (PRopaganda) flack trying to get a gov't contract?

Then consider whether the modeler did even that much research, and had the skill to stuff it all into the FDE, or were they trying to jam out a model to meet a release date, and did they know what all the numbers mean, or even care. Some do care very much, but look around the forums and see how many people tweak FDEs (worse, just the .cfg) and have no knowledge of actual performance, or only care that it can be flown by a newbie or think they can sneak in an advantage and you'll see why I'm a skeptic.

After all, there's marketing to consider... would you want a model that was slower than the best numbers you could find on the net, or in a comic book?

Then start to wonder how the model was tested. Then how much it was fiddled to hit the best numbers.

Now try to tell me that any of it is credible enough to use as a set of benchmarks when comparing two different aircraft from two different modelers. If you convince me, I'll give you a job selling the various bridges in my inventory.

Remember that, in the PacRim event the only criteria are that: a) the aircraft cannot sustain Mach 1.0 or greater in level flight, and b) that it be an unmodified model from a reputable source.

So what's the debate? That his Corvette is faster than your Mustang? Gee.. it must be running nitrous or tricked up somehow. Consider that one of the common features of most FS races is a long stint at full-power straight and level flight (unrealistic) with models that are almost all capable of max speed at max range at max altitude and you'll understand why it sounds to me like a bunch of kids at recess trying to win a debate about whether a Ferrari is better than a Hummer. - or has it become "mine is longer than yours...". Consider that 90% of the legs flown only require a pilot present for 1/6 of the time (takeoff, climb, descent, landing and a few minutes of navigation in between) and if you can choose big airports with an ILS it's not all that difficult. So the only real skill is in finding a model that is fastest in a straight line that doesn't explode enroute.

Factor in one last bit... that there is a growing tendency among racers to intimate or outright accuse people (even teammates) of fudging/cheating and (heaven forbid...) winning and you'll understand why I'm walking away from the game. The debates are inconclusive. The tone is childish. The fun is gone.

I have one commitment and that's the RTWR, where people tolerate/accept a level of inaccuracy in the spirit of competition and it's balanced by the requirement for variety to challenge and balance out the differences. It's not perfect but it's only once a year...
For the rest, the bickering about no rules, rules, too many rules, accuracy (as long as it's mine...no one believes anyone else) vs the joy of flying interesting planes, the long legs with nothing to do but read forum posts whining about 'the other guy'....

So long, and thanks for all the fish...
 
OK, in the interests of stopping this silly argument before it flames out of control and someone says something they can't take back, I hereby withdraw my A-4 Skyhawk based on the facts presented that the publisher failed to match verbatim the published real-world performance specifications.

MD, you can now take up a crusade against the next fastest aircraft that's not "by the book" exact in performance.

I'll fly on with you Dave for my own kicks and tally my numbers for my own curiosity.

Willy, PRB or Moses can you please lock my race thread so there's no flare-up over there.

Race on gentlemen. :salute:

John
 
jkcook28 said:
OK, in the interests of stopping this silly argument before it flames out of control and someone says something they can't take back, I hereby withdraw my A-4 Skyhawk based on the facts presented that the publisher failed to match verbatim the published real-world performance specifications.

MD, you can now take up a crusade against the next fastest aircraft that's not "by the book" exact in performance.

I'll fly on with you Dave for my own kicks and tally my numbers for my own curiosity.

Willy, PRB or Moses can you please lock my race thread so there's no flare-up over there.

Race on gentlemen. :salute:

John
Click to expand...
NO, NO, NO, you don't withdraw !

I will withdraw since my A/C is so poorly modeled, and my posts aren't quite correct. I was just having some fun here. YOU have shown quite a bit of restraint in this matter and I applaud you for it. There's NOTHING in the rules that keep your A/C from competition, so press on.

I'll drop out, since I have to start over anyway.
 
Factor in one last bit... that there is a growing tendency among racers to intimate or outright accuse people (even teammates) of fudging/cheating and (heaven forbid...) winning and you'll understand why I'm walking away from the game. The debates are inconclusive. The tone is childish. The fun is gone.
Click to expand...
BINGO chief, Intimidation and a little fun was the point of this discussion, it was taking a nasty turn so I walked away officially.
 
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