Autorotation’s!

[BoneBoys]

Good on you!

[Sundowner]

The '369 feels a bit overpowered in the preview, anyone actually tried to test its performance to match with the right MD equivalent ? Maybe we should use data from flight manual for the Foxtrot Plus model ?

[b101_uk]

Here is some more info,

The height velocity diagram (height above ground vs. IAS speed) & the maximum gross weight limit diagram (for calculating the maximum gross weight vs. “effective” altitude above sea level that applies to the height velocity diagram).

the area that has no cross-hatching are altitude (AGL) and speed combinations (Kts IAS) that an “average pilot” should be able to carry out an autorotation at a density altitude corrected maximum permissible take-off weight.

FYI: the cross-hatched portion on the left side of the height velocity diagram is what is known as the “Dead man’s curve” also the deeper your to the left of the curve the harder any autorotation is going to be.

Also it’s a bit hard to see, but the recommended take-off profile line continues up the 60kts IAS vector to ~295ft AGL.

http://myweb.tiscali.co.uk/toddysspace/page_5-20.gif > 100kb

http://myweb.tiscali.co.uk/toddysspace/page_5-21.gif > 100kb

http://myweb.tiscali.co.uk/toddysspace/page_5-22.gif > 100kb

[[DirTyDeeDs]-Ziggy-]

thanks for the charts oO

[b101_uk]

there are some surprises if you compare in-game to what you would expect from a MD500D with a ALLISON 250−C20B using the rotorcraft flight manual data which show that things are going in the right direction with what BIS are doing.

e.g.
in game, if you load the helicopter with full fuel and have 4 people (euroman 1 & 2 + TKON pilot etc) in it then climb to the maximum altitude it will hover out of ground effect at 9600ft MSL using pressure altitude, if you repeat the test with just the pilot and full fuel you yield 16900ft MSL with the rotor at the normal RPM. (Remember ~9600ft & ~16900ft MSL)

If I then take the official real world minimum flying weight of 1538lb, add the real world ~402lb of fuel for a full tank we get 1940lb excluding pilot/passengers, if we approximate a pilot or passenger as being ~180lb each we get a gross weight of ~2120lb with just a pilot and with a full complement of passenger we get ~2660lb gross weight. (Remember ~2120lb & ~2660lb gross weight)

Now if I get out my chart that plots a “standard atmosphere” in temperature vs. pressure altitude (also density altitude but on a standard atmospherics day pressure & density altitude are the same) and look up the temperature for ~9600ft & ~16900ft MSL I get -4°C & -19°C, now if I look up “HOVER CEILING − OUT OF GROUND EFFECT (OGE)” for the ALLISON 250−C20B powered MD500D, and look specifically for the maximum gross weight for hovering at a pressure altitude vs. temperature given on a standard atmospherics day and compare ~9600ft with -4°C I get a maximum gross weight given of ~2700lb which is extremely close to the ~2660lb achieved, if we take ~16900ft & -19°C we get ~2150lb gross weight, so it shows that even though I don’t know the exact weight BIS assign to pilot/passenger weight or the exact figure they use for fuel or the helicopters zero fuel weight one can only surmise they are close to the real world ones and using a standard atmospheric day.

[CarlGustaffa]

Don't forget at Takistan the indicated altitude is wrong, as it neglects the island altitude offset in the config. Everything deriving from that also gets wrong, like temperatures (not ISA anymore) and actual air pressure, giving us way better performance than we should get. Altimeter reads 0 feet when it should have read 6562 feet (2000 meters).

Now, for Seattle and East Asia this may not matter, if the area don't use this offset. But if we have this flight model also for Arma3, I think it becomes important if we get the OA islands converted to A3.

[b101_uk]

The actual ground altitude for “Takistan” being incorrect for the place it is mimicking is of NO relevance what so ever to the tests I did as I am using pressure altitude and then verifying it with radio altimeter, so as it is its just mimicking a place <>1000ft MSL though I have mostly been using the A2 islands. (good old symbolic folder link)

Takistan like all the other A2/A2OA islands/maps when set to the same date, time and good weather condition will all yield the same results ~70% of the time with minor deviation in the remaining 30%, it would be rather pointless to test using bad weather and unsettled conditions as there would be far to many random factors at work perturbing things,

Typically May 1st 2011 at 8am was used, as well as Aug 1st 2011 at 10am, the assent time for 9600ft was 15min to 16min with the last 1000ft being very slow in the order of 5mins, with the A2 island they both have sea so both the radio altimeter and pressure altimeter should read the exact same value when over the sea, with A2OA maps there is no sea but the borders around the main map are quite uniform or if you can stay above your take-off location you know the pressure altitude at take-off so e.g. 9600ft could be verified by adding your e.g. 1000ft MSL take-off height to the radio altimeter AGL value which then should total 9600ft as per the pressure altitude reading.

If you play around with the weather settings etc. without going to the extents of rain/storms etc you can seemingly perturb density altitude outside of a “standard atmosphere” causing +-500ft or more changes to e.g. 10100ft or 9100ft before lift/power runs out depending on the trend of the weather change.

[b101_uk]

The '369 feels a bit overpowered in the preview, anyone actually tried to test its performance to match with the right MD equivalent ? Maybe we should use data from flight manual for the Foxtrot Plus model ?

I feel you could be right, though it’s appearing as excess initial climb both in a hover and at 60kts, with respect to gross weight #1 vs. power vs. altitude it’s actually hitting the right values with respect to 9600ft maximum altitude for hovering out of ground effect performance on a ISA day if its mimicking being fitted with an ALLISON 250−C20B, if it’s supposed to be a ALLISON 250−C20R/2 power plant it is somewhat short of the expected 13200ft on an ISA day (#1 @ ~2650lb gross weight).

If we take the expected torque gauge reading for a power setting and the relating TOT gauge temperatures and rotor (NR) and N2 gauge RPM’s/% for real life & in game we should expect the following.

MD500D with ALLISON 250−C20B power plant (420SHP, 375SHP take-off, >350/320SHP continuous):

• Maximum take-off (5 minutes): 87.2 psi torque with a TOT of <810°C (~375SHP)

• Maximum continuous with TOT at or below <738°C: 81.3 psi (~350SHP)

• Maximum continuous with TOT above >738°C: 74.3 psi (~320SHP)

Transient torque:

• 87.3 to 93.0psi torque for 15 seconds at 103 present N2, if TOT >810°C to <843°C then 6 seconds.

• 93.1 to 97.6psi torque for 3 seconds at 103 present N2, if TOT <810°C.

MD500D with ALLISON 250−C20R/2 power plant (450SHP, 375SHP take-off, 350SHP continuous):

• Maximum take-off (5 minutes): 87.2 psi torque with a TOT of <810°C (~375SHP)

• Maximum continuous with TOT at or below <752°C: 81.3 psi (~350SHP)

Transient torque:

• 87.3 to 93.0 psi torque for 15 seconds at 103 present N2, if TOT >810°C to <843°C then 6 seconds.

• 93.1 to 97.6 psi torque for 3 seconds at 103 present N2, if TOT <810°C.

In game light helicopter AKA:MD500D:
Maximum torque reading ~70psi with ~103% N2 & NR and TOT of ~750°C (low alt)
Maximum torque reading ~50psi with ~103% N2 & NR (maximum alt)
Maximum TOT = just under <810°C but that’s with N1, N2 and thus NR at >90% rather than ~103%.

Possibility 1:
If we perhaps assume the torque gauge is under reading ~27.6psi so ~70psi indicated is really 97.6psi it would follow that if you reduced the ~70psi torque reading by dividing it by 1.1192 (97.6psi / 87.2psi = 1.1192) to ~62psi that would equate to Maximum take-off power (87.2psi), if you then reduced the 70psi reading still further by dividing it by 1.2005 (97.6psi / 81.3psi = 1.2005) to ~58psi that would equate to Maximum continuous power (81.3psi) etc, which gives a more “weighty” less powerful feel but is still does not feel quite right even though if you divide one power rating agenised another it would seem to agree the dividing factors above, e.g.

• 420shp / 420shp = 1 vs. 97.6psi / 97.6psi = 1 (~70psi)

• 420shp / 375shp = 1.12 vs. 97.6psi / 87.2psi = ~1.1192 (~62.54psi - Maximum take-off power)

• 420shp / 350shp = 1.2 vs. 97.6psi / 81.3psi = ~1.2005 (~58.31psi - Maximum continuous power)

• 420shp / 320shp = 1.3125 vs. 97.6psi / 74.3 = ~1.3135 (~53.29psi - Maximum continuous power >738C)

The only problem with the above range of values in-game is the drop between 70psi & 50psi between low and maximum altitude just does not fit any dividing value and is too large to be accounted for with power change or a constant ~375shp.

Possibility 2:
However if we infer any validity of the altitude tests I did for “altitude for hovering out of ground effect @ ~2660lb” for a ALLISON 250−C20B and remember that in real life this is taken at Maximum take-off power @ 87.2psi with N2 @ >102% <103%, N1 @ >102% <103% and NR @ >102% (487rpm) <103% (492rpm), then if we look at the only in-game torque gauge condition that the above other conditions will take place wile the torque gauges remains at a constant possible reading then that is with the in-game torque gauge reading 50psi from 0ft threw to 9600ft MSL, which also gives a fair assimilation of climb rate in hover being less than the climb rate @ 60kts IAS and that the @ 60kts IAS initial climb equals about ~1900ft/min from just above sea level (at ~2200lb).

Also with an in game torque gauge reading of 50psi in the above there is NO more power thus torque available ~9600ft (@ ~2660lb) so trying to increase the collective only reduces N1, N2 & NR beneath <103% to ~90% - the SHP reserve above >375SHP to <420SHP is to ensure that e,g. you still have just about ~375SHP available at a given max altitude at a given weight.

So if we take ~50psi in-game as being the 87.2psi Maximum take-off power thus being 375SHP then the following would be expected:

• ~55.96psi would = 97.6psi (87.2psi / 97.6psi = ~0.8934 thus 50psi / ~0.8934 = 55.96psi)

• ~50psi would = 87.2psi

• ~46.61psi would = 81.3psi (87.2psi / 81.3psi = ~1.0725 thus 50psi / ~1.0725 = ~46.61psi)

• ~42.6psi would = 74.3psi (87.2psi / 74.3psi = ~1.1736 thus 50psi / ~1.1736 = ~42.6psi)

How do the above values around 50psi stack up relating to “power”:

• 375shp / 420shp = 0.8928571428571429 so that would make 56psi

• 375shp / 375shp = 1 thus 50psi

• 375shp / 350shp = 1.071428571428571 so that would make 46.66psi

• 375shp / 320shp = 1.171875 so that would make 42.66psi

The only problem with this range of values in-game is the massive possible rise between 50psi & 70psi


Now, if you have read this far well done and if you have understood the above even if it’s just enough to see that out of possibility’s 1 & 2 there is some maths that stacks up for both, however BOTH fall down on one fundamental problem which is why in the game dose peek torque at low altitude peek at 70psi and at maximum altitude 50psi giving a devisor of 1.4 or ~0.7142 dependent on how you wish to divide 70psi vs. 50psi & given the real life 420shp & 375shp relationship?

if we start by acknowledging

• There is an under reading of torque by ~27.6psi if we take the gauge at face value when showing 70psi.

• If we don’t take the gauge at face value but assume ~62.54psi or ~50psi are 87.2psi Maximum take-off power then the gauge is under reading by between 24.66psi (/1.3943) and 37.2psi (/1.744) respectively.

• Simply dividing the in game torque gauge readings between its respective low altitude 70psi maximum value and it maximum altitude 50psi yields a 20psi error (/1.4)

• With the engine on and collective fully down when on the ground there ~12psi of torque registering on the gauge, if the gauge is under reading by ~27.6psi when showing 70psi how much is it under reading when its showing ~12psi of torque just sitting on the ground with the collective down?

• If the in-game torque gauge is reading a residual ~12psi when on the ground with the collective fully down then it’s quite possible we would expect Maximum take-off power to be ~12psi lower than it should be on the current <70psi gauge display range i.e. to happen at ~50psi rather than an expected ~62psi.

If we take the latter two statements pertaining to the residual ~12psi of torque and apply it to possibility 1 & 2 we get some logical consequence which solves the problem with each, which would be, if ~50psi currently in game best represents real life Maximum take-off power then it would follow that ~62psi would be the proper value in the current game if it was not for the residual ~12psi when on the ground with the collective fully down (50psi + 12psi = 62psi), if the residual ~12psi of torque was removed then then during hovering out of ground effect 9600ft @ ~2660lb instead of the torque gauge dropping to 50psi it would only drop to 62psi to represent Maximum take-off power, therefor confirming possibility 1 & 2 and how they apply to each other currently in game.

So in short:
If you want to fly the light helicopter in a realistic manner with respect to climb performance and power given the current misreading of the in-game torque gauge and excess power then you should stick to the following torque gauge readings (until such time as BIS fix the torque gauge readings to reflect what’s happening on a proper number scale and perhaps fix some fudged values relating to torque).

• ~55.96psi would be Maximum Transient torque @ 97.6psi (~420shp)

• ~50psi would be Maximum take-off (5 minutes) @ 87.2psi (~375shp)

• ~46.61psi would be Maximum continuous <738°C TOT @ 81.3psi (~350shp)

• ~42.6psi would be Maximum continuous >738°C TOT @ 74.3psi (~320shp)

If you are from BIS and are reading this then you need to look into/take note of:

• The torque gauge and correct its range of movement.

• The relationship of the TOT to other values.

• The amount of residual torque with the collective in the fully down position and controls centred (~12psi).

• How any residual torque and application of collective could conspire together to give too much effective lift by e.g. being additive (+12psi) or subtractive (-12psi) etc. (could also explain why the light helicopter is so light on the ground with zero collective)

• The intrinsic relationship between 375shp & 420shp being the same distance apart as 87.2psi & 97.6psi are to each other, which are both smaller relative gaps than the current 70psi & 50psi gauge relationship.

• To perhaps add the NR needle above the N2 needle (which is currently acting as NR) so the combined N2/NR gauge works correctly instead of inferring N2 from NR when the engine is running.

• To perhaps implement a “overrun clutch” in the physics flight modal so that when the throttle is closed/cut-off in flight (or you lose the engine – fault/failure/etc.) that the “engine” correctly disconnects from the main rotor so NR remains in the normal range during autorotation while the N1 & N2 fall to their correct value being ~65% rpm at idle or 0rpm for cut-off, as its currently implemented there is no “clutch” modelled so N1 and thus N2 are slaved to the rotor RPM (over-run clutch are fitted to MD500 to disconnect the rotor from the engine etc during shutdown and autorotation – the turbine slows at a faster rate than the rotor)

• And relating to the above overrun clutch point, hypothetically if you have gone as far as programing a “drag factor” for how quickly the turbine (engine) wants to spin down, then without a “theoretical” overrun clutch during e.g. autorotation the factor of drag from the turbine would be trying to slow the rotor causing the deficiency in rotor RPM we see in-game during autorotation? (relative to weight/ speed/etc)

[Sundowner]

Those are exactly the problems I faced trying to figure that helicopter out, unfortunately I didn't had enough time for longer tests, especially when there is no real point of reference, as half of the gauges in cockpit don't work as they should.

Changes with controllers setup, gave us ability to test the flight model (which I'm rather pleased, though still need some work), hopefully there will be something done with the gauges, and controllers (analog throttle anyone?).

I haven't spend too much time practicing autos though. When the gauges work wrong, and the flight modeling still needs improvement, I don't see the point really. Until some things will be remodeled (like the clutch you pointed out) - autorotations will feel wrong.

And the skid grip - I noticed that too doing rolling take offs and landings - for some reason with no power, and no forward speed - it will slide to sides, but take some tension off the skids and give it some forward or aft speed and it will dig into concrete like a boat anchor.

[b101_uk]

And the skid grip - I noticed that too doing rolling take offs and landings - for some reason with no power, and no forward speed - it will slide to sides, but take some tension off the skids and give it some forward or aft speed and it will dig into concrete like a boat anchor.

I have lost count of the amount of times the helicopter has nosed over when landing from autorotation’s

it definitely feels related to how the skid/ground interaction is working, it’s almost as if the collision model of the skid at the front instead of being described as a nicely radiused bend upwards in the skid tube made out of many facets (we are talking triangles and polygons) that its literally being described by a single facet at >45deg <90deg to the horizontal, thus as soon as the nose of skid is presented to the ground slightly nose down aspect you get the sharp effective edge between the horizontal facet and the >45<90deg facet digging in/giving higher resistance thus causing the nose over, and that’s without mentioning the effect of making the skid effectively shorter vs. the CoG.

You can see the above problem if you switch to the 3rd person view with the helicopter on the ground, position the view so you can clearly see the nose of the skids, start it up, push the cyclic fully forward, then apply a slight collective to initiate slowly nosing over, if you look at how the collision modal interacts with the ground it clearly is NOT curved up as per the visual modal as the nose of the skid disappears under the ground almost as if there is NO upturn to the nose of the skid.

part of thes skid problem: