TAS/GS weirdness
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I've done one more round of testing and have have achieved a good balance of 75% power cruise TAS , climb performance, airspeed buildup in the descent, and service ceiling. They are as close to book at I can get for now.
In flight_model.config
parasite_drag_scalar =0.8
induced_drag_scalar =1.88In engines.config
fuel_flow_scalar =0.73
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@j225 said in TAS/GS weirdness:
Thanks for these tweaks. I noticed similar discrepancies with Little Navmap.
On the 25/25 rule, not everyone agrees.
Agreed. I think that 25X25 is specified in my POH (for a '67 Arrow, not a III like this model, but pretty close in most aspects and both have 4 cylinder IO-360s engines) for climbs, but I get your point. Get a bunch of pilots together on a non-flying day, add a few adult beverages, and mention either lean-of-peak operations or he "right" combination of MP & RPM for a given engine, and watch the fur fly ;) I think the conversation you referenced managed to work both topics into the conversation!
I've put 1850 hours on my engine since rebuild and compressions are still good, so I'll stick with what got me this far. Fingers crossed and hoping to get to 2000 hours on this engine. The nice thing with a sim is you can do whatever you like and you wont have to pull out your wallet and pay for a top end overhaul or rebuild.
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I've done one more round of testing and have have achieved a good balance of 75% power cruise TAS , climb performance, airspeed buildup in the descent, and service ceiling. They are as close to book at I can get for now.
In flight_model.config
parasite_drag_scalar =0.8
induced_drag_scalar =1.88In engines.config
fuel_flow_scalar =0.73
@BernieV , Thanks for doing this research, and the recommended settings for achieving more realistic performance. For reference, the Parasitic Drag of any aircraft (parasite_drag_scaler) affects both the cruise speed and climb performance, while the Induced Drag (induced_drag_scaler) affects mainly the climb performance. The speed and climb performance are both determined by the ratio of Total Thrust vs. Total Drag of the aircraft...
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Just to confirm, the ASI inaccuracy issue is now fixed and our flight dynamics creator is continuing their work on power/TAS performance.
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@BernieV , Thanks for doing this research, and the recommended settings for achieving more realistic performance. For reference, the Parasitic Drag of any aircraft (parasite_drag_scaler) affects both the cruise speed and climb performance, while the Induced Drag (induced_drag_scaler) affects mainly the climb performance. The speed and climb performance are both determined by the ratio of Total Thrust vs. Total Drag of the aircraft...
@RetiredMan93231 You are welcome RetiredMan. In practice, the induced drag scalar was the parameter that tuned rate of climb, the "slipperiness in the descent" (not a book value, but one I know from experience), and service ceiling. The final values posted gave me 137 kts level cruise at 75% power at 6500 ft (FT, 12 g/h, 2500 rpm as per book), an increase in TAS of 10 kts in a 500 ft descent at 75% power out of 6500 ft (from experience I expect 15 kts pickup, but I didn't want to detune ceiling or rate of climb for this subjective performance metric), and a service ceiling of 15000 ft (book).
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@RetiredMan93231 You are welcome RetiredMan. In practice, the induced drag scalar was the parameter that tuned rate of climb, the "slipperiness in the descent" (not a book value, but one I know from experience), and service ceiling. The final values posted gave me 137 kts level cruise at 75% power at 6500 ft (FT, 12 g/h, 2500 rpm as per book), an increase in TAS of 10 kts in a 500 ft descent at 75% power out of 6500 ft (from experience I expect 15 kts pickup, but I didn't want to detune ceiling or rate of climb for this subjective performance metric), and a service ceiling of 15000 ft (book).
@BernieV , In the real world Arrow III what is the expected RPM / power level on final at 75 knots with full flaps? It seems to me that the landing gear drag and the flaps drag are both currently a little too high, requiring too much power (RPM) to maintain the glideslope on final. What are your thoughts?
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@BernieV , In the real world Arrow III what is the expected RPM / power level on final at 75 knots with full flaps? It seems to me that the landing gear drag and the flaps drag are both currently a little too high, requiring too much power (RPM) to maintain the glideslope on final. What are your thoughts?
@RetiredMan93231 Between 15 and 17 inches of MP, prop level full forward, mixture full rich (unless operating at high elevations)
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@set3times No problem. The last (3rd) notch of flaps is almost all drag. In real life, I delay using it until I am sure I'd make the airport if I lost power or unless I was high/fast on the approach and need to get down or slow down.
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@BernieV Just tested your settings and it feels SO much better now :) Thank you for your research, I can only imagine how much effort that is.
Let's see what JF brings in a future update, but until then I'll be using your setup! The EGT is a bit odd but I'll go with the fuel flow gauge, as you said. That works fine.
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I have tested those values but I have an excessive RoC at around 1300fpm at 90knots at 2200lbs. (sea level)
EDIT: I just noticed I had a rapid headwind increase during initial climb-out, so disregard last transmission, will test in calm conditions ;)
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I've found a work around if not the root cause of slower than expected TAS and lower than expected fuel flow. Basically the aircraft was unable to generate 75% power at altitude of 6-7000 ft due to inadequate fuel flow.
In engines.cfg, fuel_flow_scalar was set to .51. Through trial and error, I found this decreases max fuel rate obtainable by varying the mixture control as altitude increases. So much so that I could not get the 15 or 16 g/h I would expect in a full rich climb nor the 12.1 g/h required for 75% power at altitudes between 5 and 7,000 ft.
I set the fuel flow scalar to 1 and was see very high fuel flow rates (22+ gph) which is way to high. I suspect that's why the engine tuner set the scalar so low. Too low IMHO. I increased it to 0.73; the point were I could get 15ish g/h at 7000 feet full rich. leaning to 12 gph improved the TAS, but it was still too low 133ish.
Next through trial and error, I settled on parasite_drag_scalar set to 0.825. This allowed me to get book speeds at 6 or 7000 feet.
The airspeed indicator is still off, but this IMHO goes a long way towards allowing the modeled Arrow III to perform closer to real life.
Summary of changes:
In flight_model.cfg
parasite_drag_scalar =0.825
In engines.cfg
fuel_flow_scalar =0.73
Inflight stats with the new settings
And yes, I did update the related support tickets as well :)
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Tested in calm conditions with the values mentioned by BernieV but I find the RoC way too high (above 1200fpm) with full throttle and full prop (these are the values used in the performance manual reference, they might not be used in reality but that's the only reference we have).
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Tested in calm conditions with the values mentioned by BernieV but I find the RoC way too high (above 1200fpm) with full throttle and full prop (these are the values used in the performance manual reference, they might not be used in reality but that's the only reference we have).
@set3times Are you testing at full gross weight (2750 lbs)? I suspect not.
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Just a quick question before I open a ticket, maybe someone can confirm this issue since the situation is basically impossible with the stock performance anyway:
When flying straight leveled with autopilot HDG and ALT HOLD on, say at 5000ft with full throttle and rpm, once reaching the yellow range of the IAS scale, my aircraft starts to jitter up and down with a very small deflection and high frequency.
From the cockpit you can see this by the sun visors rattling and from the external view you can see the whole aircraft jitter/rattle with very tiny deflection and high frequency.It is almost like it's an overspeed indication but the way it looks it's more like a glitch.
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I have also noticed this "buffeting" behavior when the flaps are down... I think JF should look into it, so please open a ticket.
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@set3times Are you testing at full gross weight (2750 lbs)? I suspect not.
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Tested the performance without any modifications now with 0.3.0, I get a TAS close to book numbers.
Still the TAS scale seems to be off (showing 5kts less than real TAS for me) and now the altitude scale is set in a way that one cannot dial lower altitudes to the correct temperature since the scale starts with 0ft at the far left and cannot be dialed to the right.
Nevertheless, first impression of the performance now looks better to me. Climb performance was also realistic from what I can check on the charts.We're getting there :)
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Tested the performance without any modifications now with 0.3.0, I get a TAS close to book numbers.
Still the TAS scale seems to be off (showing 5kts less than real TAS for me) and now the altitude scale is set in a way that one cannot dial lower altitudes to the correct temperature since the scale starts with 0ft at the far left and cannot be dialed to the right.
Nevertheless, first impression of the performance now looks better to me. Climb performance was also realistic from what I can check on the charts.We're getting there :)
