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Guest BeaverDriver

Speed & Temp Issues

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Guest BeaverDriver

OK, this seems to be the one big topic of discussion for the Caravan. Rather than having several threads that more-or-less discuss the same issues, I'm wondering if we can concentrate all the discussions, fixes and tweaks to this one thread? If that's ok with all, then let me get things started now.I flew the bird tonight doing some test runs. I'm pretty much seeing what you folks are seeing, naturally. My results were:Gross Weight: 8754 lbsPressure Altitude: 4,000 ft (give or take a couple of hundred)Air Temperature: 13*CMy first run ignored the temperature, with a TRQ of 1700 and Prop at 1900: KTAS was 137 kts (remember, that's true airspeed) - I had a ITT 760*CSecond run was taking the temp into account, setting it at 740C, prop still at 1900: TRQ=1500, KTAS was 133 ktsAccording to "The Book" (which I downloaded - thanks Yoda/Ken), I should see 166 KTAS, so this is a LOT slow. HOWEVER, I have a Just Planes DVD with the Caravan and from what I could tell of that, they were seeing roughly 138 to 143 kts. Now, that's calibrated, and it's ground speed, but from looking at the water below (which I'm very accustomed/experienced to doing and judging since I flew floats in the bush for a living for a bunch of years), there wasn't a lot of wind. Maybe 5 to 10 kts at most. So even if this was a headwind, they wouldn't have been doing anymore than 150 max, and I suspect it was more a crosswind than anything. So, while I know what the book says, I'm not sure we are as far out as we might think for a RW situation. I do think this plane is a bit slow, and I think the engine temps are off the mark by some degree, but maybe it's not as bad as we perceive.I've ordered another video which will give me a lot more info on this, under RW conditions. I think we need to pick this bird up a bit, but I don't think we should get too carried away just yet. I should have the video within a week to 10 days, and I can report back more definitively at that time. I'm always a bit cautious sticking too closely to the book values, as I've very, very rarely ever seen an airplane come all that close to them.I will say that this is my only complaint to date about the airplane. I think its overall flight dynamics and handling are right on, so I'm very impressed by that. Sounds, while a bit disjointed in places, are very good to excellent. This may end up being a very small tweak, and yet it may be that for a RW airplane, this is actually right on the money. We'll know soon.OK, the floor is yours for comments/discussions/fixes/tweaks/phone numbers of loose women whose standards aren't very high Big%20Grin.gif

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Sorry Glen, I already posted in the old one...I agree with you with the fact that charts are "ideal" or "theoretical, but they should be correct within a small percentage of error. Imagine if the TORR reported in the manual is too short! :) If I read 160 KTS, I expect to be "around" that value, say between 150/55 and 165. Anyway, if you want to try what I reported in the other thread, try setting parasite_drag at 0.8.Cheers

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Guest BeaverDriver
Sorry Glen, I already posted in the old one...I agree with you with the fact that charts are "ideal" or "theoretical, but they should be correct within a small percentage of error. Imagine if the TORR reported in the manual is too short! :) If I read 160 KTS, I expect to be "around" that value, say between 150/55 and 165. Anyway, if you want to try what I reported in the other thread, try setting parasite_drag at 0.8.Cheers
OK, thanks. I was thinking induced drag since that won't affect the effectivity of the flaps. However, parasite drag will help too. Much appreciated.

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Yes, but induced drag decreases with speed, so it would alter only the low speed flying making a worst performance on landing. We needed to increase the cruise speed, so I thought parasite drag was the way to go.As you mentioned flaps, don't you think it's a bit too litlle the ballooning effect? I see there's a little ballooning above 140 KTS when setting the first notch, the other two nothces increase only the drag (it seems). Do you think it's correct? Just wondering.Cheers

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One other speed issue I've noticed was during slow flight.With full flaps, the airplane runs out of trim at 68 KIAS (with default full fuel and passengers/cargo, 2500 feet MSL).In other words, when the autopilot altitude hold is engaged and I reduce power to lower speed, once I've lowered power to the point where I see 68 KIAS the autopilot has advanced the trim wheel fully forward (19.5 deg) and any further reduction in power means the airplane will lose altitude.Makes the last moments in IFR approaches difficult and seems wrong. The stock Caravan certainly doesn't have this behavior - the autopilot can hold altitude at much lower speeds before it runs out of trim.I don't believe that has anything to do with engine power. I suspect drag, but more testing will be required. For example, it could be all the gauge calibrations are way off, or she flies like she's 2,000 pounds too heavy. Could be a lot of things.You all may want to fool around with some slow flight to check the airplane's behavior at that stage of flight. It sure doesn't feel right, but I'm not a pilot, so I'm just basing this on the way other FSX aircraft perform.

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Gents,One of the problems I've been looking at is that the ITT goes so high that you can't set the torque properly.I do think parasite drag was set a bit too high, but also the turboprop engine power scalar was too low. There's a sweet spot to be found, where the torque limit can't be achieved, and the PIH gives us that...above 42oC at sea level. So, I'll diddle with the power scalar until I get it to the point where ITT goes over 805oC at sea level when takeoff power is set.Meantime, the ability to set torque values properly will help determine the drag scalar value.

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Guest BeaverDriver
Yes, but induced drag decreases with speed, so it would alter only the low speed flying making a worst performance on landing. We needed to increase the cruise speed, so I thought parasite drag was the way to go.As you mentioned flaps, don't you think it's a bit too litlle the ballooning effect? I see there's a little ballooning above 140 KTS when setting the first notch, the other two nothces increase only the drag (it seems). Do you think it's correct? Just wondering.Cheers
Agreed, but that's why I thought of tweaking the induced drag. There will be a greater effect on the amount of drag at cruise speeds due to the "drag increases as the square of the velocity" factor. So, at least to my warped thinking (:() I believe that changing the induced drag will have much more effect at cruise, while leaving the lower end values pretty much alone, and leaving the flap drag alone. That all said, I've not yet put that to the test, so we'll see.No, I don't see much ballooning as you noted. Logic says it likely should be greater, but without having actually flown the airplane I can't really say for sure. It's a question I'll ask one of the RW Caravan drivers next time I see them (if I can remember). I probably won't play with that too much. Remember, the Caravan is a pretty heavy airplane at gross, and the flaps don't go down all that quick, so that may account for less ballooning at lower speeds. I do think you're right though.
Gents,One of the problems I've been looking at is that the ITT goes so high that you can't set the torque properly.I do think parasite drag was set a bit too high, but also the turboprop engine power scalar was too low. There's a sweet spot to be found, where the torque limit can't be achieved, and the PIH gives us that...above 42oC at sea level. So, I'll diddle with the power scalar until I get it to the point where ITT goes over 805oC at sea level when takeoff power is set.Meantime, the ability to set torque values properly will help determine the drag scalar value.
I agree totally with your first line. I think that is the root of the problem. Fix that, and the rest will fall into place, more-or-less (although the drag does have to be adjusted because [as I found out last night] even setting the right torque values, ignoring the ITT, doesn't give you near book speed). Sounds like you are on the right track though. OR...Carenado could put in an appearance here and offer to fix the programming in the ITT gauge, which is really all it would take, and maybe a minor tweak at that. That would fix everything (almost) in one fell swoop. They are conspicuous by their absence in assisting us with an issue. Just a thought (i.e. Customer Service??)

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Guest BeaverDriver

Just out of curiosity (especially Kurt), has anyone tried replacing the Carenado ITT gauge with the default Caravan gauge, just to see what would happen? Might be worth a go in terms of isolating exactly where the problem lies (with the gauge or in the aircraft.cfg file)! I've got to get to work (some real airplanes need fixing - damn :(), so if anyone here has the where-with-all to give that a try please do so and let us know what you find (if the ITT gauge doesn't do anything, try the TRQ gauge after you put the original ITT gauge back)

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I have some spare time today, I'll be playing with the ITT value and see if I can find the correct value. I'll use the takeoff power chart to get it.Anyway, the ITT is just a visual problem, I guess, as it doesn't affect the torque produced. It's all a matter of torque or drag, but I'm more prone to the drag, as the takeoff roll and climb are ok.Glen, I can't understand one thing: how can the induced drag affect the high speed cruise? And wasn't the rule that Di=(sqCl / 3.14 x A) x (p SqV S) / 2? The sentence you wrote seems to mean the opposite. But it's been a while since the ATPL, I should take a read at my book again to refresh laugh.gif It's true that induced drag plays a role in total drag, though, but at high speed it's the parasite drag to play a major role. Induced drag is caused by the high coefficient of lift, so with a high angle of attack at slow speed (clean and slow, strong wingtip vortices, etc): I think if you're going to alter that value it will take forever to land, and it will have an instant vertical speed at takeoff. As it is now that seems fine, I played at some short field, about the length of the required take off roll, to see if I could barely make it, and in fact I could take off at the very end of the runway, and having the correct climbout with a slow increase of speed after airborne. What do you think?I'll report later if I can find a useful number for the ITT (oh, and fuel flow, too)CheersP.S. For the flaps, they have their own value of drag

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Federico,I disagree with you about ITT; the ITT limitations absolutely get in the way of achieving torque targets here, even at moderate temperatures where ITT should not be a factor.As I tweak this, I've set:[turboprop_engine]power_scalar = 1.31What this does is produce more torque at a lower ITT. In my testing last night, I was able to set 1865 ft/lbs pretty easily at takeoff and at the altitudes where you should be able to, while ITT stayed within limits. This will need to be adjusted, but now it's at least possible to get the engine to the TQ limits without exceeding ITT limits.

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Ok, good to know, but what about the cruise speed? Without adjusting the drag, and by adusting the power scalar, did you notice any difference or what?

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Federico,You do get a bump in speed, but not enough to get us all the way there. I'm getting better success with a combination of the power scalar and both drag scalars.My most recent test had me a bit short of the goal of 163 KIAS (168 KTAS) at 2,000 feet.One of the things I found in developing a baseline yesterday was that when comparing the sim TQ with the book TQ at various altitudes, the engine produced too little power at low altitude and too much power at high altitudes, but was pretty close at six thousand, eight thousand, and ten thousand feet. The overall average of book to sim TQ ratios was near 1.0. Speeds were low across the board.

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Just saying thanks to all you guys trying to fix this issue.
hear, hear....thanks

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TEST RESULTSFirst thing, I'll tell you what I changed:Aircraft.cfg[GeneralEngineData]fuel_flow_scalar = 1.18 [turboprop_engine]maximum_torque = 2040[flight_tuning]parasite_drag_scalar = 0.8Air file (I use Aircraft Airfile manager v2.2.)Entry 1526ITT scale factor 0.95LIMITATIONSAs you all well know, FS has some limitations, so I had to tweak by reaching a good balance with the numbers.EXPLANATIONWhy did I decrease the torque scalar and increased the maximum torque? FIrst I increased the torque value to 2040, as it is a value "unreachable" by the aircraft if not sitting still. We need a 1970 torque during cruise, though. Do you see the red line "TO" at 1865, and then another one at 1970 on the torque gauge? Well ,that's the one. But setting the torque limit at 1865 wouldn't allow us to reach 1970. Setting it at 1970 neither. We need that value, during cruise, at cruise speed with full throttle you won't go over 1970 torque, setting the limit at 2040 in the cfg. Ok.I had to lower the scalar, though, or the climb (and the cruise as well) would be way too fast. Keep in mind I had the manual in front of me, it's not a random number. If you look at the "cruise climb" page you'll see it reaches 12000 feet. Because after that we can't reach 1865 torque any more, so you just keep full throttle and keep climbing. I managed to use that value, 0.85 (it was 0.83 originally, but it seems a bit too low), because in the cruise page I checked the values of torque at different altitudes (ISA cond), and as you can see there are strange numbers, like 1428 at 14000 feet, those seem to be absolute maximum values. But the values for lower RPM are higher! Simply because reducing the RPM will produce a higher torque, but not in FS (or not here, at least). So, if you climb above 10000 feet (about), and you want to cruise fast, just keep full throttle and 1900 RPM. If you want to slow your cruise, you can use lower settings of torque and RPM, but at least our speeds and performance aren't compromised.So remember: climb at 1865 torque and 1900 RPM until you can, monitoring the ITT, of course. Don't use full throttle from sea level, it would be unrealistic. ITT, you need to open the airfile, it's an easy step, just change that value, save and close. I tested it at 42°C at sea level, then 50° sea level with 1700 torque, as per the book. It works. ;) I think it could be lowered a little more, like 0.94 maybe, but 0.95 looks more challenging. And after all, how many times do you take off with 42°? Unless you always fly in the desert...This setting will also control the ITT during climb and cruise, where limits are at 765° and 740°.Fuel flow parameter. Not much to explain here, it was too low, this is the optimal value I could find for all altitudes. My tests were run at different RPM and torque settings at 4000, 8000, 12000 and 16000 feet.Parasite drag remains as yesterday tests, at 0.8, cruise speeds are just fine.CONCLUSIONSYou will get a balanced plane overall. If you are looking to change these values to make the plane as real as you can, you won't cheat. Yes, because you can. Increasing the torque will give you more power available, but it's not our purpose. You will fly it as it supposed to be flown. So take off at 1865 torque (be very careful when incresing the power to TO, or you'll stress the engine), take a close look at ITT temperatures during all critical phases of flight, such as takeoff and climb out. Be within the limits, and you'll have a very nice bird to fly. Gauges are just plain perfect, Carenado style. You have everything you need, so now go fly it!CheersFedeP.S. This was the result of a whole afternoon of testing, we may tweak a little more the numbers, just try it this way, and let me know

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Just saying thanks to all you guys trying to fix this issue.
Yes, indeed - your efforts to improve this (otherwise very nice) plane are very much appreciated :(

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Thanks Guys. here was my initial settings and I was not too far off fede80's numbers, so at this stage I will go with fed's numbers as he has proven record, even though my settings already produced a more suitable 208.empty_weight_pitch_MOI = 13500 //8890empty_weight_roll_MOI = 9100 //6012empty_weight_yaw_MOI = 16000 //12025[flight_tuning]parasite_drag_scalar = 0.9 //1.5elevator_effectiveness = 1.1 //1.2[GeneralEngineData]fuel_flow_scalar = 1.155 //1.1[propeller]thrust_scalar = 1.25 //1.0prop_tc = 0.0004 //0.004gear_reduction_ratio = 17.4 //17.1[TurbineEngineData]fuel_flow_gain = 0.03 //0.011static_thrust = 150 //85 [Flaps.0]extending-time =10 //5.7lift_scalar =1.1 //1.3 drag_scalar =1.0 //1.1 [brakes]toe_brakes_scale = 0.85 //1.0

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Blink, why have you lowered the lift value with flaps? It seemed already too low to me

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Guest BeaverDriver
I have some spare time today, I'll be playing with the ITT value and see if I can find the correct value. I'll use the takeoff power chart to get it.Anyway, the ITT is just a visual problem, I guess, as it doesn't affect the torque produced. It's all a matter of torque or drag, but I'm more prone to the drag, as the takeoff roll and climb are ok.Glen, I can't understand one thing: how can the induced drag affect the high speed cruise? And wasn't the rule that Di=(sqCl / 3.14 x A) x (p SqV S) / 2? The sentence you wrote seems to mean the opposite. But it's been a while since the ATPL, I should take a read at my book again to refresh laugh.gif It's true that induced drag plays a role in total drag, though, but at high speed it's the parasite drag to play a major role. Induced drag is caused by the high coefficient of lift, so with a high angle of attack at slow speed (clean and slow, strong wingtip vortices, etc): I think if you're going to alter that value it will take forever to land, and it will have an instant vertical speed at takeoff. As it is now that seems fine, I played at some short field, about the length of the required take off roll, to see if I could barely make it, and in fact I could take off at the very end of the runway, and having the correct climbout with a slow increase of speed after airborne. What do you think?I'll report later if I can find a useful number for the ITT (oh, and fuel flow, too)CheersP.S. For the flaps, they have their own value of drag
OK, I can see your point here. I will bow to your greater level of training and understanding on this one (and that's said with envy and respect, not with any malice whatsoever :(). I'm going to give your numbers posted below this post a go, but it sounds like you've got it nailed pretty good. Can't tell you how much I appreciate that! Thanks, and more thanks for this. Off to do a flight and will be back in a bit. Again much appreciated :(

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Thank you Glen. I very much appreciate it.I've been trying again, but there's a point I can't understand. Is there a value to be set in the cfg to make the torque available decrease quicker with altitude? You know, like the critical altitude for turbo piston engines. It seems the torque availabel remains a bit too high during the climb...

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Guest BeaverDriver
Thank you Glen. I very much appreciate it.I've been trying again, but there's a point I can't understand. Is there a value to be set in the cfg to make the torque available decrease quicker with altitude? You know, like the critical altitude for turbo piston engines. It seems the torque availabel remains a bit too high during the climb...
Boy, not sure on that one. I'm reasonably familiar with piston pounders but turbines are a bit of a different story for me. I think the service ceiling is pretty far up there so it may be that it doesn't matter much, even in the mountains, but it still should be tweaked if it needs. I'll keep my eyes open for something here, but I'm not too familiar with turboprops as I say.Just installed your tweaks and will give it a go in about another hour. I'll let you know how it goes (I operate from a cooler climate so that might be interesting), but I have every confidence it will work beautifully. Back in a bit... .

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I got it! Now I have to find the values.. :)

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One of the problems we have is that FSX has a terrible turboprop model...you should see ITT increase as you climb, not decrease. ITT is affected by outside air temp but also by air density; as the air gets less dense, there's less cooling airflow into the turbine, so ITT increases.I'm headed home now to try out the stuff Federico did this afternoon...I'll let you know my results.

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