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Post by Tom Goodrick on Jun 10, 2010 9:23:16 GMT -5
I'll be away from the Forum this morning and blocking all email because I am using FlightAware to track my wife's flights. I'll still be trying to improve the Twin Otter. Incidentally, I found after trying some flights that the fix with a negative min beta is itself no good and in severe need of fixing. You can set min beta=15 in the aircraft.cfg if you want to use the reat of the recent improvements (in stall characteristics). I am looking at values as low as 6.0 for min beta.
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Post by Tom Goodrick on Jun 12, 2010 9:14:04 GMT -5
I am running this household single handed now and for a few more days. That limits my time online and limits my flying time a bit more than I thought. I have 10 cats, two dogs and a bird to feed and manage. My wife is visiting relatives in Minneapolis.
Lou, you mentioned some gauges that don't seem to work right. I think it was an oil temp guage that went off scale. That is partly the fault of the gauge designer but can be adjusted by changing some numbers in the aircraft.cfg file. First any temperature gauge in FS can display the temp either in degrees F or C. It is the job of the gauge designer to tell you which he is reading. It is also possible the panel designer has used a gauge meant for a piston engine. from the way you described the temp gauge as working, it seemed to me it might be a TIT gauge. They shoot up to near 1700 F. But they are meant for the turbocharged piston engine, not a turboprop engine. Some FS designers don't know there is a difference. My only temp gauge on a turbopanel is an oil temp gauge reading in C. It warms up to about 28 C before I take off and it stays pretty close to that value during the flight.
For the purpose of checking the behavior of the engine in FS, I could give you a little digital gauge that you can post anywhere on the panel temporarily. Just tell me the parameter and the units you want to see. I sent a picture of my DG panel a week ago that shows some of these individual gauges - green digits on a black background in a white box that can be mounted anywhere on the two-D panel.
The panel.cfg file in the panel folder has a list of gauges with ther X and Y position on the two D panel. If you get a gauge file and copy it into your Gauges Folder in the FS folder, then you just add the new gauge to the list, check which other gauges you want it near, and type in appropriate coordinates. After a few trials you get the position right and the gauge works for you whenever you fly. To make it dissappear, you simply edit in a ' (apostrophe) at the front of the line for that gauge.
Recent FD files sent have improved stall characteristics. I'll check out a file with better prop performance and send it today. Try it mainly for the stall chacteristics. We probably will not get the engine behaviour exactly as you want.
For the CG, I need a coordinate for the front row of seats relative to the crew seats and then the seat pitch (30-34 inches) and the number of rows. Does the last row have three seats? Is there a head? We ought to be able to show realistic effects of full and partial loading. I normally assign a station per row for airliners.
Fuel tank positions relaive to the nose or to the crew seats would help.
I just rechecked you post of 7 June:
"Oil pressure reads too high, or is off the scale. Prop RPM should reduce to 75%, this shows about 83% or there abouts. There is no trim indicator"
Okay, it was oil pressure that did not behave. I'll check that out. It can be adjusted. I'll have to send you a panel.cfg file that fixes the gauges. I already adjusted the IIT gauge readings but forgot to send you the file. in the turboprop, Microsoft does not give and Ng indication, just N1% and N2% where N2% is the reading proportional to prop RPM. I also look at actual RPM. Don't you also get that? Is that behaving (subject to the liitations we have already discussed)?
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Post by Tom Goodrick on Jun 12, 2010 19:23:07 GMT -5
This is data from an engine start, taxi, takeoff, climb and start of cruise with the DHC6 FD dated 6/10/10.
Time__Pow Lev__RPM__KIAS__Oil c__Oil psi__TQ%__ITT c__N1% 0_____0________0_____0______14____0______0_____0_____0_____Off 0.1min 0________963___0______16____16_____0_____0_____0_____Starting 3 min_0_________966___0______23____99____13.5___533_________ 6_____10_______1021___5_____33____101____14.0___537_________ 8_____6________1299___5_____32____108____22.6___555_________Start TO 9_____80_______1700___89____31____133____95.2___671___96.1__ 10____80_______1700___112___29____131____91.4___651___94.2___Climbing 11____80_______1700___123___29____131____92.1___645___93.9___Climbing 15____70_______1506___162___28____131____79.7___612___89.1___Level at 5,000 ft Cruise at 5,000 ft 173 KTAS TPower 71.2% This flight was done at full gross with a full set of pax and 40% fuel in the front tank. (The tanks are re-defined in this set of FD to be equal in size but with about the same total capacity as before.) The RPM was directly controlled by the Prop lever without any relation to the power lever once the aircraft had enough power to fly.
I did some stalls and found the characteristics to be very forgiving. Recovery from any shallow stall is easy with power and relaxing of the back pressure on the stick. With a clean wing it was stallinig at about 81 KIAS. With 10 deg flaps it would hold steady at 78 KIAS. With 20 deg flaps it held to 74 KIAS. With 30 deg it held to 68 KIAS. With 40 deg it held to 66-67 KIAS.
I have not tried the STOL takeoff or the STOL landing. I don't think we will have the same trouble we had before. I re-shaped the Cl vs Alpha curve.
The question posed here is: "Is this behavior reasonable?" Do the magnitudes conform to your experience? All temperature and pressure values can be changed very easily. But I see the same levels in the default King Air. Everything is "in the green." Supposedly Beech has blessed the default treatment of the King Air 350. Its performance agrees with some test reports I have on it though I did write some minor revisions into the FD fiels for the King Air.
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Post by louross on Jun 14, 2010 9:51:08 GMT -5
Imade one low altitude flight about 30 minutes, and did a rather quik check just now. Here at this time- have to go to town.
The flying part is very nice. Maybe we can do some fine tuning later. Includes turns, IAS changes, flaps changes, approah and touchdown.
There is a small problem in reversing. To reverse am doing this: Normal approach (flaps 10 or 20) prop levers pulled back, touchdown at 75, props forward, press F2. Enters reverse too slow. Should come out of reverse quicker (power levers foreward then back to idle or F1- tried it bothe ways). Torque seems to increase momentarily, negating the reverseins that had been gained.
Power changes should reflect sooner than they do. REAL- on takeoff, there is a small lag in the power change when the levers are moved forward- this is well done in the sim. But the power should come up quicker than it does in the sim when pushing the levers to max power position. The lag in the sim makes it very difficul to preciselt set T.O power whether based on torque or ITT. The real technique is push the levers forward a bit and let the engines stabilize anywhere bwteen 10 and 20 oon the gauge, confirm all rngine instruments (takes about 2-3 seconds) push power levers up to max power as the torque and ITT readings follw closely behind. Can this issue be coorected?
It would appear that the PT6A taxi in beta range can not be programed in MSFS.
Then some "other stuff": Annunciator panel has lights that ar permantly on but shouldn't be; should not be flags on the NAV indicators; oil temp gauge off scale.
I will send a photo later today.
lr.
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Post by louross on Jun 14, 2010 19:54:55 GMT -5
I can say this about the DHC6 CG: There are many cfg's for this a/c- the typical pax version is: immediately behind the pilots' seat is a thin partition- then 7 rows with 2 seats in each row. Just behind the left seat in row 7 is the main entrance. If you stand on the stair just outside the door and are looking in, you see two seats side-by-side against the opposite side. Just to the left of the entrance door there are 3 seats in the that last row. This gives a seating of 19 pax. Just behind the last row is the rear cargo compartment.
I have know idea what the pitch is. What I just described is not 100% exact, but it accuratley places the pax seats for CG purposes and is simply explained.
There is a fore and aft fuel tank beneath the fuselage floor, each holding equal amounts of fuel.
If I remeber correctly, the 200 series had an extended nose (from the 100 series), but I would have to question it's utility in actual ops because the space is so small I don't know what good it would do. It does make the a/c look better tho.
They had no auto feater at least in 1975. To be honest, it's not necessary. I see in MSFS they are there, but I don't know if this is an FS invention, or actually a newer requirement. Same with auto-pilot. The a/c is extremely easy to fly, and as the pitch trim is manual, it is easy to get it exact. Auto pilot would be an unnecessay expense for the company, and it is also an add'l weight which takes away from payload. The companies I was with (both the DHC6 and B99) put on every pound of payload they get on the a/c.
Also many programs I see in FS state the airplane carried 20 pax. However, unless the regs have changed, the max pax seats in an a/c is 19; 20 or more seats requires a flight attendant, in other words 21 seats.
To me, it was a very easy airplane to fly, very stable, no special "kinks", very honest. I thought it was pretty funny looking. I left that company after about a year and a half to go with another co. flying Beech 99s. It was "more airplane" and it also looked like a "real plane". The 99 was definitely faster- takeoff, climb, cruise, touchdown. However, with no pax, there was a forward CG problem (B99). If you only had 2 pax, they had to sit in the rear because of the CG. On the other hand, if it you had a full pax load, rear CG was a real concern. anyhow, lr.
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Post by Tom Goodrick on Jun 14, 2010 22:21:08 GMT -5
Thanks for your comments. I'll go through them and try to get a handle on them. But here is my first response. Nothing in my first response is firm. I am gusseing we are comming at this from very different perspectives. I think in terms of fundamental piloting activities. I never include annunciator panels because I would have no way of knowing if they are correct. My guess is part of what you see as problems are caused by incorrect guages in your panel.
For example, oil temperature. The reason I showed you my data, was to see if anything was "off scale" as you say the oil temperature is. I saw nothing above 33 c and that was at peak power on takeoff. If that "off scale?" If so we can easily fix it. Otherwise the problem may be you are looking at a bad gauge. My data shows the exact digital value computed within the sim. Of course that may be wrong - too high or too low - but at least that is easily fixed.
You have to give in to some peculiarities of the FS environment. We can't change some things. Here is how I handle the problem of setting reverse thrust on landing. I am usually carrying a fair amount of power on final with prop levers full forward and power levers at or above 50%. When the wheels touch I tap key F1 to zero the power levers. Then I hold down F2 so that the levers pull back into the reverse region. to kill reverse when the plane slows below 50 KIAS, I tap F1. Again that zeros the power levers but this time moving them out of the reverse region. I don't care that I am not pushing or pulling levers realistically, I am getting the job done quickly and relatively smoothly on the computer. i never use artificial lever controls. They are cheaply made (within my price bracket) and seldom work well. We have had many people say they could not get zero thrust. It was because the levers they used did not go to zero. F1 always sets zero thrust quickly.
The lag you see during taleoff is something that only you would realize is a problem. I knew it was slow but not that it was tooslow (likewise the lag in the instruments) The power lag can be fixed. It will probably take us a couple comment cycles to get it right. But we will if we try. I'd like to get that one right.
I sent you a test power panel that I use to check for power-related parameters. i'd like you to try installing and using that so we can compare info. It won't help if you are using screwed up gauges. I can also send you some "stick-on" gauges for some parameters like oil temp and pressure. These gauges you can "stick" anywhere on whatever panel you are using to see if the values in the sim are correct. For any of these values, we can adjust the range and rate of change. That's a 5-minute fix.
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Post by Tom Goodrick on Jun 15, 2010 8:59:34 GMT -5
Today, once again I am busy following my wife's flights with FlightAware as she returns from MSP through MEM to HSV. T storms are forecast this afternoon.
I'd appreciate if no one sends me a big file by email.
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Post by louross on Jun 15, 2010 10:57:40 GMT -5
Look at the photo- this is a very good representation of the a/c in question. If I can't get a realistic panel, I don't use that a/c. As far as transport cat jets go, there are programs that represent older a/c very well, but I haven't found a freeware program that actually represents the real airplane. These include the Jensen (sp) DC3C, the Frolov Dash 8 (DHC8), the Tinmuse B732, a number of the HJG group, and a number of calclassics- especially their DC6B. Freeware, nothing exists to my knowledge. 1) Check the oil pressure gauge. Obviously wrong (ooopps- oil press, not temp!). 2) Look at the pilot's HSI. Radial (OBS) set, DME locked on, RMI needle okay. But the red warning nav flag should not be there. 3) Look at the prop RPM. Reads about 84-85%. Since the prop levers are full back, should read 75-76%. You might take a look at the fuel levers- they are as far back as posible but not so far as to shut off the engines. MSFS inccorrectly models these levers. If you keep them forward, eg default KingAir, the idle is way too high. Now- things not so obvious: 4) Check torque and prop rpm. If the props are pushed forward, the torque should decrease. You can not redue the prop rpm because the lever is full aft. Suppose the rpm was set at 95%. If you pull them back to full aft, the torque will move higher- possibly to over torque. This is not modelled. Remember, we are using a PT6A. 5) Reversing. Props full forward. Power levers idle. Enter reverse, when slowed, power levers forward to idle. Problem with this particular a/c program- reverse thrust is developed too slow. Not slow, but too slow. Coming out of reverse,- torque immediately increases and prop rpm runs up; if you do nothing at this point this DHC6 will increase taxi speed to very high before everything stabilizes back to idle- therefore, the necessity is to "reset" the power levers by quickly pushing forward and back to idle, then jump on the breaks. 6) Power changes are excessivley slow- actual power and guage. Now. the precedures don't change anything if the hardware and software is quality and configured correctly. You can use a good quality joy stick or contol console, but they must be correctly configured. I use the keyboard for F2 and for view changes sometimes the number pad is more convenient than the hat switch- sometimes not. I will probably switch F2 Key to the Eclipse console I so gratefully received as a gift. Before that, used an MS joystick. If anyone uses the keyboard, I can only say I really feel sorry for that because, well, it's obvious why. Since the reversing procedures do work correctly in other a/c, for example the Frolov Dash 8 and the calclassics DC6's and 7's, I must draw the conclusion that the programing for this particular a/c, at this time, is wrong. As far as that goes, none of these problems exist in other a/c I use, so they shouldn't exist here. Now the deal is each of these items is either fixable, or not fixable. I do know that these problems don't exist in the other a/c I use. Maybe the nav indicator is nothing more than a fixed photo, in which case I suppose it's not fixable. You said you are carrying 50% power to the landing. I do not know what is wrong there. It's not normal. Something is not right. I don't carry that much power in the sim, nor real world, in any airplane. Your landing procedure in the Otter is not a factor. Different companies ave different SOP's. You can land with 10*, 20* 30* or 40* flaps, depending on SOP's and conditions. There is no problem landing with flaps UP in the Otter- it's not in the manual and it's not SOP, but it is not a problem. You can land (and take-off) with 100% props, or 80%, or 75% props. All those techniques are common. They all work fine. My typical landing is: cross FAF at about 1800agl or whatever the altitude is according to the chart, or 1800agl, at 140-160 ias and prop levers full back. Reduce power and begin slowing to 100 and take 10* flaps. I may or may not use 20*, it will depend on the runway or other pertinent conditions, otherwise, my mood dictates. Power is probably more than 100 lbs torque but less than 150 within the last 1 or 2 miles. 80 knots before crossing runway threshold, just above the ground go to full idle, flare, touchdown around 70-75. Same tech used for STOL, except I set 20*, props full forward, full flaps. Since max torque is like 525 or whatever, 50% is at 250 lbs torque. Try that and see how you do. lr.
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Post by Tom Goodrick on Jun 15, 2010 19:34:08 GMT -5
Obviously we have difficulty communicating. When I said the torque levers were at about 50% I did not mean the torque was at 50%. The lever postition was agout halfway forward with full flaps on final. Even that is not exact. It was more an impression. Just consider that I had some power on before I crossed the numbers and put the mains on the runway. Then I initiated the reversing sequence of F1 to zero the torque, F2 for reverse until slow and F1 plus wheel brakes to slow for turning off the runway. Yes I have noticed a surge after returning the levers to the position for zero torque. I don't know why that happens.
I read the prop speed in RPM. You read it in %. You are probably looking at a gauge that shows N2%. If that is the normal method in the DHC-6, I will adopt it. But I have read other reports, many of them, in which prop speed is discussed in RPM.
From that photo, I cannot tell which gauge is the oil pressure guage and certtainly cannot discern its indication. is it more than 133 PSI? Is 133 PSI too much pressure? This is the answer I have been trying to get. If I got that answer, i could probably make the pressure behave correctly. But it may not make your gauge work correctly.
I will look into the matter of the rate of change of power. I think I can improve it.
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Post by louross on Jun 15, 2010 21:30:51 GMT -5
Prop RPM in a Twin Otter is measured/read/ given in %, just like the gauge shows. Prop RPM in a B99 is in RPM, which is 2200 for take-off, 2000 for climb, and 1900 for cruise. Anyway, no idea how you are getting DHC6 RPM in RPM's, as it is actually done in %. Power is in torque, measured inft lbs/ft in this a/c, not EPR or MAP, BMEP, or whatever. That's why the instruments are that way. Anything else is a fantasy invented by whoever. It would appear you're ussinga fantasy panel. You could also use the default C172 panel or the default 737 panel- seen that many times. But why not use one that at least tries to replicate the real thing? (you actually think I don't know the difference between N2 and RPM? ?? Hello!! Is anybody home? Oil gauges. Engine panel. There are two vertical rows of gauges, next to each other, in the center. There is a pair of gauges just outside the inner 2 rows. Inner gauges- there is a right side and left side vertical row. Since the DHC6 is a twin engine plane, there are gauges for each of the engines. The left vertical row is for the left engine, and the right side is for the right engine. Are you following me? Starting at the top, there are are the torque gauges- this is engine power. Next down is prop RPM, correctly shown here as %- just like the real plane. These two gauges in the photo read 84%- they should actually read 75%. (What is the actual RPM? who cares, it's not important. The props are turning at 84% of whatever max RPM is). Next are the two (left and right) guages that read ITT which is inner turbine temperature, *C, and finally we have the N2 gauges. Now we go to the outer row to the left and to the right of these two inners rows, showing 3 gauges each. The top set shows fuel flow, read in lbs/hr, in which case 300lbs/hr/ engine is what it is at cruise. Next is the oil temp gauge- the needles are obviously in the green arc. The bottom 2 are oil pressure gauges. They should be in the green. You can see that they aren't. At a lower power setting, they sit just above the red line. lr.
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Post by Tom Goodrick on Jun 15, 2010 22:30:02 GMT -5
How much psi puts your oil pressure gauge in the green? I just saw 105 psi max.
In FS, (1) N2 is shown in percent of max; (2) N2 ir proportional to the prop speed according to the gear ratio; (3) therefore N2 is also the percent of max RPM so it is prop speed in percent. But when we read prop speed in the sim we can read it in RPM. Since I apply the same gauges to other turboprop aircraft, I like to see prop speed in RPM.
FS normally gives torque in percent of max torque though we all know torque is in ft/pounds. If you fly several different aircraft, it is easier to control the engine in percent torque than in ft/pounds.
Torque is not Power. It is torque. Multiply by prop speed and a constant and you have horsepower.
(Hello. Is anybody home???)
I found tonight that I was indeed having to use a lot of power with my flight model on final. The torque levers were near the halfway point to maintain level flight at 100 KIAS with flaps and just under that coming down final. The reason for this is I have too much drag. I am operating on the backside of the power curve!! I must re-examine the drag and power used in this model.
You are very correct in one respect. I certainly DO use FANTASY panels. I do this because: (1) I must be able to read parameter values at a glance - not just see if they are "in the green." (2) I need to see parameters that most pilots never see. (3) I test fly a lot of different aircraft to help people with performance and stability problems so I use the same fantasy panel (a fancy glass panel) in all examples of the various classes of aircraft: one panel for single piston, one for twin piston, one for turboprop and one for jets.
If we can reach a common understanding, we can work together. But that may not be possible. You are a pilot with a lot of years of experience. I am an aeronautical engineer with 30 years of experience in the general area of aerodynamics and flight mechanics. (Propulsion is not my specialty.) In my engineering work for the US Army and for NASA, I did a lot of work that involved simulation of flight dynamics - even out to space and back into the atmosphere. Simulation of flight dynamics does not mean simulation of button pushing. It means understanding what goes on and why. It also means I understand the guts of any simulator. (It's all math!) For the past 15 years, even a few years while working for NASA, I have worked with the Microsoft Flight Simulator. It has fewer warts now than it did but it is still far from perfect. But it's more fun for the buck than most flight simulatiors.
Now that I have shot off all that hot air, I'll get to work and revise the drag on the DHC-6.
Your normal cruise speed on the DHC-6 is 180 ias. When most people say that they mean 180 mph indicated, at least back in 1975 and earlier. Is it 180 mph or 180 knots indicated or KIAS? 180 mph is 156.5 knots which agrees with specs I have seen. I learned to fly Cessnas back in the early 1970's and I knew the "numbers" for the 150 and 172 in mph.
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Post by louross on Jun 15, 2010 23:34:10 GMT -5
We can accept that when I say whatever about operating and a/c you can simply accept that I'm right- it's not necessay for you to confirm it. You can use whatever terminology you'd like, as I will use the common pilot terminolgy. Your position of power levers means nothing to me. Engine readings is what I care about. What is the blade angle at xxx condition? I don't know and I could care less. I'm sure it's important for you tho. I do get tired of getting the butt end of your anger, which includes, sarcasm and insults. So we can work together and accomplish something worthwhile, but cut the "nonsense". Anyhow, The DHC6 cruises at 180 kts, but reread your paragraph about that. You got it wrong. 180 has nothing to do with mph, nor km/hr. IAS? How can you be serious? The DHC6 normal cruise is 180kts TRUE (TAS). In 1975, today, and 1955 whenever an airline, or professional, pilot said cruise, he was talking TAS. What is every (any) body else talking about- most of them have no idea what they're talking about. Rotate, climb, V etc, is IAS. I gave a normal everyday typical approach sequence. You can use it, and get all the parameters you want. But "power levers at the mid point..." I can't help you with that. "Level flight with flaps..." Same thing, flaps at 10, 20, 30, or 40? But there is another issue there, flaps 10- okay 80-90 kias. Flaps 20 or more- no reason in the world I'd be flying a DHC6 in level flight with 20* or more flaps, so I can't help you there. If that is necessary for your figures, I can't help you because I'd have to actually get in the real plane and check it out. Tune the files as you can, send them, I'll do some flight checks. lr.
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Ed Burke
Member
Healthy living is fine, but it's having fun that keeps us going!
Posts: 433
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Post by Ed Burke on Jun 16, 2010 17:19:53 GMT -5
It's great to have you around Lou as we are short of people with hands on experience, especially in the commercial scene. When you guys have finished with the twotter it is going to be a great aircraft and I hope it ends up in the BGA hangar. Meanwhile you are keeping us on the edge of our seats, keep up the input 'cos the forum is too quiet right now. I was getting serious about keeping goldfish to raise the level of excitement as I am currently unable to do a lot of flying due to some serious computer woes. I hope a few more days and I'll be in the air again .
Ed
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Post by Tom Goodrick on Jun 16, 2010 22:33:42 GMT -5
Here's a progress report. I re-evaluated the engine power recalculating the max torque for a 620 shp engine at 1700 rpm and got 1915 ft lb per side. This was an increase from the old number. i reduced drag a little but then, with that increase in power, I found I could add a little drag back in.
Presently in cruise at 7,000 ft I need only 63% torque (1206 ft lb per side) to hold 180 KTAS while burning 298 pph/e. The oil pressure is 89 psi.
Check these numbers. I think it needs a little more drag and more torque at cruise with fuel flow adjusted back to where it is now.
It handles nice on approach but needs a fair amount of power on a shallow 3 degree ILS approach which I fly at 95 KIAS. I flew a STOL approach at 80 KIAS with full flaps and landed nicely with a good attitude down final and a substantial round-out.
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Post by louross on Jun 17, 2010 9:29:14 GMT -5
Sounds good. Specifically 180 tas and 298lbs/hr/eng
When I get the new files I'll make some checks.
"It handles nice on approach but needs a fair amount of power on a shallow 3 degree ILS approach which I fly at 95 KIAS. I flew a STOL approach at 80 KIAS with full flaps and landed nicely with a good attitude down final and a substantial round-out."
Very general ideas there. A very general response is your definition of "a fair amount of power", and no flap setting given. At what point does this cfg take place? Halfway down the glideslope? We now go from the possible situation where you are running a "test", or to the real world stuff. (RW) with 2000 hrs in the a/c and talks with a small number of fellow pilots during the time, that method was never used, for more than 1 reason. The FAF was crossed indicating 160, and reduction began shorly thereafter or halfway down the glide slope. 160 could be held to 3/4 mile before touchdown, but you should inform the pax what's going on because most of them knew that wasn't normal, and you had to make sudden changes- pitch, flaps, noise, which alarmed the pax. Substantial round-out. I can make no comment on that.
When you're ready, email me or post the files here at BGA (supposing it's okay to post here), and I'll check them. lr.
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