|
Post by Tom Goodrick on Nov 19, 2008 10:49:19 GMT -5
Sorry, but I know very little about the current version of X-Plane. I have an early version and know their approach to the mechanics of simulation which is very good. I know nothing about their simulation of ground effect or of hydrodynamics.
I think if you knew more about the flight dynamics involved, you would not be pursuing this course. Get some advice from people in the aeronautical or aerospace engineering department of a university. Also, talk to some people who are experienced with boats who know the typical water conditions in bodies of water like those in which you might operate. With a team of experts in those fields, you could develop your own simulation to develop the concept with a sound base in reality. I wrote my own simulations as a working engineer for parachutes, airplanes and for spacecraft that must land on runways. That sort of thing is a normal business task for a working engineer. Commercial simulators can only be used when they directly apply to the problem.
I remember seeing fanciful drawings of vehicles with hydrafoils and low-aspect ratio wings on covers of science fiction magazines. There are good resons why they never happened. I got an "A" in an aeronautical lab design project in school for making and testing a plenum-chamber ground effects machine powed by a 40 psi machine shop air supply. I could stand on it and slide around on a concrete floor. It was a good way to dent your backside. The value of a ground effects machine is that it can run from water onto land and back again. The vehicle you discuss can't do that. It is just a fast boat. But there are boats today that easily go 70 knots on water. How fast do you need to go across a small lake or bay? If you want to go farther, then you must except 2 meter waves as normal and 6 meter waves as occasional problems. They don't bother an airplane flying above 2,000 ft. A surface proximity machine could work fine over frozen lakes.
In any application where your vehicle could work, an airplane works better. If you can dispute this, go ahead.
|
|
|
Post by Tom Goodrick on Nov 18, 2008 21:18:08 GMT -5
The change you want to make is to add these lines to the panel.cfg file:
[VIEWS] VIEW_FORWARD_ZOOM=0.90 VIEW_FORWARD_DIR=2.0, 0.0, 0.0
The zoom line is useful but the value you like may be different from what I like.
The Forward_Dir line is what does the trick with a 2D panel. The first number sets the line of view downward 2 degrees. Think of it as raising you up so you can look down 2 degrees over the nose. This gives a good view of the runway on final. Experiment with different values. I find they vary for different aircraft but usually values betwee 1 and 3.5 will do the trick.
Scan the entire panel.cfg to make sure there is not a duplication of the [Views] section. I usually put this up in the top of the file so it is easy to find.
I also changed the key assignment for seat adjustment to the up or down arrow key. But that adjustment has to be done each time you fly where this change is permanent.
The pitch angle on final can also be adjusted by shifting the lift curve in table 404 to the left. But this should be done to make the plane fly level in cruise and then set the VIEW_FORWARD_DIR= to get the view right during final approach with full flaps.
|
|
|
Post by Tom Goodrick on Nov 18, 2008 11:55:49 GMT -5
Yesterday I did a fair amount of testing of the Cessna 208B Caravan with a special version of one of my "DG" panels that give me many more parameters plus the TPower Panel that shows power, thrust, blade angle and exact setting of the condition lever. I installed the original Caravan ECU gauge showing the throttles, prop, condition lever, fuel selector and inertial separator. I have not flown the Caravan much in all the years I've had this sim - a total of 11 hours, many from yesterday!
Before going farther, I'll state that the results showed me that the condition lever is insignificant even with an aircraft for which its use is intended to be very significant (at least intended so by Microsoft). My original suggestion that you just leave the condition lever at 40% (ie- "low idle") as it is after a normal engine start, is the best course of action. Presumably, Microsoft made sure that the turboprop engine model properly uses the condition lever setting in developing the thrust and power. I found in most cases there was no difference in these values during flight when you change the condition lever. I also found that it is extremely easy to shut off your engine when trying to move the condition lever from High Idle to Low Idle either using the mouse or using the "mixture" control.
I was surprised to see that there are actually two different throttles and that the choice of which to use is made in a strange way. The original FS default checklist for the Caravan says to move the condition lever from Low Idle, where it is left after the Ctrl-e start procedure, to High Idle before starting the takeoff. When you do this and you then push the throttle forward, you see the left throttle moving, the one labled in red letters for "emergency power." You get no more power or thrust by making a takeoff at Low Idle. But then you are only moving the right throttle with the silver handle. If you change the Condition Lever in flight you do not switch between throttle levers. This is all rather strange.
I am setting up the panel without a condition lever or a prop lever. I found that you get a good cruise power setting by adjusting the throttle back to 75% power (as shown on a TPower gauge). The rpm can remain at 1900 without any problem.
|
|
|
Post by Tom Goodrick on Nov 18, 2008 11:08:40 GMT -5
No.
If it can be done, it can be done with one air file and one aircraft.cfg file (which is easily edited and takes precedence over the air file.)
The biggest problem you have is that FS9 does not provide any adjustment of hydrodynamic force coefficients as it does with aerodynamic coefficients. I have looked at controlling float drag to get good performance for float planes. There are no appropriate parameters in the air file. However, I have not exhausted all permutaions of float points - number, placement and depth. It is obvious with large flying boats like the Boeing 314 that there is some hydrodynamic motion.
What is your interest here? Are you an engineer looking for an interesting field of work? The work I am aware of in past decades in this field is rather impractical. Aerodynamic effects vary with the ratio of height to wing span and the wing spans are generally short and the aspect ratios very low - less than unity. This renders the aerodynamic portion of the motion very inefficient.
If you cannot handle waves above 10 cm, you'd better quit. I don't know of any body of water worth any effort in crossing that has wave heights that low on typical days. 1 meter wave heights would be the norm on "protected" waters. But I have seen that 10 cm wave height mentioned in regard to past work in this area. That is what I mean by "impractical design efforts."
I would be tempted to try a design just for the challenge. But I can't avoid the problem of improper force calculations for ground/water height effects in FS. We could concoct a design that would appear to perform as desired but it would have no relation to reality. After all, a strong relation to reality is the heart of a dynamic simulation solution. Anything else is fantasy.
|
|
|
Post by Tom Goodrick on Nov 17, 2008 11:08:49 GMT -5
Now that I have written such a nice concise summary of the techniques for flying turboprops, I must question its accuracy in regard to the Condition Lever. Last night Jerry Luke asked me about a panel and checklist for the Cessna 208B Caravan. I read the existing check list carefully and found it is intended to be flown with the condition lever at High Idle. Then I went to the original Beech 350 checklist by MS and found it is at least flown through the approach and landing with the condition levers in High Idle. My information has come from reading articles in the aviation press about flying turboprops. The trend is to simplify the pilot's workload and the condition lever has been replaced in many aircraft by a simple on/off fuel switch. In many modern aircraft, they have even removed the Prop lever so RPM is mainly held steady during all flight.
I am going to use my TPower Panel and TPower gauge to check the effect of the condition levers on the Beech 350 and the Cessna 208B. That should indicate when it is helpful to adjust the Condition Lever for either thrust or power.
|
|
|
Post by Tom Goodrick on Nov 17, 2008 10:48:56 GMT -5
No, the FS9 still does not allow differential lift between the two wings. This is unfortunate. X-Plane is the only sim that does allow that. However, spins can be simulated to a reasonable extent by working with the stability derivative terms. I can model the dynamics of an intentional, induced spin in many aircraft and can set up many aircraft that are known to be prone to flat spins from which recovery is impossible if they are held deeply into the stall. But to start the spin in all cases the aircraft must be yawed slightly or be in an accelerated condition.
We cannot simulate the simple stall/spin accident in FS that kills many people every year. Because of that, FS gives the uneducated student an unrealistic view of the safety of flight. I have tried to help by making spins more likely to occur if the student allows a stall to progress beyond the early stage. But the true effects cannot be modeled.
|
|
|
Post by Tom Goodrick on Nov 17, 2008 10:21:30 GMT -5
Fligth Simulator does two things wrong that would make it difficult to design this vehicle and make it operate properly: 1. Objects that move on the surface of the water move rather strangely. 2. The aerodynamic forces in ground effect are not computed properly.
I tried to design a boat - just a simple 30 ft (10 meter) utility boat. It was powered by an invisible prop which is the only power available in FS unless you want a jet. I tried to keep it moving at low speed - 10-20 knots. It would work fine for a while and then suddenly flip into the air hundreds of feet and fall back and sink. I tried a lot of variation in where I put the float points. I gave up. But others have succeeded according to what I have heard. (I have not run any good boats.)
The water interface works well for aircraft to an extent but there are still strange things. For example try a replay of a landing of any float plane or flyiing boat. It will probably crash at the end of the replay even though it never crashed in the original landing.
The water interface is strange.
The model for ground (or water) proximity effect simply gives additional lift with a factor that changes as a function of height. The problem is that actual wind tunnel tests of the proximity effect have shown that only the induced drag is affected. It is reduced! Now any lifting theory will tell you taht increasing lift increases induced drag. In working on flight dynamics files for FS, I leave this lift effect alone just because it does give the pilot a feel for the change in flight characteristics when you get close to the ground during a landing. Unfortunametly it is the wrong feeling but it may be better than nothing which is the only alternative.
Here you see the problem for your wing-in-ground-effect aircraft. It should see reduced drag amking the motion more efficient. Instead it will see more drag with the increased lift slowing it down.
As far as I know, FSX has not improved the aerodynamics in any way.
Finally, no one has ever convinced me, as both an erodynamicist and as a boater of some experience, that a ground effect airplane has any efficieny with practical safety that makes it a good idea to pursue. I am aware of the many experiments conducted in Russia. It might make very good sence when used over frozen lakes where there are no waves. But wet lakes have a varying wave height that would cause a lot of problems with such a device. I note that many such devices have been ambitiously marketed and NONE have been put into common use.
This, of course, has nothing to do with "ground effect machines" which ride on a plenum of air pressure provided by powerful fans. Those have certain military uses but are not efficient in any sort of comparison with other vehicles. They are useful as landing craft because they do not have to stop at the water's edge.
|
|
|
Post by Tom Goodrick on Nov 15, 2008 23:51:05 GMT -5
OK. My fiddling with the numbers has paid off. By checking performance from FL270 to FL410, it is clear why the Piagio performas as stated in the magazine. The pilot makes it perform that way by working with the constraints of MMO (max mach, operating) and VMO (max operating indicated airspeed). Before we give the exlanation, take a moment to look at the data.
MAX CRUISE Flt Lev %Throt %Powr Mach KTAS PPH/eng KIAS<= 260 270___81______69.1___0.64__380___302______258 290___82______69.4___0.66__390___301______256 310___95______75.9___0.70__409___328______260 330___89______72.1___0.70__406___309______low 350___83______69.0___0.70__403___293______low 370___80______65.6___0.70__400___278______low 390___78______63.6___0.70__403___270______low 410__100______62.2___0.70__401___263______low
LONG RANGE / ECONOMY CRUISE Flt Lev %Throt %Powr Mach KTAS PPH/eng 310____60_____57.0___0.61__357___245 330____60_____56.5___0.62__360___241 350____60_____55.4___0.63__363___235 370____64_____56.1___0.65__373___235 390____62_____53.7___0.63__361___237 410____80_____53.0___0.63__359___224
This is for an aircraft with full fuel at takeoff and a payload of 4x180+100lbs. There is margin for a little more weight.
Flight level 310 is a special place because that is where the two constraints meet: Mach 0.70 and VMO 260 KIAS. Below that altitude, you set cruise power according to the indicated airspeed of 260. Above that level, you set cruise power according to the Mach 0.70. If turbulence is expected you must, leave a marging below these values.
In the FLYING article, the true airspeed at FL310 did not quite reach 400 knots although Piaggio says it should. The reason was that the temperature was non-standard when the flight was made for the article. Non-standard conditions do different things to the two limits. I high temperature will reduce the Mach number at a particular true airspeed so you might think you could increase the true airspeed beyond what you would use in standard conditions. But if you do this, you would make the indicated airspeed violate the VMO limit.
I have not checked the estimated range for each of these conditions. The spec is 1420 nm which leaves a legal margin for IFR flight (All flight above 18,000 ft must be under IFR.) It seems there is a considerable variation, depending on conditions and on what ground speed you will accept. I would allow a wide margin for each leg with a nominal 1300 nm as a general number. You will have to pay close attention to the GPS ETE and the fuel computer's estimate of flight time remaining and adjust your flight plan if conditions vary from the assumed condition.
I'll update the posted download file on my web site tomorrow and will send out zips with the new FD files to Bill and Allen. Both aircraft.cfg and .air files were changed. Among other things, the MMO limit can be set in the aircraft.cfg file but the VMO limit must be changed in the .air file.
|
|
|
Post by Tom Goodrick on Nov 15, 2008 18:02:17 GMT -5
The performance is not far off so you can fly the existing model without worry that it does not represent the real plane fairly well. You should change the max-mach=0.67 to 0.70 in the aircraft.cfg file. That gives a few more knots before the noise happens. But in careful comparison against the specs in the FLYING article the changes are slight. Fuel flow increases by 2%.
The tricky part is getting the performance change between 31,000 ft and 41,000 ft. At 31,000 ft you can still get pretty high power - about 86%. But by 41,000 ft this drops to about 67%. The speed should be 400 at 31,000 ft and 357 knots at 39,000 ft. Fuel flow drops from 770 pph at 31,000 ft and max power to under 600 pph at 41,000 ft (exact value is not given). The mach is increasing to max 0.70 at 41,000 ft with max throttle. There is probably a rise in drag along with this Mach increase.
Getting these numbers to come out right is the hard part. The model wants to give 370 at 31,000 ft and 365 at 39,000 ft.
|
|
|
Post by Tom Goodrick on Nov 14, 2008 20:50:43 GMT -5
I intend to do some more work on the Avanti model. I had to change the MMO setting from 0.67 to 0.70 to comply with the newer version. But I think it needs better Mach drag and maybe a little Mach pitch for any who venture beyond the limit.
|
|
|
Post by Tom Goodrick on Nov 14, 2008 20:45:31 GMT -5
Bill, I think you must have flown that trip at too low an altitude or at an inefficient power setting because the model is capable of much greater range. But 100 gallons still permits a fair amount of flying. The FLYING article gives max range as 1420 nm at 39,000 ft and 357 knots. As you go higher in altitude, there is a very big reduction in fuel flow. But it should also be noted that the performance is sensitive to weight.
Today I started a trip from KLBE to KABQ - about 1330 nm - and found the model over-performed in some ways. I carried six pax with just a little baggage allowing full fuel. I stopped the flight after 41 minutes. It reached cruise altitude of 40,000 ft in 18 minutes. The power gauges and GPS indicated it had plenty of flight time available compared to the flight time needed. When I stopped the flight after 41 minutes, it had 2:44 to go to ABQ and enough fuel for 5 more hours of flight.
I need to work on the high speed / high altitude aspects of its flight. For additional discussions of the FS model, I'll start a thread on the Flight Sim section of this Forum.
I went to FlightAware tonight and got some samples of flight plan data for the P180. (Values in parens are actual speeds observed by the ATC.):
390 at 32,000 391 at 33,000 (actual 496 kts -wind?) 397 at 30,000 375 at 37,000 397 at 31,000 397 at 30,000 317 at 14,000 370 at 25,000 (367) 362 at 34,000
|
|
|
Post by Tom Goodrick on Nov 13, 2008 21:25:04 GMT -5
I happened to find a pretty neat little airport. I found it because a friend has a retirement house near it. The airport is Gnoss Field (KDVO) in Novato, CA. It can serve as a nice "gateway" to the San Francisco Bay Area for peopl flying small aircraft. It has one runway, 31/13 that is 3300 ft long and 75 ft wide. It is used by many types of aircraft up to small jets. Indeed, based at the airport are 184 single engine, 25 multi-engine, 4 jets and 4 helicopters.
The terrain is interesting. Just west of the runway about a mile and extending to three miles is a hill that reaches about 2500 ft. The terrain from the northwest slopes down to the runway. You can stay 800 feet above the terrain from 2000 ft MSL to the runway at 2 ft MSL. This gives you visual problems flying down to runway 13. The approach to runway 31 is perfectly flat. But noise abatement rules forbid straight-in approaches to 31 in piston planes and forbid ANY approach to 31 in jets. In jets you must land on 13 and take off on 31 regardless of wind. Piston aircraft must fly a tight right base leg to 31 to avoid overflight of homes. The hill forces a right pattern for 31.
I planned a flight there today using RW. The morning weather had ground fog to 800 ft totally obscuring the airport. I wanted to do a practice landing but had to go to Buchanan (KCCR) which was free of fog. By the afternoon when I arrived after a flight from Huntsville it was very clear but the wind was blowing at 13 knots around the hill. The landing went okay but the touchdown was fast (110 KIAS) for a jet with no reverse thrust. I was bounced pretty well on approach.
The nice thing in general for this airport is that it is out of the SFO and OAK combined TCA. There is a restricted area 15 nm to the northeast for Travis AFB but that needn't interfere. I found an unobstructed direct GPS path from Pueblo, CO to the CCR VOR near Buchanan that set me up great for a low-altitude approach to KDVO. Pueblo is a good refueling airport for flights from the east. You miss all the big MOA's and restricted zones over Nevada. An alternative for non-pressurized aircraft would be to fly the southern route from Albuquerque to Palmdale and then up the San Joaquin Valley to the same CCR VOR for a turn toward KDVO.
|
|
|
Post by Tom Goodrick on Nov 13, 2008 20:44:28 GMT -5
When you fly any aircraft above 15,000 ft, make sure you have "crash with structural damage" turned OFF. The reason is that wind speeds get high and large direction shifts are common. Those will break any airplane. They are not physically possible in the atmosphere. So turning off this damage will render them inconsequencial.
Today I flew a Beech Premier from Huntsville to the San Francisco area and saw several of those large direction shifts with winds of 85 to 105 knots at 40,000 ft. I saw shifts of 40 to 150 degrees. With no structural failure possible, you just get an interesting ride for about 15 seconds.
Supposedly the Avanti gets its best speed at 31,000 ft. But it will do well at any altitude from 25,000 ft to 35,000 ft. Supposedly it has best economy near 40,000 ft. But up there you'll get runover by all the fanjets. Most common altitudes are probably from 25,000 ft to 31,000 ft. Speeds will be 350-380 knots. For this we can check the FlightAware reports. They give speed and altitude - expected and actual (but actual speeds include wind).
|
|
|
Post by Tom Goodrick on Nov 11, 2008 14:32:20 GMT -5
I have upgraded the FD for the Avanti on my web site so it reflects the changes in the new Avanti II. The package includes the aircraft, panel, new sound and new FD files. There is also a memo on flying turboprop aircraft. I posted a copy of this in the Aircraft performance, "Flying Turboprops" section of this Forum.
I have not yet updated the text on the web site.
|
|
|
Post by Tom Goodrick on Nov 11, 2008 14:26:48 GMT -5
While preparing the latest FD's for the Avanti for posting, I wrote up this memo as a brief reminder of the things that make flying turboprops different from flying piston aircraft. I will be inlcuding this in all future downloads of turboprops. FYI:
Memo on Flying Turboprops ~~~~~~~~~~~~~~~~~~~~~~
Turboprops require attention to a few details uncommon to piston planes or to fanjets. I recommend you spend enough time flying the Beech 350 King Air to become very comfortable with it before flying any other turboprop. The Beech 350 does everything well. Use it to judge the performance and characteristics of other turboprops. (Of course, I recommend you use my FD's with the 350.)
1.CONDITION LEVER The proper setting is "Low Idle" for all phases of flight. Some, like the Beech King Airs should go to "High Idle" during taxi after landing. I don't know why this is suggested unless it is to clear some fumes from the engines. Many turboprop control sets do not have this feature. To set the condition lever properly, shut down the engines and then do the start procedure (shift-E). This will set the condition levers exactly right. If you have the TProp_Power gauge, you can use the control that would be Mixture on a piston engine to set the condition lever to as close to 40% as possible. I think 40.2% is the best you can do this way.
2. GENERATOR SWITCHES When you start the engines, you must do shift-3 to make the start/gen switcthes visible. The Shift-E procedure will not set these properly. You must set the switches to GEN after each engine is running properly. If you forget to do this, your glass panel will go dark about 2 minutes after takeoff when the batteries run out of juice. The fix at that time is shift-3 and set switches to GEN.
3. TAKEOFF TRIM AND FLAPS As a general rule, turboprops have a high wingloading and must be flown off the runway with care. Set the first notch of flaps for takeoff. Remember to retract them as the aircraft climbs through 400 ft. Trim for takeoff is also very important because the stick seldom has enough power to pull the nose up at zero trim. Use at least 8 degrees of trim. Many turboprops require 10 degrees. Try to ease the nose up and keep it at the same angle after clearing the ground.
4. HIGH POWER FOR TAKEOFF While max power can often be used with turboprop engines because they have their own automatic protection controls, takeoff power setting is a little tricky. Care must be used to keep the ITT below 800 C. This is the Inter Turbine Temperature. If this temp goes beyond 800 C for any significant amount of time, the engine must be coinsidered damaged and goes in for an expensive inspection. Usually, one pilot manages pitch for takeoff and the other works the throttles and gear while keeping an eye on the ITT gauges. Generally a throttle setting between 85% and 95% will work. To simplify single-pilot operations, you should just select 85% throttle on takeoff. This may extend the takeoff run somewhat. On a short-field takeoff, The single pilot must watch ITT after clearing the trees. Note that we use throttle settings rather than power settings because the power gauge has some lag during the takeoff run.
5. SETTING CRUISE POWER Companies that fly turboprops have many different ways of setting cruise power. The most common is fuel flow. They will have a preferred fuel flow for the type and will insist that pilots use that setting. Some use a value of ITT. The efficiency of each particular engine installation may dictate the dependence on these parameters. With the recently-invented TProp Power Gauge, you can set 80% power as a general rule for cruise regardless of altitude. Some aircraft manufacturers' marketing managers like to show specs where 85% or even 90% power is used. This shortens engine life in reality though it gives cruise numbers that compete well with the fanjets. But the folks paying the maintenance bills prefer 80%. Those who pay the fuel bills prefer to use a fuel flow which essentially limits power as well.
6. SETTING RPM Not all turboprops give the pilot RPM control. This may be fixed or set by the engine computer. In general the max RPM setting is used in all phases of flight. For some aircraft RPM can be reduced about 200 during cruise. The throttle can be adjusted to maintain a desired power value. The point is to reduce the cabin noise level. This was a common practice in Beech King Airs until recently. Beech has experiemented with various ways of active and passive noise cancellation. Currently they use tuning forks as vibration dampers in the wall panels. These are optimized for 1700 RPM so that is the value that should be set. This is often the max RPM. In FS the sound files do not always reflect the proper sensitivity to RPM so this adjustment may not be noticeable. If in doubt, leave the setting at max RPM and don't worry about it. In the Piper Meridian, a single-engine turboprop intended for the owner-pilot, they removed the prop lever and set the engine to maintain 2000 RPM at all times when the throttle is advanced. There is no condition lever either so the pilot only has one lever - the throttle.
7. POWER FOR DESCENT Engine bleed air is used to create cabin air pressure. Abrupt changes in power setting will be felt by the passengers. Thus part of the pilot's technique is to monitor the cabin air pressure while reducing power for descent. All my turboprops have a cabin altitude gauge which should be glanced at. You will see excursions but should try to keep them low to moderate. The first reduction is usually from 80% throttle to 50%. When the cabin altitude starts to descend, reduce power further, as to 30%. The normal descent rate is -1500 fpm but as much as -2000 fpm can be used. Various methods for descent management can be used in a turboprop. If the air is perfectly smooth, you can hold crusie KIAS most of the way down. But this is seldom advisable because of turbulence at lower levels. Unlike in piston aircraft, the engines will not be damaged by going to flight idle in a turboprop. But the ears of everyone on board will hurt a bit as cabin pressure builds quickly. The FAA speed limit of 250 KIAS below 10,000 ft is often the limit used in any jet under 10,000 ft. It is close to the VMO limit of many turboprops. Combine this with idle power and the final descent can be quite steep. You can even make this steeper by going to negaive prop pitch. This is very dangerous and will be discussed separately.
8. FINAL APPROACH AND LANDING Turboprops require more power on final than most piston aircraft. Carry at least 30% throttle on final and increase this as you go to full flaps to 35% or even 40%. Don't hesitate to increase throttle to arrest a high descent rate. But you will notice considerable lag when trying to get power back down. Thus, it is best to know the right power to set on final and use it consistently. You must hold this 30% level of power until starting the flare. Then you can cut power and prepare to push into reverse thrust once the nose wheel is down. This is where I find the keys (F1, F2, F3, F4) very helpful in throttle control. As I get ready to flare, I hit F1 to cut to idle power. Then I get my finger on F2 and push it as soon as I lower the nose so the props go into reverse. Hit F1 again when the speed goes below 50 KIAS and use wheel brakes until slow enough to turn off the runway.
Your airspeed on final should be at least 110 KIAS. Some aircraft like the Avanti require a little more - up to 130 KIAS though touchdown speeds are as low as 105 KIAS with the Avanti. The documentation should indicate what Vref to use.
9. BETA POWER APPROACHES In many aircraft, this practice is outlawed. But where it is permitted, it can be very useful for getting into place that would otherwise be impossible. A certain airport in the French Alps comes to mind (Courcheval). The procedure is to apply negative thrust while lowering the nose to maintain airspeed and then flare over the runway. With airspeed kept well above stall, you can keep the engiines in reverse thrust until stopped on the runway. If you try to get out of reverse thrust to use normal thrust after levelling off, you just extend the lending considerably, defeating the purpose.
To make an extremely steep approach into a short runway, set up a normal approach but aim a little high. At about 200 ft above the runway, go to idle and then pull the throttle back into the "Beta" or negative region. Keep your eyeballs on the airspeed and then runway. Adjust power as needed to fly the desired path and adjust pitch to keep the speed high enough for safety. You will watch the ground come up quickly. Do not flare too early or too late. Obviously, this is very dangerous. You can reduce the thrust back toward idle but don't get into normal thrust. Flare and touch with a good thump. Then you'll stop quickly. Be sure to cut power as the airspeed drops below 50 KIAS to avoid injesting objects into the engines. The props will blow dust and debris ahead of you.
There are many ski airports in the Alps where this technique is helpful. I have flown the Beech 350 into and out of most of those as well as many challenging airports in other areas of Europe such as the fjords of Norway.
Tom Goodrick
|
|