AVSIM Commercial FSX Aircraft Review

Lear 20 Series

Product Information

Publishers:  Xtreme Prototypes

Description: Commercial add on Aircraft, Learjet Models 24, 25 and 28.

Download Size:
133 MB

Download & CD
Simulation Type:
FSX; SP2, Accel or FSX Gold Edition
Reviewed by: Proflig8tor - AVSIM Contributing Reviewer - April 2, 2010


The 20 Series Learjets are icons of high performance, status and pure sex appeal. Those who owned them were cooler than anyone else and those who flew them were envied by their peers. A friend of mine recently had an early Lear 20 Series pass through his ownership. Among the people it had carried were Frank Sinatra, Paul McCartney, Clay Lacy, Dean Martin and Elvis, who borrowed the jet to marry Priscilla Presley in Vegas. Some of the stories that old airframe could tell.

The Learjets were not the first light jets, nor were they the “best” if someone were to measure them by objective load carrying ability, comfort, or range. What the Learjets had was raw performance in a simple and relatively inexpensive package. Driven by two diminutive but powerful General Electric CJ610 engines the lightweight, yet very strong, airframe was a screamer. The limited internal volume offered by the thin wings resulted in the need for tip tanks to hold fuel to feed the thirsty engines. Limited by their knowledge of transonic aerodynamics Bill Lear, Gordon Israel, Hans Studer and Don Grommesh made the jet sharp edged and sleek. The result was an airplane which looked like a personal jet fighter and it performed like one.

The early Learjets had the power to operate in the high transonic speed range, but lacked the aerodynamics to operate there. Transonic airflow separation over the wing and fuselage would lead to loss of control and in flight breakup of the structure. As a result the maximum Mach speed of the jets is limited to .82 above 30,000 feet. Further, to operate at a speed above Mach .74 (or .78 depending on the model), required use of the autopilot, which has a “stick puller” which will put the aircraft into a climb to avoid speeds above Mach 0.82. Loss of control at high altitude and high airspeeds resulted in a few accidents. This report from the National Transportation Safety Board outlines one such loss.

Still, Mach .78 to .80 was plenty fast for its time and business jets did not go much faster than this until supercritical wings were designed and put into use.

The straight, single spool engines were efficient at two settings, idle and at full power. If held to low altitude the aircraft’s endurance was very limited. Although there is not a history of losses due to fuel exhaustion, friends who flew these airplanes all tell stories about having to make unplanned diversions for fuel and recall instances where fuel was a concern as a result of air traffic control holding the aircraft down to lower altitudes.

With excess power and light weight, the airplane climbed very rapidly and is operated most efficiently at a service ceiling of 45,000 feet. (Even today with much more modern engines and aerodynamics very few airplanes operate above 41,000 feet – allowing airplanes that operate here the ability to usually enjoy direct routing from Air Traffic Control and unrestricted cruise speeds) Later, at the pinnacle of the type’s evolution, the Lear 28 was certified up to 51,000 feet and was used by Astronaut Neil Armstrong to set time to climb records, then subsequently flown by other owners to best even those records. As a result, high altitudes above where even jetliners of the day could climb became known as “Learjet Country.”

Early Learjets sold well and are still in operation today, outliving many of their competitors. However an outcome of increasingly tight noise restrictions, mandates for more accurate avionics and autopilots to use our increasingly crowded airspace, as well as the availability of more modern airframes and engines, means fewer and fewer 20 series Learjets are in use these days. But, the ones still flying are as fast as they ever were and continue to get admiring glances from across the ramp.

Installation and Documentation

Purchase Cost & Availability – Currently a reasonable $39.99 from Extreme Prototypes available by download any CD ROM.

Installation – The installation downloads a 133MB file. Users of MS VISTA and Windows 7 (those with user account controls) will want to ensure they right click on the installation file and “Run as Administrator.” Then typing in your registration key provided with purchase completes your install and has you running in minutes.

You’ll find two Learjet Model 24’s, two Model 25’s and two Model 28’s are included in the package. The specific subtype is not referenced, which is disappointing given the attention to detail found elsewhere in this package. The Lear 24 and B sub type had 2,850 lb thrust engines while the later models and most Lear 25 had slightly more powerful 2,950 lb thrust engines. The Lear 24E and F models had a different, “Century III Series” wing. So it would be fun knowing whether the model is an A, B, C, D, E or F version. The models are probably a 24E, a 25C and a 28.

Some users have complained they would have liked to have seen a Learjet 23 included in the package from Xtreme Prototypes. The Learjet 23 was a substantially different airplane than the 24, with a much different cabin window that would be difficult to design and which would take a toll on frame rates. More importantly, the Lear 23 is a much different airplane systems wise, having been designed to avoid the stringent regulations which would have certified it for use for hire.

It was mostly a “personal” jet which lacked the electrical redundancy, avionics and some of the more docile flight characteristics of the later models. Since most operators were using two pilots anyway, it made sense for Bill Lear to expand and grow his concept beyond a single pilot jet restricted to operations below 12,500 pounds. What we get are the 24 Series Learjets and their derivatives prior to the introduction of Garrett 731 Fan Jet power and loss of performance.

Getting the Learjet 28 is a treat. It was a higher performance aircraft and much more useful than the original Lear 23. If you are an Air Hauler fan, you want the 28 anyway. The supercritical winglets compliment the aircraft’s lines and make the airplane appear thoroughly modern.

Documentation – The package comes with a nice 84 page manual with versions in both French and English. It includes an enjoyable review of Bill Lear’s interesting history as an entrepreneur and the details about the aircraft he built. It then gives a simplified overview of systems, detailed panel descriptions and instructions, flight planning, and normal and abnormal procedures sections. The included documentation is kept on a level which allows the more casual user to get a basic understanding of the airplane and is well illustrated with screen captures which easily remove ambiguities.

In the interest of simplicity, some of the key differences between the Lear 24, 25 and 28 are missed. I’d like to see the Lear 28’s spectacular 51,000 foot ceiling inserted and its fuel panel corrected, but most users will not notice these omissions. The simplified performance and planning section gives just about the perfect amount of information to be useful, but not overwhelming.

A simple one page reference card was also thoughtfully included in the documentation. For those of us with a lot of flight time and familiarity with similar aircraft, this reference card is all we are looking for to get flying right away.

Aircraft Model & Paint

The Xtreme Prototypes Lear 20 Series jets are modeled very well, with a sense that things are well proportioned to scale. Complex curves, like the supercritical winglets on the Model 28 are elegant. The aircraft are pleasing to look at and there are lots of details here. The interiors are model correct, which is important given the changes between the models 24 and 25 were to accommodate additional seating. It is also an indication of their level of modeling that they got the aileron servo tabs, control linkages, static wicks and attachment fittings spot on perfect. This is one of those models that you like more and more as you spend time with it.

The cabin windows, interior and cockpit are particularly satisfying when viewed from the exterior, with the windows showing nice depth and the highly polished lower windshield reveal panel reflecting the passing scenery. The exterior is bump mapped and thankfully they were conservative with the effect. I’ve forgotten the exact layout of the 20 Series Fuselage skins, but this model certainly looks correct. Contrails are modeled at altitude, as is lens flare. The whole package works well in FSX, Direct X 10, with no orphan parts, lights unattached from the airframe or any of the other gremlins we occasionally have seen.

These days Lear 20’s are often used at night in the real world, as their rock star clientele keep odd schedules and the rest of the fleet carries high priority cargo until the early hours. Using this product after dark left me a little disappointed. It appears the landing lights and navigation lights were modeled into the tanks but they do not appear at some angles and do not reflect from the ground. Another nice touch would have been to model the wing inspection (aka “ice lights”) since these would highlight the beautiful wing and in practice pilots use these to illuminate the airframe for external inspections at night.

It also would be nice to see modeling of airframe icing. While per the checklist I kept the windshield heat on, some modelers have started including trace amounts of airframe ice even with the de-icing systems on. This is a realistic effect and would have been a nice touch on an aircraft which operates in all weather to accomplish its demanding missions. Also, some producers are really doing nice lighting effects with 3D gauges, with needles getting brighter as they get closer to the bulb and very perceptible depth which is emphasized at night. Unfortunately the cockpit lighting in this application nearly completely masks that there are 3D gauges in this model. Somebody obviously put a great deal of work into this virtual cockpit, but the lighting hides their efforts.

Balancing out these minor quibbles is the terrific way they modeled the cockpit and interior lighting from the external views. The model also includes low speed vortices, high altitude contrails, engine smoke and fire effects.

The paint is good, but rather conservative for the type. The quality of this external model just begs for repaints, from wild to historical.

Note bump mapping and interior detail around windows   Engine Fire on #2, bottles armed

Flight Model

The flight model is good, with accurate roll and pitch response for the 20 Series Learjet. The aircraft is easy to fly and land, although ground handling may be difficult for those not used to using a little differential power and braking. Remembering to switch on the nose wheel steering obviously helps.

The aircraft is stable on approach and landings are easy to judge. The autopilot will hold the aircraft on pitch and heading up to 4X acceleration. Above 4X the pitch becomes increasingly divergent with speed.

Two areas of the flight model worked out particularly nice. One is the ability to load the aircraft very accurately and the single engine flight characteristics. The airplane is a realistic hand full while executing a single engine missed approach.

Test System

Intel E6600 Clocked to 3.0Ghz
4Gb linked & sync’d at 667Mhz, 1333 FSB
EVGA NForce 680i
Single GeForce 8800 GTS
Microsoft Vista SP1
Flight Simulator FSX + Accel

Flying Time:
40 hours

Observed Frame Rates:
Average 15 to 17 FPS in dense scenery, over 20 at altitude with weather and scenery effects turned up very high.

Brakes and spoilers are realistic in their operation and effect. I like the subtle pitch change with speed brake deployment. The engines’ spool up time at low level is spot on accurate. It seems to be a problem with FSX that engines remain equally responsive at high altitude. (In reality, very basic early jet engines like these GE610’s require tweaking to avoid exceeding temperature limits and are slower to respond at the high edge of their flight envelope. In the early models, the GE610 was only expected to run 800 hours in between overhauls and careful monitoring of temperature limits was absolutely essential. In later models the number went as high as 5,000 hours.)

The Learjet has a realistic, easy to use, Flight Director which should be used on every flight. This airplane flies nicely at altitude, but most users will use the autopilot in cruise and while setting up for approach. The flight director / autopilot will track a heading, or whatever is tuned in NAV 1, whether an VOR, or ILS with Glideslope is tuned. As a result of the aircraft’s speed, it travels from one VOR to the next quite rapidly resulting in a lot of tuning and twisting. Most modern pilots would link the jet to the GPS, but the Xtreme Prototypes folks did not install a switch to tie the GPS to the Course Needle in the Horizontal Situation Indicator. Worse, the black on black theme of the knobs on the VOR tuning head make it a little fussy to tune since it is difficult to tell if your mouse is on the inner, or outer, knob. The approach function of the autopilot is very basic and like an old rate based system, does not seem to be quite able to keep up with the control inputs needed to fly an ILS to minimums. At best, this system is one you want to have off before 1,000 feet AGL and three miles from the point of intended touch down.

The pitch trim is not completely accurate, which is in my opinion a good thing since having correct pitch trim is absolutely required to achieve rotation in the real Lear 20 Series and requires constant adjustment over the aircraft’s speed range. A nice compromise was made.

A more serious concern about the airplane’s flight model is that parasitic drag seems to be modeled much higher than your reviewer believes could be possible in the real Lear 20 Series. Most modern jets will descend clean at idle indicating 250 knots between 1,200 and 1,800 feet per minute. Anything more than a 4 to 4 ½ degree descent usually requires adding drag. When slowing in level flight usually one mile is needed for every 10 knots (with airplanes like the 737 and 757 with winglets being even slicker than this).

The Xtreme Prototypes Learjet seems to slow entirely too fast (loss of 50 knots in 2 to 3 miles) and idle descents at 4,500 + feet per minute. (This high drag profile extends to the Lear 28, which back in the day was promoted as the lowest drag airframe of its type ever created. The winglets were allegedly responsible for a 20% decrease in induced drag, but realistically they must have gotten the decimal in the wrong place. Winglets usually reduce fuel burns by only 2% to 6% in practice) This high drag profile does make the model easy to fly, but it does not seem realistic. I hesitate to criticize any designer’s work since they have spent many more hours in its creation than I spend working up a review, but still the drag profile of this model seems high based on experience with similar aircraft.

Another concern is the modeling of the Engine Pressure Ratio, which is simply the ratio of the pressure at the jet pipe compared to the pressure sensed at the first stage compressor. In this model the cockpit indication is very low. In more modern aircraft EPR has become less relied on and most power settings are based on N1 (in this case shaft rotation speed). Since the EPR gauge was unreliable, most users will transition to N1 to learn the power settings that work for flying the Lear. Also, the hydraulic system and pneumatics appear to have been simplified, as there are no temperature changes with anti ice use, or hydraulic pressure bumps with aircraft configuration changes.

None of the transonic effects of the airplane are modeled, nor are the auto pilot’s stick puller, or pusher. Like just about all FSX models, the sim simply stops and states the aircraft has been overstressed.

Quick comparison with default Lear 45 Exterior Lighting Extreme Prototypes Learjets
Stalls are easy to recover from, animating the AOA probe would be a neat addition 51,000 – Learjet Country Nice Office

Virtual Cockpit and Systems

The Xtreme Protypes Lear 20 Series uses only a Virtual Cockpit. Thankfully, the Virtual Cockpit is well laid out, nicely to scale and very simple to use. The throttles are particularly well shaped. Clicking on the opposite side yoke will remove the onside yoke, allowing an unrestricted view of the forward panel.

The Lear 24 and later models were Certified to Part 25 of the Federal Aviation Regulations, meaning there are systems which provide electrical, hydraulic, flight control and fuel system redundancies. In addition, the aircraft has dual loop fire / overheat sensing, fire switches to isolate the engines and extinguishing ability. Most systems are monitored via a Master Annunciator / Crew Alerting Panel across the glare shield. Once the engines are running and providing plenty of electrical power, one simplified way to ensure you are prepared for take off is to review the Annunciator panel and confirm the warning lights are extinguished. The system monitors pitch trim with its own warning light, although the flight model is forgiving enough, resulting in the aircraft being easy to handle, even out of trim for take off.

Some of the systems are modeled with a high degree of accuracy. For instance, you have to have the bleed air valves switched open to use the aircraft’s de-ice systems which rely on bleed air heat. The wing temperature indicator then functions very convincingly. Other systems seem less so, like the aforementioned engine EPR indications and the hydraulic system, which never indicates anything but normal pressure and whose electric aux pump appears to draw no current. The fuel panel in the Lear 28 and 29 was different from the earlier models due to the deletion of the tip tanks, but that distinction is missing here.

The developer makes a point of their work to create a fully 3D gauge cockpit, but a user really has to look close to tell that this is not the old refresh rate eating 2D indicators. There is little depth, or variation in lighting to show off the designer’s work. In fact, without the cockpit lights on, it is a dark and nearly illegible place.

The cockpit textures are more basic than many add ons provide these days. I happen to prefer this “well kept” look, while others prefer “well worn.” The designer states that their goal was to create an aircraft which is simple, enjoyable, and well suited for a single pilot’s operation. Xtreme Protoypes has achieved that goal.


In light of what some producers have created very recently, the sound files for this airplane were a bit of a let down. The interior sounds are better than the exterior sound files, with an almost perfect blend of wind noise which is much more prominent in this airplane.

FSX allows a lot of creativity and some add-on aircraft have very distinct sounds allowing the user to distinguish the high pitched whine of the compressor at the front of the engine, low pitched rumble of the exhaust gasses, the hiss of hydraulics and the clanks and thumps that provide feedback on what the airplanes systems are doing. Even some older FS9 add-ons have much better sound files. (To this day I’m amazed at how the “grrr” of the brushes in the auto throttle servos provided great feedback on what Leonardo’s Mad Dog (MD 80 sim) was doing. Another example of an outstanding sound file is Lotus Sim’s L39.)

It is unfortunate this product isn’t in the same league as those because the little straight pipe GE610 engines are a big part of the Lear 20 Series’ personality.

Summary / Closing Remarks

Xtreme Prototypes has produced a most pleasing add-on Lear 20 Series jet. It isn’t hyper realistic, or overly complicated and Flight Safety ground instructors probably will not be using it for systems demonstrations. The design is a compromise that will be easy for new users to enjoy and has sufficient detail that more experienced users will not find it boring, or toy like.

The Xtreme Prototypes has a pleasant flight model that wouldn’t be a threat to those who would want to use this with Air Hauler. (Xtreme Prototypes Lear 28 has become my default jet for that application) It is reasonably efficient and will not be too great a drag on users with computers having average performance.

Our readers seem to like our comments about what works and what doesn’t work and we try to meet their expectations with our experience and a lot of research. What we sometimes fail to adequately convey is what we think is fun. The Xtreme Protoypes Lear 20 Series is a lot of fun. We hope you have the opportunity to enjoy it.


What I Like About The Lear 20 Series

  • Well modeled aircraft, beautiful to look at
  • An interesting jet which is a lot of fun to fly
  • Simple to operate (as it is in real life)
  • User friendly flight model
  • Reasonably priced


What I Don't Like About The Lear 20 Series

  • 3D Instrumentation could have been better executed to show off the designer’s work
  • The autopilot should be linked to the GPS to facilitate easier enroute navigation.
  • Exterior lighting is sufficient, but there is room for tweaking
  • The sound file could be improved to bring the character of the GE610’s into the model
  • Not convinced the flight model correctly reflects engine performance, or airframe drag



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The review above is a subjective assessment of the product by the author. There is no connection between the product producer and the reviewer, and we feel this review is unbiased and truly reflects the performance of the product in the simming environment as experienced by the reviewer. This disclaimer is posted here in order to provide you with background information on the reviewer and any presumed connections that may exist between him/her and the contributing party.

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