• Review: Classic GLJ Model 25 Special Edition


    Chase

    A review by Ray Marshall.

    This is a review of the recently introduced Xtreme Prototypes’ Classic GLJ Model 25 Special Edition aircraft add on for FSX and P3D.  This is a significant step forward in providing an affordable, but yet sufficiently complex model of one of the many classic LearJets.

    I know, I know – why don’t the developers get away from the round dial old stuff and give us a Lear 60XR with a fully integrated ProLine 21 system?  That one is indeed in work and will, most likely be available by a different developer in the next couple of years or so, maybe sooner.

    Meanwhile, we now have an up-to-date, high performance, high definition, highly accurate representation of a classic early LearJet designed for our modern PC and video cards for both FSX and P3D. This one breaks new ground in advancement and efficiency because it is an all new design specifically intended for new high end PCs using the most up-to-date version of FSX:SE and Lockheed Martin’s P3D v2-3.  It is not perfect but any glitches or limitations are prominently discussed in the 160 page Flying Manual with suggestions for workarounds and hints on how to avoid any limitations of the simulators.

    Other than being thoroughly modern, one of the most requested features for FSX/P3D add ons nowadays is included – the ability to place your Flight1 GTN 650/750 combo in the HD VC panel.  Not only the F1 GTN but you can also have your working REX/Milviz Advantage weather radar.  Not only is this feature available, it is super simple to accomplish and even easier to switch to alternate avionics such as the large EICAS panel from the default Lear45 or most any other payware gauge that will physically fit in the designated area.

    Some of the animations only work either in the Lockheed Martin P3D edition or FSX, but, the performance and pleasure of flying a high performance classic Learjet with 3d gauges in an ultra HD virtual cockpit using our latest 3rd party avionics is outstanding.  

    Exactly which specific model is this Classic Learjet?

    We all know the LearJet has gone through several iterations by 3 primary aircraft companies.  Sure, there were some additional company names involved, but we can narrow it down to Bill Lear’s Lear Jet, Charlie Gates’ Learjet, and Bombardier’s Learjet designs.

    Xtreme Prototypes’ hybrid model – the Classic GLJ Model 25 Special Edition – is based on one of the last true or original Lear Jet designs at the start of the Gates Learjet tenure.  XP’s GLJ 25 was ‘inspired’, according to the manual, by the Model 25D with a few real world options added, such as the Dee Howard thrust reversers, Century III wing with SoftFlite Boundary Layers and some more recent additions such as the availability to add some of our 3rd party avionics to the VC panel such as the popular Flight1 GTN 650/750 combo or one of the newer weather radars.  You can also add EICAS gauges from the Lear 45 FSX/P3D default model.

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    Panel space is naturally very limited in a classic Learjet, but an improved and very nifty one-click rotating choice of three gauge clusters is available. This method was first used by Lionheart Creations in their Lear 24B add on and makes great use of the limited panel space.

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    The Learjet 25D was first built in the mid-1970s but is still flying today.

    The real world Model 25D was in production from 1976 to 1982, long after Bill Lear had moved on to other things, but was, in fact, just one of the many variations of the Model 25 that was a true Bill Lear design.  The Model 25 was introduced just prior to Gates taking over the majority ownership of Lear Jet in late 1966. Of course, the Model 25 was an improvement of the Model 24 that had replaced the original Model 23 – the one that started it all.

    There were several Model 25 Learjets starting with the basic or original Model 25 that was introduced as the Stretched or Long Range Learjet.  A bit of a misnomer, the Long Range should be taken with a grain of salt.  You can only carry so much fuel and still have room for a few passengers. With literally a thousand gallons of jet fuel, you will not be able to fly 2,000 nm at anything other than at a reduced economy cruise setting.

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    The GE CJ610-8A engines came directly from the military inventory.  They are practically identical to the engines in the supersonic T-38A Air Force jet that the Thunderbirds flew for years, except the civilian version does not have the afterburner.

    But, the good news is that you will be flying one of the fastest civilian airplanes in the sky.  If you happen to be overtaken at normal cruise, which could be at 51,000 feet, it will be one of the Gulfstreams or a Citation X or another Learjet. (the Learjet 25D was certified for FL510)

    Gates did not make any significant changes to the Model 25D because it was near the end of the design cycle for the highly inefficient fuel-guzzling GE turbojet engines and the short wings with the huge tip-tanks to carry the necessary fuel.  Back in the real early days, fuel efficiency wasn’t a big concern mainly because jet fuel only cost 18 – 20 cents a gallon. True!  Neither was long range endurance – it was pure speed and the ability to get over the weather that moved corporate aviation to the jets.

    The Gates Rubber Company purchased all of Bill Lear’s interest for about $28 million in early 1967.  A Denver based subsidiary Gates Aviation, was already a major Lear Jet distributor so they already knew a lot about airplanes and specifically the Learjet. Mr. Gates took over as President and COO of Lear Jet and Bill Lear stayed on for a year or so as Chairman but wasn’t involved in the Lear Jet project or day to day operations.

    The day to day operations went to Harry Combs for several years as Gates gained momentum and established their sales strategy to promote the ‘new’ Gates Learjet.  Photo:  Charlie Gates on left, Harry Combs on the right.

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    Gates was able to immediately improve the financial stability of Lear Jet and brought in their kind of proven management controls and marketing savvy that had generated profitable and dynamic growth of their parent company – Gates Rubber – for the last 55 years.

    Some of the milestones credited to Gates’ leadership was actually accomplished prior to the Gates takeover.  For instance, Gates supposedly upgraded all the production models to FAR 25, Transport Category certification level aircraft, while in fact the Model 24/24A aircraft were certified as Part 25 aircraft 8 months prior to any Gates involvement and the Model 25 was already in the approval process.

    The Gates’ team was concentrating on designs to replace these General Electric turbojet engines with the much more fuel efficient Honeywell turbofan engines and designing new supercritical wings with winglets rather than wingtip fuel tanks.  The future of corporate jet travel was going to require more seats, more efficient engines, and decent cabin headroom.  They already knew how to build jets that would fly faster and higher than the competition, now they needed to increase the number of seats, expand the cabin width and height, add some small things like toilets and food service, and extend the endurance with larger and more efficient engines.

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    Due to the many buyouts, mergers and takeovers, Garrett engines may be referred using the original name – Garrett AiResearch, or AlliedSignal, or Honeywell.  I tend you use the Honeywell name for the engines.

    It is almost always mentioned the reason for the push to abandon the GE 610 turbojet engines was the spiraling cost of jet fuel and the fact that just about every ounce of efficiency had already been squeezed out in the many upgrades and modifications since the first Lear 23 flew with the 610-1 version.  These two important reasons are near the top of the priority list, but the fact that most everyone was convinced that taming the noise levels of this military adapted gas guzzling high performance turbojet engine was going to be near impossible. 

    As those folks that built or bought homes near the new airports and then discovered just how loud these little Pocket Rocket Learjets could be as their dishes rattled and windows vibrated they pressed for more and more stringent noise controls.

    Gates thought a replacement for these late model 20 series jets should be fairly straight forward and they managed a great replacement with the introduction of the Gates Learjet Model 35.  It took a year or more to realize they really needed an updated Model 35A and an extended range Model 36A. But first, they needed to stop the bleeding and improve the cash flow at their newly acquired Learjet factory.

    The very first change was to replace the laid-back free-wheeling style of management with more professionalism for the sales team.  No more barrel rolls by the demo pilots, no more geographic sales regions within countries, no more price cutting or undercutting sales prices by competing salesmen. 

    The pitch would be to corporate American and the world that the new Learjet was a safe and efficient means of doing business.  New safety features were high on the priority list like the Century III wing design with SoftFlite to improve the low speed handling characteristics to appeal more to the general aviation corporate pilots and less to the ex-military trained corporate pilots.

    Every conversation stressed the Learjet’s FAR 25, Transport Category certification, the very same certification level as a Boeing 747.

    How to Identify the Model 25D Learjet.

    It is fairly easy to narrow down the identity of a Learjet with 3 or more small fuselage windows with large wingtip fuel tanks.  Unfortunately, this is not quite sufficient but, will eliminate the earlier Model 23 (large oval window) and the Model 24 (2 windows) and all the more recent follow-on models with winglets in lieu of the large wingtip tanks, except the Models 35/36 that are easily confused with the Model 25D.  The Models 35/36 and all the winglet models have much larger engines cowlings and a slightly longer fuselage than the Model 25D.

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    Almost all Learjet models have one less fuselage window on the left side because the cabin door does not have a window as opposed to practically all Cessna Citations that do have a window centered on the door.

    Of all the models that you are likely to see in the skies that have the large wingtip fuel tanks the most numerous in descending order are:

    • Learjet Model 35/36 – 677 total built (including 80 USAF C-21A)
    • Learjet Model 24/25 – 521 total built
    • Learjet Model 23 – 32 total built

    All the more recent models with larger wing area with winglets, longer and/or larger fuselages and larger diameter engines are:

    • Learjet Model 60 – 323 + built (in production
    • Learjet Model 45 – 300 + built (in production)
    • Learjet Model 31 – 221 total built
    • Learjet Model 40 – 90 + built (in production)
    • Learjet Model 70/75 – 75 total built (in production)

    The grand total as of a few years ago was 2,330 Learjets of all models by all LearJet companies.  This pales in total numbers when compared to the Cessna Citation family of business jets that is more than 6,000 and counting. Embraer is the latest manufacturer entering the business jet market with the Phenom and Legacy lines of business jets.  The Phenom 300 is marketed as direct competition of the smaller Bombardier Learjets and Citation CJ3/CJ4.

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    Before we get into the specifics of our Xtreme Prototypes’s simulated GLJ 25 SE model, I would like to tell you the story, very abbreviated of course, of the trials and tribulations of designing a replacement for the Model 25.  There were only a handful of 20 series models after the 25D.  There was never a 25E model, but there was a 25F that was grouped in with the 25D production numbers.  The 25G was introduced in late 1980 mainly to set or break some speed records for publicity. Lear never used an ‘A’ designator for any production Model 25, only on the Model 24.

    Other than a few improvements in avionics, tires, adding anti-skid brakes, and fuel dump valves in the tip tanks, and introducing single point refueling, most of the later model 20 series Learjets were simply trading passenger seats for larger fuel tanks or vice versa.

    Photos:  Original Model 23 (at Smithsonian) on left, yet to be built Model 85 on right. Both look like Learjets.

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    The Model 28 and 29 Lears were test beds for adding winglets and testing early version of the eventual Garrett AiResearch fanjet engines that were first used for the Model 35 and 55 Longhorn.  One of Gates priorities was to improve the low speed handling of the Learjet while keeping the top end speed somewhere in the low Mach 80s.

    The Model 25G received a thicker wing section where the wing joins the fuselage.  A new cuff was designed to accelerate the air movement in this area that smoothed the flow between the engine nacelle and the wings trailing edge.  This has always been a choke point, restricting airflow and creating drag at high speed.  So effective is this thicker wing cuff that the 25G can cruise at 0.81 Mach on the same fuel flow as the 25D cruising at 0.78 Mach.  A side benefit was the thicker wing section adds 15 square feet of wing area and allows for 81 more gallons of fuel.  In addition to the speed efficiency the 25G gained 370 nm in range compared to the normal 25D.

    The first modification to the original Learjet wing came in 1970 when the tip tanks were realigned.  The original tips were aligned with the longitudinal axis.  In cruise flight the Learjet flies at about a three-degrees nose-up angle so the engineers lowered the nose of the tip tanks three degrees.  In normal cruise, the tip tanks are streamlined with the airflow, reducing drag, even though the tanks appear to droop when the plane in parked on the ramp.

    Here is a photo of a Model 25 test plane with a Garrett fanjet on the right and a standard GE CJ610-6 turbojet of the left side.  If there was to be a Model 26, it would have most likely been powered by Garrett fanjet engines.

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    The Century III wing modification alone lowered the final approach speed by an astounding 15% without any loss of cruise speed while reducing the landing distance by nearly 1,000 feet for the new Model 35.  The vortex generators, those rows of little metal tabs, and small fences were replaced with newly designed cuffs for the wingtip fins and Boundary Layer Energizers, BLEs. Small stall strips were place on the leading edge with a newly designed stall fence.

    This Century III wing enhancement was introduced by Gates in 1976 for the new Model 35, but we also got the benefit because the Model 25D was a concurrent production airplane in the late 1970s. The original model 25 wing had a fairly sharp leading edge designed for high-speed cruise.  This Century III modification formed a constant radius curve that significantly lowered the stall speed of the Lear 25D but just as important, it cut the rotation speed by 14 knots and shortened the takeoff runway requirement by more than a 1,000 feet.  Approach reference speed was cut by 12 knots and the landing runway requirement was reduced by more than 800 feet.  Pretty heady stuff, this Century III wing mod.

    This Century III wing did not alter the Learjet’s tendency to roll off sharply during a stall. To correct for the wing drop, in 1979 Gates introduced another improvement call Softflite.  This added a stall strip and full-chord wing fence to create an aerodynamic warning and a straight-ahead stall.  The Softflite wing has boundary layer energizers in place of the vortex generators that were mounted ahead of the ailerons on the original Learjet wing. These boundary layer energizers are small spanwise ridges on the upper wing surface just ahead of the aileron.  At high cruise speeds, they delay the onset of turbulent flow over the ailerons more effectively than the vortex generators and create less drag.  This doesn’t raise the cruise speed Mach limits but does provide a greater safety margin in turbulence or when maneuvering at high speeds.

    Our GLJ 25SE flight model does indeed have the updated BLEs instead of the older vortex generators.  I was not able to tell for sure if the Century III wing mod was designed into our model, but the VR, VREF and runway requirements should tell the story.

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    I would like to recount the history of the General Electric CJ610 engine used in all the 20 series Learjet models, including our GLJ 25SE and hopefully get back to the story of how the original Garrett AiResearch TFE731 engine came to be. Both stories are somewhat amazing to me.  Even more interesting might be why the Model 35 and 36 have that funny shaped 2-foot wing extension and why the plane is a foot or so longer than planned.

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    The Garrett engines were designed to be fuel efficient, and quiet enough to meet present and future airport noise rules.  The original design guideline was to increase thrust over the GE turbojets just enough to make sure the new model was at least as fast as the Model 25 that it was to replace.  There were no plans to increase the length or height of the small tube fuselage so this Model 35 would not be in competition with the future 40 and 50 series’ enlarged fuselage models.

    Evidently this was sound planning because at the end of production, the 30 series, small fuselage, Garrett powered models accounted to just shy of a thousand airplanes delivered to happy Learjet customers.

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    While writing this review, I got sidetracked with some new introductions to some of my older stuff that I had written reviews a couple of years ago.  I now have these items properly introduced and scheduled in my new more leisurely work schedule. 

    Just when I thought I had it all together and had a plan of action to get this review done by Christmas, along comes Black Friday week, then Cyber Monday and then all those extended deadlines.  I did manage to only buy one pair of shoes, one add-on aircraft, and commit to only three more reviews.  Just so you know the details – Timberland shoes, Flysimware Learjet 35, SPAD.next, Volair Avionics Panel, and the new Aerofly FS2 simulator.

    Now about that General Electric CJ610 turbojet engine.  Some of this research was done for the Lionheart LR24B review and the follow-on comparison of the Learjet 24B to the T-38.  You can read those reviews here and here.

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    http://www.avsim.com/index.php/_/reviews/aircraft/review-learjet-24b-by-lionheart-creations-ltd-r2543

    http://www.avsim.com/index.php/_/reviews/aircraft/review-a-comparison-of-2-jets-r2567

    OK. I am getting a little lazy in my old age so I am going to paste the GE engine history here in lieu of typing it from scratch.  Here are some excerpts from the book ‘The History of North American Small Gas Turbine Aircraft Engines, written by Richard A. Leyes and William A. Fleming, available for purchase at Google Books.

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    This graphic show how different, yet how similar the full line of Learjets are from the first Model 23 to the most popular of the modern large cabin Model 60XR.  Our Model selected for this review is in the center.

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    To complete the design efforts that started with the somewhat simplified plan of upgrading the Model 25 with newer fuel efficient and quieter engines with a little more thrust turned into a longer, wider, more powerful new model with much improved low speed handling while retaining excellent cruise speeds at the highest flight levels allowed.  This Model 35/36 would be the last Learjet with those large wingtip fuel tanks.  The Model 31/31A would be the final adaptation of the small bore fuselage but add large delta fins at the rear for yaw control and added 4 foot extensions to each wing with 4 foot high winglets for improved efficiencies and more docile handling.  The Model 31A /ER was the long range version which added an additional 275 miles to the range. Many consider the Model 31A the best of the 30 series and even the best flying Learjet of all small fuselage models.

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    In case you just skipped over the CJ610 engine history, the highlights are that every production Model 20 series was powered by some version of the GE CJ610-1 through the CJ610-8A turbojet engine rated at 2,850 or 2,950 lbst.  The Model 25D with the -8A mods was actually a better performing engine at very high altitudes than the Garett TFE731-2 fanjets designed for the Model 35.

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    The Model 25D will climb with bursts at 8,000 fpm and will climb from Sea Level to FL430 in 13 minutes.  Neil Armstrong, the first man to walk on the moon, was a director at Learjet and set 3 climb time speed records in a Lear 28.  How about time to climb to 15,000 meters (just shy of 51,000 feet) in 12 minutes, 27 seconds?

    The Model 28 had the same fuselage and engines at the Model 25D but, totally different high aspect ratio wings, larger wing surface area and the first winglets for a production business jet.

    Photos:  Left,  Lear 28 flown by Neil Armstrong setting climb records, Middle, Photo from newspaper article with Armstrong in left seat, Right, the exact same Lear 28, s/n 28-001, flown by Armstrong on February 19 and 20, 1979 for record setting events with modern paint job and new tail number.

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    Garrett fanjet Engines for the Model 35 – a real hodgepodge of parts

    The low pressure compressor was taken from Garrett’s 660-series APU used on the 747, the high-pressure impeller is scaled from one used in the TPE 331 and T76 engines, and the turbine components are from the APU used in DC-10s. They put out 18.6 percent more thrust at sea level than the GE CJ610s used on the Model 25, and nine percent more thrust at 40,000 feet. But they consume 40 percent less fuel at takeoff thrust and 24 percent less at cruise. This combination makes the 35 and 36 much less costly to operate than a 25B or C and it will give them one of the best single engine angles of climb of any of the jets.

    And, of course, the TFE 731 meets FAR 36 noise requirements and is a much cleaner running powerplant than the GE was. The big news is that the decreased fuel consumption increases the range of the airplanes about 40 percent. On the same amount of fuel the Model 35 has a range of 2,630 nm against 1,621 for the Model 25B; the Model 36 endurance is 3,146 nm to 1,861 for the 25C.

    In addition to doing more work on less kerosene, the Garrett TFE 731s are 11 inches larger in diameter (to accommodate the 2.82 bypass-ratio fan) but, weigh almost twice as much as the engines they replace (747 pounds to 392).

    Photo:  A Gates Learjet showing enormous size of fanjet engines.

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    This increased weight is significant because the additional 710 pounds aft gave Gates’ engineers a real cg problem that precluded a simple change of engines on the Model 25, as the original plan intended. To overcome the problem, they added 13 ¼ inches to the fuselage ahead of the wings leading edge.  This puts the crew on a longer arm to help bring the cg within the envelope.  This created a little unexpected legroom in the cabin, and they even gave the crew a few more inches. The crew seats now have three inches more fore and aft travel.

    The panel has been cleaned up, regrouped and made somewhat prettier. The lower console is now wider, not double wide, but somewhat wider. This creates room for one or dual INS control heads, which are necessary in these Lears since either of them has the range to pop over to Europe and on down into Africa or the Orient.

    The engineers have effectively picked up another foot of cabin room by switching to a narrower, people-sized cabin door in place of the old cargo-width entrance. (But the cargo door is still available as an option.) This creates room for a big-airplane-type refreshment cabinet on the left side of the cabin.

    Although Lear is saying the 35 and 36 have eight- and six-passenger cabins respectively, the arrangements they’re showing are really seven and four for practical purposes. The 35 has a bench-style rear seat that will accommodate two wide bodies, or 3 very thin ones on short trips, four forward facing chairs and a side-facing potty/jump seat opposite the door.

    The 36, because the normal behind-the-aft seat baggage area was removed to make room for the larger fuselage fuel tank, has a small luggage area opposite the door under which a slide-out potty is stowed. The passenger compartment has the bench seat and two individual chairs arranged in club configuration.

    Bob Berry, Lear’s engineering test pilot and director of product assurance, says the program calls for the airplanes to have the same performance and handling characteristics of the Model 25. So, because the 35 and 36 are 2,000 pounds heavier than the 25, wing area had to be added to match the 25’s performance. This was done with a two-foot extension on each tip.

    It’s amusing to speculate on the problems this much have given the engineers. The leading edge of the standard wing sweeps back at a 13-degree angle to a straight trailing edge. Had they continued the sweep they would have run out of wing-tip chord and structure upon which to mound the tip tanks, or they would have had to move the tanks back, thus aggravating the cg problem. This explains why the extensions are constant chord. The leading edge now sweeps back to the extensions, then’ breaks forward and parallels the trailing edge.

    Moving the tip tanks out undoubtedly added inertia and so, to increase lateral control without heavying up the feel, spoilerons are now used for additional roll command.

    The company is careful to emphasize that the 35 and 36 are additions to the line and not replacements for the 24D, 25B and 25C. An acoustical kit is being developed for those earlier airplanes and they will remain in production for a little while longer.

    Credit: FROM THE OCTOBER 1973 BUSINESS & COMMERCIAL AVIATION. COPYRIGHT © 1973, THE McGRAW-HILL COMPANIES, INC. ALL RIGHTS RESERVED.

    So, in summary, it appears that Gates was going down a path of basically adding two new engines and whatever electrical, mechanical, hydraulics-wise and otherwise was required to make them work on an existing well developed airplane to move from turbojet engines to fanjet engines.  This would solve all three disadvantages of the Model 25 Learjet. The fuel inefficiency, the limited range, and the airport noise problem. 

    When designing a new engine, they could add enough thrust to overcome the additional weight required to carry more fuel in more tanks, in this case only larger fuselage tanks to make a truly intercontinental range Learjet. One big problem it would not solve is the headroom and elbow room.  But, the standup and walk around Learjet cabin would arrive at a later date with the 40 and 60 series.

    As a matter of fact, Gates announced at the Paris Air Show of 1969 what appeared to look and sound like a Model 25 with new Garrett fanjet engines.  They even had the engine model numbers and thrust level properly identified.  See this picture and article found in the June 23, 1969 edition of Aviation Week and Space Technology magazine.

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    What is not shown in the accompanying artist’s sketch is just how large those new Garrett engines would be, or the fuselage stretch, or the increased wing span with that now familiar looking two foot section added out near the tips.  When all was said and done, this “New Version of the Learjet 25” was none other than the Model 35 which first flew more than 4 years later on August 22, 1973 but, not certified for almost another year in July, 1974.  The Model 35/36 would go on to sell an astounding 738 units.  Most accounts state that 64 base model 35s were built before the Models 35A and 36A arrived with upgrades throughout but mostly increased fuel load and therefore increased endurance.

    The Model 36A is identical to the 35A with the exception of the larger fuselage fuel tank and the necessary reduction in fuselage seats and baggage area to make room for the extra fuel.  Simply put, a shorter cabin to make room for more fuel.

    So why are we talking about the Model 35/36 in a review of the Model 25D?  Mainly because the two models were designed and built alongside each other and practically all the improvements being designed for the newer, slightly larger and better selling Model 35/36 were also being applied to the Model 25 provided it was cost efficient.

    Remember, back at the time of production, the Model 25D was a full million dollars cheaper than a new Model 35.  With practically identical cabins and cockpits, a million dollars would buy a lot of jet fuel or a lot of extra goodies for the panel.  The official price of a barrel of Saudi Light crude oil was $12.37 in the mid-1970s.  In July, 2008 this same barrel of oil hit a new high of $147.27.  Today’s price is more like $50.00 a barrel.

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    The AirNav price of Jet A fuel is currently somewhere between a low of $1.99/gal and a high of $9.00/gal with an average of 3,682 FBOs nationwide of $4.11/gal.  The often mentioned price of Jet fuel in 1975 across the nation was less than 30 cents/gallon, but would go absolutely insane a few years later.  I remember Clay Lacy stating that Jet Fuel for the Learjet was 18 cents a gallon in Southern California when he was giving demo rides in the Model 23/24 in 1965.

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    I suppose you heard the current joke, Owner - “How much do you think my beautiful, well maintained Gates Learjet 25 is worth?” Salesman – “That all depends on how much fuel is in the tanks!” Sigh.

    Actually Bill Lear himself summed it up nicely.  Quote: ‘When I finally got the cabin worked out, I damn near shot myself—not enough room. It had the old Air Force engines on it. Plus, the first jets, straight jets, ate fuel like it was going out of style, and they had quite a restricted range,” This is not exactly what Bill Lear was telling his potential customers at the time, but was obvious to the new Gates team that had to pick up the pieces and move forward.

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    Aftermarket mods for the Learjet 25

    Raisbeck Engineering has made a business of designing and marketing improvement to a large range of corporate aircraft. They have their own book for the 30 series Learjets.  Some were very popular and others were just bad timing or too expensive to justify. 

    Robertson, of STOL fame, also took a crack at adding small winglets on top of the wingtip fuel tanks to try to enhance the endurance of the Model 25 along with replacing the GE CJ610 engines with PW JT15D-5 engines to add STOL capability to the already hot Model 25. The PW JT15D-5 powers the Hawker 400XP with 3,400 lbst. Only $1.1 MM for the full mod.  See cover of AW&ST, December 6, 1982.

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    March 28, 1980 - Gates Learjet flies high with its one-thousandth sale.

    Gates Learjet delivered its one-thousandth airplane – a Model 35A – in late March to Eaton Corporaion of Cleveland, Ohio.  There are more Learjets in service than any other business jet.  The largest seller is the Model 25, but more 35’s were sold in the past six years.  Flying Magazine, June 1980.  These numbers were soon eclipsed by Cessna and their Citation line of business jets.

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    One of the Learjet milestones was the delivery of the 500th Learjet, Learjet 25D on April 8, 1975 to the Mexican Navy.  The 1,500th Learjet was delivered in June, 1986.

    Talking about those small fuselage Learjets, take a look at this comparison of a Lear Model 25 fuselage diameter compared to the Learstar 600 design.  Now, that is a really small diameter fuselage. 

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    By the Numbers – Recent Learjet sales is a very weak third place behind Cessna and Embraer.

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    Fuel Burn Data. Check column 5, for the 1,000 nm comparison of the fuel burn.  It is easy to see why the turbojet was on the top of the list for replacement with fuel prices skyrocketing.

    1,000 nm fuel burn for the Model 25D is 3,920 pounds, compared to 2,530 pounds for the Model 35/36, and 2,480 for the Model 31A.  Ouch.

    Finally, the Xtreme Prototype’s Classic GLJ Model 25 SE.

    Enough of the background and similar Learjets, let look at the Learjet 25D that ‘inspired’ the Xtreme Prototype’s design team.  Just to whet your appetite, I have a few closeup screenshots to show some of the HD detail.  The thrust reverser paddles are removable with a single click so we can see the partially hidden switches.

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    The EICAS panel can be added from the default Lear45 with a couple of lines of code added to the panel.cfg file and then cycled with one click on a hot spot on the VC panel to the standard GPS or Flight1 GTN750, should you own one.  This is a very handy feature.  Just about any gauge can be added to this area with a little adjustment to the height and width of the gauge to fit the area available.

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    High Res Exterior Screenshots.

    You can find a series of great screenshots of the XP GLJ 25 SE in flight in our screenshot forum. These were contributed by none other than Ryan Butterworth in his mini-review as it is being called and a few others fans of the Classic GLJ25.

    10 very nice repaints are included.

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    All three installers are included.  No extra charges for P3D.  FSX Boxed, Steam, P3D v2-3.

    Time to Look at the Excellent Flight Manual

    Alain Rouleau at Xtreme Prototypes is known for his excellent flight manuals and this one ranks right up there at the top of this list.  It comes only as a pdf and in two editions – the full blown 160 pages that in provided to registered user and a still excellent 70 page Sample Version for those who wish to see some detail prior to purchase.

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    I understand that a new French language edition of the manual is almost complete.

    This free Sample Version has more information in it than most developers provide for competing products.

    Logically laid out, with tons of high resolution, close up screenshots with lots of bullets, detailed descriptions of every bit and piece of the aircraft, charts, tables, checklists, procedures, illustrations, references, known issues, and so much more.

    The aircraft description and specifications section, instrument panels, systems description have their one chapter or section along with a an excellent flight planning chapter.  The Normal Checklist and Procedures are far more than simple lists – each item has a reference to a page number and a figure in the manual in addition to the action required.  Tips and recommended settings for beginners are included but so the seasoned pilots that want to get up and flying quickly Alain has included a separate 2-page Quick Start. Near the back of the flight manual is a full page Limitations with all the V speeds and Placard speeds.

    Each system has a detailed description along with a key to every switch, gauge, and instrument.  A fully outfitted and animated cabin in included with 70’s style airwork.

    I read that this new VC has over 1,500 parts and 250 custom systems, animated gauges, switches, knobs, levers, light indicators and flight instruments. They also make good use of tooltips that a useful description of the selected device, not just what it is.

    Practically everything is the cockpit is clickable, moveable, animated in some way and can be used to simulate an action or procedure.

    What is missing in the Manual?  Not much, but  . . . . .

    As good and as detailed and as beautiful as this GLJ Model 25’s flight manual may be there is still room for improvement.  I was disappointed that the developer did not include any climb, descent, or cruise performance charts in the Flight Planning section. Now, it is loaded, maybe overloaded, with takeoff and landing calculation charts, tables and data. One summary table for fuel burn (1st hour, 2nd hour, etc) is included and a simplified example of a 950 nm flight is included which is more than most other developers include so I may be coming down a little hard on them.

    It would have been a wonderful addition if they had spent another day or so and added the climb, cruise, and descent details to the example. Even better would be a full-blown tutorial flight or example flight.  Now, that would be ideal, maybe even make a video.  Sorry, sometimes I get carried away with this stuff.

    I did notice that the Sample Manual does not have the full Flight Planning section that is only available to those that purchase the add-on.  Fair enough.

    The good news is that you can download some excellent training manuals that have color illustrations, full systems descriptions and the necessary performance charts specifically for the Model 24/25 Learjet – not all of them but the full pack for Mach 0.77).  These are intended for training real world pilots and is a free download until the link is removed or broken.  Search for the string “learjet 24/25 MrMoo pdf”. I was rewarded with free download links for a ‘Learjet 24/25 Cockpit Reference Handbook” and the ‘Learjet 25 Operating Handbook” that has the performance charts.

    What Else is Missing?

    Maybe missing is not the correct word, but I sure do miss the ability to perform a fuel dump or fuel jettison procedure so I can practice returning to the airport after taking off with a full load of fuel.  All the early or classic Learjets had to burn off about 2,000 pounds of fuel to get the weight down to the Maximum Landing Weight.  This was caused by the weight of all that fuel in the tip tanks.  As strong as that 8 spar wing might be, when you put more than a ton of weight on the wingtips and then land a little hard with a 7 ton airplane moving at 120 knots or so, something is most likely going to break and when it does it is very flammable.  Hence, the reduced Max Landing Weight. 

    To demonstrate the how much the fuel those tip tanks hold, this is what can happen if a greenhorn fuel boy fills one wing with the other being empty.  Oops.

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    This GLJ 25D (rw) would have been required to have the standard Fuel Jettison pumps, switches, and lights working for any flight.  For some reason, this XP GLJ 25D SE has all the switches and lights but does not have the system coded.  This is really my only disappointment  in the cockpit.  When I asked, the developer about it, he agreed that Fuel Jettison would be a nice feature, but stated they have to draw the line someplace or they would never complete the package.  You know, that old “just a few more lines of code, thing.”

    Being an optimist and knowing the Xtreme Prototypes design team, both of them, love their work and their products, just might be receptive to making this addition.  If enough folks who buys this add-on and also wishes it included the Fuel Jettison feature would simply ask that it be put on the list for any possible updates, changes, fixes, etc. we might get it one day down the road. It only takes about 5 minutes to jettison the necessary fuel from the tip tanks, but it is so enjoyable.  The Fuel Jettison switch and lights are already installed on the add on Fuel Control Panel, it just needs a little more code added to make the system work.

    The Autopilot

    As most of you already know, Bill Lear invented the autopilot during World War II, and every Learjet that ever left the factory came with a Bill Lear designed J.E.T. autopilot.  Some better than others, but all much better than none.

    The XP GLJ-25SE does not identify the AP model number anyplace in the manual, but it is a probably model as a J.E.T. FC-110 with Yaw Dampers. The add-on AP looks identical to the rea world version and probably works the same with the exception of those features that are not coded – Roll Turn Knob and Pitch Command Wheel.

    The autopilot head unit is mounted on the lower center console immediately below the Fuel Control Panel.  The Mode Selection switches, Altitude Pre-selector, and AP Vertical Speed Selector are mounted helter-skelter, just as the real world classic Learjets.

    You will want to read the manual and maybe read the forums to become familiar with this early Automatic Flight Control System (AFCS).  The real world procedures are much easier than the simulated ones mostly due to the AP switches mounted on the control wheels in the real airplane not being accessible in our flight simulator add on.  This has to do with the AP over rides of the pitch and roll and the VS modes.  It is tough to click on a button with a mouse or press and hold a switch for temporary changes in the flight path while also keeping a hand on a joy stick or simulator yoke.

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    Just remember that it all starts with the Altitude Pre-selector and it is a lot easier if you have the airplane already at the correct airspeed and in the proper climb or descent attitude when the AP is engaged.  Any changes are a little more difficult until you fully understand the logic and procedure.

    The “Go Around” feature is especially well done, be sure to learn more about it.

    The XP design team did a good job with what they had to work with.  Coupled approaches work very well and the integration of the GPS and GTNs is excellent.

    Animations and unexpected nice touches.

    You will find more and more nifty features designed into this add on as you spend more time flying.  I read that you can expect to find 80 animations and in another paragraph I read that there were hundreds of cockpit animations so start looking and expect a few pleasant surprises.  If you own the previous 20 Series add on from XP, keep in mind that this version 2.0 Special Edition is not an update or upgrade - this is a totally and completely redesigned new version.  I wonder why they decided to start with a new version 2.0? hmm.

    Make sure you checkout the Approach plates and the iPad on the side panels. The Sun visors do more than flip up or down.  There are several extra lights and switches throughout the cockpit and cabin.

    One of my favorites is the show/hide throttles feature so I can see the light switches.  This is not a problem in the real world cockpit but is a pain in most desktop simulator models.

    Don’t forget to add you own person music files to the sound folder.  One click on the 8-Track tape player will start, move to the next selection, or stop the music.  Nice touch.

    Limitations page.

    This is from the XP Flight Manual. I think the upper level VMO is actually 350 kts, provided it has the Century III wing.  The 51,000 feet altitude Certification was added for all 25D/F models, although the specs are a little vague  in the XO manual.

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    This GLJ-25 SE should easily cruise at FL510 at ~450 kts with half fuel and 4 passengers.  The 1,000 nm NBAA IFR mission can be flown in 2.1 hours, the 600 nm mission in 90 minutes.  You can use 15,300 pounds as ramp weight with a MTOW of 15,000 lbs.

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    I use the following for my personal flying in the flight sims.

    High Speed Cruise – 475 kts
    Normal Cruise Speed – 443 kts
    Long Range Cruise Speed – 418 kts

    Rate of climb – 6,050 fpm, one – engine ROC 1,910 fpm

    I seldom fly with more than 4 passengers, but many times I reduce the fuel load to the Max Landing Weight of 13,300 because the fuel dump procedure is not included.  For practicing the return to the airport procedure, I start with 13,500 pounds Gross Weight so I can burn off 200 pounds of fuel on takeoff and return for a landing.

    I exchanged a few emails with the developer about the Empty Weight found in the aircraft.cfg file and therefore in the dropdown Fuel and Payload box. I suggested the Empty Weight be reduced from 8,120 to 7,468 and the fuel load increased to 910 gallons.  I doubt not a single person could tell the difference when flying this add-on in any of the 3 sims, but it makes for more realistic loadings when I use real world flight planning data.

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    I took it one step further for my personal flying and in effect made an XR version for a little Extra Range.  Heck, if Learjet can do it, why can’t we.  Be careful though, and make sure you have a backup of your aircraft.cfg file and if you screw it up don’t email the developer and ask for help.  It is simple enough to modify the fuel capacity for a fuel tank and it is easy enough to modify the Empty Weight of the aircraft.  Just use the Find function and locate the values in the aircraft.cfg file and make your changes.

    I decided on an Empty Weight of 7,168 pounds and a total fuel capacity of 1,055 gallons.  With this setup I can use standard weights of 170 lb men and 120 lb women and carry a small amount of baggage with full fuel and be slightly under Max Ramp Weight of 15,300. I also changed the MTOW to read 15,300 (Max Ramp Wt) knowing I will be at the official 15,000 MTOW with a few minutes of taxi time.  This is an FSX limitation, no Ramp Weight field.

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    Frame Rate, Smoothness

    Because this new release is specifically designed for newer PC and video cards, you can expect superior performance.  I can’t speak for the Legacy systems, but Ryan Butterworth says he has a ‘something less than the best’ system and he has posted some Frame Rates compared to some of his other addons.  You can find that post in the screenshot forum.

    The Classic GLJ Model 25 SE runs smooth as butter on my test system.  My screen images are not as sharp as it should be but, I just can’t seem to find to time to tweak it.  I have a fast PC with a 970 video card, I should have bought a 980, but didn’t.

    Conclusions

    I like this Classic Learjet a lot.  I was a dyed in the wool Cessna Citation fan for a long time and really still am, but you have to love the speed and power of these early Learjets.  I get frustrated with the older autopilots but they usually do what they were designed to do. 

    If you are looking for an up-to-date modern design, high definition, and highly detailed Classic Learjet, you can’t do any better than this one.  I just need to find the time to find all those 80 animations in the cockpit. Wow.

    The closer you zoom in to the panel to more you appreciate just how well these new 3D gauges are performing – super sharp image for my old eyes.

    I especially like the fact that we get all three installers, 10 very nice repaints, an outstanding flight manual and a highly tuned flight model that will cruise at Mach 0.82.

    And best of all, I can place my Flight1 GTN combo in the VC panel with a super simple line change in the aircraft.cfg file.  I even like the default EICAS panel feature because I am only one click away from having the GTNs or weather radar in the panel. That is really nice.

    Bottom Line:  A most definite Buy RatingGo get it here.

    Selected information from the www.Xtremeprototypes.com website.

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    Additional comments

    Many times I receive offers or invitations to review a product and the offer comes at an inconvenient time mostly due to my haphazard work schedule.  Of course, I always reserve the right to refuse but should I take the add on, I always do my best to provide a fair and balanced review.

    This one got interrupted a couple of times and I feel guilty that it took me so long to finally complete the review.  I forced myself to cut it short and I left out a lot of my research material.  This material was mainly about the influence the late model 25 and 28 Lears had on the follow on models – mostly the 30 series and to Longhorn 55.

    It is very obvious to me that I only scratched the surface when describing the depth and details of many of the systems and procedures that can be simulated when flying this classic Lear 25D.  There is no doubt that I totally overlooked several items that probably required months to research and code and I didn’t even notice or failed to suitable take notice.  For these faults, I apologize.

    Overall, this is one of the most detailed and complete add ons that I have in my virtual hangar.  The problem it creates for me is that I have so many similar Learjets that after a while many of the systems seem to run together and I start confusing one with another. 

    Credits:

    Thanks to Alain Rouleau at xtremePrototypes.com for answering all my questions and providing the evaluation software.

    Test System and Qualifications:

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