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Aircraft Review: STMA HpH 304 S Shark 18 Meter Sailplane for X-Plane 12

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Aircraft Review: STMA HpH 304 S Shark 18 Meter Sailplane for X-Plane 12


By Dan Hopgood



Gliders, the pioneers of controlled flight, have been soaring through our skies since Otto Lilienthal's successful flights in 1894. They have since become a popular avenue for learning to fly, as mastering flight without an engine equips a pilot with invaluable skills. Today, gliding is a widely enjoyed recreational and sport activity. Modern materials and technology have given rise to high-performance gliders, and piloting these to their full capability—leveraging the natural forces of wind and weather—is a true test of airmanship.


The HpH 304S Shark is a product of HpH, a Czech company. Its lineage traces back to the Glasflügel 304 from 1980. After Glasflügel folded due to financial difficulties, HpH revived the 304 and progressively developed it. The 304S Shark, boasting an all-new wing and HpH’s own airfoils, first took to the skies in 2006. It offers wingspan options of 15, 18, and 20m, with the 18m span version being the most popular and the one modelled here.



The Test Setup
As a freeware X-Plane developer with some real-world gliding experience, I tested the Shark at V1.0 on a mid-range system running Windows 11 at 1920x1080 resolution. The model was not tested in VR. Installation was straightforward—simply drop the aircraft folder into the X-Plane main aircraft folder. The provided documentation includes an 18-page "Speed to Fly" guide, a 3-page guide on making the best use of water ballast, L/D and speed polar graphs for the 304S, and an LXNAV user manual for the LX90xx and LX80xx GPS/Vario systems. The nature of the documentation—lacking X-Plane specific information—suggests that this aircraft is aimed at pilots already familiar with the basics of glider flight who are looking to stretch their capabilities with a higher performance aircraft.


The aircraft loaded without issues, although some users have reported plugin compatibility problems. The X-Plane plugin admin screen indicated a 5FPS performance hit with the VarioTone plugin, but the in-flight framerate seemed typical for similar aircraft. In X-Plane, the process for choosing a winch or tow start and selecting a tug aircraft is identical to that of the default ASK-21 glider. Upon loading, a pop-up menu is available in all views, allowing you to adjust water ballast settings and open or close the canopy.


Water ballast enables the glider to maintain the same maximum glide angle at higher speeds, albeit at the cost of a reduced climb rate. Deciding how much ballast to carry and when to release it is part of the challenge of optimizing performance. The aircraft uses standard keyboard/joystick commands for main controls like the canopy, minimizing the need for aircraft-specific setup. By default, the aircraft loads with full negative flap. In reality, it's safer to select zero flap before take-off to prepare for potential launch issues (more on flaps later).


Visual Appearance
The original aircraft features complex compound curve wing and stabilizer tips, all of which seem accurately modelled here. The rest of the internal and external visual model also looks good, with the exception of a poor fit around the back of the cockpit canopy. Comparing the cockpit internals to videos of the real aircraft, the layout closely matches reality. The double yaw strings on the canopy have tape visible at their base, but only in external views. Learning the cockpit isn't difficult given the limited number of controls, but the lack of pop-up instrument descriptions would be useful—especially considering there's no description elsewhere. There's a strange visual effect on the top of the instrument panel, which may be the reflection of the compass itself. On a hard runway, the main undercarriage tyre appears flat while sitting on the runway. This issue, which can be easily adjusted in Plane Maker, is common in many aircraft as X-Plane evolves through different versions.


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The aircraft comes with a single "4k" paint scheme, which is acceptable given that modern gliders are typically white. While no paint kit is provided, the object textures are easy to interpret, making custom paint schemes a breeze. Particle effects in the form of water ballast release are included, appearing as two narrow streams of water from each wing. And, of course, the pilot is female.


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In the Air
Tow launches proceeded without issue. The roll control, likely due to the full-span flapperons, is excellent, and the wings flex in a believable manner. Upon tow release, the aircraft felt authentic in cruising flight. The elevator response requires relatively large control movements, but this is quickly learned and contributes to an overall feeling of smooth handling. Winch launches were similarly uneventful, with a dedicated tow point near the main wheel. The speed during all stages of the climb is almost constant, which differs from my experience with other X-Plane gliders. This could suggest some customisation via a plugin. The stall is gentle and easily controlled. Accurate flight performance around the stall is crucial for gliders, as they are often flown near the stall deliberately. The performance in this area does not disappoint.


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Pilot weight is not adjustable, so the centre of gravity is not readily adjustable either. Changes in water ballast have no effect on the centre of gravity. The aircraft won't spin, which may be due to the very shallow lift roll-off in the airfoil polars at high angles of attack. The full-span ailerons allow for graceful execution of all standard glider aerobatics. The rudder is powerful enough to allow side-slipping to increase the descent rate. Flaps are used only for trimming and optimising glide performance, not controlling the landing approach. Landings are controllable and smooth, with powerful spoilers necessary for such a good glide performance.


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Cockpit & Instrumentation
Electronic instruments include an airspeed indicator, altimeter, vario, G-Meter, clock, transponder, com radio, and "LX Zeus" GPS.
The large central "Zeus" instrument features a moving map and course and heading indicators. The map can be zoomed in and out, but that's the extent of its functionality, despite a full set of clickable buttons. The control stick has a clickable number pad on it, but it has no function. However, clicking on the main screen results in a pop-out XP Garmin 530GPS.


HpH304s - 2023-06-07 13.39.53.jpg


The com radio and transponder are modified X-Plane instruments, although the manipulator on the com radio volume is awkward to use, with the volume increasing rapidly by clicks but decreasing slowly if held. The electronic altimeter and airspeed indicators are simple and clear to read, calibrated in feet and knots, with both indicated and true airspeeds shown. The G-Meter shows max and min g recorded as well as the g load at any given moment in time.


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The most useful instrument in a glider is arguably the variometer—a compensated vertical speed indicator that helps detect lift and sink. On the right of the panel is the electronic vario/speed to fly indicator. It is calibrated in km/h and metres, which is at odds with the units of the other instruments. The rate of climb and descent are indicated with shaded areas, making it easy to use peripheral vision to understand height gain or loss. Actual rate of height gain is shown on a green arc. There is some energy compensation taking place, but there appeared to be no difference in functionality between vario or speed to fly modes. Without documentation describing the operation, it's difficult to know if functionality has just been misunderstood. In searching for lift, the audio and visual aspects of the vario work well, although a volume control for the audio was not found.


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Under the Hood

X-Plane models rely on both a visual model and a typically unseen Plane Maker model, which is crucial for accurate flight performance. This aircraft's Plane Maker model is of high quality and detail, which is commendable. Correct airfoil data is critical for a high-performance glider model. This model uses custom wing airfoils that represent those designed by HpH for the real aircraft. However, only one Reynolds number has been used for the airfoil data, despite multiple Reynolds numbers being an option in Airfoil Maker, which could enhance accuracy at the extremes of the flight envelope. The model includes comprehensive FMOD sounds, such as the sound of the wing tips touching the ground. However, the mixing of some volume levels, like the quiet ground roll, may not be to everyone's taste. Sound preferences, after all, are subjective.


Flap Performance
All versions of X-Plane to date, including XP12, have a limitation in the Plane Maker flight model where the resultant L/D from applying either positive or negative flap is always worse than at zero flap. This is not true for high-performance flapped gliders, where slight negative flap at higher speeds provides a higher L/D than the zero-flap condition at the same speed. From my observations using on-screen data output functions, the model appears to be adjusted for the correct maximum L/D of 51 at 55 knots, but at the full negative flap setting in the cockpit, rather than the real-world setting of zero flap to achieve maximum L/D. In the model, the L/D deteriorates as flap setting moves from full negative to full positive, regardless of airspeed. At neutral flap, the L/D at 55 knots is about 42.


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While the maximum performance is correct, the real-life performance of the flaps is not fully accurately modelled. Unfortunately, all other XP gliders I'm aware of have some compromise in their flap setup. This model still pushes the standard flight model as far as it reasonably can. However, pilots should be aware of this flight model limitation to get the best out of the aircraft.

Pros & Cons

  • What to Like:
  • Smooth, controlled, and believable flight performance
  • Wing flex modelling
  • Detailed 3D model, both inside and out
  • Electronic Flight Instruments and GPS
  • FMOD sound
  • Areas for Improvement
  • Flapped flight performance, although this would be challenging to achieve given the current limitations of X-Plane.
  • More detail in the instrumentation, particularly the vario and GPS
  • Minor issues with 3D modelling, such as detail around the canopy.
  • The ability to adjust pilot weight would be a nice addition.
  • Model-specific instructions for the included avionics would make the aircraft easier to fully understand.

Currently, this aircraft is the only payware flapped glider available for X-Plane 12. It offers a good visual representation of the original aircraft, complete with modern and glider-specific custom electronic instrumentation. The Shark presents an excellent opportunity to learn about high-performance gliders, especially with the more accurate representation of thermal lift in XP12. The flight performance is smooth, and it possesses that elusive quality of "feeling right" in the air.


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The focus of this model is on handling and flight dynamics, which are crucial when simulating glider flight. It's less about the visuals and largely irrelevant features like being able to move the air vent in the cockpit. The price at the time of writing is modest. STMA has stated that, depending on sales of the default "starter kit" aircraft, self-powered and/or self-sustaining versions could be added. These are real-world options and would enhance the versatility of the model. The Shark performed well on a typical hardware setup, with no noticeable frame rate issues during testing.



As it stands, this model has great potential but needs further work. The plans for further improvements to the "starter" version are unclear, but STMA is a very long-established and respected developer. This model is ideal for a large group of users who are familiar with the basics of gliding and are looking to expand their skills, such as cross-country or "task"-based glider flight. These can be a lot of fun and present a new and different flight challenge.






The HpH 304 S Shark 18 Meter Sailplane by STMA is now available from the X-Plane.Org Store here:


HpH 304 S Shark 18 Meter Sailplane

Priced at US$29.95



  • Full 3D cockpit with ample room for functional growth as demand dictates.
  • GPS equipped for cross country tasks
  • Polar data and soaring references included for your best start in soaring experiences
  • Flap and Airfoil data modified for best negative flap experience
  • LX-styled Instrument package featuring both Imperial and metric data
  • MacCready number setting on the variometer for optimum energy management
  • Variometer and Speed to Fly modes toggle to provide airspeed guidance
  • Vario with both color and sound indicators provide instant energy gain/loss assessment
  • Configured correctly for both winch and aerial tow pulls
  • Ballast control from the STMA dock feature – load it or lose it from cockpit
  • Rain windscreen for when the clouds let go
  • Edge of envelope flight characteristics 
  • Accurate stall speeds for all configurations
  • 45-degree dives in full spoiler configuration without overspeed
  • Accurate approach and landing speeds



X-Plane 12 
Windows, Mac, or Linux
4 GB VRAM Minimum. 8 GB+ VRAM Recommended 


Review System Specifications

AMD Ryzen 5 5500, 32GB RAM (3000Mhz), RTX 3060, Windows 11



Aircraft Review by Dab Hopgood
9th June 2023
Copyright©2023: X-Plane Reviews


(Disclaimer. All images and text in this review are the work and property of X-PlaneReviews, no sharing or copying of the content is allowed without consent from the author as per copyright conditions).





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