In the RC aerobatic arena there is something about flying a model airplane in a manner that delivers maximum satisfaction and freedom of expression. This inner desire to freely express and it look really good on the aerobatic canvas is infectious. So much so “it” can become ones sole purpose for modeling just to see the performance results of the next creation on the bench. Your getting excited knowing this new plane has something to offer that just might allow you to venture even further than you ever imagined, a model that performs the most difficult of maneuvers with ease. A model that is so neutral and predictable offering no bad habits, this is an aerobatic pilots dream. This all sounds very inviting and fun doesn’t it? Now let’s throw a little curve into the mix and suggest this is now being done in the most extreme style of RC glider aerobatics, on a hilltop slope, with a glider. That’s right, no propulsion! Some well managed kinetic energy coupled with natural lift on a uniquely shaped slope. Interested?
check out this video from Steve Lange (www.slopeaerobatics.com)
Welcome to the world of VTPR Aerobatics. Huh… You mean Vitiper? No, V.T.P.R. Translated from its French origin means “voltige très près du relief” or aerobatics very close to the terrain. How close? Ground 0 close! With a glider? Yep with an engineless model in manners that seem at times to defy gravity. You see, Vtpr is performed without inertia and extreme agility. Sound scary? Let’s dig deeper.
VTPR by definition requires the model proximity to the terrain be very close, even touching ground through overland performance maneuvers including tip & tail drags combined with fluidic figures that compliment the whole presentation within a prescribed sky box boarder. These figures and the performance as a whole are of similar understanding as freestyle figure skating except we are painting the sky with a purpose built aerobatic glider controlled by a computer mixing radio.
Freestyle model airplane flying no doubt has been around for decades since Free Flight modeling beginnings when there were no radio waves guiding the models. Modelers designed and hand tuned their creations to net a given flight result once tossed to glide on their own.
The easier and more directionally stable the model could produce the flight was the desired goal even way back then! Then radio communication devices came along and here we are today in all its sophistication. In the background of this fantastic history of modeling were a handful of Freestyle pioneers in France and England who dared to risk hard work to see their prized model take to the air without a motor in a new and daring way never seen in the history of simple aerobatics. They basically began a new and dangerous relationship with the ground with their fantastic flying machines daring each other to get closer to earth for some crazy reason! That reason was fun.
Today in the US and recently within the last 5 years we see another small tight knit group of modelers/flyers in the RC modeling world take to the slope with their fantastic flying machines performing some pretty incredible and technically beautiful aerobatic figures one doesn’t normally see at the flying site. Americans and Europeans have been freestyle flying model gliders for decades and have always called it such. The VTPR acronym in and of itself originated in France from groups of weekend fun flyers taking glider aerobatics to the extreme and calling it VTPR for short. This in turn differentiated it from conventional larger airspace aerobatics that we commonly see on slopes worldwide. We use acronyms all the time for many reasons, this just happens to be the one that was chosen for very close to the terrain aerobatics. One of the key features of this “style” of flight is its slower speed and floaty appearance of the model. At times you can actually see the ship hang in the air as if on a string, then zoom off into the next figure of the performance.
And all of this is happening real close to the ground in a small air space ranging from 1 to 6 feet off the deck. The larger span models up to 160” require more airspace to get started but even they approach ground 0 and boy do they really dazzle! The French in the Brittany area of the country have perfected large model VTPR performances more than any. And it’s beginning to catch on in the US. It’s almost non-eventful to see a slow moving 12 pound 160” Air-100 wooden model flying inverted above the deck around 1 meter until you realize the model just went into a half roll right off the deck and propels itself up into a stall turn back down inverted for another pass the opposite direction. Again these are gliders! It’s a wonderful sight to say the least. When all the chips are down in front of spectators and your peers the pilot wants to soak in the whole experience a click above his or her last flight and they want to dazzle the crowd and the world if it gets on YouTube. No doubt ego plays an important role whether one wants to admit it or not. When one has mastered the art of VTPR it’s a very beautiful sight the pilot should be very proud of. I used to work with Navy pilots on the A6 Intruder jet aircraft aboard aircraft carriers. Talk about ego maniacs. I really had no problem with their demeanor because I knew they were going off to war risking body and plane for us. I knew I wanted the best and most over confident pilot on the sticks of that bomber. An extreme example but maybe you get the reasoning that slope aerobatic pilots as well are sometimes ego filled risk takers especially the VTPR group. Some are quiet and unassuming and others are in your face but all of them love risk and the adrenalin pump.
The models are purpose built for VTPR. EPP foam is a popular building material for its durability but it needs strategically placed carbon fiber components to obtain rigidity in the important areas of the airframe. The model that took the VTPR stage early on is called Le Fish. Secondly traditional wooden models with splashes of carbon fiber and fiberglass cloth are now becoming much more durable due to what has been recently learned with the low mass inertia component. One of the popular lightweight designs in wood are the new PSP designs (profile slope plane). VTPR models weigh lighter as compared to our conventional slope model counterparts. They possess very large flight control surfaces with gobs of travel, have longer nose moments for balanced rotational stability, larger tail feathers and have purpose designed wing airfoils. These airfoils allow the model with its light weight airframe to accelerate from a stall quickly and efficiently into the next figure of the performance.
A good VTPR model pointed into say a 10mph wind should be able to easily stall and float in one spot, do a half-roll to full roll without forward momentum and lose very little elevation (inches). It should also be able to do a 180 degree flat tail-hook slide in the horizontal plane, stall and fly the opposite direction without losing elevation. Inverted flight must be as easily done as right up flight. Another must feature is the model should have virtually no tip stall. Or a very gentle stall that allows the pilot to correct without any attention to the fault. Since the typical VTPR flight is slow and smooth high roll rates are demanded of the model for a few reasons. The larger aileron surfaces offer more efficient wing pressure management netting less drag on the model. They also give the pilot the ability to move the model in extreme maneuvers close to the ground as well as slow speed insurance for getting out of trouble if needed. Large expo mixes are the norm on VTPR models. Another very important feature of a good VTPR model is its durability. None of us gets any enjoyment loading up a broken model from occasional impacts with the ground and in VTPR the ground is 100% of the equation. Any good VTPR pilot knows he will hit the ground a few times every outing as he pushes his personal envelope. So as a result these models must be designed to take into consideration all aspects of how it will get damaged and design and assemble them accordingly.
The AUW (all up weight) is the first specification that needs to be determined on a new design. Or if you are looking to purchase an already built ship it is good to know what the AUW is and what the WL (wing loading) is. Planes that are too heavy won’t easily perform floaty VTPR. They will perform faster VTPR. Typically on a 60” – 100” wingspan model the desired range of WL should be 7.5 – 10 ounce WL. There are also the newer UL (ultra light) versions that have been prototyped with success that almost halve these numbers and reduce the fly box greatly. The goal in either case is to get the model mass down for impact resistance and be able to add color to the figures being performed with ease. This combined with special airfoils allows these models to accelerate at a high rate but they never usually want to fly faster than say 35 mph. But they get there quick. Veneer sheeted white foam core wing panels are still very desirable and popular in Europe and the US. They offer an economical way of putting together a lightweight and rigid panel and are easy to repair or replace. EPP constructed wings are more durable but a bit heavier. Molded hollow core wings are super clean aerodynamically and very light but expensive to fix. Whichever material choice the goal is to produce a wing panel that is as light as possible to save overall weight but also to reduce the rotational inertia load on the wing in roll mode. This makes the plane very responsive and low speeds. In VTPR often times the model is hanging or in a stall and must be able to have a great roll rate in any given situation. Building lightweight wings means there is a possibility of breaking one. This is where the intuitive modeler utilizes certain amounts of materials and techniques to overcome this lingering fear when approaching the ground in VTPR mode. Confidence in your model is paramount and translates to the performance level produced.
Flexibility in a fuselage is becoming the norm in VTPR now. Conventional wisdom dictates you want a stiff fuselage to keep the empennage stable to eliminate dirty aerodynamic horizontal and vertical stabilizer input. This is being rethought and demonstrated with the advent of some lightweight EPP foam models and some new wood/carbon fiber versions coming out of Southern California. The thought is much slower air speeds and extreme maneuvering cancel out minimal empennage movements. This also greatly aids soaking up impact blows to the plane to save the tail boom and ultimately result in continued flight with minimal field repairable damage if any. On average a risk taking VTPR pilot will crash the model numerous times in a single outing. There is also experimentation surrounding the idea of a flexible tail boom being able to store minute amounts of flexible rebound energy to aid even more aerobatic maneuverability. Imagine a sling shot component while in knife edge or a stall turn into a slide that can then allow this stored energy to slightly propel the plane into another figure simultaneously where it couldn’t before. It’s all very innovative.
Finally the radio mixing with the onboard servos have come so far in the last 20 years. The equipment upfront costs are so incredibly inexpensive now anyone can have a full range 6 channel computer mixing system for less than $200. Metal gear servos are a must for durability. You notice I keep coming back to the durability issue. It really is of prime importance on a dedicated VTPR ship because as you probably gather by now they hit the ground often. Sometimes even on purpose when wing tip and inverted tail drags are performed or a full inverted landing. The model must be lightweight, take a lot of abuse and keep on flying. VTPR isn’t for the faint of heart. One of the VTPR pilots favorite radio mixes is “snap flaps”. What occurs when the elevator is pulled up or down, both ailerons travel together in the opposite direction of the elevator. Typical ELEV/FLAP mix ratio is 33%. What this gives the pilot is the ability to perform a very tight and efficient inside or outside loop without loss of momentum. Snap flaps are usually left on all the time as they also help keep the plane aloft at low speeds when one naturally wants to pull up elevator. In this case which is often the trailing edge of the ailerons go to an under-camber condition automatically making the pilot look good when he is low on the edge of a stall. With all this said the ultimate goal to designing, building and flying a VTPR dedicated model is that the model allow the pilot to naturally produce a fluidic and seamless aerobatic performance with ease. All of these and more I have not mentioned for reasons of space make up the unique design parameters of a successful VTPR grade model.
The Flying Site:
The ideal slope site is what is known topographically as shallow and rounded. This translates into a gradual grade rolling slope shape with consistent laminar airflow. This type of slope is primarily located near ocean coastlines or inland areas with unobstructed wind flow. The most famous shallow slope in the world and of which is every VTPR pilots dream to visit is Menez-Hom in Brittany France. It is here and other slopes nearby that VTPR was born and is still the driving force for future enthusiasts of VTPR. In comparison in America it would be equal to the Indianapolis Motor Speedway. The reason it is preferred to fly an open and shallow shaped slope with a good headwind is to be able to perform all manner of VTPR without limitation. What we mean by all manner is everything you can think or dream up you could possibly do with a glider very close to the ground. The headwind flowing over this shallow slope allows the current to remain consistently more horizontal to the ground angle as to actually allow the model to hover in place in a hands-off fashion if desired. This balance of nature and model is the sweet spot of VTPR. There is no limit to ones expression with a model when all the aforementioned specifications and natural terrain components are combined to a style of flying that delivers the most satisfaction in this authors opinion. I have personally flown gliders very fast and in many other forms since 1990. None of them come close to the rewarding experience VTPR style of aerobatics delivers if one dares to jump into the arena.
VTPR Aerobatics goes Global!
We have put together a comprehensive website dedicated to VTPR that showcases particular models with video flight links. The website is titled “Slope VTPR Aerobatics”. You will find on this website many shapes and sizes of model aircraft specifically made for this exciting flying style. VTPR though is suited for those who wish to venture into the extreme “on the edge” flying experience to the pilots and models full capabilities. All in all, VTPR aerobatics offers the pilot a canvas to explore the ultimate adrenalin rush in a dangerous yet slow, smooth and majestic style of model glider flight.
Also more information about this exciting flying style can be found at www.slopeaerobatics.com.
–BY ERIC JOHNSON