<- back to description

3-view

Aerodynamics

The SALpeter represents the latest fine tuning of the proven Aspirin concept. Improvements were particularly strived for in the following points (in order):

•  dead air sinkrate
•  glide ratio against the wind
•  launch height
•  climbing in thermals

For the therefore a set of five different airfoils along the span was designed, matched to the local Reynolds numbers, lift range and thickness constraints. The Aspirin airfoil was still constructed for a larger relative thickness of 7.3%, to be able to compart reasonable servos without exterior parts and achieve an excellent stiffness-to-weight ratio.

With the AH160_9 series developed in month-long fine work the luxurious reserves in the negative lift range were reduced to the benefit of the most often used region. Relative thickness became smaller in the main part of the wing accordingly and was only kept where the servos are mounted.

Airfoils again were equipped with a contour kink and by this optimized for two preferrable settings (0/2 deg). In slow gliding the top surface remains smooth to avoid unnecessarily large laminar separation bubbles and reduce pressure drag. The kink in the lower surface does not lead to early transition then and the thin separation bubble can even reduce friction drag somewhat.
In fast flight the lower surface is made smooth, to keep the boundary-layer laminar up to nearly 100%. The shape parameter development was optimized in such a way, that the laminar drag bucket reaches to lower lift coefficients then compared to the Aspirin.

When the Aspirin was flown very heavy (> 310 g) in wind and with a too negative flap setting, sometimes a loss of glide performance returning from thermals could be noticed. It was not given to everybody to find the "sweet spot" concerning flap setting, ballast and velocity. The SALpeter offers a significantly wider optimum, with lower off-design performance loss.

The outer wing was kept a little more narrow and less swept than at the Aspirin, to optimize the last nuances of flight characteristics. For our taste the Aspirin sometimes tended a little too much to stalling in the middle of the wing and take down the nose subsequently. This gentleness was not needed for the experienced pilot.
Making this change of course it was taken care of adjusting stability and circling characteristics such, that the competition pilot does not need to be too fixed on the model but has a good indication of thermals.

Accordingly an intermediate aspect ratio as the optimum compromise concerning stiffness, Reynolds number and mass-wing-loading ratio for best allround performance in typical wheather conditions was chosen. A glider with a huge operation spectrum should be made, one which always works.

The vertical tail of course is profiled asymmetrically again, to reduce the yaw excursions after release as quickly as possible. The Aspirin sometimes showed hardly noticable yaw wiggles in slow flight, which were removed on the SALpeter. Nevertheless the airfoil is still strongly oriented at the HT23 and delivers high maximum lift.
Compared to the Aspirin span was marginally increased from 240 to 244 mm and also area is hardly changed with 1.70 dm². Despite that effectivity was increased, yet without producing too much mass, inertia and drag with a too large vertical stabilizer. Simultaneously core volume was reduced saving mass. Of course again each a left and right-hander version is available.

Also the elevator was slightly enlarged and adapted to the larger lift slope of the wing. The minimally lifting airfoil creates an even more harmonic slow flight behaviour, whereat it was daintly paid attention to not cause drag penalties in launch.

Dihedral was increased a tic to 6.2 deg, to allow circling with minimal stick inputs. It is not detrimental to launch heights at all. And upon floating in quiet air most of the corrections can be made with rudder only.

Construction

As already for the Aspirin the motto was again "As simple as possible, but as sophisticated as necessary!". So for a high-performance DLG some effort is required. Again highly precise moulds for all parts were CNC-milled. Especially for the wing the most accurate reproduction of the desired contour is important.

Wing geometry was transferred into CAD with self-programmed tools, which avoids airfoil distortions that otherwise can easily occur in the tip region.

To be able to employ reasonable servos in the wing without parts sticking out, they were mounted in the middle of the wing. This saves mass inertia around roll and yaw axis. At the Aspirin this way was not chosen initially, fearing flutter problems.
But with our stiff and free of play RDS system (since the Aspirin readily installed with two DS281 in the wing without weakening cut-outs) and adapted flap reinforcements the flutter boundary is sufficiently beyond the speed range occuring.

Wing

The SALpeter wing is available in a multitude of versions. The standard competition version provides superior stiffness and strength for the highest launches at lowest weight. This of course requires acribic manufacture from materials with better specific mechanical properties.

Therefore Rohacell is used as core material, which compared to Balsa is more pressure resistent and allows better contour accuracy. From our point of view the most reasonable is the reinforcement with carbon lattice fabric (Disser wing), as this brings the lowest additional weight. It is strong enough for throws above 60 m and offers the best handling.

Based on this standard version many different measures for further increasing stiffness and robustness can be taken. CFK-D-Box (normal or spread-tow), full carbon and full Kevlar are possible.

The flaperons are hinged on the lower surface by Kevlar-Elastic-Flap, which compared to the silicon hinge allows slightly better stiffness and precision. The smooth connection and air tightness ensure minimum disturbances of laminar flow over the flap combined with high robustness. The gap on the upper surface is closed with a special foil seal.

For the electrical connection of the servos a two-row pin connector is directly plugged in the servo connectors, such that soldering work is reduced to a minimum and redundance is given.

Fuselage

The fuselage is made as integral part in pressure bladder technique using UD and braided carbon. This ensures ultimate strength at lowest weight, as no more bonded joints are necessary. Furthermore inaccuracies in alignment of tailboom and pylon are eliminated - everything perfectly reproducable. In the pylon the elevator horn is hidden aerodynamically.

The tailboom is reinforced with high-modulus UD carbon. Through the different fibre angles bending and torsional loads are taken optimally. Cross section is flat oval, to maximize area moment of inertia at lowest possible weight.

The more slim, but FAI conformal, nose is best filled with 4 of the newer AAAA-NiMH cells in block arrangement, with the receiver behind. An alternative configuration is e.g. 2x2 2/3AAA cells, slightly overlapping with the receiver.
Standard is equipment of the fuse with two servos. No messing around with linkages from the fuse and maximum flaperon torsional stiffness were again the reasons for that. The slightly smaller canopy makes the fuse even more stable, while still allowing good access from the top to the RC components.

The wing is fixed with two screws and two bolts in all directions after well-proven principle.

Below the wing 30 g of ballast can be fixed (with other systems), to extend operation range to higher wind speeds.

If desired the pod is made from non-shielding material to use 2.4 GHz receivers without protruding antennas.

Tail surfaces

The tailplanes are built in negative moulds again, ensuring best reproducability of flight characteristics. Therefore the technology with CNC machined Rohacell massive core without glueing joint was developed by us to series-production readiness. This way extremely light and robust tails can be made, which have redefined the limits of possible.

The complete set weighs about 10.5 g! They are equipped with Kevlar hinges, to prevent a migration of the flap under the pressure of the torsion spring. The elevator is fixed with two screws on the pylon. Vertical tail is bonded to the boom with the help of an enclosed template.

Actuation of elevator and rudder by Kevlar thread and torsion spring, elevator horn integrated in pylon aerodynamically favorable

Throwing peg

The carbon throwing peg from negative moulds is profiled and therefore less detrimental to aerodynamics. It is sanded to desired shape individually. The load transmission area is reinforced by doubled carbon, of course.

Mass balance

Masses of the parts have to fulfill strict tolerances (+- 5%). This ensures quality and the intended flying characteristics.
Take off weight is typically 250-260 g. Light planes can be built from about 240 g if desired. The more robust D-Box versions end up at about 270-280 g, which marks about the upper limit of reasonable allround weight range (without ballast).

The SALpeter is delivered almost ready to fly. Only the rudder linkages have to be completed and RC-components have to be installed. The following parts can be used for that:

prices ->