PISTON — JET

PISTON JETEvery year fewer and fewer aircraft with piston engines. Lightweight, economical running on cheaper than gasoline, fuels, jet engines replacing piston even from agricultural aviation. But in any aeromodelling competition still reigns “piston era”. On kartodromo you will see the masterfully made copies of “Ilya Muromets”, “Nieuport”, I-15, Yak-3… do Not attempt to only search for a model jet aircraft — the era of rapid modern machines in modeling has not yet arrived. The reason is the lack of jet motors or at least their imitators: piston motors with impellers. Unfortunately, numerous attempts by modelers to create quasirational the engine was not successful — usually these devices have extremely low efficiency and did not develop the thrust required for steady flight of the model.

 
A more successful version of the EDF managed to build a veteran Soviet aircraft modeling gorkovchanin p. P. Smirnov. “Desyatkova” two-stage motor fan with own weight 830 g develops a thrust of 2.25 kg/s. And that is enough for a flight not only cord, but radio-controlled models-copies.
 
In the work to create quasirational engine optimal design proposed to be included and the readers of our magazine, to talk about self-developed structures to share ideas and plans. The best solutions will be published.
 
The design of impeller before me stood a task — to obtain maximum thrust (and therefore maximum efficiency of the propeller) with a minimum diameter of the fan. This was possible only when the impeller two-stage scheme. The blades of the first and second stages are located in the annular channels between the blades guide vane units.
 
Initially, the air flow gets to the inlet guide vanes is an annular channel in which are 11 radial profiled blades. Each of them is installed at an angle of 15° to the direction of the air flow that gives you the opportunity to spin it in the direction of rotation of the rotor. This reduces the flow velocity relative to the rotor blades of the first stage impeller.
After the first fan, the air enters at the intermediate directing vanes. Unlike the input it has more blades (22), the chord of which is parallel to the axis of the channel. Further, the air flow supplied to the second stage, is accelerated and passes through the output guide vane unit. The latter is arranged similarly to the input and has the same number of blades, but the angle of their installation is the opposite — it is necessary to equalize flow. Then air rushes into the receiver — the main bulk with great speed passes through the nozzle, and part of it wraps around the cylinder head of the engine, cooling it.
 
Details of the impeller made of a magnesium alloy with a density of 1.78 g/SMZ is allowed to create a design relatively low weight. Those who intend to repeat my quasirational engine, be aware that magnesium is very easily oxidized, so all parts of it must be oxidized followed by painting and polishing. I recommend this to apply the polyurethane and pentaphthalic enamels with pre-primed composition of EP-56, as other paints will dissolve with methanol.
 
Very briefly about the design features. “Decategorify” nitro engine impeller fixed to the frame, which is part of the output guide vane apparatus. The hubs of both rotors and bow cook pulled together into a single unit threaded stud, screwed and the motor shaft. The front bearing unit — a rolling bearing, planted in case the inlet guide apparatus. Hub rotors machined in such a way that between them and the housing intermediate the straightener apparatus is a gap of 0,5 mm — this allows the rotors to rotate freely and at the same time does not create excessive resistance to air flow.
 
The rotors are composite, each of them assembled from the hub and twelve blades. In the hubs for fastening the latter drilled for 12 equal spaced radial holes. The blades are quite complicated profile cross — sections each has a variable chord, thickness, and also the end section of the blade is twisted relative to the cross-section with a chord equal to 21 mm. to more accurately align the blades relative to the rotor hub, I used a simple template. On both the fans and the blades are mounted at the same angle is 41°9′ to the plane of their rotation relative to the chord.
 
Impeller design P. Smirnova
 
Impeller design P. Smirnova
 
The impeller design P. Smirnova:
 
1 — inlet guide vanes (MA-8), 2 — nasal Kok (MA-8), 3 — cone bushing (PT. 45), 4 — threaded rod (30KHGSA), 5 — notched nut (Art. 45), 6 — bearing (12x24x6 mm), 7 — the hub of the fan first-stage (MA-8), 8 — shell intermediate guide vane apparatus (MA-8), 9 — fan hub of the second stage (MA-8), 10 — blade fan (MA-8), 11 — output straightener (MA-8), 12 — external fairing of the receiver (fiberglass and epoxy), 13 — internal cone of the receiver (fiberglass and resin), 14 — conical bushing (PT. 45), 15 — clamp (ML-2), 16 — sides of the output guide vane apparatus (MA-8), 17 an intermediate guide vane apparatus (MA-8), 18 — spacer (30KHGSA, Т6Х0,5 mm), 19 — sides of the input guide apparatus (MA-8), 20 — M3 screw, 21 — nut (MA-8), 22 — screw M1, 23 — motor.

 
After final Assembly pritachivajut rotors on a lathe so that the outer diameter of each was 98 mm — this ensures that the annular gap of 0.25 mm between the shell and the fan blades. In conclusion, balancing of rotors, which should be done very carefully, given the high inertial load.
 
Developing the design under your existing engine, please note that the mounting angle of the fan blades is chosen in accordance with the frequency of its rotation (my engine, in particular, develops a 14 thousand rpm), while the thrust is maximum. If your engine has a smaller (or greater) frequency of rotation, the angle of the blades must increase (or decrease).
 
The inner and outer shell of the receiver is laminated of fiberglass and epoxy resin. To mold them better on a turned wood mandrel, pre-oiled parquet mastic. When drawing the contours of the shells, note that the area of the nozzle at the exit of receiver should be 75-100% of the area of the annular channel of the impeller. The fastening elements of the receiver to a shell —” clips of the magnesium alloy “electron”. In the outer shell cut a hole width of 8 mm, through which air enters to cool the motor.
All internal surfaces of the channels you need to Polish, this increases the efficiency of the impeller and, consequently, traction.
 
To access the electrode shell fairing slotted hole Ø 10 mm. the needle of the carburettor and the lever control the engine speed derived from the contours of the impeller.
 
The rotor spins counter — clockwise, if viewed from the side of the nose of Coca. To start the engine should the starter trick a shaft which has a rubber nozzle with an inner cone. Eat start, be careful — very intensively impeller sucks air through the inlet guide vanes.
 
In conclusion, a few recommendations for those who want to make a similar device. You should not confuse some “pereprodannosti” quasirational engine. This is because my design had to provide the ability to customize the varying angles of the fan blades, the selection of profile and angles of the vanes guide vane units. After identifying parameters in accordance with the engine speed many elements of the design can be significantly simplified, using advanced technological methods such as molding of synthetic resins and glass and carbon fiber. So, in particular, it is possible to make the fan blades or even the whole fan as a whole. In General, there is something to smash his head experienced modelers.

Noticed mistape? Highlight it and press Ctrl+Enter, to inform us.

Recommend to read

  • RACING MODEL — THE CHAMPION OF EUROPERACING MODEL — THE CHAMPION OF EUROPE
    In the early 70-ies before the Soviet athletes-automodellista was a challenge: dvuhsotmetrovy to exceed the threshold speed in the class of models 2.5 cm3. These days, the speed has...
  • SUPERDATABASESUPERDATABASE
    Only laudatory conclusions on flight characteristics received from everyone who was able to make her acquaintance, new polupoltina RC car. A great combination of handling and...

Spelling error report

The following text will be sent to our editors: