DE2850171A1 - TOWING DEVICE ON AIRCRAFT - Google Patents

Description

-A-

DORNIER GMBH
7990 Friedrichshafen

Reg. 2445

Device for towing on aircraft

The present invention relates to towing devices on aircraft, such as tow bags, tow bands or flags, in particular for air target display.

A peculiarity of such devices made of flexible materials is their tendency to flutter during the towing process. This results in a significant increase in air resistance. At slow flight speeds, up to around 200 knots, the flutter phenomena are counteracted by using tow bags the hose-like part has one or more openings at its end in the area of the bottom wall through which the air inside can escape to the outside. It is also known to use drag bags with a diameter tapering towards the bottom wall, this measure is also applied together with the openings. During the towing process, the

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Tow bag creates a strong internal pressure, which causes stiffening and keep the tow bag inflated.

At higher flight speeds, however, this training takes place of tow bags the air resistance increases so much that the performance of the tow planes can be uneconomically high got to. For this reason, tow bags are used for higher speeds, the air inlet cross-section of which is only insignificant is larger than the cross section of the air outlet in the area of the bottom wall.

In particular in the rear area of the tow bag and in the same way also in the case of tow lugs due to the separation of the flow caused flutter phenomena, reach such an intensity at higher dynamic pressures that the firmness of the tissue is exceeded many times and cracks form, which within a short time lead to the destruction of the towed facility as a whole to lead.

The present invention is based on the problem of the disruptive and destructive flutter phenomena on flexible devices, such as tow bags or towing flags, to eliminate or to reduce without causing adverse effects in terms of air resistance. It is also an object of the invention to provide such Facilities for towing qn aircraft for higher

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To make flight speeds more suitable than was previously the case.

The object is achieved according to the invention in that in the area of the rear end of the towed device or several disruptive bodies protruding into the flow beyond the contour of the towing device walls around which the flow is flowing are arranged.

The inventive design ensures that an increased pressure is applied to the front side of the disruptive body in the direction of flight (Damming up of the flow), whereby the tensile stress in the material of the towed device is increased. This will make the Causing of flutter vibrations, namely reciprocal rocking of the changes in the curvature of the tissue, as a result of the local Pressure changes in the flow around the facilities prevented or significantly reduced. The disruptive bodies can be made of metal, Plastic or, given a suitable shape, be made of elastic material.

In the drawing, conventional and towing device designs according to the invention are shown in comparison and based on explained in more detail in the following description.

It shows:

Fig. 1 as a comparison to the training according to the invention in

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perspective view one for low airspeeds used tow bag with bottom wall and flow openings,

2 shows a further known embodiment of a tow bag without a bottom wall for higher flight speeds in perspective Depiction,

3 shows the execution of a tow bag in a perspective representation according to the invention,

4 according to FIG. 3 the flow conditions at the rear part of the tow bag, which is shown here in longitudinal section,

5 shows a further embodiment of a tow bag according to the invention, shown in longitudinal section,

Fig. 6 shows the rear part of the tow bag in a longitudinal section in another embodiment of the tow bag and

7 shows a perspective illustration of the design according to the invention on a towing flag.

The towing devices shown in FIGS. 1 and 2 are to generally known designs, namely according to FIG. 1 to tow bags for slow flight and according to FIG. 2 for higher towing speeds.

According to FIG. 1, 1 denotes the tow bag, which is known in the art Way consists of a cylindrical or slightly conical hose part 2 formed from flexible material, the hose part 2 is open against the oncoming flow via an opening 3 and is closed off at the rear end by a bottom wall 4. In the field of

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rear bottom wall 4 has the hose part 2 distributed over the circumference Outflow openings 5 to discharge the air flowing into the hose part 2 in a certain manner to the outside, so that the tow bag is kept inflated. With 7 the towing gear and with 8 that of the towing device, not shown here subsequent tow rope and S denotes the flow surrounding the tow bag.

According to the known embodiment according to FIG. 2, a bottom wall, as in the embodiment according to FIG. 1, is not present for higher flight speeds. The rear opening is denoted by ^{3 1.}

Compared to the known embodiments, in Fig. 3 according to the invention a tow bag 1 is shown, which at the rear end of the hose part 2 extends over the outer contour of the hose part in the flow S extending disruptive body 11 in the form of a ring part firmly carries. The ring part has an L-shape in cross section on, the cylindrical connector 13 with the cylindrical, tubular tow bag part 2 by riveting, gluing or the like is firmly connected and the circular ring disc 14 protrudes outwardly into the flow as an interfering edge.

In FIG. 4, the flow conditions are explained on the basis of the exemplary embodiment according to FIG. 3. In addition, 15 and 16 mean close to the wall

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Stream threads, while the signs +, ++ and - over- and underpressure areas in relation to the static pressure of the undisturbed flow. Here h is the height of the protruding into the flow Annular disk 14, where h ^ the local boundary layer is dimensioned at maximum towing speed. 16 'indicates the stagnation point line. The air flowing into the tow bag 1 via the front opening 3 can be unhindered via the rear opening 3 ' flow away. The flow close to the wall on the outside of the tow bag hose part 2 (stream threads 15, 16) must be the obstacle in the form of the circular ring disk 14, with an increased pressure area in the interior of the hose at ++ and an overpressure area on the outside + builds up. In a known manner, a negative pressure area is created behind the circular ring disk 14. As a result of this pressure distribution the end of the bag is prevented from fluttering even at high towing speeds. As a result, tow bags of the type mentioned can also be used for towing speeds that are far higher than previously possible.

In the embodiment shown in FIG. 5, instead of the interfering body 11, which is L-shaped in cross section, according to FIG. 3, the engagement In the flow in the area close to the wall, a flow body 18 with a funnel-shaped widening in the direction of the flow S Section 19 is provided. The disruptive body 18 is over

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a cylindrical section 20 is connected to the hose part 2 of the tow bag, e.g. by gluing or riveting. The flow diagram shown in FIG. 4 is also valid here. When towing, forms in the area close to the wall · within the Tow bag part 2 an increased overpressure area ++, outside a Overpressure area + and behind the disruptive body 18 a negative pressure area - the end. The height h of the funnel-shaped subsection 19 is also here = the local boundary layer at maximum towing speed. The stagnation point line running around the circumference is also indicated at 16 ".

In Fig. 6, a further embodiment is shown in connection with a tow bag. Here, the disruptive body 21 has a T-shape Cross-section, the cylindrical section 22 for connecting the disruptive body 21 to the hose part 2 of the tow bag 1 serves. The ring part 23, 23 'protrudes from its cylindrical section 22 radially over the outside and inside of the tow bag hose part 2 into the flow S, both inside and outside at least approximately the conditions for the height h or h 'for the partial ring section 23 or 23 = the local boundary layer is adhered to at maximum towing speed.

Finally, FIG. 7 shows the disruptive body according to the invention in connection with one that can be towed by a towing device

Towing vane 25. Here, in the area of the trailing edge of towing vane 25, the cross-sectionally T-shaped disruptive body 26 is arranged, which is attached to the towing vane 25 via its web section 27 and its belt section 28 or 28 'on both sides of the towing vane by the same amount h, h ¹ intervenes in the flow close to the wall of the ^{drag vane 25 with h or h 1} = the local boundary layer at maximum drag speed. In this case, the pressure and flow conditions indicated in FIG. 4 arise when there is flow around them during the tow plow. In addition, in the embodiment according to FIG. 7, the belt section 28, 28 ′ lying transversely to the flow has mutually parallel slot-shaped openings 30 for the flow. A perforation or the like is also conceivable instead of the slots.

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Nov. 13, 1978 J ^

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Claims (1)

DORNIER GMBH
Friedrichshafen Reg. 2445 Patent claims: 1. Devices for towing on aircraft, such as tow bags, Towing straps or flags, in particular for air target representation, characterized in that in the area of the rear At the end of the towed device (1; 25) one or more into the flow over the contour of the towed device walls around which the flow is flowing protruding disruptive bodies (Π; 18; 21; 26) are arranged are. 2. Device according to claim 1, characterized in that the height (h, h ¹ ) of the disruptive bodies (11 ;, 18; 21; 26) projecting beyond the contour of the device is dimensioned to be equal to or greater than the local boundary layer at maximum towing speed. 3. Device according to claim 1 or 2, characterized in that the disruptive body (11 ;, 18; 21; 26) consists of an elastic material. / 2 030021/0492 4. Device on tow bags according to claim 1 to 3, characterized in that that the disruptive body (11) by a in cross section L-shaped ring part with connecting piece (13) is formed and whose circular ring disc (14) protrudes into the outer flow (S) as an interfering edge (with the height h). 5. Device according to claim 1 to 3, characterized in that the disruptive body (21) has a T-shaped cross section and with his Ring section (23, 23 ') inside and outside of the tow bag hose part (2) (with height h, h ') protrudes into the flow (S) as an interfering edge. 6. Device according to claim 1 to 3, characterized in that the disruptive body (18) extends in the flow direction (S) from a section (20) for the tow bag connection in a funnel shape to the extending into the flow protruding section (19) (with the height h). 7. Device in the manner of a towing flag according to claim 1 to 3, characterized in that the disruptive body (26) has a T-shaped cross-section and engages with its web section (27) on the towing flag end and that the belt sections (28, 28 ') on both sides of the Towing flag (25) (with the height h, h ¹ ) protrude into the flow (S). «30021 / OA82 / 3 285-71 8. Device according to claim 1 to 7, characterized in that that the strap sections (28, 28 ") openings (30) for have the passage of the flow. Nov 13, 1978
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