A frame for four servos is pro - vided in the fuselage. There is enough mounting space for two elevator-, a rudder and a tail wheel servo in standard size.

High-power LEDs (e.g. Seoul Emitter, 3.5 W) can be installed as position lighting in the wings and at the rear. Due to the high core temperature, they must be applied to heat sinks using thermal adhesive. These are usually rodlike, made of aluminum and have a diameter of 8 mm. The appropriate mount positions have already been structurally prepared. Control via constant current sources can be done by the gearCONTROL.846 .

The glare shield, an area for the instruments panel and a cockpit tub are prepared for further design on one´s own. Balsa of medium hardness is used here. The cockpit unit can be moved out in one piece. To lock, pins reach into the fuselage out of the backside of the unit. The unit is secured by a Bowden from the open nose.

In order to model the cock - pit canopy´s typical lattice frame, milled fiber glass components are bonded to each other. This results in a stable framework to be glued into the clear acrylic canopy.

The flaps servos can either be inserted and screwed from below through the flap ope - nings or from above through the canopy opening into two vertical servo frames. The servo arms are then screwed through the flap opening onto the servo drive.

The aileron servos sit in prepared frames that can be taken out of the wing at any time, e.g. to replace a defective servo drive.

Seven screws keep the main landing gear assembly in place. It can be mounted/dismounted as a single assembly group in minutes. The brus - hless outrunner and the electronic speed c o n t r o l l e r (ESC) are quite easily accessible through the landing gear opening either. By doing without a removable fiber glass cowling, weight could be saved. The wheels have a diameter of 125 mm. The wheel pant slides a bit into the inte - rior of the nacelle with the gear being extended.

D.H. 88 Comet.

Technical Details.

All spars arrangements are designed as „comb boxes“. That is, like a comb, the casing elements are inserted into the wing along the spars from above or below. This leads to a significant reduction in construc - tion time.

6. „Comb Boxes“

The places where the linkage cables are glued to the fuselage frames are already specified by design. The Bowden tubes thus follow a perfect curve between the servo and the rudder horn, which has the largest possible radii. This minimizes the friction of the cores and the rudder lash.

Unlike the original Comet , which has a tail skid, the glattCAD model has been given a relatively simple tail wheel for better practicality. Its rede - sign should therefore be reserved for the (scale) modeller, if desired. The steering is carried out via two steel braids. Fiber glass rudder horn, spring steel, wheel, adjusting rings and steel braid are included in the kit.

5. Tail Wheel

9. Cockpit Unit

Rudder, elevator and ailerons move in fillets. The axles consist of core and 0.8 mm spring steel of standard Bowden cables, which are normally used for controlling rudders of all types. They are pulled out of the tubules at the side or top, so that the rudder blades can be easily removed at any time. All rudder horns are included in the kit as milled fiber glass parts. They are bonded in the front balsa elements of the rudders. This results in reliable and practical controls.

The vertical and horizontal tail fins are built without the help of special jigs. Instead locating ele - ments in the regarding fuselage´s area guarantee right-angle and rail-guided bonding. Rudder and elevators are placed on jigs and still covered there with balsa on the upper side. As already mentioned above, all jigs can be (quickly) remo - ved from the assembly table at any build stage and be located elsewhere without risking warpage!

10. Rudder

12. Servo Frames

Further back in the battery duct, the bat - tery carrier abutment can be seen. A removable aluminium pin in the middle allows the abutment to be relocated. The 5.5mm „gold contacts“ glued into it auto - matically provide the electrical connection when pushing the carrier backwards. They also contribute to secure keep the battery in position. In addition it is secured from the front. An unintentional twisting of the abutment is constructively prevented by means of a pine rod directing backwards. It can be reached through the canopy opening.

The fuselage nose is removable. It is secured by four strong, guided pin magnets, which adhere to four flat magnets on the fuse side. These will be glued to the back of the four balsa blocks visible in the picture above. The linear guide, com - bined with the rare earth magnets, reliably ensure that the nose cannot bid goodbye in flight. The battery pack fixed on a fiber glass carrier is inserted from the front into the appropriate duct. The series of pictures on the right shows, from top to bottom, how to take the battery pack out. The battery duct is filigree and robust at the same time. It allows the fiber glass battery carrier to be locked in various defined positions. Small, milled, circular holes in the duct´s two protruding tongues serve this purpose. This concept offers the advantage to precisely adjust the center of gravity at any time and without any structural change. In the front area, under the duct, a receiver battery and a battery to power the retractable landing gear can be stowed away.

7. Battery Pack

Each core or cable that is to be run over a longer distance in the model lies in a thin- walled tube. Long party straws are used for this purpose. The corresponding circu - lar holes were specially designed in the related components. The wire ducts (orange) of the central electrical connec - tion between the fuselage and the wing is shown.

8. Wire Ducts

It is suffi - cient to secure the jig with a few weights or needles on the construc - tion table against slipping. As soon as a few more components have been instal - led, a fuselage or a wing half can be easily transported to another work station together with the jig. Any table or a door from the hardware store with the dimensi - ons 165 cm x 78 cm is perfect as a building board for the assembly.

Formers, wings- and empen - nage ribs are equipped with small „legs“. They are put into the corresponding slot of the poplar plywood „jig“. A war - page in assembly is practically impossible, provided that a straight construction table is used as a base.

1. Jigs

2. Main Frames

With the full-length double spar pairs made of pine wood and the balsa on the front and back, the two main frame boxes are very sturdy while being lightweight.

The central piece of the Comet includes the two engine nacelles with the undercarriages mounted in them. The width is 78.5 cm and can be easily put in a car with folded rear seats for transport.

Accessories Recommendation.

• 2 brushless outrunners e. g.: 400 .. 450 gr, Ø 50 mm, length 60..65 mm, KV = 250 .. 300 U/min/V • 2 HV electronic speed controllers 50 .. 80 A • Lipo 8s, 5000 .. 5800 mAh • 2 two-blade propellers ca. 15" x 12", best: left- and right-turning • 2 spinners Ø 76 mm • LED-lighting (according to your own idea; see also manual for gearCONTROL.846) • Wheels Ø 125 mm, width 45 mm

An electrical connector system is required to control the servo and the LED position light installed in the outer wing. The corresponding slots for installing “multiplex” connectors are already milled into the root ribs.

A high-quality STRONGAL® fuselage-surface connection from Petrausch Modellbau with 16mm pipe thickness ensures safety. Due to the jig system explained above, an absolutely par - allel duct of the two tubes in the fuselage central piece and outer wings is guaranteed.

3. Wing Connectors

Flight Properties.

For the development of the glattCAD D.H 88 Comet , a number of important parameters were analyzed and determined by software. They were incorpo - rated in the construction. The Reynolds effect was counteracted with the implementation of a moderate twist from the root ribs towards the tips at the expense of aerobatic capability. Fow slow loops, this causes the glattCAD Comet to fall out of the figure at the apex. This can also happen during inverted flight. That these maneu - vers do not really want to succeed is the price paid for more aileron effectiveness and safety. You can live with that, because the original Comet was not intended for such maneuvers either. In order to improve the dynamic stability around the z- axis, the tail surfaces have been slightly enlarged to improve the chance to react on an engine failure (combustion engine). The theory´s correctness has been confirmed in practice with excellent results! However certain peculiarities shall also not be concealed which could only be countered by design features to a limited extent. It takes a bit getting used to the Comet´s take-off behaviour, since it shows the ususal breakout attempts typical of a twin-engined plane. But experience proved that this bad habit can be eliminated with the installation of a modern electronic gyroscope. Counter-rotating propellers are also recommended. When landing, the gyro has another useful task: As a model with a conventional (taildrag - ger) undercarriage, the glattCAD Comet also tends to jump if the landing is not optimal. As soon as the tailplane bobs downwards at touch-down, the large underside area of the fuselage together with the wings´typical, rear - ward-pulled trailing edges at the root ribs support the tendency to bounce. A gyro per - fectly eliminates this rotation about lateral axis. The glattCAD Comet is designed to be driven by two brushless outrunners, but she can also be equipped with combustion engines. On request, suitable firewalls for the rear wall mounting are supplied for the chosen combustion motors.

A Comet as an RC model?

Sometimes the Comet is said to be „difficult to fly“, because of her incompa - rably elegant wing outline. It is said that she tends to sudden stalls and is not easy to pilot basically. Some constructive weaknesses are inevitably „impor - ted“ from the original aircraft. The strikingly tapered wing tips of the original aerodynamically may not be an issue for the full-scale Comet . In a quarter scale model, however, the running length of the air flow in the area of the outer wings is worryingly short. Moreover the flight speed is correspondingly lower. In the tip area of the wing, where small and larger flow detachments actually have to be parried with the ailerons, these are no longer fully effec - tive as a result of the physically unavoidable Reynolds effect - also known as the „scale effect“. The flight characteristics of a model aircraft depends on the design of its wings to a large extent. The „scale effect“ would best be faced by defusing the taper (apart from increasing the flight speed), because this would incre - ase the running length of the airflow. However, this is forbidden if you do not want to change the outline (top view) of the model. It is better to smartly select the wing airfoils and their distribution over the span. Naturally, Mr. Reynolds does not strike so hard, when the angle of attack of a cambered airfoil will be reduced to the outside. This measure is acceptable in terms of keeping to the outlines of the original aircraft, because it is prac - tically invisible. The RC model´s static and dynamic intrinsic stability via its three axes must be „preset“ constructively. In this regard, too, interventions in the outline of the model are largely forbidden. Again other variables depend on the stabi - lity, for example the landing speed, which is partly determined by the effectiveness of the flaps.

The undercarriage kit is available in the shop, except the wheels. It includes a grinding aid of milled MDF for preparing the steel tubes. The grinding aid has some grooves and holes, so that the tubes can be prepared for hard- soldering. Similarly, a jig made of milled ver - miculite helps to align the prepared tubes perfectly to each other for the welding process and to fix them on the fireproof material.

4. Main Landing Gear

The landing gear is retracted and extended by a small geared 12V DC motor that drives a spindle on which the drive nut slides. Waterproof micro switches can be used to detect the end position and switch off the geared motor. The switching states can be read and processed by the glattCAD gearCONTROL.846 . In addition, this small controller can also switch the landing headlight, and the rear and wing position lightings.

11. Flaps

The flaps are two-piece, as with the great original Comet.

13. Position Lights

The wire pairs can be sto - red cleanly in plastic tubes through the wing ribs, respectively fuselage for - mers.

Build Manual.

D.H. 88 Comet

Build Manual.

D.H. 88 Comet

Build Manual.

D.H. 88 Comet

Build: Ludwig Retzbach

Erbauer: Ludwig Retzbach

Technical Data.

Scale: 20% Wingspan: 268 cm Length: 177 cm Take-off weight: 7 .. 11 kg

Technical Data.

Scale: 20% Wingspan: 268 cm Length: 177 cm Take-off weight: 7 .. 11 kg

Technical Data.

Scale: 20% Wingspan: 268 cm Length: 177 cm Take-off weight: 7 .. 11 kg

Technical Data.

Scale: 20% Wingspan: 268 cm Length: 177 cm Take-off weight: 7 .. 11 kg

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General Terms

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Data Privacy

D.H. 88 Comet.

All spars arran - gements are designed as „comb boxes“. That is, like a comb, the casing elements are inserted into the wing along the spars from above or below. This leads to a signifi - cant reduction in construction time.

A frame for four servos is provided in the fuselage. There is enough mounting s p a c e for two elevator-, a rudder and a tail wheel servo in stan - dard size.

Rudder, elevator and ailerons move in fillets. The axles consist of core and 0.8 mm spring steel of standard Bowden cables, which are normally used for controlling rudders of all types. They are pulled out of the tubules at the side or top, so that the rud - der blades can be easily removed at any time. All rudder horns are included in the kit as milled fiber glass parts. They are bonded in the front balsa ele - ments of the rudders. This results in reliable and practical controls.

The vertical and horizontal tail fins are built without the help of spe - cial jigs. I n s t e a d locating elements in the regarding fuselage´s area guarantee right-angle and rail-guided bonding. Rud - der and elevators are placed on jigs and still covered there with balsa on the upper side. As already mentioned above, all jigs can be (quickly) removed from the a s s e m b l y table at any build stage and b e located elsewhere without risking warpage!

Further back in the battery duct, the battery carrier abutment can be seen. A removable aluminium pin in the middle allows the abutment to be relocated. The 5.5mm „gold contacts“ glued into it automati - cally provide the electrical connection when pushing the carrier backwards. They also contribute to secure keep the battery in position. In addition it is secured from the front. An unintentional twisting of the abutment is con - structively prevented by means of a pine rod direc - ting backwards. It can be reached through the canopy opening.

T h e f u s e l a g e nose is remova - ble. It is secured by four strong, guided pin magnets, which adhere to four flat magnets on the fuse side. These will be glued to the back of the four balsa blocks visible in the picture above. The linear guide, combined with the rare earth magnets, reliably ensure that the nose cannot bid goodbye in flight. The battery pack fixed on a fiber glass carrier is inserted from the front into the appropriate duct. The series of pictures on the right shows, from top to bottom, how to take the battery pack out. The battery duct is fili - gree and robust at the same time. It allows the fiber glass battery carrier to be l o c k e d in various defined positions. Small, milled, circular holes in the duct´s two protruding tongues serve this purpose. This concept o f f e r s the advantage to precisely adjust the center of gravity at any time and without any structural change. In the front area, under the duct, a receiver bat - tery and a battery to power the retractable landing gear can be stowed away.

F o r - mers, wings- and empennage ribs are equipped with small „legs“. They are put into the corresponding slot of the poplar plywood „jig“. A warpage in assembly is practically impossible, provided that a straight con - struction table is used as a base.

A high-quality STRONGAL® f u s e l a g e - s u r f a c e c o n n e c t i o n f r o m Petrausch Modellbau with 16mm pipe thickness ensures safety. Due to the jig system explained above, an absolu - tely parallel duct of the two tubes in the fuselage central piece and outer wings is guaran - teed.

Seven screws k e e p the main landing gear a s s e m b l y in place. It can be mounted/dismounted as a single assembly group in minutes. The brushless outrunner and the electronic speed controller (ESC) are quite easily accessible through the landing gear opening either. By doing without a removable fiber glass cowling, weight could be saved. The wheels have a diameter of 125 mm. The wheel pant slides a bit into the inte - rior of the nacelle with the gear being extended.

High-power LEDs (e.g. Seoul Emitter, 3.5 W) can be installed as position lighting in the wings and at the rear. Due to the high core temperature, they must be applied to heat sinks using thermal adhesive. These are usually rodlike, made of aluminum and have a diameter of 8 mm. The appro - priate mount p o s i t i o n s have already been structurally prepared. Control via constant current sources can be done by the gear - CONTROL.846 .

Technical Data

Scale: 20% (1:5) Wingspan: 268 cm Length: 177 cm Take-off Weight: 7 .. 11 kg

Build Manual

D.H. 88 Comet

A Comet as an RC model?

Sometimes the Comet is said to be „difficult to fly“, because of her incomparably elegant wing outline. It is said that she tends to sudden stalls and is not easy to pilot basically. Some constructive weaknes - ses are inevitably „imported“ from the original aircraft. The strikingly tapered wing tips of the origi - nal aerodynamically may not be an issue for the full-scale Comet . In a quarter scale model, however, the running length of the air flow in the area of the outer wings is worryingly short. Moreover the flight speed is correspon - dingly lower. In the tip area of the wing, where small and lar - ger flow detachments actually have to be parried with the aile - rons, these are no longer fully effective as a result of the physically unavoida - ble Reynolds effect - also known as the „scale effect“. The flight characteri - stics of a model air - craft depends on the design of its wings to a large extent. The „scale effect“ would best be faced by defusing the taper (apart from increa - sing the flight speed), because this would increase the running length of the airflow. However, this is for - bidden if you do not want to change the outline (top view) of the model. It is better to smartly select the wing airfoils and their distribution over the span. Naturally, Mr. Reynolds does not strike so hard, when the angle of attack of a cambered airfoil will be reduced to the outside. This measure is acceptable in terms of keeping to the out - lines of the original aircraft, because it is practically invisible. The RC model´s static and dynamic intrinsic stability via its three axes must be „preset“ constructively. In this regard, too, interventions in the outline of the model are largely forbidden. Again other variables depend on the stability, for example the landing speed, which is partly determi - ned by the effectiveness of the flaps.

Flight Properties.

For the development of the glattCAD D.H 88 Comet , a number of important parameters were analyzed and determined by software. They were incorpora - ted in the construction. The Reynolds effect was counteracted with the implementation of a mode - rate twist from the root ribs towards the tips at the expense of aerobatic capability. Fow slow loops, this causes the glattCAD Comet to fall out of the figure at the apex. This can also happen during inverted flight. That these maneu - vers do not really want to succeed is the price paid for more aileron effectiveness and safety. You can live with that, because the original Comet was not intended for such maneuvers either. In order to improve the dynamic stability around the z- axis, the tail surfaces have been slightly enlarged to improve the chance to react on an engine failure (combustion engine). The theory´s correctness has been confirmed in practice with excellent results! However certain peculiarities shall also not be con - cealed which could only be countered by design features to a limited extent. It takes a bit getting used to the Comet´s take-off behaviour, since it shows the ususal breakout att - empts typical of a twin-engined plane. But experi - ence proved that this bad habit can be eliminated with the installation of a modern electronic gyros - cope. Counter-rotating propellers are also recom - mended. When landing, the gyro has another useful task: As a model with a conventional (taildragger) undercar - riage, the glattCAD Comet also tends to jump if the landing is not optimal. As soon as the tailplane bobs downwards at touch-down, the large underside area of the fuselage together with the wings´typical, rearward- pulled trailing edges at the root ribs support the ten - dency to bounce. A gyro per - fectly eliminates this rotation about lateral axis. The glattCAD Comet is desi - gned to be driven by two brushless outrunners, but she can also be equipped with combustion engines. On request, suitable fire - walls for the rear wall mounting are supplied for the chosen combustion motors.

Accessories Recommenda-

tion.

It is sufficient to secure the jig with a few weights or needles on the construction table against slipping. As soon as a few more components have been installed, a fuselage or a wing half can be easily transported to another work station together with the jig. Any table or a door from the hardware store with the dimensions 165 cm x 78 cm is perfect as a building board for the assembly.

With the full-length double spar pairs made of pine wood and the balsa on the front and back, the two main frame boxes are very sturdy while being light - weight.

The central piece of the Comet includes the two engine nacelles with the undercarriages mounted in them. The width is 78.5 cm and can be easily put in a car with folded rear seats for transport.

An electrical connector system is required to control the servo and the LED position light installed in the outer wing. The corresponding slots for instal - ling “multiplex” connectors are already milled into the root ribs.

The undercarriage kit is available in the shop, except the wheels. It includes a grinding aid of milled MDF for preparing the steel tubes. The grinding aid has some grooves and holes, so that the tubes can be prepared for hard-soldering. Similarly, a jig made of milled vermiculite helps to align the prepared tubes perfectly to each other for the welding process and to fix them on the fireproof material.

The landing gear is retracted and extended by a small geared 12V DC motor that drives a spindle on which the drive nut slides. Waterproof micro swit - ches can be used to detect the end position and switch off the geared motor. The switching states can be read and processed by the glattCAD gear - CONTROL.846 . In addition, this small controller can also switch the landing headlight, and the rear and wing position lightings.

Build Manual

D.H. 88 Comet

Unlike the original Comet , which has a tail skid, the glattCAD model has been given a relatively simple tail wheel for better practicality. Its redesign should therefore be reserved for the (scale) modeller, if desired. The steering is carried out via two steel braids. Fiber glass rudder horn, spring steel, wheel, adjusting rings and steel braid are included in the kit.

Build Manual

D.H. 88 Comet

Build Manual

D.H. 88 Comet

Each core or cable that is to be run over a longer distance in the model lies in a thin-walled tube. Long party straws are used for this purpose. The corresponding circular holes were specially desi - gned in the related components. The wire ducts (orange) of the central electrical connection bet - ween the fuselage and the wing is shown.

In order to model the cockpit canopy´s typical lat - tice frame, milled fiber glass components are bonded to each other. This results in a stable frame - work to be glued into the clear acrylic canopy.

The flaps servos can either be inserted and screwed from below through the flap openings or from above through the canopy opening into two vertical servo frames. The servo arms are then screwed through the flap opening onto the servo drive.

The flaps are two-piece, as with the great original Comet.

The aileron servos sit in prepared frames that can be taken out of the wing at any time, e.g. to replace a defective servo drive.

The places where the linkage cables are glued to the fuselage frames are already specified by design. The Bowden tubes thus follow a perfect curve bet - ween the servo and the rudder horn, which has the largest possible radii. This minimizes the friction of the cores and the rudder lash.