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Scale Build-Off – RQ-7 Shadow

HilldaFlyer

Well-known member
#1
Last year before winter set in, I embarked on a project to build the RQ-7 Shadow using foam core.
I thought I would share the process...



The RQ-7 Shadow
is an unmanned aerial vehicle (UAV) with a high-wing, constant chord pusher configuration with a twin-tail boom empennage and an inverted v-tail elerudder. The aircraft is powered by a 38 bhp Wankel (rotary) engine and has fixed tricycle landing gear. It is launched with a pneumatic catapult and it is recovered with the aid of arresting wire similar to jets on an aircraft carrier.
Full-size Stats:
General characteristics

  • Length: 11.2 ft (3.4 m)
  • Wingspan: 14 ft (4.3 m)
  • Height: 3.3 ft (1.0 m)
  • Empty weight: 186 lb (84 kg)
  • Gross weight: 375 lb (170 kg)
  • Powerplant: 1 × Wankel UAV Engine 741 used only with Silkolene Synthetic Oil , 38 hp (28 kW)
Performance

  • Maximum speed: 127 mph; 204 km/h (110 kn)
  • Cruising speed: 81 mph; 130 km/h (70 kn)
  • Range: 68 mi (59 nmi; 109 km)
  • Endurance: 6 h/ 9 h Increased Endurance
  • Service ceiling: 15,000 ft (4,572 m) ELOS (Electronic Line Of Sight)




Why build a single motor pusher?
My first model airplane was the Dynam Hawk Sky. I purchased it as a trainer because of a wise recommendation that a beginning pilot should not have the motor in the front of the plane. The pusher design has proven effective as the motor has survived numerous nose-first encounters with mother Earth, roofs and trees.
Ever since flying the Hawk Sky, I have had a desire to create a pusher configured twin-boom plane. Why a twin boom, you may ask? Well, designs like the Hawk Sky, Bixler, Sky Surfer etc. have single boom and a motor mounted above the wing. The limited distance between the motor and boom limits the prop size, not that this is bad. It also puts the thrust direction out of line with the wing and fuselage so that the thrust from the motor is pushing down at the center of lift. It is logical to thrust toward the center of lift to prevent deviations in pitch when throttling up or down, but at the same time, it just seems counter intuitive to thrust down to go up. A twin boom would allow the motor to push directly in line with the wing.
When researching different twin boom tail configurations, I got really excited about trying the inverted “V” tail because through my reading I learned that one of the benefits was the angle of the tail control surfaces produced a obligatory coordinated turn since the yaw, roll and pitch were all linked through the control surfaces on the tail. My first thought was to build the MQ-1 Predator, but I dissuaded myself with the argument that the downward projecting control surfaces would not survive landings on a grass field.
In my searches for inverted “V” tail construction, I ran across the real deal, the RQ-7 Shadow. The twin boom configuration allows the motor thrust to be placed directly behind the main wing and in front of the tail controls surfaces. There was only one problem - I searched the internet again and again for plans, but didn’t find any. Even coming up with 2D drawings was hard, however, through my intensive searches I was able locate a few profile photos of the RQ-7 Shadow as well as a couple profile drawings.

The first prototype was small hand-launch glider that did not have mechanized control surfaces.


The prototype worked well and even with static control surfaces, flew (glided) quite nicely.
The powered version was created from the plans scaled up to give a 100 cm wingspan. The 100 cm wingspan was deliberately planned to conveniently be double the width the width of Readi-Board. The only non-scale part of the RQ-7 Shadow-100 was the enlarging of the tail control surface size because they just didn’t look big enough.


 

Attachments

jhitesma

Some guy in the desert
Mentor
#6
Ohhh, another build off build I'm going to have to pay attention to :D Got to see one of these up close in person at our local airshow last March. I only got two photos but here they are in case they help you out any:

11018178_10152606668906805_1346327390_o.jpg

11028705_10152606669066805_369019816_o.jpg

If you want higher rez copies for reference drop me a PM (in case I forget to check the thread again soon!)
 

Jaxx

Posted a thousand or more times
#8
For some reason I can't seem to find any good 3-view drawings of this aircraft. Anyone else had any luck?
 

jhitesma

Some guy in the desert
Mentor
#9
Great photos! I think the biggest challenge is to find a material for the tail booms - skinny and strong.
Well, carbon fiber is always a good but expensive option :)

You could also make your own composite material. Do a search on youtube and you can find a number of videos on how to do it. Instead of using CF you could use fiberglass, or even paper or silk or some other light material.

Or you could do something like use 1/2" wood dowels and just add a paper shroud around them so the strength comes from the wood boom but the paper makes it look like a tube.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#12
True . . . but 4mm tube is not quite to scale with a 1m span -- that sets the scale at roughly 30% and a 40mmx1770mm boom depicted in the 3-view is closer to 12mmx530mm . . . so perhaps this?

http://www.hobbyking.com/hobbyking/store/__9784__Carbon_Fiber_Tube_hollow_12x750mm.html

Not pocket change, but $11+shipping for a major structural element (you'll need two) isn't crazy either -- even available in the US-West, if you order now ;)
 

PHugger

Church Meal Expert
#13
Mandrel Wrapped Kite spars.
These are much lighter than Pultrude carbon sticks (like arrow shafts).
They have different characteristics. The wrapped sticks are very light, hollow and strong, but more expensive.

I'm fairly familiar with Avia and Skyshark brands and would endorse either.
They have two types - tapered and "straight"
All mandrel wrapped sticks are tapered otherwise you could get them off the mandrel, but the "straight" ones are barely tapered.
The "straight" sticks are normally used for the center Spine of a normal dual line stunter.
Screen Shot 10-20-15 at 05.04 PM.JPG

Another good source for straight sticks would be Revolution kite spars. This is a quadline kite that has a long multi-section spine at the top.
Screen Shot 10-20-15 at 05.05 PM.JPG

Just about any online kite shop will carry replacement sticks.



Best regards,
PCH


PS - I think Nerd Nic used some type of CF sticks one of his models....
 

HilldaFlyer

Well-known member
#15
True . . . but 4mm tube is not quite to scale with a 1m span -- that sets the scale at roughly 30% and a 40mmx1770mm boom depicted in the 3-view is closer to 12mmx530mm . . . so perhaps this?
;)
You hit it right on. For a plane with 1m wingspan, those booms should be 1.2 cm thick. While CF is light, a CF tube that big is pretty hefty, and it is all behind the CG. It will take a lot of nose weight to compensate.

So far I'm seeing what will happen with triple wide foam and 3 mm carbon tubes, one acts as a control rod chase.

DSCN3122.JPG
 

HilldaFlyer

Well-known member
#16
Mandrel Wrapped Kite spars.
These are much lighter than Pultrude carbon sticks (like arrow shafts).
They have different characteristics. The wrapped sticks are very light, hollow and strong, but more expensive.

I'm fairly familiar with Avia and Skyshark brands and would endorse either.
They have two types - tapered and "straight"
All mandrel wrapped sticks are tapered otherwise you could get them off the mandrel, but the "straight" ones are barely tapered.
The "straight" sticks are normally used for the center Spine of a normal dual line stunter.
Another good source for straight sticks would be Revolution kite spars. This is a quadline kite that has a long multi-section spine at the top.
Just about any online kite shop will carry replacement sticks.

Best regards,
PCH

PS - I think Nerd Nic used some type of CF sticks one of his models....
Great Idea - I'll have to check it out.
 

HilldaFlyer

Well-known member
#19
Mounting the servos

Made some progress over the Christmas vacation. Mounting servos into the wing needs special placement so that the servo are is at just the right height so the control rod can be fed through the carbon fiber tube to the tail.






After cutting a hole in the bottom wing panel, I needed to build a "platform" for the servo to sit on. I just made a bunch of little pieces and glued them in the hole to the inside of the top wing panel.


The servo wires were fed to the middle of the wing.



And the control are and servo installed.



This is how the tail end looks.