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My first foam plane.

quorneng

Well-known member
#1
I am sure like many aero modelling had to take a back seat to my career and family although 'building things' did return when my eldest expressed an interest in Lego and guess who took it to an extreme.
As the career wound down and I could afford it I decided to try an modern electric RC RTF a humble Artech Wing Dragon Sport. First released in 2000? but by then (2009) it was decidedly 'old hat' and as result it was 'on offer' . Old habits die hard!
ARTF1.jpg

A brushed 540 with 9.6V 1000 mAh NiMh battery on 35 mHz but it did fly well enough and was modestly aerobatic although each flight was not very long.
To my mind it was pretty crude.
'Foam' aileron hinges which meant its four 9g servos had to work quite hard to simply deflect the control surface. The long metal control rods for the rudder and elevator weighed nearly as much as the servo moving them and a 'floppy' set of tail feathers.
The solid foam wing felt rather heavy and with just a short dihedral brace it was not a particularly good structural use of the foam material.
The cheap Tx and Rx supplied did work pretty well but by far the best bits were the nearly indestructible polypropylene blow moulded fuselage and the glass fibre tail boom.
Within a few months of the Wing Dragon I bough my first sheet of 3 mm Depron which set me wondering, how much lighter might a direct replacement wing be but built hollow and in Depron.
Built in a conventional style with ribs. Depron sheet is quite strong, particularly in tension, so no spar as such just a shear web at the maximum wing thickness. All the loads to be carried by the wing skin, or in other words a true monocoque construction.
RHwing2.jpg
With very free moving top tape hinges much smaller and lighter servo could be used.
servo1.jpg
The end result gave a remarkably bland and smooth finish for just half the weight and it certainly felt plenty strong and rigid enough.
Rcompl1.jpg
Shaving off 2 oz (50g) off the all up weight along with improved wing aerodynamics made a startling difference to the performance.
WDdepron2.jpg

Loops and rolls could be performed at any time and it could now 'cruise about' at reduced throttle for twice as long as before.
Then came 'brushless and LiPo' but that is another story.
Picture5.JPG
It is still flying 10 years on. Guess which bits are still original Wing Dragon! ;)
 

quorneng

Well-known member
#2
Perhaps I should complete this story although technically it is still going on.
The great improvement in performance using the built up 3 mm Depron wing was more than matched by the change to LiPo and brushless.
I selected an Timex 2812 1500 kV motor as it seemed to have similar power to the 480 'race' brushed (It had replaced the worn out 540) and it was only 1/3 the weight.
1500kV.JPG


Cowling.JPG

The lower weight suggested it would need a lighter battery to maintain the CofG so a 1500 mAh 3s LiPo was selected.
Overall this combination gave 50% more capacity and shaved a further 5 oz (114 g) off the already lightened 25 oz (680 g) Wing Dragon.
Performance was greatly improved.
The next items were the 9g servos, the servo tray, the long metal push rods & the flimsy tail feathers.
3 mm sheet Depron with a balsa leading and trailing edge were quite as stiff and a bit lighter than the original plastic ones. I had already set up the ailerons in the Depron wing to have a differential action which virtually removed the need for a rudder so it could be flown 'bank and yank' with just an elevator servo.
Elvtrservo.jpg

By placing the servo in the tail with just a short link rod to the elevator horn a much smaller 3.7g servo was perfectly adequate.
Finservo.JPG

The servo wire and the rx aerial both ran inside the boom to keep clear of the prop.
The net result meant a further ounce was saved. Removing the undercarriage (no loss as I fly from a rough grass field) saved a bit more weight and improved the aerodynamics further. The ready to go weight was now just 18 oz (510 g). Vigorous aerobatics and flights of 30 minutes were now quite possible.
With so much weight removed I felt the wing area was actually more than required so keeping the same span but tapering the wing to reduce the area to 70% would not only allow it to fly faster and handle wind better but would also provide a better structural solution.
Just for fun I added flaps as well.
Fullflaps.JPG

The final variation, and how it has been for the last 5 years, was to change to a V tail.
Picture5.JPG

Such a tail works well with a grass belly lander and by keeping all the tail surfaces out of the direct prop wash actually improves the performance just a bit too.
The single servo 'buried' in the root of the left hand tail plane works both elevators.
The V tail and smaller wing are lighter than before so exactly compensates for the two extra servos required to work the flaps. It thus still only weighs 18 oz (510 g).
A short edited video of it doing it stuff in 2015.
It can and still does! ;)
 

Monte.C

Well-known member
#4
Perhaps I should complete this story although technically it is still going on.
The great improvement in performance using the built up 3 mm Depron wing was more than matched by the change to LiPo and brushless.
I selected an Timex 2812 1500 kV motor as it seemed to have similar power to the 480 'race' brushed (It had replaced the worn out 540) and it was only 1/3 the weight.
View attachment 185911

View attachment 185915
The lower weight suggested it would need a lighter battery to maintain the CofG so a 1500 mAh 3s LiPo was selected.
Overall this combination gave 50% more capacity and shaved a further 5 oz (114 g) off the already lightened 25 oz (680 g) Wing Dragon.
Performance was greatly improved.
The next items were the 9g servos, the servo tray, the long metal push rods & the flimsy tail feathers.
3 mm sheet Depron with a balsa leading and trailing edge were quite as stiff and a bit lighter than the original plastic ones. I had already set up the ailerons in the Depron wing to have a differential action which virtually removed the need for a rudder so it could be flown 'bank and yank' with just an elevator servo.
View attachment 185916
By placing the servo in the tail with just a short link rod to the elevator horn a much smaller 3.7g servo was perfectly adequate.
View attachment 185917
The servo wire and the rx aerial both ran inside the boom to keep clear of the prop.
The net result meant a further ounce was saved. Removing the undercarriage (no loss as I fly from a rough grass field) saved a bit more weight and improved the aerodynamics further. The ready to go weight was now just 18 oz (510 g). Vigorous aerobatics and flights of 30 minutes were now quite possible.
With so much weight removed I felt the wing area was actually more than required so keeping the same span but tapering the wing to reduce the area to 70% would not only allow it to fly faster and handle wind better but would also provide a better structural solution.
Just for fun I added flaps as well.
View attachment 185920
The final variation, and how it has been for the last 5 years, was to change to a V tail.
View attachment 185921
Such a tail works well with a grass belly lander and by keeping all the tail surfaces out of the direct prop wash actually improves the performance just a bit too.
The single servo 'buried' in the root of the left hand tail plane works both elevators.
The V tail and smaller wing are lighter than before so exactly compensates for the two extra servos required to work the flaps. It thus still only weighs 18 oz (510 g).
A short edited video of it doing it stuff in 2015.
It can and still does! ;)
Wow look at that old motor. Reminds me of what we were using 30 years ago!
 

quorneng

Well-known member
#5
ScottyWarpNine
The fairing was made of Depron so weighed just a fraction of a gram so balance no problem although I doubt it made any discernible difference. It had a hollow centre it still let cooling air out not that there was much anyway as it requires very little power to fly. The outer surface of the bell was also in the full airspeed airflow so added significantly to the cooling.
Monte.C
Nothing wrong with that style of motor if you are after electrical efficiency rather than absolute power. ;)

The final chapter was when I wondered how long it could fly if I put in a big battery? Like a 5000 mAh 2s.
5Ahbatt.jpg

Along with a light weight (no flaps) wing of the same span as the original Wing Dragon wing.
Picture4.jpg

The answer was a very boring 90 minutes, power on the whole time.
This posed the question if I kept to the same formula and convenient size but started again from scratch and optimised everything for endurance how much longer would be possible. :unsure: