D-KJTN
didn’t have a wing dolly system when I purchased here, the aircraft
was always in the hanger fully assembled. However part of the purchase
negotiation was that the previous owner would provide me with a basic
support system for the aircraft, which made me quite happy so at least
I was able to fold the wings for storage on arrival at the NATO airbase
in June 2007.
Modifying the dolly with some metal bookshelf’s
After ferrying the aircraft from Germany to Belgium it became immediately
clear that the design lacked some sturdiness. After hanging in the
wings the wing support had the tendency to bend. We solved this problem
initially with some wooden blocks as temporary solution. The next
week I added a steel bookshelf support so the whole thing wouldn’t
collapse.
So after a year flying and assembling the bird by lifting wings it
became clear that a less muscle intensive system would be highly desirable,
if I wanted to save my back! Having renovated a house and doing most
of the labour intensive work, didn’t do any good on my lifting
capability. A support tool for wing lifting/rotation would avoid a
regular visit to a physiotherapis. For your information each half
of a wing weighs 75Kg.
Mounting the wings is not that difficult but still requires minimum
two persons and some supporting frames in order to put on the flippers
on. My techniques consisted of supporting the left wing, while shoving
in the right wing, this avoids that the oleo on one side compresses
and the airframe bents to one side making it more difficult to slide
in the remaining wing.
Design
Requirements
Starting
to draw
During last summer period in 2008 It became clear I had to design
my own system. The objective was to make the system as less muscle
intensive as possible. In order to achieve this I opted for an all
electric linear actuated system. Firgelli automation makes these wonderful
electric actuators which are NOT at all expensive if compared to other
industrial equipment. I started to draw based on my requirements.
Drawing some ideas on paper
The requirements were:
- one man should be able to tow and assemble the Taifun. All Taifun
owners know the problem when assembling. Sometimes it goes like a
breeze sometimes, however you end up sweating and swearing…
- Another requirement was the alignment should be flexible in at least
two axes. The aircraft is on oleos and this means the height between
the left and right wing tip is not always the same. On top the tarmac
in front of our hangar has the tendency to go down on all sides.
To weld
or not to weld?
Drawing a nice idea is one thing, execution is another! I was looking
for welding expertise someone who could help me out on that. After
several phone calls I finally found a technical school teacher that
was willing to help on the welding part….After spending an evening
and several phone calls to the person in question it became very clear
that he don’t have the time or the motivation to continue with
the project…
In addition if I wanted to execute the project idea, I had to learn
to weld and do glass fiber lay-up work! I realized also that during
the project execution a lot of small adaptations had to be made as
the whole thing was more or less a proto-type….
After
some reading and investigations on the internet I decide to buy me
an inexpensive inverter welding machine of max 160A.
Today’s
welding machines contain some sophisticated electronics IGBT or Insulated
Gate Bipolar Transistors. Modern Electronics has made it possible
to “invert” a D.C. signal into a medium frequency (400
to 1200 Hz) A.C. signal which is applied to a compact medium frequency
Welding Transformer. The physical iron core cross sectional size and
weight of a Welding Transformer is inversely proportional to the input
frequency; therefore, Medium Frequency Inverter Welding Transformers
are much more compact than conventional 60 Hz Welding Transformers.
The output of the Welding Transformer is rectified to produce a clean
D.C. output with no Inductive Loss. Advanced high-speed electronic
circuitry within the Welding Control samples IGBT and Welding Transformer
output signals in real time and automatically compensates for variances,
which may occur during the welding sequence. This method of Closed-Loop
Feedback makes Inverter Technology the clear choice for critical metal
joining applications.
Getting
back to basics.
After
starting my welding exercise I realised soon I had to reduce the complexity
of the device and make the whole system manual and not electrically
actuated as on the initial plan. This would significantly reduce the
cost for the whole project.
Also I was going to change the wing support and make the whole thing
out of glass fibre in order to reduce the weight and stress on the
wing.
In stead of the electrical actuators I opted for jack-screw solution.
I found in Hungary some old fashioned jacks which were of Polish-Russian
origin…. The really are very strongly build, strong enough to
lift a T34 tank, well almost.;-))!
Lay
it up
In
order to build the actual wing support in glass fibre, I had to build
a positive mould. I was total novice in moulds or even on glass fibre.
I decided to build a mould in wood and polystyrene. I found the FX-67
profile on the website of The Department of Aerospace Engineering
at the University of Illinois.
http://www.ae.uiuc.edu/m-selig/ads/coord_database.html#F
Then
I plotted the profile on a piece of triplex based on the x/y ratio
calculation with respect of the actual (measured distance from the
fuselage) wingspan. After having two pieces I bolted two pieces of
threaded steel tubes of M8 with several rectangular pieces of polystyrene
in between so the actual thickness was about 40cm. I build an electrical
cutting wire from the remainder of the triplex wood, connected it
to a 15V DC supply with current limitation and started cutting the
wing profile out. This worked very well. Caution, don’t inhale
the fumes as they are very toxic! Do this only in a very well ventilated
environment!
Almost finished positive mould
After sanding the small dents etc out of the foam and wood I applied
some epoxy filler and laid a layer of 300g fiberglass over the mould.
The whole thing was then finalized with some clear epoxy gel coat
to make it smooth. Before starting the layup work the mould was release-WAX
sprayed for easy removal.
The
whole mould was then screwed onto a flat wooden base so it was much
easier to manipulate during the glass-fiber lay-up work. I opted for
a sandwich construction as this seemed to offer the best stiffness!
The inner base consists of three layers of 300g glass fiber. Then
at the center, a piece of triplex wood is used as support for the
hinges, when rotating the wing horizontal. The middle layer consists
of a special PVC cell foam material then can be cut in 2cm pieces.
This material is also used to build the two stringers (ribbons). The
foam is 5mm thick and each ribbon consists of 11 layers soaked in
epoxy. The ribbons are then sanded and equalized with epoxy filler
so a smooth surface was obtained. The outer Schell is then laid up
with 3 layers of 300g of glass. The ribbons are covered with three
layers of 100g glass. The 100g is much easier to fold and manipulate
in the corners.
First example reaches its roll out. Note: The adjustable center gravity
for the wing balance.
It was a very time consuming exercise and I was quite relieved when
the whole work was done. Please when working with epoxy glass, always
use the necessary protection cloths and masks.
I learned a lot from it and also understand better how critical bonding
is on glass fiber aircraft…..
Building
the metal frame
I spent several weekends on welding exercises I used some small pieces
of material I was going to use to build the frame, after a while I
got a better feeling on it but still I believe welding remains an
art to be fully understood after several years of working in that
profession..
The tubes I used were 25X25mm thickness 1.5 mm for the inner telescope
20x20mm thickness 2mm. I used the metal bookshelves (again) to fix
the structure and obtain a nice 90 degree angle.
Although
far from perfect I believe the frames are strong enough for this non
critical application. On top I build in some mechanical redundancy
so a single weld failure would not lead to catastrophe. Welding an
engine mount is another ballgame..;-))…not for me…
On beautiful autumn day I finally could test drive the system.
Getting some air for a slide-in test.
The towing
gear
After building two folding systems it was time to build the towing
system. The requirements here were:
- able to move the aircraft in and out of the hangar all alone
- a manual push-pull bar in combination with an electrical tow system
- a system to lower the tail and lock it without using to much force
The challenge here was to find the right angle between the back folding
wings and the tow system. I solved this issue by using a double T
which can be moved over limited degree angle. The hinge is made with
a massive bold of M12.
The cradle had to be massive enough so that when pulling the tail
downward the whole system doesn’t float. I didn’t use
a force spring to measure how many kilograms pull force was required.
The weight was estimated on empirical basis (lifting my kids to bed
every day gives me a good idea how much kilo’s you can lift..;-).
For the electrical tow system I used a relatively cheap (made in China)
caravan mover. The thing can pull 2,5 tonnes and moves really very
slowly. I works great when you are manoeuvring left and right to get
the position right.
The cradle and the electrical towing gear. Note, the manual reversion
handle in parallel
The cradle has three castering wheels. Also on the back I mounted
a small winch, with this device I am able to pull the tail downward
and put a locking pin in the tie down hole.
The whole frame is connected together with four easily removable locking
pins. The whole play is about 10cm and not critical as several adjustment
holes are drilled in case the wing support is a bit more for or backward
with respect to the central cradle.
The final
result
It took a very long time to build and to think on all small details.
However I am very happy with the result. I am able to roll out, assemble
and move my aircraft back in the hangar all alone.
After folding out the wings its just a breeze to rotate the wings
90 degrees, align the height with the jacks and do a minor angle adjustment
so the guidance pin go smoothly in the fuselage. The assembly takes
less force and less mechanical stress which is good for the wear of
the locking mechanism I believe.
I am up and running in less then twenty minutes and feeling physically
OK with no pain in my back. On top I feel much more comfortable when
flying with a non aviation passenger as you don’t need to explain
all the assistance you need in detail, with even a chance the person
does a wrong move and something expensive brakes.
Old and new a last time together
In addition it is very easy to wax the wings and perform some additional
maintenance task e.g. removing the stabilizer as I use the cradle
to stand on.
Together with the hydraulic landing gear jacks I believe I have now
most of the major tools required to operate and maintain the bird
in confidence.
Neatly packed together, ready for some action
Unfortunately I don’t have drawings of the whole system. Anybody
who has ideas to improve I would be much happy to receive some feedback.
Feel free to comment through Henk’s site.
Good luck if you plan on building a similar device!