June 2007
Contents
Dream Flying in the Alps
Good and Bad Engineering
'How was your day, dear?'
Spanish Fly??
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Dream Flying
in the Alps
This page sponsored by
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By Clive Mason
FLIGHTLINE ONLINE
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June 2007
Flightline Online
I had a phone call from a good friend, Kevan, one Saturday afternoon. He said ‘Clive, How do you fancy a trip to France in RG?’
Here’s me thinking of somewhere like Adville, so I replied ‘Yes,
that would be cool’ but little did I know he actually meant the
south of France in Gap, for two weeks, with Alpine Vol.
Kevan had been wanting to learn how to fly trikes for over 18
months, but after bad weather hindered the lessons he had booked
with Flylight in Northamptonshire, along with a heavy workload.
He received a tip-off from a friend that in Gap you could fly everyday, and to give Marcus a call at Alpine Vol and get booked in for
two weeks of solid flying. So it was booked that very same day.
So, what would be my role in this trip? Well, Kevan had volunteered me to fly us down to Gap in RG (an Air Création Tanarg).
There was no asking twice, all the plans were made and French
charts bought and our fingers crossed for good weather. Plan
B was prepared ‘just in case’. We had a trailer ready to tow RG
instead. And as the British weather so often does… it let us down
a couple of days before the planned departure, so plan B was put
into action and we headed off to Sywell to pack away the Tanarg
for the trip.
After looking forward to the flight to our destination, the drive
started off as being a little disappointing, but after lots of stops
on the journey and getting to answer all the curious questions
from those who saw the trike on the trailer, smiles were soon on
everyone's faces, including ours.
We arrived at Tallard, Gap at about 12:30pm. Marcus was soon
there to greet us and even gave us a moment to help get the wing
back on the trike. Despite the grim looking weather when we first
arrived, the low cloud soon cleared and the day became flyable
again. Marcus suggested a flight straight away; he would join us
in the air in his GT450 and show us the area and all the reporting
points we would need.
We flew for about 45 minutes and we were stunned with
Page 2
what we could see. Amazing is an
understatement. Many people have a
vision of when they die, they want to
go to heaven. At Gap you don’t need
to wait to experience heaven, it’s all
there before your eyes.
The next morning Kevan was
asked to be at the hangar for 9am,
so I thought we could start the day
off with a nice ‘jolly’ before his lesson
began. I met Kevan at the hangar at
6am pre-flight and off we went to
visit heaven again. We climbed up to
11,000ft and had a great flight, and
plenty of time to take the first of many
photos. I was surprised at the number
of green fields in the valleys and even
on the mountains.
An engine out was not going to
be a problem, so we did a practice at
6,000ft on the way back and almost
touched down on a long grass field at
4,000ft. We landed back at Tallard in
good time for Kevan to re-fill with fuel
and have a classroom chat before his first lesson with Marcus.
This was my time to relax. As I started to head off for a walk to
the village I saw people jumping out of the ‘Otter’. With so much
happening at the airfield I didn’t want to leave. I headed for the
café at the side of the runway - a perfect place to sit and not have
to miss a trick. Even the pretty waitress was a pilot and we spent
several minutes chatting about all that goes on there.
I spotted Kevan on the down-wind leg, so headed back to
Aeropoll. As soon as I saw the big smile on his face and the laughter, there was no need to ask if the flight had been good. Marcus
introduced us to the other students Pete, Andy and Olive, and the
two instructors Bill and Colin.
Kevan was assigned Bill as his instructor for the two weeks,
but as both guys had been in the services the hangar chat was
now biased.
Kevan was in the air by 8am every day; no room for my jollies
in the Tanarg, but still having plenty to watch from on the ground.
A friendly chap called Dave came over and asked if I would like
to fly with him in the back of his GT450 for a couple of days. He
was on holiday from Scotland, and it was a great opportunity to
take more photos while learning about the Alps and of course the
GT450. After six days of flying, Kevan went solo. The smiles were
off the scale. It was off down the local inn that night for a celebratory drink. I found it amusing to listen to Kevan telling the other
students how to land. Six days ago he could not fly; it just shows
what a difference the chance to fly every day makes.
At the end of the two weeks, Kevan had clocked up 25hrs and
six solo hours. So not only do you get the chance to fly every day
at Alpine Vol, you get results. And for those of us waiting on the
ground there is still plenty to see and do and lots of friendly folk
to chat to, making the days a pleasure to be there. Please enjoy
the photos…
June 2007
Flightline Online
Page 3
Good and Bad
Engineering Practice
By Peter Lovegrove
This article, from the
Nov/Dec 1981 issue of
Flightline, explains
in layman's terms the
ways in which bad design
can torture the metal
that holds us in the
air. For those thinking of venturing into
the world of ultralight
microlights, it it will
give you a good idea of
the things to look out
for in a new design and what to look for on
your daily inspection.
singling out any particular ones, and see
what engineering implications there are
to consider.
Let us first look at struts and ties, that is
to say, members in compression and members in tension. These should always be
straight when installed and kept straight
during their useful life. A strut with any
kind of bow or kink in it is many times
more prone to buckle than one which is
really straight. Suppose you wish to have
a pusher engine behind the pilot and have
a bracing strut from beneath it to the extremity of the tail.
There can be no doubt that, without the
almost explosive development of hang
gliders, there would be no second and
third generation microlights today. For
that we should be grateful. However, there
is an obverse to the coin. That is, people
are too quick to design — I use the term
'design’ somewhat lightly — on the basis
that it was OK on such and such a hang
glider, so it will be just as OK on their new
microlight. Often, nothing could be further
from the truth. The stress levels in microlights are significantly higher than in their
more lightly-loaded antecedents. And
remember, some hang-gliders had very
small margins of safety in their design. So
let us look at some of the more common
features of current microlights, without
The arrangement shown in Figure 1 is
next to useless; that shown in Figure 2 is
fine. The little bit of triangulation allows
the whole system to be in proper compression. The extra bit of tube adds weight, you
say? Well, if you are
daft enough to use
a bent strut, the very
This page sponsored by
least you should do,
to help you in your
daftness, is to use a
fairly thick-walled
Sywell Aerodrome, Northants. NN6 0BT.
tube. With the trianTel 01604 494459.
gulated version, all
tubes are able to be
Website <www.flylight.co.uk>.
of a thinner gauge,
For all microlight tuition needs.
since the loads are
along their axes. The
Manufacturers of the Doodlebug
only additional point
foot-launched aircraft, UK importers for
to be given adequate
Air Création and Sky Ranger.
consideration is the
question of side
loads.
Flylight Airsports Ltd
One often sees frames attached to main
fuselage members as shown in Figure 3.
For the reason shown in that figure, this
is bad engineering. You should never use
single-shear bolts to hold such an assembly
together, if it can readily be avoided. For
the particular problem area depicted, the
method shown in Figure 4, which many of
you will have seen on one popular microlight, is a far better solution. The second
bolt forces the tube to transfer its loads in
a nearly true single-shear mode.
I reckon that the most potentially-lethal
single- shear joint I have seen on any ML
(it takes too long to keep typing “microlight” with two blunt fingers, so ML it shall
henceforth be!) is that shown in Figures 5
and 6. Here, two lift struts are tied to the
axle with a single bolt.The struts — actually
ties for most of their operating life — have
bends in them, which are always attempting to straighten out under tension, that
is, during flight, and trying to bend more
under ground-handling loads. The direct
and inescapable result of this is that the
bolt is worked back and forth, so moving
June 2007
This page sponsored by
Flightline Online
P &M
possible, always — to
suit what you are doing with it. This does
not mean picking a
nice soft saucepan
alloy.
Remember, you
are probably the
idiot who is hanging
Unit B, Crawford Street, Rochdale,
his neck on the final
contrap tion! If you
Lancashire. OL16 5NU.
want to commit suiTel 01706 655134.
cide, go and jump in
the river and save the
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cash for your wife.
After making a bend
in any alloy tube, it is
towards a stress- corrosion failure. It will
a wise policy to check it with some form
break between one or both of the struts
of aerosol dye-penetrant; they are simple
and the axle. Extra torque on the bolt will
to use. At the very least, examine the bend
not help; it will only crush one of the tubes
with a strong magnifying glass. You are
without altering the situation.
looking for extreme stretch-marks and
lines running around the tube.
On one machine, I saw an undercarriage
assembly where the wheels were supported with bent tube braces (Figure 10).
This is clearly not the way to go; the wheel
should have been supported by some simple triangulation above it, to get rid of the
bend in the tube, or by means of a proper
bracket like that shown in Figure 11.
Page 4
foolishness to try hang-gliding, it was
common practice to join the spar to the
leading-edge with a vertical bolt through
Aviation
In general, single-shear joints should be
used with extreme caution (Figure 7). If you
feel obliged to use one, try to get a second
joint close enough to assist in keeping the
tubes straight (Figure 8). If the tubes cannot
bend, the bolts are also unlikely to do so.
Let us look at bent tubes a little more
closely. Try to avoid drilling holes on or
very close to a bend (Figure 9). Pick the
tube and the radius—the latter as large as
Cables seem to be tied to airframes
wherever they happen to alight when
stretched around the aircraft. Cables
should never be attached to the midlength of tubes (Figure 12). It causes high
and unnecessary stresses in the tubes and
tends to prevent the cables doing what
they were put there for. As the tube flexes
under load, the cable is allowing the other
end to move and redistribute the loads.
Such movements beget wear which begets
cracks, etc., so do not be afraid to lengthen
the cables by six inches and attach them at
the next firm joint on the structure.
On one commercial machine I saw a
prop-shaft which was flexibly mounted
and passed through a round hole in a plate
firmly fixed to the fuselage tube. There was
plain evidence that the shaft had moved
around under the influence of g forces
and gyroscopic precession. The plate was
quietly starting to saw its way through the
prop-shaft. A modicum of simple thought
would have prevented that hazard.
In the days when I had the energy and
the two tubes, as shown in Figure 13.
This is, of course, a single-shear joint
which derives its acceptability from the
large bending strength of the big tubes
involved. However, this joint is worthy of
study; so let us take a closer look at it.
If the outer portion of the wing is taking
only lift loads, the stresses are highest at the
top and bottom of the tube cross-section.
Any bolt should therefore be horizontally
through the tube (i.e. through the ‘neutral
axis). However, other factors enter the argument. For example, the leading edge has
drag forces upon it over its entire length
and there is thus a bending effect around
the spar end-joint (Figure 14).
So the best position for the bolt is a
some location slightly tilted slightly back
wards from the horizontal. But certainly
the vertical bolt is bad news so, if you have
some roughly comparable situation, con-
sider the pros and cons carefully.
This principle applies to all bolted joints
in members. If the forces are all or substantially in one plane as shown in Figure 15,
put any bolts with their axes at 90° to that
load plane, as depicted in Figure 16.
June 2007
Where you fit internal or external doublers to a tube, avoid using square-ended
pieces of tube, which concentrate the
stress at the end of the doubler (Figure 17).
Instead, consider how the loads operate
and use a sloping-ended doubler fitted
appropriately (Figure 18).
Never, but never, use a cable without a
thimble. Cables will happily fail one strand
at a time until the time comes for ten green
bottles and one green pilot to accidentally
fall. The stress produced by a 3mm cable
carrying only 50kg is quite large, as shown
in Figure 19, if no thimble is used.
The thimble used will be just as highly
stressed, but flows under compressive
failure to increase the bearing area. A
Flightline Online
bare cable just loses
strands; ‘nuff said!
Finally, I would like
to take a close look at
one idea which is
currently gathering
momentum in trike
designs.
It concerns the
use of cable-braced
separate undercarriage legs as shown
in Figure 20. On
one such machine, I
measured the angle
between the leg and
the horizontal as 10°.
The overall machine was typical of its ilk
and weighed, I would estimate, between 64
and 77kg. Let us assume it weighed 68kg.
In the event of a 3g landing, which is not
at all inconceivable in the light of some I
saw, the force belting down the vertical
centre-line of the trike would be 205kg.
If the landing were only fractionally off
the vertical — a very likely happening —
the force on one leg of the undercarriage
will be greatly increased. So we can reasonably take a sloppy 3g landing as producing,
Page 5
say, 113kg (rather than only 102kg) on one
side (Figure 21). Remember we are talking
of an acceleration condition, where inertia
of the airframe plays a major role.
To withstand this force, the bracing cable will have to take a force of 113 divided
by tan 10° which is 644kg. If we use a 500kg.
cable, is that so bad, you might ask.
If the cable is anchored at each end by
a lug bolted through the undercarriage
leg with a 1/4 inch diameter bolt (and isn’t
it always?) what stress do we get in the
leg material? If the tube is 0.058
inches wall, very commonly used,
the area closest to the lug is 0.25
times 0.058 square inches (equal
to 0.0145 square inches).The cable
force of 644kg produces a stress
of 6742 bar (atmospheres). Now
HT30TF tube won’t like that so it
will fail under compressive stress.
Eventually, new metal will build up
to resist the force to some extent
(Figure 22) but will have cracks in
and around it. The cable will also
stretch and you will find that it
becomes more and more difficult
to jack the middle of the trike up
by tensioning the cable.
Where the bolt passes through
the top of the undercarriage
leg (Figure 23) a much smaller
stress is produced in restraining
the bolt, because of the leverage
involved.
So, in conclusion, do not take
it for granted that if the bits of
airframe meet this or that way, the
bolts, etc., go thus.
Think about it for a while.
'How was your day, dear?'
'Oh, Up and Down. You know.'
Here’s how skydiving instructor Jay Stokes spent his Saturday off last September.
Got 130 friends to help out at his local airfield in Greensburg, Indiana. Jump in the
plane at sunrise, and get out again at 2100ft. Land 40sec later. Ditch the old ’chute,
hitch on a new one, step in the plane, and do it again. And again – every 2min 14sec
for the rest of the daylight hours. Volunteers repacked the ’chutes and even placed
a step for him to walk back into the aircraft. He beat his old record (534, set in 2003)
by over a hundred. 640 to be precise. He tore a muscle halfway through the morning,
and landed outside the field once and had to hitch a ride back, so there’s obviously
room for improvement… Check out <www.mostjumps2006.com>..
June 2007
Flightline Online
This page sponsored by
Flylight Airsports Ltd
Sywell Aerodrome, Northants. NN6 0BT.
Tel 01604 494459.
Website <www.flylight.co.uk>.
For all microlight tuition needs.
Manufacturers of the Doodlebug
foot-launched aircraft, UK importers for
Air Création and Sky Ranger.
Page 6
And from the same issue, Nov/
Dec 1981, here's proof that
even then an instructor's
life wasn't just a question
of mixing 50:1 and circuits,
and that Gerry Breen wasn't
the first to head for sunnier
climes.
An one wonders what happened to
Pascaline...
Spanish Fly??
By Dave Garrison
My car was running perfectly until the moment we set off for
Plymouth to catch the ferry to Spain. Within ten miles it was
overheating, setting the scene for a journey best forgotten. Driving through Madrid at mid-day, with the heater going flat out to
keep the needle off the red, is an experience could do without.
Bill Machin following on his motorcycle thought the weather
was marvellous.
That was in early June when Bill and I were on our way to
Marbella on the Costa del Sol to set up the first microlight school
in Spain. Since then we’ve learned a lot about the way things are
done here. The first lesson was to change all our esti mates from
weeks to months. Nowhere is the philosophy of Mañana practised
more effectively than in Andalucia. For example — ‘You would
like a telephone Señor? Certainly Señor, how would February
1983 suit you?’
However, despite this sort of problem and the ongoing frustration of dealing with Spanish bureaucracy, progress has been made.
We have formed a microlight club (Club de Microvuelos Costa del
Sol) with currently 50-plus members, many of whom are pilots
from the Aeroclub de Malaga. There is considerable enthusiasm
for all types of flying here as until fairly recently all aviation was
under control of the military and only the very wealthy with good
connections had a hope of getting airborne.
The school started operating in November and we have arranged with a British travel company to offer 14 day package
holidays with return flight, accommodation, hire car and microlight
training course, beginning in April next year.
Flying conditions here are excellent. No thermal underwear
necessary! There is a period in the middle of the day during the
summer months when thermal activity is quite strong, but close
to the sea this doesn’t present too much of a problem. Winds are
generally light and visibility is good. The scenery is magnificent.
Recently I took the Pterodactyl up to 9000ft. for a superb view of
Gibraltar and the North African coast.
Speaking of North Africa, on 23 August Raphael Frutos, a hang
gliding instructor from Malaga, flew a Hiway Skytrike/Demon
combination from Malaga to Melilla in Spanish North Africa. This is
a flight of 210km over open sea. He didn’t use a back-up boat but
had four aircraft escorting him in relays. The pilots said they got
dizzy going round in circles! Raphael was flying for five hours 24
minutes and was carrying fuel for seven hours. He said afterwards
that he didn’t think he would like to do it again, his main problem
was cold through not considering fully the effect of prolonged
wind-chill. Is this the first intercontinental microlight flight? Incidentally, Raphael and his partner had fitted
a different reduction-drive, carburettor
and exhaust after some problems with the
original equipment.
I haven’t attempted any such feats of
endurance here yet, but both Bill and I have
had some great flying. A particular pleasure
is cruising along the shoreline at around
100ft waving at all the bronzed ladies on
the beach, always keeping an eye open for
the Piper Pawnee towing a Bell’s Whisky
advert doing likewise. Another potential
aerial hazard here is Adnan Khashoggi’s
Jet Ranger helicopter fer rying Princes and
Presidents to his floating palace at Puerto
Banus.
We enjoyed an interesting diversion
a short while ago when the Pterodactyl
co-starred with a young Parisienne named
Pascaline in a photographic session for
a Penthouse type magazine. Needless to
say we were in close attendance in case of
technical problems.
So far I don’t feel too bad at having
swapped Wellesbourne airfield and the
delights of Stratford on Avon for Marbella
and the beach, but I’m beginning to dream
of Chicken Dansak and Bhindi Bhaji. If they
open a Tandoori restaurant here life will
be perfect.