Thursday 27 June 2013

Reflex glider - how does it work - part 1/4

Reflex airfoil in paragliders

One of the paraglider pilots from Poland has explained quite well with simple words how the reflex airfoil in our gliders works and what makes it 'safe'.

At the very beginning I have to apologise  to all aerodynamic experts for the simplifications which I have had to make to make this article  comprehensible to all paraglider pilots.

To explain what a reflex airfoil is we have to go back to the beginning of aviation. These were times when planes looked like flying scaffolding. Some designers decided to get rid of the plane's tail. The problem was that the airplane was then pitching down. Why was it pitching down? Apparently the  lift force which was created by the wing was fixed to the point behind center of airplane's gravity causing the rotation.

The point where lift force was 'attached' to the wing is called the center of pressure. Its value and position depends on the total sum of all the forces acting on the airfoil. The airfoil is simply a wing's cross-section.

To solve the pitching problem described above the only solution is to put the center of pressure at the same place as the center of gravity. Only then will  the weight of the wing (airplane) will be pulling the wing down and the lift force will be pulling the wing up without rotation in any direction (which means without changing the angle of attack).

Unfortunately the airplane has to pitch  the nose down during landing. When the angle of attack decreased, the center of pressure was moving backwards but the center of gravity stayed in the same place. This caused an increasing tendency to pitch the nose down.  

The same effect was obtained when the angle of attack was increased (the nose was pitching up). The center of pressure movies forward and causes the wing to pitch up more.

The breakthrough was when aerodynamic experts designed an airfoil (reflex airfoil) where the center of the pressure was working in the opposite way - causing the nose to pitch down when the angle of attack was increased and vice-versa. This happened as early as 1906.  (A lot of people who think that the reflex airfoil was invented by/for paraglider pilots).

These two pictures will be helpful to understand what is the difference between classic and reflex airfoils. 
Classic airfoil:

How paraglider classic airfoil works

The top picture shows the wing flying on a high angle of attack. The lower picture shows the airfoil on a small angle of attack. The arrows show the pressure distribution along the airfoil and the arrow 'inside' the airfoil shows the magnitude of the lift force and its attachment point (the center of pressure). You can see that when lowering the angle of attack the point of pressure is moving backwards.

Reflex airfoil:

How reflex airfoil works in paragliders

This picture shows the reflex airfoil flying on high (upper picture) and low (lower picture) angle of attack. The arrow inside the airfoil shows how the center of pressure moves forward when the angle of attack is decreased.

This is the end of part one. Next part will be published in one week.

Take your time to understand the above because in the next part we will look more into what is happening to the airfoil when it is changing angle of attack in the reflex mode.

The author of the original text is Zbigniew Gotkiewicz. It was presented on Leszek's blog

If you have any questions please post a comment or send an email to lukaszpg (at)

Thursday 20 June 2013

Moster expansion chamber problem

Moster paramotor

Leszek Klich, webmaster of and experienced paramotor pilot has reported a problem with his Moster's expansion chamber. He found this issue during a preflight check. Luckily he did not get airborne with this.

A little crack is seen in the black circle:

Crack on Moster paramotor engine expansion chamber
Crack spotted on expansion chamber
This crack has appeared after about 60 hours of Moster's airtime.

Leszek used this smart tool to remove the springs holding the expansion chamber.

Paramotor Moster smart springs removal tool

The cause of the problem were vibrations. The weakened part was welded and polished carefully. After the painting was finished the expansion chamber was installed again.

Moster's expansion chamber has been fixed and installed on the paramotor again.

Do your preflight checks carefully. This one saved him at least a prop...

The author of this article is Leszek Klich.
The original version of the post can be found here

Monday 17 June 2013

Flying with monopod

Recently I have bought monopod on ebay in order to experiment with different gopro positions and angles.
After a few days I tried it when free flying in Stanwell. I am sitting on the free end of the monopod and that is how it is hold in place.
Next time I will take it when going paramotoring.
I had so much fun that day, almost three hours in the air. Good flying conditions and great company on the hill.

Flying like a bird in Stawell

Paragliding with monopod in Stanwell Park

Approach to top land in Stanwell park

Stanwell Park and the ocean view from my gopro

Wednesday 12 June 2013

Flying with G15


Flying with DSLR is not very handy, but I like the picture quality which comes with it. I was looking for some kind of compromise and decided to give Canon G15 a go.
I am surprised how good quality pictures I get with this camera. During last days of May I had chance to fly with it.
Enjoy a few pictures from the Sunday. From now on I will always fly with this camera. Relatively small, handy, taking nice pictures and records movies in full hd. You cannot ask for more for ~$350
DSLR is going to be sold on ebay...

My paramotor and glider ready to fly

Brett is about to take off

Brett inflating his glider

Brett is just about to lift off

Paramotoring in NSW

Brett flying his Nirvana rodeo

Brett flying with fields below

Paramotoring over beautiful NSW area

Paragliding above Picton

Picton paramotoring

Paramotoring in Picton

Beautiful paramotoring eveining

Brett flying in from of me

Brett paramotoring above Camden South

Paramotoring photography

Paramotoring over construction sites

Dudek synthesis above Picton

Paragliding over construction site

Interesting patterns from the air

Paramotoring sunset

Paragliding over Camden bypass

All gear ready to be packed

Friday 7 June 2013

Camden flying movie


Recently I put together a movie showing paramotor flying in Camden with Brett. Enjoy!

2013/05/12 Camden Sunset flight from lukastu on Vimeo.

Sunday 2 June 2013

Daniel's pictures of us flying

The other day my friend Daniel came along with me to take some pictures of us flying paramotors. Thanks Daniel.

paramotor flying in Australia

Lukasz Studniarz assembling the paramotor

Dudek Nucleon WRC taking off

Lukasz Studniarz paramotor pilot

Sean flying his paramotor

Lukasz Studniarz just about to take off

Lukasz Studniarz taking off

Paramotor take off

Paramotoring in Camden NSW