klik here to download the EXCEL calculation sheet to build NPW21
Right click and save target as!
In 1970 Nasa tested over 30 "all flexible parawings".
Bill Rasmussen made a summary of these test on his web page:
NASA Parawing Reports
NASA Parawing models 1-10 are described in technical report NASA TN D-5936,
NASA Parawing models 17-24 are described in technical report NASA TN D-5965,
found at the NASA Technical Reports Server.
When reading Bill's summary I realized that of all 24 models tested October,
1970 in a Low-Speed Wind-Tunnel
model 21 has the best L/D ratio: max lift/drag ratio: 3.25
(3.48 with longer lines and nose line modification).
Some of the modifications like the angle of the A-bridle or the nose line
look very similar to the NPW9B and To finally the TEEGA.
The NPW 21 Is simpler in construction because there is no C-bridle : 12 bridles less.
All these arguments were good enough to try NPW21 as a Kite.
Including the longer bridle lines, a change untried on the npw9 and teega.
The First model a 2,9sqm did fly out of the bag;
Still it looked like it needed some less flutter on the wing tips ,
so a "leach line" in the TE gives the wings just that little more inflation.
The NASA engineers were on the right track this kite has a great window!
As good as any npw I have built , if not better.
After building this first test model;
I was approached by Chris W..He was looking for a traction kite to pull him and
his sled over the arctic snow.
Chris W. Had already some experience with sled s and huge NASA wings mod 5.
Chris agreed on me building him an 8sqm NPW21.
These are Chris own words:
I used the kite in Fram Havn on Ellesmere Island on the sea ice -
this was at latitude 79 degrees - about 1000 km from the North Pole.
It flew very well and easily pulled me and my sled (about 150kg in total)
in a light wind of about 9knots. The kite was easy to fly and moved well in the sky.
I flew it mainly on the edge of the window.
It was a little difficult to tell how much wider the window is compared to the NPW5 but
I have no doubt it is better or at least similar.
The kite is wonderfully light to pack and carry around and easy to set up.
Another experienced kiter who had brought much heavier kites was quite jealous.
He said that mine was the ideal expedition kite.
There was not a lot of wind on this trip and my companions were mainly non kiters but
I was really happy to give your kite a try in those conditions.
If you want to make more of these kites I would love a smaller one for more powerful winds.
Say a 3.5 metre (No hurry).
I will definitely be carrying the 8 metre kite you made me on all of my trips.
I am making a new version of my kite buggy.
I have got a frame that weighs 9.8 kilos.
I am aiming for a total buggy weight of less than 20kg.
That way I can easily move the buggy around with my supplies when there is no wind.
I expect to do an expedition with the kite buggy next year.
Many thanks to Chris W. for giving the npw21 a good test.
Guess I'll have to build some more NPW 21 kites!