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Launch report: Red Slim FTC 01.06.2002 and later

Red Slim FTC Banner

VCP sketch of Red Sim FTC

By chance I happened to find some sort of a FTC in Germany. It's outer diameter is 29,5 mm, length 125.5 cm. Having had problems with internal bulk heads in other tubings, I used bottle tops and shrinked them onto the FTC, then glued them with Bison Power PUR. The resulting volume is 0,75 liter. Please note that this was not a construction going for altitude, but rather for gaining experience on backgliding FTC water rockets.

Fins of the red FTC

Backsliding rockets fascinate me, therefore this my first FTC has to be a backglider! To understand the backgliding phenomenon, click here.

This pic shows the laminated orange cardboard fins, which are so quick to make, attached with brown and blue tape. The balancing weight for backgliding is taped on (red). The blue bottle cap is just for transportation.

Start of Red Slim FTC

 

Video of Red Slim FTC
(1,2 MB)

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since 4.6.2002

To make it backglide, I tried to do swing tests. However, these gave a completely false result.Without any weights at the tail, the FTC always sideglided during the test swings. It never flew straight like a rocket should, no matter how we started to swing. On the contrary, in real flight, the first test launches with reduced pressure presented us a nosediving rocket.

As usual, we trimmed the fins somewhat and added carefully weights to the back, until we had it back-/sideglide in a stable manner. Watch it on the video (left)!

Rolf, Stefan, Ulrich

Here is today's launch crew: Stefan, Rolf, Ulrich (from the left). We had about 20 launches of variously sized rockets and lots of fun!

Addendum:
Surprise about the destroyed Red Slim FTC


On other launch days we had 5 perfect launches. The rocket backglided well each time.

On the 6th launch with zero wind the following happened: at apogee, the rocket fell back about 6 metres without tilting, nose straight up, gaining more and more speed downwards. After this taildive, the rocket top swung over rapidly, exceeding the (up to today stable) backgliding position in one go. It quickly found it's other stable position and flew nose ahead towards the ground. The rocket nose was destroyed on impact.

After this I took the trouble and measured  the CG, calculated the CLA with a small excel sheet and the BCP with the VCP program. It appeared that the CLA had a clearance of only 13 mm or 0.44 calibers from the CG. See the drawing on top of the page.

Conclusion:

Under conditions with winds greater zero or launch angels unequal 90°, these kind of rockets usually tilt early enough to find their second stable position, the backgliding position, and stay there.
Under conditions with winds = zero and launch angels = 90°, these kind of rockets may "swing over" this second stable position and find their first stable position, nose down.

Remedies:

a) greater clearance between CG and CLA and
b) avoid launch angles of 90° in low wind conditions.

 

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Stand / Last Revision:  24.07.2002

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