Hello,
I have four 4S 3000 mAh 20 C Zippy batteries that have been used for more than hundred full pattern flights with my eParrot this summer and fall.

EParrot received a new wing that is a bit larger than before and has a different airfoil. The wing was spray painted directly on bare balsa with green fluorescent Tamiya paint, left overnight to dry, sanded lightly, spray painted again, left overnight to dry again and covered with Doculam. The effect is, in my opinion, quite satisfactory (please see the attached).

The model flies better, grooves better and is very responsive after the wing replacement.  I have changed also the control system geometry and installed narrower flaps.

The "old" eParrot, with wing folded using the PFP (paper-foam-paper) board, weighted RTF 1405 grams (49.5 oz.).
The modified eParrot weights RTF 1330 grams (46.9 oz.).

This difference in the RTF weights puzzled me as the initial calculations indicated the possible weight savings ~30 grams (~1.0 oz.).

I did not know where  49.5 - 46.9 = 2.6 oz. weight saving was coming from until I discovered yesterday that my Zippys have very different weights.
The lightest one weights 313 grams (11.04 oz.), the heaviest: 336 grams (11.85 oz.). I have also one weighting 323 grams (11.4 oz.).

EParrot's 1330 grams (46.9 oz. ) RTF weight is with the lightest Zippy (313 grams - 11.04 oz.). I do not know which one of my Zippys was used when I weighted the "old" eParrot to get 1405 grams (49.5 oz.) but this is not important at the moment.

What is important, though, is the location of the modified eParrot C.G and trimming in flight.

I will have to mark the position of each Zippy after the trimming is done as almost 7% difference in the batteries weight will affect the flight dynamics.

Comment: Thunder Power 5S 2800 I have for my next plane differ in weight only 0.6%.

We all know that Zippy batteries are so called "cheap" with the individual cells selected randomly and the Thunder Power batteries suppose to be of better quality and longevity, with cells matched. They are also of course more expensive.

Your comments are welcome,
Regards,
M
 

 


 

Do the batteries lose weight as the power is used?     By the way the paint on the wood before covering I did on the John Lowrey Stukas a few years ago.  Does make for a light finish using SLC at the time.  Can't find my pictures of them so I guess the old camera will have to be dusted off.   Plane looks good.

Hello and thank you for your thoughts,

Traian,
I am already using a semi-rigid foam as the battery stopper and it works ok.
The battery is pushed forward into the fuselage front "box" after the entire cabin is removed. To secure the battery in the box, I am also using semi-rigid foam pieces. The battery front is protected from the aft sticking shaft of my Cobra 2820/12 by another piece of foam that stays permanently just behind the fire wall.

I am currently experimenting with the CG location. The battery will be most likely moved back 1/2-3/4" to improve the response in corners.

I agree regarding Doculam. I like the ease of use, appearance and the fact that indeed it adds some bending and torsional stiffness to the wing. It also suppose to stay tight and without wrinkles when exposed to the direct summer sun. I will test this Doculam's property next summer.

My only concern is Doculam's strength and fatigue durability. EParrot wing is 575 - 580 in.sq. with relatively wide ribs spacing and I wonder if Doculam will survive the flight loads, pressure differences and turbulence in, say, 200 pattern flights?

What about larger wing - 670-700 in.sq.? Can such wing be safely covered with Doculam?

I will publish this question as a separate thread.

John,
The batteries do not lose weight. I received four having different weights. The lightest one weights 313 grams (11.04 oz.), two heaviest: 336 grams each (11.85 oz.) and one 323 grams (11.4 oz.).

I am trying to find the CG location providing good tracking/grooving and, at the same time, a rapid response for the handle input in corners. This sweet spot is of course affected by the batteries weight differences and I have decided to equalize the batteries weight by making them all 336 grams.

I will simply add some lead to lighter batteries.

I will be testing this idea as soon as the weather in Toronto becomes flyable again.

Regards,
M