Battery Upgrade 14S to 16S

[Jamie Shore]

I asked Luka a few question about upgrading 14S batteries in Lak sailplanes to the new batteries, 16S. Here is the Q&A. My questions in black and Luka's answers in blue. 

Jamie Shore  mini Lak FES

1) In order to help me organize the differences in my head, I compiled info (from the LZ Design Battery manuals)  comparing the 14S to the 16S: https://docs.google.com/document/d/1fQkPM80tVfN35wEiR14vY2K7gx7LUKCgqggbEup4OuY/edit?usp=sharing 

Luka's Answer: Your comparison of 14S to 16s is correct.

2) Can Lak gliders built for 14S batteries be retrofitted to accommodate the 16S batteries?

Luka's Answer: Battery compartment in LAK gliders is already pretty small, and to accommodate 16S to glider which was built for 14S is a problem. Rear battery is wider so it would not fit inside properly due to rear corners of battery. Main problem is control pushrod which goes below the floor of battery compartment, so floor can not be moved more down.

3) What is involved in the retrofit? Does the battery compartment need to be physically altered? Any new electrical components or just a software update?

Luka's Answer: A lot of headache, leave it as it is.

4) Do you have any real world comparisons for level cruise distance with the 14S compared to the 16S?

Luka's Answer: Main difference is not in level cruise, but higher RPM, which means better climb rate. If you have now max 4700 RPM (22kW), with 16S there is about 5300 RPM (28kW)

[Matt Herron]

Based on Luka's responses, I wrote to Vytas asking whether buying the large battery pack would mean that I could not carry water in the MiniLAK FES slated for delivery to me this fall. This was his answer:

Hello Matt,

Bigger Battery Pack has nothing to do with water ballast.
MAX TOW is 350 kg for the 13,5m competition. We have increased MTOW to 420 kg on our FES-JET Experimental glider where the main load is fuel in the water tanks. It is possible to carry water in the glider, but not in 13,5 m competitions due to 350 kg MTOW rule.

In EXPERIMENTAL category I would choose more powerful version. 

Best regards

Vytautas Maciulis

 

[Steven L. Bair, Psy.D.]

Thanks Matt - that is welcome news. I prefer the information you were given to that given to me.