How short a flight time is OK for newbie students?

[haygood]

Hi all. I'm starting a club for Junior High students. We will build Mini Speedsters and Mini Scouts.

I would like to keep the planes light, so I am interested in using the smallest battery I can get.

Using a Hextronic 20g 2300kV with a 5x3 prop, I'm expecting something like a 4.5amp current draw.

I'm considering the following two batteries:
Rhino 610mAh 2s 20C/2C 35grams, and
Zippy Compact 800mAh 2s 25C/5C 44g.

Given Flitetest's estimated weights for the planes before batteries (115g), The larger battery would result in a 7% heavier plane. Flight time would be .61Ah*(60min/hr)/4.5a = 8 minutes with the small batt., or 10.7 minutes with the larger.

Which would cause the least frustration; a 7% heavier and therefor faster plane, or an 8 minute flight time instead of 11 minutes (before battery swap)?

Keep in mind these are 7th and 8th graders, so I want them to have something that is as easy to fly as possible. The batteries cost $4.90 and $5.33, so despite our razor thin budget, this is probably not the place to save $0.86 per student.

 

[Julez]

I don't think the larger batteries will be a problem. If you're flying outside, I'd say the larger batteries are the best choice because of the added weight for wind penetration and they'll enjoy the longer flight times after they get past the learning stage.

 

[Spastickitten]

I would try both. The larger battery will give you longer flight time, but it might be too heavy to do more advanced maneuvers/ climb quickly. The lighter battery will mean less weight, and that means it can climb/ do more advanced maneuvers.

 

[quorneng]

I am not sure the difference in weight between the batteries will be all that noticeable.
Saving 9g in 155 is only 6% - this is less than the normal drop in power available as a battery becomes discharged.

 

[Montiey]

I'm going to say the larger battery will give the student more practice in a single continuous flight which will probably make learning faster and easier than going with a lighter setup.

 

[Snarls]

One thing to consider is that if these are kids completely new to flying they are most likely not going to be able to fly through a whole battery in one takeover and landing. More likely they will crash multiple times over the course of a charge so really 8mins worth of charge may take half an hour to go through. Lighter batteries will also do less damage in a crash, although 9g is not a significant difference. Overall I would go with the larger battery. The extra flight time will be worth it in the end. You'll end up with more than 9 additional grams with all the hot glue and extras the kids will add when fixing their planes anyway.

 

[stay-fun]

The plane will fly more slowly with a lighter battery (stalls at lower speed), which can be helpful. I found it helpful when I started with planes. On the other hand, maybe the kids just wanna rip
Other than that, I think it doesn't really matter. To keep it in the air for an entire class non-stop, you'll need multiple batteries. Why not get like 4 of each?

 

[dgrigor02]

For me, it's never about the flight time it's the lightest battery I can use and still balance the plane without adding nose weight.

I'd build a prototype plane play with servo location and battery location see which battery and servo config balances out the plane the best.

 

[haygood]

"Why not get like 4 of each?" Because $$$$. Donate $80 and I'll buy an extra for each kid!

I'm going to have to place a big order from Hobby King before I get all the parts in hand to build a prototype. I will still be able to move servos, batteries, ESCs, and even the motor pod to get things balanced.

I think I will get a couple of the smaller batteries to use for the 2 classroom planes the kids will take their first flights on. Those will have a wireless buddy box in them, which means a second receiver, too. That totals 14.5grams. At least the lighter battery will help offset those. I found some 500mAh that are 15grams lighter than the 850mAh batteries I will get for everything else.

Thanks again, Flitetesters, for the input. Good stuff.

 

[Snarls]

If you buy from Hobbyking you maybe be able to save some money by going to the product page of the battery you want when you are not logged in. If you wait 5mins or so there will be a popup on the side of the page that says 'you've been looking at this for a while, why not try it at a lower price' and will offer you a slightly lower price which can save a good amount of money if you are buying bulk. The price saving is the same as if you are an elite member, which you are after like 10 orders.

 

[haygood]

Thanks. That's definitely worth mentioning. Some day I will be elite, between ordering stuff for the club and for work. I didn't realize that gets you the discounted price more easily. That would be great. So far I haven't bought anything from them without waiting for the one-time-offer. You can get another one-time offer by clearing your cache, by the way, in case you miss one.