I am new to electric and have reviewed the FAQ section. Is there a rule of thumb for cooling inlet size vs cooling outlet size. I want to electrifty a great planes super chipmunk. I am assuming 15 lbs for weight. According to Maxxprod website I need alot of voltage/amps. 10s lipo.

How do I know the size of the inlet and outlet holes? So I can see if there is room to put them etc without sacrificing structural integrity?

How long does a 10 s pack typically take to charge at the field?

Cooling outlets out to be at least twice the inlet size. Naturally the more area both have the better, but keep the ratio and be reasonable and you'll be fine.

the charge time will depend a bit on your charger, but 1 -1/12 hours is typical, unless you've got some of the new very high end fast charge cells. My guess is that if you had them you wouldn't be asking the question.
Walt

Size of the holes matter, but location matters probably a bit more than size.

You want the intake area to be directly in front of whatevery it is you're wanting to cool. Everybody knows that already, right. Actually there is more to it than that. You really don't want openings that are away from the hot parts especially if those other openings have the majority of the total intake area. And that bad intake balance really matters when the exhaust area is limited. Hot air is harder to move than cool air. So the air we find easily plowing through the cowl and filling the exhaust area is going to be cool air if it's given the chance. Let excess cool air into the cowl, and the excess that isn't pushed directly into hot air is going to happily move along to the exit. And whatever cool that does run into hot air is going to move right around it and join the other cool heading for the exit. And the hot air is going to get hotter still and even harder to push.

The ratio of exhaust area to intake area actually can be as low as 1.5:1 when the intake area is good, intelligently restricted intake. Block out parts of the intake where that air won't cool anything. It'll actually cause you promlems at the exhaust unless that's much larger in area than needed.

BTW, the exhaust also needs to be looked at for more than it's area. If it's in a low pressure area (outside airflow sucks the inside air out) it can be smaller. If it's in a high pressure area (outside air wants in) it will have to be larger. How do you know whether an area is high or low pressure? Look at your airplane from the very front. One simpleminded way..... The fuselage you can see from the very front is high pressure. If you can see into the exhaust from the very back, it'll be low pressure. Also, an area behind a projection (like behind cowl flaps which are opened) will see negative pressure.... uh, will be a low pressure area.

Control line speed airplanes used to burn their engines up quite often. They needed cooling BIGTIME. And they were cooled very well with tiny openings directly ahead of the cylinder and with about 1.25X the opening directly behind. And their cowl was built up inside to force all the airflow directly around the cylinder. There was almost no clearance. And if the flyer didn't set his needle too lean, the engine would HONK and stay cool enough doing it. Heck, some of those speed guys thought that ratio was too generous.

By the way, if your model is one of today's Chinese ARFs, chances are better than even it won't have ANY heat exhaust opening at all anywhere. Why? ....let's not go there.......

The last 4-5 electrics I've had anything to do with certainly had no openings anywhere. And their manuals didn't mention making any.

I just helped a buddy rebuild and recover his Telemaster electric. We used a soldering iron to put two decent sized holes in the bottom aft of the fuselage. I just did the same thing to an EFlite Pitts. And a buddy's EFlite Mini-Edge. It's nice if you can put the openings in negative pressure areas, but for sure, you need openings somewhere. One ARF line of profiles comes with a battery box that completely seals the battery into the sucker. No openings at all. Batteries live longer if they're kept from melting themselves down.

It really hurts to have NO exhaust area.

Wow, 10S, 42 Volts. This must be a pretty big airplane.

Charging the battery at the field should not take any longer than charging at home. Set the charger per the instructions at 1C, one times the Capacity of the pack, and as Walt says, 60-90 minutes depending on how depleted the pack is.

Most 10S packs are made up of two or more packs, two 5S, a 6S and a 4S, two 3S and a 4S, etc.. Each pack requires its own chager unless you're using the Cellpro 10S from FMA.

So, can I assume the battery needs serious cooling also?

They last longer when they're not deep fried.

The ESC really benefits. So if you're trying to get some cooling air to it..............

I use the bottom of the engine compartment for a LOT of exhaust holes. I happen to mount most motors upside down for that reason. The small GWS Corsair has 6 small 1/2" holes drilled in a downward and backward direction. 6 small holes DO NOT weaken a structure as much as 1 big hole of the same area.
If you use offset gearboxes you can REALLY get the motor low & directly into the airflow.

Air flows from the inlet straight to the outlet. Even if a motor is directly in the way.

Think like that and you should come out fine.