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Old Oct 01, 2011, 02:33 PM
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United States, CA, Santa Monica
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How to increase flight time?

Hi,
Does anyone know how I can increase my flight time? Specifically, I want to know how I can hold more battery power in my plane (be it adding extended batteries or getting a better one). If I have a 1300mAh 3s Lipoly Battery (about 20 minutes of flight time) atm, what do you think is a good upgrade so I get at least an hour of flight in?

Thanks a lot for the suggestions.
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Old Oct 01, 2011, 02:52 PM
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An hour of flight time is a tall order, but not impossible. It depends on a couple things. First, the actual plane you have will be an important piece of info...

Next, you'll be able to increase flight time with a bigger-capacity battery, but this will also add weight. More weight will increase the speed the plane needs to fly, will slightly increase drag for a given airspeed, and will reduce handling somewhat. At some point you'll find that adding battery capacity just doesn't help any more, or causes more trouble than it's worth.

Another thing to do would be to maximize the efficiency of the rest of the plane. Run a smaller prop to reduce current, try to cut down drag as much as possible, and get rid of any unnecessary weight.

It'll be easier to make suggestions if you tell us which plane we're talking about here...
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Old Oct 01, 2011, 05:37 PM
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A 3S 1300mAh LiPo gives 20 minutes of flight, right? Simple math. Buy 2 more of these batteries and fly one for 20 minutes do a quick landing and change the battery and fly 20 more minutes and then land one more time and change to the 3rd battery for 20 minutes. That is a total of 1 hour.

It is nice to dream about long flights but if you want long flights you have to start with the right plane that is built as light as possible and then pick the right power system and the right battery. So to fly a plane for an hour would normally start with a concept and then pick everything from there to reach the goal, not pick a plane and then try to figure out how to get it to fly for an hour. Like TP16 said, using a bigger battery will add flight time but also adds weight. If you add enough battery (enough weight) the plane will not be able to fly at all.

Freddy
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Old Oct 01, 2011, 07:17 PM
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Why would you want to fly for an hour ???? ENJOY !!! RED
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Old Oct 01, 2011, 07:26 PM
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Perhaps he has a puppy and it never stops yapping unless he ties it to a tree at the park. He would rather be flying than sitting at home listening to a barking two-month-old beagle.

I hit my personal limit around 8 minutes or so. Flying is fun, yes, but flying for too long can start grating on the nerves.

I once timed my Slow Stick at 25 minutes. Worst decision of my flying career I've gotten ~14 minutes out of my smaller flying wings in the past, but that's tolerable because they're not painfully boring after the first three minutes the way the Slow Stick is.

I could probably strap a bunch of lipos in parallel to my Slow Stick and get an hour easily, but I'm most definitely not going to
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Old Oct 01, 2011, 09:15 PM
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Well, I was thinking more along the lines of FPV capabilities. I would like to be able to fly hour long missions instead of just 20 minute excursions. But thanks for the input anyway.
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Old Oct 01, 2011, 09:20 PM
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That's mostly the answer I was expecting. Very few are crazy enough to fly LOS for an hour.

Again, it depends on your plane. A Slow Stick can do an hour pretty easily. Something like an EasyStar may be able to do it, but that would take some brain matter.
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Old Oct 01, 2011, 10:47 PM
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Even if you can obtain an hour of flight, you have to realize that you are still limited to distance. The radios we use today communicate a long way, BUT if you are not careful you will fly out of range very quickly.
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Old Oct 01, 2011, 10:48 PM
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Quote:
Originally Posted by Lpbug View Post
Well, I was thinking more along the lines of FPV capabilities. I would like to be able to fly hour long missions instead of just 20 minute excursions. But thanks for the input anyway.
Get a really long extension cord and attach it to a car battery.... Sounds funny but someone actually did this with a heli...

Seriously..

First: You've got a LOT of reading to do...
http://www.rcgroups.com/video-piloting-fpv-rpv-469/

Next you need to select a plane................

Then the equipment it will carry.....

Then the ground station.....

Then how to implement the above......

Then build the above....

Then get some experience flying FPV....

Then worry about breaking the up time record..

---------------

TP16: How would a larger pack increase (parasitic) drag?

Jim
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Old Oct 01, 2011, 10:58 PM
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Jim, adding weight means the wing needs to produce more lift for any given airspeed to keep the plane afloat. We have to increase the angle of attack to get that extra lift.
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Old Oct 01, 2011, 10:58 PM
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Quote:
Originally Posted by tacx View Post
Even if you can obtain an hour of flight, you have to realize that you are still limited to distance. The radios we use today communicate a long way, BUT if you are not careful you will fly out of range very quickly.
It's more a problem of the video signal depending on the equipment, none of which is even mentioned here..

Few people use 2.x GHz radios for FPV... 72MHz is preferred (some more so than others) and the serious guys use UHF modules that will go past 20Km.

Jim
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Old Oct 01, 2011, 11:02 PM
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Originally Posted by TP16 View Post
Jim, adding weight means the wing needs to produce more lift for any given airspeed to keep the plane afloat. We have to increase the angle of attack to get that extra lift.
Stall speed goes up... But AoA? In level powered flight? I don't see how that would change except perhaps in a dead stick landing..

Jim
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Old Oct 01, 2011, 11:18 PM
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If you're flying straight and level at 30mph and your plane weighs 20 ounces, then your plane is producing 20 ounces of lift. If you increase your weight to 23 ounces and you don't change the airspeed or AoA, the total lift will still only be 20 ounces and you'll hit the dirt at those same 30 miles per hour*. Usually breaks stuff.

By slightly increasing the AoA, the wing will produce those 3 extra ounces of lift and we can get back to flying and not crashing. More drag, so probably a bit more throttle (more current wasted), but the same airspeed.

*Yes, I get that the vertical dropping here will add to the total speed. Just means we smashed the airplane a little more, eh?
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Old Oct 01, 2011, 11:45 PM
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Originally Posted by TP16 View Post
If you're flying straight and level at 30mph and your plane weighs 20 ounces, then your plane is producing 20 ounces of lift. If you increase your weight to 23 ounces and you don't change the airspeed or AoA, the total lift will still only be 20 ounces and you'll hit the dirt at those same 30 miles per hour*. Usually breaks stuff.

By slightly increasing the AoA, the wing will produce those 3 extra ounces of lift and we can get back to flying and not crashing. More drag, so probably a bit more throttle (more current wasted), but the same airspeed.

*Yes, I get that the vertical dropping here will add to the total speed. Just means we smashed the airplane a little more, eh?
Okay, you may be right but I don't see it yet.

Stall speed is the minimum.... Past stall speed you have equal to or greater than the amount of lift needed not a fixed amount...

IOW once past the stall speed you have already beaten gravity--the airspeed ala power is the variable which allows the given design to fly.

As an example: Be it a scantly occupied cabin of a 747 or a completely packed 747--once we are cruising in *level* flight my coffee sitting on my tray is still bang level in its cup. If the nose were up more when crowded it would not be. Level flight is level flight...

I see AoA as a design element of an air-frame, where this is the AoA of the wing WRT the fuse, not AoA of the actual aircraft--as in a harrier maneuver.

I'll double check with my FI.

Jim
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Old Oct 02, 2011, 12:00 AM
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The angle of attack is simply the angle at which the wing meets the airstream. It's not the only way to change the lift properties of a wing; for example, in your example with the 747 there are also flaps available to increase or decrease lift as needed to keep the plane's pitch the same no matter how much of a load it's carrying.

For our basic modeling purposes, AoA is the easiest way to get the same result. You could do it with flaps if you really, really wanted. Heck, you could go backwards and use spoilerons as well

Quote:
Stall speed is the minimum.... Past stall speed you have equal to or greater than the amount of lift needed not a fixed amount...
If lift is exceeding gravity, then your plane will be accelerating upward (and note that I say accelerating). A plane in level flight is a one-to-one balancing act of thrust, drag, lift, and weight. Stall speed is the minimum speed the plane will fly at because at some point you can't increase the AoA any more without partially or totally stalling the wing. Since the plane's weight remains unchanged in this case, the AoA has to increase to keep lift constant as airspeed drops.
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