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Old Feb 03, 2013, 11:17 PM
A Global Force For Good
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USA, OH, Cincinnati
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Fully extended fowlers flaps always leave a massive gap. You hardly ever notice the gapping slot because the spoilers that cover these gaps are only rarely deployed until after landing.
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Old Feb 04, 2013, 12:29 AM
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Originally Posted by LuvEvolution7 View Post
don't do anything about those gaps before we talk. the gaps aren't as big an issue as you think they are. if anything, I'd actually leave the gaps there. the turbulence you think starts at the gap, actually starts much sooner than that. if you didn't have the turbulence, you wouldn't have lift. people incorrectly think that lift is about laminar flow, when it's about creating turbulence and putting it to use. there are two types of airfoil..............laminar and turbulent. that being said, even a laminar airfoil doesn't remain laminar for long. if you want to make use of the turbulence, you need to run a turbulator strip of zig zag tape. you could also get into deturbulating too, but sealing the gap won't accomplish what you think it will. in fact, it might even hurt you more than you think it will fix your issues. either that, or open up a slot from underneath to allow the turbulence to reattach to the control surface. simply putting a gap seal won't accomplish that.
Turbulence in some areas does actually help but here i'm not sure Rich, I changed the BAC-111's flaps from her maiden flight 2 years ago & maybe that's a factor in her poor performance yesterday.
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Old Feb 04, 2013, 12:32 AM
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Originally Posted by jmpdgs View Post
Fully extended fowlers flaps always leave a massive gap. You hardly ever notice the gapping slot because the spoilers that cover these gaps are only rarely deployed until after landing.
Right Joe but on the Fowler flap the actuators move the flap surface out and down "enlarging the wings surface" I don't have that luxury with my simpler flap design.
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Old Feb 04, 2013, 03:09 PM
A Global Force For Good
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USA, OH, Cincinnati
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Originally Posted by demondriver View Post
Right Joe but on the Fowler flap the actuators move the flap surface out and down "enlarging the wings surface" I don't have that luxury with my simpler flap design.
It makes no difference Chris, the gap issue can still be remedied through the use of some spoilers, functional or non it wouldn't matter. What you're after is their effect in their closed position and actually if you're using simple flaps this makes your mod that much easier.

The other option is to smooth the flaps leading edge and wings trailing edge to create a "slotting" effect which has a whole different set of benefits. Although it still creates more drag than the other option it also augments lift and stability so that's something you might consider.

Just an idea for ya to mull over.

Cheers
Joe
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Old Feb 04, 2013, 07:39 PM
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Originally Posted by jmpdgs View Post
It makes no difference Chris, the gap issue can still be remedied through the use of some spoilers, functional or non it wouldn't matter. What you're after is their effect in their closed position and actually if you're using simple flaps this makes your mod that much easier.

The other option is to smooth the flaps leading edge and wings trailing edge to create a "slotting" effect which has a whole different set of benefits. Although it still creates more drag than the other option it also augments lift and stability so that's something you might consider.

Just an idea for ya to mull over.

Cheers
Joe

I'm mulling Joe! Those are ALL great points and I've found some solutions hearing all this great advice from you and everyone here on RCG.
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Old Feb 04, 2013, 09:55 PM
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Turbulence in some areas does actually help but here i'm not sure Rich, I changed the BAC-111's flaps from her maiden flight 2 years ago & maybe that's a factor in her poor performance yesterday.
my point is that the airfoil is turbulent long before any forms at that gap. your airfoil might be the issue and not that gap at all. I'd like to see some sort of tuft test done on the wing to see if it's the whole airfoil that's the issue. you can do it without the use of a wind tunnel. the sharp LE of your airfoils could be creating the issue and the turbulence is forming well ahead of the normal separation point of an airfoil. turbulation and deturbulation may take care of this, but you need to get a baseline first. the only way is to do a tuft test and see what you get.

remember that lift is all about circulation. if your circulation sucks, then you have no lift. the airplane will rotate, but will not lift off. when the airplane starts to roll on its takeoff run, a vortex is started and is then shed. it is at this point that lift is started, due to the perpetual shedding of this vortex. plus, upwash at the LE and downwash at the TE all contribute to this lift production. if anything is out of whack, you get loss of lift production. too sharp an LE and upwash can't happen.
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Old Feb 05, 2013, 09:08 AM
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gentlemen watch this video of the two T-tails I had out Saturday, you'll hear their EDFs never really had the proper power.

http://www.rcgroups.com/forums/showthread.php?t=1825276
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Old Feb 05, 2013, 05:35 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
North AL, USA
Joined Nov 2009
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DD, did you ever get a "second opinion" on the battery charge or did you trust your charger? I realize that you may have a high-end charger but I still wouldn't trust one opinion.

Unbelievable, I know a guy with a big heli that didn't have anything to take to the field but after he saw my meter he was going to get one. He never knew how much he had drawn the battery down after the flight, just the recovery voltage an hour after he got home. He was being very conservative on his flights as he didn't know how much he had left but was able to tell he could easily stay up three more minutes and not even be close to LVC.
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Old Feb 05, 2013, 07:26 PM
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DD, did you ever get a "second opinion" on the battery charge or did you trust your charger? I realize that you may have a high-end charger but I still wouldn't trust one opinion.

Unbelievable, I know a guy with a big heli that didn't have anything to take to the field but after he saw my meter he was going to get one. He never knew how much he had drawn the battery down after the flight, just the recovery voltage an hour after he got home. He was being very conservative on his flights as he didn't know how much he had left but was able to tell he could easily stay up three more minutes and not even be close to LVC.
Great point Kevin! I'm looking at my chargers as well, its possible they simply are Not providing a full charge.
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Old Feb 05, 2013, 08:30 PM
A Day @ a Time - Matt. 6:25-34
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Great point Kevin! I'm looking at my chargers as well, its possible they simply are Not providing a full charge.
That is what the meter will tell you, not only total voltage, but also voltage of each cell.

One more question... Have you done any internal resistance testing? If you think your batteries showed a good charge and just didn't seem to have the punch you would expect, you might want to check the internal resistance. What happens is when you get a big load the high resistance will cause a significant drop in pack voltage under load without being able to recover. A good battery tested from 100% charge will have some initial drop but not too much; back off the throttle to 30-50% and you should see the pack voltage come up too.

Check out this video on YouTube:
LiPo INTERNAL RESISTANCE TESTING - a simple 12v load tester (17 min 37 sec)


I'm building a load tester that will have toggle switches and four of the 12 50w halogen bulbs. The box is big-enough to expand to six bulbs and switches.

I viewed the video again... what was the temperature like at the field? If it was really cool that will affect your power output too as resistance goes up with lower temperatures. According to the video you can record unacceptable resistance levels on a good pack, so watch those temps!

Hope this helps...

Kevin
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Old Feb 05, 2013, 10:07 PM
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St.Catharines, Ontario
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Originally Posted by demondriver View Post
Great point Kevin! I'm looking at my chargers as well, its possible they simply are Not providing a full charge.
how are you using the charger(s)? you running them from the wall, or from a power supply? running from the wall isn't good enough IMHO. you need a good power supply of 12 Volts. if your charger is capable of it, 24 Volts is even better. I ran off the wall and when I finally got a power supply, I couldn't believe what a difference it was. I can charge packs twice as fast (sometimes faster) AND, they peak and balance much, much better. and I'm only using a crappy old B6.
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Old Feb 05, 2013, 10:57 PM
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Originally Posted by ruff1 View Post
That is what the meter will tell you, not only total voltage, but also voltage of each cell.

One more question... Have you done any internal resistance testing? If you think your batteries showed a good charge and just didn't seem to have the punch you would expect, you might want to check the internal resistance. What happens is when you get a big load the high resistance will cause a significant drop in pack voltage under load without being able to recover. A good battery tested from 100% charge will have some initial drop but not too much; back off the throttle to 30-50% and you should see the pack voltage come up too.

Check out this video on YouTube:
http://www.youtube.com/watch?v=usRE3gLFnOc

I'm building a load tester that will have toggle switches and four of the 12 50w halogen bulbs. The box is big-enough to expand to six bulbs and switches.

I viewed the video again... what was the temperature like at the field? If it was really cool that will affect your power output too as resistance goes up with lower temperatures. According to the video you can record unacceptable resistance levels on a good pack, so watch those temps!

Hope this helps...

Kevin
Wow Kevin I needed to see this!

I'm a Old Gas head I learned on Nitro & gas engines, my first electric plane was a Graupner Glider I bought in 97 or 98 and my first lipo powered plane was in 2002 or 2003 so I'm still learning the inns & outs of Lipo batteries.
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Old Feb 05, 2013, 10:59 PM
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Originally Posted by LuvEvolution7 View Post
how are you using the charger(s)? you running them from the wall, or from a power supply? running from the wall isn't good enough IMHO. you need a good power supply of 12 Volts. if your charger is capable of it, 24 Volts is even better. I ran off the wall and when I finally got a power supply, I couldn't believe what a difference it was. I can charge packs twice as fast (sometimes faster) AND, they peak and balance much, much better. and I'm only using a crappy old B6.
Your right Rich, I run them off a 12 volt car battery and a battery charger.
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Old Feb 05, 2013, 11:23 PM
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St.Catharines, Ontario
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the car battery is good for the field, but get yourself a good supply for charging at home. I got mine from a guy that converts computer power supplies. best 40 bucks I ever spent. I actually got two from him by mistake and he let me keep both, so I have 24 Volts when I get the new TP charger. can't wait to get that one, once I sell my Miss Bud hydro.
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Old Feb 06, 2013, 05:47 AM
A Day @ a Time - Matt. 6:25-34
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North AL, USA
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Good points LE, especially if you are running the larger batteries. I don't have anything larger than 3S 2200 mah, you guys have hungry EDFs and your batteries run a bit bigger. I run mine off the wall using a 5 amp 12v dc charger at home, we have a 12v charging station with a deep-cycle marine 12v at the field that we keep topped up with one of the Harbor Freight solar panels. We're able to charge up some 5 and 6S batteries with that rig. Nice having some retired engineers in the club!
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