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-   -   faster set up for my 6s wing? (http://www.Wattflyer.com/forums/showthread.php?t=73637)

exiged 04-25-2014 01:31 PM

faster set up for my 6s wing?
 
Hi Guys,

I have a slipstream 40" epp wing which currently has a ntm 35-36 1800kv 875w motor (supposed to be 4s max i think but its been running fine for a few months so far),1300mah 6s 45-90c lipo,60A esc and 5.5 x 4.5e apc prop.

Its definitely fast and still handles nicely with this set up,but as a little project id like to see if i can go even faster.

Can anyone suggest a set up to get me there please?

thanks!

CHELLIE 04-25-2014 07:12 PM

Quote:

Originally Posted by exiged (Post 946530)
Hi Guys,

I have a slipstream 40" epp wing which currently has a ntm 35-36 1800kv 875w motor (supposed to be 4s max i think but its been running fine for a few months so far),1300mah 6s 45-90c lipo,60A esc and 5.5 x 4.5e apc prop.

Its definitely fast and still handles nicely with this set up,but as a little project id like to see if i can go even faster.

Can anyone suggest a set up to get me there please?

thanks!

use a lipo with more Mah, 1300mah is not enough, 1300 mah will drop voltage real Quick, 2200mah would be better to use to keep up the voltage, more voltage = more speed, the little extra weight will help to give the wing more momentum. try a 5x5 apc prop. check your amp draw with a Wattmeter to be on the safe side. Hope that helps, Chellie

solentlife 04-25-2014 09:11 PM

As you try to go faster ie by upping prop to say the new 5.5 x 5.5 speed prop on HK ..the amps draw will rise significantly ... the 1300 pack will drain too fast or just plain puff / restrict the power available due to voltage drop.

It's a never ending circle .. and you have to keep balancing it each step of the way .. as Chellie says - WATTMETER ... it rules supreme.

My speed toolkit compromises :

Wattmeter
Optical tachometer
Calculator

and on-board is a V3 Eagle-Tree Pitot speed sensor. This is the best way as it gives you actual airspeed and that means you are not concerned about wind direction or speed. You get direct results that you can compare to see if any improvement.

Nigel

fhhuber 04-25-2014 09:50 PM

You can keep adding power (bigger motor, bigger ESC and bigger battery to spin a higher rpm and/or higher pitch prop) but at some point you will actually start to slow down instead of gaining speed.... or it will become too heavy to take off.

Already pushing the motor past its rating so I wouldn't try pushing it harder.

Its probably time to look at a different model that is "cleaner" and thus capable of more speed on the same power. Thinner airfoil with sharper leading edge (F-104 had to have guards on the leading edge to keep people from getting cut when they brushed against it) Very low frontal area and great care in seeking the most streamlined form possible will improve speed.


************

I'm preparing to see if stepping DOWN from the 127mm BVM EVF using 12S 5000 mah on the plane in my avatar photo to a 90 mm and 8S 4000 mah will make it faster...

solentlife 04-25-2014 10:41 PM

One off the problems I encountered was the speed barrier and then requiring incredible amounts of power to get past it.

On the Parkjet ... 150 - 180kph was relatively easy and attainable without resorting to insane setups. 180 to 200 started to look crazy ... 200 and up was just plain out of this world ..
I hit 222kph with one ... and it took a lot of power .. literally destroyed the LiPo doing it ...

My T45 50mm with high kv .. 4s ... etc. hit the barrier 140kph .. it has 1.2 to 1 Power to weight .. and high efflux speed but the airframe said enough at 140kph. My other same airframe - I installed a 3700kv pusher with 4.1 x 4.1 with 4S .. that hits 180kph .. again - insane set-up to get that extra speed.

Each airframe has a natural barrier based on its' drag shape ... parasitic, dynamic etc. It all adds up and increases as speed goes up until it matches the thrust .. then no matter what - it stops accelerating.

Nigel

kyleservicetech 04-26-2014 02:03 AM

Quote:

Originally Posted by solentlife (Post 946541)
One off the problems I encountered was the speed barrier and then requiring incredible amounts of power to get past it.

On the Parkjet ... 150 - 180kph was relatively easy and attainable without resorting to insane setups. 180 to 200 started to look crazy ... 200 and up was just plain out of this world ..
I hit 222kph with one ... and it took a lot of power .. literally destroyed the LiPo doing it ...

My T45 50mm with high kv .. 4s ... etc. hit the barrier 140kph .. it has 1.2 to 1 Power to weight .. and high efflux speed but the airframe said enough at 140kph. My other same airframe - I installed a 3700kv pusher with 4.1 x 4.1 with 4S .. that hits 180kph .. again - insane set-up to get that extra speed.

Each airframe has a natural barrier based on its' drag shape ... parasitic, dynamic etc. It all adds up and increases as speed goes up until it matches the thrust .. then no matter what - it stops accelerating.

Nigel

Yeah
If my feeble understanding of aerodynamics is correct, doubling the air speed of a model requires eight times more watts on the propeller shaft. And, going from 100 MPH to 125 MPH requires doubling the watts up front. That's power on the prop shaft, NOT the input power to the motor. Sometimes really increasing the power input to a motor results in its efficiency dropping like a rock. And, overheating the motor in the process.

For those with scientific calculators, its the ratio of the speed raised to the third power. Or (V2/V1)^3.

solentlife 04-26-2014 07:47 AM

Ships actually have same problem .. the only difference is the water is higher density than air.

A merchant ship reaches its waterline length balanced speed. To go faster means unbelievable increases in power. Compare a Container ships power to a larger normal merchant vessel.

Go even further and look at a warship .. you'd think that a warships shape being long and thin would be advantage and reduce such power needs .. think again. The long thin doctrine has been shown many times to be based on faulty maths. A small company on the Isle of Wight, UK entered a tender to MoD for a new warship .. they put forward the wide, shallow hull base for gun-platform. Admiralty threw it out. Swedes picked it up .. ran with it and produced one of the best coastal gunboats .. it's economic on fuel, has good speed, and stable for gun use.

Nigel

exiged 04-26-2014 01:12 PM

Thanks for the info guys.

Yes weight is soon defo going to be a problem.I might just look for a more suitable motor and try a 2200mah 6s as chellie suggested.

Having said that i have spotted a nice HK500 heli motor H3126 1600kv (1500w max),perhaps a 2650-3000mah 6s lipo,200A esc but that will be a heavy set up and as mentioned i may have issues launching by hand.

soarrich 04-26-2014 02:39 PM

Quote:

Originally Posted by fhhuber (Post 946539)
Thinner airfoil with sharper leading edge (F-104 had to have guards on the leading edge to keep people from getting cut when they brushed against it) ..



At subsonic speeds sharp doesn't help, it just gives you a bad airfoil.

kyleservicetech 04-27-2014 02:29 AM

Quote:

Originally Posted by soarrich (Post 946574)
At subsonic speeds sharp doesn't help, it just gives you a bad airfoil.

Out of curiosity, then an 1/8 inch thick flat wing with a lot of power up front wouldn't be much good??? (That is if you could make the wing strong enough.)

Or, would that flat wing provide a lot of drag because of its lousy efficiency?

CHELLIE 04-27-2014 02:55 AM

Quote:

Originally Posted by exiged (Post 946569)
Thanks for the info guys.

Yes weight is soon defo going to be a problem.I might just look for a more suitable motor and try a 2200mah 6s as chellie suggested.

Having said that i have spotted a nice HK500 heli motor H3126 1600kv (1500w max),perhaps a 2650-3000mah 6s lipo,200A esc but that will be a heavy set up and as mentioned i may have issues launching by hand.

take a look at the Power systems being used on page 1, in the 100 mph club Thread and that will give you a very good idea of what to expect with different motors, props and batterys, take care and have fun, Chellie

http://www.wattflyer.com/forums/show...t=100+mph+club

soarrich 04-27-2014 03:55 AM

Quote:

Originally Posted by kyleservicetech (Post 946606)
Out of curiosity, then an 1/8 inch thick flat wing with a lot of power up front wouldn't be much good??? (That is if you could make the wing strong enough.)

Well...not exactly.

I've never used a flat 1/8" sheet to make a wing, but I did use a 3/16" to make a elliptical wing with about 6 to 1 AR, it flew great! At first you would think, it's pointy why isn't it a bad airfoil? The thing that makes a normally thick airfoiled wing with a pointy LE bad, is the stagnation point jumps from the bottom of the point to the top very quickly making the airfoil hunt. A flat plate will have to have more AoA than a airfoiled wing so it will keep the stagnation point under the LE, so it won't hunt.

Lots of guys use flat-plate airfoils on small electrics with great success, and if you are making a delta it makes lift with the platform's shape, not so much with the airfoil.


Quote:

Originally Posted by kyleservicetech (Post 946606)
Or, would that flat wing provide a lot of drag because of its lousy efficiency?

Yes and no. On a large wing, say 60" and 600 sq. in, yea it would be bad. On the other hand a 30" wing with 150 sq. in could be OK. When you start making smaller wings the air appears stickier to them and they work OK. I've built a Honker and a TopCat sailplane using sheet wings, they both flew great, but they had camber built into the wing. I have a Magnum that has a 3/8" solid wing that has some airfoil carved in, and it's suppose to do 200 MPH.

How big of a plane are you going to make, and what power?

This may be of interest. http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

kyleservicetech 04-27-2014 04:16 AM

Quote:

Originally Posted by soarrich (Post 946609)
Well...not exactly.

I've never used a flat 1/8" sheet to make a wing, but I did use a 3/16" to make a elliptical wing with about 6 to 1 AR, it flew great! At first you would think, it's pointy why isn't it a bad airfoil? The thing that makes a normally thick airfoiled wing with a pointy LE bad, is the stagnation point jumps from the bottom of the point to the top very quickly making the airfoil hunt. A flat plate will have to have more AoA than a airfoiled wing so it will keep the stagnation point under the LE, so it won't hunt.

Lots of guys use flat-plate airfoils on small electrics with great success, and if you are making a delta it makes lift with the platform's shape, not so much with the airfoil.




Yes and no. On a large wing, say 60" and 600 sq. in, yea it would be bad. On the other hand a 30" wing with 150 sq. in could be OK. When you start making smaller wings the air appears stickier to them and they work OK. I've built a Honker and a TopCat sailplane using sheet wings, they both flew great, but they had camber built into the wing. I have a Magnum that has a 3/8" solid wing that has some airfoil carved in, and it's suppose to do 200 MPH.

How big of a plane are you going to make, and what power?

This may be of interest. http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html


Thanks for the quick response!!

As for me, I was just curious, and have no plans to build such a model. :oops:


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