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Dec 09, 2018, 06:39 PM
Careful,.. confident,.. CRASH!
Dukejet's Avatar
Quote:
Originally Posted by headlessagain
I'm not sure how long that high a kv motor on a 7x5 prop on 3s is going to last
A 6x5 on a 2200kv is about the max so I'd expect something to smoke
Andy
Damm right!!... Danger!!!
This will definitely burst into flames within......2minutes.......
The motor is designed for a car, running a cog.
Bout the only prop this would turn successfully would be an edf.

Pls remove it OR make sure someone is videotaping it
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Dec 15, 2018, 02:52 AM
vtpraerobatics.blogspot.c om
oldscooler's Avatar

True FB airfoil


Do I choose A on left or choice B on right?

Just did this test sample true foam board airfoil (A). 11” chord. Really happy with the process and result. Designing a 2.8m Park aerobatic E glider. This will do the trick.

More here:
https://www.rcgroups.com/forums/show...e-VTPR-Channel

And here:
https://www.rcgroups.com/forums/show...robatics-Intro

E
Dec 19, 2018, 08:50 PM
vtpraerobatics.blogspot.c om
oldscooler's Avatar

2.8m foam board glider wing


The 2 piece aerobatic glider wing is final glued ready for final details and mounting to fuselage. These are the longest (54”) single panel wing panels I believe ever done. That is unless somebody knows of others, I would be interested in seeing them.

E
Dec 22, 2018, 09:22 AM
Let's fly!
[QUOTE=Dukejet;40639773]Damm right!!... Danger!!!
This will definitely burst into flames within......2minutes.......
The motor is designed for a car, running a cog.
Bout the only prop this would turn successfully would be an edf.

Pls remove it OR make sure someone is videotaping it [/QUOTE


****UPDATE*********

Puffed a battery - but I also didn't really push it. I've got some 6x5 and 5x5 props. I'll try those and push a little harder.
Dec 22, 2018, 03:50 PM
Careful,.. confident,.. CRASH!
Dukejet's Avatar
Yeah Flying Slow, with electrics, if you over load/prop the motor it will "draw" more power/amps through the system.
More amps =more heat. If you go outside the design parameters you get fire.... all electrics are rated for maximum amp rating.
Your battery puffed cause the motor and esc was able to handle the amps longer than the battery could supply the amps untill it was over discharged-- puffy--
Rule of thumd --Higher the kv the smaller the prop.
Imho- hope this helps
Dec 23, 2018, 12:33 AM
vtpraerobatics.blogspot.c om
oldscooler's Avatar
Stay tuned...
Dec 23, 2018, 07:52 AM
Jack
jackerbes's Avatar
I know the conversation has moved on but I don't really agree with some of the things said here about using that 3650 Kv motor with a 7 x 5 prop.

You really have to look at the motor's specs and the propeller specs to figure these things out...

Quote:
30 inch wingspan
Turnigy XK2845-3650kv Inrunner
60 amp ESC
7x5 prop

3S 1500-2200 batteries...
The details on the motor are here:

https://hobbyking.com/en_us/turnigy-...-inrunner.html

And it says:

Spec.:
Size: XK2845-3650KV
Poles: 4
KV: 3650
Max Current: 48A
Max Voltage: 16.8V/4S Lipo
Case Length: 46.5mm
Case Dia: 28mm
Shaft Dia: 3.175mm
Total Length: 60.5mm
Weight: 125g

If we apply the 3 or 4 Watts per gram rule of thumb to that motor it is a motor that will handle 375W to 500W continuous. And on 3S at 12V that would have it drawing about 31 to 42 Amps (W / V = A).

If you go to flybrushless.com and look at a 7 x 5 prop (I'll use the APC 7 x 5 Thin Electric as an example) you can see what that prop will draw:

http://www.flybrushless.com/prop/view/68

You can see that it drew about 500W at around 16,000 RPM so it will not really threaten that motor at that RPM. The max recommended max RPM for a 7" Thin Electric prop is 145,000 / diameter in inches so the 7" prop is OK up to about 20,000 RPM or so. But we've all learned that there is not good reason to use APC TE props at their max ratings because they are so power hungry and inefficient at those speeds that it does not make any sense to use them at that level. The 16,000 RPM seen in the testing data there is a good example of a sensible max RPM for that prop.

And when you get to cheap Chinese props things change a lot. That sensible max RPM can drop by 1/3rd or even half when you go to thinner more flexible props.

The real concern here is that the 3S pack and a 3650 Kv will have that motor at over 43,000 RPM (3645 x 12 = 43740) at full throttle so he will need to keep the thing well below full throttle and fly at 1/4 to 1/2 throttle at the most. Even going to a 2S pack will have that prop up to speeds that don't really make sense.

I came here to electric RC about 10 years ago and started keeping notes as people helped me get smarter about things. The attached text files with rules of thumb and RPM limits are the things I have learned here and I think they are generally true and very useful...

Jack
Dec 28, 2018, 09:10 AM
Let's fly!
Quote:
Originally Posted by jackerbes
I know the conversation has moved on but I don't really agree with some of the things said here about using that 3650 Kv motor with a 7 x 5 prop.

You really have to look at the motor's specs and the propeller specs to figure these things out...



The details on the motor are here:

https://hobbyking.com/en_us/turnigy-...-inrunner.html

And it says:

Spec.:
Size: XK2845-3650KV
Poles: 4
KV: 3650
Max Current: 48A
Max Voltage: 16.8V/4S Lipo
Case Length: 46.5mm
Case Dia: 28mm
Shaft Dia: 3.175mm
Total Length: 60.5mm
Weight: 125g

If we apply the 3 or 4 Watts per gram rule of thumb to that motor it is a motor that will handle 375W to 500W continuous. And on 3S at 12V that would have it drawing about 31 to 42 Amps (W / V = A).

If you go to flybrushless.com and look at a 7 x 5 prop (I'll use the APC 7 x 5 Thin Electric as an example) you can see what that prop will draw:

http://www.flybrushless.com/prop/view/68

You can see that it drew about 500W at around 16,000 RPM so it will not really threaten that motor at that RPM. The max recommended max RPM for a 7" Thin Electric prop is 145,000 / diameter in inches so the 7" prop is OK up to about 20,000 RPM or so. But we've all learned that there is not good reason to use APC TE props at their max ratings because they are so power hungry and inefficient at those speeds that it does not make any sense to use them at that level. The 16,000 RPM seen in the testing data there is a good example of a sensible max RPM for that prop.

And when you get to cheap Chinese props things change a lot. That sensible max RPM can drop by 1/3rd or even half when you go to thinner more flexible props.

The real concern here is that the 3S pack and a 3650 Kv will have that motor at over 43,000 RPM (3645 x 12 = 43740) at full throttle so he will need to keep the thing well below full throttle and fly at 1/4 to 1/2 throttle at the most. Even going to a 2S pack will have that prop up to speeds that don't really make sense.

I came here to electric RC about 10 years ago and started keeping notes as people helped me get smarter about things. The attached text files with rules of thumb and RPM limits are the things I have learned here and I think they are generally true and very useful...

Jack

*****UPDATE*******

I installed a 6x5 prop and set my timer for 3:00. I flew it conservatively, but also turned it loose a couple of times. I've also added some slightly undercambered wing tips, making the wing span closer to 38 inches instead of the stock 30 inch. The wing tips take away some of the tip speed, but really help tame stalls and landings.

After the 3:00 flight the battery was a little warm, but not hot. When I recharged it, it took I think 1200 mah, so I might add 30 seconds to the timer next time and push a little harder.

The plane trimmed out nicely, and I'm really pleased with the outcome.


Adam "Flying Low"
Dec 29, 2018, 11:24 AM
Jack
jackerbes's Avatar
Good job! I think it is one of the joys of the hobby when we study the specs and test data and work out the details as to what a motor can or cannot do. The limits are almost always signalled by excessive heat in the motor and/or the battery. And if you work up to higher power levels and watch what is going on you can always do it safely.

Many will say that they don't have the test equipment to figure thing out, things like watt meters and the like. But if you are interested you can almost always find a way to get around those limits. Here are some of the things that got me started on this:

$3 Watt Meter - https://www.rcgroups.com/forums/show...23-3-Wattmeter

And this is where it took me eventually

Using the Eagle Tree Systems eLogger Data Logger - https://www.rcgroups.com/forums/show...ystems-eLogger

Jack
Jan 06, 2019, 02:27 PM
Arizona Rim Country

How to Liquefy Hot Glue


I found a video that shows how to make hot glue liquefied. I have not tried it yet to see if it dissolves foam.
DIY plastic (polyethylene) primer (7 min 1 sec)
Jan 07, 2019, 07:51 PM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
Thanks PC , that looks like it may have lot more uses than just painting balloons … Like a primer on EPP for paint or Tape … Hmmm???
Latest blog entry: Lost plans
Jan 08, 2019, 03:20 PM
flyin' fool
goldguy's Avatar
You can't do electric without a wattmeter, the most important tool required.
Jan 12, 2019, 11:57 PM
Careful,.. confident,.. CRASH!
Dukejet's Avatar
Quote:
Originally Posted by Flying Low
*****UPDATE*******

I installed a 6x5 prop and set my timer for 3:00. I flew it conservatively, but also turned it loose a couple of times. I've also added some slightly undercambered wing tips, making the wing span closer to 38 inches instead of the stock 30 inch. The wing tips take away some of the tip speed, but really help tame stalls and landings.

After the 3:00 flight the battery was a little warm, but not hot. When I recharged it, it took I think 1200 mah, so I might add 30 seconds to the timer next time and push a little harder.

The plane trimmed out nicely, and I'm really pleased with the outcome.


Adam "Flying Low"
Good to see there was no flames FL. Glad you got it flying
Feb 18, 2019, 07:21 AM
Registered User

Twin boom FPV plane


Here are a few pics of my latest foam board scratch build. I design and 3D print a lot of small parts to enhance my foam board planes. This is one example. In the wing there are multiple 3D printed ribs (19). The center rib is 2.5" wide and provides 6 wing mounting holes. In the fuselage there are two bulkheads that help form the fuselage and provide blind 1/4-20 nylon nuts. 1/4-20 nylon screws go through the wing and center tip to mount the wing to the fuselage. The twin booms are 1 section of a 4 section telescoping fishing rod from Walmart called a WonderPole. I 3D printed mounting brackets to attach the booms to the wing front and rear. I also created 3D brackets to make the horizontal stab and vertical fins mount to the twin booms. Lastly I created a 3D printed rear bulkhead/motor mount which provides some down thrust to the motor. Also, I created 8 wheel hub halves and sandwiched pool noodle tires between hub halves. The aircraft takes off from the ground and lands great avoiding sliced hands from hand launching (don't ask). I intend to add FPV gear to this plane soon.
Feb 18, 2019, 10:47 AM
Registered User
Flysfloats's Avatar
Now this is an interesting plane! Good for you coming up with many innovative ideas. I have taken a break from foam board planes after having less than stellar results and constant repairs. Built an old Great Planes Super Kaos 60 kit and waiting for first flight and good weather. May have to try to duplicate your plane.


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