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Old Sep 04, 2012, 05:39 PM
That's a funny word
NE Ohio
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http://www.electrifly.com/miscproducts/gpmq6610.html They are using these SF props with 1000 kv motors and 3s. My MM and a couple others use the 9x4.5 and then the mini ep uses the 9x6 SF , but only 950 kv motor. In comparing them to other "SF" props they seem about like some DD props , but not as wimpy as some of the GWS props I've used.

In any case you are saying that I'll be better off with a thin electric prop even for my stock 1000 kv motor? and the stock setup is borderlined being overspeeded? Going to a 1100 kv is even worse. I gotcha.

I do have plenty of 9 inch electric props (not SF) in 3.8 , 4.7 , 5 , 6 , 7 pitch. This is not the first time that I concluded that perhaps Hobbico , GP , Flyzone was at the very top of the RPM limit for the props used. It is also possible that they are using slower motors than the specs that they list.

Ideally I'd love to use that smaller 950 kv motor that I already have and pull only 13-15 amps. Perhaps starting with the stock 9x4.5 and then going to the 9x6 later. I can't imagine this plane going 50-60 mph , but hey maybe it really is going that fast. It's pretty quick for me I know that. I sure gotta keep my eyes on it.
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Old Sep 04, 2012, 08:19 PM
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Quote:
Originally Posted by gulio View Post
http://www.electrifly.com/miscproducts/gpmq6610.html They are using these SF props with 1000 kv motors and 3s.
Guilio, I have no technical information on this particular brand and model of propellers. If the manufacturer says they are safe to use on 3S, then it should be okay.

WebOCalc only knows about GWS and APC "Slow Flyer" props, and therefore you won't see these Electrifly props there. However, there is an APC 9x4.5 Electric prop, and you can play with WebOCalc to see under what circumstances it shows up. You have to slow down the "desired top speed" a LOT, from 60 mph or so down to around 35 mph - 40 mph, at which point you will be getting warnings about inadequate speed from WebOCalc.
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Originally Posted by gulio View Post
Ideally I'd love to use that smaller 950 kv motor that I already have and pull only 13-15 amps.
We can make that work..just use an APC 9x6 Thin Electric (estimated 11.5 amps, 44 mph pitch speed). There isn't going to be great performance, though. Just mild aerobatics, and enough speed to fly, but not to bring out the models best.

You can try your Electrifly 9x6, perhaps it will draw more current and give you more thrust than the APC version.
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Originally Posted by gulio View Post
I can't imagine this plane going 50-60 mph , but hey maybe it really is going that fast. It's pretty quick for me I know that. I sure gotta keep my eyes on it.
It won't be going that fast with your present prop (9x4.5), but that is how fast this model "wants" to fly.

The reason: the wing area is pretty small (only 268 square inches) and the model is very heavy for its size (27 oz). Because of this, the wing loading is really too high for a parkflyer, and because of this the model stalls at a rather high estimated speed of around 19 mph.

That means in practice it really won't be comfortable to fly under 25 mph or so - it will be right on the edge of stalling and falling out of the air.

Usually these sorts of models will start to feel like they're flying properly "on the wing" by the time you speed them up to twice the stall speed. In this case, that is around 38 mph or so. So at 40 mph it should fly like a tame little Cessna at cruise - nose a little high, control response a little mushy, but at least it will be flying properly.

And if you want the model to fly like the sporty little racer it's supposed to be, it needs to go considerably faster yet - up to maybe 3 times the stall speed, which is 57 mph in this case.

It's really unfortunate that this model is so heavy. It would be much nicer (and easier to fly in a park, at slower speeds) if it shed at least half a pound.

By the way, this is another use for WebOCalc - it's steered me away from some purchases in the past, because I found out those models were too heavy by running their numbers through the program and looking at the predicted flight performance.

-Flieslikeabeagle
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Old Sep 04, 2012, 08:29 PM
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Quote:
Originally Posted by nordemoniac View Post
Hi!
I'm new to RC, and wanted to start with the Bixler from HK. I've ordered a NMT 2836 2200kv motor, 2200mah 3s battery, and the HK 6S radio.

I'm very confused about the propeller, as this is a pusher, and it is limited to a certain size.
Welcome to the hobby, nordemoniac!

Your instincts are on the right track. The Bixler appears to be a copy of the Multiplex Easy Star, and both models are restricted to too-small propellers.

That means WebOCalc really won't work on these models. The whole idea behind WebOCalc is to find an efficient propeller that matches what the model needs. Because these models are restricted to very tiny models, this is physically impossible to do!

What happens in practice with these models is that the prop is very small (and therefore very inefficient). To compensate, you push lots of power through it. This in turn speeds up the prop, making way too much pitch speed - also extremely inefficient. It is a lot like taking a low-torque, high-revving engine from a 1-litre motorcycle, and installing that in a slow, heavy tractor. Just a bad, bad, power system.

Of course, you gain the benefit of not having a propeller in the nose of the model. That is the reason why the model is popular with beginners who crash a lot, and FPV pilots who don't want a propeller in the cameras field of view.
Quote:
Originally Posted by nordemoniac View Post
I think the original propeller is a 6x4 APC. What kind of thrust etc. can I expect?
There are a number of (free) motor/prop/battery calculators out there. Any of them can give you an approximate thrust, current draw, etc for your combination (motor, battery, prop). There is a long list of motor calc software (with links) in the first post of this thread:
http://www.rcgroups.com/forums/showthread.php?t=606703
Quote:
Originally Posted by nordemoniac View Post
Will I be able to do FPV with this plane?
Unfortunately I am completely ignorant when it comes to the requirements for FPV flying. But IonSlo's link to the Bixler thread should turn up some people who know this model and can tell you what is known to work.

Good luck!

-Flieslikeabeagle
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Old Sep 05, 2012, 09:32 AM
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United States, WV, Morgantown
Joined Aug 2012
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Absolutely the BEST!!! educational thread...
Thank you very much "NoFlyZone" for starting such thread, until today I would just guess my what motor/prop to put on my planes but that is about to change

Thank you again!
Paisa
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Old Sep 05, 2012, 09:40 AM
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United States, CA, Marina Del Rey
Joined Jun 2012
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Quote:
Originally Posted by paisa View Post
Absolutely the BEST!!! educational thread...
Thank you very much "NoFlyZone" for starting such thread, until today I would just guess my what motor/prop to put on my planes but that is about to change

Thank you again!
Paisa
Nofly is no longer around but kudos should go to flieslikeabeagle. Without him and his WebOcalc there wouldn't even be a thread.
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Old Sep 05, 2012, 09:27 PM
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After I created WebOCalc and refined it to the point where it was a useful tool, I started more than one WebOCalc thread to let people know about the software and how to use it. A few people did start using it, but none of those threads took off and became popular enough to help a significant number of people. I had good information to share, but I never managed to reach that many people with it.

Chuck (NoFlyZone), on the other hand, did such a great job of communicating when he started this thread that it really took off. Here we are a couple of years later at post number seven hundred and seventy one - and the thread is still going, and people are still being helped!

So I echo paisa's thanks to NoFlyZone - he did a wonderful job with this thread, and I raise my hat to him and thank him for it.

-Flieslikeabeagle
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Old Sep 06, 2012, 12:44 AM
If I build it, it will fly
United States, NY, East Rochester
Joined Jan 2012
701 Posts
I didn't see the last page of replies in my notifications... Now I see why the low low pitch props are hard to find, thanks.

I am at war with myself on a motor choice... My aim for this bipe is slow sport aerobatics. I will be using a 3s (2200mah for now, 1000mah might be an option later). My bipe wings are 30"x7"x2 (420 sq/in). Ailerons are 2"x9"x4, Rudders are 7"x2"x2 (box fuse with integrated Vert stabs), Elevator is 18"x2" (Hor stab mounted on top of Vert stabs).


The air frame weighs in at 180g without electronics or L.G.
Battery is 204g 3s 2200mah 35-40c
Planning on this 25g 30a ESC W/2a BEC
The RX will be from my recent freebee TX/RX kit 25g
Servos Hextronik MG-14g x2=28g (tail surfaces) & a Futaba s3151 43g ailerons
Some ultra light wheels @ 25g for 2front & 1 rear (not sure on what to use for LG that will hold a ~30oz rough landing)

The above puts me at 530g. (I am thinking of cutting triangles out of the fuse sides to lighten it without hurting rigidity much)
I still need:
landing gear for the ultra light wheels
control surface horns & linkage
Motor & hardware kit
prop

I would like to get the remaining gear under 200g (730g is just under 26oz), I think it can be done, but I'm still in the learning to build stages of RC life lol.


Here are the motors I favor:
1050kv motor
20a (23a peak)
1050kv
73g

850kv motor
28a
850kv
80g

750kv motor
30a (no peak listed)
750kv
70g


the lower kv pair might be ~80%eff on 3s looking at the A/V/W numbers... W-O-C says no larger than a 9" prop but its hard to find one that small to put out 26oz+ thrust & not be going 50+. What do y'all think? any ideas? I think I've just been looking at it too long. I'm going to bed lol.

~psguardian
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Old Sep 06, 2012, 02:48 AM
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Quote:
Originally Posted by psguardian View Post
<snip>
W-O-C says no larger than a 9" prop but its hard to find one that small to put out 26oz+ thrust & not be going 50+
APC 9x6 Slow Flyer, 850 rpm/V motor, 10.5 amps, 25 oz thrust, 40 mph pitch speed. That's from putting your numbers into WebOCalc.

This bipe won't be a slow and lazy flyer - notice that "Advanced Glow Trainer" prediction? That means it's going to feel on the hot and heavy side in the air. I think that's mostly because of the fat and stubby wings, 30" long and 7" wide, which gives them an aspect ratio of barely 4:1. Stubby wings are aerodynamically inefficient and don't make as much lift for their area as longer, skinnier wings would have.

The short wingspan is also the reason for keeping the prop size down to 9" or less. When the prop diameter gets too big compared to the wingspan, you start to get serious effects from motor torque - every time you open the throttle the model will roll left!

Incidentally, if the motor current is only going to be 10.5 amps, you can use a much smaller battery (1000 mAh or even less), and probably a lighter motor as well. The only trouble is smaller and lighter motors are likely to have higher Kv, which may force you to use a smaller and less efficient 8" prop. That's why gearboxes were such a nice technical solution before outrunners took over!

So far I haven't seen any Hobby King motors that get near 80% efficiency. More often they peak out somewhere between 65% and 70% efficiency, about the same as a fifty-cent brushed Speed 400 can motor! But they have lots more ventilation for cooling air, and no brushes to burn out, so they can handle more power than the brushed motor can even though they aren't really significantly more efficient.

-Flieslikeabeagle
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Old Sep 06, 2012, 11:49 AM
If I build it, it will fly
United States, NY, East Rochester
Joined Jan 2012
701 Posts
Ahh. I wondered why such a small prop recommendation, makes perfect sense. (If I was to do something like aileron/throttle mixing I could potentially use larger, but that would be a bit advanced for me lol)

So lets focus on the 850kv, I like the sound of only a 10.5a draw.

850kv | 28a | 11.1v | 275w (output)

So my understanding of these numbers is as follows: 28 X 11.1 = 310.8w 310.8w X .885 = 275.058w... As per our prev exchanges, I now doubt their numbers that are based on 11.1v 3s power sources, lets run it with W-O-Cs default of 10.8 (makes more sense anyway since thats what it will be calc'd with)... 28 X 10.8 = 302.4w 302.4w X .91 = 275.184w.

Sooooo, is this legitimately a 275w output motor on 3s with ~90% eff, or is it more like a 211w-226w motor (70-75% eff)?

~psguardian
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Old Sep 06, 2012, 05:15 PM
That's a funny word
NE Ohio
Joined Apr 2003
3,686 Posts
Quote:
Originally Posted by flieslikeabeagle View Post
After I created WebOCalc and refined it to the point where it was a useful tool, I started more than one WebOCalc thread to let people know about the software and how to use it. A few people did start using it, but none of those threads took off and became popular enough to help a significant number of people. I had good information to share, but I never managed to reach that many people with it.

Chuck (NoFlyZone), on the other hand, did such a great job of communicating when he started this thread that it really took off. Here we are a couple of years later at post number seven hundred and seventy one - and the thread is still going, and people are still being helped!

So I echo paisa's thanks to NoFlyZone - he did a wonderful job with this thread, and I raise my hat to him and thank him for it.

-Flieslikeabeagle
I agree, I have a hard time with patience and attention. This is the 3rd time I visited the calc and thread and it finally sunk in. I'm no expert yet , but Chuck;s post , the calc and you taught me a lot about props , speeds, stall speed, wings and weight. In fact our dialog taught me more about planes than I've learned in a long time. It makes a lot of sense. Thank you.
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Old Sep 06, 2012, 09:43 PM
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Quote:
Originally Posted by gulio View Post
In fact our dialog taught me more about planes than I've learned in a long time. It makes a lot of sense. Thank you.
You're very welcome! It's wonderful that things are making more sense now!

-Flieslikeabeagle
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Old Sep 06, 2012, 10:17 PM
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Quote:
Originally Posted by psguardian View Post
Sooooo, is this legitimately a 275w output motor on 3s with ~90% eff, or is it more like a 211w-226w motor (70-75% eff)?

~psguardian
I'm going to take a tiny detour in my answer, if you'll pardon me for it.

It has become well known that scientists are the worst people at catching crooks who pretend to have extra sensory perception, telepathy, etc. That's because scientists expect the experiment to be honest - it doesn't occur to them that the experiment itself is rigged, that the observations are lies.

Con men and professional magicians are much better at catching these crooks who claim ESP - because both good con men and professional magicians are good at tricking other people, they recognise trickery and cheating when they see it.

You, psguardian, must be an honest man, because like the scientists studying the lying crooks, you've assumed honesty on the other persons part; that the data on the Hobby King website is honest and accurate.

Unfortunately, historical evidence shows that this is an incorrect assumption. In my experience with Hobby King motors, the only numbers you can somewhat trust are the published Kv and the motor weight - and even those may have significant errors.

The "performance" numbers, like internal resistance and maximum current, are usually complete nonsense. Most HK motors would fry like an egg long before they got anywhere near the stated maximum current or output power.

Lacking any trustworthy data, some of us have come up with usable approximations. 75% peak efficiency is one of them. Another is that most of these motors can handle a maximum of about 3 watts per gram of motor weight. (So an 80 gram motor will probably be maxed out at 240 watts).

These are only approximations, and any given motor may be worse (which happens more often than you'd think!), or perhaps a little better (rarely if ever).

From what I've learned, a crudely machined, sloppily wound motor with big air-gaps, poor balancing, low-grade bearings, thick laminations made of low-grade steel, and weak magnets is unlikely to do much better than 75% efficient. That's the way these budget motors are made.

To do better, you need precision manufacturing, very tight air gaps, expensive low-friction bearings, high-strength magnets, precise windings with thick (and hard to wind) wire that completely fills all the available space, thin motor laminations, high-grade steel, etc. All these things cost money and labour, so these motors are never going to sell as inexpensively as the Turnigys and so on.

As long as we know what we're getting for our money, there's nothing wrong with using the budget motors. Just be aware that in exchange for the lower cost, we also get lower efficiency, higher weight, and reduced power output compared to higher quality (but more expensive) motors.

My philosophy on this was to use the cheap, heavy, and inefficient motors on those models that didn't suffer too much from these characteristics: low-performance models (Cubs, etc), heavy models (warbirds, etc), and so on.

There are some programs (like Christian Persson's DriveCalc, http://www.drivecalc.de/ ) that include long lists of motors with painstakingly measured data, including efficiency curves. You may find it interesting to look at some of them.

-Flieslikeabeagle
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Old Sep 07, 2012, 09:48 AM
If I build it, it will fly
United States, NY, East Rochester
Joined Jan 2012
701 Posts
Sadly I was leaning towards the false/overly-optimistic numbers as your answer. Approximately 3w p/gram, that's a new one to use. I'll download that calc also.

At last I won't have to worry about these guys being too efficient lol... Wonder if any of these cheaper ones are worth rewinding.... I'd be willing to try that out.

~psguardian
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Old Sep 07, 2012, 10:06 AM
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United States, CA, Marina Del Rey
Joined Jun 2012
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If it were just the windings that needed improvement it might be rationalized. But as beagle points out all the corners are cut to build a cheap and inefficient motor.
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Old Sep 07, 2012, 10:59 AM
Sure, I can fly after sunset!?
United States, MI, Novi
Joined Jan 2011
512 Posts
HELP: Can I convert the Hanger 9 Xtra Easy?

My daughter picked this up for me at a garage sale, but no engine. It is a Hanger 9 Xtra Easy. I have NO experience with fuel, so don't want to go that route.

http://www.hangar-9.com/Products/Def...ProdID=HAN1300

I put the info in the latest version of Webocalc

Weight 100oz
Wingspan 69inch
Wing Area 793 in sq

I came up with

6S battery 1500 or better, 24C = 21.6V
APC-TE prop 17inch 12 pitch
ESC 42-49 amp

Need motor:
300Kv 32.6amp

Q1: Did I do this right?
Q2: Where do I find such an engine?
Q3: What will this cost?

I fly a SuperCub and a Radian with ease. I can fly my PZ S.E.5a on a calm day or light wind. Is it worth the cost, considering the plane was free?
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