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Old May 01, 2014, 09:01 AM
Flying = Falling (Slowly)
dharban's Avatar
Tulsa, OK
Joined May 2004
2,492 Posts
While there are certainly less expensive motors that can provide good performance, there is no free lunch in motor selection. I was a bit surprised at the suggestion that anyone would recommend an un-geared inrunner for a sailplane application so I took a look at the motor on eCalc and compared it with a couple of geared motors with which I am familiar.

The Mega 16/14/7 is an 80 gram motor with an advertised Kv of 1300 -- low for an inrunner but still high enough that the motor will require a very small prop. According to eCalc, with an 11x6 prop (Mega's recommendation) the motor will have a power input of about 315 watts and a power output of about 188 watts (60% efficiency). This motor will be one hot momma when it is running like this and the pitch speed will be about 33 mph -- not enough to get a 45 oz. glider to 200 meters in 30 seconds. (It could be that Mega knows something we don't, but these numbers are pretty far off the target that you would be looking for for a 45 ounce plane.

The next motor I ran numbers for was a Neu 1105 with a 6.7 gearbox (motor Kv is 3800, effective Kv is 567). With a 15x10 prop it has an input of 323 watts and an output of 289 watts (efficiency of about 89%). Pitch speed of about 48 mph. Total weight is 120 gms. I ran this combination in a 48 oz. AVA pro and it had a climb rate of about 2100 fpm.

The next motorI ran numbers for was a Neu 1105 with a 4.4 gearbox (motor Kv is 3800, effective Kv is 863). With a 13x7 prop it has an input of about 393 watts and an output of about 346 watts (88% efficiency). Pitch speed was about 49 mph. I ran this in the AVA and in spite of its higher wattage, its climb rate was around 1900 fpm. Total weight is 120 gms.

I could not run the numbers on my Powerline but in identical applications against the Neu with the 4.4 it produced identical performance. It weighs 100 gms.

Besides the obvious differences in motor efficiency, there is a substantial increase in propeller efficiency (Propeller output power/Propeller input power) as you go to larger slower props. I would very conservatively estimate that the 15x10 is at least 10% more efficient than the 13x7 in this application and 20 % more efficient than the 11x6. So for a given input the 1105 with the 4.4 is about 11 percent less efficient than the 1105 with the 6.7. And the direct drive Mega is probably 45 percent less efficient than the 1105 with the 6.7. This is not an indictment of the Mega -- if you went to a faster wind (16/15/3), a 4.4 gearbox and a 13x10 gearbox you could reasonably expect the motor efficiency to rise to around 85% (from 60%).

None of this matters if the performance for the motor you select suits your purpose. I would suggest that for a guy who is concerned about cost, the first place to save money is to set up a plane which will perform over a wide enough range of flying conditions that only one plane is needed -- in the case of the Kappa, that would be a power system which can launch the plane plus about 15 oz. ballast to 200 meters altitude and 300 meters out in 28 seconds into an 18 mph wind. The Mega you referenced will not come close.

Believe me, I have nothing against inexpensive solutions to problems. But I am sort of keen on defining the problem and making certain that my selections will get the job done.

Happy Landings,

Don
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Old May 01, 2014, 09:22 AM
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Lenny970's Avatar
Greeley, Colorado, USA
Joined Feb 2000
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Some good comments Don.
I agree it seems silly to worry about saving a few bucks on a cheap motor while spendIng a couple grand on a model.
I would choose the most suitable motor (considering power, weight, and ability to turn an efficient prop) and if it costs a little more than a cheap solution, that's OK.

Lenny
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Old May 01, 2014, 11:37 AM
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Why NOT save money where you can if it doesn't make that much difference,, I've seen plenty of good contest winning pilots flying expensive moldies with an inexpensive but high quality outrunner,, no sense in throwing money away :-),, I mean the motor is only for getting the plane to soaring altitude so who cares if it is cheaper
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Old May 01, 2014, 11:48 AM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
232 Posts
Quote:
Originally Posted by dharban View Post
While there are certainly less expensive motors that can provide good performance, there is no free lunch in motor selection.
... (nip) ...

Believe me, I have nothing against inexpensive solutions to problems. But I am sort of keen on defining the problem and making certain that my selections will get the job done.

Happy Landings,

Don
To think well and correctly in advance is the way to go IMHO.
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Old May 01, 2014, 12:31 PM
MrE
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United States, WA, Gig Harbor
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I agree with Dons reasoning on powering this model.

I would buy it for the low weight and plan to balast in windy conditions.

Why screw that up with a slightly cheaper but significantly heavier power system or one that couldn't handle the ballast?

On the other hand, I would be very tempted to go Kevin's rout, screw the efficiency, and put in a super light power system that barely got the job done on a dead calm day and save this one for floater conditions

Either way, cost would be waaaay down on my list of considerations.
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Old May 01, 2014, 12:48 PM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
232 Posts
Quote:
Originally Posted by MrE View Post
I agree with Dons reasoning on powering this model.

I would buy it for the low weight and plan to balast in windy conditions.

Why screw that up with a slightly cheaper but significantly heavier power system or one that couldn't handle the ballast?

On the other hand, I would be very tempted to go Kevin's rout, screw the efficiency, and put in a super light power system that barely got the job done on a dead calm day and save this one for floater conditions

Either way, cost would be waaaay down on my list of considerations.
"(nip) ... The tough thing about all of these planes is being able to accommodate servos in the pod AND no weight in the tail. At least to me it is crazy to spend 2 1/2 grand on a super light-weight composite and then strap a couple of quarters to the tail. But that's just me.

Happy Landings,

Don "

Don, dharban in post #10 suggests an interesting question at least to this noob. Why spend $2500, or whatever, on a flyweight plane only to have to add weight, taped coins or something, to get the thing to balance just so you could fly it in light air? Is it really a 45oz "RTF"?

Secondly, is this a light air only plane or by properly adding ballast you can fly it in the seemingly more common windier conditions we see out West... and if ballast is necessary, what is the point of a 45 oz plane?

Third, these carbon planes are works of art IMHO and certainly sexier than a Radian, for example, but what is actually gained saving a couple ounces for the price other than performance in calm conditions?

Thanks, interesting thread.
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Old May 01, 2014, 01:47 PM
MrE
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United States, WA, Gig Harbor
Joined Aug 2007
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You would only have to add weight to the tail if you used a heavy power system. Even then, you might be able to get by moving things under the wing. Dont know if thats possible or not with this one.

I personally wouldn't be averse to cutting the nose off and moving the motor back if necessary.

However, the whole point of building these lighter models is to save weight - for those light, marginal lift conditions.

Even in windy conditions, a good pilot can take good advantage of a lighter model.

The wind doesnt always blow a gale
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Old May 01, 2014, 02:10 PM
Flying = Falling (Slowly)
dharban's Avatar
Tulsa, OK
Joined May 2004
2,492 Posts
Quote:
Originally Posted by suddenstop View Post
Don, dharban in post #10 suggests an interesting question at least to this noob. Why spend $2500, or whatever, on a flyweight plane only to have to add weight, taped coins or something, to get the thing to balance just so you could fly it in light air? Is it really a 45oz "RTF"?
The point behind these posts is that there IS (or may be) a motor selection which can meet all of your criteria -- it just may cost more than 80 dollars. The problem with some of the less expensive options is that you either have to add weight to get where you want to be or you have to sacrifice USABLE power and NOT get where you want to be if you opt for some of less expensive options. RIght now I have two Maxas -- a heavy one and a light one. And I have tried enough power combinations to know that I could get to a 60 ounce plane (same wing loading as the smaller Kappa) and still have the option to power and ballast up if I wanted to. But not with an 80 dollar motor.

Quote:
Secondly, is this a light air only plane or by properly adding ballast you can fly it in the seemingly more common windier conditions we see out West... and if ballast is necessary, what is the point of a 45 oz plane?
Everybody has to look at their own needs. I certainly fly in a windy place. But I also fly on windless mornings and evenings -- and at some contests all day long. In those conditions, the Maxa (and I suppose the Kappa) are exceptional. Besides having low wing loadings, these planes are very light in the ends and the difference relative to planes with more weight in the extremes is VERY noticeable -- even in stronger winds. Planes with less weight in the ends signal lift better in most conditions and they are much more nimble working with small bubbles.

Quote:
Third, these carbon planes are works of art IMHO and certainly sexier than a Radian, for example, but what is actually gained saving a couple ounces for the price other than performance in calm conditions?
There are days when the box my Radian came in could max out all day long -- in fact, there are days when the Radian pisses me off because I can have so much fun with it for so much less money than the carbon planes. But when the going gets tough, whether it is light winds and no lift (the Maxa's CONSISTENT dawn flight time is about 9 1/2 minutes), when you have to transit out of sink or when you have to get back home from a long downwind excursion, the higher tech planes will simply outperform the Radian. One of the things to remember for ALES is that when we are flying to 200 meters, there is not a huge amount of "lift time" that any plane has to find on an average flight -- maybe 3 minutes or so. When launch altitudes drop to 100 or 150 meters planes will have to find a lot more "lift time".

That said, I am pretty much of a putz pilot and I fly the carbon planes because they are fun. But if you look at the way scores sort out right now in TD contests, our future will likely see top 10 finishes separated by seconds in the near future. Can a Radian consistently perform like that -- maybe. But as Damon Runyon once said, "the race is not always to the swift nor the battle to the strong -- but that's the way to bet."

Happy Landings,

Don
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Old May 01, 2014, 06:48 PM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
232 Posts
snip "...One of the things to remember for ALES is that when we are flying to 200 meters, there is not a huge amount of "lift time" that any plane has to find on an average flight -- maybe 3 minutes or so. When launch altitudes drop to 100 or 150 meters planes will have to find a lot more "lift time".

That said, I am pretty much of a putz pilot and I fly the carbon planes because they are fun. But if you look at the way scores sort out right now in TD contests, our future will likely see top 10 finishes separated by seconds in the near future. Can a Radian consistently perform like that -- maybe. But as Damon Runyon once said, "the race is not always to the swift nor the battle to the strong -- but that's the way to bet."

Happy Landings,

Don

Thanks for a great answers. Great quote too. I suppose a cheap, insufficient motor to save a few bucks would be like putting curb feelers (or better, a 6 cylinder Buick motor) on a 2015 ZO6 'vette,

I can see the benefits, as your post explains, of light weight, light ends, and the ability to change weights for the conditions as well as flying cool planes. The best equipment deserves the best components IMHO or what is the point of flying such technology? Rhetorical, no comment needed. Thank you, Don.
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Old May 01, 2014, 07:13 PM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
232 Posts
Last noob post...at least for a while.

Don previously, "...But if you look at the way scores sort out right now in TD contests, our future will likely see top 10 finishes separated by seconds in the near future. Can a Radian consistently perform like that -- maybe."

My questions are related regarding the future of RC Sailplane competition.

Will it become one design or class racing with specific limitations to the equipment like Sailboat racing? Will there be minimum weight restrictions ala Bike racing in the Tour de France or even Nascar, F1, etc?

Will there be an effort to equalize the equipment so the competition is more about the pilots than on who or which programs can buy the most exotic airframes?

Or not? Thanks again
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Old May 02, 2014, 04:50 PM
Glider Guider
United States, PA, Harrisburg
Joined Oct 2012
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Anyone lay down cash and build one yet???
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Old May 05, 2014, 02:26 PM
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banjo328's Avatar
Albuquerque, NM
Joined Jan 2010
122 Posts
I have one on order, 6-8 week delivery time. I missed the order window on the first batch in stock.

The motor selection discussion is very informative but I'm going to wait until the plane arrives, and install everything except the motor, see what it takes to balance, then decide what motor to use. I have several outrunners on hand that can do the job, if they will fit. If not, then may have to go the inrunner/gear box route. AD at Skip Miller says the new Neu 707 with P29 gearbox is impressive but I can't find any data....

Found some:

http://www.soaringusa.com/NEU-Motor-...9-Gearbox.html
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Old May 05, 2014, 03:12 PM
Glider Guider
United States, PA, Harrisburg
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Old May 05, 2014, 03:34 PM
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Albuquerque, NM
Joined Jan 2010
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Thanks Jeffrey. I'll watch that build. Is it really necessary to use such a large prop ? Wouldn't the current draw be less with a smaller prop with better batt. duration, and on that light of a plane , wouldn't climb performance still be adequate ?
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Old May 05, 2014, 03:58 PM
Glider Guider
United States, PA, Harrisburg
Joined Oct 2012
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