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Old May 05, 2014, 03:00 PM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
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A Noob guide to the Raptor PNP - @ SMM

I thought it might be helpful for beginners, noobs like me, to share what I have learned with my first electric glider build and first high g landing.

If you are a beginner and are considering the cute, relatively cheap Raptor like I purchased from Skip Miller Models:

http://www.skipmillermodels.com/4Ch_...v_p/raptor.htm

THINK about it and do some homework FIRST!

This forum has a WEALTH of good advice and knowledge if you seek it out. I am a noob. Consider that as you read this.

* First of all, IMHO, the 6 ch FH Raptor, no matter how inexpensive, is not a good beginner plane. No matter how benign the float characteristics are you will probably need an able instructor at your side if this is your first electric FH glider. Native intelligence doesn't necessarily mean you can translate that immediately into good pilot skill. It might on a Radian with some previous experience, but... the Raptor? You decide.

* Consider not taking the advice of those selling you something without doing the homework. Trust, but verify in advance of a purchase.

A couple good starting points outside this forum as examples IMHO are:

http://www.radiocontrolinfo.com/RCca...Calculator.php

http://www.ecalc.ch/motorcalc.php?ecalc&lang=en

You can plug in some of the motor, prop, ESC, battery, elevation, pressure, etc. parameters into a simple grid at eCalc, for instance, and see if what is recommended (by anyone) is prudent to buy. For example, and it will be interesting to see if it changes soon, SMM lists as power options:

"Recommended Motors:

Hacker A20-12XL, SB-55 ESC, 12 x 8 prop

Hacker A20-8XL, SB-55 ESC, 9 x 5 prop"

Being a noob I could be wrong, and eCalc could be wrong as well, but at least plug in the numbers in advance of your purchase. Either way it is conflicting and therefore confusing. How do you know what is right?

I bought the Hacker A20 12 XL and the SB 55 PRO ESC. It initially was shipped with a 10x6. The "new" recommendation" is 12x8 and 9x5. The eCALC results show:

http://www.rcgroups.com/forums/showp...&postcount=153

You decide who you trust. Do you trust eCalc showing a 12x8 @ over power, prop stall, and HOT temps; or, a 9x5 @ 9358 RPMs which shows most efficient? I personally think a 11x6 or maybe 11x7 may be better given what I have read on this forum and eCalc's grid.

It is nice to have the info available to match the power to your needs in advance of a purchase. You can then ask the retailer for clarification based on your homework, in advance of purchase, before making a decision. It could be the noob is incorrectly interpreting the data.

Also, you can "shop" different configurations easily seeing the differences in power, weight, size, heat, etc. before you buy or to verify a seller's recommendations. I reordered a 10x6 for the second Raptor and recieved a 10x7. Plugging the numbers into eCalc seems to suggest that prop is not a particularly good choice for the power combo. Who is right?

BTW: note the eCalcs data disclaimer at top left: "Accuracy. +/- 10%

The numbers could be up to 10% better... or worse. A pre-purchase margin of error might be contemplated.

I plugged numbers in with 1000 ft. elevation, inHG @ 29.91, Lipo 2500, 20-30C, 12 XL, 55 SB ESC, weight 25 oz. if you are curious to follow examples.

* The Raptor, or any other kit, will vary in quality.

http://www.rcgroups.com/forums/showp...&postcount=119

IMHO, I would seriously consider INSPECTing any kit after opening and not simply glance at it before beginning a build. It will be MUCH easier to make a return or exchange if sent back in the condition you received it. Duh, that's why all the build logs show builders inspecting their kits. Noob rush can be more expensive than need be.

* Will it do or is it best? For example, at this point with this plane, I would not buy a linear ESC/BEC but would instead buy a switching ESC/BEC without a hot and heavy heat sink. Go light and cool or consider extra weight ballast with an, uh, increased thermalling component.

It was a tough but surmountable challenge balancing the plane with the purchased components. It was nose heavy after the initial installation. After ditching the Rx 5 cell NiMH battery things got easier. Some other changes followed and it seemed well balanced for a first flight at about 76 MM back from the leading edge as I recall.

Linear and switching ESC's can each work well but which is better for your Tx-Rx and installation? With digital servos, 2.4 radios, heat, reliability, etc this forum and perhaps other sources may give you more accurate, up to date, and usable information than found on a sales website. Just saying, do the homework in advance as parts and pieces become more complicated and higher performance dictates.

* Consider your skills as builder and pilot. Better yet, ask a better builder and a better pilot what they think. On a kit you have to make decisions such as, how am I going to secure the wing servos ... and which ones should I use? This Raptor kit did not have a booklet or plans in the box. Ask in advance. SMM thankfully provided links to this forum containing Raptor builds, for example, as well as a PDF of how to build the Raptor.

Videos are available on you-tube as well, here is a good start:

http://www.rcgroups.com/forums/showp...&postcount=119

A word about duplicating what others do. You may find a solution that works better for you by thinking the problem through. I have built two Raptor V-tail sub-assemblies from the Raptor kits. One I tried to epoxy together all at once. The second I did one side at a time. The second was easier, cleaner, and gave a better outcome for me. There may be a better way for you if you are having a challenge duplicating a better builders technique.

* Share what you have learned. Perhaps view early challenges and failures as a gift, not a curse, and if viewed in the light of earned wisdom and experience they will lead to future benefits. If it weren't for the posters here this noob at least would have a much steeper and an undoubtedly much more expensive learning curve.

Thank you all. It is great being able to learn from those who have done it many times before or as a noob does and learns something new. Consider returning the favor given by others by asking questions and sharing knowledge you gain and have earned as a noob. A newer noob than you is watching.
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Old May 05, 2014, 08:37 PM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
232 Posts
What is the relationship between battery charge and power?

I have a question. I plugged some numbers into eCalc to try to find the most appropriate motor-prop-esv-battery combo for my intended flying.

http://www.ecalc.ch/motorcalc.php?ecalc&lang=en

My previous numbers were generated with a Lipo at a 'normal' charge sate. I revisited the eCalc site and changed the battery to a 'full charge' with the other settings kept the same.

What had been acceptable performance numbers are now over limit and looks unsafe, and what previously was bad is worse. Kind of scary when you are not careful with your initial parameters when checking.

How does or why does a fully charged battery supply more power than 'normal' (less charge state) and when figuring out power needs in advance... figure it with max battery charge?

This sounds like a good reason, if the battery charge is critical to a 30 second motor run to 200 meters of altitude, to always use fully charged batteries with each launch or at least be aware the performance changes as the battery discharges. No?

Thanks

Thanks
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Old May 05, 2014, 10:07 PM
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Hi, suddenstop. You are learning!

I have learned that one shouldn't place too much trust in ecalc or any other "calc". It can give you a very general sense but there's no replacement for checking things out with a tachometer and watt meter. The various combinations of motor, prop, ESC, and battery simply overwhelm the system. For instance...

I have been using motors that draw about 30 amps for the two years I have been using modern electric power systems. My old batteries work very well with these motors but then I went to a bigger, 50 amp class, motor, and I was gravely disappointed in my realized performance despite the fact that the numbers seemed to work. Then I got a 2150mah, 30C, battery and it really opened my eyes. My old batteries, in theory, should provide adequate performance but now I know that an insufficient battery simply won't perform above it's class. Live and learn.

About props: Drawing on over 40 years of glow engines, and my more limited experience with electric motors, one wants to go with the biggest blade area that your motor or engine will spin "happily". In general; this means that one wants to use a large diameter and a low pitch. For a sailplane, as opposed to a "hotliner", there really isn't much need to go above about a 6 inch pitch. A larger pitch will provide higher speed and cruising efficiency but the low speed thrust we want demands the biggest blade our motors will handle.

Keep learning and keep asking.

Cheers!
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Old May 05, 2014, 10:59 PM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
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Originally Posted by peterlngh View Post
Hi, suddenstop. You are learning!

I have learned that one shouldn't place too much trust in ecalc or any other "calc". It can give you a very general sense but there's no replacement for checking things out with a tachometer and watt meter. The various combinations of motor, prop, ESC, and battery simply overwhelm the system. For instance...

I have been using motors that draw about 30 amps for the two years I have been using modern electric power systems. My old batteries work very well with these motors but then I went to a bigger, 50 amp class, motor, and I was gravely disappointed in my realized performance despite the fact that the numbers seemed to work. Then I got a 2150mah, 30C, battery and it really opened my eyes. My old batteries, in theory, should provide adequate performance but now I know that an insufficient battery simply won't perform above it's class. Live and learn.

About props: Drawing on over 40 years of glow engines, and my more limited experience with electric motors, one wants to go with the biggest blade area that your motor or engine will spin "happily". In general; this means that one wants to use a large diameter and a low pitch. For a sailplane, as opposed to a "hotliner", there really isn't much need to go above about a 6 inch pitch. A larger pitch will provide higher speed and cruising efficiency but the low speed thrust we want demands the biggest blade our motors will handle.

Keep learning and keep asking.

Cheers!
Peter, thanks. I get the idea of large diameter/low pitch and batteries are getting smaller, more powerful all the time... How or where can one find out in advance which motors, props, esc's, etc. work well together?

For example, SMM sent me a 10x6 and a 10x7 for the Hacker motor I bought from them. Currently they are recommending a 12x8 or a 9x5 ... which seems counterintuitive to me. If anything, shouldn't it be a 9x8 or a 12x5?

I would love to know how to test these things and I have bought the Naton Electric Sailplane vids but even then, how would you test the combinations available before purchasing? At this point in my sailplane education I am a bit leery of simply buying what sellers recommend. No offense meant but I would like to know the why so I can make my own informed decisions. Ideas?

Thanks for your help.
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Old May 06, 2014, 12:37 PM
...one of my nicer landings
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Originally Posted by peterlngh View Post
Hi, suddenstop. You are learning!

I have learned that one shouldn't place too much trust in ecalc or any other "calc". It can give you a very general sense but there's no replacement for checking things out with a tachometer and watt meter. The various combinations of motor, prop, ESC, and battery simply overwhelm the system. <snip>...
Thanks for the ideas...

OK, just downloaded the Motorcalc trial version @ http://www.motocalc.com/ to compare with eCalc.

I have a couple engineer friends from church and the fire department; and one, my dad, a retired NASA/Boeing EE who began in the space race to help extricate me, a business major - go figure, from the confusion that seems to surround me with the information I seem to locate. Can't be rocket science, can it?

Hopefully beginning this weekend, and using the Radian and Hacker stuff, batteries, and different props as a basis for comparison, I can begin to make sense of this in order to gain some predictable expectation of future performance.


It can't be rocket science, can it?
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Old May 06, 2014, 05:27 PM
...one of my nicer landings
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I have been playing a bit with motocalc(.com). Cool program. Interestingly, in its help section it has some of the info I have been curious about. For example, what is a good "pitch speed"? It says the ideal is about 2.5-3 times the stall speed. If true, fairly simple but interesting to know the relation to prop speed and airspeed.

Plugging the mostly 'same' numbers as before in eCalc with the addition of the Selig 4083, a similar battery, and std pressure 29.92, std temp 59F, filter max 30A (about half ESC)

led to very similar results to eCalcs results excepting motocalc gave more performance data for props 9-12x5-8

motocalc reports:

prop stalled: 9x7,9x8,10x7,10x8, 11x8

11x6, 11x7, 12x5, 12x6 at least theoretically: >= 1000 fpm or >500 fpm in 30 secs for ALES.

12x6 @ 1046 fpm, 6086 rpm;
11x6 @ 1031 fpm, 7041 rpm

Best battery time, (as in eCalc) was 9x5 @ 8.58 min, 9221 rpm
11x6 battery time 5.55 min

partial notes for 10x5: "The full-throttle motor current at the best lift-to-drag ratio airspeed (18.2A) falls approximately between the motor's maximum efficiency current (12.8A) and its current at theoretical maximum output (68.5A), thus making effective use of the motor."

"The static pitch speed (40mph) is within the range of approximately 2.5 to 3 times the model's stall speed (14mph), which is considered ideal for good performance."

"At the best lift-to-drag ratio airspeed, the excess-thrust (20.7oz) to weight (36.9oz) ratio is 0.56:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver."

The report also list stall speed and optimal lift speeds... which is interesting in its own right. Regardless, this was the first and a quick stab at the program. So fine tuning (exact model weight, actual bench testing, etc) would be prudent.

To the noobs out there I would at least consider "calculation programs", perhaps with a cautious eye, in determining your needs in advance of a purchase. At least you could ask your component "consultant" why(?) if what they recommend is greatly different than what your 'calcs' show.

Perhaps they may have actually bench tested their recommended combos at your field altitude, etc. Heck, perhaps they just "heard it through the grapevine". Somehow, they came to their recommendation.

Anyway, these calc programs are fun to play with.

edit: correct for wing loading slightly changed things. 11.6oz/sq ft sound reasonable @ 39.9 oz rtf, 496 sq in. wing area, 78.74 in (2000mm) span?

11x6, 12x6 gave best climb performance as you said, Peter.
12x6 1061fpm @ 1100 msl, 59F

10x7 last sold appears to 'prop stall'. Apparently not a best option

Fun program
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Old May 06, 2014, 06:21 PM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
232 Posts
Last today: The most recent motor sent me was a Hacker A20-8XL

Changing nothing but the motor type from 12 XL to 8XL had same prop stalls and several hundred feet per second greater climb rate, however, this is what is scary to me:

partial note: "The full-throttle steady-state motor temperature (321F) is extremely high, which will likely damage the motor unless full-throttle is used sparingly and cooling is good (even then, damage is possible).
Current can be decreased by using fewer cells, a smaller diameter or lower pitched propeller, a higher gear ratio, or some combination of these methods."

The temps with 12XL were <100F with certain props, motocalc, about a bit higher with eCalc.

* the Raptor has no vents, none are called for in the manual, and are said to be not needed.

My question, If a noob or a real pilot flew with a 8XL for a 30 sec full throttle climb given these numbers if true, is that safe? How long does it take a motor to reach these temps and how soon before damage is done?

Furthermore, I think I would warn noobs to be certain YOUR power system performs as you hope and not as anothers with a DIFFERENT system.

Last question, if a 4:1 or whatever gear system were installed with the 8XL, wouldn't that help solve the heat problem by slowing the motor down while maintaining prop speed?

Thanks
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Old May 06, 2014, 08:54 PM
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Originally Posted by suddenstop View Post
Thanks for the ideas...

OK, just downloaded the Motorcalc trial version @ http://www.motocalc.com/ to compare with eCalc.

I have a couple engineer friends from church and the fire department; and one, my dad, a retired NASA/Boeing EE who began in the space race to help extricate me, a business major - go figure, from the confusion that seems to surround me with the information I seem to locate. Can't be rocket science, can it?

Hopefully beginning this weekend, and using the Radian and Hacker stuff, batteries, and different props as a basis for comparison, I can begin to make sense of this in order to gain some predictable expectation of future performance.


It can't be rocket science, can it?
It's not "rocket science". It's "propeller science". It's really more of an art. There are just so many variables that it's hard to come up with the perfect solution without testing your individual setup both statically and in flight. Going beyond the diameter and pitch, things like the weight of the blades and even the airfoil and shape of the blades have their effect. Plus; a given set of blades might perform differently with a different spinner/yoke assembly. You seem to be pursuing the right train of thought but the raw numbers might not make a lot of sense compared to using the different setups in flight.

Here is what I would suggest.

First? Get a watt meter. I'm using a cheap HobbyKing multi meter and I use it to ascertain if I will burn up a motor if I use full throttle for more than a few seconds. (Lacking a watt meter; one can assume that a prop that makes your motor too hot to touch in 10 seconds is too much prop.)

Then? Try a few props to see which one gives the performance you desire. I began by getting three cheap, plastic, props that should work with my motors and then tried them out. I soon found out that the best prop for my motor and glider was an 11X6 so then I spent a few more dollars on a 11X6 carbon composite prop. The lighter, stiffer, blades increased my climb performance and actually reduced the amount of current I draw.

When all is said and done; one just needs to try out a few combinations to see what works best. A calculator might tell you that a 14 inch prop will burn out your motor but it can't tell you which specific prop will provide the performance you desire.

Cheers!
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Old May 07, 2014, 01:15 AM
...one of my nicer landings
United States, WA, Walla Walla
Joined Mar 2014
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Originally Posted by peterlngh View Post
It's not "rocket science". It's "propeller science". It's really more of an art. There are just so many variables that it's hard to come up with the perfect solution without testing your individual setup both statically and in flight. Going beyond the diameter and pitch, things like the weight of the blades and even the airfoil and shape of the blades have their effect. Plus; a given set of blades might perform differently with a different spinner/yoke assembly. You seem to be pursuing the right train of thought but the raw numbers might not make a lot of sense compared to using the different setups in flight.

Here is what I would suggest.

First? Get a watt meter. I'm using a cheap HobbyKing multi meter and I use it to ascertain if I will burn up a motor if I use full throttle for more than a few seconds. (Lacking a watt meter; one can assume that a prop that makes your motor too hot to touch in 10 seconds is too much prop.)

Then? Try a few props to see which one gives the performance you desire. I began by getting three cheap, plastic, props that should work with my motors and then tried them out. I soon found out that the best prop for my motor and glider was an 11X6 so then I spent a few more dollars on a 11X6 carbon composite prop. The lighter, stiffer, blades increased my climb performance and actually reduced the amount of current I draw.

When all is said and done; one just needs to try out a few combinations to see what works best. A calculator might tell you that a 14 inch prop will burn out your motor but it can't tell you which specific prop will provide the performance you desire.

Cheers!
Thanks Peter

I have a multi meter I should dig out and mess with. Great idea... duh, sheesh.

I wondered about the assumptions generally made re: different components such as prop airfoil shapes by different manufacturers, mass and materials, etc. affecting their formulae. They recommend as you do to confirm your choices by testing both static and in the field.

It is interesting though to see changes as different components are combined. For example, you can view how changing pitch affects rpm, climb, heat, endurance, efficiency, etc. Frankly, as long as I can climb to 200m within 30 secs without ruining equipment I'm happy.

Additionally, the weights for components, at least the ones I have checked, seem accurate which makes it an easy way to shop and compare with an eye on at least general performance differences. What started this was understanding the difference between a linear ESC/BEC shipped when I ordered a switching ESC/BEC. I ordered one motor and was sent another one. Ordered one prop size and was sent a different one, supposedly better... which both programs don't seem to validate.

Regardless, it is fascinating to this noob. Seems like the best thing is to spin a motor fast, gear the prop down, use appropriate sized components, go light as possible, add ballast when needed, and it all is moot... if the plane isn't in lift or landing for max points.

Thanks again for your inspiration to dig a little deeper. Sheesh, why in the world did I agree to BBQ for some engineers this weekend. Man oh man...
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Old May 07, 2014, 06:01 PM
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Quote:
Originally Posted by peterlngh View Post
It's not "rocket science". It's "propeller science". It's really more of an art. There are just so many variables that it's hard to come up with the perfect solution without testing your individual setup both statically and in flight. Going beyond the diameter and pitch, things like the weight of the blades and even the airfoil and shape of the blades have their effect. Plus; a given set of blades might perform differently with a different spinner/yoke assembly. You seem to be pursuing the right train of thought but the raw numbers might not make a lot of sense compared to using the different setups in flight.

Here is what I would suggest.

First? Get a watt meter. I'm using a cheap HobbyKing multi meter and I use it to ascertain if I will burn up a motor if I use full throttle for more than a few seconds. (Lacking a watt meter; one can assume that a prop that makes your motor too hot to touch in 10 seconds is too much prop.)

Then? Try a few props to see which one gives the performance you desire. I began by getting three cheap, plastic, props that should work with my motors and then tried them out. I soon found out that the best prop for my motor and glider was an 11X6 so then I spent a few more dollars on a 11X6 carbon composite prop. The lighter, stiffer, blades increased my climb performance and actually reduced the amount of current I draw.

When all is said and done; one just needs to try out a few combinations to see what works best. A calculator might tell you that a 14 inch prop will burn out your motor but it can't tell you which specific prop will provide the performance you desire.

Cheers!
I too was having problems trying to get the most use out of my power system without over amping my gear.Then i found this tool and added a amp draw meter,RPM meter, temperature gun, gram scale. I pulled some motors from my scrap box and started testing different props to get my highest rpm without over amping the esc and motor, Then went to my planes and pulled the power plants and started testing, It gave me a better understanding and optimized my electric and nitro power systems.Hope this helps http://www.candelaresearchcenter.com/about-us.html
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Old May 07, 2014, 11:52 PM
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Thanks Ric, great looking stands. Been working on one myself... bookmarked link
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Old May 08, 2014, 10:04 PM
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Thanks Ric, great looking stands. Been working on one myself... bookmarked link
NP cheers
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Old May 09, 2014, 12:42 PM
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NP cheers
Hope to test this weekend. Basic idea, to help visualize, Is a narrow sliding 'drawer' tugging a digital fish scale. Motor mounted to front of drawer which slides on rails, battery etc. behind drawer front, back hooked to digital fish scale. Can't wait to be shot down be mechanical engineer friend.

Anyway, weather perfect for this messing around stuff.
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Old May 12, 2014, 11:32 AM
...one of my nicer landings
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Originally Posted by suddenstop View Post
Thanks Peter

I have a multi meter I should dig out and mess with. Great idea... duh, sheesh.

I wondered about the assumptions generally made re: different components such as prop airfoil shapes by different manufacturers, mass and materials, etc. affecting their formulae. They recommend as you do to confirm your choices by testing both static and in the field.

It is interesting though to see changes as different components are combined. For example, you can view how changing pitch affects rpm, climb, heat, endurance, efficiency, etc. Frankly, as long as I can climb to 200m within 30 secs without ruining equipment I'm happy.

Additionally, the weights for components, at least the ones I have checked, seem accurate which makes it an easy way to shop and compare with an eye on at least general performance differences. What started this was understanding the difference between a linear ESC/BEC shipped when I ordered a switching ESC/BEC. I ordered one motor and was sent another one. Ordered one prop size and was sent a different one, supposedly better... which both programs don't seem to validate.

Regardless, it is fascinating to this noob. Seems like the best thing is to spin a motor fast, gear the prop down, use appropriate sized components, go light as possible, add ballast when needed, and it all is moot... if the plane isn't in lift or landing for max points.

Thanks again for your inspiration to dig a little deeper. Sheesh, why in the world did I agree to BBQ for some engineers this weekend. Man oh man...
We had the BBQ

It ended up being a party with about 15 kids and a half dozen spouses ... Mother's Day. Sheesh. Anyway, all was not lost. There were two engineers and a irrigation pump specialist. One engineer is an environmental electrical engineer who designs heating/cooling systems for very large applications and the other mechanical... who designs CAD computer printing CNC things and programs them kind of geek. No rocket scientist. He's in TN.

We didn't get to fully test the different props and motors. Hopefully, next Saturday, without all the bipedal distractions.

What we did discuss for a while was the reliability of prediction programs like eCalc and Motocalc.

Paraphrasing: they all agreed the programs were probably fairly accurate and maybe even more accurate than a salesman constrained to sell what they have in stock, for example. Over time these programs tend to get more accurate as feedback and verification improve them which is why engineers the world over use them tohelp them.

While they may be some variance due to manufacturing tolerances, environmental differences, etc. which added together give a different predicted result than what you may find in the real world, you would want to verify things by testing.

They pretty much agreed if the programs gave a "safe" set of paremtersre: heat, watts, prop, batteries, etc. then it probably was fairly safe ...if not too close to the edge so to speak. They agreed, as long as a motor run is a short blast at max, and relatively infrequent, the heat issue may be not too problematic... as long as the motor isn't grossly over-propped or over-revved to the point the prop is stalled and inefficient or if the heat isn't grossly out of line.

Heat is not good for the electronics and all suggested creating air holes for airflow in the Raptor regardless.

I have a thermal scan gun from the fire department to use and a temp probe with the multi meter for inside the airless cowling. We plan to put all the stuff sold with it in it then take out the NiMH, for example, and use a smaller ESC seeing if the extra space makes much difference.

Hopefully, we can create a time/temp curve to see the effects of heat then cut some holes for airflow and see how effective the changes are. Hopefully... this week. This sounds like a midwinter project given the spring weather, so, we'll see.

I guess my question is, how hot is too hot? Components melting is a bad sign and the Hacker SB 55 melted the foam tape stuck to the opposite side of the heat sink. How hot can a LIPO get before problems? I think the motor can stand some extra heat before things fail.

Problem is, it is such a tight space for all the stuff sold with it and I'd hate to crash and start a fire, ... which I guess can happen, not to mention ruin stuff for no good reason. I sure am going to know before I commit to a much higher dollar plane and risk so much more. Anyway, thanks.
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Old May 12, 2014, 05:07 PM
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Cooling.

Here's a pic of the cooling scoops I added to my Specter. There were oval recesses, about 1/4" X 3/8" that I drilled out and then I made the scoops from the handle of a plastic spoon. I also added a 1/2" hole in the bottom of the fuse as an exit. I don't have a picture of it but I also drilled some 3/16" holes that match the ones in the front of the motor. There isn't much gap and I don't have a flow-through spinner but my guess is that it can still draw in a bit of air around the front bearing.

My quick and dirty temperature check, for a glider motor, is to run the motor flat out for 20 seconds, since I never use more than 15 seconds of power while flying, and give it the touch test. If I can't keep my finger on the motor for more than five seconds? I figure it's too hot and drop down a bit in prop size.

I have also found that my motors, inexpensive motors from Hobbyking, do need a couple minutes to break in. It's not as prolonged or critical as a glow engine that might need a gallon or two of fuel through it before it's broken in but both theory and experience suggest that it does take a bit of running to get the bearings spinning properly and remove any imperfections.

When I first tried my first HK 2834 I thought I had a lemon. With a 10X6 prop it actually smelled hot and singed the plywood within 5 seconds and drew far more current than I expected. So, in an effort to get some use out of it, I switched to a 9X5. It still got hotter than I liked but it seemed manageable. Well, after a few flights I tested a different battery and discovered that the current draw had dropped substantially. Now I run 11 inch slo-fly props and 11X6 inch folding props with no overheating on my three HK 2834s and all of them got really hot the first couple times I ran them. I found an ancient nylon 9X4 in my junk box and I use it for about the first two minutes of run time and that seems to provide sufficient break in.

While I don't have a Raptor; my Specter 1800 is its little brother and I can offer some insight into the flying portion. Feel free to ask when you run into questions. You are correct that the Raptor/Passer-X/Specter do demand a bit of flying skill but they are very capable general purpose sailplanes. If you are comfortable with even one plane they won't turn and bite you but the art of soaring might take a little more practice than with a Radian or other pure "floater". On the other hand; I have confidently flown my Specter in winds gusting up over 25 mph and a lot pf sailplanes are not as capable.

Cheers!
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