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Advice needed

Old 08-14-2014, 03:37 PM
  #1  
Lenl1540
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Default Advice needed

Hi all,
A bucket wish - since getting close to death you think about these more often - Something I would love to be able to do before crossing over to the other side, is to see my fathers plane fly. The story - a very long time ago my father kit built a 'U" control stunt plane. He spent a very long time doing the build but never completely finished it or flew it. It would have been his first plane. He has now passed and I have taken the time to remove all of the old 'Japanese Silk' (That was the covering of the day.). Recovered it with Monokote, made the wing removable (for R/C electric access.) Installed the control tray and rods for R/C (ailerons, rudder and elevator) and a new set of light wheels.
I thought that if I could get familiar enough with electrics (with a lot of help from others) I might be able to get it off the ground at least one time - for him.

I am now ready to get the electrics together for this build and need some advice on the motor, speed controller and battery. The specs on the plane is as follows:
Weight without electrics - motor - receiver - controller or battery = 413.7 gram or 413.7/30=23.79oz
Will have rudder,elevator, ESC, ailerons (3 servos)
Space for electrics as follows:
Front hatch - 2 1/4 x 3 1/4 x 2 1/4
Max wing thickness space under fuselage - 1 1/2 taper to 1/2
Wing length opening - 7 x 2
Fuselage compartments as follows:
Rear - 1 3/8 x1 1/8 x 2 3/4
Center - 4 1/2 x1 3/8 x7/8
Front - 2 x 2 x 1
Wing span - 48"


I could use any advice you could give about how to power this model.

Thanks for your help,
--Len
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Old 08-15-2014, 05:42 AM
  #2  
Bill G
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This sounds almost exactly like what I did with a Sterling Peashooter that dad built years ago as a rubber display model. I recovered it and converted it to r/c. Some years later after realizing that my initial experience with both converting and flying was insufficient, I made some changes to the "rebuild" and managed to get a surprisingly good flying model out of it. Both your model and the Peashooter are certainly challenging subjects for flight, but a good challenge is always rewarding.

What I try to do whenever possible, is to build to a good known spec. I would ad a liberal 12oz for motor/gear/battery to you AUW, and then find good known flying electric sport models as close in spec to your own, to use as a reference. It would also be a good idea to determine how much batt/motor weight is required to balance the model. After determining the weight of a practical motor for your spec, you could experiment to determine what size of battery would balance the model in the area of the battery compartment. It's always good to avoid dead ballast weight, whenever possible.
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Old 08-15-2014, 09:14 AM
  #3  
nuteman
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Great you're doing this for your dad.
The electronics/motor/prop won't be an issue. I've found that the Turnigy D2836/8, 1100 kV, running a 10 x 4.5 prop with plain-vanilla 30A ESC works great and has plenty of thrust for a plane like yours (40 oz thrust at least - so you'll likely have a thrust-to-weight ratio greater than 1).
Typical 9 gram, metal gear servos will be perfect for that plane.

The real question is your experience level - both build skill and flying skill.
It's not clear from your post where you are with both.
If your experience is limited, the following may be useful:
Getting all the electronics installed, balancing the airplane properly, adjusting control throws, etc. is obviously critical. You don't want a servo detaching or the engine detaching mid-flight
Perhaps even more important: That is not a "trainer" airplane. It's a low/mid wing, taildragger, with probably challenging handling characteristics.
If you're not too finicky about keeping the "stock" set-up, I recommend several things to maximize chances of success (you may need to look up terminology):
1. Convert to nose-wheel ("tricycle gear") plane - minimize chance of ground looping.
2. Add drooping leading edge cuffs to outboard third of each wing - minimize chance of wing-drop (or "tip stall").
3. Add very small canted winglets (improve roll stability or "self righting"), since it doesn't look like that plane has any appreciable dihedral.
4. Set up mechanical differential for ailerons. This is done by positioning servo arms appropriately - there's some stuff on youtube that shows how to do it. It is very obvious once you see it working and involves no fancy transmitter mixing. This prevents adverse yaw. Make sure you haven't done it in reverse. You want the upward displaced aileron to displace more than the downward displaced aileron.

Last edited by nuteman; 08-15-2014 at 12:00 PM.
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Old 08-15-2014, 01:50 PM
  #4  
WingmanArt
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Default Electric Power Options

Hi Len,

If you could provide me with total wing area, max diameter of propeller that would fit (allow for ground clearance - in level flight/ground roll) and exact empty weight I can run the iphone rc-wingman application to give you a number of options for a workable electric system. If you also know the max size of lipo battery that would fit I would be able to narrow down the options for you, if not thats ok, you will just need to decide which option for battery size you would like best.

Oh one more thing, the style of flying you would like to do would be useful as well as the style will help with options would be:

1. Park/Slow
2. Trainer/Slow
3. Sport/Fast
4. Advance
5. Light 3D
6. Unlimited 3D
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Old 08-15-2014, 06:16 PM
  #5  
Lenl1540
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Default Bringing a U Control to R/C flight

Hi All,

Thank you for your replies. Now let me answer the questions asked:
- I have been flying on and off since 1965 but have been away from it for the past 24 years and now am getting back into it because of the major advances in electrics and I am now retired and have more time.
- For right now I will stick to the trainer level to build up the reflexes again.
- My fathers plane is definitely for a most advanced flyer - I will get it ready for flight but wait until I am 'back in the saddle' as they say.
- His plane must be flown fast at all times and I understand what I must accomplish before I am ready to fly it.
_ The empty weight is 23.79 oz.
-The Max prop size that would still give clearance is 12".
-The wing area is 10"x47" = 470 sq in or 3.264 cu ft.
- The area for the Lipo - I would need to make modifications if necessary.
- I am familiar with obtaining the CG, control surface throws, types of hardware to use for major stress points and etc.
- I have scratch built 10 various types of R/C planes
- I have designed two Gliders - one powered electric - one non-powered
- All completed planes flew well - two gas and three old time electric.
- I am now in the process of converting all of the planes to new generation electrics so there is a some of a learning curve for me, as to what's available etc.
-I have a finished, 39" AT-6 TEXAN which will need to be electrified - It is like new and has never flown or had any engine, servos, gas tank etc. mounted so it is clean.
- I just replaced an electric engine in a scratch built 40" low wing, open cockpit beauty - the motor I replaced was a brushed Astro Flight .075 that weighed 121 grams and used a 7.2v battery that weighed 205 grams, including a heavy Cirrus Receiver. It was all replaced with an 18a Brushless ESC,480/500 Brushless Outrunner motor, Turnigy 1000mAH Lipo pack, and a very small, light 6 channel receiver. The replacement parts weighed nothing compared to the old ones. SOOOOOOOOO, as was said, balancing this bird was a challenge. Lead needed to be added no matter where I placed the parts in the fuselage. She is a tail dragger so the addition of a tail wheel was needed to improve ground handling.

- I also have a Piper Cub CJ-3 - 60" span, built for electrics and has been flown with old electrics. I will be converting to brushless with the addition of an ESC and Lipo power. It flies to scale and should be a very relaxing flyer wen I'm finished. I had thought about putting floats on it but decided that I could not water proof it enough and since its 32 years old, I don't want to loose it to an inevitable hard water landing.

_ I have just finished a foam, twin engine, PBY and will be testing/flying it this week end. It is a very large plane, but again, with the new electrics, will fly on a single 11.1 v 2200 mAh Lip battery, and is very light.

I believe I have cover the majority of my background, except to say that my first plane was a .049 Cox "U" control model. Now you can guess how old I am from that. If you remember them, you right in there with me.

Thank you again for all of your help,

--Len
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Old 08-15-2014, 11:14 PM
  #6  
mclarkson
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I don't have much advice to offer - that plane is largely beyond my area of expertise - but I do want to wish you the best of luck with the project. I missed the chance at something similar and have been kicking myself ever since.
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Old 08-16-2014, 03:42 AM
  #7  
fhhuber
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I would look for an electric motor that would turn the same prop as used when it was glow C/L about the same RPM or a bit more.

As an RC plane it will be a little heavier than CL, but you have less drag because you aren't towing the control lines.
Long ago I converted a Top Flite Combat Streak to RC (Ailerons, Elevator, Throttle) and while the plane was supposed to be rated for .19 to .35 for C/L. For RC it had more than enough power with an old Enya .15. Strapped on some landing gear (the Combat Streak was a hand launch) and it flew just fine.
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Old 08-16-2014, 04:27 AM
  #8  
kyleservicetech
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Originally Posted by fhhuber View Post
I would look for an electric motor that would turn the same prop as used when it was glow C/L about the same RPM or a bit more.

As an RC plane it will be a little heavier than CL, but you have less drag because you aren't towing the control lines.
Long ago I converted a Top Flite Combat Streak to RC (Ailerons, Elevator, Throttle) and while the plane was supposed to be rated for .19 to .35 for C/L. For RC it had more than enough power with an old Enya .15. Strapped on some landing gear (the Combat Streak was a hand launch) and it flew just fine.
Brings back memories of a glow powered model I had in the 1960's with one of those Enya 15 engines up front. That engine ran great, but it was a real to start. Finally made an electric starter for it, using a motor from work that did the job.

That model had the only crash I ever had where the model was a total loss, but didn't have a mark on it. This was back in the 27 Mhz radio days, with a galloping ghost servo (Don't ask) The model got hit with CB interference, and went by by. This was after we had a lot of rain in the area. Some farmer kids found it. That model hit the side of a very wet farmers manure pile, and was full of ****!
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Old 08-16-2014, 04:40 AM
  #9  
kyleservicetech
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Originally Posted by Lenl1540 View Post
Hi All,

Thank you for your replies. Now let me answer the questions asked:
- I have been flying on and off since 1965 but have been away from it for the past 24 years and now am getting back into it because of the major advances in electrics and I am now retired and have more time.
- For right now I will stick to the trainer level to build up the reflexes again.
- My fathers plane is definitely for a most advanced flyer - I will get it ready for flight but wait until I am 'back in the saddle' as they say.
- His plane must be flown fast at all times and I understand what I must accomplish before I am ready to fly it.
_ The empty weight is 23.79 oz.
-The Max prop size that would still give clearance is 12".
-The wing area is 10"x47" = 470 sq in or 3.264 cu ft.
- The area for the Lipo - I would need to make modifications if necessary.
- I am familiar with obtaining the CG, control surface throws, types of hardware to use for major stress points and etc.
- I have scratch built 10 various types of R/C planes
- I have designed two Gliders - one powered electric - one non-powered
- All completed planes flew well - two gas and three old time electric.
- I am now in the process of converting all of the planes to new generation electrics so there is a some of a learning curve for me, as to what's available etc.
-I have a finished, 39" AT-6 TEXAN which will need to be electrified - It is like new and has never flown or had any engine, servos, gas tank etc. mounted so it is clean.
- I just replaced an electric engine in a scratch built 40" low wing, open cockpit beauty - the motor I replaced was a brushed Astro Flight .075 that weighed 121 grams and used a 7.2v battery that weighed 205 grams, including a heavy Cirrus Receiver. It was all replaced with an 18a Brushless ESC,480/500 Brushless Outrunner motor, Turnigy 1000mAH Lipo pack, and a very small, light 6 channel receiver. The replacement parts weighed nothing compared to the old ones. SOOOOOOOOO, as was said, balancing this bird was a challenge. Lead needed to be added no matter where I placed the parts in the fuselage. She is a tail dragger so the addition of a tail wheel was needed to improve ground handling.

- I also have a Piper Cub CJ-3 - 60" span, built for electrics and has been flown with old electrics. I will be converting to brushless with the addition of an ESC and Lipo power. It flies to scale and should be a very relaxing flyer wen I'm finished. I had thought about putting floats on it but decided that I could not water proof it enough and since its 32 years old, I don't want to loose it to an inevitable hard water landing.

_ I have just finished a foam, twin engine, PBY and will be testing/flying it this week end. It is a very large plane, but again, with the new electrics, will fly on a single 11.1 v 2200 mAh Lip battery, and is very light.

I believe I have cover the majority of my background, except to say that my first plane was a .049 Cox "U" control model. Now you can guess how old I am from that. If you remember them, you right in there with me.

Thank you again for all of your help,

--Len
Your empty weight is about 1 1/2 pounds. If you assume the model will weigh in at about double that, or 3 pounds ready to fly, that would call for a power system of around 200-400 Watts up front, using 75 to perhaps 130 watts per pound of airplane. For real wild (Read NOT TRAINER!), run that up to 150 watts per pound, or around 450 Watts.

Running perhaps 300 Watts, while pulling 30 Amps max, that would require a battery pack of 300 / 30 or about 10 Volts. This puts your battery pack in the 3S size.

You may have run across the "C" term in this electric power stuff. Here is a bit of information on it.
"C" and what it is
http://www.wattflyer.com/forums/showthread.php?t=65869

There are a number of good computer programs to help you out in the selection of your power system. The one I use is www.motocalc.com, free for 30 days, then $39. Just enter in your electric motor, battery pack, prop size, wing span, wing area, weight without motor/esc/battery, and check the programs "Opinion" function.
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Old 08-16-2014, 01:24 PM
  #10  
Lenl1540
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Default Thank you

Thanks all for the input

--Len
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Old 08-16-2014, 01:24 PM
  #11  
WingmanArt
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Default RC Wingman Results

Hi Len,

I ran the information through the iPhone App RC Wingman and decided to use a 3 cell lipo as a battery size. I can use others if you like. The minimum results were:

FlightStyle BurstAmps MAH Watts
PropD PropP KV "C" Rating Thrust/Weight Ration
Park/Slow 11 5 7 585 13 700 80 0.7
Park/Slow 10 3 8 818 15 700 90 0.76
Park/Slow 12 6 8 505 15 700 88 0.78
Park/Slow 11 4 9 669 14 800 96 0.82
Park/Slow 12 5 9 566 15 800 103 0.89
Park/Slow 10 2 10 992 14 900 107 0.91
Trainer/Slow 11 3 10 781 15 900 115 0.97
Trainer/Slow 12 4 11 644 14 1000 121 1.03
Trainer/Slow 11 2 12 938 15 1000 133 1.14
Trainer/Slow 12 3 13 747 15 1100 142 1.2
Sport/Fast 12 2 14 890 14 1300 160 1.39

Sorry about how squashed up the results are. I also used a 5 minute min flight time. The way to read this using the first line of results is:
1. The style of flying is Park/Slow
2. The propeller Diameter is 11" with a Pitch of 5"
3. Min motor Burst Amps should be around 7amps
4. Min KV to be considered for these results should be 585
5. Lipo Battery 3 cell with a "C" rating of 13 with a min mah of 700
6. Motor Watts should be a min of 80
7. Power System will provide a thrust to weight ration of .7

Now bare in mind the results are minimum recommendations base on the information provided. Now you can compare the results against available manufacture power systems and choose one that comes the closest to what you would like. For a speed controller; and only as a suggestion, you would want to consider something that is at min 15% to 20% greater than the motors max burst rate. There are a number of views on how big you need to go with the speed controller but generally speaking; and in my view, I always like to have something that has a greater bust capacity then my motors burst capacity and I personally use 20% greater rating than the motors.

If you send me your email address I can send the spreadsheet that the app created to you directly.

I hope this helps

Art
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Old 08-16-2014, 08:26 PM
  #12  
solentlife
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Interesting ...

OK - here's my take on it for what it's worth.

Span 48" and all up weight without gear at 413gr.

Assume a flying weight more like 700gr.

Looking at photos - it's a stunt machine ... no floater or trainer. So needs to be FLOWN. That means it needs to be well powered and no marginal stuff. It's straight wing ... so no inherent stability ... and LOW wing to boot. Straight plus low often means hairy.

We have Denny with his up to 200W ... and Wingman with his 80W.

Sorry Wingman - 80W in my book would be too low and definitely with a 11x5 prop - I'd expect her to be torque roll happy. She'd be grossly underpowered and hard to keep airborne.

Me ? I'd be looking at 180W ... 200W ... a reasonable prop of 9" with decent pitch ... so to keep torque roll down - but thrust up. Especially if we stay with 3S ... so a 1000Kv or more on a 9x6 but of course that means a decent sized LiPo and not less than 20C ...

There's a good maxim : You can always throttle back, but you can't do more than full throttle ..... meaning over power is flyable, underpowered is not.

My 2c's worth anyway.

Nigel
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Old 08-16-2014, 09:58 PM
  #13  
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Interesting ...

OK - here's my take on it for what it's worth.

Span 48" and all up weight without gear at 413gr.

Assume a flying weight more like 700gr.

Looking at photos - it's a stunt machine ... no floater or trainer. So needs to be FLOWN. That means it needs to be well powered and no marginal stuff. It's straight wing ... so no inherent stability ... and LOW wing to boot. Straight plus low often means hairy.

We have Denny with his up to 200W ... and Wingman with his 80W.

Sorry Wingman - 80W in my book would be too low and definitely with a 11x5 prop - I'd expect her to be torque roll happy. She'd be grossly underpowered and hard to keep airborne.

Me ? I'd be looking at 180W ... 200W ... a reasonable prop of 9" with decent pitch ... so to keep torque roll down - but thrust up. Especially if we stay with 3S ... so a 1000Kv or more on a 9x6 but of course that means a decent sized LiPo and not less than 20C ...

There's a good maxim : You can always throttle back, but you can't do more than full throttle ..... meaning over power is flyable, underpowered is not.

My 2c's worth anyway.

Nigel
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Old 08-17-2014, 04:12 PM
  #14  
Lenl1540
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Default Stunt Plane

You are absolutely right Nigel, this is definitely a stunt pane. I will have to wait until I have more flight hours under my wings before I attempt it, but I would like to have it ready to go beforehand (as incentive to get more 'Stick Time') whether it's nice, cold, rainy or snow .

I don't know about you, but as I grow older and more physical problems set in, I find my enthusiasm starting to wane, especially as the wounds from fighting the war in Viet Nam become more evident every day (not complaining - just a fact.)

I have many Planes in the hangar that I have already built and just now converting each to modern electric. It's a wonderful change. I have a small school yard trainer (high wing, converted to electric) that I built from scrap many years ago that fly's well and I am able to get stick time on it because I can fly it almost any ware.

I'll get there if I have enough time left. Thanks for your input,
--Len
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Old 08-17-2014, 09:39 PM
  #15  
WingmanArt
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All,

Sorry away for my daughters wedding.

I think there is a miss understanding, the spreadsheet I offered up suggests anything from 80 Watts to 160 Watts depending on flight style and are only starting points for consideration.

Also, the propeller performance with each option provides a Thrust to Weight ratio that ground static tests have proven to be fairly accurate - using several types of models.

The mathematical formulas that generates the results have been proven successfully on several of my own models as well as others.

An other consideration is putting to much power resulting in gyroscopic precision challenges. In other words: at what prop size (rotational inertia) do you start to get coupled pitch/yaw effects, or torque roll, that are significant enough to impact the control of the model.


My overall recommendation is to firstly try something within the Trainer/Slow flyer of 100 to 150 watt range and conduct a static ground test with recommended propellers. The best way to do this is to put a scale (I use a electronic fish scale) tie it to the tail end and run the motor at 50% throttle than 100% to see how much thrust your getting. If the thrust is better that 75% to 80% of the total weight of your model I would suggest you may be in a pretty good spot to do some field testing.

As a final note / food for thought, is that the Weight, Wing Area and overall propeller size are critical starting points for establishing a proper power system. The solution will naturally vary depending on the style of flying a person chooses to do with their model. As we all know, A particular propeller Diameter and Pitch will have a dramatic impact on performance - Speed and Thrust. The challenge we all face is Density Altitude, Wing Design, Ideal Propeller Diameter and Pitch combinations etc and picking setup for one day may not always be ideal on another.

Overall thought and in my humble opinion, a good static ground test is the best place to start once you have selected your power system. I would even be happy to run the application against a specific motor if you like to give you a better idea for which prop may be best.

I would be happy to extend this offer to others on this thread as well, as a bit of a test if anyone is interested. Also, it may also help me be able to provide better application results for my fellow enthusiasts.

I hope this helps

Cheers!

Art
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Old 08-18-2014, 11:17 AM
  #16  
nuteman
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Another thing that affects the decision of minimal acceptable thrust:
Will you be hand launching?
Where I fly at most of the time, that is the only option.
For hand launching, the minimal thrust-to-weight ratio can vary hugely based on the wing loading and stall speed. You can have a mid-size model plane (say 40 to 50 inches) with really low wing loading and get away with a thrust-to-weight ratio less than 1.
For somewhat high wing loading or high stall speed, a higher than 1 thrust-to-weight ratio is likely needed.

Acceptable wing loading for a particular plane is another hugely important factor for takeoff (whether it be off a runway or hand launching) and for reasonable stall speed. And it changes dramatically with scale.
As you go down in size, the build precision challenges become greater (another frequently overlooked issue: unfavorable Reynolds number at lower scale leads to stalling more readily).

Examples of "typical" wing loading:
Full scale Boeing 747: 136 lbs per square foot
Full scale Pitts Special:16 lbs per square foot
Full scale Super Cub:11 lbs per square foot
101" span P-51 model: 2.3 lbs per square foot

This is overwhelmingly a function of airspeed (if all the planes are flying in the same fluid/air), since lift is proportional to the square of airspeed (Lift = (1/2) density * airspeed^2 * Wing Area * Coefficient of lift). So for a plane that lands at 60 MPH (a typical full scale light plane), you've got 60 squared = 3600, while for a model sized plane landing at say 12 MPH, you've got 12 squared = 144 (MUCH less). For a 747 landing at 120 MPH, you've got 120 squared = 14400 (MUCH more).
So it's not surprising that acceptable wing loading drastically changes for the planes mentioned.
Now, it's obviously also affected by wing area, but not nearly as much as the affect of airspeed.
The outcome: If you want your plane to land at a relatively sedate airspeed (and keep potential damage low), keep that weight (lowering wing loading as well) nice and low. Despite the oft-repeated "build to to fly, not to crash" - we all crash these birds from time to time. Low kinetic energy on impact is definitely advantageous. This is besides the other benefits, such as reduced thrust and battery use, increased glide ratio, etc. So building light satisfies both "build to fly" and "build to crash" as far as I can tell.
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Old 08-18-2014, 01:15 PM
  #17  
Lenl1540
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I will follow your suggestions.

--Len
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