Most efficient setup

[Aussie_G]

I am wondering if anyone knows of the most efficient setup for my 450, I mean the best motor/esc combo to get the best run-times from my 2200's

Im currently running a 430XL 3700 & Hobbywing 30A esc, with a 3A BEC.

I figure the switching BEC is better on my machine for heat & reliability of my reciever & servo's. - Although the extra wires are a little bit of a pain.

I wonder if I should switch out from digital servo's on the cyclic to analog's

[MiniBichus]

Wassup...
I can fly mine for almost 20 minutes with this setup out of my Thunderpower 2200 Extreme V2 packs. I can probably push it a little further but I haven't tried yet. I have an RCT-450 Skyshark, very similar in most areas to a TREX450se v1

Here is the setup of the MB - 3 (RCT-450 Skyshark)

-B.B. Ceramic bearings all around.
-Scorpion HK-2213-16, weights 54 grams, very light and powerful.
-Kontronik Jazz 40 ESC (lightened)
-Spartan DS760 lightweight gyro
-Logictech 3100G lightweight servo. (The 9257 is on the shelf now! )
-Titanium screws in certain areas like rotor head.
-Plastic tail rotor (replaced the CNC tail linkage/grips, not the tail rotor boom CNC cage)
-Carbon fiber tail boom.
-Carbon fiber tail blades.
-Ditched most of the blingy-bling alloy parts from non-critical areas of the helicopter.

I am probably forgetting something somewhere, but that configuration gives me plenty time for practicing precision flight and coordinated moves. Not a cheap setup but you get your money's worth in long flight times with less batteries.

Hope this helps.

G.

[jgatorman2266]

Minibichus you say that your getting 20 minutes on a pack? Just curious for that is unheard of. How many mah are you putting back on the pack? PS Has anyone else ever got 20 minutes on a 11.1v 3s 2200mah pack?

[MiniBichus]

Yo,
yes, althought its not quite 20 minutes, it is 19:38 seconds to be exact. I don't have a charger that shows me the input mAh anymore (my ICE took a burn) but the cutoff on the ESC is set at 3.0V and it kicks in when I land it.

I get kicked out (friendly way) regularly by the other guys at the airfield when I hit the 15 minute flight time... I can usually keep my 450 longer in the air than most of the nitros around here. At the airfield I get only 16 minutes b/c I fly higher headspeed to take advantage of the great wide outdoors. :)

The secret to this is the Jazz ESC and the lowheadspeed. Heli flies awesome for slow backyard, where I don't need headspeed. Allows me to work my orientations and to be very precise with my inputs to do the little tracks perfect.

Cheers.

MB.

[ZephanRC]

MiniBichius,
That seems like awfully long flight times to me as well. Not sure it's a good idea to fly until the 3V cutoff, that could be a bit rough on your packs. How many cycles are you getting out of your packs? When you say "low headspeeds", what kind of headspeed are you running?

[Skarn]

I'd have to see that one to believe it! I've personally NEVER seen anyone go more than about 12 minutes...and that's with an 11 tooth pinion, 2200mah 25c battery and basic flying only.

I'd be willing to pitch in $20 to actually see some type of proof of a 19 plus minute TREX 450 flight with a 3 cell lipo battery. Anyone else willing to pitch in to see it? LOL!

Skarn

[jmmccain]

The power requirement is (roughly) proportional to the cube of the head speed. I'm guessing MiniBichus is running at approximately 60% of the design head speed. Why?

0.6 * 0.6 * 0.6 = 0.216 ~ 22% power required (25% (or 1/4) power = 4x run time)

At 60% of the design headspeed the (rough) power requirement is less than 25% of the design power requirement. Pitch must be increased due to the lower headspeed and this will increase the power requirement. However, the increase in power required for the increase in pitch is approximately linear as opposed to the cubic function related to headspeed. Also, the motor likely won't be as efficient at the reduced speed, but this is another relatively small effect.

For others, note that such a drastic reduction in headspeed as described here will kill other aspects of flight performance. Don't expect to do much more than hover and minimal "forward" flight. Escaping ground effect may not even be possible...

So, MiniBichus, what percentage of the design headspeed are you running? Just wondering how close my guess is. Reducing the weight helps, but not that much.

Skarn, try setting your throttle curve to peak at 60% (or as low as you can and still maintain a comfortable hover). You should immediately see significantly extended run times.

[HFG]

Why on earth would you buy top of the line electronics than run a SUPER slow HS to get 20min of flight ?!?!?!??!?

P.S. Skarn the record for a 450 flight is 45min ....... but that was heli slope soaring.

[jmmccain]

Skarn, I'll pitch in $0.02 (and whatever the cost was to charge the battery :P )

I obtained 18 minutes with (sorry, not a TREX):
Blade 400 (stock drivetrain, E-Flight 2100mAh)
~30% throttle (0, 25, 27.5, 30, 32.5)

It would just hover (mostly in ground effect) at these throttle settings. The motor was loaded pretty well by the high pitch that was required. Also, the tail was a little loose. 40% provided some performance and ~16 minutes.

Most efficient setup (by effectiveness and ease of application):
1. Lowest head speed that yields satisfactory flight performance
...lower throttle settings
...gear ratio (pinion with fewer teeth)
...lower kV motor
2. Lightest weight achievable
...similar component selection prioritized by weight
...other components go on a diet (start drilling holes in things :lol: )
3. Longer blades
...combined with further reduced head speed, otherwise efficiency suffers
...unless a significant change is made (>10%), probably not worth the effort

For my test flight, if the battery was 90% depleted:

flight time = 18 minutes * 60 seconds/minute = 1080 seconds
battery energy, total = 2.1 Amp hours * 11.1 Volts = 23.31 Watt hours
battery energy, used = 0.90 * 23.31 Watt hours * 3600 seconds/hour ~ 75500 Watt seconds
battery power = 75500 Watt seconds / 1080 seconds ~ 70 Watts
battery current = 70 Watts / 11.1 Volts ~ 6.3 Amps

[Skarn]

Thanks for the details JM.

Ok, so while I see it IS possible, as others have pointed out....why??? I guess if you simply wanted to literally hover in place for 18+ minutes.....hey go for it!

Skarn

[daijoubu]

You only have 2 batteries and a charger that can only do 2C...
You want to perfect hovering in all orientations and want to maximize practice time...
You have a small space and are happy with something in the air...

You only have an old 5C pack and don't want to kill it doing mad 3Dz.

[jmmccain]

Exactly. After all, this is the newbie forum and orientation practice time is a good thing! The only item I might add to daijoubu's list:

With low throttle settings, a heli becomes less sensitive to changes at the stick. At high and low head speeds, the same change in pitch creates significantly different amounts of thrust. This may make it easier to hover, since the heli doesn't just zoom off into the blue or slam into the ground with a change in throttle. Cyclic response decreases as well.

There are two major drawbacks. First, the tail doesn't have as much authority (especially in one direction). Second, if the winds are strong, there isn't much response available to recover from gusts.

[MiniBichus]

Skarn,
I can do way more than just hover, I can do all sorts of FF manuevers, even pracice constant piro orientation while doing little circuits, can do stall turns and all that for 19 minutes, but if you want to run your space heater for 8 1/2 then go for it!

Don't expect tic-tocs out of this low headspeed but for practicing 1-2 hours a day, you can't beat it.

I finally got my first prolite 4S pack and I get 3 1/2 minutes longer flight times. Since the weather has being really sucky here in Florida lately I haven't had the chance to test the thing with FF and more than just a hover indoors. I plan on shattering the 20 minute barrier this weekend with single cell. 42

I got the expensive electronics so I can do anything I want with it, and now with the 4S power I can flick a switch and get it up to 3000+ RPM headspeed while keeping the capabiliites to do super low headspeed for 20+ minute flight times for practicing.
As for tail authority, I haven't noticed any decrease in tail authority, granted I am running a DS760 Spartan so that might be helping it, but the heli tail feels about the same as it feels with higher headpseed.

Yes, I did put my Skyshark on a diet as well, replacing a lot of bling-bling with plastic or composite for non critical parts of the helicopter.

The specs of my helicopter are on my signature.

BTW, heli lost 1 1/2 minutes of flight time average when I tried 335 blades vs. the conventional 325 blades. I am going down to a 10 tooth pinion to make up for the longer blades so I can run even lower headspeeds with the longer blades...

crazy..

MB.

[MiniBichus]

This is not completely true I think. Its called Expo and Swash Mix. With those two parameters you can get the heli pretty responsive at lower headspeeds too, that is, with high negative exponential and a higher swash mix it is like higher headspeed. Same appies for high headspeeds, positive expo and reduced D/R... For me the lower headspeed is to increase flight times.

However, I see no point in trying to learn fast when someone can't even go slow. For comparison, you don't start practicing scales on the guitar at 160 BPM, and if you do, then chances are that you'll never be as clean on your notes as someone who played the scales slowly from the beginning to get it just right. Additionally, crashes at this low headspeed are only a bent feathering spindle and sometimes, rarely, a bent main shaft.

But hey, everybody learns their own way.

Exactly. After all, this is the newbie forum and orientation practice time is a good thing! The only item I might add to daijoubu's list:

With low throttle settings, a heli becomes less sensitive to changes at the stick. At high and low head speeds, the same change in pitch creates significantly different amounts of thrust. This may make it easier to hover, since the heli doesn't just zoom off into the blue or slam into the ground with a change in throttle. Cyclic response decreases as well.

There are two major drawbacks. First, the tail doesn't have as much authority (especially in one direction). Second, if the winds are strong, there isn't much response available to recover from gusts.

[MiniBichus]

Thanks for the details JM.

Ok, so while I see it IS possible, as others have pointed out....why??? I guess if you simply wanted to literally hover in place for 18+ minutes.....hey go for it!

Skarn

Hovering is probably one of the hardest thing for the battery/motor, and a hover only flight reduces the flight time by a considerable amount. Hovering for 18 minutes straight is only possible now with the 4S on my current configuration (with 335 blades, 11T ), but when you start doing lots of FF, flight time increases rapidly. My 19:36 minute average flight times were recorded with a good deal of FF on them. I do more than just hover man but if you want to tell that to yourself, then go for it!

MB.

[MiniBichus]

Hovering in ground effect will increase flight times by a lot, but it has no useful purpose to do it besides for the heck of it. The flight times I am talking about on my posts are useable flight times, far above ground effects and include plenty of FF.

What ESC are you running? A Jazz? I can't think of any other ESC that will allow you to run a 35% throttle/governor without melting the motor/battery/ESC.

MB.

Skarn, I'll pitch in $0.02 (and whatever the cost was to charge the battery :P )
.
.
.

It would just hover (mostly in ground effect) at these throttle settings. The motor was loaded pretty well by the high pitch that was required. Also, the tail was a little loose. 40% provided some performance and ~16 minutes.
.
.
.
.

[HFG]

I get 4:30 min on my setup, no wussy flying for the capi :)

[MiniBichus]

I get 4:30 min on my setup, no wussy flying for the capi :)

I get about 10 minutes with the 4S @ 3000 RPM headspeed, no wussy flight times for me neither.

Cheers.

MB.

[HFG]

Even with 4S 10min is still gunna be wussy :)

[jmmccain]

Hovering in ground effect will increase flight times by a lot, but it has no useful purpose to do it besides for the heck of it. The flight times I am talking about on my posts are useable flight times, far above ground effects and include plenty of FF.

What ESC are you running? A Jazz? I can't think of any other ESC that will allow you to run a 35% throttle/governor without melting the motor/battery/ESC.

MB.

I was just testing how low I could go on the throttle and stay in the air. I started at 60%, went to 40%, then 30%. That was with a totally stock Blade 400 powertrain except for the E-Flite 2100mAh batteries vs. 1800 stock. The motor was a little warm. The battery was no warmer than it usually is. I didn't put a finger on the ESC, but I can do it again and find out if you like.

At 40% throttle the available lift was probably sufficient to let me fly around and still get 16 minute or longer flights. I suspect I'd feel more comfortable at 50% - in case trouble found me unaware and with dumb thumbs.

It was dark when I made those three flights. I was out on the carport under a house light, so I couldn't actually do any real flying. I was just trying to see how long I could keep it in the air in order to confirm, for myself and those expressing doubt, that a 20 minute flight is within the realm of possibility. I knew that it would be, but since I'm still learning I decided to just go out and see what my heli would do! As stated... for the heck of it.

:cheers

[MiniBichus]

Even with 4S 10min is still gunna be wussy :)

are you a wuss?

:lolol

[MiniBichus]

Hey man,
Wasn't meant the wrong way or anything, I was just curious. 18 minutes is pretty damn good... specially for a non Jazz ESC AFAIK. The three ESCs I had previously all thermaled after 5 or 6 minutes of hovering at anything under 60%. I think long flight times are a great way to learn, specially when you don't need the punch to do 3D and want to concetrate on correct coordination of the sticks.
I agree, but if you start doing long runs in FF your 18 minute flight times will be longer. Probably 2 or 3 minutes longer from my experience.

Cheers.

MB.

I was just testing how low I could go on the throttle and stay in the air. I started at 60%, went to 40%, then 30%. That was with a totally stock Blade 400 powertrain except for the E-Flite 2100mAh batteries vs. 1800 stock. The motor was a little warm. The battery was no warmer than it usually is. I didn't put a finger on the ESC, but I can do it again and find out if you like.

At 40% throttle the available lift was probably sufficient to let me fly around and still get 16 minute or longer flights. I suspect I'd feel more comfortable at 50% - in case trouble found me unaware and with dumb thumbs.

It was dark when I made those three flights. I was out on the carport under a house light, so I couldn't actually do any real flying. I was just trying to see how long I could keep it in the air in order to confirm, for myself and those expressing doubt, that a 20 minute flight is within the realm of possibility. I knew that it would be, but since I'm still learning I decided to just go out and see what my heli would do! As stated... for the heck of it.

:cheers

[jmmccain]

BTW, heli lost 1 1/2 minutes of flight time average when I tried 335 blades vs. the conventional 325 blades. I am going down to a 10 tooth pinion to make up for the longer blades so I can run even lower headspeeds with the longer blades...

EDIT *** This post is wrong!. Just wrong! Try the one further below... ***

Here's an equation I've developed that might help choose an appropriate head speed to go with those longer blades. This is for a single rotor blade, but it will work fine for determining the effects of changes:

P = ( π^2 Θ^3 Cd ρ A / 432000 ) ( R^4 - r^4 )

P = power, (Watts)
π = 3.14159
Θ = head speed (revolutions per minute)
Cd = drag coefficient (unitless)
ρ = air density (kilograms per cubic meter, 1.2 - 1.1 is a good range)
A = area of rotor blade (square meters; length times chord)
R = rotor blade outside (tip) radius (meters)
r = rotor blade inside radius (meters)

Since r^4 will typically be a very small value, it may be neglected. This yields:

P = π^2 Θ^3 Cd ρ A R^4 / 432000

Don't try to use this with drag coefficients that one might think are correct values. Doing so will yield results that are off by an order of magnitude or two. Just use a value of 1 for the drag coefficient. Now, plug in numbers for the original blades and head speed to get a reference number for power. Then, change the radius and area to see what change in head speed is required to get back to the reference number.

For this particular change in blades (325 to 335 and assuming the same chord):

.35^4 = .0150 (listed stock rotor diameter of 0.700 meters)
.36^4 = .0168 (new rotor diameter of 0.720 meters)

The change in the power requirement (at the same head speed and angle of attack) is:

0.0168 / 0.0150 = 1.1193 (or an increase of ~12%)

From 3000 rpm, to get back to the same power requirement:

3000^3 = 27,000,000,000
0.88 * 27,000,000,000 = 23,760,000,000 (0.88 is 88%, or a 12% decrease)
23,760,000,000^1/3 ~ 2875 (suggests a decrease of ~125 rpm)

Edit: I forgot to include the change in area, but it's small, and the effect is linear (not to the third or fourth power).

This method completely ignores changes in angle of attack and efficiency that take place. With longer blades at the same rpm, a lower angle of attack is needed to perform equivalent maneuvers. When the head speed is reduced, the angle of attack has to go back up. These changes in angle of atttack are not identical and will skew the results a little. In this example, the change was small, so the results should be quite good.

Also, the change in efficiency in this example will be less than 1% (the change in blade length was only 3%). Finding the exact change in rpm needed to take proper advantage of this increase in efficiency is tedious to say the least. However, it will be in the vicinity of the rpm suggested above.

Ah well, work is slow, this post is getting long, and I've put the flybar back on my Blade. I'm going to go fly. Enjoy!

P.S. MiniBichus, if you already know these relationships, feel free to slap me. My mom lives in Orlando, so you might get a chance! :lol:

P.P.S. This equation was developed from the one often seen for fixed wing drag. Applying the knowledge that the air velocity varies over the radius and integrating led to this (admittedly, rather simplistic) result. If anyone is curious, I'll happily post the derivation.

[MiniBichus]

LOL... man that is most impressive. I have an AE degree but I ended up programming computers in every possible field but none related to anything I've studied for AE... so my aerodynamics knowledge is nothing but a bunch of forgotten memories... so you can be assured I won't be slapping you any time soon! heh.. haha... LOL.

I should be getting the 10 tooth hardened steel pinion today and I am hoping that I can break the 20 minute barrier in a hover (or at least get in the very high 19s)

I reverted back to the 325 all CF blades since I like to maximize my practice times but I'll try the 335 blades with the new 10T pinion as well.

Thanks!


MB.


Here's an equation I've developed that might help choose an appropriate head speed to go with those longer blades. This is for a single rotor blade, but it will work fine for determining the effects of changes:

P = ( π^2 Θ^3 Cd ρ A / 432000 ) ( R^4 - r^4 )

P = power, (Watts)
π = 3.14159
Θ = head speed (revolutions per minute)
Cd = drag coefficient (unitless)
ρ = air density (kilograms per cubic meter, 1.2 - 1.1 is a good range)
A = area of rotor blade (square meters; length times chord)
R = rotor blade outside (tip) radius (meters)
r = rotor blade inside radius (meters)

Since r^4 will typically be a very small value, it may be neglected. This yields:

P = π^2 Θ^3 Cd ρ A R^4 / 432000

Don't try to use this with drag coefficients that one might think are correct values. Doing so will yield results that are off by an order of magnitude or two. Just use a value of 1 for the drag coefficient. Now, plug in numbers for the original blades and head speed to get a reference number for power. Then, change the radius and area to see what change in head speed is required to get back to the reference number.

For this particular change in blades (325 to 335 and assuming the same chord):

.35^4 = .0150 (listed stock rotor diameter of 0.700 meters)
.36^4 = .0168 (new rotor diameter of 0.720 meters)

The change in the power requirement (at the same head speed and angle of attack) is:

0.0168 / 0.0150 = 1.1193 (or an increase of ~12%)

From 3000 rpm, to get back to the same power requirement:

3000^3 = 27,000,000,000
0.88 * 27,000,000,000 = 23,760,000,000 (0.88 is 88%, or a 12% decrease)
23,760,000,000^1/3 ~ 2875 (suggests a decrease of ~125 rpm)

Edit: I forgot to include the change in area, but it's small, and the effect is linear (not to the third or fourth power).

This method completely ignores changes in angle of attack and efficiency that take place. With longer blades at the same rpm, a lower angle of attack is needed to perform equivalent maneuvers. When the head speed is reduced, the angle of attack has to go back up. These changes in angle of atttack are not identical and will skew the results a little. In this example, the change was small, so the results should be quite good.

Also, the change in efficiency in this example will be less than 1% (the change in blade length was only 3%). Finding the exact change in rpm needed to take proper advantage of this increase in efficiency is tedious to say the least. However, it will be in the vicinity of the rpm suggested above.

Ah well, work is slow, this post is getting long, and I've put the flybar back on my Blade. I'm going to go fly. Enjoy!

P.S. MiniBichus, if you already know these relationships, feel free to slap me. My mom lives in Orlando, so you might get a chance! :lol:

P.P.S. This equation was developed from the one often seen for fixed wing drag. Applying the knowledge that the air velocity varies over the radius and integrating led to this (admittedly, rather simplistic) result. If anyone is curious, I'll happily post the derivation.

[jmmccain]

Impressive or not, unit analysis tells me I've done something wrong - probably when I integrated. I've got an extra meter in there somewhere that shouldn't be there...

Working with rps instead of rpm:

V = 2 π r Θ
Θ = V / 2 π r (1/seconds)

π (unitless)
Cd (unitless)
ρ (kilogram / meter^3)
A (meter^2)
R^4 (meter^4)

P = π^2 Θ^3 Cd ρ A R^4 / 2

(1/s^3)(kg/m^3)(m^2)(m^4) = (kg m^3)/(s^3)

kg m / s^2 = force (Newtons)

(kg m^3)/(s^3) = Newton m^2 / s

(N m / s) = power (Watts)

N m^2 / s = Watt meters !!!??? :YeaBaby:

No wonder it's off by an order of magnitude or more! :arggg:

Any mathematicians or physicists around here? Meh, I'll ask the fellas at http://www.physicsforums.com/ and see what happens.