Ideal forward speed for max. distance on a charge?

[Mark The Droner]

This question has come up quite a few times in the short time I've been here. Nobody's ever come up with an answer that was anything other than a guess.

I used to think that the RTH speed may be the most efficient, but now I don't think so.

I think some of the best guys to ask about this is the long distance guys because they're the ones risking their aircraft time and time again and they're the ones that watch that battery like a hawk the last five minutes of the flight.

I know it doesn't make any sense, but it appears the most efficient speed is flat out screamin' home on lithium vapors. That's what the long distance guys do.

If somebody can come up with evidence that some other speed is more efficient, that would be great, but so far, nobody has.

 

[D'sAdvanced]

Check out some of the posts by dirtybum and Ed209 on distance. i completed this run yesterday and used GPS and ATTI. Calculated that for 1% of battery usage in ATTI, I was getting 475'.
With GPS, I was getting 515' of range for every 1% charge.
Both were at full throttle.
Happy flying all!

 

[flyNfrank]

Am I wrong, or do you have a problem with my question and my proposed way to find a ballpark answer?

The thing is......because of the variables, the numbers you seek do not exist. And again......because of the variables, the spread would be so wide that the data collected could never provide enough detail for a meaningful answer. In other words, the best type of responses you would come up with would be say somewhere between 17-22mph. Or, say.....between 65-80% locked throttle input.

To say that the primary conditions of the atmosphere/weather elements, in this case are those of--- wind speed direction, temperature, pressure, and humidity.....is a joke. In this situation, it is these things that are responsible for range.

In my opinion, altitude, wind speed direction, wind resistance, throttle input, and battery temperature all will dictate what's going to go on when it comes to range.

 

[dehnstjohn]

I love reading the posts in this forum. I have learned so much from all of you and appreciate it all. In my opinion, ANY info that we can collectively learn and share about these tempermental, glitchy birds is more tools in our tool boxes. I like that people think outside the box and come up with new and different ways to test the limitations.

 

[ferraript]

I took DAT log from my longest flight (max distance 5.5 km) and ran it through DAT converter
then I compared columns speed versus Watts (only those, where altitude is the same)
result is, best ratio speed per Watt, is at speeds 11.3 - 11.8 m/s, then the ratio is ~ 0.1 m/s per Watt
for example at speed 16 m/s, ratio is only 0.07 m/s per Watt

 

[D'sAdvanced]

I took DAT log from my longest flight (max distance 5.5 km) and ran it through DAT converter
then I compared columns speed versus Watts (only those, where altitude is the same)
result is, best ratio speed per Watt, is at speeds 11.3 - 11.8 m/s, then the ratio is ~ 0.1 m/s per Watt
for example at speed 16 m/s, ratio is only 0.07 m/s per Watt

If my calculations are right, 11.5 m/s = 25.72 mph. Seems RTH speed is not that far off optimal speed.

 

[flyNfrank]

I took DAT log from my longest flight (max distance 5.5 km) and ran it through DAT converter
then I compared columns speed versus Watts (only those, where altitude is the same)
result is, best ratio speed per Watt, is at speeds 11.3 - 11.8 m/s, then the ratio is ~ 0.1 m/s per Watt
for example at speed 16 m/s, ratio is only 0.07 m/s per Watt

@ferraript --

I'm guessing you went into a consistent section of data from your flight log?

Something that might add additional depth to your findings, would be to include data from "Roll" and "Pitch". The combo of those would show the effects of the wind while in flight.

 

[ferraript]

@ferraript --

I'm guessing you went into a consistent section of data from your flight log?

Something that might add additional depth to your findings, would be to include data from "Roll" and "Pitch". The combo of those would show the effects of the wind while in flight.

yes, but I didn't want to make it more complicated

1. There was a lot of discussion in this topic, but no actual numbers. So at least I wanted to come out with something real and not just estimate.
2. I gave simple guide how to get that ideal speed. Anybody with basic Excel knowledge can do it by his own and it's up to him to choose the "good" sample of data.

 

[Fplvert]

Interesting thread; definitely worthy of testing.

GA aircraft the rule is around 3/4 throttle being the most efficient use of power. I'd bet it's close to that for our Phantoms too!

Looking forward to your test results!

 

[flyNfrank]

Interesting thread; definitely worthy of testing.

GA aircraft the rule is around 3/4 throttle being the most efficient use of power. I'd bet it's close to that for our Phantoms too!

Looking forward to your test results!

I tend to throw up a lot of redflags at times, but they are most those that don't get thought about. So....speaking about redflags, I have seen several instances where a user's R/C 3/4 throttle input was actually, and unknowingly, set at 100% throttle instead. This of course is a product of the user not calibrating the R/C properly.

 

[Yeager74]

I took DAT log from my longest flight (max distance 5.5 km) and ran it through DAT converter
then I compared columns speed versus Watts (only those, where altitude is the same)
result is, best ratio speed per Watt, is at speeds 11.3 - 11.8 m/s, then the ratio is ~ 0.1 m/s per Watt
for example at speed 16 m/s, ratio is only 0.07 m/s per Watt

For us mortals, that's about 11.5 m/s scientifically, and 11 m/s practically. Obviously this was the performance under the environmental conditions of that given day. Maybe on a Thursday, when the sun hits the plane slightly on the left side of the fuselage and the wind is more northerly, the speed would be 10.5 m/s scientifically, and call it 10 m/s practically. I might just pick 10 m/s, for all practical reasons and then add or reduce from that number depending on HW/TW.

yes, but I didn't want to make it more complicated

1. There was a lot of discussion in this topic, but no actual numbers. So at least I wanted to come out with something real and not just estimate.
2. I gave simple guide how to get that ideal speed. Anybody with basic Excel knowledge can do it by his own and it's up to him to choose the "good" sample of data.

Good job on doing that @ferraipt - thanks.

The thing is......because of the variables, the numbers you seek do not exist.

@mikesmiley was looking for a "..ballpark answer.." and my guess is that he'll likely be pretty satisfied with a ballpark number of 11-12 m/s for max range speed, give and take a bit.

To say that the primary conditions of the atmosphere/weather elements, in this case are those of--- wind speed direction, temperature, pressure, and humidity.....is a joke. In this situation, it is these things that are responsible for range.

Yes, those things are all part of the optimum equation, but they will only be perfecting/adjusting the actual number for that max range speed, they will not be the main factor "responsible for range". The main factor remains a reasonable ballpark number (forward speed) and work from there, plus or minus some. RTH is 10 m/s (GPS Ground Speed), and @ferraript came up with 11.5 m/s. There's your ballpark number. Some would just call that 10 m/s, some would call it 11.7 m/s - whatever floats the boat.

 

[Yeager74]

GA aircraft the rule is around 3/4 throttle being the most efficient use of power. I'd bet it's close to that for our Phantoms too!

Back from my training days a long time ago, I seem to recall that, that rule of the thumb, was the ballpark "number" for max endurance and not max range.. But then again, when talking about rotary quad choppers, maybe the difference between the two falls into the category of an overkill ;-)

 

[ferraript]

I have new result folks
this time I compared six of my flights where I believe there was minimum wind involved
I put it into charts and then I joined them into one chart:

it could be said that all individual charts consist of a few linear lines
I think each of them represents one acceleration/deceleration period
so when Phantom accelerates, it's going up at one line, then conditions (wind, ...) change a little bit and so when Phantom decelerates, it's going down at different line

and as you can see, there is no parabolic curve with local maximum at some speed, so that means only one thing:
the most efficient is always the maximum speed

 

[wsalopek]

Because multi-rotors expend most of their energy maintaining altitude, the best range speed (as opposed to max endurance) is max throttle, esp if flying in a headwind, as the less time spent in the headwind, the better.

The only real factor/variable that comes into play is additional wind resistance due to higher speed, (which increases as a square of the speed...like, go 2 times as fast and wind resistance increases by a factor of 4). But that doesn't much come into play at Phantom speeds, and in any case, the additional power needed by the Phantom to maintain a faster speed is much less than the additional power needed to fly for the additional time at the slower speed.

All the other variables, like temperature and air pressure (and altitude) and such, make a difference, but only if a person can choose the day/time they will have their emergency.

The only technique for getting more range (using less battery) would be to descend at a rate so the multi-rotor reaches the ground at the same time it reaches the landing zone, so you're not spending time descending from cruise altitude right over the landing zone.

 

[Ed209]

Optimal speed for a stock P3 is 31.3mph. I think this guy has done a thorough enough test. long range drone DJI Phantom 3 professional

 

[skipilot1]

I completely understand that. But, there's got to be a general air speed range that's the most efficient, battery-wise. I'm just curious as to what that is.

All aircraft have a speed where fuel economy is maximized. As speed increases, so does drag on the fuselage. At some point, the drag increases to a rate where fuel economy starts to drop.

I used to fly a Cessna 172. Best rate was 110 to 115 knots. Fuel usage would be 10 gallons per hour. Below or above that speed, fuel consumption would increase. I could easily fly at 130 knots if I were not paying for the avgas. I also used to fly a sailplane where your altitude represented your fuel as the glide ratio is calculated on how far you can fly forward based on your altitude. When you are not climbing in a thermal, then you are descending. There was always a minimum sink speed. Go above it or below it and your sink rate increases regardless of temperature or altitude.

Your props are just a spinning wing and your fuselage is designed to minimize drag. With lift comes drag on the prop and speed creates drag on the fuselage. The point is to find a sweet spot. I do not know what it is, but flying around without being in a tailwind or headwind, my max speed is usually 15 to 17 mph or about 30mph. If I had to take a rough guess, I would guess at about 15 to 20 mph.

You can experiment with this. Temperature and altitude will not affect things appreciably. However, you can only test it flying in low (5 mph) or no wind conditions. If headwind, tailwind and crosswinds vary on different tests, you are going to get different results.

 

[Yeager74]

Optimal speed for a stock P3 is 31.3mph. I think this guy has done a thorough enough test. long range drone DJI Phantom 3 professional

Awesome. That's all I need, 14 m/s, good stuff, thanks.

 

[mikesmiley]

I appreciate very much all of your replies. This is the sort of conversation I was hoping for.

I set a little Litchi waypoint mission that I could do from my front yard, 18,500' round trip. I did it three evenings in a row after work, using the same battery. I had very similar weather conditions all three nights. Basically identical.

First night, 20 mph. Returned with 53% battery.
Second night, 29 mph. Returned with 63%
Third night, 33.6 mph (fast as you can go in Litchi), Returned with 64%

 

[GadgetGuy]

I appreciate very much all of your replies. This is the sort of conversation I was hoping for.

I set a little Litchi waypoint mission that I could do from my front yard, 18,500' round trip. I did it three evenings in a row after work, using the same battery. I had very similar weather conditions all three nights. Basically identical.

First night, 20 mph. Returned with 53% battery.
Second night, 29 mph. Returned with 63%
Third night, 33.6 mph (fast as you can go in Litchi), Returned with 64%

From my experience, the P3 is most efficient at full throttle, unlike the P4, where it is most efficient at 60-70% throttle in P mode with OA off, because it can easily fly 38-40mph in P mode at full throttle, which is too fast.

 

[yorlik]

I have new result folks
this time I compared six of my flights where I believe there was minimum wind involved
I put it into charts and then I joined them into one chart:

it could be said that all individual charts consist of a few linear lines
I think each of them represents one acceleration/deceleration period
so when Phantom accelerates, it's going up at one line, then conditions (wind, ...) change a little bit and so when Phantom decelerates, it's going down at different line

and as you can see, there is no parabolic curve with local maximum at some speed, so that means only one thing:
the most efficient is always the maximum speed

EXCELLENT, COMPLETE, TOTAL ANSWER FARRARIPT!!!!!!!!!!!

Many other guesses and discussions of what effects speed and efficiency, but at the end of the day, none of those gave a definitive answer. YOU DID!

Maybe it would make sense to restate your definitive conclusion so there is no ambiguity or further second guessing:

MOST EFFICIENT BATTERY USAGE ON THE DJI MODEL YOU TESTED IS MAX THROTTLE SETTING. PERIOD. 100% ACCURATE.

WELL WELL DONE!!!!

Now, the only additional info I could add is this: the initial question was not quite correct. As lots of folks stated, effectivee ground speed varies with flight conditions. So there is no correct answer to the initial question. BUT there is a definitive answer to the ACTUAL question, and stated the way it was intended that question is:

"What is ideal forward THROTTLE SETTING for max distance on a charge?"

THIS the question that was answered definitively by Farrript and none of that other parameters have any effect on it.