Ultralight 7" vs. 4" | flight time comparison | 18650 Li-Ion

[@anthonyshort8957]

Very interesting. The heavier 7" quad needs more energy to stay airborne, so I think you just proved that disk loading is not the only factor involved here. A 7" quad is typically not flown with the same battery as a 4" quad. If you're aiming for the longest flight time you pick a battery that is optimal for the size of quad you're flying. I put a 6S2P VTC6 pack on my 7" and it flew for 22:40.

[@badfourlife]

i also have 6s2p packs on my 7" but theres no way his motors or frame can handle that weight... a 5s1p or 6s1p would probably be about right for this rig im guessin and just scale the throttle to not overamp the pack

[@jhughes2286]

@@badfourlife I suggested 5s1p Li-ion pack

[@bren42069]

Yea I like that. What if you increase the disk load of the 7" to be more comparable to the 4 inch. Then you might have a better comparison.

[@DaveCFPV]

Yes, that's basically what I was testing. Does it make sense to further decrease the disc load or does the extra weight cancel out all the benefits. Of course, I could put a 2P pack on the 7" but then I would end up with basically a normal 7" disc load again

[@chemistt]

The disc loading is very important. Problem here is that the motors Dave chose are too hungry. The only thing you should not spare weight on an endurance quad is the motors. All my 7" LR setups are based on minimum 2307 motors. Best results for me are using BH 2507 1850kv motors and 4S2P LG MJ1 packs. These motors are far from light but I can cover 25km in 24 minutes of flight without worrying too much about calm weather.

[@showdownz]

Removing the wobble out of the system is VERY important. As long as there is wobble the motors are constantly speeding up and slowing down to fix the wobble the flight controller is experiencing. This will DRAMATICALY reduce flight time. I would first try tuning, but if not stiffen up the frame. Until you do that you won't get meaningful results. It was fun to watch the attempt though. Good effort. Its cool you're doing this.

[@johncgibson4720]

Love this episode. Finally a German man talks about metric curves like a real engineer.

[@DivergentDronesChrisLemire]

Two things: So on my Sub 250g 7” with the 7038 props, I could get over 9m with a 4s 650mah battery, when I switch to the 7042 props the same battery only gave me around 8m. Sound, your prop area is greater, creating more wind resistance. Don’t match the speed of the two aircraft, match the attack angle and then compare distance and flight time of each aircraft.

[@gvngoheavy]

was going to comment the exact same thing. Increased speed, from my understanding, is a major factor to going with larger props for long range, so a similar speed test is handicapping the larger prop. Im thinking of how quads will fly for longer when moving forward vs. just hovering. Eitherway thank you loads for these experimentations. MiniLongRange is definitely next on the building block once I get back to quads. I think it was mentioned on your instagram but those 2305 superleggera motors might be a good fit?

[@DivergentDronesChrisLemire]

So I put an emax 2306 1600kv on an AUW 500g 7” with a 4s 1300mah battery. It flys bobble free and is very efficient, about 12m. I believe GepRC put a similar 2306 motor on their 7” as well, but it’s a much heavier quad. I think each weight increment 250g, 350g, 500g, etc... will have an optimum motor size for a 7” prop.

[@immortalsofar7977]

Yes, I agree. Dave should measure distance travelled to 3.3V and compare those. I always measure the efficiency of my fixed wing aircraft in mAH/km, so perhaps something like that instead.

[@alerx94]

@@immortalsofar7977 you should measure the efficiency in wh/km since mah only won't give enough info. Obviously 50mah/km on 6s is way different than 50mah/km on 3s

[@showdownz]

Also food for thought... I learned years ago that the very ends of the blade is where the most drag not being converted to lift occurs. Its why some of the props now have the little spikes on the trailing edge out at the end. With bigger props this effect is exaggerated because the tips are moving faster all else being the same. Using ducted props is the most effective way to reduce the tip drag turbulence, but has the undesired effect of causing a drone to auto level due to the way ducts work when moving in a direction other then up (in the case of drones). Ducted propellers are the most efficient way to produce lift. Its why all modern jets use ducted engines. I'm thinking maybe a very thin duct just to break up the drag might work? Ducts are a whole rabbit hole. The guy on RCmodel Review explained them pretty well if I remember right. Also Also wind resistance/drag increases exponentially. I don't think the extra wind resistance on the body of the the 7" vs 5' would make much difference at 30mph. Like I said, ... Food for thought.

[@kaikart123]

Ducted fans are theoritically have better efficiency than non-ducted fans, BUT in practice, it's very very hard to make because the low tolerance of the distance between the prop tips and the duct to prevent vortex generation, also the duct's intake and exhaust itself are very hard to design to get the best efficiency. This is why many improperly designed EDFs in the market has lower efficiency than simple open props.

[@slickfast]

As an aero engineer for a rotorcraft company this was both amazing and frustrating to watch! I'm not going to go into all the details but suffice it to say that you're on the right track, keep exploring! Incredible work, and I love my flywoo explorer LR. It's very cool to be able to see how rotorcraft theory is playing out for you in reality with off the shelf parts. Rotorcraft are complex in their design, and playing with different parameters can produce very different results... often due to extremely nuanced reasons. Keep going!

[@DaveCFPV]

Thanks! Yes indeed reality is always messy. At least for now FPV development is trial an error to a large degree. Probably it will also stay that way since the parts are cheap and quickly pit together compared to running simulations with an acceptable degree of accuracy

[@marc_frank]

the effect of drag increases as disk loading is lowered

[@smooth_ops2942]

You're becoming a mix of JOSHUA BARDWELL/KABOB with the style of your videos 👍🏻

[@DaveCFPV]

That's really nice to hear since these are basically my favourite content creators out there! :-)

[@smooth_ops2942]

@@DaveCFPV Well you are spot on 👍🏻. I love that 7in frame, is it for sale?

[@DaveCFPV]

@@smooth_ops2942 A 5" version of it will be for sale soon. Not sure about a 7" version yet since the testing wasn't super promising

[@nuhbiwan]

@@DaveCFPV but please not from flywoo. Very disappointed by them. And german retailers would be fine, too? Or you order more and sell them to me directly 😂🤪might be possible we are from the same area in Germany

[@DaveCFPV]

@@nuhbiwan It won't be Flywoo. But honestly not because I don't like Flywoo but because I wanted to start a new brand specifically for LR. Sure, they messed-up the Explorer release big time but probably anybody else would have too. Nobody expected that level of hype and demand.

[@northernflyer5311]

Dave_C, great video and set of tests. Disc load and drag, are major factors. I’d like to see more testing on where the battery sweet spot falls. We can fly micro long range 2s, 3s, 4s,5s, even 6s. In each case, there are trade-offs between power delivered by each pack and weight. I typically fly 3s. For motors, we’re looking for the most thrust, able to exceed the total overall weight and provide power to fly in some wind conditions etc. so for motors, there is a sweet spot also of KV, weight & thrust. I have one build I fly with 6 inch, 3S 18650 pack, on Lumenier 1806 2300kv motors. I typically get 9 to over 20 minutes without carrying a GoPro.

[@novet001]

...you would also need to fine-tune the drive-train. Check steeper and shallower pitch. Every motor has it's sweet spot of RPM vs torque - you just need to find the right prop to get it there... Keep going, man! :)

[@DadRandom]

Glad you are putting yourself out there with your experiments. It is ok to be wrong. You can’t learn from always being right. Like the 7inch design. Maybe 5” props?

[@mikel3419]

I have 4 of your frames I am working with. My best flying, longest flying is the 4" frame but with 5" arms. I don't have the arm braces installed. The 4" with 4" arms flys great but it gets about 3 minutes less flight time. The 5" I have like the one you are showing with the bicycle connector flys great but does not get the flight time of the 4" with 5" arms even though the weights are within 10 grams of one another. IMHO I think the biggest difference are the props. GemFan Hurricane props fly better and longer with all of mine than similar HP or other props I have tried. I think the center of gravity is enough different on these to have an affect as well as the relationship of the motors in the design.

[@dangerous8333]

What five inch arms are you using with the 4-in frame? Is that the 4-in Explorer frame you're talking about? Version one or two? I have version 1 and would like to experiment with 5 inch arms after reading your post. Thanks!

[@hoverbotfpv1425]

I liked when the 7-10" quads were norm with naze32 and afroflight etc for the noise factor. Hopefully people will adopt endurance racing say the FPV version of motorcross and last guy flying wins with laps done. It's that in remote areas or indoor racing only in near future LOL!

[@lharrobang]

Enjoyed this technical outlook on the two variations. Interesting to see which direction you head next. Subscribed

[@DaveCFPV]

Thank you!

[@EnglishTurbines]

It's obvious, the elephant in the room which you omitted from your calculations was...Drag. Those big 7 inch discs whilst giving bags of lift, also creat a lot of drag and need more power to drive them. Specifically, frontal area with the quad tilted at an angle to achieve 40kph. The bigger disc area = bigger drag...🤔🤔😀🇬🇧🇬🇧🇬🇧🇬🇧🇬🇧

[@ferdifant_fpv686]

Actually there wouldn’t be an increase in drag for the props. When you think about it, then you’ll see, that the propellers actually don’t create any drag because they spin through the air like a screw...

[@EnglishTurbines]

@@ferdifant_fpv686 Lol....that was funny...Don't give up your day job...🤔😀🇬🇧

[@H.J.B]

The drag from the props is reduced with a lower disc loading in fact as the props can spin slower to produce enough lift and because the drag is proportional to the square of the velocity a prop spinning at half the speed gives a quarter of the drag This is just for the actual prop drag not the aerodynamics of the quad itself

[@EnglishTurbines]

@@H.J.B More utter rubbish....🙄🙄

[@grayscalefpv1748]

@@ferdifant_fpv686 Props do generate drag, but it's cancelled out by the thrust they generate. Thing that actually increases the drag are the longer arms required to fit the props

[@H.J.B]

Loved the video it would be great to see props better suited to this ultralight 7 inch size factor

[@carlcrott8582]

LOVE that someone is breaking out the graphs. On the flight testing, should you be using the same battery though? Id expect you'd want that scaled up proportionally to the weight no? Another variable: forward surface area -- the 7" is going to have a much larger silhouette. On a different note, Dave your frame layouts are elegant AF. Like they're aesthetic candy -- nice work dude.

[@carlolson198]

Thanks Dave for all your hard work to help us all get in the air. One metric it might be interesting to fix is mAh to disk loading? Probably set that from the 4" and scale the appropriate battery for the 7". Having 3000 mAh battery on the 4" then a 5250 mAh on the 7" would be about the mark for the same mAh per cm2. It is a more even point to make your testing from I believe. Thanks again for everything Dave I would be stuffed without you JB and all the others.

[@bizioFPV]

Awesome content Dave!, I really love this deep dive into ultralight LR platforms! Anyway I don't think pure flight time is really a useful data for us. I mean what I care about is "how long (in term of distance, not time!) I can fly". So cruising speed is actually a thing! 18 minutes on the 4'' cruising at about 40 km/h means a12 km trip while 10 minutes on the 7'', cruising (I'm kind of guessing) at 70 km/h means... again roughly 12 km! While I loved my 4'' micro LR, I recently switched to 5'' mini LR because I can simply fly the same distance... but faster!

[@DaveCFPV]

Thanks! They both cruised at exactly 40 km/h so I guessing that the 7" will do less than 10min at 70 km/h. But sure, picking a pretty low speed might have been an advantage for the 4". If the test was done at 60, 70 or 80 km/h the 4" could start to get much more inefficient since it getting close to its top speed.

[@milkismurder]

I really love your channel dude thanks for sharing the results of your research

[@KremerFPV]

Thanks for the info!

[@obesesoldier1]

Hey Dave, interesting video. Do you think the tune could substantially decrease efficiency on the 7" quad? I have not been able to tune a 7" to perform decently.

[@H.J.B]

Yes the tune can change the efficiency of a 7 inch dramatically on my 7 inch with a more control centered tune from UAV tech it drew almost double the current compared to the defaults

[@silvanbraendli]

same, 7inch tuning can be frustrating

[@FerralVideo]

Tuning definitely matters. People literally fry motors and ESCs with too-ambitious tunes. Running at power draws amps, but hard acceleration of the props themselves as demanded by a tight tune draws even more. A tune with high frequency oscillations will be even worse by spending longer in that hard acceleration zone. So an ultra-tight tune will draw more current than a looser, easier tune, and an over-ambitious or troubled tight tune will draw even more.

[@nathanielakkermans]

Hi, Nice vid! The main benefit to go larger in propsize is the cruise speed for me. A couple of years ago I build a 3"ultralight with 2s 18650 for long range. I managed to get 25 minutes of flight but the biggest thing I found out that the cruise speed is quite low, and is you go faster then you lose efficiency. My 7" goes for 20+minutes on one 4s lion pack but at a cruise speed of about 70kmh. And got long range I find the speed also very important. What would be interesting to test them at there own cruise speed and look at the distance they flown. And what also would be interesting is to do the same test only then both at 70kmh. Ps, a bad tune also costs a lot of energy.

[@widgget]

bad tune uses a lot of extra power. and yes, i agree, the more interesting test would be a real world flight of each to 2.5v.

[@DaveCFPV]

Yes totally agree. at 70 kmh the 4" will probably start to get way less efficient in comparison. Indeed the PIDs are pretty high to make it stop wobbling like crazy. Pretty sure that costs efficiency. 2204 might be too small after all...

[@nathanielakkermans]

@@DaveCFPV I have the tbs endurance motors on one of my 7" and these are not big, 2306. Dry weight of the quad is also not licht with 451 dry without GoPro. But it's flying super smooth. Also with a big battery. But 2204 is a lot smaller then 2306 of course. I'm curious to see where this project is going!

[@mildsauce5019]

Dave can you do a video on 2-blade props vrs 3-blade props?

[@sketchpv3080]

Those MB2204 are pretty neat for builds like this 7”. I’m surprised I had never seen them before. Apparently there was also a 2450kv variant that would be great for a 5” on 3-4S but those are next to impossible to find.

[@badrx5783]

You always put the GPS in the wrong place! Above the GoPro is by far the best place I've found. Thanks for the video!

[@davidrgilson]

Here are my thoughts. You concentrated a lot on g/cm², but as you mentioned earlier on, we need to look at g/W too. So I think you're right at the end of the video that you need to further test motor and propeller combinations. A couple of ways you could test this against the 4" quad. 1) The in-situ method. Measure the wattage consumption while hovering until the battery runs down to your cut off voltage. BF black box should be useful here. This is subject to a lot more random errors, but would be more 'real world'. 2) The bench method. Get a table top thrust meter, measure the power to thrust relationship of the 4" prop and motor, then find the best motor and 7" prop combination that matches.

[@colinmetzger6755]

You should look at the efficiency curve of brushless motors, even with the greater weight of a bigger motor, since you'd be at a much lower portion of it's torque potential, you should be able to get a very significant efficiency boost. I'd be curious to see you go in the complete opposite direction and get a 2806ish size motor then test the fight time. Should also significantly help with the feel of the quad.

[@jhughes2286]

I agree with a smaller stator the stator gets saturated with energy much sooner than a larger stator, therefore even a larger stator can be more efficient because it does not have to work as hard it's not near its maximum potential which is when the increase in amps causes a decrease in efficiency losses through heat etc.

[@H.J.B]

I think the idea behind the lightweight design of this seven inch is to directly compare the seven inch to a four inch with the same battery as you can get a seven inch to carry a good 600 or so grams of battery which would blow a microlongrange out of the water with flight time Because the 4 inch is at the limit of its carrying capacity with that battery whereas the seven inch would be perfectly capable of double or even triple the battery size And he was mainly testing the efficiency of having a low disc loading But if he where to load up the seven inch to the same disc loading I think we all know that it would win

[@beefybeef1326]

Very interesting test and results. Maybe you could try another test where the battery mass fraction is the same for both quads....

[@jana171]

@Dave_C FPV , I was thinking if the bad tune on the 7" would use up the battery... seems logical that if it's wobbly it will have to correct more during each PID loop, thus taking up more unnecessary battery power. But since the results were massively different, other stuff like the props you mentioned is also a good idea. Love this channel, keep it up !. Happy new year !

[@DaveCFPV]

Think so too. The results were so clear there must be several things (possibly tune, drag, wind, weight, props, more battery sag...) going against the 7" flight time. Thank you! Happy new year!

[@liampeck24]

Great video! I've found that the tune helps a bit with regard to efficiency.

[@heggy_fpv]

what did you alter in your tune that affected efficiency the most?

[@amitsekhon]

Great test Dave!! Just an idea...make this frame little bigger to use DJI phantom motors with DJI low noise 9"props😊

[@jimster1111]

by using the same battery the 4" had a much higher ratio of battery power to weight, there seems to be an efficiency curve here where not only is the right ratio of disk load to total mass important but the right ratio of battery weight to total mass.

[@trajanfpv]

Interesting video, thanks Dave.

[@The_Privateer]

load up the 7" with enough battery to get similar disc loading of the 4". I think that would be a more "apples to apples" comparison. People that are into long range don't use a larger quad to carry the same small battery - the point of a larger quad for long range is to carry the weight of more battery.

[@kaikart123]

With the same disc load, the 7" would have to bring about 900g battery, so almost 4x of the pack. That seems unfeasible in that small frame.

[@pirateradioFPV]

Drag is higher on the bigger quad and there’s the prop+motor efficiency. Most 7” start to wobble because of the aerodynamics, the bigger prop starts to inhibit fixed wing properties and the quad starts to feel the wind like a flying wing does.

[@Kriselice]

I think that you cannot start from the "disk load" as you do to judge the efficiency but that you must start from the effective efficiency of the propeller motor torque (grams per watt at X% Throttle where X is the gas level necessary to fly at 40km/h) before making the comparison. And again, even doing this using the engine manufacturers' tables, it is false, because these tests are done statically. There is no concept of "simple" wing loading for a rotary wing, and your test demonstrates this with talent. Since I'm thinking about the design of an ultra-light 7" I came across your remarkably interesting video 3 years later. Thank you for that.

[@fermilabratphd5864]

There's a publication Modeling Flight - NASA that is a 6 MB PDF file on line. Flight efficiency does not scale at a linear rate. A rough estimate based on disc area would be energy consumed versus time. So if you scale up the disc area you would want to see how long it would take to consume the same amount of Watts. Because the discharge rate curve of the batteries are important you would want to use a battery that has proportionally higher weight and amp hours as disc area increases. You're dealing with the issue of cross-sectional surface area goes up by the square as the volume and possibly mass goes up by the cube. I like the smaller quads, they have lower inertia and are less likely to self-destruct if they hit something.

[@ed4415]

Having a Flywoo explorer and built one of your mini long range frames (both excellent) I think you hit the sweet spot at 5 inch for li-ion and 4 inch for light weight li-po flying. The 7" might be a worthy experiment to test capability but less necessary (plus it's less of a looker!).

[@dronepilot1333]

I am thinking if you could spin a 8" props on 7" frame and reduce its motor kv would give a longer flight time with the same battery capacity or may be a much longer flight time with a higher battery capacity.

[@inhisimagefpv7826]

I have the 5 and 6 inch rekon quads. It would be very nice if you would also provide a 7inch version of the quad, with a larger battery carrying capability for longer long-range flights.

[@austntexan]

I need to do a faster flight, but went 70 min with a lightweight rig based off of the Black Opal 6". Battery pack was a 3S2P 3500mAh Li-Ion. Arducopter was set for ~13kts running a circular do jump pattern. Non-HD rig, super light 215g before the Li-Ion(290g). I think if I increased my speed slightly, it might be more efficient.

[@Atlas_FPV]

That 7" looks epic

[@yannickg6904]

I like the happy compromise that a 6in prop brings. Your 5in frame adapted to 6in props, with t-mount 2204s and HQ T6x2.5x3 would be a nice combo.

[@DaveCFPV]

could be absolutely right. 6" has also been my favourite on more classic setups. I think the next thing I will try is just putting some 6" props on it.

[@yannickg6904]

@@DaveCFPV So many new props and motor sizes are coming out, it's hard to keep up. I spotted the SPCmaker G2204, but I'm unsure of the quality. The 4in LR is still a very hard design to beat.

[@emielleclercq]

You should try the mavic motors and props. With the amount of money dji invests in there drones they are probably very efficient. Banggood has a frame that uses the mavic motors mounting holes.

[@yannickg6904]

I saw that there's an 8in frame available on AlieExpress and BG called the "Andy HD8" that uses the motors for the Mavic. I always wondered what could be done with the motors from a mavic mini or a Spark on a light carbon fiber frame.

[@flyingdream777]

@@yannickg6904 I think the biggest factor is the way the props are mounted, each blade can lead and lag individually and that helps with efficiency, I have ordered some Mavic Mini / Mini 2 props to experiment.

[@larssmith2170]

Have you ever thought of the concept of having a small airfoil, like the tail of a DC-9, attached to the top of the quad which would generate lift at cruise speeds thereby allowing for much reduced power settings in cruise and longer flight times? The angle of attack of the wing would have to be optimized for a certain speed so as not to create more drag than lift. Anyway just a thought.

[@DaveCFPV]

I played around with quad / wing hybrids but mostly it was extremely difficult to make them fly well. Seems like the flight controller really has issues handling them

[@MCsCreations]

Pretty interesting results, Dave! Surprising! I'm curious to see what you do next! 😃 Happy new year! And stay safe there with your family! 🖖😊

[@DaveCFPV]

Happy new year!

[@romanbader]

Exactly what i was looking for, thank you :)

[@jamesmason7124]

Please make more videos about the Explorer LR 4 v2 maybe a ultimate build video without Dji components

[@JoshHefnerX]

I'm thinking you should be looking into the props as far as being properly matched to the motor - to produce 'enough' lift for the weight of the quad

[@benjaming9835]

The larger quad will have much more drag maybe more then double. also square/flat surfaces are not your friend, round/curved leg sections would be better. but why not just use the same 4" body/base with long 7" hollow round legs. Or/and try larger dia motors with lower volt/rpm

[@flyingdream777]

Hi Dave the TBS pizza box frame will be around 36g cut from Rohacell.com 1mm Carbon skins with polymethacrylimide plastic foam core, would love to see your experiment with this stuff.

[@Rcschim]

Great concepts, good test! Are you sure flying till 3.3v on 2 different packs (that might be in slightly different condition) gain a good comaprison? Have you checked how many MAHs you charged back into both packs after the flight? Could have been quite different MAH consumption / cell behaviour. I say this because I noticed in my last test (regarding LIONs) that temp playes a huge role. The one day (cold, around 0°c) I got horrible flighttimes (and only 2000mah out of a 3500mah pack until the volts dropped down and I had to land, the other day the same pack got me 2900mah and volts were still ~3v/cell only difference: 9°C this time and packs in a plastic bubble wrap... Just got into micro longrange by testing the iFlight Chimera4 and the "great" Shadow Fiend - sorry, both rip-offs of your Explorer - but the Flywoo LR is so hyped it wasnt available really ;) Today just for fun, I flew a few 650mah packs and got ~ 7mins of save flighttime ;) greets from Austria, Mario

[@DaveCFPV]

Hi Mario, honestly I didn't bother because the result was so clear with roughly +80% of flight time on 4". I noticed the same thing with the temperature and the test was indeed done around only 2°C. With Lipos I always managed to get the battery warm with a few punchouts but on LiIon they come down dead cold.

[@MABdrone]

A doubt: at 08:30 you said that a 7" have 993 cm2 prop area. Where is this number coming from? It's the prop specification or is there a calculation that you made? Thank you!

[@sganzerlag]

Dave, thanks for making this video. Really enjoyed it. On the graph of disk loading vs efficiency, you drew a curve that sort of looked like a smile (the mouth on a happy face). I could be wrong, but maybe the actual curve looks a bit more like a frown (the mouth on a sad face). If the curve did look like a tilted frown, then once you go below a certain disk loading, you get into a region of rapidly diminishing returns. I'm not sure about this, but it might be something to think about. Would explain the lack of significant endurance gains with 50% less disk loading on the 7 incher. Or maybe the 7 inch props just had too much pitch? Either way, super interesting comparison. Fyi, I bought myself a Flywoo Explorer LR4. Can't wait to get my hands on it. Thanks for making the LR4 a thing! Best regards from Brasilia, Brazil.

[@DaveCFPV]

There must be a point of diminishing returns i think. No curve is exponential forever... Hope you enjoy your Explorer! :-)

[@terminsane]

Disc loading doesnt really account for the extra power needed to swing the larger props on the bigger motors, does it?

[@friendlynomad9840]

Fantastic video! Thanks! Next, can you do a range test? For example, if there is a particular mountain I want surf down, how close must I drive my car to be close enough to fly my drone to the top of the mountain? If the 7" has a higher cruising speed than the 4", then perhaps less efficiency won't matter so much if I can fly to the mountain sooner. Much appreciation.

[@DaveCFPV]

On all of these setups your range should be limited more by the video signal than anything else. The 4" can cover over 20km round trip on those batteries :-)

[@hectorgreen5638]

I think you should do the same thing again but switch the batterys because even though the batteries are the same the resistance might be different

[@gus8378]

Have you thought about stacking the AIO and Vista and mounting the battery behind it? You could ditch the top plate and standoffs to save some weight, and basically get a top mounted unibody.

[@LoneStarUAV]

You should try the 7" with a 21700 4S1P with 4100mah Li-Ion pack (Sony | Murata VTC6A 21700 4100mAh). Right now you are decreasing the discload but increasing the AUW with a unchanged capacity of battery, but I think with an increase of AUW you also need to increase the capacity of the battery, so 360gr on 3000mAh or with the 21700 batteries 580gr (I added 100gr for the heavier cells) on 4100mAh. your discload is still considerably less while the 21700 battery also gives you an increase in amp draw. I would also run a test with 18650 packs in 4S2P and 6S1P configuration.

[@gammagonad1657]

I like the route TBS is going with their Pizza Box frame which is in production right now. The one piece 7” frame, which is SUPER light, as it’s very thin carbon fiber sandwiched around some type of foam. Then has a small canopy that will fit a Vista and and maybe a “Beast AIO”. I think they have their own AIO coming as well. The quad is not very crash worthy, but I think they are onto something.

[@DaveCFPV]

Oh wow I wasn't even aware of that one. Are there any infos online already?

[@gammagonad1657]

@@DaveCFPV Not that I know of. They have shown it on the TBS Couch live stream a couple of times, and said that it is finally currently in production. It is a pretty neat design. Like I said it’s one piece (well two thin pieces of carbon with foam sandwiched between), so you don’t have all of the hardware weight, as well as the foam taking the place of the heavy carbon. The only issue they talked about was figuring out how to keep the motor screws from squishing the foam is on the motor mounts. The other is that it probably won’t crash well, but with a long range cruising it should be great. They have been calling it the Pizza Box or they were calling it something else that was mentioned on the stream. Don’t think they have settled on the name. I’ll try to find some information for you. It is super light.

[@gammagonad1657]

@@DaveCFPV Search “TBS Couch - Squarce Maiden” I think that’ll get you a look at it

[@kwadkenstine4988]

Hi , In mho regardless of prop loading it costs a given amount of power to lift a given weight . decreasing numerical disc loading does not compensate for the extra power needed to lift a heavier craft. and spin a heavier prop, If you had scaled the battery up so it matched the mah per gram of the 4 inch , then your results would have been closer to what you expected , yes because your actual disc loading on the 7 would still be less than the 4. Lifting heavier things costs more power .

[@DaveCFPV]

Yes absolutely. I would have expected the decreased disc load to at least compensate for the extra weight but it seems it wasn't even close. Plus other factors like drag and the tune ..

[@artply]

great video, idea.... motor amp draw at same cruising speed would be higher on the 2204 than the 1404 and at both running 4s. What if you ran the 7" on 5s or 6s, bring disc load closer, and with a higher cell count you can pull fewer amps to get the same cruising speed?

[@felixtheRHYTHMCHEF]

The 7 inch had additional carbon fibre supports on the arms, while you flew the explorer without them. Air resistance is no joke. If the supports are necessary for the stability of the quad, then maybe the disc load theory simply needs materials science to catch up before it can be used in quads of this size. Perhaps folded aluminium would work

[@divingfalconfpv4602]

Omg can't wait to see tmount 7" motors and props. Now wondering if the new t-mount design from iflight 2005 might be a design testing for this.

[@woodrunner51]

While the 7 inch has less disc loading, if you give it the same battery you still have more weight to carry. So what if you had the same ratio of battery weight to all up weight?

[@marcusdutra7091]

"1 year later..." lol Definitely the high pitch of 7"prop induces a lot of drag which ate the expected efficiency from the larger diameter prop. Another thing: ~120g lift per each 7in prop is very low and its rpm is very low as well. Not sure if this is the case but, at very low rpm, the efficiency is horrible (just imagine, e.g. 30 rpm producing 0 g thrust at 1A, efficiency = 0) and increases sharply as rpm increases reaching a peak followed by a gradual decrease at high rpms. It would be cool to see a bench test comparing W/g thrust per each motor in both setups.

[@peterboy209]

Maybe reducing the discload by using the same prop/motor combo like on the 4inch and choose a hexa/octacopter frame would be more comparable. The "right" motor/prop combo seems to be crucial in terms of amp draw.

[@user-uh9mc7xb8t]

Hi~ Let me ask you a question. It's a 3 inch cine hoop. In the video, there are videos of making a pack with 4 lithium-ion 18650 batteries and flying it with an FPV long range. With excitement, I ordered batteries and made a pack. LGDBHG21865 3000mA. The problem is... When I hovered, the yaw tick symptom reappeared after it came up, and, after a few seconds, the low-voltage buzzer sounded and the aircraft sank. If I open it again, it opens again,,,,, repeat... So, I changed the low voltage warning in Beta Flight to 2.7V, and when I turned it on, there was no sound. If I take a break for a while, it will float again. But it sinks again... The battery is hot, and the voltage is 3.8V... TT I bought 40 tablets... but I can't use them all? How do people use? Batteries were also made by buying anything. Is my FC the problem? Or is there a special setting for Li-ion? FC is IFlight SucceX Mini F4 V3 Stack, and the manual says 2~6 Lipol. Do I have to use only Lipol? Can I change FC? Why is this happening? It's a waste of money/work time. I'm serious~~ Please advise.~~ TT

[@lorenzo220580]

Hi,I decided for your frame but I'm having a lot of yello. Have you some solution to suggest me? Thanks a lot

[@jenshenrikson7693]

Thanks, this was exactly the video I was looking for. Did you measure the resting voltage afterwards? Since the 7 probably draws a bit more current the LiIon would drop voltage harder. Anyhow - in my case I'd value the total trip distance before flight time, so I'm guessing the 7" would win.

[@helidrones]

Nice work. 👍🏻 I guess, the 7“ props were either too large or too steep pitched for the motors to hit the sweet spot. The efficiency drops drastically when the motors are even slightly overloaded. As it comes to the additional weight, this is already included in your calculated disc loading. For example last year i got >20g/W out of this build ( kzbin.info/www/bejne/hYWzlGqlgMx-iqc ). The disc loading has been about 0.089g/cm2. If i put significant heavier batteries onto it, i need to reduce the prop size by one or two inches to hit the sweet spot, otherwise the flight time will drop at some point.

[@thomasgehring3008]

Interesting comparison, taking into account that both quads are limited to use the same energy. But the 7" is heavier and these 7" props weren't designed for efficiency. Props should have low drag, similar to glider plane wings: slim airfoil and low pitch are the way to go. I'm getting the same flighttime of around 28 minutes at similar speed from the same LiIon 4s-pack 3.000mAh VCT6 in no wind conditions: 1) stock 370g AUW EXPLORER LR and 2) 540g AUW Geprc MarkIV 7" frame driven by T-motor MN1806 / 2.300kV and low pitch T-motor CF props 7x.,4. Those props are razor sharp and only fit on the T-motors. Both are nearly impossible to source now. T-motor CF 7x2.4 props are amazing, it would be great to get CF 4" props with same airfoil and actual 5mm T-mount for the EXPLORER LR.

[@divingfalconfpv4602]

I see Rekon7 coming soon.. real curious on motors. cause i was thinking when i was going to build myself 2303.5 with gemfan new lightweight LR 7035.. arm look so long and skinny.. surprised no braces connecting left and right motors along with front and back

[@matejbludsky8410]

you could do ardupilot or inav and make autonomous mission to compare the results so you remove yourself from the equasion

[@TheConfigurat0r]

My guess is, that the power to weight ratio of the batteries is less efficient on the 7" quad. You should use a way bigger battery and see how that works.

[@WRXMSK]

The key to achieve maximum flight times is to decrease dead weight as much as poss and increase the weight of battery in the same way, given that you use a battery with a maximum power density available on the market.

[@puntenpol]

a lower pitched 7 inch prop would be nice. implementing Prandtl lifting line theory in propellors could also give an enormous boost in flight time.

[@JustinHunnicutt]

Has there been any real world implementations of this theory? I read through a few papers but it seemed to be a different way to frame the calculations or a different way to calculate a wings properties. I didn't see anything about it being a game changer in effeciency. I'm not trying to disagree with you or anything, I really just don't know much about it.

[@puntenpol]

@@JustinHunnicutt there aren't many planes built this way, Albion Bowers (NASA chief scientist ret.) Claimed a total gain in efficiency of about 60% . The papers he published, are based on measured data. People who built the prototype confirmed a great gain in efficiency (not 60% tough). Had something to do with the plane not being full size. I don't know why the aero industry seems to ignore it, maybe for the same reasons they mostly ignore canards.

[@birdhz]

your 7 frame from rekon6? or what

[@twinturbostang]

Doesn't make sense to use the same size battery for both. You wouldn't use the same size gas tank for a sub-compact size car and a full size sedan. The 7" can carry a whole lot more battery than that. In general, larger props are more efficient. So I think if you have an optimized 7" quad, you can get it to fly longer (and definitely farther due to higher speed) than a 4".

[@Flash-FX]

A few years ago, I was going to build a medium/large camera platform (a lightweight quad with carbon/foam core, and 10-12" props)(never completed it), and at that time there was only big hexacopters being used. Some research led a link to Hobbyking, and did offer a motor that they developed to run on 8s. Their approach for longer flight time was higher voltage motors and lighter wiring gauge using 10c lipo batteries. That stuff never became popular and is no longer available. Here's a link for that concept if you are interested....kzbin.info/www/bejne/mH_EmoGEe5yNeNU.

[@fpvkabo]

Also, add compass to your units and use inav with waypoints for testing, then all you have to do is tell the quad to run a mission, have a seat and take a nap. And your results will be using the same power (speed) and course for each test of each quad

[@kelleysislander]

I also use a full inav setup that way for repeatability, taking out the human factor so you are getting a more consistent flight each time. I make my missions to be at least a km, then it’s easy to calculate the W/h used per kilometer. This will vary day to day based on wind conditions, but the measurements are still valid within the same day where the conditions remain consistent.

[@fpvkabo]

@@kelleysislander exactly!!!!

[@sams9716]

Have a question. New to quads. Have a hubsan h501ss don't count that. I do fly long range fixed wing fpv however. Would like to get a long range quad and wondering what to get. All my batteries are 4s lipo and liions so would like to stick with those. Don't care about freestyle or racing or any of that, just long range cruising. What do you think would be a good place to start?

[@FPFPV]

I think the footage may look different because you may have changed the camera settings for one of them. As far as I know, if you change saturation, EV comp, etc., the changes are not applied to the goggle but only to the air unit/vista you're currently connected to. Might be wrong though. Great video. Your Micro Long Range has kinda obsoleted 7" for longe range, imo 😅

[@DaveCFPV]

Must be the setting but I actually never touched them. Seems like Caddx might have updated them between the time these two units were produced. 7" will still have its place but, yes I agree Micro Long Range is basically coving a lot of 7" use cases at a fraction of the cost, noise and overall weight of stuff to carry around

[@EnglishTurbines]

The 4 inch is the sweet spot for 4 X 18650 cells basically....A quad to fit 4 cells of this type....Try fitting 3.5 inch blades, see if it gets better or worse?...🤔🤔

[@tedbundy6882]

Wow, almost stays up as long as my Original 5 year old DJI Mavic

[@Diown]

What’s currently the pitch of the 7” prop? I guess you should have a very low pitch with a maybe a slightly lower stator but bigger diameter. Maybe you can divide the pitch to disk area and use that factor to divide that with the motor specs and get some factor out of there what you maybe can get some conclusions out of and optimize

[@KAJBS]

Can CNC made easy cut the 7 inch arms? Getting ready to order another 5inch mini LR . Awesome research by the way. Thank you for all the hard work you do.

[@stelic9515]

I have an dji pfantom 2 copy with 2212 920kv motors 9450 props. Do you think will work 3s sony li-ion battery.? Thank you for show the experiments.

[@humankapital2000]

It seemed to be pretty windy on that day. Maybe that caused the gap because of the much bigger surface area of the 7"? And how about going for 6S? Btw. Happy new year, Dave!

[@DaveCFPV]

Happy new year! Yes probably the wind played a role along with many other things. Since the different is so big I assume there is more that one factor that is reducing the effiency of the 7"

[@lr7974]

Definitely need to factor in mah per gram of auw and if you want to directly compare efficiency removing this needs to be part of the equation. As the mah per gram of auw should be equivalent to try to directly compare efficiency

[@FireDFPV]

I would not compare 4" and 7" with the exact same battery to see the real perfomance of each one. The point of having less disk load is that it could carry more weight in this case, larger battery. And larger motors and props mean they need more energy to do the same work, cruising in this case. You should put the battery that give the same disk load on both 4" and 7" only then the 7" will shine.

[@citizenworld8529]

Basic formula Total Weight to Total Lift ratio If one motor lifts 200 grams at 80% thrust then your total weight (includes battery) can not exceed 800 grams 200g x 4 motors. lithium Ion cut off voltage is much less then LiPo and thus great for longer air time. Hower Lipo has more power discharge per millisecond then lithium Ion battery and thus better for speed bursts drones.

[@the_holy_waffle]

Wouldn’t the 7” cover more ground than the 4”? If you were more concerned with a distance I think the 7” would still win if we are actually doing long range. Maybe instead of using a 7” with these motors, I wonder if changing the prop to 5.5”-6.5”? Looking for the efficiency/ distance covered sweet spot.

[@frankyfrench5279]

if you have to keep 33% more weight in the air it is not for free. You should add extra cells to the 7 inch, so you end at the same discload as the 4incher than compare.

[@mdmkoopman]

I put both configurations in ecalc. and it looks like the 4" has a hover endurance 34.4min and a range of 8.2km. at 40km/h that's 12.3min. The 7" configuration has a hover endurance of 37.6min and a range of 7.6km. at 40km/h that's 11.4min. although not a perfect match this does indicate the same trend you found during your testing. Consumed power is not linearly correlated to disk loading. lower disk loading increases efficiency. but it's more like going from 50% to 70%. To increase your flight time you want to shed weight. dropping 20g of your 7" config increases your range by 5%. dropping 50g increases it by 13% Furthermore the 7" prop is slightly too large for the motor which hurts motor efficiency. you could drop to a 6" prop but the motor efficiency gained 65 - 75% is roughly halved by reducing the prop diameter. try screwing on a Emax AVAN Long Range 6X3.8X2 prop that should increase your range (thus flight time at 40km/h) by 7.5% if I may ask, what is the bare frame weight of the 7" configuration?

[@DaveCFPV]

Thank you for doing the calculations, that's super interesting! I'm also expecting the motor and tune to be pretty inefficient on 7". I think I might still have some Avan long range somewhere that I can quickly try. The frame is around 80g including the TPU parts.

[@3dprinting_and_aviation]

4" platform reasonable only in under 250g format. And your solution not optimal for flight time, but has advantage in field of dynamic.

[@williamtrepp579]

What was the difference in speed during the flights?

[@williamtrepp579]

I think flight speeds might impact flight times

[@richado0110]

Really very interesting, thank you! Definitely worth a subscription...;D. Here are some thoughts on why it didn't work out with flight time: A ballpark calculation (momentum theory) on the hover powers=f(AUW, DL) of the two configurations shows that the 7" drone should require about 12% less propulsive power than its smaller brother. Twelve percent is a decent potential, but it can be quickly eaten up by parasitic secondary effects. One of these is certainly the added drag of the larger configuration. However, I would take another look at the propeller selection in particular. A low disk loading also means that the propeller must deliver a comparatively low thrust for its size. So it may be that if the propeller is incorrectly selected, it will be operated almost exclusively at low part load. Drastic losses in efficiency are quite possible here. Maybe lowering the propeller pitch could be solution for you. BTW: Did you log the flight data?

[@chemistt]

Hmm we found out that its quite the opposite. Me and my friend are chasing the best LR endurance possible and so far we found out that best performing props on low disc loading quads are beefy bullnose props. Also for such quads its important to have steeper prop pitch rather then lower one. Its because when travelling the motor does not have to spin as fast to cover the distance in RPM - in short - the prop travels further. To put it in example - we were flying with triblade HQ props on 3.5pitch and DalProps on 5.6 pitch. HQ could only fly 56kph on 14Amps where DalProps ran 14Amps on 70kph. During one flight its close to 5km difference on covered distance.

[@jhughes2286]

Dave those 7inch bi-blade props look very high pitch? I know there are not many out there to choose in 7inch class, you should get Gemfan to make some 7035 bi-blade?

[@EssexRc]

Very educational! I tried to take in as much as possible 🙃 I am planning on ordering the 5" from cncmadness next week and wondered if they have the latest iteration?

[@DaveCFPV]

Thanks! Sure they have the latest version