Help to find test details on iflight 2806.5 1800 KV motor on 4S

OwenN

Active member
I want to run 7x5.5 props, 2 sets, one reversed, for a vertical launch twin-prop model.
1) what free rpms and amps will it run at statically?
2)) what is the static thrust?
3) how long do I have at static thrust before it overheats? I expect to level off at 60-100 meters, which only needs about 5 seconds running.
I am looking at this motor because it is a large frame design, used for quads running 7 inch props, and looks well cooled.
4) is a standard 25 amp esc sufficient?
5) How many mAh do I need to get 10-15 minutes flight?
6) I am planning to use ardupilot as the controller firmware. I think I can set this to do input override and return to base on low battery.

It should glide, so just needs reserve power for the actuators , receiver, flight controller.

I will try to set it up so it will just land if it is close to the base station, not do something dumb like pop to 60 meters, circle, then come down again.
It will be set up to do a tailsit landing. The proposed controller is a Matek f765 - I will try to set lots of range, dead stick overrides, hold throttle, etc.
The design is not auto-stable to any great extent. - I think it has very little built-in crash avoidance.
 

LitterBug

Troll Spammer
That is a very loaded question with too many variables to answer. Changing the prop profile can have a large impact on it's own. Twin blade, tri-blade, quad blade??? Pitch, twist, tip?

...


LB
 

OwenN

Active member
https://www.masterairscrew.com/collections/all-products/products/electric-only-7x5-5-propeller
Looking at this one .
This looks pretty basic for efficiency-more a scale aircraft prop.

If I can find a reverse one as well, there is probably a sports/race style available somewhere, which would be more efficient.
Just take this one as the worst case. The motor is designed to take tri-blade quad props without any sweat, so overheating is unlikely.

Mainly I want some prop/amps/volts/rpm profiles, and an estimate of 4S battery size. I was thinking 2500 mAh, but considering
voltage droop and usable margin, I may need twice as much. The motors can be dialled right back to 2 amps each and still fly.

So I would like to narrow down my battery choice. what is the no-load amps, for instance? Do I need a voltage adapter for the flight controller?
 

TheFlyingBrit

Legendary member
I agree with Litter bug too many variables, I usually start with the model weight and wing loading and select a motor appropriate for the weight of model I want to fly and how I want to fly it ?
I may choose a different motor for pottering around the sky to one that would allow extreme 3D, yet it may be the same model ? Yes you can over spec your motor and dial the throttle back and reduce throws, but do you need the extra weight or a 4s lipo when a 3s will work ? Plus big powerful motors can produce more torque roll which you may have to contend with ?
Once you have a motor that suits the planes weight and how you plan to fly it, then you look at the prop sizes suitable for that motor depending on the Cell size the motor uses (usually in the manufacturers specs eg motor X may allow a 3s to use 9x5 to10x4.5). Finally you select your ESC depending on the max current draw and add 5+ amps on top (ie if the max current draw is 35amps get a 40 amp ESC) I always go extremely over the top with my ESC choices, if the max currents 30 I use a 40amp never had a brown out yet .
These days I do a bench test first with a watt meter, that provides: peak amps, watts etc and I can physically check the temps too afetr a run.
There is a lot to think about.
Start with your thrust calculation :unsure: thrust to weight ratio ?
Glider Trainer 0.35 to 0.55
Scale flight 0.60 to 0.70
Sport/ slow aerobatic 0.7 to 0.8
Fast aerobatic 0.8 to 1.0
Jets & 3D 1.0 to 2.5

To calculate your thrust Thrust = Weight X Thrust weight ratio
Eg A plane weighing 1200g or 1.2 Kg thats needed for Sport or Scale needs a thrust ratio of 0.7
So 1200grams X 0.7 = 840 grams of thrust, then you can select an appropriate motor.

Eg knowing you need 840 grams of thrust, you can calculate the power needed
Power in watts = Thrust X power to thrust ratio (which is dependent on air speed required and linked to the KV of the motor).
Watts = 840 x 0.26w/g therefore the watts of power will be 218 watts obviously you select a higher wattage motor so you can run at 50 to 60% throttle not flat out all the time to produce the 218 watts.

Hope this helps.
 

OwenN

Active member
The 2806.5 1800 KV motor is fine at 3S - plenty of lifting thrust, good top speed. I still don't know what size battery I need at 3S.
I was thinking 1200-1500 mAh, but people tell me that the practical run time will only be 3 minutes.
So I will look at 3000 mAh, 3S and check how that affects my weight target.

This thing may get so heavy-up to 1 kg - that I need to look at more wing area. It is over a meter long, with a span of
500mm. I am not to sure if butting a delta wing hard up against a front canard plane would be very stable.

The canard is offset vertically about 60mm. At the moment, I think I have 1400 N thrust, which is marginal at 1 kg takeoff weight for a tailsitter VTOL. - then I would look at 4S, tho A 30 % increase in rpm would give maybe 15% more thrust.
Also, I can go from 7x5.5 props to
8 x 5. The motor should still handle it, and likely make more thrust.

At the moment I am extrapolating off the flybrushless test of the Suppo A2208-12, although the 2806.5 is far more efficient and heat-resistant
at those loadings. Amps and torque appear similar.
I am assuming a flat torque curve for the motor, and prop torque rising at the square of rpm.

Is this a valid approach? I want to do all this in theory before buying the motor,esc, flight controller, and actually building the airframe.

What is a reasonable wing loading to aim for with a top speed of 55 mph, wanting to be aerobatic, and to turn reasonably tight
loops, turns etc?
I want to be able to drop down to 40 mph for aerobatics, and do landing approaches under 20 mph.
The delta-canard is good for that. with enough thrust, it should smoothly rotate to tailsitter attitude. The Ardupilot landing assist software will help, to dial thrust back up again as angle of attack is increased.
 

OwenN

Active member
Flat on the bottom- the no-lift line is raked up at about 2-3 degrees. Depth to chord ratio is between 11% and 19% at the tip, to support the tip fins. Some details have changed, but the small version of the drawing is now too big to get in the scanner.
vtol wing 5.jpg

Rear fins are now raked and bigger, more evenly distributed top and bottom, and tip pods have been added for ground stability on grass.
I have been told that the inner section can be straight across, and the tip deltas can be made bigger. I may do this if my weight totals get out of hand.
 

TheFlyingBrit

Legendary member
If they hadnt got a chord and where flat design you could have modified it to a swing wing version, using a single servo operation. that would change your wing loading in flight to give aerobatic or speed characteristics.
 

TheFlyingBrit

Legendary member
The motors would have had to be mounted on a boom not an intrinsic part of the wing. Ignore the suggestion it was an idea I came up with not having seen your design before.
 

TheFlyingBrit

Legendary member
1606531925003.png

Looks like the 9x5 triple blade prop is a good option with 60 amp ESC's you should have more than enough thrust there with two motors ?
and 4s lipo's would be ample.
 

OwenN

Active member
What is the motor? how many mAh?
I am working on a wing mod that will give me more area without moving the Aerodynamic center relative to the rear edge,
and keep the same canard size and location. Also, motors are re-spaced to allow 8 inch props. I would prefer to keep 2-bladed props-they are the best for normal aircraft models. 3-bladers have an advantage for quads in rapid flips or turns.
If I go up to 33 inches span, it should be ok for the weight range: 500-900 g.
 

TheFlyingBrit

Legendary member
Its the specification for your 2806.5 1800 kv motor obviously you need to do the maths for your mAh based on Watts/Volts =Amps and actual measurements taken or just work it out from the table above for an estimate. Take the load current in amps for a specific throttle response eg 50%, you can get the esimated milli amps by multiplying by 1000 so for 50% throttle it would be 17050 milliamps load etc etc
Sorry dont mean to teach my grandmother to suck eggs, you get the maths Im sure.
Just remember to take into account that 16 volts is a fully charged 4s not one thats been under load, the voltage gradually drops off.
 

OwenN

Active member
What percentage reserve do I need for a battery? I can set the flight controller to turn the motors down at a certain voltage, then how much do I need to return to base and land? I estimate a minimum landing cycle could take about 1 minute, to lose height and line up on a landing approach- estimated outer range to be 500m, altitude 200m. I could cut that down by dive-bombing it, but still need to lose a lot of energy to get to landing speed, when I can get to a high angle of attack. Straight-line time is 31 sec.

On another point, the original wing area is 64 sq ins. I have devised a new wing plan of 91 sq ins that fits the original fuselage, by reducing the sweep angle to 40 degrees and increasing span to 33 inches. The leading edge also cuts back to a shallower angle to clear the props inside the motors.
The canard is also wider. 91 sq inches should be more appropriate for 2 lbs + all-up weight,
The AC moves back by 2 inches, which is still well within the equipment bay. Thus, I can jam 3500 or so mAh 4S in there.
You say Escs should be 60 mAh? do I need 9 x 5 props? I just revised for 8 inch props. I need to move the motors out another
half inch each side.

What do you think. am I on the right track yet?
 

OwenN

Active member
1) I have a source for a 50 A Esc that will do 60 A in bursts. it is $26.50 nz vs next 60 A at $60 nz. If the cheaper one will do, I would prefer it.
I doubt that it would actually overheat??? I see the motor does 54 A max.
2)what is a good style of 9x 5 inch 2-blade prop? I could get the old Master Airscrew classic-style, or should I try to get something fancier?
The master airscrew unit has a pusher option. not many others do contra-props.
 

OwenN

Active member
I have found a possibly suitable prop, but it has no specs regarding material or rpm limits, It is AEO 2-blade MA Prop.
Where can I find specs? AEO.com? - I will try.
 

OwenN

Active member
I can't find props online with a reasonable spec. I want polycarbonate, no glass reinforcing. Most cheap ones don't specify material or rev limits.
Apparently you can't specify prop material on google enquiries. - Carbon race props also not wanted. (no-one lists material as a searchable attribute).
Also, here is the new 91 square inch wing plan. Probably best if I go 4S, 4000 mAh - those are heavy! 300-odd grams?
The proposed cog is 1/4 the length of the center panel mean chord forward of the AC .
Is this OK or do I need more?
new wing 28 nov 20.jpg
 
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TheFlyingBrit

Legendary member
Simple solution which I use on my gliders, use a separate 4.8v flight battery to supply the receiver and servos
20201128_112955.jpg
Weights less than 500gms but worth the added weight as you retain servo control for landing. The ESC will automatically cut out the power to the lipo when its too low leaving a safe reserve in so it doesn't go flat.
You need to disconnect the +ve terminal from the ESC to receiver lead, you only need the signal and earth, the BEC will be disconnected.
 

OwenN

Active member
A separate battery won't work as I run a flight controller which needs about 7.5 volts. The servos run off this. It does the delta elevon multiplexing (integrated pitch and roll) plus a lot of other autopilot features. - engine ramp-up to suit angle of attack, center-stick flight stabilisation in pitch ,yaw, roll, motor constant power on stick center.

The aircraft would need constant controlling without it.
I think it counteracts a slight roll command to maintain a banked turn?
With Ardupilot, it is programmable to the point of protecting power reserves and taking action to set up a landing. It can work this out with the gyro.
I just need to do the last bit of getting it on the ground in a suitable spot. - not in a bush or on top of someone.