Help! Ultra micro warbird build

The Fopster

Master member
A dumb question, but are you sure the ESC was calibrated correctly? If not that would account for less than expected thrust. I'm sure you've already thought if it, but mentioning it just in case...


Master member
Maybe try scratch building with foam? Or maybe get some thick insulation foam and carve one out. It shouldn’t be too bad and the plane would look nice with some work. Also thanks, Ketchup is a nickname that my friends call me.
im slowjo, cant ketchup :cautious:


New member
Hello to everyone who replied to my last post back in May. My apologies for taking so long to reply, as life has been crazy for me due to covid and many other unexpected things over the past 6-7 months.
Anyway, first, I will answer the questions that were asked. To the Fopster: Yes, I did check the eflite UMX receiver/ESC board programming and settings. In fact, I even performed some testing with different motor timing settings. The default is 15 deg. and I tried as high as 25 deg. with no noticable change in power output or current draw.
To the Slowjo: The foam airframe is quite light and really not an issue. I tried making just the basic airframe out of the lightest foam material I could find and the weight was slightly more than the manufactured scale airframe.

So this is what has transpired since my last post on May 26th, I did some slight changes to the model. I was able to remove a few grams of weight and upgraded my control linkage for better control. I also changed the esc motor timing from 15 deg. to 25 deg. I made several launch/ flight attempts, which failed due to lack of power. By this time the airframe was starting to have extensive crash damage and the fuselage had to be scraped. I have a new replacement airframe, but decided I would not build another model until I can resolve the lack of power issue.

The biggest issue is trying to obtain the required power and trust, without over loading the model. Due to the model size, restricting motor compartment, model weight restrictions and current draw limits of the eflite receiver/esc it is very difficult to find a motor that will work. The maximum motor diameter cannot exceed 23mm. From what I have found, only a 1804-1808 size brushless outrunner will fit, as anything larger has an outside diameter that is too large. I currently have three (3) brushless motors that I have done bench testing with.
1.) GForce 1806-3100kv brushless motor.
2.) Tomcat 1806-3100kv brushless motor.
3.) Flite Test Radial 1806-2280kv brushless motor.

1.) GForce 1806-3100kv: Surprisingly, the GForce motor is the most powerful of group. The first thing I noticed on this motor is the internal magnetic strength of the motor. Super, super strong! When turning the motor by hand, it feels like the motor has large de tents or gears. Wow! I have never had a brushless motor with magnets that strong. At first I thought it was a defective motor, so I purchased a second one which is exactly the same way. The motor runs fine and only draws 4.9-5.1 amps at full throttle with a 6x4 three blade prop. After running the motor at 100% power for 45 seconds (bench testing) it is still stone cold! I believe this motor really benefits from the super strong magnets, which is how it has the power and torque without the high current draw. The only downside, is the rpms under load. I do not believe the 3100kv rating is accurate and appears to be the slowest of the group at full throttle with full battery voltage.

2.) Tomcat 1806-3100kv: This motor is super smooth, but not as powerful. I cannot operate it to 100% power, as the current draw will exceed the 6 amp rating of the eflite esc. Also, if I hold the throttle to around 5 amps, within 20 seconds the motor become quite warm, not hot but very warm. That is surprising, since it is rated for 8 amps continuous and 10 amps burst with a 4x4 to 6x4 prop. Based on my testing, I believe the prop speed would be higher than the gforce motor at 100% throttle, but I would need a higher rated esc. I also tested this motor with a eflite UMX P47 4.5x3.0 four blade prop. The current draw was around 4.7 amps and was barely warm after operating for over 30 seconds. The speed and thrust is more than the stock 3000kv eflite motor, so it would make a great upgrade motor to the eflite UMX P47.

3.) Flite Test Radial 1806-2280kv: This motor is larger than the other 1806 motors. This is because the motor size is based on the internal rotor size, not the exterior motor housing dimension. So, even though it has a lower kv rating, the larger rotor size gives this motor increased torque, thus has the least amount of rpm loss under load. But like the Tomcat 1806, I could not operate the motor at 100% throttle with a full charge due to the current draw will exceed the esc rating. It did not become hot at all, just barely warm during my test. This motor is very smooth and is at the maximum outer diameter of 23mm, so it will fit in the airframe. This motor appears to have the most amount of thrust and may have enough to get my model to fly well, providing I can use a higher amp esc without increasing the model weight.

I'm going to do some additional testing with different brands of batteries, esc timing settings and possibly different esc to see if I can find a winning combination. I also have a propeller rpm meter ordered, to help with my testing, which should arrive any day now. More to come.


New member
Hello everyone,
I know its been some time, but life in 2020 has been crazy as everyone knows. Anyway I have done a lot of testing and calculations to answer some of my questions and concerns for building my model. I purchased a few items to help determine my next steps in building my third attempt of a UMX P40.
First, I purchased a 12 amp ESC to test the larger Flite Test radial 1806 motor and I also purchased a infrared rpm meter to check prop and motor rpm's under load. What I found is the Flite Test 1806-2280kv motor is the best motor for this model. Under load of the 6x4 prop, it has the least rpm drop out of the three (3) motors tested. Here are the RPM test results:

GForce 1806-3100kv motor; 8180 rpm's , 5.7-5.8 amps max. (motor temp cool)
Tomcat 1806-3100kv motor; 8002 rpm's, 6.7-6.8 amps max. (motor gets hot in 20-30 seconds)
Flite Test 1806-2280kv motor; 10,076 rpm's, 7.7-7.8 amps max. (motor temp stays cool)

The rpm's are the prop speeds with a fully charged 300 mah 2s lipo battery, 45-90c, for each motor test. I was going to do the same test with a three (3) cell battery, but decided not to, since there is no 3s battery that is not too heavy for the model.

So I have begun building my third attempt using the Flite Test motor and FMS 12amp ESC. I also found some very nice 3.6 gram servo's to help reduce weight, since I cannot use the eflite receiver/esc board and linear aileron servos with this motor. I'm still not sure if this combination will work.
My first attempt was way under powered and overweight. I had the Gforce motor and the total flying weight was 200 grams!
The second build was slightly better, as I was able to reduce the weight to right around 150 grams, but the eflite esc reduced the motor/prop rpms and the thrust was too low to compensate for the overall flying weight.
This third and final attempt has much better thrust, but the weight (175 grams) is more than the 2nd attempt.

During my calculations, I do not use the recommended watt per lbs theory. Watts is just an indication of motor power consumption and does not directly reflect thrust output of the motor/prop combination, which is what really matters when determining required thrust to weight ratio. The one benefit I have to help me is a eflite UMX P47 model. That model is slightly smaller, but close enough for me to use as a base starting point for what I would need. The thrust to weight ratio is fantastic, which helps give it's great flying characteristics. I find eflite does a fantastic job at making UMX model planes, because they are able to keep the weight to a minimum. That enables them to use smaller and lower thrust power systems, which is easier to accomplish rather than trying to find higher thrust power systems that do not overweight the model.
Here is a parts list for my final build attempt:
1.) EPO 550mm Foam model kit. Weight 80 grams. (Originally designed and manufactured by FlyFly Hobby. Includes all airframe parts, plastic detail pieces, control linkage/horns, decals and all needed assembly hardware)
2.) Motor; Flite Test 1806-2280kv brushless outrunner. Weight: 25.2 grams (includes custom aluminum prop adaptor, motor mount board and hardware)
3.) Receiver; Spektrum AR400 four channel. Weight: 5.8 grams.
4.) Servos; Four (4) EMax ES9251 Series II. Weight: 3.6 grams each.
5.) ESC; FMS 12 amp. Weight: 13.4 grams.
6.) Prop with spinner; Master Airscrew 4x6 three blade prop with scale custom made scale plastic spinner. Weight: 11 grams.
7.) Battery; Turnigy Nano-Tech 450 mah 2s 65-130c. Weight: 26 grams.

I will keep updating this post as things progress. Anyone with suggestions, please feel free to chime in.

The Hangar

Fly harder!
GForce 1806-3100kv motor; 8180 rpm's , 5.7-5.8 amps max. (motor temp cool)
Tomcat 1806-3100kv motor; 8002 rpm's, 6.7-6.8 amps max. (motor gets hot in 20-30 seconds)
Flite Test 1806-2280kv motor; 10,076 rpm's, 7.7-7.8 amps max. (motor temp stays cool)

The rpm's are the prop speeds with a fully charged 300 mah 2s lipo battery, 45-90c, for each motor test. I was going to do the same test with a three (3) cell battery, but decided not to, since there is no 3s battery that is not too heavy for the model.
I'd be interested in the rpm/apm draw on a 3s - do you think the amp draw is under 12 amps on 3s?