RPM (thrust) Test --- PART 7

I did test 4, 5 and 6 again with a 7 x 4 inch folding prop. With this prop I got less thrust, but a higher RPM. This means that the accelartion of the aircraft will be slower due to less thrust. But eventualy the max airspeed will be the same due to the higher rpm. The 7x4 folding prop also draws less amps compared to the 8x4.5 folding prop. So if I would just make some training flights, nothing special. Then acceleration is no must and I could choose this 7x4 prop and extend my flight time.

I hope I can test my modified setup as soon as possible and upload a video. First in air test flight will be the modified setup with the 8x4.5 prop and the 2cell Lipo. Second thest will be the modified setup with 8x4.5prop and two Nimh batteries

RPM (thrust) Test --- PART 6

And now the test with dual Nimh batteries. I connected 2 x 7.2v nimh 700 mAh batteries in parallel. So I should get the equivalent of 1 x 7.2 nimh 1400mAh. This setup will give my plane the same weigth as the original setup with 1 battery. We got 7000rpm that is almost the same as with the 2cell Lipo. 270 grams of thrust. Compared to the 2 cell lipo 800mAh, we have a little less thrust, have more weight, but have more battery (energie) capacity. So at normal cruising speed this setup would have longer flight time.

RPM (thrust) Test --- PART 5

Now see what thrust we can achieve with this modified setup, but with the old crapy 7.2v Nimh 700mAh battery. This type off battery isn't a good performer but due to the efficiency of the 1700kv brushless motor we got more thrust then on the original setup. As you can see 6000rpm ~ 190 gram thrust. Because this rebuild is 70 grams lighter than the orignal setup I could even place a second Nimh battery. to be continued ...

RPM (thrust) Test --- PART 4

We take this Tin Goose Rebuild to the testbench. Equiped with the 1700kv brushless motor a 8x4.5 folding prop and the 2cell 7.4v 800mAh lipo battery. This setup produces 7200rpm. This will result in 290 grams of thrust. Total weight is only 350 grams. This is a great result, but you have to keep in mind that the maximum flying speed with 8x4.5@7200 will be slower than 4.3x3@12000 rpm.

RPM (thrust) Test --- PART 3

There is one test left to run on the original setup. Replacing the battery with a 3 Cell lipo. I currently have no small 3cell lipo that fits in to the original battery holder. Small 3Cell 11.v 800mah batteries exist and they have the same weigth as my nimh battery and would fit in to the original battery holder.

In the movie you see I use a large 3cell lipo. The result of 19000rpm is enormous. This will produce 170 gram of thrust per motor. When I would use a small 800mah 3cell lipo the result may be different. But you can be shure that you will get at least 16000rpm resulting in 120 gram of thrust per motor. With a 3cell lipo you will get a ratio around 1:1. With this amount of power you can fly it as an acro plane.

The only problem with a 3cell lipo is that these motors are not made for this voltage (wattage). So flying full throttle for a long time can overheat and damge the motors. So only try this at your own risk :)

RPM (thrust) Test --- PART 2

The next test is obvious. Replace the Nimh battery with a Lipo battery. We all know that Lipo batterys are more powerfull and weigth less. I replaced the "7.2v nimh 700mah battery" with a "2Cell 7.4v lipo 800mah battery". This type of replacement will fit nicely in to the original battery holder. This will also result in a total aircraft weigt of 420 gram (30grams less).

As you can see in the movie I got 12000rpm with this 2cell lipo battery charged up to 7.58v. Thats a good result so far. This will produce 60grams of thrust per motor. Giving me 180grams of tot thrust. And that should be enough to fly this plane as a trainer in no or low wind conditions.

But we would like to have even more power. Just to fly it like a sportsplane or just to add more weigth like an onboard camera or an autopilot board. Testing continues.

RPM (thrust) Test --- PART 1

I took the Tin Goose to the testbench to get an idea of the exact power/thrust. First test is a test with the complete original setup. 3 x fk180 motor, 3 x 4.3 inch prop and the 7.2v Nimh battery. 

As you can see in the movie I only got 9500rpm with the Nimh battery charged up to 8.12volt. With the 4.3 inch prop this will result in 40grams of thrust per motor. A total thrust of 120gram on a plane that has a 450gram  of total weigth. The conclusion is simple. This amount of thrust is not enough to fly this plane.

A RC Trainer should have 1/3 (trust/weigth) ratio.So for this plane it should be at least 150gram of thrust. The original setup is bad. Don't follow the manual because it just don't work that way. You can try to mount a 7cell or 8cell Nimh battery or a 6cell Nimh battery with more capacity. But then your battery pack won't fit in to the battery slot an you will get a more weight. These little brushed motors are just not effecient enough to get good results (thrust) with a nimh battery.