GPS installed in Twinjet Brushless

 

I was waiting to do the test for quite sometime, and finally, did it. The idea was to use the GPS unit I usually used for hiking, skiing, or driving, for measuring the maximum speed the Twinjet is getting, and as a bonus, look at the course of the plane, by downloading it into a PC, after the flight.
This GPS sounded a good fit as small enough and light enough. The Twinjet was chosen as the fastest plane in the fleet and also the most powerful one. Since the Twinjet is able to carry, without any problem a 8x3000 NiMH battery, I decided that he should be just fine to carry a 10xCP1300 or 10xCP1700 + the GPS.

GPS Setup


GPS Data - Garmin Etrex Summit Model

  • Dimension: 4.4 x 2.0 x 1.2 (inches)
  • Weight: 5.64 oz. (160 gr)

On this day, we got 8 satellites around, so GPS precision was at it's best.
All data reseted, during each flight

 

Twinjet Setup

  • Multiplex Twinjet Blue Shark
  • 2 Kontronik Brushless 400-23
  • SMILE 40-6-12 ESC BEC
  • CAM 5.5 x 4.3 Prop
  • 10xCP1300 and 10xCP1700 Batteries
  • 2 x HS81 Servos

 

 

As you can see, the Cockpit was removed, for the occasion, and the GPS was just installed at the front, hold by few rubber bands. Since all the parts are strongly taped inside, normally, nothing should move during the flight

And here is a zoom

 

 

First Day Test Results

#1 - 10xCP1300 Battery 
Measured Max Speed: 154 km/h - 95.7 miles/h 

#2 10xCP1700 Battery 
Measured Max Speed: 175 km/h - 108.7 miles/h 
The added speed, was in a dive.

Note that going home, I was able to extract the course of the Twinjet, for this test
003 is the take-off/land section.

 

So I came home with all my results, so proud to be able to claim a Twinjet that fast, and wondering if it is really true. Got to the Ezone, shared the numbers and got warned that something must be wrong, that a plane like this could not reach such speed.

I certainly believed something must be wrong as I was so surprised myself of such numbers.
Decided to share this, with my good friend, Bernard Chevalier (BungyMania). Bernard, scientist and to the fact, asked me details about the Twinjet, and confirmed as well that 80 km/h (around 50 miles/h) would already be very fast and that chances are that the GPS is having some issues with itself.
Bernard also made me revise my physics lessons, by reminding me that vē = 2gh, meaning, the speed won't be impacted from the heavier load.

So I decide to take the whole thing upside down, verify everything step by step, and try to understand where the GPS fails.

Does another test with the car and the GPS, to compare both speed, and the GPS as always, gives as little less that the speed measured by the car. so seems that at least, this is fine.

Decide then to go back for a second day of test, making sure there is almost no wind to limit the variables, check that there is again enough satellites around and go.

Second Day Test Results
First, number of tours per minute, for the propellers, with this setup

  • 8 x CP1300: 15200 tr/mn 

  • 10 x CP1700: 18200 tr/mn 


Then, some speed measurement: 

#1 - Straight line, without any dive 
8xCP1300: 88.3 km/h (51.6 miles/hour) 
10xCP1300: 128 km/h (79.5 miles/hour) 
10xCP1700: 135 km/h (83.9 miles/hour) 
The speed, going horizontal seems compatible with the 1st day test. It is still fast, but consistent.


#2 - Going as high as possible, then vertical dive, full speed 
10xCP1700: 244 km/h (151.6 miles/h) 
This is too much for me...

How can I go back to the Ezone or Bernard, and dare to share this number, as much as I acknowledged myself that it does not sound right. I decide to share it, as it is, and understand either we all missed something, either the GPS has some issues, which I did not find, which creates erroneous data to be calculated.

Anyway, I'll let someone else continue the test, and run with this. It was fun :)

For #2, The GPS is telling me that the altitude was about 250m (820 feet) when starting the dive, we are about see level on the field (exactly 26 m above (85 feet) which makes the dive of about 190m (625 feet) and then I started to pull for a straight line and climbing up immediately with the shortest possible pull, seeing the wings of the Twinjet bending while I did it... 

Note the flying field on the left. Then I left the GPS ON, while going back home.

And here is a zoom on the flying area


I don't know if the speed that the GPS is giving is accurate, but I can tell you that I am abusing this poor twinjet 

The extra load, with the 10xCP1700 and the GPS inside the canopy, when pulling full speed. It was tough for him but it did it !!! 

Whatever it is, Brave Twinjet !

Summary