GPS installed in Twinjet
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 Data - Garmin
Etrex Summit Model
- Dimension: 4.4
x 2.0 x 1.2 (inches)
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
- 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
#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
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
|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 !