Bushnell Comparison

[bjaffee]

As promised, I was finally able to compare the Bushnell radar gun along side with another, more expensive gun (a ProSpeed). Conditions were mild, with 120mph being the top speed read. The plane was was a friend's Sting.

In most of the readings, the speed readings were within .5-1 mph of each other (the Bushnell does not show 1/10 mph increments, while the ProSpeed does), within the entire speed range that we were seeing.

When we did see a variance, the Bushnell always read slower (by 4-8mph, usually). It was pretty obvious that this was due to the Bushenell just not reading the plane from the optimum angle. Never once did the Bushnell read higher the the ProSpeed, nor did it ever give any readings that I'd consider out of whack.

So, I don't have any problems expressing confidence in the Bushnell's readings...at the very least you'll know that you are going as fast, or slightly faster then what the gun is saying. Whether it's a good value due to the lack of range is still debatable, I guess.

[bjaffee]

BTW, one thing that became obvious in testing out the two gun were the differing styles we had to use to get good readings.

With the ProSpeed, the more powerful gun, the best results were gained by holding the gun around the spot the plane was going to pass through to get a reading. Moving the gun around too much was avoided (not sure if this is an issue with other guns). I belive that this, and most of the other guns use pulse radar.

The Bushnell, OTOH, uses doppler radar. That means that, rather then calculating the time between pulses, it gets a speed by reading the frequency shift of the returning pulse. What that means is that it only reads speeds of objects coming toward or away from it. Moving the gun rapidly from side to side has no effect on the speed reading, even if there's stuff relatively close by in the background. So, you can use the gun to track the plane all the way around the loop, rather then holding it stationary. This drastically increases the chances of getting a good reading over holding the gun in the same spot and waiting for the plane to pass through it.

[NZBandit]

Has anyone tried the new FDR (Flight Data Recorder) thats made in Finland?

It records air speed, altitude and G-Force that you later download into a PC. I get the feeling that it's been designed for the model jet market but would be rather interesting for DSing too.

[bjaffee]

How's it record airspeed...does it have a pitot tube?
Sounds interesting, got a link?

[NZBandit]

Yup it uses a pitot tube system.

Check it out at: http://www.realdesign.fi/

or the US distributor: http://www.greatnorthernmodels.com/

It comes standard with the 3 sensors I've mentioned but you can buy others that will gauge things such as prop revs, current draw, engine temp, etc. I've always wanted to know what my current draw was, in flight, in my electric pylon racers.

Plus it would be fantastic to see speed in relation to altitude on and F3B launch and speed run.

I want to get one but at 440Euro I was hopeing someone could give it a good reference.

Cheers

Bandit

[bjaffee]

Interesting, though you'd get some crazy airspeed spikes as the plane went through the boundary layer.

[NZBandit]

It would be really interesting to see the stresses that the plane is actually under while in the DS. Airspeed vs change in airspeed and the G-forces info would help us to build better planes.

So far down here in NZ no one has been able to build a DS plane that will stay together. I've got some Blades on their way to me but I'd really prefer an Opus.

It'll be interesting to see how long the Blade will last as our local DS spot is very handy, but rather lumpy. We DS in a volcanic crater in the middle of the city. Couldn't be closer but its a real plane breaker with such a turbulent sheer layer. But because the volcano is pretty much round, you can DS in just about any wind direction so it sort of becomes so handy, you don't want to go anywhere else.