Sudden realisation.

Driving to work this morning, I had a sudden Epiphany!
I was watching the road, but for some reason from the corner of my eye I was also casually watching the street lights and trees on the A55 flashing by too. For some reason my eyes drifted, and I noticed that the tops of the street lights and tree branches were passing me (what seemed to be) reasonably slowly. Looking at the speedo, I was doing in excess of 70mph! (naughty boy! - I will deny everything if it goes to court!)

................Thats when it hit me.

When flying my models about street light height, or higher, my models approach, and pass overhead roughly the same speed as the street lamps were passing my car this morning! - This means that my models on average must be flying at least 70mph full pelt, or even faster!

Know someone will probably shoot me down in flames, and say that that speed is unreasonable with the set-ups I run, but I just never realised or appreciated the potential speed of model aircraft until this morning! - Its no wonder people get mangled if they get hit by one!

Would that be 70mph upwind, or downwind?

Also, it's actually quite surprising how fast modesl are actually flying. The other surprising thing, is how the size, and noise of the model, affect the apparent speed.

For example, I have a small EDF foam delta, about 15inches wingspan, that sounds and looks like it is doing the speed of sound. But in real terms, it takes it about 3 seconds to travel 50 metres which equals about 35mph or so.

Then there is (or was rather) my 3metre graphite. According to an onboard GPS log, the maximum speed I got on a screaming vertical dive followed by a pass across the field, was about 120mph. At the time, it appeared to be a lot slower than the little foam delta....

Similarly, the little green thing of mine. Flat out everyone thinks that must be doing about 800mph. Again, the gps log as clocked it as doing about 120mph in the straight and level....

Also, The faster they go, the further out they land, eh Ben?!

the green thing looked more like it was doing 799mph not 800mph

It's that prop noise as you back off that does it

Wait till you hear it now, complete with reconfigured ESC brake that means......

The "Booong" is back!

it must be doing more than 120mph

Not according to the GPS it wasn't.

There could be some error in the signal I suppose, it does tend to lose track a bit in teh really sharp turns. The 120mph was the average speed over 8 data points, which were a straight and level pass, starting as far out as I dare, past me, and as far out as I dare, all at about 50m altitude. According the points it travelled about 370m, in more or less a straight line, in 7 seconds (1 sample per second).

I would prop it up a bit, but I'm scared....

Airspeed or ground speed?

M

The GPS log will be ground speed. No idea what the windspeed on the day was, but looking how smooth a straight line I was flying in, it is safe to assume there wasn't much wind!

I should get the FPV above it to watch in real time, lets hope we can get on the field soon

I'll have the green thing with me next Sunday, The Graphite needs some, er, repair work doing obviously.....

Andy, ever thought of using the gps on a variety of rockets?
You would be able to find the best power to weight.

GPS tends to be a bit rubbish when it comes to accurate height measurements, not unusable, but you do need to have a fix from a large number of spread out satellites to get a good resolution and accuracy in height. Differential GPS on the otherhamd, would be fantastic.

Of course, that's providing the GPS systems can cope with the stupid accelerations you get in small rockets. In fact, using an accelerometer based measurement would more than likely give far better data.

And, when it comes to model rockets, there are only two types. Low and slow, or, "where the fxxx did that go?"

Andy

Bring it with you on aerotow day, I've got a shedload of dinky motors that will easily lose it!

LOOOL OK

So there you go Stubbsie. That's what happens if you mix religion with staring into space whilst driving!

On that day you were only out by 7. The leading 7. The next digit was fine