Trex 250 and Park flying

[SandMan123]

I think a 450 is probably too dangerous to fly comfortably at a park, even when there appears to be nobody around. Is this the general consensus?

So the 250 seems to me like the only semi-acceptable 3D bird to fly at a park, assuming you are still careful that you don't fly it near people. What do you guys think? I mean, yes, of course there could be some theoretical scenario in which the 250 hits someone in the right spot and causes injury, but I think the chance of serious injury with the 250 is just so much lower than a 450 or a larger bird.

[kenn_palmer]

If you have a spotter to keep you informed about folks trying to commit suicide then a 450 is fine. It all depends on the size/usage of the park though.

[SandMan123]

So 250 without a spotter is ok you think?

[RocketSled]

I routinely fly both my 250 and 450 in the street in front of my house (sometimes to the chagrin of my neighbors as they drive past). Both these helis fly quite comfortably in this small a space in spite of things like trees, street signs and mailboxes.

The area you fly in and the heli you fly in that area are not what's important. There is one critical factor only - your skill level. Don't fly in spaces or around people or objects if you're not confident of your ability to control the heli in that space.

My flying in the street is also a huge distraction for the neighborhood kids. When they get too close, I land immediately and then caution them to give me more room "or I have to stop flying". Since you should always be looking at where the heli is headed, not just at where it is that that moment in time, you should generally be able to see someone coming in to your "space" long before they're at risk. My biggest problem is cars, I always have to be taking quick glances over my shoulder to make sure nothing's coming my way before I rip down the middle of the road. But it's eminently doable, and doable safely, if you don't let your ego write checks your body can't pay (to steal the quote from Top Gun).

[SandMan123]

Do you find your 250 more difficult to fly outside, or is it about the same as the 450?

[GormPedersen]

I got a 250 and I find it more difficult to fly outside than the 450. It is affected by wind, and it flies almost as fast as the 450, so you loose sight of it pretty fast. But on a calm day or just a little wind, you can easily fly it in a park. Just remember to keep it relatively close to you.

[RocketSled]

It is small and fairly quick (although I'm flying with the Align Hughes 500 scale fuselage). So outside, it doesn't take too long before it's mighty hard to see anything but a silhouette. And being smaller the wind does move it around more easily, but it's perfectly flyable in quite gusty conditions (you just have to remember to keep it a little higher in strong wind). It's definitely not an indoor only heli.

[AverageJoe]

Originally Posted by SandMan123

So 250 without a spotter is ok you think?

No, you stated that there are people in the park. It is not their responsibility to avoid you.

250 vs. 450? The 250 should have a 3 to 5% reduction in the number of stitches required.

[SandMan123]

It seems like such a small bird couldn't do that much damage? High head speed, then?
I mostly worry about dogs since there aren't many people where I fly, but dogs have approached my Raptor V2 before and caused me to stop flying there. I don't know if they would even notice the 250

[1BADAIR]

AMA considers 450 a park flyer

[RocketSled]

My 250 thrashes the air a lot harder than my 450 seems to. I suspect it is running with quite a bit more head speed (though I am too lazy to check actuals). The 250's blades are also "sharper" than the 450's blades, they have a thinner cross section and a nasty tapered tip. I have no doubt the 250's blades could do a lot more harm than my 450. I have in fact flown my 450 in to my leg, shattering the blades but leaving nothing more than a deep bruise on my shin. Same thing with the 250, I bet it would have cut through my jeans and left me with a deep gash.

[SandMan123]

I don't doubt that the 250 has a higher head speed, but I bet the tip speed of the blades is pretty close (fewer rotations, but more travel distance). Given that, it seems like the heavier blade of the 450 would do more damage because there's more inertia behind it.

[smccrory]

Originally Posted by SandMan123

I don't doubt that the 250 has a higher head speed, but I bet the tip speed of the blades is pretty close (fewer rotations, but more travel distance). Given that, it seems like the heavier blade of the 450 would do more damage because there's more inertia behind it.

Maybe, but then again, force equals mass times speed squared.

[AverageJoe]

Originally Posted by smccrory

Maybe, but then again, force equals mass times speed squared.

Force = (mass) x (acceleration)

Momentum = (mass) x (velocity)

Kinetic energy = 1/2 x (mass) x (velocity)²

[smccrory]

Originally Posted by AverageJoe

Force = (mass) x (acceleration)²

F=MA. http://galileoandeinstein.physics.vi.../momentum.html

[AverageJoe]

Oops! too many squares this morning. Force = (mass) x (acceleration)

I had a hard time getting the square symbol to post up. My bad.

[AverageJoe]

Any way around it, whether it is a 250 or 450, a spotter would be wise. Either bird can cause serious injuries.

[Zenom]

I feel it is pertinant to add something everybody already knows I'm sure, to wit: Mechanical failure can undo any amount of skill someone has.

[Hell_Cat]

Originally Posted by SandMan123

I don't doubt that the 250 has a higher head speed, but I bet the tip speed of the blades is pretty close (fewer rotations, but more travel distance). Given that, it seems like the heavier blade of the 450 would do more damage because there's more inertia behind it.

Think about this...
The average 450 is spinning between 2000rpm and 3000rpm headspeed.

The average 250 is spinning between 4000rpm and 4500rpm (I have seen some Pros push it up to 5000rpm and even close to 5500rpm!) The 250 is heavy for it's size and is designed with a much higher headspeed out of the box to compensate for this.

I did the math on blade tip speeds and this is what I found.

Trex 450
710mm diameter
2229.4mm circumference

2000rpm
Blade tip speed
4458.8 meters/min
74.3 meters/sec
266kph
14624.86 feet/min
243.75 feet/sec
166mph

3000rpm
Blade tip speed
6688.2 meters/min
111.47 meters/sec
395kph
21736.65 feet/min
362.28 feet/sec
247mph

Trex 250
460mm diameter
1444.4mm circumference

4000rpm
5777.6m/min
96.3m/sec
349kph
18905.53f/min
315.84f/sec
218mph

4500rpm
Blade tip speed
6499.8 meters/min
108 meters/sec
387kph
21319.34 feet/min
355.32 feet/sec
242mph

5000rpm
Blade tip speed
7222 meters/min
120.36 meters/sec
430kph
23688.16 feet/min
394.8 feet/sec
269mph

5500rpm
7944.2m/min
132.4m/sec
456kph
25072.98f/min
417.88f/sec
285mph

By the way a Trex 600 at 2000 rpm has a blade tip speed of 316mph.

Don't let it's small size fool you into thinking it will do less damage. In most setups the 250 has the same or higher blade tip speed as the 450. When setup for extreme 3D the 250 will be a blood thirsty beast with a much higher blade tip speed than an equally setup 450. Pair that with it's razor sharp blades and it probably wouldn't hesitate to slice right through the leg of your or somone elses jeans.

Be extra carefull with these awesome little helis. As always BE SAFE and HAVE FUN.

[smccrory]

Very cool calculations Hell_Cat, thanks for sharing those! You're totally right - the 250 is a band saw and must be respected for the damage it can cause.

Anyone want to try their hand at calculating how much energy would be imparted by powered blade so that it could be compared to ballistics figures? A few thoughts to get started:

• We could assume a carbon blade in use - most people use those - and accordingly I think nearly all of the energy would transfer before any parts break
• F=MA, which is also to say that Force = Mass times Speed squared. We may want to add some amount of energy transferred from the spinning motor, but alternatively we could eliminate that variable assuming that the operator would hit throttle hold as soon as the heli struck its subject
• For mass, you could use the blade's weight and gravitational constant, i.e. W=mg and g=9.8 m/s^2

Any takers?