Scale speed...

[HeliMix]

Watching a heli fly over my office this afternoon I was wondering, for the scale, what is likely the top speed in forward flight for the B400? Anyone have any idea what it might be?

[skigolfmike]

1000 mph - at least that's what I tell everyone.:thumbup:

[HeliMix]

:lol: sweet!

[sokal]

5-10 kts actual

probbly 130-150 kts scaled

150-170 mph


1000mph would be about 2 times the speed of sound mach 2
no helicopter can achive that

max helicopter speed is the point of loss of lift
if it move faster than the speed the retrating blade move you will loose lift to one side of the rotor

[HeliMix]

...retrating blade move you will loose lift to one side of the rotor
I think I recall hearing that on Military channel when they did the top helis.

[skigolfmike]

That was tongue in cheek. I get asked that all the time and man they want to know that more than how it works. So I tell them 1000mph scale speed. Who knows what it really is.

The thing that matters aerodynamically is the actual airspeed. You don't fly your heli through miniature air molecules. Scale speed is kind of if that were a full scale heli, how fast would it be going. I figure 40 mph at the best out of a Blade 400. At 1/10th scale that's 400mph. 1000mph sounds better.:cheers:thumbup:

[HeliMix]

Eh, sounds justified to me. ;)

"Hey mister, will that thing hurt you if you stuck your hand in there?"
"I don't know, you tell me. It's only going about 1000 mph. You think it would hurt?"

See, sometimes you just have to stretch the truth to get your point across.

[Mon_t]

Heli's have a never exceed speed, This is the speed that as mentioned before stalls the retreating blade. Also a heli blade can never be allowed to exceed the speed of sound as the resultant shockwave from the sonic boom will do very very very bad things :)

[skigolfmike]

1000mph is a joke. It's what I say to someone when that's the only question they ask, over and over again.:Bow
Let's stop :DH here.

[BigAl07]

Heli's have a never exceed speed, This is the speed that as mentioned before stalls the retreating blade. Also a heli blade can never be allowed to exceed the speed of sound as the resultant shockwave from the sonic boom will do very very very bad things :)

I don't believe that to be true but I could be wrong. I know for a fact that some heli's with larger blades have the outer portions exceed the speed of sound and it doesn't seem to cause catastrophic break down. It does cause the potential for "un-even" pressure but rotor blades are designed with this in mind. That's why rotor blades DO flex as much as they do. It's possible to create a rotor blade that's very rigid and initially it would be more efficient but at higher speeds and under aggressive flying it would indeed self destruct.

Not trying to be "the Arguer" but I've read several times about "Speed of sound" on the rotor blades.

Allen :)

[BigAl07]

I've read some more and it's "Not recommended" for the heli to exceed 350mph to minimize this effect. So it CAN happen but it's one of those "Don't Try this at home" things.

So I'm sort of right and sort of wrong? Get 1/2 credit? :D

[HeliMix]

Since I asked the question, sure, I will give you half credit Al. ;)

Again, I do recall something about this on the Military channel. I watch it too much, but obviously did not pay that close attention to what they were saying. I was probabbly flying on the sim when it was on. :lol:

[skigolfmike]

Yeah, real helis have all kinds of compromises. They have to deal with the advancing blade exceeding the sound barrier and retreating blade stall. Our helis aren't fast enough and don't have a full scale heli's tip speed either.

This scale speed thing comes up all the time. Essentially, it's meaningless because the only speed that matters is the helis actual speed. Even if it is a 1/10th scale model of a full scale flying at 60mph in level flight, it's flying 60mph. It might look like 600 mph scale, but it's not flying 600mph, it's flying 60 mph. Scale speed, real or imagined, is NOT a factor in how our helis fly.

Now, where scale speed actually matters is in scale competitions. The goal in scale is not just to build a model that looks like the real thing, it has to give the perception of flying like the real thing too. Notice I said perception, in reality most models look like they are flying scale speeds when they are they are actually flying a little faster. i.e. real heli A cruises at 150 knots, the 1/5th scale model should cruise at 30 knots to look exactly like the real thing. However, flying at 35-40 knots will give a better perception of scale cruising speed.

That said, honest to God I had an exchange with someone that went sort of like this:

How fast does it go?

40 mph, I haven't really thought about it.

What's the scale speed?

It's not a scale model of any thing, so I don't know.

If it were real, how fast would it go?

I really don't know.

Ah come on, you know don't you.

OK, 1000 mph - fast enough for you.

Wow - that's neat.

and that was to an adult.:thumbup: Gotta love it.

[HeliMix]

:lol: Yes you do, you've got to love it.

[BigAl07]

How fast does it go?

40 mph, I haven't really thought about it.

What's the scale speed?

It's not a scale model of any thing, so I don't know.

If it were real, how fast would it go?

I really don't know.

Ah come on, you know don't you.

OK, 1000 mph - fast enough for you.

Wow - that's neat.

and that was to an adult.:thumbup: Gotta love it.

That's an adult ? :lol: makes you go hmm doesn't it :)

[sokal]

if you can find 1 aircraft that has mph on the gauge that would be coool i guess

but the blade does not go 40mph (maybe a powerless dive)
i say 20 at best
so 18kts or so
scaled sould be 180kts
761mph is mach 1 or 662kts

also the blade tip do not come close to the speed of sound
that would be a myth

the ch-47 head speed is 224rpm blades are 30ft long if you do the math you will find the tip speed

and thats 3 blades

a uh-60 head speed is 202 and that 4 blades

a uh-1 has 324 rpm 2 blades

the sound you hear is the sound blade slaping air
our heli blades are rigid so they dont flap
all we have is lead-lag