400mph RC Jet: video inside

[coxmaster]

Weight does not affect drag, it affects acceleration. Aerodynamics affect drag.

More weight means you need more lift to fly. Right?

Generating more lift means you are generating more induced drag..

To me, it seems that weight does in fact affect drag.

 

[Eli]

Hmmm. That's a good point. Hey, I'm a car guy.. leave me alone.

But wouldn't that still be "aerodynamics" and not weight?

If you put a model airplane that weighed one pound into a wind tunnel and measured drag at 0.10Cd, then added ten pounds of weight inside the fuselage, wouldn't the drag be the same?

Reading the Wiki on drag, it appears that I'm neglecting the whole flight thing. Yeah, carry on.. It's totally different for a car vs. an airplane. Interesting.

 

[coxmaster]

Hmmm. That's a good point. Hey, I'm a car guy.. leave me alone.

But wouldn't that still be "aerodynamics" and not weight?

If you put a model airplane that weighed one pound into a wind tunnel and measured drag at 0.10Cd, then added ten pounds of weight inside the fuselage, wouldn't the drag be the same?

Reading the Wiki on drag, it appears that I'm neglecting the whole flight thing. Yeah, carry on.. It's totally different for a car vs. an airplane. Interesting.

Heh, thats why aerodynamics is such a complex thing. Everything is inter-related. If you change one thing, you are going to change everything in regard to the aircraft. Simply moving the weight can add/subtract drag even.

And I'm car guy too I just happen to be studying this stuff in school

 

[SamurAchzar]

Weight does affect drag, but there's no direct correlation, because many other factors come into play, such as optimization of the airframe for specific conditions. In other words, the lift generated by this model at top speed is probably high enough that you can make it weight twice is much and still fly just fine at that speed. It'll be a bitch to land, maybe, but for that you have flaps, variable wing geometries, etc.

So no, weight does not directly affect top speed.

 

[AeroEngy]

Weight does affect drag, but there's no direct correlation, because many other factors come into play, such as optimization of the airframe for specific conditions. In other words, the lift generated by this model at top speed is probably high enough that you can make it weight twice is much and still fly just fine at that speed. It'll be a bitch to land, maybe, but for that you have flaps, variable wing geometries, etc.

So no, weight does not directly affect top speed.

Again that is not entirely true. If you added any weight to that specific airplane it would not go as fast during level flight. Because the wings would have to generate more lift. They would do this by being at a higher angle of attack wrt to airflow. The higher angle of attack generates the higher lift levels required to support the extra weight. The higher angle of attack also introduces more aerodynamic drag.

Drag is a function of the amount of lift in a given airfoil + overall plane geometry. The amount of lift required is a function of the weight of the plane. Therefore drag is proportional to weight.

I would agree with you completely if this were a car. But in an airplane the extra force to keep the plane in the air (from increased weight) has to come from somewhere. In a car this doesn't matter because it is resting on the ground and just slows down acceleration.

 

[SamurAchzar]

Again that is not entirely true. If you added any weight to that specific airplane it would not go as fast during level flight. Because the wings would have to generate more lift. They would do this by being at a higher angle of attack wrt to airflow. The higher angle of attack generates the higher lift levels required to support the extra weight. The higher angle of attack also introduces more aerodynamic drag.

Yes I didn't think of the AoA required. Obviously at these speeds the AoA will be marginal, but cause lots of drag. Still, a difference. My point is that unlike acceleration, you can't correlate weight to airspeed without knowing the other parameters.

I would agree with you completely if this were a car. But in an airplane the extra force to keep the plane in the air (from increased weight) has to come from somewhere. In a car this doesn't matter because it is resting on the ground and just slows down acceleration.

It's probably true for cars as well, but to a lesser degree. The weight distorts the tires contact patch, increasing the rolling resistance... Oh well, you learn something new everyday

What about my question about turbine output compared to airspeed? You have any idea?

 

[AeroEngy]

Aren't the turbine blades "stalling" at some speed? I guess a turbine has two propulsion components, one is the accelerated airflow (like a prop) but the other is the expansion of the gases due to heat. I'd figure both are dependent on the surrounding airspeed.

Not really. I am not a jet turbine expert but propulsion effeciency in jet engines actually increases with speed. See Pic.

I think (reaching back > 10 years to turbine class) this is because the first set of blades in a turbine are to compress the incoming air. If the airspeed is high then they do not require as much work. As the air enters the turbine it is slowed and the pressure increases naturally instead of mechanically.

Interestingly enough a jet turbine can stall but for exactly the opposite reasons. If you are at high speed and perform a maneuver at high AoA the airflow can separate from the turbine inlet and cause the turbine to stall because the air speed is no longer fast enough. This results in a rapid reduction in output force and possible a flame out.

 

[SamurAchzar]

Didn't know that. Thanks It's good that I only deal with software for a living...

 

[CZroe]

I live right next to MCAS Miramar base (Marine Corp Air Services; was once the Navy base where the Top Gun program/class was and where the Top Gun movie was filmed). It's amazing how similar that thing sounds to real fighter jets which are constantly maneuvering overhead.

 

[polarmystery]

awesome!

 

[JMapleton]

But can it play Crysis?

 

[mizzou]

how the hell does he control it?

 

[rcpratt]

Wtf, that is ridiculous. I was kind of hoping that he would accidentally lose control and fly it into his chest, to be honest.

 

[mizzou]

http://www.realflight.com/free-g5-demo.html

lol, this just confirms how bad i suck at flying thousand dollar aircraft

 

[JMapleton]

how the hell does he control it?

That's what she said.

*oh snap!*