# Tag Info

51

It's partly inherent in the way things scale. If you double the length of the model, then the wing area (length times width) increases by a factor of 4, but the weight and volume (length times width times height) will increase by a factor of 8 ... so doubling the size means halving the weight-to-lift ratio. In the most extreme cases, a tiny model will blow ...

30

Model aircraft are generally built with much lower wing loading and much higher power to weight ratios. This can be done partially because they have no real payload, and do not have to fly for long durations. Having a plane that is more lightly loaded and has more power results in the traits you mention. Also, being lighter means wind gusts and other ...

24

The laws of physics are not scale invariant. Area scales with the square of dimension while volume scales with the cube of dimension. Aerodynamic effects roughly scale with area. Mass roughly scales with volume. Inertial scales with mass. Moment of inertia scales with mass times dimension. The end result of this is that the models have far stronger ...

20

What does mean "fl oz"? "fl oz" means fluid ounce (1 fl oz ≈ 30 ml), which is a unit of volume, as opposed to dry ounce, which is a unit of mass. How are they calculated the 30:1 ratio? By ratioing 128:4.26, it is 30.05:1, so 30:1 is a good approximation What does mean "2-cycle oil"? It is oil for 2-cycle/stroke piston ...

19

Almost certainly not. Given the comments specifying a $0.5$ inch radius (blade length,) that means the circumference of the path of the blade tips would then be $$2 \pi \cdot 0.5 \, \text{inches} \approx 3.1415 \, \text{inches} \approx 0.2618 \,\text{feet}$$ To get to the speed of sound (which is approximately $1,126 \,\frac{\text{ft}}{\text{s}}$ at sea ...

16

The aircraft in the video is a remote-controlled (rc) airplane. Why it can "hover" is simply: The thrust generated by a big fan / rc-jet-engine is much higher than the weight of the plane. If the force generated by the turbine is the same as the downward-force of weight of the airplane, it hovers. By very carefully adjusting the thrust and placing ...

13

I'm not sure whether you are asking only about the physics involved, so hopefully this isn't too tangential - but one factor that's not really been touched on much is pilot input. In addition to dealing with the disruptive influences that people have already mentioned, the pilot of a model would have to ignore its actual maneouvering capability and use a ...

12

The FAA has interpreted the rules to mean that the operator must have a line-of-sight view of the model aircraft at all times, and that FPV does not qualify. Based on the plain language of the statute, the FAA interprets this requirement to mean that: (1) the aircraft must be visible at all times to the operator; (2) that the operator must use his or ...

12

The rotor is gyro stabilized. The balance bar is the gyro. If the machine rolls right, the balance bar wants to stay in a level plane and generates a correction by influencing the rotor blades to go where the balance bar wants to be. The Bell 2 blade teetering rotor system used on the '47 and the Huey used a much smaller version of the same thing, to ...

11

Worth noting: when instructions say 2-cycle or 2-stroke oil, make sure you use this specific oil type. Just any oil will not be ok, in worst cases using wrong type of oil will cause the engine to seize. I bet some numbnut will rush here to "say I've flown hundreds of hours with just regular 10w40", but, nope, it's not ok: Wikipedia: Two-stroke oil ...

10

It depends on the pilot, too. I have seen a guy fly a 5-foot wingspan model of Piper Cub just as if it were the real thing. Much longer than necessary (for the model) takeoff run with lifted tail, held back on the throttle to simulate scale speed, flew the pattern for the landing, and rolled it out. Very pretty flight. But he could have hot-dogged it like ...

9

Interesting question, and I can only answer in general terms because much depends on speculation. Short answer: use one central exhaust one big blower is better than two small ones one short flow channel is better than two long ones suction on top might be beneficial for high lift Radial-flow compressors are very light and achieve high pressure gains per ...

8

According to the UK CAA, a model aircraft is defined as: any ‘Small Unmanned Aircraft (SUA)’ (0-20 kg) used for sporting and recreational purposes and a ‘large model aircraft’ is defined as any ‘Unmanned Aircraft’ (over 20 kg) used for sporting and recreational purposes. The following rule applies to all "small unmanned aircraft", i.e. up to 20kg: ...

8

Of course. More and bigger blades is more drag. Drag is also proportional to the velocity squared. Even maintaining the RPM, a bigger propeller (diameter) will have the additional diameter flying faster. To maintain a higher RPM (or to use a bigger prop) the force to cancel the increased drag is higher, and thus the torque (force times distance) that drives ...

8

The top rotor is a hinge offset rotor with a very serious stabiliser bar. These rotors exert torque via the mechanism in item 1 in this answer, and the body will align itself with the top rotor. But the other way around as well: the rotor aligns itself with the shaft, it just depends on what it controlled, the rotor angle (like in a regular helicopter ...

8

It needs to go just under the tip of the nose to have any chance. This connection is equivalent to the thrust line of an engine, except that because the connection isn't rigid, the longitudinal location matters; the farther forward, the more stable (if the attachment is rigid, like an engine/propeller, it doesn't matter whether the thrusting component is ...

7

First for those who wonder what F3J is: This is the FAI model aircraft category for thermal soaring. Quick answer: This answer describes what resources are available on the Net. Your choice of airfoil depends on the wing loading and the size of the model, because those will determine the Reynolds number of the flow over the wings. Soaring flight requires ...

6

The maximum altitude you can operate your RC plane or copter vertically without any clearance from ATC or another government body is the upper limit of class G airspace in Germany, which is the first available airspace from GND to the lower vertical limit of controlled airspace C/D/E, which can be 2.500ft AGL1, 1.700ft AGL or 1.000ft AGL, depending on ...

6

Navigation or Position Lights are meant to be used at night-time and can be used when precipitation or weather in general deteriorates to the point where the lights will help you identify an aircraft's position, distance and orientation of the aircraft. During daylight operation, the use of navigation lights is not required as you can identify the shape of ...

6

The navigation lights are meant to give away the airplane's orientation (i.e. which direction it is travelling) at night. The red and green lights are small. Their purpose is to be observable from a long distance, which only requires a small light. For the same reason, the anti-collision red lights of tall structures are small as well. The landing lights (...

6

It's possible, but I would say unlikely. Supersonic propeller tips really mess with efficiency. The tip speed of many aircraft propellers is close to supersonic, and if not properly controlled can exceed the speed of sound, but most models don't get up that fast (and your blade tips don't have to be supersonic to be annoyingly loud). There is a formula to ...

6

For best results, put good flaps on the wing and forget using a winglet. If you insist on bending the wing up at its end, just continue with the tip airfoil and select the incidence such that your circulation distribution over the wing and winglet will become elliptical when you plot it in a straight line. The small size of your airplane implies that you ...

6

See this very relevant discussion on Space.SE: Can a miniature Saturn V get to the moon and back? The square-cube scaling problem was already mentioned in other answers, but another important factor will be that the Reynolds number of the air does not scale with the model. You can think of this as the air being more viscous from the smaller scaled craft's ...

6

Lots to consider here. "Free-flight" model airplanes and gliders fly without any control inputs from a pilot whatsoever (and no automatic electronic stabilization systems either). One branch of this is called "towline gliders" and the "pilot" runs along pulling on a line attached to the glider to get the glider into the air. ...

5

Hovering is far easier and more common is propellor driven RC planes than jets. Very few RC jets have thrust vectoring, and even fewer have hovering capabilities. Propellor driven aerobatic RC planes are able to hover, also due to a thrust to weight ratio > 1, however, they are controlled by the normal control surfaces rather than thrust vectoring nozzles. ...

5

Is it legal to build and fly a scale 1m:20cm Boeing C-17 for use in flying from the U.K. [...] Building an aircraft is likely not regulated (intellectual property laws still apply), it's probably like building a car in your garage, however using an aircraft, specially outside your own property is regulated. Drone use, in UK, is regulated by CAA as for any ...

5

It might. Depending on how close to the wingtips your props are. If you put the props right at the wingtips, then the conventional rotation to minimize precession and torque actually decreases efficiency by promoting tip vortex (the direction of the prop is the same as tip vortex thereby adding to tip vortex). This reduces lift for the same amount of ...

5

Thank you for giving more information, but I still have to resort to speculation. Here are some things you might want to consider: A rear-mounted prop stabilizes the aircraft. Full throttle limits your control power. You would had a better chance of recovery with engine idle. No incidence means that the plane needs to compensate for the c.g. location with ...

5

My vote is that the surfaces aren't rigid enough and get twisted so much that the control surfaces can't overcome the effect. How floppy (non-rigid) are the wings and the canard surfaces? The wing looks to be sagging under its own weight! My thought too is that you're tail heavy, tail heavy will pitch both ways and you can get stuck in either positive or ...

5

There's no specific altitude restriction for model aircraft anywhere in part 101 (that I can see). Even within 5 miles of an airport you only have to inform the tower, per 101.41(e): When flown within 5 miles of an airport, the operator of the aircraft provides the airport operator and the airport air traffic control tower (when an air traffic ...

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