APenNameAndThatA

16 hours ago, kgwilson said:

. Ground effect affects high wings far less.

15 hours ago, old man emu said:

There's not a lot of difference in distance between the bottom of a Jabiru wing and the bottom of a Moran Sierra wing.

Ground effect affects high wing aircraft less than low wing aircraft. It is wrong to imply that ground effect affects a Jabiru and a Moran Sierra the same. As the FAA book says, 

"When the wing is at a height equal to its span, the reduction in induced drag is only 1.4 percent. However, when the wing is at a height equal to one-fourth its span, the reduction in induced drag is 23.5 percent and, when the wing is at a height equal to one-tenth its span, the reduction in induced drag is 47.6 percent. Thus, a large reduction in induced drag takes place only when the wing is very close to the ground."

edited...

No need for personal attacks....mod

On 07/06/2020 at 9:04 AM, pluessy said:

If you have an ABN, look at data share SIM, that way you can share the data with your phone/other devices (needs to be by the same provider). Telstra is $5/month incl 100MB.

I think Telstra dropped the data share SIM for personal use, they don't show anymore.

IIRC, getting an ABN takes about five minutes online. 

31 minutes ago, old man emu said:

A bit OTT. The wing rib plan I posted above is only 36 inches long - and I wouldn't dare convert the measurements to metric. Sometimes when building off old plans you have to keep to cubits or things go out of design.

 

You could draw it out using a CAD program, then have an architect office print it up for you. That's what I did. For a few simple CAD jobs you could use one of the free CAD programs. FreeCad is supposed to be the best of these. https://freecadweb.org/ 

OP stated “Mr FV is not computer savvy”

My car says my average speed is 50 kph. I drive a mixture of city and highway. The service interval is 15000 km, or every 300 hours. Cars are pretty tired at 200 000 km, or 4000 hours. Given that they operate at lower power than airplane engines, they seem kind of vaguely comparable. 

2 hours ago, RossK said:

Basically the POH says to drag it in, low and slow with power. The risk is if the engine quits, you've got no safety margin in airspeed or height.

If you are approaching at 55 kt, with minimum rate of descent, would you also be in the region of reverse command. That is, might your rate of descent increase if you moved the control column forward or backwards? 

I agree with your comment, of course. Slow, with. power and hight AOA is tricky. 

I read it in the end, OME. It is best to forgive liars when they confess, otherwise there is no motivation to fess up. 

Riddle me this, OME, with the second scale you posted, if you hung a litre of water off the scale, would it show 10 N and 1000 g, or would it show 1 N and 100 g? 

Just to be clear, the Shinco scale has newtons on the left and grams on the right. (Newtons and kg seem to be in the Grade 7 curriculum in Australia, so there will be lots of spring scales marked with both.) 

And OME, I have a confession. I said I read the link you posted. I didn’t. I lied. Can you let us know your real name in case we meet you one day? I’m Andrew Nielsen. 

I’ll have one last go at straightening this out. See the spring scale you posted a pic of? 10 N = 1000 g = 1 kg. 

F = ma

10 = 1 x 10

with units 

10 N = 1 kg x 10 m/s/s

If we look sub in the spring scale, we see 

1000g weight = 1 kg weight = 10 N weight = 1 kg mass times 10 m/s/s acceleration due to gravity on Earth. 

I am so sad to see this end. The sooner it does, the sooner we can move onto angle of attack meters. 

Once again, look at the scale *you* posted. 1 x 10 = 10 N, not 10 kg. 

☹️

Apart from anything else, can you imagine if there were two meanings of kg that were an order of magnitude apart? There would be so many accidents. And, OME, if you are trolling, you really shouldn’t because some people listen to you. But if you are trolling, you won and gave me a laugh. 

It’s really funny knowing every brick but being clueless whether you have a cathedral or a pile of rubble. 

Fancy doing that with what looks like his daughter. Attempting a Double Darwin. 

OME, are you saying that a litre of water has a weight of 1 kg and a mass of 100 grams? 

So you are saying that an average light sport aircraft has a mass of about 40 kg? 

1 hour ago, old man emu said:

Yes. But you keep seeming to dispute that. There must be some words that are causing confusion because the maths is correct. Please indicate what is confusing you.

 

Correct. Mrs Einstein told Albert to go an buy her three kilograms of potatoes for her cooking. Albert came back with a quantity of potatoes that Mrs Einstein recognised as about right for her version of three kilograms of potatoes. Albert said, 'There you are my Love, 300 grams of potato matter'. 

So does that mean that if an RAAus aeroplane has a maximum takeoff weight of 600 kg it has a maximum takeoff mass of about 60 kg? 

20 minutes ago, old man emu said:

What's the point of posting links to explanations given by people other than myself when the enquirer obviously won't follow them?

I did follow the link. I am clarifying that you still say that something with a weight of 3 kg has a mass of 0.3 kg. 

17 minutes ago, old man emu said:

Sorry that I didn't jump to reply to your demand for a reply, but I've wasted too much time trying to show someone who has no understanding of the manipulation of algebraic equations and a complete lack of primary school arithmetic ability to know that three divided by ten is the decimal fraction 0.3 .

 

How you are ever going to be able to do the simple calculations required for aerial navigation has me stumped.

So you are saying that something with a weight of 3 kg has a mass of 0.3 kg? 

OME, you stated before that something with a weight of 3 kg has a mass of 0.3 kg. I am asking you if you still believe that. 

5 hours ago, old man emu said:

And the materials and structure of the desk are able to exert a force of 10 N as an equal an opposite force. Try putting 1000 kg on the desk and see if the 1000 kg accelerates downwards.

We need to hear about the 3 kg vs 0.3 kg, please OME. 

hours ago,  APenNameAndThatA said: 

You can have a force without anything being accelerated.

I bet you can't explain that statement 

It is easy to explain that statement. If I sit a 1 kg weight on my desk, it exerts about 10 N force on the desk but neither it nor the desk are accelerating. 

So can we just straighten this out? Does something on Earth that has a weight of 3 kg have a mass of 0.3 kg. Before you said it did. I don’t know what you think now. 

Aro is right, BTW. You can have a force without anything being accelerated. At first I thought that Aro was being picky when he picked you up on the following. 

"I think we agree that the magnitude of a force is the result of the acceleration of a mass, which we can calculate using the equation F = m.a"

But on reflection, he is quite right.  Force might be expressed in in terms of acceleration, but clearly force can exist without a mass being accelerated. If I sit a book on a desk, it is not accelerating but the book and the desk are each exerting a force on each other. If you want to go around teaching people, you need to make sure that you are right. 

What Aro said was actually *important*. I used to be confused and thinking to myself, "If the gravity is accelerating the book on the desk at 9.8 m/s/s, then how come it isn't moving." The answer is that that amount of force would accelerate the book if there was not contrary force. Force can be expressed in terms of the acceleration that it would produce if it was unopposed, but it is not defined in terms of acceleration but in the units newtons. ***a newton is not an expression of acceleration but of force***.  

And, to repeat myself, I think it is poor form that you would ask a question, have people go to the trouble on answering it and not attempting to come up with a consensus or even reflecting on the correct bits of their answers. One answer in particular about the change in the amount of lift of a wing because of diagonal flow across the wing was changed. It means that if someone is side slipping steadily that the wings will be producing unequal lift. There are questions about pilots changing AoA, it happening automatically. There are questions about the roll axis being different from the axis along whitch the AoA is measured and that being different from the angle of incidence. It brings up the question of how much pilots doing hesitation rolls are motivated to not lose height and how much they are motivated to no move laterally across they sky. Thanks for nothing. 

Furthermore, when you said that the answer was C or "same", all you had to do to explain what you meant was  "Lift is defined in terms of being at right angles to chord of the wing". That means that a) Your answer was wrong, because it was too simple, and b) even if you accept the assumptions that would have made your answer right, your explanation was wrong. So, you have no business telling others that they know "f-g nothing". 

2 hours ago, old man emu said:

aro, I am crying tears of blood. You keep saying that I know f-all about physics. I cry because you know f-nothing. 

 

In physics, a force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newtons and represented by the symbol F.

 

Characteristics of Force:

Forces are due to an interaction of at least two objects.

It may change the state of motion of an object.

It may change the shape of an object.

 

The very definition of Force involves a change in velocity over time (acceleration)  F = m.a  Force is proportional to acceleration, which is defined as the rate of change of velocity. It is also proportional to mass for a particular acceleration, but we don't usually talk about varying the mass, except if we are talking about stall speeds at different amount of load a plane is carrying, but let's not go there right now.

 

Work is the energy transferred to or from an object via the application of force along a displacement. Work is a scalar quantity, so it has only magnitude and no direction. Work transfers energy from one place to another, or one form to another. The SI unit of work is the joule (J), the same unit as for energy.

 

To calculate the amount of work done we use the equation W = Force . distance (W = F.d = m.a.d) The units of Work are Joules which have the dimensions

which is the result of multiplying mass by acceleration by distance

 

In your example of a box being pushed across the floor, consider Newton's Third Law - equal and opposite forces.

If you want to move the box in a certain direction, you apply a force to it. Because of the surface of the box and the floor are not perfectly smooth (an impossible situation, ever an molecular level) they lock together.

To get the box moving you have to overcome that mechanical interlocking. That resistance to movement due to mechanical interference is called Friction, which is a Force acting in the opposite direction to the desired direction of movement. The level of friction that different materials exhibit is measured by the coefficient of friction. The formula is µ = f / N, where µ is the coefficient of friction, f is the amount of force that resists motion, and N is the normal force, or force acting at right angles to the desired direction of motion. In this case, it is the force of gravity.

 

Moving the box involves exerting a Force that is equal to Force to overcome the Friction force. Once that force has been overcome, the box will move and Work will be done. To keep the box moving you have to apply a force that is greater that Friction force. Since the force due to gravity never changes while you are applying the force to overcome Friction, you can assign it a value of 1 in calculations and add the real value in at the end of the calculations. Perhaps this diagram will help.

 

 

 

By your definition, if I am forcing a box steadily across the floor, I am not exerting a force on it because it is not accelerating. I think that we can agree that that is wrong. 

Also "To keep the box moving you have to apply a force that is greater that Friction force." Actually, the same as the friction force. If it was greater than the friction force you would accelerate the box. 

I also think that it is poor form to accuse someone on knowing f-ing nothing when you repeatedly state that something with a mass of 0.3 kg has a weight of 3 kg. 

3 hours ago, aro said:

 

 

We do not agree. That is an equation about acceleration. You can have a force where acceleration is zero.

 

If you push a box of bricks across the floor at a constant speed, you are exerting a force to overcome friction. You can measure the work done as force x the distance you moved the box. Acceleration (once the box is moving at a constant speed) is zero, but you have a force that must be used if you want to calculate e.g. work and power.

 

Likewise, when an aircraft is straight and level at a constant speed (i.e. no acceleration) we do not say that there is no force acting on the aircraft. If we add all the forces we get zero net force, true, but that does not help us define force.

You do like complex explanations.

 

That doesn't really answer "what is a kilogram?", it answers how much is a kilogram. Previously there was a lump of stuff with a mass of exactly 1 kg for comparison, but the problem is any physical object can gain or lose mass to the environment. So that is the answer they came up with for how do you define a kilogram without using something that can physically vary.

 

For our purposes, the mass of 1 litre of water, or the mass of a reference object of 1 kg is almost certainly sufficient.

 

A kilogram is the measurement of mass: how much "matter" is in an object. Effectively a measure of how many protons, neutrons etc. it contains in it's atoms. (Can we ignore relativity please!)

 

Kilogram-weight is a measure of force - the amount of force exerted by gravity on a mass of 1kg on earth. We want to measure kilograms (mass), but scales measure force. Calibrating them in kilogram-weight and calling it kilograms is convenient. We could measure newtons and divide by 9.8, that would be less convenient.

 

So, we can agree, finally, that something with a mass of 0.3 kg does NOT have a weight of 3 kg? 

13 hours ago, old man emu said:

Using the hesitation roll was a bad choice of illustration. What I really wanted to show was a wing generating lift at an angle the average pilot rarely goes to. I admit it screwed up what I was intending to discuss.

 

This is where the fight begins. Sorry, but this is going to involve some definitions.

 

I think we agree that the magnitude of a force is the result of the acceleration of a mass, which we can calculate using the equation F = m.a  

 

The biggest problem in understanding this is getting our heads around what exactly is a kilogram. The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10^-34 when expressed in the unit Joules times s seconds, which is equal to kg m2 s -1 , where the metre and the second are defined in terms of c, speed of light and ∆νCs,( radiation produced by the transition between the two hyperfine ground states of caesium (in the absence of external influences such as the Earth's magnetic field) has a frequency, ΔνCs, of exactly 9192631770 Hz.)

 

I don't know about you, but I can't visualise that as a ball of matter. 

 

Let's look at something tangible. Suppose we had a box of a dozen golf balls. They are manufactured to a standard, so we can assume that each one has the same amount of matter in it as the others. That represents the "m" in the equation. If I take a spring balance and cover the inscribed scale with masking tape, I have a device that that obeys Hooke's Law - the force (F) needed to extend or compress a spring by some distance (x) scales linearly with respect to that distance. If I connect the box of golf balls to the spring balance, the spring will stretch and I can mark the position of the pointer that indicates the length the spring has stretched on the masking tape.

 

Let's say that we apply Hooke's law by taking the length of stretch of the spring and working out the force required to stretch the spring that far and plug that value into our original Force equation. For the sake of the discussion, let's say that the value of the force was 14 Newtons, and we know that the acceleration due to gravity where we did the weighing was 9.81 m/s/s. The units of mass  are kilograms because we are working in Newtons. So we have

F = m.a

14 = m. 9.81

Dividing both sides by 9.91

14/9.81 = m

1.427 kg = m

So the force registered by a scale is not really a measure of the amount of matter being weighed. The weight of an average adult exerts a force of about 608 N.

608 N = 62 kg × 9.80665 m/s2 (where 62 kg is the world average adult mass)

 

 

So, to finally answer your question, a one kilogram-weight is the force resulting from the from the acceleration of (1 divided by 9.81) kilograms of matter due to the Earths gravitational attraction acting on the mass. 1 divided by 9.81 = 0.102 kg of matter.

 

If you go to the greengrocer to buy a 1 kg mass of potatoes, his scale will be marked off with symbols that say kilograms, but you know that in reality, when he puts your potatoes into the weighing pan, the spring in the scale will stretch is response to the application of 9.81 Newtons of force.

 

Scales show Kilograms because that is what people understand best, but it is really just an estimate of the mass above them. Scales should really show Newtons, but that might confuse people!

 

Thanks for coming. I'm here 'til Thursday. Try the veal.

 

 

 

 

I have to say that I think that it is poor form to have everyone come up with interesting answers to your question and then decline to think about them because it turns out that the only thing that you were interested in was that sine 45 = 0.7. 

One more question: what is "kilogram-weight"?