Glider A & B Crets.

[EI1638]

Don't think I've ever seen a Yagi fly well. They seem to have centre of gravity and control surface issues...
John: Best left for really strong wind conditions (force 10 and above)

Keith:
Moving slightly back towards the original topic I wonder whether the radiation pattern really is omni-directional.
I'm not arguing about the radiation pattern of the dipole, because there is nothing to argue about there.

When we're flying though we tend to be standing behind the tx, (I've only ever seen one pilot sit) so effectively there is a 'mirror' (in terms of RF energy - i.e. the human pilot - even if we're not great rf mirrors) on one side of the antenna, distorting the textbook donut shape of the field. I know I'm long since past being able to do the calculations on this - the exam was passed and promptly forgotten about - but does the pilot not distort (extend) the lobe and effectively add some gain in front of the pilot (and reduce the size of the pattern/donut/lobe behind the pilot)? i.e. better/more range (stronger signal at the model) if we always turn and face the model, assuming the antenna is vertical. Of course, standing on a slope will realign the radiation pattern too as the ground is no longer horizontal...

I'd better shut up before anyone starts to think I know anything about this stuff. It was a long time ago in a galaxy far far away.

I hope none of my old lecturers see this....

[Happy Days]

Good heavens Chris, you're asking me detailed questions about stuff I did over 30 years ago! (oh god, I feel another white hair coming on ) The matter of exact rf energy field strengths, as you may know, is highly complex and was certainly never my strongest point.( In fact, I haven't got a "strongest point" in any topic!  )

You imply that the pilot standing behind the radiating element could be acting as a reflector element.
Assuming he is wearing shoes that electrically insulate him from the ground I would have thought that as he is not a resonant wavelength of the radiated signal, nor probably at the correct distance  'behind' the radiating element, he would likely absorb as much rf as he reflected.
Certainly the pilot will distort the radiation pattern, though whether he would enhance any lobes I couldn't say.

Of course, we could always get a field strength meter and stroll about the slope doing tests Chris. (Providing everybody else stood still). However, while it can be interesting to ponder such matters, when I go to the slopes i prefer to fly and I'm sure you do too!

[EI1638]

Lets leave it there. My antenna theory is very (very) rusty and was never used in anger (except during the relevant exam).

Still, the human body is not a great conductor and weirdly, neither is the ground (it helps that there's a lot of it though), so if the shoes were conductive(ish) there would be a kind of reflector behind the antenna.
Remember that some antennae are designed with a built in ground plane to shape/redirect the radiation pattern.

Having said all of that you're right though. When I'm flying I'm usually too busy trying to keep my airplanes out of the ground (and trees...) and away from everybody elses airplanes, not wondering about this stuff.
And besides, my models would probably be invisible long before I reached the extremes of the default theoretical radiation pattern anyway, never mind seeing if it was extended in any direction.

Looking back over this dicussion I'm reminded of a VHF radio operators course I did many years ago. One of the participants (not me)  insisted on stating that at VHF signals would go 'over the horizon' Whilst in the extremes of Maxwells Equations he may have been technically correct, for all practical purposes they don't, which was all that was important to everybody else on the course.

I'll shut up now and let people get back to posting about A and B certs. 

[Happy Days]

Er,..... I am a little confused Chris. (A state of mind that is quite common for an old git like me.)

On the 8th Feb you asked the question, Quote; "Keith, you mean like my satellite dish or the Yagi Uda we used to watch TV with?"

Now it becomes apparent that you not only have knowledge of, but indeed have passed an exam on, RF antennas. So by implication you must have known the answer to your own question. So why ask in the first place?

[EI1638]

Keith,

You started the rot!

I asked  a simple question about an acronym I'd not come across before and you introduced antennae with gain!
I thought you'd pick up me having named the yagi as for most people it's a TV aerial. Tongue firmly in cheek.

Not that any of it makes any difference when we're struggling with the sticks, or the pinkies are freezing off on the big L.

I still hate acronyms though

Chris

[Happy Days]

Thanks John. Now I know.

Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power transmitted from a theoretical half-wave dipole antenna. It is differentiated from effective (or equivalent) isotropic radiated power (EIRP) mainly by use of relative antenna gain instead of absolute gain in the calculation. In the case of ERP, antenna gain is calculated as compared to the maximum directivity of a half-wave dipole antenna, whereas EIRP is calculated using antenna gain referenced to an ideal isotropic radiator, otherwise known as "absolute" gain. The term "antenna gain" is assumed to be absolute (referenced to isotropic) unless specifically stated to be relative. The gain is then multiplied by the power actually accepted by the antenna to result in the actual ERP value (or EIRP). Power losses which occur prior to the antenna, e.g., in the transmission line or from inefficiency in the generator itself are therefore not included in the calculation of ERP or EIRP.

courtesy of wikipedia...

[Happy Days]

Chris,

I feel we should stop any further forum exchanges on matters of R.F. and allow this thread to return to it's original topic of A & B Certs. Consequently this will be my final post on the subject.

If you have any genuine questions you'd like to ask me in respect of Radio Frequency please feel free to contact me by Personal Message.


Keith

[Fred]

Keith, do you want me to keep your RF conversation in another thread? And you can continue there instead of privately?

I read the posts, and find them very interesting Would be a shame to "lose" all these informations

[Happy Days]

  Hi Fred
I think there are two points. One is the fact that RF is certainly outside the remit of this thread.
Secondly, I'm getting the distinct feeling that Chris and I may have some 'crossed wires' that have very little to do with radio waves and are of a somewhat more personal nature.

In my experience, if these wires are ever to become 'uncrossed' it's more likely to happen out of the public gaze.

But thanks for your offer Fred

Keith

[EI1638]

I've stepped back from this one Fred.

I'm easy either way with how you want to handle it.

[Flamingo Flier]

Been busy so it been a while since I logged on and I have only this evening read Appendix L for the A/B cert tests.

I know i'm weird and all that but..............

How can any question relating to a propellor / motor / engine be applicable to a glider?

A glider has none of these things. A plane with power is a power plane - the clue is in the name. Good luck explaining to the judge that the two wheeled device you were riding is a bicycle even though it had an engine.

JIM

PS I've been flying gliders for about 27 years and have never flown a plane with an engine. A new guy arrived with an electric model one day and needed someone to test fly it and help him through his first few flights. We, and he, had a couple of satisfactory flights with it - maybe half an hour or so. Never plugged the motor in however..........
I wonder if he charged the ballast before he flew it again!
   

[Flamingo Flier]

Hmmmm
Just realised my bicycle analogy was pretty bad. I suppose some electric bicycles are still called bicycles. I should have read it over before I posted.

A powered plane is still a power plane however
Jim

[Happy Days]

Ha! Don't they say that "If it looks like a duck, and it quacks like a duck, then it is a duck."

I'm not so sure the world is quite as black & white as that Jim.

I'm thinking that as Powered models are normally flown with some degree of power applied virtually all of their flight time, and Powered Gliders only use their prop thrust to obtain height and spend the rest of their flight time gliding, I'd say a hybrid is a glider more than it's a powered model. Although I take your point that hybrids do have a motor & prop their aspect ratio and small flight battery lend the them towards gliding far more than powered flight wouldn't you say?

Keith

[Flamingo Flier]

Hi Keith,
Good to hear your voice.

Yes I agree that as I get older many things that were black and white are now many shades of grey. As I started my working life I knew the right way to do things. 30 or 40 years later and some of these early jobs no longer pleased me. I could see things that could have been done better.  White was now grey. Black was also grey as I could see some merit in the wrong way of doing things. It was time to retire. (That is why the best soldiers are very young - they know they are right and do not see the other side of the argument)

But life is better when things are black and white and many things are clear cut. Pregnancy for example - or death!

In my eyes a plane is also one thing or the other. A plane with power is a powered plane.

I hope to see you next weekend.

JIM

PS There is no value judgement whatsoever in my differentiation between powered and unpowered