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Ballerina by EarlyBird


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Peter

I read one of your posts where you cut a ventilation hole in front of the pilot, so I did the same even though I thought the reason being was to keep the pilots feet warm. Ahh so now I can stop searching for a pilot with feet.

I am feeling happy today can you tell? The medication must be working!

Steve

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All looking good Steve, good to see you having fun!

Regarding cooling, Peter is quite right. Wind (and cooling draught is only wind, missus!) relies on a difference in pressure. To get a draught from the front of the model to the rear, the pressure must be higher in front than behind. To achieve this, you need a bigger outlet than inlet. Otherwise, not much happens, apart from drag.

It's also worth considering what happens to the moving air inside the model. It needs to go past the hot bits and the tendency is to take the shortest and easiest path. Creating what appears to be small gaps is beneficial, because to maintain constant pressure, if volume is decreased, velocity must increase (we know what happens when you put your thumb over the end of a hose). So don't be afraid to add baffles.

There are some great shots of really effective baffling on one of the Laser threads. I think it's Jon's Hurricane. Jon has baffled the engine very tightly, and he knows a huge amount about cooling!

I have done similar for my Tempest. The design has a massive chin scoop, that would have been useless for cooling! The exhaust area is much smaller, and the path to it was direct. Instead I am using the cutout behind the spinner and creating an air path around the battery and ESC to exit in front of the leading edge.

Physics lesson over, as you were...

G

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Thanks G

Yes it is all about having fun.

Physics lessons! I remember Bernoulli. At college my favorite subject was hydraulics laminar and turbulent flow come to mind.

How can that possibly have been fifty years ago.

I wasted forty eight years by starting RC only two years ago.

Steve

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My method is measure, measure again, cut try then start again. smiley

That way I get more practice.

Can I ask because there are some things I do not understand why OHmen and not Ohmen for one and what does IIRC mean?

Spell check says there is no H in omen hmmm I get it now.

Steve

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Oh yes.WE all "cut and try",usually a few times!!

the "OHmen" is my lousy typing!

Yes,you got the "Ohm" part of it. Several non modellers and one or two modellers didn't get it.

I also once did a plan called the Ohmsick Angel"

I don't use IIRC but I think it means "If I ReCall" but I could be wrong there. May be I should use "ISTR" just to baffle a few!!!

(I seem to remember)

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Posted by Bob Cotsford on 15/07/2020 14:36:15:

iirc - If I Recall Correctly thumbs up

Nothing more satisfying than taking a razor plane to an unsightly lump of balsa and ending up with a streamlined, elegant shape. Oh yes, and a bin full or two of shavings!

I see what you mean definitely satisfying even though it is hardly a bin full of shavings. Just a bin and some shavings.

dscn0334.jpg

Next stage was to sand so I went outside in the warm sun and found it very pleasant, a warm glow inside as well as on the outside plus some free Vitamin D.

dscn0335.jpg

More work to do of course. I will pinch in the cheeks below the spinner and turn the vent slot into a smile. I like happy planessmiley

Steve

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I was looking at this this morning.

dscn0336.jpg

and thinking about cooling. This is my first ventilated spinner, well first of any kind. What struck me was there looks to be a large air gap around the spinner and more than the slot. So the questions. Is the slot necessary? Does this style of spinner provide more than enough ventilation?

Steve

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I would say that your ply nose ring is restricting the flow throught the spinner. I would be tempted to open out the hole a bit just to make sure that there is plenty of through flow.

Too much cooling is far better than not enough.

At the moment I am seriously considering a very non scale hole in the nose of my new model and also flying without the spinner is it restricts the scale intake.

With a 1 3/4" spinner there is only a narrow intake round the spinner.

025.jpg

Edited By Peter Miller on 17/07/2020 08:10:46

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Peter

'I would say that your ply nose ring is restricting the flow through the spinner. I would be tempted to open out the hole a bit just to make sure that there is plenty of through flow.'

That's a good idea and easily done.

'Too much cooling is far better than not enough.'

It sounds like we share a belts and braces approach, as many do, which is exactly why I included the slot. Unfortunately I have come across instances where this approach leads to overengineering and causes a bigger problem, obviously not the case here.

While typing I thought "so opening up the nose ring increases the air flow so there must be a point at which enough air flow through the spinner makes the slot unnecessary'.

Well in this case it has both and that is how it will stay.

So anybody reading this take note I do not know what I am doing and please do not copy me. smiley

Thanks Peter.

Steve

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You sound like me!!

I am looking at mine and thinking the intake round the spinner or prop shaft if I leavethe spinner off will cool the motor.

Shall I have another hole (non scale) lower down to put a direct flow over the the ESC and from there up into the battery box?

I think that I will because I will be turning a bigger prop which means more load and more heat,

The trouble is that I know what I am doing with ic engines. Electric is a black art!!

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I don't think you'll have a problem. The hole beneath the prop looks plenty big enough.

My cowled electrics have one hole at the front by the motor. The hole is not usually very big at all. The ESC just goes inside the fuselage, in the path of the cooling airflow, just behind the motor.

As long as the air has to go past both things, it'll be ok.

Just make sure the "out" hole will actually suck out the air that goes into the "in" hole. Ramps or lips might be needed. Behind the wing seems to be a good place to put the hole. Although I like the cockpit idea.

This one has narrow "in" slots either side of the spinner:

20181217_230453.jpg

and the out hole is about 1.5" square, sits behind the wing, this one needed a ramp to encourage things along a bit:

20190131_220416.jpg

This is again, narrow slots either side of the spinner. The spinner isn't fitted here, but the diameter matches the height of the cowl front, and it leaves a fairly narrow intake:

tmp_32254-20180221_121320800200648.jpg

and again, another 1.5" ish hole, behind the wing:

tmp_17737-20180224_224849800200648.jpg

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Could you make the hole an inverted tear drop?

I have had two years of electric and some people were appalled by my approach. Why did you chose that motor?

Because I had it.

How did you chose the prop size?

Well I had it and it looked about right.

A long winded one sided discussion follows in which watt meters, temperature sensor and telemetry are mentioned.

It goes right over my head or in one ear and out the other.

So now, and I hope you do not mind, I say I ring George at 4-Max he tells me what I need and if I have not got it I buy it.

And where did I learn that????

Steve

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Posted by EarlyBird on 17/07/2020 10:48:05:

rs, temperature sensor and telemetry are mentioned.

It goes right over my head or in one ear and out the other.

So now, and I hope you do not mind, I say I ring George at 4-Max he tells me what I need and if I have not got it I buy it.

And where did I learn that????

Steve

You and me both Steve.

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NigelR

Yes I have made similar comparisons. Take the WOT4 Foam-e for example I was surprised at how little ventilation it has then stuff an esc and battery in a very tight space. It has no problem.

We have all seen, I assume, the esc fixed to the outside of the fuselage for maximum cooling but it does look ugly IMO.

Yes placing the esc in the path of the air flow is what I have learned to do, once I stopped putting the esc on the outside, I have found that below the motor mount or battery tray to be a good place.

I like the plate on the exit to increase the Venturi effect. I will incorporate that on the next build that is if you have not patterned it. smiley

Hm just checked Venturi and I am not sure that is correct.

Thanks

Steve

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