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Old 04-16-2012, 03:48 PM   #1
npomeroy
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Default Forum for aerodynamics, physics, engineering?

This is a great site with forums for lots of topics, especially equipment brands, but sometimes general issues come up that are in the aerodynamics, physics and perhaps "engineering" realm. I usually see them in the main forum and the thread gets diluted with lots of posts that seem to miss the original technical point. One poster recently said (in the thread about on-board electricity generation) that perhaps RC Groups might be a better place to look for support. But for myself, I have little enough time to use Helifreak and don't look at any others unless specifically directed to them.

So, users and moderators: Should these sort of more scientific topics continue in the main forum or is there case for yet another sub forum where we nerds can really get our teeth into that sort of stuff?
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Old 04-16-2012, 06:14 PM   #2
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I usually find that the guys that are interested will chime in. No matter where the subject is posted. If the subject hits home, educated individuals will hop on board. Both good and bad. And like all thread they tend to drift a little.

It is true however that the deeper engineering subjects get more response over at Rc groups. There are several committed threads there where we have created and burned our own chips, gyros, esc's, ect ect ect. And educated sane avionic mechanical engineering is discussed in much greater detail. I even have Nasa engineers posting on one thread.

But I still prefer this forum, and I honestly don't see a need for a separate section. If the subject bears merit. Guys will post no matter where it is found.
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Old 04-16-2012, 10:50 PM   #3
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There already is a forum for the DIY, engineering types.

http://www.helifreak.com/forumdisplay.php?f=279


Though what I've followed are threads which become incredibly technical specific to a particular heli. The most recent example I've been following is the ongoing work on the mCP X here:
http://www.helifreak.com/showthread.php?t=357151

So while there might not be much activity in the DIY forum which would cover generic topics, here are in-depth technical threads in progress.

Mike
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Old 04-16-2012, 11:09 PM   #4
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Quote:
Originally Posted by TowPilot View Post
There already is a forum for the DIY, engineering types.

http://www.helifreak.com/forumdisplay.php?f=279

Though what I've followed are threads which become incredibly technical specific to a particular heli. The most recent example I've been following is the ongoing work on the mCP X here:
http://www.helifreak.com/showthread.php?t=357151

So while there might not be much activity in the DIY forum which would cover generic topics, here are in-depth technical threads in progress.

Mike
OK Mike, I hadn't taken notice of the DIY forum. The sort of thing I was meaning was more generic topics that involved aerodynamic and energy principles. There are quite a lot of discussions about headspeed, ESC throttle %, and the recent inferno about on-board electricity generation. Fortunately there are so many knowledgeable people here that even when I post on the Scale or Skookum forums I can usually get some genuinely knowledgable replies.
I guess I just get frustrated when a query generates a whole lot of rule-of-thumb vague stuff with very few hard facts or data.
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Old 04-17-2012, 12:45 AM   #5
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That MCPX thread is going pretty deep into what looks like Atmega code/flashing at first, then moving to Silabs stuff later on to keep up with gov cycles. Very cool stuff.

What really gets cooking is the guy who dumped the 3n1 all together (feeling that now with the less awesome V2 boards from horizon) and put a stripped down beastX/dual ESC on his heli with a custom frame ALL while staying pretty light. I think he's going to flash the gov enabled code for the ESCs from that first listed mcpx post. World's most badass mcpx? (Also most expensive haha)
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Old 04-17-2012, 12:46 AM   #6
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Quote:
Originally Posted by npomeroy View Post
OK Mike, I hadn't taken notice of the DIY forum. The sort of thing I was meaning was more generic topics that involved aerodynamic and energy principles. There are quite a lot of discussions about headspeed, ESC throttle %, and the recent inferno about on-board electricity generation. Fortunately there are so many knowledgeable people here that even when I post on the Scale or Skookum forums I can usually get some genuinely knowledgable replies.
I guess I just get frustrated when a query generates a whole lot of rule-of-thumb vague stuff with very few hard facts or data.
People with a guess won't refrain from posting in amongst those with the engineering degrees That's just life on the net and incurs the need of the OP to sift the wheat from the chaff.

It's the world we live in. It might be different on Mars but we won't know until we put humans up there. So far the bots rule (when they land safely).

Mike
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Old 04-17-2012, 12:57 AM   #7
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Hi Nelson

Just on the aero/engineering side of things-

It is one thing to ask a question that is specific to a small domain (i.e. what is the coefficient of drag on canopy X mounted on airframe Y given flow vector Z?). But a problem in our hobby is that the domain is huge; there is no single design point for a helicopter, or for a subsystem. And that is, to borrow a phrase, an ‘inconvenient truth’ for people more interested in being heard than in learning. What is the ‘best’ rotor blade? What is the ‘best’ canopy profile, etc. It is absurd.

Additionally, very few people have any capability to objectively measure a sub-system. How would someone without a REAL data acquisition system (and analysis software) gain insight, when many performance deltas are below the noise levels of uncontrolled variables? So it degenerates into the ‘I think X is better’, which is, to the core of your post, what you don’t want to see; few hard facts- or much worse in my view- invalid data, presented as fact.

Tow’s comment on wheat/chaff is the catch-22; you cannot make that determination if you don’t know. Facts are not subject to consensus; at one time the consensus was that the Earth was flat, etc.
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Old 04-17-2012, 03:25 AM   #8
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Quote:
Originally Posted by extrapilot View Post
Hi Nelson

Just on the aero/engineering side of things-

It is one thing to ask a question that is specific to a small domain (i.e. what is the coefficient of drag on canopy X mounted on airframe Y given flow vector Z?). But a problem in our hobby is that the domain is huge; there is no single design point for a helicopter, or for a subsystem. And that is, to borrow a phrase, an ‘inconvenient truth’ for people more interested in being heard than in learning. What is the ‘best’ rotor blade? What is the ‘best’ canopy profile, etc. It is absurd.

Additionally, very few people have any capability to objectively measure a sub-system. How would someone without a REAL data acquisition system (and analysis software) gain insight, when many performance deltas are below the noise levels of uncontrolled variables? So it degenerates into the ‘I think X is better’, which is, to the core of your post, what you don’t want to see; few hard facts- or much worse in my view- invalid data, presented as fact.

Tow’s comment on wheat/chaff is the catch-22; you cannot make that determination if you don’t know. Facts are not subject to consensus; at one time the consensus was that the Earth was flat, etc.
I take your points extrapilot, but it does not need to be that hard. People endlessly speculate about headspeeds and flight times and trot out the "ESCs are most efficient at 100%" argument. But with a simple recognition of heat wattages you can literally feel that ESC's seldom disippate anything more than a tiny % of the total power. And simple measurements of mean amp draw per minute (calculated from flight times and recharge mAh) consistently in my experience show less draw at lower throttle settings. Yes I know it's complicated by pinions etc.
Anyway I'm raving. I just hope for better science education.
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Old 04-17-2012, 05:58 AM   #9
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If you guys decide you want the forum, I can make it for you no problem.
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Old 04-17-2012, 10:41 AM   #10
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Quote:
Originally Posted by npomeroy View Post
I take your points extrapilot, but it does not need to be that hard. People endlessly speculate about headspeeds and flight times and trot out the "ESCs are most efficient at 100%" argument. But with a simple recognition of heat wattages you can literally feel that ESC's seldom disippate anything more than a tiny % of the total power. And simple measurements of mean amp draw per minute (calculated from flight times and recharge mAh) consistently in my experience show less draw at lower throttle settings. Yes I know it's complicated by pinions etc.
Anyway I'm raving. I just hope for better science education.
+1

I also vote for the forum. There really is a lot of misconception about electric power systems.

Not that this new forum will ever clear that up.
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Old 04-17-2012, 11:14 AM   #11
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Quote:
Originally Posted by ahahn View Post
+1

I also vote for the forum. There really is a lot of misconception about electric power systems.

Not that this new forum will ever clear that up.
+1

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Old 04-17-2012, 11:27 AM   #12
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A forum to discuss established fact/controlled repeatable experimental outcomes/science/applied science/engineering data, void of anecdotal evidence or even worse-speculation and heated opinion, would be great...and likely elusive. But I'd vote YEA
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Old 04-17-2012, 12:41 PM   #13
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this has been tried elsehwhere with less than ideal results. imagine a hospital full of first and second year med students.
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Old 04-17-2012, 02:43 PM   #14
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Hmmmm. I can see the point that a new forum won't prevent misinformed opinionated posts, but if it has a scientific/engineering title the casual H'freak probably wouldn't go there much. For example I always look at the main forum plus about 3 others in my line of interest. The title could be a good question - I'm sure we all have different ideas on what we'd like to see in it. But since I opened the discussion, my thought is "Physics of flight and power systems". That distinguishes it from the DIY forum. Any other thoughts?

If I may tell story: A psychologist, engineer and physicist were invited to solve a problem of sick cows on a farm.
-The psychologist said "The barn is the wrong colour and needs to be painted pastel blue"
- The engineer said "First, I must measure the width of the stalls".
- The physicist said "there are too many factors here: First, assume a cow is a sphere."

The point here is that as extrapilot said there are often too many factors for people to get the answer they want on helicopters (the engineer's view). But the physicist in me says "OK, all other things staying unchanged, what happens if I alter this factor and measure that?" Thats the experimental approach. The other thing is that there fairly straightforward concepts, especially in energy/power/electricity, (at about school grade 12 level - where I teach anyway) that are misunderstood by most, and appy beautifully to helicopter power.

Excuse the rave - I wanted to give a picture of where I was coming from.
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Old 04-17-2012, 05:03 PM   #15
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I would love to hear some more fact based discussion on various subjects, let's get this forum made. I understand it will be hard to control properly but at least it gives a good place to start and if it better educates just a few soles on HF (of which I hope to be one), then this surely has to be a positive move.
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Old 04-17-2012, 05:26 PM   #16
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How about "RC helicopter physics and engineering" as a title.

Edit
Ahem.. maybe I should delete the quote in my signature.
Reminds me of a poster I once saw with a guy saying "I'm a bit of a bullshitter myself but do like to listen to a real expert - please continue... "
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Old 04-17-2012, 06:08 PM   #17
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That is a great idea...HELL YES!!! I visit 4-5 forums regularly, and 2-4 others "here and there". I would alway visit a physics forum...not that I would understand it
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Old 04-17-2012, 06:09 PM   #18
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Quote:
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The point here is that as extrapilot said there are often too many factors for people to get the answer they want on helicopters (the engineer's view). But the physicist in me says "OK, all other things staying unchanged, what happens if I alter this factor and measure that?" Thats the experimental approach. The other thing is that there fairly straightforward concepts, especially in energy/power/electricity, (at about school grade 12 level - where I teach anyway) that are misunderstood by most, and appy beautifully to helicopter power.

We cannot isolate systems in our application and hope to have any meaningful understanding of in-flight performance. The physicist in you should know- ‘all other things staying unchanged’ is simply not achievable given the context. In fact, by definition, you almost have to change other things to evaluate.

Example- rotor blades. Change the blades, test, repeat, right? Wrong. Blades have different Lock numbers, which affects phasing. Blades have different spanwise and chordwise CG, different chord, different mechanical properties. If you want to evaluate their maximum performance, you have to retune the machine to best leverage them.

Even for your example- I would challenge the statement that something like power systems/electricity is straightforward in the way you imply. A very simple derivation from the 12th grade (I^2R, V=IR) stuff: for a given output power, resistive losses are always lower for higher-voltage systems.

But, you have to capture ALL the factors in question- including motor reactance, FET RdsOn, slew rate (time in linear mode), switching frequency, source resistance/reactance, etc. And, some of this is specific to the flight regime. So the context becomes much more specific- which pack, which ESC, what ESC config, which motor, etc…

So, if this is the sort of information you think should be relayed in a subforum, great- we all have a LOT to learn from each other’s core areas of expertise. But if you hope to see universals, Id suggest few exist unless the domain is very limited.
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Old 04-17-2012, 06:28 PM   #19
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It sounds like a good idea - a place to relax and just get weird.
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Old 04-17-2012, 06:42 PM   #20
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Quote:
Originally Posted by extrapilot View Post
We cannot isolate systems in our application and hope to have any meaningful understanding of in-flight performance. The physicist in you should know- ‘all other things staying unchanged’ is simply not achievable given the context. In fact, by definition, you almost have to change other things to evaluate....
I respect your points, but let me elaborate on two examples:

Flight time vs Throttle setting (and hence HS:pitch relationship). Anybody can run a series of different flat line TCs and measure the power consumption. (Been done: flight duration increased with lower HS) Sure there are variables which complicate the interpretation such as the stability desired, and whether different gearing would be better. The result of this will indeed show for that helicopter and its mechanics/electrics what the pilot can expect with varied throttle settings.

ESC efficiency: People are often urged to use 100% throttle "because ESCs are more efficient there". You don't need to get into the complexity of zero crossovers, hysteresis, resistive losses, to measure the power consumption of the system and relate that to the flight power achieved.

There are often science principles that can indeed act as an intelligent starting point.
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