Forum for aerodynamics, physics, engineering?

[npomeroy]

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?

[Luvmyhelis]

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.

[TowPilot]

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

[npomeroy]

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.

[Commodore8888]

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)

[TowPilot]

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). :thumbup:

Mike

[extrapilot]

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.

[npomeroy]

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.

[WillJames]

If you guys decide you want the forum, I can make it for you no problem.

[ahahn]

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:thumbup:

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.:face

[nirtza79]

+1:thumbup:

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.:face

+1

It will be a second home for me!

[Bikersurgeon]

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

[koppterx]

this has been tried elsehwhere with less than ideal results. imagine a hospital full of first and second year med students.

[npomeroy]

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.

[Carapau]

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.

[npomeroy]

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... :lol:"

[Mike2112]

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 :clap

[extrapilot]

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.

[laminarjack]

It sounds like a good idea - a place to relax and just get weird.

[npomeroy]

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.

[npomeroy]

...from the 12th grade (I^2R, V=IR) stuff: ....

V = IR doesn't mean much with brushless motors I agree.


Not familiar with your education system. Our final year high school physics students (17 yr olds) are into more sophisitcated energy principles including induction effects.

[Fredo0709]

I'm new to the forum and new to this hobby. I'm actually hoping to use RC helicopters as a testbed for experiments relating to my doctorate thesis. I also work as a full-time engineer at a helicopter company.

A forum that's focused on the science/physics/engineering would go a long way in educating other members as well as spread knowledge around. As long as we speak with open minds and clarify points when we explain, this forum will be productive. Otherwise, it's people disrespecting each other and egos get in the way.

The previous posts between the physicist and the engineer I found to be very interesting. I believe it boils down to difference of explanations when simplying assumptions are made. Are we talking about real-life observations (which requires a lot more complexities to factor in) or are we going to generalize and say, "Given this variable constant, this is what we observe," or "this is what we can say."

I hope to contribute and learn a lot if this forum is started.

Austin

[GoFastMike]

I would definitely be interested in a purely technical forum, there's a ton of very cool physics, math, engineering with flight in general and heli's in particular. Discussing that stuff as they relate to our birds would be great fun...

I also agree that we have to try to keep it objective. It would be nice if we could develop some fundamental understanding of how current real world models and components alter/improve flight behavior; how headspeed relates to blade selection relates to servos relates to all up weight... etc. So when someone says I have a 450 with standard bits we can say you should have these kind of flight characteristics.

As for context... well, the more variables the better but we should try to remain practical, not everyone is going to know barometric pressure at 200 ft agl or what the Reynolds number on their blades is, but we can work out the basics I think. Sounds like great fun.

[soko]

+1 for such a forum guys

Soko

[npomeroy]

I'm new to the forum and new to this hobby. I'm actually hoping to use RC helicopters as a testbed for experiments relating to my doctorate thesis. I also work as a full-time engineer at a helicopter company.

A forum that's focused on the science/physics/engineering would go a long way in educating other members as well as spread knowledge around. As long as we speak with open minds and clarify points when we explain, this forum will be productive. Otherwise, it's people disrespecting each other and egos get in the way.

The previous posts between the physicist and the engineer I found to be very interesting. I believe it boils down to difference of explanations when simplying assumptions are made. Are we talking about real-life observations (which requires a lot more complexities to factor in) or are we going to generalize and say, "Given this variable constant, this is what we observe," or "this is what we can say."

I hope to contribute and learn a lot if this forum is started.

Austin

Thanks for the support Austin, and others.

Yeah, the scientist/engineer approaches tend to be different, and both have their places. My PhD was in bumblebee biology - now there's a field where the complexity of factors may make people think the applicablity of any controlled experiments would be buried under variables and "noise". But my supervisor persuaded me that unless you simplify things down to a single experimental variable you can you go round in circles complaining it's all too complicated. By doing controlled experiments I was able to nail down some effects that over time with further study and practical trials could lead to practical applications (bumblebees are a multimillion dollar industry used for pollination in greenhouses - nothing to do with normal beekeeping).

I would like to see some people post actual data, and if there was an audience for it it might stimulate me to do more with my science students, and post the results. Analysis of hover power consumption w.r.t. load weight, related to battery mass comes to mind. It is an interesting optimisation problem for scale builders who already have extra ballast on their helis.