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  #16  
Old 05-22-2007, 08:00 PM
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It might have distorted some in my screen shot but the top profile is an exact mirror image of the bottom profile.
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  #17  
Old 05-23-2007, 03:04 AM
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Quote:
Originally Posted by TMann View Post
I may be wrong but I don't recall seeing a 'flat top' airfoil on any aircraft.
The Berkut strakes have cambered upper strake skins but I'll bet more "wild ass guess" led to that mod than number crunching.

Dave Ronneberg might've figured that the stall AOA of a "barn door" is lower than that of a cambered airfoil... so why not make the strakes less "barn door"'-ish?

D
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  #18  
Old 05-23-2007, 09:37 AM
Wayne Hicks Wayne Hicks is offline
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In reality, by changing this to a symetrical airfoil, you increase the volume of the strake thus increase the fuel capacity.

------> There are easier ways to increase fuel capacity. Build a sump tank inside the fuselage, or simply add another bulkhead inboard of the inboard strake rib and turn baggage storage area into fuel volume. None of these muck with the plane's aerodynamics.
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  #19  
Old 05-23-2007, 10:14 AM
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Wayne.....thanks for your input.
The objective here is not to enlarge the fuel capacity but to improve the airflow over the strakes.
I'm using the Infinity R/G system so the area behind the rear seat will be converted to a sump/tank which will more than offset any loss of capacity due to the gear storage in the strake.

What I am doing here is taking a 65-210 airfoil, mirroring the top half of the profile to create a symetrical airfoil.
This airfoil design seems to meet my criteria for a low profile while still giving me the thickness required to mate up nicely with the centersection spar.
The additional fuel capacity is just a consequence of the curve of the profile.
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  #20  
Old 05-23-2007, 12:57 PM
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Quote:
Originally Posted by --D-- View Post
The Berkut strakes have cambered upper strake skins but I'll bet more "wild ass guess" led to that mod than number crunching.

Dave Ronneberg might've figured...

D
You guys are a riot with your regard to professional people producing a design that is MEANT for PUBLIC consumption.
Just a riot.
I've not heard anything from Mr. Ronn..but from Mr. Riley's posts here he appears to be anything but a WAG guy...
I dunno..maybe you ARE doing more work on YOUR 'one-off' homebuilt than those guys DID on their 235 knot high perf speeder.
Don't know.
Ya got me.
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  #21  
Old 05-23-2007, 01:43 PM
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Quote:
Originally Posted by Marc Zeitlin View Post
You cannot tell whether flow is laminar or turbulent by looking at tufts - all you can tell is whether it's attached.
Well, that is very well theroretically said. What is seems to leave out is that attached flow that is over a layer of micro turbulence is very undraggy compared to turbulence.

My object is to take as much of the flow as possible that is not laminar OR "attached turbulent" and make it so.

My other personal object is to reduce cooling drag, which i have heard accounts for as much as 30% of all drag, and reduce it as much as possible.

Some airplane designers and some airplane modifiers are highly educated in that specific area, most do not seem to be. They learn some simple rules to modify and design by and then go for it.

Some of both camp die trying.

The pattern seems to be to take an educated guess and see what really happens.
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  #22  
Old 05-23-2007, 01:57 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by TMann View Post
The objective here is not to enlarge the fuel capacity but to improve the airflow over the strakes.
I guess I'm at a loss to understand what you think needs improvement, or what you believe will change when you use the airfoils you're planning on using.

I've got the Aerocad strakes on my COZY MKIV. They're slightly more rounded, both top and bottom, than the plans COZY strakes. Not a big difference, but enough to notice, and enough to get about 3 gallons more per side fuel. Now, AFAICT, there's no performance difference between my plane and any other COZY, or if there is, there's no way that I can attribute it to the shape of the strakes.
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  #23  
Old 05-23-2007, 02:00 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Dust View Post
Well, that is very well theroretically said. What is seems to leave out is that attached flow that is over a layer of micro turbulence is very undraggy compared to turbulence.
See the last paragraph of message #12 in this thread.
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  #24  
Old 05-23-2007, 02:18 PM
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Quote:
I get the impression that you've done some cursory reading of aerodynamic theory, not understood it very well, and then attempted to redesign the aircraft without understanding the ramifications of the modifications you're proposing. I will say, you're in some good company here.
Yeah....we all read that Marc.
Yes....we know you work at Scaled Composites.
...and we all know that you graduated from MIT...

The problem with the feedback you provide is that it is usually so heavily laced with condescending attitude and sarcasm that it makes it very difficult to pick through it to find any relevancy. I think you're a smart guy but not too sharp with your communication skills.

The quote (above) that you seem so proud of speaks volumes of your abilty to interface with others both on and off the forum pages.
.......and that's sad, because you could have had some important things to add here.

yeah....I'm in some good company here..........too bad you can't relate.
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  #25  
Old 05-23-2007, 02:21 PM
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Well, saw that and if you are saying that what you said is what i said then, good to go
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  #26  
Old 05-23-2007, 04:04 PM
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We're building derivatives of an evolution of an amazing airplane.

Some parts are acknowledged by all to be critical and no one (or almost no one) deviates from plans for them.

Some other parts are less critical.

The airfoil of a strake seems to be one of the (much) less critical parts of the airplane. It mostly seems to be the shape that is easiest to make that encloses some critical parts of the airplane, the spar and fuel tanks.

I for one don't mind the sharp tones I see sometimes here, I've been on the receiving end of it a couple of times. It seems to stem from a desire to teach quickly and concisely, not from a desire to be abusive. After perusing the different forums for a while it looks like some folks have been conditioned to automatically respond with stronger, shorter, and possibly rude tone (if it were in a formal dinner environment, for instance) because when technically correct answers were given they were disputed by people with less skill and experience.

I'd rather keep the knowledge and skills around and adjust my expectations for how I'm responded to.

Another thing I keep reminding myself is that an 8 hour (maybe more) a day full time job doesn't leave much time/energy left over to look at my possibly boneheaded suggestions and respond. I appreciate the time and energy put in to look at all the posts and respond.

Last edited by cptomes : 05-23-2007 at 04:16 PM.
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  #27  
Old 05-23-2007, 04:35 PM
Marc Zeitlin Marc Zeitlin is offline
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Originally Posted by TMann View Post
Yeah....we all read that Marc.
Yes....we know you work at Scaled Composites.
...and we all know that you graduated from MIT...
None of which is relevant here, and none of which has ever been brought up by me. My explanations stand on their own, and I provide references for further review to almost all of what I put forward. I NEVER rely on "proof by authority".

Quote:
Originally Posted by TMann View Post
The problem with the feedback you provide is that it is usually so heavily laced with condescending attitude and sarcasm that it makes it very difficult to pick through it to find any relevancy. I think you're a smart guy but not too sharp with your communication skills.
Actually, my communication skills are excellent. What I'm not good at is spoon feeding people who feel like they're owed something because they've learned to parrot some buzzwords, but don't think it's necessary to put in the time it takes to actually learn something (or, maybe, don't have the capacity to do so).

After many years of dealing with people who either can't or refuse to learn/understand what they're being told, think that because they've studied something for 10 minutes that they're now experts in it (and that the REAL experts all have a vested interest in keeping the newbies from proving to the world just how much more they understand than the experts do), being patient with getting the SAME questions over and over and over and over again is difficult.

You're in software, IIRC. If I told you that I was planning to use some sort of sort algorithm for a certain task, said that I was doing so to achieve <X>, and then asked you a question regarding sort algorithms that indicated that I didn't have the slightest clue which one was good for what purpose or why, and then repeatedly argued with you when you explained what my misunderstanding of sort algorithms was (and then did this over and over again, for database queries, file access, XML parsing, etc.), how much patience do you think you'd retain for a person who repeatedly did this over the course of years?

Quote:
Originally Posted by TMann View Post
The quote (above) that you seem so proud of speaks volumes of your abilty to interface with others both on and off the forum pages.
Feel free to contact folks that I've worked with over the last 25 years who will contradict your impressions. Present something more than hand-waving and buzzwords, and you'll get a different response.

Quote:
Originally Posted by TMann View Post
.......and that's sad, because you could have had some important things to add here.
If you could articulate your question in a way that indicated the barest minimum of understanding, I might be able to understand what information you're looking for. I asked over and over again "what are you trying to achieve". All you could state was "laminar flow".

When you posit that "I know what I'm doing, I'm using <X> airfoil to make <something> better", and then articulate a complete misunderstanding of the underlying basis of your decision making, other than pointing out the error of your ways, I'm not sure what you'd like added.

Quote:
Originally Posted by TMann View Post
yeah....I'm in some good company here..........too bad you can't relate.
Believe me, I am extremely pleased that I cannot relate to the people to whom you're referring.

I don't think you can imagine the low standings in which SOME of the goings on here are viewed by folks that understand aircraft, and I'm NOT referring to me. There are many extremely knowledgeable folks who peruse this (and other) fora who refrain from participating because they have long since learned what I apparently have not, regarding wrestling with a pig.

I've spent the past three weeks watching the builders pour concrete for the house we're building. I don't know jackshit about concrete, and I KNOW that I don't know jackshit about concrete. The concrete guy has been nice enough to entertain my questions about why they're doing what they're doing, what would happen if they did things differently, and has explained a lot to me. I've learned a lot. But 2 hours worth of conversations with a concrete guy who's been doing it for 17 years and a couple hours of reading on the web about concrete do not make me a concrete expert.

If I walked up to Juan and said "I'm going to pour some concrete like <this> in order to achieve <the other>", and Juan explained why my thesis of concrete usage was flawed, but I argued with him about it, continuing to indicate that I didn't understand concrete in the least, I'd expect to get smacked upside the head.

No different here.
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  #28  
Old 05-23-2007, 05:18 PM
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Quote:
Originally Posted by Marc Zeitlin View Post
being patient with getting the SAME questions over and over and over and over again is difficult.
That, my good sir, is what the internet is all about, the newby, the eagerness, the fresh ideas (to them), that is the fun of the internet.

to keep it alive and not squash it
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  #29  
Old 05-23-2007, 06:54 PM
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The recurring theme in your post here seems to center around the perception that I am arguing with you.
It is apparent that there is a communication problem in explaining my plan modification hence the reason I included my drawing.

Nobody is arguing with you Marc. All I was looking for as stated initially was some confirmation as to whether or not I was on the right track to reduce drag in this area and has anyone given this area some attention. Your involvement in this topic is quite voluntary. Nobody here is calling you at home, sending you email or bugging you at work. You chose the topic to respond to.

As a software consultant, I give people my best advice. I have long learned that not everyone is going to take that advice. It makes no difference to me. That is one of the freedoms we live with.

As far as dealing with people who are unschooled in my field, I would venture to say that I experience that a lot more than you. Everyone who has a problem with a spreadsheet or email figures I'm a resource for them and I would venture to say that I am very skilled in my area of expertise but it would be unrealistic for me to assume that you have the same skill set. That doesn't mean I think you are 'beyond your scholastic ability' if you come to me with a data sort issue. It would be silly of me to expect that everyone knows as much as me.......in my area of specialty. At the same time I would consider myself a little nutzo to think I know as much as everyone in every subject area.

I have spent a lot of time reviewing this thread and cannot for the life of me find an area where I disagreed or argued with your input.

Initially, when I saw that you decided to provide some input to my question, I was excited to review your post. Now……I really question you motivation entirely.

We now return you to our regular forum.
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  #30  
Old 05-23-2007, 07:29 PM
Jason Heath Jason Heath is offline
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Quote:
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I have spent a lot of time reviewing this thread and cannot for the life of me find an area where I disagreed or argued with your input.
I can, message #7 and then #11 when it looks like you've completely discredited the information given to you and started over with your questioning, it all went to shit from there!
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