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Old May 15, 2012, 10:33 PM
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Philadelphia, PA
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...here's a compilation video of those first few flights described in my last few posts -- including stalls, crashes and repairs!

SNice Icon A5 R/C Scratchbuild - 52" version - Initial flight testing (7 min 25 sec)
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Old May 16, 2012, 12:15 AM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
Joined Sep 2011
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Hey SNice, you are doing a fine job there mate, looks like you are getting on top of it

I have sent you a PM

Cheers

Lockey
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Old May 16, 2012, 12:41 AM
skumgummi dave
Gresham, OR.
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SNice:

Very much enjoying your progress. Very well done!

Dave-
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Old May 16, 2012, 07:28 AM
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SNice,

You do have a great deal of research done. Isn't it amazing how a simple model build can turn into a real technical achievement. This has all become extremely interesting for sure.

I am still smiling thinking about "Daddy wanted to run too".......... plus "hey mister, where are the servos?" Classic!

Off to deliver on of mine to school........
Take care, and good luck.

Fred
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Old May 16, 2012, 07:32 AM
Slipping the Surly Bonds
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Attica, MI
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Quote:
Originally Posted by SNice View Post
Thanks for the suggestion, and kind words, Ken! Also, thank you for the material - Model Plane Foam! (www.ModelPlaneFoam.com)

Center of Drag - Didn't think of that one! Yet another directional force to add to the mix ( I am assuming it points rearward - at a height related to the model's surface area distribution). In this model, it would definitely be low and would rotate the model down -- makes sense. It there a way to reduce all of these forces to vectors and resolve them?
We have:
Center of gravity
Center of lift?
Center of Mass?
Center of Drag
Thrust - the acting point of the thrust - can we resolve the entire thrust of the prop to a single point?

Do any of these forces ALWAYS line up with each other or are they all acting at different heights?

Thanks again, guys!
Center of drag can be best visualized from looking at a front or rear view profile. Sometimes referred to as frontal area. It represents air displacement, and while the airframe may be sleek and displace the air around it smoothly. It still produces drag to be able to push it through the air. I am not familiar with any particular formulas to calculate the center of drag, other than to simply find the point at which the area on one side balances with the whats on the other. I do this visually pretty well (my spacial relationship skills kicking in), but one could cut a cardboard profile of the frontal area and find the balance point on a horizontal edge. That would pretty closely determine the center of drag.

Quote:
Thrust - the acting point of the thrust - can we resolve the entire thrust of the prop to a single point?

Do any of these forces ALWAYS line up with each other or are they all acting at different heights?
I may be mistaken and please forgive if I have misunderstood, but these Q's seem to be one in the same. I will try to answer them as such in as concise a manner as the lack of formal education will allow.

The main problem with trying to resolve all these forces through one point is that our designs primarily emulate full scale aircraft. That is we have cabins, landing gear, propeller clearances, and the like. All things that pertain to people be able to fly in airspace. That is compounded by our models not being full size, which is to say air density relative to drag and thrust is not proportional to scale.

What works at full scale can be emulated, but require some compensation at model scale. The smaller the model the greater the compensation required. Some simple examples are;
- Enlarging tail surfaces for stability
- Thrust angle changes for directional stability through the power curve
- Larger wheels to get through what is a pebble at full size and a boulder at our scale
- Larger propeller blade width to grab more air molecules
We do these things in our designs because the enviroment is not scaled with the model.

The only time all these forces come into line is in one of two ways.
1. The model is purpose built to do so.
2. Compensation is the means of managing misalignment due to design constraints (its a scale model, did not think of that, it looks cool, etc...).

I am always in awe of nature (The Creator of it actually). The birds make it look so easy. The reality is that their brains are processing so many calculations that their flight looks really smooth. Maybe akin to flying an F-16, which without its fly by wire computer interface would be impossible to control.

Hope this helps,
Ken
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Old May 17, 2012, 12:12 PM
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"Wind tunnel" testing...

Thank you, Ken for the detailed explanation! Very helpful. In all of my previous models of full scale aircraft (including this one), I have used the Full Scale 3-views - so I generally do not resize wings and tail surfaces. I do resize control surfaces. My strategy in the past has been - 1) build an airframe 2) make it fly. I do see how rescaling and tweaking the model in the design phase can yield better flight characteristics so I may try this approach in the future (complex calculations, equations, etc! lol!)

I too am amazed at birds! I could watch them all day! Even watching a Canadian Goose come in for a landing is amazing to me! I once saw an indoor Hawk and lure demonstration -- The speed and agility of the bird in such a small space was unbelievable. You also mention "Fly by Wire" -- at the airshow my family went to, the Thunderbirds performed. At one point, one of them did a High Alpha pass -- I was surprised that I could actually see the tailerons moving to keep the correct AOA -- I remember wondering who was in control - Pilot, computer, or both...Cool stuff!

...So I was able to do some "wind tunnel" testing with an old vertical fan that I should have thrown out a loooonnnng time ago (but didn't ). The wing cuffs appear to do their job!!!! I realize my test conditions are not perfect, but I was pretty surprised by the results! What do you guys think?!
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Old May 17, 2012, 05:38 PM
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Very cool thinking and testing. My cousin was killed in a mid-air flying an F-16 when they were new. That was about 1977-78??????? Practicing mock dog fights over the Nevada desert. He was a cool cousin/friend. They had electrical wiring issues in the beginning, but do fly good in most any scale. Sometimes these things happen on the way forward with progress.

Any fan conversion is simply explaned as an improved method to make sure you are keeping the wife's house clean and free of any potential odors, however doubtful. Tell her the long extension with you airplane in it is a chamber to direct the flow where intended. Say it speeds the airflow to improve the performance (leave out 'what'). That my friend, is not a lie. But maybe BS, but good BS I'm sure.

Fred
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Old May 18, 2012, 09:14 AM
Tony Audsley Retired Locksmith
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Nice thinking SNice, hope it achieved what you wanted, did you run the same tests without the cuffs? If so what differences did you find?

Lockey
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Old May 18, 2012, 01:37 PM
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I just finished my 40" Icon. I still need to do some sanding and painting but she flies. All i have to change is from 2s to 3s. Would the cuffs also be a update for the 40" Icon or not?

IconA5 (1 min 24 sec)
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Old May 18, 2012, 09:10 PM
Tony Audsley Retired Locksmith
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Nice flight Sabastian,

SNice, why does the smaller version fly so well and you are having problems with the larger version? Have you changed anything mate?

Lockey
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Old May 18, 2012, 10:24 PM
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Philadelphia, PA
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Great build and great flying, SebastianG! Your 40" looks like a floater! Nice job -- hopefully your paint job won't add too much weight. My 40" ended up at about 18oz. Yours looks much lighter! Mine was light until I added all the paint and extra coats in an attempt to waterproof the hull! The 3S should give it a bit more "kick" if that is what you are looking for... Please post your power system and flying weight (if you don't mind) - I am very interesed in your stats. As far as the cuffs go -- I don't think the 40" needs them for whatever reason. "If it ain't broken, don't fix it!" The only time I got my 40" to stall was after a double snap roll attemp (don't ask me what I was thinking) - I went into a spiral and was able to recover a few feet above the ground. Other than that, I have had no issues with the 40". She even flies inverted great!

Lockey - without the wing cuffs, the entire wing pretty much stalls at the same AOA. Forgot to take pictures of the "bare" wing! I'm hoping the cuffs will hold off that stall a bit at the tips and keep the ailerons more effective at near stall speeds.

The only difference between the 40" and 52" builds (other than size) - is the wing construction. The 40" version has a much sharper leading edge (due to wing construction) and the 52" wing leading is much more round and uniform the entire length of the wing. On the 40",I actually sanded the leading edge of the wing tips a bit lower than the leading edge of the inner part of the wing in an attempt to create some washout.

As far as the 52" pitch issues -- The engine thrust line adjustments/experimentations were unnecessary - the motor is fine at 0deg up or down. SebastianG - at what angle is your motor pointed if any? The issue was the wing incidence which could possibly also be related to the shape of the leading edge. I probably would have caught the incidence issue had I done some glide testing prior to maiden. I think the cuffs are going to make a big difference so I am excited for the next few test flights!
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Old May 18, 2012, 10:36 PM
Tony Audsley Retired Locksmith
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Seems like you are experiencing the same thing as I had with my V2 of the Seawind, only difference was the wing

On V1, I used a flat wing with the G of G at about 60mm from the LE, on V2 I used the airfoil wing and with the C of G in the same place, it went into a spiral dive and smashed into the ground.


I wonder if the new wing now has more lift and needs the C of G quite a bit further back?

I have rebuilt the V2 but as yet havenít had chance to fly it with the C of G at about 40mm form the LE.

Just a thought

Lockey
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Old May 18, 2012, 11:15 PM
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Hmmm... very interesting, Lockey .... You may be on to something. Perhaps the wing incidence was not the issue and I was just very nose heavy due to an improper CG!? I haven't gone inverted with the 52" yet so I don't really know! Time to plug some numbers into a cg calculator!
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Old May 19, 2012, 12:01 AM
Tony Audsley Retired Locksmith
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Tail heavy !! this will send it into a spin and make it very unstable

Lockey
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Old May 19, 2012, 12:05 AM
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OK - just ran some numbers (http://adamone.rchomepage.com/cg2_calc.htm-- thanks, Lockey!) - used the 2-stage wing calculator to get a CG value. The value I got is at least 1" aft of where I had it. According to the calc, my cg should be 2.25-3" behind the leading edge of the wing. Mine is currently 1.25" aft of the LE. The calculator also associates the CG value with something called a "Static Margin". It says this wvalue should be between 5% and 15%. My original CG measurement (1.25") corresponds to a Static Margin value of 31% - WAY outside of the "safe" range. The website also says the following:
"Too much Static Margin makes the aircraft nose-heavy, which
may result in elevator stall at take-off and/or landing."

Elevator Stall!!! Perhaps this is what I have been experiencing. Maybe all I needed to do was move the CG back! We will see.... also, with the huge surface area of the fuse, it has to kind of at like another flying surface so I am not sure how to add that into the equation. In any event, it seems that my CG definitely needs to move back.

Thanks again for all the help and input. I have learned sooo much - and hopefully we will get to the bottom of this BEFORE I destroy this airframe!
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