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Old Today, 07:25 AM
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Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
5,515 Posts
Quote:
Originally Posted by PeterVRC View Post
I am not sure this is right....?
Any given wing, with the same AUW as another, at the same airspeed, flies at the SAME AOA...
Trim does not alter lift, and thus the AoA needed to achieve that. All trim does (apart from some small drag) is give LEVERAGE, due to authority, to "re-align" the Pitch to achieve that required AoA state. eg The Nose heavy plane needs Up trim to push the rear down and compensate for that nose end imbalance - the correctly balanced plane of the same AUW does not need that. But BOTH will fly along at the same AoA profile.
Airfoil lift curve slope (Cl vs AOA or Alpha) of any given airfoil shape determines AOA at a specific weight.

to sight an extreme example, we all know that a symmetrical airfoil produces no lift at 0 deg AOA. A 15% Clark Y airfoil needs to be at -4 deg AOA(leading edge down!) to produce 0 lift! A clark y may support a 40 sized trainer at cruise at 0deg AOA, but the symmetrical airfoil might need to be at 2,3 or even 4 degrees to produce the same lift at the same airspeed! In full scale aircraft design a great deal of attention is put to determine the correct relationship between the angle of the fuselage and the angle of the wing. You don't want a big honkin fuselage (like a 747) flying a a relatively high angle of AOA during cruise! You will notice that the root airfoil of airliners are set at quite high of a positive AOA relative to the centerline of the fuselage.

Trailing edge reflex is like adding a simple "flap" but going in the "opposite direction". Though the deflection is small, this changes the lift curve slope from a non-reflexed airfoil. The more the reflex, the less "up" lift the wing produces... very simple principle. If the aircraft is to maintain altitude, the speed must be increased or the AOA increased..... you're choice.

so TRIM, especially elevon trim GREATLY effects the overall lift and drag of a flying wing. The "total" lift is the same (for level, unaccelerated flight), but happens at a higher AOA.

Even in an aft tail aircraft, (where the horizontal tail lifts DOWN), elevator trim will effect the distribution of lift created by the aircraft. If elevator "trim" is required to keep the nose level, the negative lift of the tail increases, forcing the wing to produce more lift to maintain level unaccelerated flight. Forcing the wing to fly at a higher AOA makes the fuselage fly at a higher AOA increasing drag further.

Tom
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Old Today, 07:34 AM
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Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
5,515 Posts
Quote:
Originally Posted by Jman841 View Post
So, should the phantom stabilizers be cut down as well?.
When the weather improves around here, I will begin experimenting with reducing the size of the vertical tails of the Phantom, I bought an extra set just of tails just for this purpose.

Quote:
Originally Posted by Jman841 View Post
As for verticle stabilizers on the wing tips, if it is not a good idea, why are the Northrop Grumman BAT's and the Boeing Scaneagle running them way out there?
I cannot comment on the Boeing, but I am familiar with the BAT a bit. It has imbedded rudders in the vertical tails out on the wing tip, and from the design, I believe that they are trying to get a little Aspect ratio improvement by utilizing them as winglets also. Sized properly, outboard wing tip vertical tails can be very a good option.

The BAT is also a flying wing that utilizes a very twisted wing AND a reflexive airfoil!
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Old Today, 07:44 AM
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United States, HI, Honolulu
Joined Dec 2013
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Quote:
Originally Posted by Tom Hunt View Post
When the weather improves around here, I will begin experimenting with reducing the size of the vertical tails of the Phantom, I bought an extra set just of tails just for this purpose.



I cannot comment on the Boeing, but I am familiar with the BAT a bit. It has imbedded rudders in the vertical tails out on the wing tip, and from the design, I believe that they are trying to get a little Aspect ratio improvement by utilizing them as winglets also. Sized properly, outboard wing tip vertical tails can be very a good option.

The BAT is also a flying wing that utilizes a very twisted wing AND a reflexive airfoil!
Thank you're the response!

I have become very intrigued by the Bat/killerbee. They seemed to have been able to far exceed their competition in payload capability and endurance for the size of aircraft that it is, which is very impressive. Is there any articles outlying the details of the design? I can't even tell how they are using the elevons for control from the pictures, never mind the airfoil type or seeing rudders integrated in the verticle stabilizers!

Thanks again!
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Old Today, 08:09 AM
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Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
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Quote:
Originally Posted by TNug View Post
[*]Waggle (oscillation after a disturbance) comes from being overdamped - I'd like to hear the explanation
When most modelers attempt to talk about "stability" they often are only speaking about "static" stability. The other kind of "stability" in an aircraft is dynamic stability and is often hard to quantify and cannot be assessed by wind tunnel testing alone (which can EXACTLY quantify static stability at a known CG position).

Over-damped conditions are not easy to explain without lots of math and figures, but essentially what happens in gusty conditions is that the vertical tail responds to the change in AOA (in this case off-axis YAW angle) by correcting with a side force to point the model into the oncoming gust…. Then the gust goes away and the model returns to its original heading. When the tail is TOO large, this sets up a oscillation period depending upon the moment arm, yaw moment of inertia of the model and the lift coefficient of the tail. Let’s take away the tail entirely….. then there is NOTHING for the gust to act on, therefore no oscillation. Adding some tail will make the model “respond to the gust” but the size of the tail, properly matched to the moment arm available, and the inertia of the model will dampen out the gust with less “period” and displacement.

Don’t know if that is helpful.

I can tell you that you can clearly see this phenomenon in models that “wag their tail” in gusty conditions that don’t when it is calm. There are a number of models that do this out there…. Most recently the Parkzone Spitfire (1100mm) Mk9 with the out-of scale oversized vertical tail, wags terribly on gusty days. I cut the tail down to “scale” size and the wag went away.

An opposite problem was the Multiplex Twister (EDF). This model had TOO small a vertical tail and it showed up in tight turns (high AOA flight). It also “wagged” its tail on CALM days…. Which is also a sign of an under-damped aircraft. Adding some vertical tail area above AND below the fuselage made it an “honest” aircraft.
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Old Today, 08:19 AM
Still flying
Ramnes's Avatar
Oslo, Norway
Joined Feb 2009
793 Posts
My FX-61 build

At last, my FX-61 is ready to fly! I've never laminated aanything other than plane paper befor, but it went well to be a first timer. I replaced the stock ESC with a working one today.

I fly with stock motor and a 10x6 and a 10x7 propeller. The new ESC is a 40amp and the batteries is 3S 5000mah 35-70.

Here are my build pictures.

Jorn
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Old Today, 09:26 AM
Seattle, WA - USA
mark_q's Avatar
Joined Sep 2003
3,575 Posts
Quote:
Originally Posted by Ramnes View Post
At last, my FX-61 is ready to fly! I've never laminated aanything other than plane paper befor, but it went well to be a first timer. I replaced the stock ESC with a working one today.

I fly with stock motor and a 10x6 and a 10x7 propeller. The new ESC is a 40amp and the batteries is 3S 5000mah 35-70.

Here are my build pictures.

Jorn

Very nice laminating!
You, my friend, are a very patient man!!

BTW, a zippy compact (31mm) or multi star (34mm) would probably fit

Mark
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Last edited by mark_q; Today at 09:36 AM. Reason: Btw
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Old Today, 09:29 AM
Seattle, WA - USA
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Joined Sep 2003
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Quote:
Originally Posted by f2001m View Post
mark_q or any other expert who are using folder prop
I have recently bought two type of carbon fiber 10x6 and 11x6
I have noticed one on each set the root for mounting screws it is rotate easily
i don't thing it is normal, am i right?
Sorry,
I haven't seen these except in pictures. If they are not supposed to turn, can you simply add some CA?

Mark
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Old Today, 09:46 AM
Still flying
Ramnes's Avatar
Oslo, Norway
Joined Feb 2009
793 Posts
Quote:
Originally Posted by mark_q View Post
Very nice laminating!
You, my friend, are a very patient man!!

BTW, a zippy compact (31mm) or multi star (34mm) would probably fit

Mark
Thanks Mark
Usually i'm not a very patient man! :-) I'll look into the batteries you mention, but i've also read that you have done some testing on Panasonic 18650 batteries which i might go for. The price for them in Norway is quite high but I want to try them if they're ok.
Can you point me in the direction of some good reading and tests?

Jorn
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Old Today, 10:00 AM
Registered User
Joined Oct 2004
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Quote:
Originally Posted by Ramnes View Post
At last, my FX-61 is ready to fly! I've never laminated aanything other than plane paper befor, but it went well to be a first timer. I replaced the stock ESC with a working one today.

I fly with stock motor and a 10x6 and a 10x7 propeller. The new ESC is a 40amp and the batteries is 3S 5000mah 35-70.

Here are my build pictures.

Jorn
Good job my friend! Looks really nice. Can't wait to see it fly!

G
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Old Today, 10:15 AM
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Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
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Yes, very nice covering job! I doubt I could have done better..... and I've being using document laminating material on my "wood" models from almost 20 years! I never had the courage to try it on foam!
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Old Today, 10:37 AM
Still flying
Ramnes's Avatar
Oslo, Norway
Joined Feb 2009
793 Posts
Quote:
Originally Posted by neavissa View Post
Good job my friend! Looks really nice. Can't wait to see it fly!

G
Thanks G
Do you really want me to fly this beauty to?!
Well, sunday is maiden day if all goes well.

Quote:
Originally Posted by Tom Hunt View Post
Yes, very nice covering job! I doubt I could have done better..... and I've being using document laminating material on my "wood" models from almost 20 years! I never had the courage to try it on foam!
Thanks Tom
The 1,7mill laminate i bought from Aloft Hobbies was a thin film, nothing like the laminating pouched i practiced on on another plane. I believe I used about seven hours on the whole plane over two days. It's no problem laminating on foam, just don't stop on one place to long and your'e good.

Jorn
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Old Today, 11:24 AM
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Joined Feb 2012
88 Posts
Quote:
Originally Posted by mark_q View Post
Sorry,
I haven't seen these except in pictures. If they are not supposed to turn, can you simply add some CA?

Mark
Thanks mark, I submit RMA on HK to get replacement ,
Revived FX-61 yesterday just waiting for prop and motor mount (manufacture local).
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Old Today, 11:36 AM
got any foam to bash?
Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
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Quote:
Originally Posted by Ramnes View Post
The 1,7mill laminate i bought from Aloft Hobbies was a thin film, Jorn
I was buying 1.5mil from Filmsource some years ago. They also had a 3.0mil that I bought smaller rolls. At the time you had to buy 2 rolls at a time and the smaller rolls were 250ft x 18". I wanted something wider so I went for the 26" and they only came in 500ft rolls! needless to say, despite selling some of it, I still have quite a bit! Maybe I will practice on a "strike" aircraft (in aerospace terms a "strike" aircraft is one that had a bit of an accident but is not economically repairable!)
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Old Today, 02:52 PM
Preserve our right to FPV !!!!
melsailsnorth's Avatar
United States, CA, Chico
Joined Dec 2010
1,118 Posts
Hey Tom, thanks for the explanations.

My area of expertise is about as far as you can get from Aero Eng. but I'm still a huge fan and love to try and make sense of it all.

One thing that I've always wondered about is this.... I see/hear many comments/posts about all the different shapes and airfoils used with flying wings (or any RC design for that matter) but i've always wondered how important an airfoil is to our models when so many are mostly traveling at very slow speeds. I'm probably wrongly conditioned because I started-out making so many of my first planes with flat wings from dollar store foam, and relying purely on attack-angle physics ( kind of a Newton vs Bernolli argument here).

Is there a certain speed at which the airfoil of a model actually begins to show an appreciable effect or is this aspect of design just as relevant in the scaled-world (and much slower speeds) as compared to the full- scale designs that you work with? I've just always wondered if most aspects of airplane design "scale down" nicely and cleanly or if there's a lot more to it then that.

Sorry, I know this is way off topic so feel free to PM me
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Last edited by melsailsnorth; Today at 04:05 PM.
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Old Today, 05:52 PM
Registered User
United States, HI, Honolulu
Joined Dec 2013
430 Posts
Pixhawk is installed and setup, servo's just got installed (Metal gear digital servos), and just waiting for the new CNC motor mount.

The Pixhawk can be frustrating to learn as a lot of it is not very intuitive, and basic things like setting your servo horns to 90 degree's, is either not possible or I can't figure it out.

I decided to go with the servo's on the bottom as I did not want to make a ton more cuts int he wing. It is definitely a bit more risky for landing, but, hopefully it will be ok.
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