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Old Jul 19, 2012, 10:04 PM
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United States, PA, Lebanon
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Radian Motor Mount

I had a problem with the motor mount cracking and also the prop hub breaking on my radian after a year of flying. I have already bought a replacement aluminum hub and spinner and yoke to use with the stock motor.

Id like to somehow construct a plywood motor mount and remount the motor and keep flying the airplane.

I bought a new fuselage and plan on adding all the components from the original radian. I bought aluminum Aeronaut parts to replace the plastic spinner so the yoke wont break again in flight.

Any suggestions on making a new plywood fire wall? I was just going to trace the old one and epoxy it into the foam.

Also will the aeronaut hub stay on the shaft of the old motor since its mounted differently than the parkzone motor? The original had the square aluminum piece with the small threaded insert in the shaft.

I was planning on beefing up the firewall so I could keep flying the airplane.

Thanks for any suggestions.
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Old Jul 20, 2012, 01:51 AM
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RadioActive, great documentation of your mods. It'll come in handy.
Thanks a lot
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Old Jul 20, 2012, 12:11 PM
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motor mount cracking

[QUOTE=ChrisFlysRC;22212873]I had a problem with the motor mount cracking and also the prop hub breaking on my radian after a year of flying. I have already bought a replacement aluminum hub and spinner and yoke to use with the stock motor.

Hi-if you look at post #11153 you'll see what I did to get round the weak firewall problem. Since that post I've had another bad landing which compressed the foam in the cockpit area but the firewall was fine. The carbon fibre and epoxy resin seems to work just fine.
Best wishes
Geoff
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Old Jul 20, 2012, 03:02 PM
Zor
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[QUOTE=geoffrich;22217549]
Quote:
Originally Posted by ChrisFlysRC View Post
I had a problem with the motor mount cracking and also the prop hub breaking on my radian after a year of flying. I have already bought a replacement aluminum hub and spinner and yoke to use with the stock motor.

Hi-if you look at post #11153 you'll see what I did to get round the weak firewall problem. Since that post I've had another bad landing which compressed the foam in the cockpit area but the firewall was fine. The carbon fibre and epoxy resin seems to work just fine.
Best wishes
Geoff
I went to 11153 where you said you would post pictures in the next few days but I could not find these pictures.

Zor
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Old Jul 20, 2012, 03:45 PM
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[QUOTE=Zor;22218966]
Quote:
Originally Posted by geoffrich View Post

I went to 11153 where you said you would post pictures in the next few days but I could not find these pictures.

Zor
They are there, saw 'em an hour ago. Try again Zor.
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Old Jul 20, 2012, 05:26 PM
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Old Jul 20, 2012, 06:50 PM
Zor
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Originally Posted by Radio.Active View Post
Thanks Radio.Active.

Got the pictures now.

My stupid computer does not always behave like it should.
Often I cannot open links.

Zor
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Old Jul 20, 2012, 07:06 PM
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The Hawk picture is beautiful!
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Old Jul 20, 2012, 07:15 PM
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Howdy ZOR.

Quote:
Originally Posted by Zor View Post
One example is the pitch sensitivity.
I have read many times that due to decreased decalage (a smaller angle or near or at zero angle) and the CG moved rearward is the cause of more senstive pitch control.

I have not read any reason that I can recall.
Here is a nice page which explains CG and pitch...
http://www.polecataero.com/handlaunchu/cg-location

Quote:
Is it real or just psychological ?
It feels very real to me. I fly mostly slope gliders... many of them acrobatic models with symmetrical wings. However since I fly at inland sites, there is a lot of thermal flying too. I like a very neutral CG... one that will let my glider hold a 45, up- or down-line (upright and inverted) with little to no elevator inputs. I have noticed that as I push my CG back to achieve this balance, my elevator inputs become much more sensitive. As a result I ALWAYS reduce my elevator throws as I push the CG back. That way I avoid "over control"... the bane of most acrobatic pilots (thermal pilots too).

Quote:
Does some claim that higher sensitivity just because someone else wrote it ?
I suppose. But I always suggest that when folks experiment in moving the CG back... that they always dial down their elevator throws accordingly. Most every glider I have tried appears to behave this way... from combat wings to slalom racers.

Quote:
I certainly would appreciate a logical reason that explains the reported difference.
I am not a scientist; but It seems logical to me that as you move balance point of your glider closer to its COG, that it become less pitch stable and as a result need less elevator pitching force to induce a given pitch angle. Granted that in aerobatic flying, where equal upright/inverted and inside/outside performance is desired, a neutral CG is very important. For pure thermal-style flying the neutral CG may be unnecessary or unwarranted.

Regards,

Dawson

P.S. FYI: The reason I like the decalage mod (near 0) on my Radian is that is gives me a nice SPEED RANGE without having to use too much compensating elevator input. I like that I can go into a dive or hit the throttle and not have my glider make a drastic pitch (up) change. It also helps with inverted flying... although that may not be important to this (TD) group.
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Old Jul 20, 2012, 07:32 PM
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Full flying stabs... and flutter.

Over in the slope forum there is a group of acrobatic flyers that have been experimenting with full flying stabs that move 180... allowing us to do some very crazy maneuvers... like flips (see my Avatar). In the process of developing these "Mad Stabs" we have learned a lot about flutter (a prevalent issue early on) and how to deal with it. I think what we have learned might be applicable to you thermal flyers as well.

The main things you can do to eliminate flutter are:

Keep the stab lightweight (and do NOT fly too fast )

Linkages and bearing surfaces should be a tight as possible.

Pivot point for the stab should be at 25% of Mean Aerodynamic Chord (MAC).

And most important (for us)... was to balance the stab fore and aft. This usually involved adding weight to the leading edge of the stab. It is amazing that even with a "loose" setup, the balancing gets rid of the flutter.

Just for fun, here is a short video showing my latest Mad Stab which utilizes a pulley system (oval servo pulley for mechanical EXPO).
Mad Stab using a new oval pulley (0 min 44 sec)


Dawson
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Old Jul 21, 2012, 02:47 AM
Zor
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Hello dawsonh
Blue text by Zor (except for the link)

Quote:
Originally Posted by dawsonh View Post
Howdy ZOR.


Here is a nice page which explains CG and pitch...
http://www.polecataero.com/handlaunchu/cg-location

It feels very real to me. I fly mostly slope gliders... many of them acrobatic models with symmetrical wings. However since I fly at inland sites, there is a lot of thermal flying too. I like a very neutral CG... one that will let my glider hold a 45, up- or down-line (upright and inverted) with little to no elevator inputs. I have noticed that as I push my CG back to achieve this balance, my elevator inputs become much more sensitive. As a result I ALWAYS reduce my elevator throws as I push the CG back. That way I avoid "over control"... the bane of most acrobatic pilots (thermal pilots too).

I understnd what you wrote but the discussion here is about Radians that do not have symmetrical airfoils and were not designed for aerobatics or to play inverted.

You say "it becomes much more sensitive" but you are not explaining your understanding why it is so.

I suppose. But I always suggest that when folks experiment in moving the CG back... that they always dial down their elevator throws accordingly. Most every glider I have tried appears to behave this way... from combat wings to slalom racers.

Again you are not discussing Radians.

I am not a scientist; but It seems logical to me that as you move balance point of your glider closer to its COG, that it become less pitch stable and as a result need less elevator pitching force to induce a given pitch angle.

Careful here _ _ _ the stability with a nose heavy (CG forward) is due to the fact that up elevator is needed to fly near level so in a descent as the model gains speed the elevator have more negative lift and force the nose up resulting in less speed and going back toward level.

Moving the CG toward the tail needs less up elevator for level flight but it does not change the size of the elevator nor its moment arm. Then how can you explain that the elevator motion needed would be reduced ?

Granted that in aerobatic flying, where equal upright/inverted and inside/outside performance is desired, a neutral CG is very important. For pure thermal-style flying the neutral CG may be unnecessary or unwarranted.

I do not know what you understand as a "neutral CG" .
To me a neutral CG would be a CG at such a location that in self stable gliding the decalage is optimized for best lift to drag ratio and the elevators is neutral in line with the stabilizer.

Regards,

Dawson

P.S. FYI: The reason I like the decalage mod (near 0) on my Radian is that is gives me a nice SPEED RANGE without having to use too much compensating elevator input. I like that I can go into a dive or hit the throttle and not have my glider make a drastic pitch (up) change. It also helps with inverted flying... although that may not be important to this (TD) group.

With neutral stabiliy the pitch attitude does not change due to speed. In a steady descent or steady climb the lift is equal to the weight.

The lift is directly propotional to the lift coefficient which is a straigh line up to near the stalling angle of attack.
Our flying is done well below the stalling angle. The best L/D ratio is betwen 3 and 4 derees angle of attack. Assume for a moment that it is 3.5 degrees. At 1.75 deg we have half the lift and at 7 deg twice the lift.

With the proper decalage angle and neutral elevator the model will self adjust to a descent angle (flight trajectory) and a speed that is stable and has minimum rate of descent.

A zero decalage does not determne the flying speed capability. The speed is still controlled by the elevators and in the range of the angle of attack (2 to 6 deg) we should use very little elevator rotation is needed; something like less than 10 degrees.

One of the main problems many pilots have is due to the inability of judging the nose attitud within this 2 to 6 deg and letting the model stall. When it stalls the nose drops and the pilot command nose up which leads even more to stalling again.
Does not the above make good sense ?

Zor
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Old Jul 21, 2012, 03:31 AM
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Originally Posted by Zor View Post
Hello dawsonh
Blue text by Zor (except for the link)

You say "it becomes much more sensitive" but you are not explaining your understanding why it is so.

Moving the CG toward the tail needs less up elevator for level flight but it does not change the size of the elevator nor its moment arm. Then how can you explain that the elevator motion needed would be reduced ?

Does not the above make good sense ?

Zor
Sorry, no. With a more backward CG the forces needed to counteract the wing's pitching moment are smaller, hence less elevator throw needed... look here , especially the drawing:
http://en.wikipedia.org/wiki/Longitu...atic_stability

and this :
Quote:
Neutral point

A mathematical analysis of the longitudinal static stability of a complete aircraft (including horizontal stabilizer) yields the position of center of gravity at which stability is neutral. This position is called the neutral point.[1] (The larger the area of the horizontal stabilizer, and the greater the moment arm of the horizontal stabilizer about the aerodynamic center, the further aft is the neutral point.)

The static center of gravity margin (c.g. margin) or static margin is the distance between the center of gravity (or mass) and the neutral point. It is usually quoted as a percentage of the Mean Aerodynamic Chord. The center of gravity must lie ahead of the neutral point for positive stability (positive static margin). If the center of gravity is behind the neutral point, the aircraft is longitudinally unstable (the static margin is negative), and active inputs to the control surfaces are required to maintain stable flight. Some combat aircraft that are controlled by fly-by-wire systems are designed to be longitudinally unstable so they will be highly maneuverable. Ultimately, the position of the center of gravity relative to the neutral point determines the stability, CONTROL FORCES, and controllability of the vehicle.[1]
CG remains a matter of preference as is well explained in the Polecat/Drela link. A different CG goes with different decalage. This can be achieved by trimming the elevator and /or changing it's incidence relative to the wing (which is the same for an all moving stab). Only a really huge trim adjustment would "need" the "decalage mod" IMHO. So that mod is only a minor thing, it does not instantly and by itself transform the Radian into a contest winning machine like some people here seem to believe.It's just the "final touch" See also this quote from Mark Drela:

Quote:
Originally Posted by Mark Drela
It seems to me that decalage is greatly oversold. Changing decalage simply
biases the elevator position, and can be entirely compensated via the elevator
trim on the TX as long as the elevator deflection remains modest. There should be
no effect on handling.
FWIW more F5J contests have been won with Radians without the decalage mod than with it...,yes, against high end F5J machines ,only proves good pilots can win with any plane (The F5J rules are very well made IMHO)
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Old Jul 21, 2012, 04:11 AM
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Both are 50mm
Still too small, and heavy. My Reisenauer 54.5mm fits perfectly and is a lot lighter. It is a bit expensive though... :
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Old Jul 21, 2012, 06:46 AM
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Originally Posted by Gore-Tex View Post
RadioActive, great documentation of your mods. It'll come in handy.
Thanks a lot
..what he said... thanks for that..
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Old Jul 21, 2012, 07:49 AM
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[QUOTE=Raften;22219328]
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Originally Posted by Zor View Post

They are there, saw 'em an hour ago. Try again Zor.
+1 Geoff
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