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Old 06-27-2014, 11:22 AM   #1
rajkojus
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Default weight distribution/aerodynamics problem ? help !!!

Greetings !

Im new to this forum and overall rc world,

First of all, i wish to thank anyone who replies to my 1st thread ever. Im not even sure if this topic belongs here or maybe it got mentioned earlier or in some other thread, so forgive me if thats the case. My english is not very good either.
To make my story short:
I Have no experience in rc flying whatsoever, but i got interested in rc airplanes 3 months ago when i decided to build one from scratch. I have/had no basic aerodynamics/rc airplane knowledge, but i decided to try.

First of all, i managed to make 3d model of desired airplane (p47) in google sketchup, then i printed out, glued on balsa, and cut out the profiles and parts which then i again glued together to get the basic structure.
Of course before i merged it all togehter, i have installed ESC, battery, servos etc. My brother is electrical engineer so he helped alot about electronics.( i will write specifications later)

In the end it turned out to be nice looking wooden airplane !!!
BUT... it wont fly Thats why im here. Ill post pics of plane with its specifications, so you could help hopefully help me.
Apparently, it gets enough speed and acceleration, but it wont get off the ground, OR it keeps steering to the left and gets its nose rammed in the soil.

I know that i was not supposed to try to make this complicated plane since i am a beginner, and i will probably crash it even if it gets to fly.

Specifications : (most of these are chinese manufactured, ordered from china)

-2700 kv brushless motor,
-3x 9g servos - 1 for aelerons, 1 for rudder, 1 for elevator
-13cm/5.11in propeller
-30A ESC
-1500mah, wild scorpion, li-poly battery
-transmitter FST6 by flysky

Airplane mass : 360g / 12.6oz

If you need any other kind of photos of info, feel free to ask !! Thanks !


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Old 06-27-2014, 01:08 PM   #2
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A+ on the effort, not an easy plane to built for a first attempt. It's doubtful this will fly however in it's current configuration. Your wings look way too big, completely out of proportion. Another issue is your center of gravity, you'll need to figure that out. I think there is a free program/utility out there for that, I'll hunt around and see if I can find it.

Even if the plane was perfectly built, this is not one you probably want to start with. Warbirds in general are harder to fly and require more skill than entry level. Go with a 3 or 4 channel glider, or better yet a high wing design like a Cessna 172.

Welcome to the hobby, prepare for the addiction.
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Old 06-27-2014, 01:39 PM   #3
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http://adamone.rchomepage.com/cg_calc.htm

or

http://www.rcgroups.com/forums/showthread.php?t=1106300
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Old 06-27-2014, 02:02 PM   #4
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Great effort - but there are several significant issues with design.

The wing aspect ratio is off. The span is too great. This is more like a glider would use. That isn't the worst part however.

Your tail moment is MUCH too short. That "moment" is the distance from your wing to the tail surfaces. This distance affects stability sadly your looks to be aerodynamically unstable.

The other is mass. The plane is constructed in a manner that has lead to excess weight, another penalty for proper flight performance. Your use of thick wood just creates too much weight. Airplanes fly better when they are mostly air.

Ailerons are too far inboard another factor in stability and control.

These items combine, as you have found, means it will not be controllable or stable in flight.

Design elements for planes are a blast but there are rules that help you to have a better design off the table.

A fantastic effort and labor - but we can get you trained - with designs that are proven!

Where are you located? Maybe we can get some help for you....

Mike
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Old 06-27-2014, 02:10 PM   #5
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Default Flaperons

Can any one help me set up flaperons on my DX8 TX?? I took off the Y harness and used the ail port and the AUX 1 port on my 6 channel RX for the servo's and when I set the TX to duel flaps or flaperons, It only works the servo on the AIL port.

HELP !!
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Old 06-27-2014, 02:14 PM   #6
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tocar64/Tom B....

Tom - you would be much better served to start your own thread with this question. Posting in this thread, having nothing to do with radio setup - will have your request lost in discussion about something else.

Mike
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Old 06-27-2014, 03:10 PM   #7
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Thank you for your answers !!!

Im not sure how to quote yet, Porcia83, thanks for the calculators, ive seen them earlier, but im not sure how they work - im not sure what MAC means, what does it mean etc.
However ive "figured" out CG and tried to apply it on my plane, i can balance it on the tip of my fingers approximatly on 25-30% from the front tip of wings - thats something right ?

The other issue, rcers mentioned - wingspan. If i make them shorter, will that affect tail moment ? Since this is a scaled version of p47 (except few modifications - ex. wings), shouldnt my tail moment be good ?
I understand problem for wingspan and what it causes, should i cut them 2 inches ?
Thanks for explanation for tail moment, i think i know what You mean, but its a scaled model , i didnt make any changes there, wasnt it supposed to be fine ?

Second problem - mass. Whole plane was made out of balsa wood, as you can see in the attached picture, i made skeleton out of balsa rings, then i covered full plane with 1mm thin balsa. Plane weights ~360g/12.6oz, but the motor and battery is STRONG. plane gets acceleration very fast, it goes on the field very fast, but it keeps steering to left and eventualy hits the ground with nose.
My point here is that seems to me it has enough power : weigh ratio. What do you think ??? is my configuration (motor,battery..) with this weight ok ??? Is this mainly aerodynamical problem ?

Im not trying to sound very smart about anything, as i have said i have no experience whatsoever , im just implying some pros and cons as they APPEAR to me - perhaps im wrong.

I live in small town in Montenegro called Herceg Novi (You probably never heard of it )
but also i often spend time in Belgrade, Serbia.

Any help much appreciated, thanks for answers in advance
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Old 06-27-2014, 03:24 PM   #8
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Just a quick look at the pictures... you have terribly inadequate tail surfaces for the size of the wing. There would be no way to maintain control of that aircraft.

So even if CG and weight are reasonable (without checking your numbers) you have something to hang from the ceiling, but not something to fly.

I have seen cases where the ailerons were small and inboard such as yours and it can work for control of a high speed aircraft. We use less effective style ailerons to deal with an overly roll-sensitive airplane such as when doing pylon racing. If the other aspects of the design were reasonable I wouldn't be worried about the ailerons at all.
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Old 06-27-2014, 03:41 PM   #9
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Originally Posted by fhhuber View Post
Just a quick look at the pictures... you have terribly inadequate tail surfaces for the size of the wing. There would be no way to maintain control of that aircraft.

So even if CG and weight are reasonable (without checking your numbers) you have something to hang from the ceiling, but not something to fly.
Is there any way i can fix it ? make my wing shorter few inches both ?
In the pic below u can see elevator a bit better


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Old 06-27-2014, 03:45 PM   #10
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Originally Posted by rajkojus View Post
Thank you for your answers !!!
You are most welcome...

Originally Posted by rajkojus View Post
...i can balance it on the tip of my fingers approximatly on 25-30% from the front tip of wings - thats something right ?
That is likely pretty close, yes one thing right.

Originally Posted by rajkojus View Post
...wingspan. If i make them shorter, will that affect tail moment ? Since this is a scaled version of p47 (except few modifications - ex. wings), shouldnt my tail moment be good ?
I understand problem for wingspan and what it causes, should i cut them 2 inches ?
Thanks for explanation for tail moment, i think i know what You mean, but its a scaled model , i didnt make any changes there, wasnt it supposed to be fine ?
No - making the wingspan shorter does not lengthen your tail moment. Only making changes in plane length do that. You need more distance from the tail to the wing. The wing is MUCH too big 2" isn't enough.

Exact scaling of our RC models from full scale typically DOES NOT work well, especially WW2 aircraft. While the P47 (Jug) is a great subject for a scale RC model we typically make changes for the RC side.

We normally make the wing area and span a touch bigger. We normally make the tail surfaces larger (10-25% generally) and the tail moment is sometimes increased.

All of this is to make for a better flying experience. While we do exact scale of some full sized models, most of the time we adjust to get a better flying model.

Originally Posted by rajkojus View Post
Second problem - mass. Whole plane was made out of balsa wood, as you can see in the attached picture, i made skeleton out of balsa rings, then i covered full plane with 1mm thin balsa. Plane weights ~360g/12.6oz, but the motor and battery is STRONG. plane gets acceleration very fast, it goes on the field very fast, but it keeps steering to left and eventualy hits the ground with nose.
Yep too heavy! 1mm skin is heavy! We normally use coverings that are MUCH lighter.

See my pictures below - you will see what a light built up structure looks like.

Originally Posted by rajkojus View Post
My point here is that seems to me it has enough power : weigh ratio. What do you think ??? is my configuration (motor,battery..) with this weight ok ??? Is this mainly aerodynamical problem ?
Power is good but it is not the only factor. So no - I don't think your weight is OK, rather a bit heavy. Not horrible though.

Originally Posted by rajkojus View Post
Im not trying to sound very smart about anything, as i have said i have no experience whatsoever , im just implying some pros and cons as they APPEAR to me - perhaps im wrong
You are asking questions and that is good! So no - your tone is just fine!

This picture of a P-47 will give you an idea of what I mean about being "mostly air".

See these pictures you have mostly built up structure and super light plastic type covering. This plane is VERY light and flies wonderfully! But it is NO trainer. !!! So you really can't learn to fly with any P-47. That is why we make trainers.

Remember in the war the Pilots that flew the P-47 first flew trainers - several versions of them, before they flew the Jug.

Mike


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Old 06-27-2014, 04:05 PM   #11
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OK. Thanks alot .... What would be Your solution to these problems ?? What can i do, IF i can do to make it fly ?
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Old 06-27-2014, 04:12 PM   #12
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Honestly - get a trainer aircraft (one designed for success) and learn to fly with that.

Then tackle scratch building. It is hard to fix what you have, since there are several pretty key things off.

I don't want to discourage you, but success lies in a proven design while learning to fly. After that you branch out!

Mike
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Old 06-27-2014, 04:33 PM   #13
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Originally Posted by rcers View Post
Honestly - get a trainer aircraft (one designed for success) and learn to fly with that.

Then tackle scratch building. It is hard to fix what you have, since there are several pretty key things off.

I don't want to discourage you, but success lies in a proven design while learning to fly. After that you branch out!

Mike
Ok thanks, great advice. Ill find some traineer airplane to fly, but preferably i would like to build one. can you provide me with some preferences, blueprints, or some useful links ? I could try to find by myself, but im not sure if icould find the right choice in the sea of so many planes.

Im interested in this mainly cause of "thrill" of building one plane im artistic person, and i love designing stuff - therefore i get much pleasure seeing my design working. In this case i have made a mistake clearly

If You come up with any solutions for previous design (p47) please inform me

Thanks

Rajko
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Old 06-27-2014, 04:44 PM   #14
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One more thing,

Is profile of the wing (airfoil) of my plane ok ? Does it really have great impact on take off ? could it be one of the problems ?
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Old 06-27-2014, 04:46 PM   #15
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Here are a couple:
Q-Tee
http://www.outerzone.co.uk/plan_details.asp?ID=1350
MEN Trainer:
http://www.outerzone.co.uk/plan_details.asp?ID=4101
RCM Trainer:
http://www.outerzone.co.uk/plan_details.asp?ID=3030
One of the best....The Telemaster (you can make this smaller):
http://www.outerzone.co.uk/plan_details.asp?ID=5043

Some good solid balsa built up trainers. Remember covering - not sheeting!

Mike
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Old 06-27-2014, 04:49 PM   #16
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Originally Posted by rajkojus View Post
One more thing,

Is profile of the wing (airfoil) of my plane ok ? Does it really have great impact on take off ? could it be one of the problems ?
Yes your airfoil is an issue too. It appears from the pictures to be too thin for decent low speed performance.

Another reason for a trainer. See the links above and note the differences in those details. Wing size, tail size, control surface size, airfoil, weight, aspect ratio, wheel size, landing gear placement and many other things. All this stuff matters!

Mike
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Old 06-27-2014, 05:00 PM   #17
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Originally Posted by rcers View Post
Here are a couple:
Q-Tee
http://www.outerzone.co.uk/plan_details.asp?ID=1350
MEN Trainer:
http://www.outerzone.co.uk/plan_details.asp?ID=4101
RCM Trainer:
http://www.outerzone.co.uk/plan_details.asp?ID=3030
One of the best....The Telemaster (you can make this smaller):
http://www.outerzone.co.uk/plan_details.asp?ID=5043

Some good solid balsa built up trainers. Remember covering - not sheeting!

Mike
Are these fine with electrical motors not gasoline ? they seem quite big thats why im asking
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Old 06-27-2014, 05:03 PM   #18
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Yes they can be converted to electric flight. The Q-Tee and Telemaster are both excellent designs. The telemaster can be made much smaller and you can use your electric setup you already have.

Mike
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Old 06-27-2014, 06:46 PM   #19
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I flew a Q-Tee years ago and its an excellent, simple aircraft. For electric, you may have to secure a lighter and smaller motor, ESC, and battery than what you have. Mine came in at the one pound range with a Cox .049, four AA battery cells, and two lightweight (for the 1970s) servos.

The Telemaster is a proven design and is scalable. Might be the best choice to fit your existing motor, etc., by adjusting the size.

Just remember to build light.

Good luck, and let us know what you decide. Photos always appreciated.

(And you are not alone in the love of designing and Nothing wrong with starting with someone else's ideas, building, and then earning to fly on a trainer. But as the saying goes, you gotta learn to walk before you can run.)

Behind every successful man is a woman. Behind the fall of a successful man is usually another woman.
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Old 06-27-2014, 07:28 PM   #20
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OK How about i start with foam trainers ? Ive found quite some with free build plans ?
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Old 06-27-2014, 07:32 PM   #21
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Originally Posted by rajkojus View Post
OK How about i start with foam trainers ? Ive found quite some with free build plans ?
Nothing wrong with building with foam...except maybe to the "Balsa Purists"....lol

Might be of help to you if you'd post links to the plans you're looking at and seek advice on those...

BTW, great looking work on what you did so far....good luck in your future builds...
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Old 06-27-2014, 07:48 PM   #22
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Originally Posted by DEG View Post
Nothing wrong with building with foam...except maybe to the "Balsa Purists"....lol

Might be of help to you if you'd post links to the plans you're looking at and seek advice on those...

BTW, great looking work on what you did so far....good luck in your future builds...
Thank You very much

Im more of a balsa-person, if i can put it that way, i like details and artistic feel to it more than just functionality, but it seems that i have made a mistake this time i should have balanced functionality with esthetics for the first time building

Will post new pics , thats for sure, i ve found trainer similar to telemaster, but its a .skp file
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Old 06-27-2014, 07:54 PM   #23
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If you do decide to build with foam, a couple of good things you'll discover if you don't already know them.....it's much cheaper than balsa and much easier to repair in case gravity goes to work on you.....

Telemaster is a good choice.....converted to foam and built light, it should make a great trainer for you.

If you have a link to the plan you found, please post it....
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Old 06-27-2014, 07:57 PM   #24
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https://3dwarehouse.sketchup.com/mod...155ddc002a8f77 Here You go

It looks something like trainer to me, right ?
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Old 06-27-2014, 08:00 PM   #25
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Looks like a foam Telemaster to me......if the plans are good that's a great choice....
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