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Mar 29, 2018, 12:36 PM
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cg is usually measured from the leading edge of the wing backwards. some plans with have the cg marked with an atomic sign.
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Mar 29, 2018, 12:48 PM
IMO ( In My Opinion ) →
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Quote:
Originally Posted by jawsqb
1 ) I'm in the process of adding that right now, I just wanted to check with you first if the 400g weight was excessive for a 100% scale model or not

2 ) also how is the motor attached to the plane?

3 ) At what location do I measure cg on the wing?

4 ) Also is it okay if I use a tri blade prop?

1 ) OK , the polyhedral is a very important part of the EzFly design ...... that's what gives it stability . It would have been easier to add the polyhedral to the wing BEFORE you installed it onto the plane .
400g is not unreasonable . The heavier it is ( relative to the wing area ) , the faster it is forced to fly . The lighter it is ( relative to wing area ) , the slower it is able to fly .

2 ) The spot on top of the fuselage ( where the motor/prop goes ) is designed for a 10mm stick mount , but you'll just have to improvise a way to mount your motor so the PROP is straight and centered in the vertical & horizontal prop slots . The two forces on a motor mount are : thrust ( pushing forward ) and torque ( twisting OPPOSITE of motor rotation ) . So mount the motor in a way that it won't come loose from thrust or torque .

3 ) At the wing tips , the starting CG is about 1/4" to 1/2" in front of the KFm step . Then adjust the CG ( in small increments ) forward or rearward for optimum flight . I mount the batteries on velcro right on top of the nose , leaving room to move the battery forward/rearward as needed . For the slowest flight , move the battery rearward until the plane flies just shy of porpoising at half-throttle .

4 ) A triblade prop will be fine if it's appropriate for your motor/voltage and fits in the prop slots .
Last edited by balsa or carbon; Mar 29, 2018 at 12:59 PM.
Mar 29, 2018, 02:55 PM
Registered User
Got it!

I tried to make it the lightest I could, there isn't much more I could do regarding weight.
Should I add more wing area if its still too fast for me?

What exactly do you mean porpoising?
Mar 29, 2018, 03:46 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
Quote:
Originally Posted by jawsqb
Got it!

I tried to make it the lightest I could, there isn't much more I could do regarding weight.
Should I add more wing area if its still too fast for me?

What exactly do you mean porpoising?
Yes , you can increase the wing area by cutting off the polyhedral ends and replacing them with LONGER polyhedral ends .

Porpoising is when the nose rises and drops , rises and drops , etc .



Here are some “first flight” instructions : find an area with the thickest grass cushion and no wind , then with the rudder & elevator centered and the throttle at 1/4 to 1/3 , throw the plane STRAIGHT AHEAD , making sure the wings are level when the plane is released from your hand . Then RESIST the temptation to move the rudder or elevator , and observe what it does as it’s heading gradually towards the ground . If it pulls to the right , adjust the rudder trim a little to the left . If it noses down SHARPLY , move the battery rearward a little bit , etc .

Once it’s going fairly straight , then increase the throttle to 1/2 to 3/4 and throw it straight ahead with the wings level .... it should then gently climb . Again , resist moving the rudder or elevator until it has a little altitude .... then make a GENTLE turn with as little banking as possible .
Last edited by balsa or carbon; Mar 29, 2018 at 05:20 PM.
Mar 29, 2018, 06:58 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
I just want to make sure you understand : the rudder and elevator need to be centered/neutral when the transmitter is turned on & the battery is plugged in ...... WITH HANDS-OFF the control sticks on the transmitter . If they are NOT ..... adjust the pushrods , clevises , servo arms , TX subtrim , or whatever is necessary to get them in a centered/neutral position BEFORE you launch the plane .

In your post #1 video , the plane is launched with UP ELEVATOR .... so it immediately noses up and climbs steeply . I'm not sure if the elevator was preset that way , or if you were holding "up elevator" on the transmitter control stick . For a trainer plane , you want to gently climb from gradually increased throttle input .... NOT from holding "up elevator " input !
The elevator control surface on a trainer plane is for :
1 ) bringing the nose back up to ( or maintaining ) level flight ...WHEN... the nose goes down by itself ( like in a steeply banked turn ).
2 ) recovering from a nose-dive .
3 ) a SLIGHT flare when landing .
4 ) doing an inside or outside loop .

If I haven't mentioned it already : ( assuming you have a mode 2 transmitter ) plug the rudder servo into the aileron channel , so you control throttle ( ONLY ) with the left stick ..... and all directional control ( roll/yaw & pitch ) with the right stick .





Launching a $200 plane with "up elevator" :



RC Plane Crashes into a Gate (0 min 35 sec)




"WHOOPS !"
Last edited by balsa or carbon; Mar 30, 2018 at 11:32 AM.
Mar 30, 2018, 10:55 AM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
One more thing ...

The EzFly does not have a good "power off" glide , so land it by gradually reducing the throttle ..... don't KILL the throttle while it's in the air . Since the motor & prop are on top of the wing , it's perfectly OK to land the EzFly with the prop spinning .

And to avoid "cartwheel" landings , don't try to make any turns when the EzFly gets close to the ground .
Mar 30, 2018, 04:43 PM
Cheese eating monkey.
Regarding the OP flight, I think that may be the pitch of the propeller is too low, so the plane doesn't get enough speed to fly on its wings and end up being suspended off his prop hence the weird attitude.
Mar 30, 2018, 08:32 PM
IMO ( In My Opinion ) →
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Just to let you know what the possibilities are for extremely light wing loading :



F3P - indoor pattern, 2014 season sequence. (5 min 15 sec)



Last edited by balsa or carbon; Mar 31, 2018 at 08:35 AM.
Mar 31, 2018, 12:57 PM
Registered User
So I did first flight, I wasn't about to get a video.

But here are some issues I had:

It seems to immediately pitch forward and nose dive when thrown.
- Perhaps Its not being let go fast enough?
- I tried a different battery and had a lot more push so may have just been the battery not providing enough power. Unfortunately I broke my motor mount when I tried this new battery
so I haven't had chance yet to try again.

I'm measuring cg from the point where the kb doubler ends, perhaps cg is farther along the chord?
Mar 31, 2018, 01:55 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
Quote:
Originally Posted by jawsqb
So I did first flight, I wasn't about to get a video.

But here are some issues I had:

It seems to immediately pitch forward and nose dive when thrown.
- Perhaps Its not being let go fast enough?
- I tried a different battery and had a lot more push so may have just been the battery not providing enough power. Unfortunately I broke my motor mount when I tried this new battery
so I haven't had chance yet to try again.

I'm measuring cg from the point where the kb doubler ends, perhaps cg is farther along the chord?

Did you follow these instructions from post #49 ? :
" find an area with the thickest grass cushion and no wind , then with the rudder & elevator centered and the throttle at 1/4 to 1/3 , throw the plane STRAIGHT AHEAD , making sure the wings are level when the plane is released from your hand . Then RESIST the temptation to move the rudder or elevator , and observe what it does as it’s heading gradually towards the ground . If it pulls to the right , adjust the rudder trim a little to the left . If it noses down SHARPLY , move the battery rearward a little bit , etc .

Once it’s going fairly straight , then increase the throttle to 1/2 to 3/4 and throw it straight ahead with the wings level .... it should then gently climb . Again , resist moving the rudder or elevator until it has a little altitude .... then make a GENTLE turn with as little banking as possible ."

And I think I forgot to mention : start with low rates on your rudder & elevator . Do you know how to set up low/high rates on your FlySky transmitter ?

The hand launch throw needs to be hard enough to get past the stall speed , but not so hard that the nose pitches up a LOT . Getting the hand launch throw right is just another one of those things that takes practice .

If you get a video of your next flight attempt , I can analyze it to see what you're doing right or wrong . Don't worry about beginner issues , EVERYONE OF US here on RC Groups was a beginner at one time ..... and I guarantee you I've crashed WAY more planes than you have .

Here's one ( or two ) of my crashes on video :



More throttle....duh.....oh $#!& ! (1 min 22 sec)
Last edited by balsa or carbon; Apr 01, 2018 at 06:04 PM.
Mar 31, 2018, 02:02 PM
Scratch building addict
rotagen's Avatar
Measure your cg from the front of the wing , if it is an angled wing it is measured from the leading edge at the root (center of the 2).

Go to an online cg calculator that includes the tail dimensions - enter everything as accurately as possible, use 12% static margin to calculate the cg - this figure has worked great for at least 6 planes for me. Mark it on your wing with a line and balance it onto a homemade cg stand (couple 1/8" dowels in a heavy flat board. Now don't deviate from there. and you can eliminate cg as the problem.

First off someone mentioned probably duck tape is usually way too heavy unless you're flying a sloper and you need the extra weight.

Since your wing looks like a solid piece of dense foam and the fuselage looks like pretty fat portions of the same material, you may have a very heavy plane there.

You can try to get away with it by using a lighter battery placed in the correct position (further forward) for proper cg - flight will be shorter.

Nosing down immediately on takeoff, it could be too heavy, it could be nose-heavy, it could have too little wing incidence, it could be improperly trimmed at elevator, the horizontal stab could be pointing too far upwards in front, your motor thrust angle could be downwards.. I bet on number one or two.

Use my method for making a light wing, use a 5mm or so lightweight foam as the lower surface of the wing, use a light 3mm carbon fiber rod (hollow) for support, just make 2 for dihedral., use a light strip glued vertically to lower surface of the same foam to give the high point (30% of chord back from LE) of the airfoil. Glue some super light material in front and back bending over foam strip to give the top surface of wing, it will bend gradually to make the airfoil, I use 1mm depron but waterproof paper would work, use light foam for the fuse and not too much glue... no heavy tape except if you want a small bit in key areas.

If you try this wing method you will never go back., super light and floats forever.

To give you an idea of weight you are shooting for, my 30 inch wingspan planes of average wing area weight around 9-11 ounces and they can fly as slow as you can walk.

When I started out I made one car shaped like a plane, I used a solid wing similar to yours with some foam way denser than dollar tree or styro or even bluecor 3M 77 laminated spray. It had wheels and never got off the ground, way too heavy.

A good test would be throw some wheels on it, if it doesn't take off within about 25 feet at full throttle you are super heavy.

That EZ flyer looks like a great design !

I found my new simple cutlass pusher jet to be another very forgiving slow flying plane.
Mar 31, 2018, 02:13 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
The blue mark ↓ on the wing tip is my EzFly's CG , about 1/2" in front of the KFm step .
Last edited by balsa or carbon; Mar 31, 2018 at 05:12 PM.
Mar 31, 2018, 03:25 PM
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balsa or carbon's Avatar
When I fly tomorrow morning I'll shoot a demo video of hand launching my EzFly .
Mar 31, 2018, 07:08 PM
Registered User
you need to verify your setup before doing a maiden, otherwise its just going to be another crash. if its built as per the plan and the CG is where it should be, theres no reason why it should not fly other than user error or incorrect setup.

have you verified your control surfaces move correct;y

if you push forward on the right stick, the elevator should move down, pull down on the stick and the elevator moves up
right stick right, right aileron goes up, left aileron goes down ( if you have ailerons that is)
left stick left , rudder goes left, left stick right, rudder goes right

with a correctly setup plane and cg in right place, it should travel fairly straight with little control inputs.
Last edited by bazsound; Apr 02, 2018 at 03:18 AM. Reason: correcting fatal error
Mar 31, 2018, 07:11 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
Quote:
Originally Posted by rotagen

That EZ flyer looks like a great design !

Nosing down immediately on takeoff, it could be too heavy, it could be nose-heavy, it could have too little wing incidence, it could be improperly trimmed at elevator, the horizontal stab could be pointing too far upwards in front, your motor thrust angle could be downwards.. I bet on number one or two.
rotagen ,

the EzFly really IS a great design , you should build one !

If you take a look at the plans ↓ , you'll see that the KFm wing & h-stab are flat foam and are both on the same horizontal plane ... there is no positive incidence or negative incidence on either one . And the prop is centered vertical in a vertical slot , and centered horizontal in a horizontal slot ..... so there is no downwards thrust angle . But it has some down thrust effect because the motor/prop are mounted slightly ABOVE the pitch axis ( and center of mass ) .


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