• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Not CRAZY but simple trainer needs help

erice3D

Junior Member
#1
Hey guys.. I built a little trainer to get my family and friends into the hobby.
I have helped build several nutballs for people and I am getting complaints that they are too (floppy).
So I threw this together. Triangle fuse 23" with 30" under camber dihedral wing.
coupled with a Hobbyking Donky 2204 1550kv and 2-5g servos. I since switched motors
to a hextronx 2211 1700kv and added a 1" wing riser.
Both motors work great with a 500 to 800 2 cell. All up weight of 7oz with the Hextronx.
Maiden went great flew right off the bat. plenty of power control just don't glide all that great.
Tried 2 wing styles flies best on dihedral.
My big question is? how can I make it fly better without changing its simplicity?
I scribbled some plans on a piece of paper to give an idea. I think the wing riser can be cut in with
the fuselage but for the prototype I wanted to be able to move it. Misspelled some stuff. lol
 

Attachments

DamoRC

Well-known member
Mentor
#2
Nice simple build.
Question would be, if it flies well, why would you change it? Or is there a specific characteristic that you want to improve? You say that it flies well but doesn't glide well. Have you tried pushing the CG back? Do you need a lot of up trim to keep her flying level? I think there is probably a lot "tuning" that you could play with that would not change the design and build drastically but might get you the flight characteristics you are looking for.

Good luck!
 

erice3D

Junior Member
#3
Guess what I meant by flew (well) is it didn't end over or nose dive.
I have the cg at 2-3/4".
Have to give down trim. it tends to pitch up with throttle
even with slight down thrust.
The thing will only glide about 10ft then nose dive.
Better when I dropped an oz with the motor change.
 

DamoRC

Well-known member
Mentor
#4
2 and 3/4 seems a long way back for a 6 inch chord. Then having to add down trim to get it to fly level and the fact that it nose dives off power, I would say you may be tail heavy. Try to reset the trim and balance at 1 3/4 - 2 inches.

Google "dive test CG" to see why I think you are tail heavy.
 
#5
You have a narrow wing cord...so you don't have much leeway to balance.

How wide is your wing front to back (this is the wing cord).

Shoot for a CG 25% back from the leading edge.
If the wing is 5" front to back... the CG should be 1.25 inches from the leading edge.
If the wing is 6" front to back... the CG should be 1.5 inches from the leading edge.
If the wing is 7" front to back... the CG should be 1.75 inches from the leading edge.

Draw a little pencil mark back from the leading edge on the bottom of the wing on either side of the fuselage where the CG should be located.
You can extend the pencil mark to the bottom of your fuselage.
Mount the wing where you designed it to be mounted.

Balance to the pencil mark by moving your heaviest internal components forward or back...don't move the wing to balance.

As you can see you don't have much leeway to make mistakes...1/4 of an inch either way will make you nose heavy or tail heavy.
The normal range is 25% to 30%.
25% is best to start out with...it will fly straight.
Nudge the CG balance point back for more maneuverability(more 3D)...but don't go beyond 30%.

If you were starting at 2.75" back from the leading edge...there's no way it would fly...
2.75" on a 6" wing cord is 48%...that'll never fly.

A 25% balance from the leading edge of the wing will do wonders.
Remember...conventional wing...25-30% GG from leading edge.
I prefer 25%-27%.

Be as precise in you measurements and balancing to 25% as possible.

Please report back your findings.

PS. If this doesn't fix the problem then we need to look at angle of attack of the wing.

Your angle of attack may be too high.

If your COG is at 25%, but your nose still rises when you apply power...that's a giveaway.
It means the front of your wing is mounted too high. By mounting your wing up on that pod, when you apply power the wind from the motor is hitting mostly the bottom of the wing, causing the nose to rise.

If your angle of attack is too low...the nose will dive on throttle up.

This will take a little designing, but if you are willing to experiment, here's how to proceed.
Keep the height of the back of the pod as it is, but trim the pod in a straight line so when it gets to the front of the pod it meets the fuselage.
In other words. the pod is now a long triangle with the full pod height in the back...and no pod height where it ends in the front.

Mount the wing and balance to 25%.
Try to fly it.

If adding throttle still makes it climb...the wing is still too high in the front.
Add a loose spacer of foam thickness on the wings trailing edge, and try again.

If adding throttle makes it dive...then the leading edge of the wing needs more height...
Add a foam spacer to the leading edge and try again.

At some point you will get to the proper shape of the pod, giving you the proper angle of attack for that specific wing with a CG of 25%.
It should fly and glide straight and true...under power...or with power off.

The CG of 25% is very important...it must be maintained...and the angle of attack of the wing becomes the factor you are changing.
Once you get the pod trimmed to give the wing the proper angle of attack, it should be suitable for most wing styles.

Hope this made some sense.

PPS. Another method is to mount the motor with some washer spacers to pitch it down...but do this only after addressing the angle of attack as well as you can.

PPPS. Maybe rather than cutting the pod down totally to start with...go in 1/4 inch increments.
Measure down 1/4 from the top of the front of the pod.
Draw a straight line back to the top of the back of the pod.
Trim the pod along the line
Balance to 25% COG and try it.
As you lower the angle of attack by 1/4 inch increments you should see gradual improvement...until at some point you may go too far and the nose will dive on throttle.
You've gone past the ideal angle of attack.
Back up to the point the plane flew and glided the best (at 25% COG).

Please report back any findings.
Remember...always set COG at 25-27%...then adjust for proper angle of attack.
If at some point you get rid of the pod and mount the wing closer to the fuse...you can still play with the angle of attack.
 
Last edited:

jamboree1

Active member
#6
I think Burly said it best with the main wing angle of attack, i prefer the wing to be level with the tail feathers for scratchbuilds like this
 

erice3D

Junior Member
#7
I originally built this plane to have the wing right on the fuselage, but it didn't bank well in turns .. Here is what I did. I trimmed some fat off the tail end and moved 2- 3.7 gram servos further forward. Pushed the wing back an inch to get the CG to 1.75. I think 7in wing would be more productive. I did get it in the air BUT it has been TOO windy here to get an accurate assessment. My original prototype is getting pretty sketchy, its also realty realy wet here not to mention its hit the ground quite a few times. Think I need to throw another one together.
BUT its full on maple syrup season so I have been preoccupied. After work hauling sap and late nights cooking to keep up.
 

jamboree1

Active member
#8
I think your bank turns problems are due to the amount of dihederal in the main wing, dihedral is meant to keep the plan on an even keel. Being rudder only, direction is changed by creating yaw, while a lot of applied rudder can make a plane bank turn a bit your other issue looks to me that your rudder is a bit small for rudder control only
 

VolksRocket

Rocket Scientist
#9
Hi,

Well, you have built an aircraft with the minimum of what is necessary to be a first flight trainer to a 3d flyer! Congratulations!

You can change this design a hundred different ways to make it fly the way YOU want! The only thing you can do to make it fly better is find the CoG and then move parts around to get the flight characteristics you want.

I built this almost exact aircraft design about 40 years ago.....except it was cardboard and rubber band powered freeflight!

Straight Wing - Dihedral Wing - Polyhedral Wing - Flat Wing - Camber Wing - Round Tips - Stick Tips - ..... the possibilities are endless!

Sincerely and Respectfully,
Terry W. Wheelock
natural born Citizen
Independent Candidate for President of the United States 2016
Vote! WHEELOCK! 2016
 

erice3D

Junior Member
#10
Here is the Frankenstein.
7in wing 2- 3.7 servos. hextronx 2211 1700kv with a 8x4.3 prop on a 800-2s.
Balanced out in front of the 2in under camber. 7.2oz all up weight.
floats SO slow, you can walk faster, has good control. no more up pitch with throttle.
It still will not glide well unless pull back on the stick. Tried to move the CG back some then it gets a slight stall/glide-stall/glide repetition. With CG at1.75 it will glide with full stick back and no stall all the way to the ground.

(REVISION- 2 deg or 1/4 in in the front of the wing improved the glide)
SD530225.JPG
 
Last edited:

erice3D

Junior Member
#11
So I tried something else with this design. I modified it to accept the power pod off the Nut Ball.
It doesn't fly As slow maybe 4 more inches on the wing length would fix that.
BUT it does fly fairly well. SD530232.JPG