Hip Pocket Builders' Forum

Radio Control Forum => Stick and Tissue R/C => Topic started by: simpsd on January 16, 2016, 02:43:39 PM

Title: Fairchild 22
Post by: simpsd on January 16, 2016, 02:43:39 PM
I have been working on a 33 inch wingspan Fairchild 22 from plans by Hurst Bowers.  I have put a SA 250 motor in it and plan to use a two cell lipo 700 - 800 size.  It will be three channels- just rudder elevator and throttle. The only major modification so far is the construction of the wings.  I have opted to make laminated ribs rather than cut them out of sheet stock. I think this makes a lighter wing while keeping the strength where it is needed and... I just like the process and the way it looks.  For similar reasons I plan to cover it with tissue and just not fly it when it is damp out - I have other planes for those days.

Title: Re: Fairchild 22
Post by: Konrad on January 17, 2016, 01:12:09 AM
I gotta say I love your work!

Title: Re: Fairchild 22
Post by: Pops on January 17, 2016, 02:04:46 AM
Beautiful model with beautiful building techniques and also beautiful craftmanship it seems! Allow me to steal the rib laminating technique for one of my own designs, pretty please!?!? :)

I guess you have one solid spar in the wing instead of two spars top/bottom? What would the RTF weight of this model?

BTW, I found and downloaded a Bowers plan for the 22 with a 47" WS, and I do have an old OS .10 FP I've saved for a special occasion - this design might be it! :)

Title: Re: Fairchild 22
Post by: julio on January 17, 2016, 11:04:51 AM
WOW :o!!
What a clean build! What a technique! Are you using glue or this is a new ultrasonic balsa welding method? What glue and if possible, what method do you use to apply the glue?
Great photographer too.


Title: Re: Fairchild 22
Post by: simpsd on January 18, 2016, 09:48:30 AM
Thanks for the complements :) The laminating process is not difficult but it does have its share of limitations.  For instance it is nice to place the spars in the wing where the wing struts will attach or where other structural considerations would have you put them but using my method the shape of the curve of the upper surface of the wing pretty much determines the spar(s) location(s).  Also I have not tried this method on an other than flat bottom airfoil.  What I do is glue up the bottom cord of the wing then experiment with different spar locations until I find the locations that produce the curve in the top laminating strips that I want.  Because I use 1/32 strips the wing is quite fragile until the second lamination goes on. I use regular titebond glue.  I brush it on with an old paint brush. Sometimes one rib does not bend just right and needs an extra lamination and careful sanding to get it level with all the other ribs.

Title: Re: Fairchild 22
Post by: Pops on January 18, 2016, 11:31:23 AM
- So you don't use a template for the rib laminations, you just bend the strips over the spar and glue them down in each end? (Or did I misunderstand now?)

Title: Re: Fairchild 22
Post by: simpsd on January 18, 2016, 03:33:17 PM
You're right. It's that simple. Someday I do intend to build up some ribs on a jig the way real airplane ribs were once made, but I haven't slowed down enough for that yet. Still too excited to get them in the air.

Title: Re: Fairchild 22
Post by: julio on January 18, 2016, 04:48:25 PM

Many thanks for your answers. Following with interest.

Someday I do intend to build up some ribs on a jig the way real airplane ribs were once made, but I haven't slowed down enough for that yet.

Take your time, I think you are doing fine by now... ;D


Title: Re: Fairchild 22
Post by: Don McLellan on January 18, 2016, 08:46:02 PM
Exceptionally nice work!! 

Title: Re: Fairchild 22
Post by: OZPAF on January 18, 2016, 11:07:36 PM
Lovely work S.

as for laminated ribs - here is an alternative when many are required. I have used this approach a few times now and it works well.



Title: Re: Fairchild 22
Post by: simpsd on February 13, 2016, 08:33:41 PM
Getting close to complete.

Title: Re: Fairchild 22
Post by: Don McLellan on February 13, 2016, 10:18:15 PM
More pics please!

Title: Re: Fairchild 22
Post by: Balsa Ace on February 14, 2016, 08:37:01 AM
Great work.


Title: Re: Fairchild 22
Post by: Pat Daily on February 15, 2016, 09:27:38 AM
Hurst is smiling!

Title: Re: Fairchild 22
Post by: simpsd on February 16, 2016, 02:46:57 PM
The Fairchild 22 is closer to completion now.  All that I plan to do before I fly it is to add the exhaust pipes, the battery hatch door in the belly and the instrument panels.  Once I fly it and get it trimmed out and all adjusted, I plan to permanently attach the wings (get rid of the rubber bands etc.) and add the wing struts.  The wing is quite strong as is so the struts will be just for scale appearances.

Title: Re: Fairchild 22
Post by: OZPAF on February 16, 2016, 06:26:12 PM
What a nice model of a great subject. It should fly as well as it looks


Title: Re: Fairchild 22
Post by: simpsd on February 17, 2016, 06:07:43 PM
I'm just back from the field.  The Fairchild flies nice, but I'm having trouble with the power.  I can't get much more than half throttle out of the Stevens Aero 250 before it starts to surge and pulse and sort of fail.  I knew it was having this problem but flew it anyway because I thought for the just 7 ounces the Fairchild 22 is that would be enough... and it was, just barely.  I did eak out a long very scale like take off from matted down bumpy grass but mostly I hand launched it.  It is just a bit nose heavy but for now I handled that with a little up trim.  So what is wrong with my power system.  I have the same motor in an 8.5 oz 33 inch wingspan Citabria and it has plenty of power and does not break down at the upper rpms.  The Citabria has plenty of power for basic acrobatics.  The only difference in the set up is the Citabria has a Hobby king 10 amp speed control and the Fairchild's is a 10 amp by Horizon Hobby.  Does this sound like a weak connection, or a motor problem or what?  (It's not the prop I have tried the same one as on the Citabria and still have the problem)

Title: Re: Fairchild 22
Post by: OZPAF on February 17, 2016, 08:09:11 PM
It sounds like a motor problem to me. If possible try running the Fairchild motor on the Citabria speed controller. If the problem persists then it is the motor.

If it runs ok then it is the speed controller.

If one of the motor phase wires - 1 of the 3 wires from the motor may be partly broken or shorting.

Good luck

Title: Re: Fairchild 22
Post by: Pops on February 17, 2016, 10:43:22 PM
As long as you use the same battery pack on both setups I agree with John. But my first suspected culprit would be the battery pack, then the wires and connectors between battery pack>ESC>motor -all this indicating that the motor is starved of energy. It might also be a timing problem, where the ESC can't "follow" the motor on high RPMs and then it "cogs over" so to speak.

John's way of testing will help you figure out where the problem is. Check ESC programming regarding timing and cut-off voltage and ensure that it has proper cooling.

Title: Re: Fairchild 22
Post by: Pit on February 18, 2016, 09:32:24 AM
I'm guessing a bad solder connection...

Title: Re: Fairchild 22
Post by: simpsd on February 18, 2016, 11:40:15 AM
I replaced the speed control with a spare hobby king 10 Amp esc. and the problem went away.  Some things I observed along the way: 1, there was a difference between batteries.  With some batteries the surging began just under half throttle and with others not until three quarters throttle.  2, I found the programming instructions for the horizon esc which read:
 "The default settings (from the package) for your
E-flite 10-Amp Pro ESC are as follows:
 • 3S (9V) auto cut-off for Li-Po
 • Brake Off
 • 4-pole and greater timing (outrunner or 6-pole motors)
 • Throttle input range set to Auto Select Mode
Programming Menu 1 – Voltage Cut-off
Use this option to set the voltage at which the controller will shut down
the motor to prevent damage to your battery, when it reaches the cut-off
voltage. You will know that your battery pack has reached auto cut-off
when you hear the motor “pulse” repeatedly.
 1. 3S Li-Po voltage cut-off – Full Throttle
 2. 2S Li-Po or Ni-Cd/Ni-MH voltage cut-off – Idle
 3. 70% Smart Cut soft cut-off (See below for Smart Cut information)
NOTE: To access the 70% Smart Cut option, leave the stick at full throttle for 7 seconds while in menu
item 1, until 7 beeps are heard, then continue through the program normally. This option will activate the
soft cut-off at 70% of startup voltage. For example, if your pack measures 10.0 volts at startup, then the
soft cut will occur at 7.0 volts. The Smart Cut option will check the startup voltage every time you plug the
battery into the controller, so beware of using partially charged packs, as the system cannot protect your
Li-Po batteries if you are using Smart Cut and connect a partially charged pack.
You will know your battery pack has reached soft auto cut-off when you
hear the motor “pulse” repeatedly. We recommend you land your model as
soon as you hear the motor pulse (indicating the pack voltage has dropped
to the cut-off voltage level) to prevent over-discharge of the Li-Po battery
pack, and to prevent sudden power loss."

So I figured the ESC was still set up for three cells and I attempted to reprogram it for two cells.  Though I tried this reprograming many times It had no effect on the surging problem.  If there is a bad solder joint, this time it is not my fault as the horizon esc comes with all connectors already to go.

Anyway ... problem solved, so if the wind will just quit blowing...   Thanks for all the help everyone.

Title: Re: Fairchild 22
Post by: USch on February 18, 2016, 12:50:11 PM
Some thoughts on the pulsing motor.
If the ESC is overloaded it will not pulse in a quit mode but will rattle with a nasty noise.
This can happen with the same motor and ESC, but different batteries with different internal resistance (mΩ). The battery with lower resistance will deliver more push in terms of Amperes and therefor higher rpm's. This in turn leads to overload the ESC which is loosing the exact position of the poles as Pops wrote. The battery with higher internal resistance will deliver less Amp's and the motor is turning at lower rpm's and not overload the ESC.
It has certainly nothing to do with the setting about 2 or 3 cells. This will be recognised automatically by the initial tension (V) by the ESC himself, at least most ESC do so because voltage of 2 and 3 cells are not overlapping. 2 cells have a V range of 8,4V at fully charged down to 6V discharged, 3 cells have 12,6V to 9V.
Some ESC's from the same manufacturer have different behaving's at the top end because of tolerance's in the electronic bits and pieces.


Title: Re: Fairchild 22
Post by: OZPAF on February 19, 2016, 05:52:02 PM
Well that's interesting S - thanks for the info.  However the main thing is you have now resolved the problem.
The one time I may have experienced cut off in the air  - I lost the model (a small Fox park flier)
I find it much safer to fly by stop watch(talking count down timer) and not to ESC cut off and aim to take my batteries no lower than 35-40% full charge.
Happy Flying.