Larry and I are continuing the trim process on the SS 350e.  Things were going well until we let a  friend fly the plane, his initials are Eric Rule.  I have to be honest Larry and I knew about this problem and Eric was not ready for it.

Here goes we can now do every maneuver in the pattern, but we do have a serious problem to resolve.  Above 45 degrees the plane has a yaw in tendency.  This makes for dicey overhead and for that matter anything up high.  The problem is less serious with the wind you your back, but where we fly the wind tends to change direction frequently.  That, in my opinion, is what got Eric.  I took the plane home and made the repairs, I also removed some test lead in the nose and move the battery forward to get the CG where Larry believes it should be.  We discussed the yaw problem and think it could be related to gyroscopic pressesion above 45 degrees.  The yaw does not occur in outside maneuvers and line tention below 45 degrees is perfect.  Anyway I am taking some advice I got on this site about using a  pusher prop and reverse the motor direction. 

Larry and I will hopefully get a chance to test the latest changes sometime this week.  We are both still very hopeful on this project.
Andy

Hi Larry/Andy,

Dennis is sending me some APC 11 x 4.5 pusher props. I will get them to you when they arrive. They may help with your problem. The pusher helps all the time in all plane positions. :-)  If you are using the 12 x 6 , I have an extra pusher for you too.

Great truck, a friend has one and loves it!

Regards, 

I installed a pusher 9 x 4.5 yesterday and reversed a couple of the motor connections.  I am waiting for an opportunity to go flying with Larry to see what if any effect the pusher makes.
Andy

Mike
That is an interesting observation.  If reversing the motor does not eliminate the problem that would be a good next move.  I am concerned that the fins sticking out at the end of the horizontal stabilizer could cause some problem.  I have to be honest we have never seen the problem on the half-A version.  But that does not mean it can't happen on a larger model.  Thanks for your input.
Andy

Ahem and harrumph, there seems to have been a problem, Houston.  It seems that the stab was canted to give in-turning rudder with the twin tails.  I shall blush on behalf of the culprit who built the model, and myself for not looking at that earlier.  We will have another test session tomorrow.  That problem has been corrected.  No names, please.

I took out my kid's gyroscope and did some live testing, and if precession really was a problem, it would be exactly the opposite of what we thought.  With a right hand (standard rotation) prop, you get outboard yaw on up and inboard on down.  Reality beats theory every time!  Dang.  

I sit here shamed before my friends and fellow modelers.  Yes, I confess yesterday afternoon I took a good look at the elevator and low and behold it was off by a couple of degrees.  I worked feverishly to correct the problem and this morning our yaw problem was solved.  Oh well who among us has never erred.  This now allowed us to move on to the next two issues.

Issue number 1.  We have observed this problem twice today on two different battery packs.  After flying for a couple of minutes we landed to tweak some trim settings and when we returned to flight the power was way off.  I swapped the battery and everything was fine until we landed again to switch pilots and we had the same power drop problem.  Now I will confess these are cheap Li Poly battries and maybe this is "You get what you pay for" type problem, has anybody else seen this kind of problem.

Issue number 2.  When running the motor at full throttle in static tests if we make sudden changes in pitch the motor makes some not so nice sounds and seems to slow a bit.  It sounds like maybe some side load on the bearings is causing the bearins to howl a bit.  Again this is not a high end motor.  Again it may be another attack of "You get what you pay for".


Appreciate any help on these issues.  As I mentioned to  Larry at least we are making progress, every step seems to be a step in the right direction.  Larry also made an observation, it probably was not a good decision to attempt this project with a untried plane and untried power system.  But we are learning.
Andy

Hi Andy,

Being one of those few "... who among us has never erred".....  NOT, ..... I even err in my dreams! .....

Here is my humble opinion:

1. We need to know how much of the battery (%) you are using for a complete flight. This may help us find the problem. But here are some ideas: Look at the "cut off" setting in your ESC. If you are using a CC ESC with the USB computer hookup then you can see this on your computer screen. Your setting may be so low that a little drop on the battery is not enough to keep your RPM up after a restart. Are you using the governor mode on your ESC? Give us your settings if you can, it will get you some solid answers from others on this forum. What size are your batteries and what are their C rating?

2. I found that our outrunner motors move more than 1/8" on their axis during a flight. This is a measured amount. So if you have anything near your motor, it may be rubbing. This will cause noise, heat, and waste battery energy (don't ask how I know this ;-).

3. Your 3rd point is well taken. I am a big fan of: "you get what you pay for". I know others have used very cheap equip. in RC and CL and it still works. Some of the guys at our ERC field use this cheap equip. Most of the time it works OK. In RC a failure is seldom catastrophic because we cal always roll upright and land etc. There are many failures at our field but they are just laughed off and the failed part is easily, cheaply replaced. IMHO it is different in ECL. Our system stress points are always in precarious parts of the flight. A failure of any part in the ECL power system is often catastrophic to the plane.

I don't expect everyone to select Plenttenberg motors but there are many high quality motors at more modest prices between the top and the bottom cheap motors. The same is true for the other parts of our systems. The price of our quality batteries, Thunder Power and Hyperion, has come down to the point that they are now much less expensive than glow fuel.

Please don't misunderstand me, I am not trying to convince anyone what to buy, I do not have any financial interest in any part of the hobby. My take on this issue is that I like to have everything work well and I try to eliminate every possible weak link in the system. In my career these were important issues to take care of and helped insure my (and others) survival. I know there will be those who will chime in and tell us that cheap is OK, and that is fine for them, but I still believe that when it comes to aviation that old saying still applies: "..... penny wise, pound foolish ....".  This is also true: "to each his own" :-)

Regards,       

A couple of clarifications:

1.  We were still using the radio system to control the motor, so the timer and it's functions were out of the loop.  With the radio, high throttle is constant input, no matter what  the battery voltage.  In addition, the power was just fine when we shut the motor off, and anemic when we fired it up again a couple of minutes later.  Howard Doering (current AMA electric C/L speed record holder) points out that the battery is probably warming up as it sits, due to the cessation of airflow over it, and that increases internal resistance.

2.  I was careful to rotate the model at the rates we see in maneuvers, not violently pitch it up and down as fast as possible.  Even the relatively slow pitch of a round maneuver caused the noise.

3.  Air only cavitates at hypersonic speeds.  Separates, yes, but that is a whole different thing.  Separation causes turbulent airflow in the wake, cavitation causes a true vacuum in the wake.