ORIGINAL: sbaugz

polikarpov i16, I have to disagree with you. My airplane is in no way stalling when it snaps. Even when pulling up from a high speed dive, the plane snaps to the right, indicating that slow speed stall is not the issue as you suggest.
Maybe its not a true snap- maybe its a roll to the right. Either way, the plane is in no way approaching a stall speed. I think what is happening, is that the right elevator is moving slightly differently than the left elevator. I am also sure that torque has something to do with it as well.

ORIGINAL: sbaugz

Maybe I used the wrong term- AlexF is probably summing it up correctly when he says its probably doing a barrel roll versus a stall.

ORIGINAL: polikarpov i16

if your airplain is rolling to the right witch is diferent than a snap it has to do with the propeller
you do not notice it on a 40 size because you have a small prop
the gyroscopic forces of a 15 inch prop are huge
enough to roll your airplain over

ORIGINAL: sbaugz

YNOT,
I guess you must be the expert then.

Steve,

Thank you for your enquiry. Sorry to hear about this situation. I am hesitant in saying this, as many will view it as the manufacture saying what they have to in order to make a sale, but we are truly no experiencing the same issues as you are explaining. I do have many, many years of experience in RC. So I will do everything I can to help resolve this matter the best I can. I have read some of the posts on RCU......some members are saying the right things, and others are not, in my opinion. Here is a list of items I would check and comment on:

First, our set-up on our plane is 100% stock. All the stock hardware and accessories with no modifications. We are using a Saito 82 which is demonstrated in our videos, and we are using all high torque ball bearing servos, only because this is what we had available to us. We are using Hitec 615MG servos on all control surfaces which provide a lot of torque.

I would like to discuss the "rolling / snapping" tendencies which are mentioned. This clearly needs to be analyzed. Meaning, is it a slow rolling maneuver, or a high rate, more violent maneuver. If it is a slow rolling maneuver, it is not a stalling situation. If it is a more violent rolling maneuver, it is a stalling situation. There is such a thing as a high speed stall. Most don't fully understand what it is. Almost every airplane can be coaxed into a high speed stall. Too much throw is the first cause. Tail-heavy is another. A combination of the two can become very violent and uncontrollable. If it is a slow rolling maneuver, it can be a couple of issues. Flex in the control surface is one. More throw on one elevator vs. the other is another. Torque is another. Lateral balance, yet another. Inadequate servo torque is one more. There are some tests which can help to determine what is happening. You already know what the results are in a full speed pass or a dive. Try a half throttle pass and see if the symptoms still exist. Also, fly inverted and fly both full and half throttle and test the results to see if they are the same. The reason for this, if it is the elevator pushrod, in one direction it pushes, in the other it pulls. The pushing side is usually always the side that flexes, and also puts more strain on the servo. If it does not do it inverted, I would suggest it is the pushrod, or inadequate servo torque causing the problem. Another thing, if it is performing a more violent type maneuver, than it is more than likely a high speed stall which would require reduced elevator throw, and possible changing the CG. My test for this is full speed loops and reducing the elevator until they can successfully be completed continuously without any rolling / snapping tendencies. This is the rate of elevator I would use for normal flying. You may need more elevator for landing, although not usually, and if this is the case, you will need to run dual rates. We use full elevator, as much as we can get, for 3D type maneuvers. However, we perform these maneuvers at low throttle settings and rely on power to be the elevator....controlling altitude. But you have to keep in mind, this plane is a Katana, not a Funtana, and is sensitive in high alpha maneuvers which require skill. Funtana's provide you with a sense of security as it is a sport scale airplane designed for fun with thick airfoils for added stability. OK.....enough rambling.......here are some points of interest.

1. Elevator Pushrod - There has been a lot of discussion here about this issue. This type of set-up has been used for years successfully.....however, this type of set-up can present problems. First, un-equal elevator deflection. Second, lack of support, sometimes causing flexing. Third, you need adequate servo torque to support the system. This type of system is very difficult to make perfect, but can be done. This type of linkage almost always provides for more strength (holding power) in one direction vs. the other. This is due to the fact the servo is pulling in one direction and pushing in the other. Most inconsistencies and flex occur on the push side. The pull side is usually very strong. This is why the plane may perform better in one axis vs. another.

2. CG - The center of gravity on this size plane is very critical. Meaning, 1/4 ounce of weight will make a noticeable difference in the CG location and the flying characteristics. CG is an adjustment of personal preference. This is why there is a range. Also, it is based on your level of flying. With the problems being noted, I would recommend changing the CG to a more nose heavy position along with the other changes in the elevator control throw as mentioned in an effort to solve the situation. Once the situation is resolved, additional changes can then be made to "fine-tune" the model for your type of flying and feel.

3. Lateral Balance - Lateral balance will have an affect on the way a plane flies. I once saw a plane drop a wing on take-off and landings all the time, but fly well in the air. Once it was balanced properly, it flew perfectly. This check should always be part of the set-up process and pre-flight checks before flying a plane, but in my opinion, bases on what you are saying, I do not think this is the issue in your case.

4. Right Thrust / Engine Torque - This could very easily be the issue too. Part of my first flights and initial set-up, I always check the engine thrust. Here is how I do it......Vertical climbs, hands off. I pull up straight and level and punch the throttle. I then take my hands off the sticks and watch the plane. If it veers off to the left, it needs more right thrust. To the right, it needs left right thrust. If it pulls to the canopy, more down thrust, and if it pushes towards the gear, more up thrust. I keep making changes until it performs a perfect vertical upline hands off. This technique always works for me.

Now, there is such a thing as too much power / torque. I once had a plane that was so over powered, on vertical climbs, the plane would do a slow roll to the right. Flying straight and level, it would roll to the right. On take-off, if I punched it hard, it would torque over to the right. So, here is another test. Fly straight and level at half throttle, plane trimmed perfectly, and punch the throttle, then throttle back, if the plane starts to roll to the right, you have a torque issue and it may be difficult to solve. One way to remedy is to experiment with props. In my case, I was so over-powered, I experimented with 3-blade props which helped significantly, but still didn't solve the problem. I ended up making am ix in my computer radio with the throttle to my ailerons to re-trim the plane with different throttle settings. For me, it worked fine and the plane was enjoyable to fly from that point. By the way, I am referring to a giant scale plane with a large gas engine.

5. Wing Incidence - Lastly, this could very easily be the issue too. One wing positive and one wing negative will easily cause the same issues you are mentioning. If you have not checked the incidence with an incidence meter, I would highly recommend it. Even the planes that are pre-set from the factory should be checked. It is VERY easy to change the incidence, and most don't even know when they did.

So in closing, (sorry for the long winded email), I do believe a dual elevator installation will help. BUT, you will need to refer to all the above recommendations to fully solve the problem and set-up the airplane. There are many successful Katana's flying out there so I know it can be done. I am also aware of the posts, so thus the lengthy email to you. Please share my comments with everyone..... my hope is to help everyone so they can thoroughly enjoy the Katana. Please do not hesitate to contact me with any additional comments or questions. I look forward to speaking with you again soon and I really hope your changes and attention to these details will prevail in a success for you.

Sincerely,

Ultra-RC
Brian Hughes