I know, adding tail weight to a plane that snaps is completely contradictory too conventional wisdom.
Sounds nuts. I know.
Myself and two other guys have the same Sig Cap 231 Breitling. We all fly together occasionally. And we compare plane setup and engine performance.
I am running a big ST engine in my plane, and the other two guys run a Saito 180.
We all had the exact problem that craftsman described. Same exact problem. High speed snaps with full elevator on high rates.
We started trimming the planes according to the sheet that we got from the guys at Aeroworks. I had to add a boatload of right thrust to mine. And even some down thrust. Other guys had to add lot of down thrust and one guy had to also add a lot of right thrust.
Just try what I described in the above post. Try it BEFORE you mess with the balance, that way you have a reference point. Remember, the balance point that most manufacturers provide is only a safe point for starting out. It isn't written in stone that you must not go beyond those specs provided by the manufac. You'd be amazed at how far back I have some planes balanced. According to the plans and specs from the manufac. ; the plane should not fly, but they fly GREAT!!!
Once again; for checking the balance, use the following procedure:
Full throttle flat and level.
Pull to a 45 degree upline and roll inverted.
DO NOT TOUCH THE ELEVATOR
Plane should continue on a 45 degree upline without changing pitch very much.
If it starts to drop the nose, then you are still nose heavy. If the nose goes up and the tail drops, then your tail heavy.
For right or left engine thrust:
Come in about half throttle- flat and level
pull straight vertical and wait for it to ALMOST stop
Slam the throttle full open and then close it quickly
Do it again
Slam it full throttle and then close it quickly
If your plane torques too the left more than you'd like, then add right thrust. If it's gonna torque left; then it will happen when you slam it full throttle when vertical.
If it doesn't torque left, then your probably fine.
When checking the engine for UP or DOWN thrust, there are a few different methods. I usually try both and come too a happy medium.
Checking for proper up or down thrust is a bit more fun:
Come in flat and level- about 1/2 throttle
pull staright vertical
go Full throttle when perfectly vertical
LET GO OF THE ELEVATOR!!!!!!!!
Watch it and see if the nose comes back onto the top or if it goes towards the belly of the plane.
If your nose comes towards the top of the plane and you would need to add down elevator to keep it vertical, then you need more DOWN thrust.
If the nose falls towards the belly and you would need UP elevator to keep it vertical, then you need more up thrust.
The other way; I usually do the next method after the vertical test
Take it up HIGH.
Start out HIGH-200' or 300'- whatever you consider high
full throttle and flat and level
shut the throttle quickly and let it glide
DO NOT TOUCH THE ELEVATOR
watch it and look to see if it falls quickly
Your plane should glide reasonably well. If it is nose heavy, then it will come down fast and accelerate at an idle.
Keep in mind that aerobatic planes don't really glide very far, but most; if properly built and have reasonable wing loading, will glide for awhile. Any plane that drops like a rock after shutting the throttle is most likely, too nose heavy, has improper engine thrust or has DRASTICALLY high wing loading.
Check your incidence. Incidence meters are great. I use them on every plane I build. But there's no substitute for checking the plane in flight after setting it according to plans.
To check wing incidence:
Take it up REALLY REALLY HIGH- at least 300' maybe more
flat and level1/2 throttle
close the throttle down to a nice idle
put the plane into a VERTICAL dive at idle
TOTALLY VERTICAL
LET GO OF THE ELEVATOR
watch it
pull out and throttle up before you get too close for comfort
What your watching for is to see what the plane does in a totally vertical position at an idle. You must do this Vertical, with the nose pointed DOWN at the ground. Thats why I say- start out HIGH.
If, when vertical, the plane comes down and pulls out to level flight. Then your wing incidence may be positive too much. On a plane that calls for ZERO incidence on all surfaces-(wing, stab and engine), it should come straight down.
Some might just come up towards the top of the plane and creep towards level. It might appear as if you are adding just the slightest touch of UP elevator That might be fine. Depends on the plane.
If, when vertical, your plane tucks towards the belly and starts too come around and push out and go inverted, then your maybe a little on the negative side of the incidence.
Now for my disclaimer: I'm no genius. I read all this stuff in books and heard it from other more experienced pilots than myself. I do each and every one of these tests on all my planes now. Yes, I spend almost a gallon of fuel doing all these tests again and again. Each time; landing and adjusting. Then going through the test again. Sometimes I spend MORE than a galloon of fuel to get a plane right where I like it, but in the end, its money and time well spent.
I only try and adjust one thing at a time. One day I will take a new plane out and only work on engine thrust. Next time I take that plane out to the field, I will only work on balance or wing incidence. The point is; only adjust one thing at a time. And above all BE PATIENT!! (thats the hardest one for me)
Sometimes, you might think you have the engine down thrust right where it should be, then you go and start checking the incidence, and you wind up going back and changing the thrust again to make up for an adjustment that you made to the wing.
Believe me, I've spent a few hours chasing my tail when doing this stuff. But, a little tweak here and a little thrust there; and before too long, your plane is flying like you never thought it could.
Try some of the things I've suggested, you might learn something and it will be fun too. I'll bet your plane will fly nicer when your done, too.
Sorry I got so long on this one.