Clint - how about a 'plug' to fill those wing tip 'hand grip holes' in at lease a semi-permanent fashion. Maybe two piece with two or four long screws to hold the top to the bottom. Kinda goes along with your stab tips, I think. Best to you.
If I calculated correctly, 2.2 pounds added to the stabilator will have the same
affect on aircraft balance as 4.6 pounds in the baggage compartment.
That affect can be mitigated by eating a few more $100 hamburgers.
I have them on mine and I think they really improve the looks of the airplane.
Has anybody noticed a change in performance with the tips?
...he says they make the airplane tail heavy and the stab more wobbly...
Bad choice of word. The airplane undulates, up and down, not to lose control, but noticeable. All the other RV12 he has built and flown do not do that. The stick does not always stay in place during flight as with the other airplanes. The stab has a noticeable drop when you try to place in neutral position on the ground.
Bad choice of word. The airplane undulates, up and down, not to lose control, but noticeable. All the other RV12 he has built and flown do not do that. The stick does not always stay in place during flight as with the other airplanes. The stab has a noticeable drop when you try to place in neutral position on the ground.
The balance of the stabilator is relative to where the hinge point is.
Note that 2/3's to 3/4's of the tip is aft of where the hinge point is.
That is going to add most of the tip weight to the aft portion of the stabilator and change the static balance.
I don't know how much these tip fairings weight so I don't know if the change in balance is an issue or not.
One consolation is that the stabilator is actually over balanced slightly with the standard balance weight supplied in the kit. If you disconnect the cables it will swing trailing edge up.
The reason it seems balanced with the cables connected is that the control column has mass and the hinge point of the control column is at the rear. So with the airplane at rest, the mass of the control column and sticks is attempting to swing forward, while the extra mass of the stabilator balance weight counters it trying to swing the sticks aft. The result is a closed loop system that as a whole is balanced.
The common opinion is that the balance of the movable control surface on its own is the primary concern. So, on RV-12's with stabilator tips installed, if the stab is balanced or still slightly nose heavy with the cables disconnected, it is probably still ok.
Disclaimer - The standard design of the RV-12 was flutter tested to prove a good margin of safety beyond VNE. Any modification (including adding stabilator tips) could have negatively altered the airplane so keep in mind that my statement above is just a personal opinion and until the flight test was repeated to prove it, the opinion is worth what you paid for it.
Anyone making modifications to the flight control system on an RV-12 must realize they are truly experimenting.
I personally would not casually add parts to a flight control system component without careful consideration of all the ways it might have an influence and at the very least confirming that it has not become negatively balanced.
Side comment - Even if changing the balance with the addition of stab tip fairings doesn't adversely effect the flutter margin, it could still change the pitch control feel slightly because you have altered the relationship of the control surface inertia vs the opposing force of the antiservo tab. Probably not enough to effect it in a negative way, but very possibly enough to notice a difference.
This got my interest up, so I tried out the theory at the hangar. Mine stays in any position I put it! To be truthful I think the autopilot servo is providing enough resistance to keep it wherever I put it;
This got my interest up, so I tried out the theory at the hangar. Mine stays in any position I put it! To be truthful I think the autopilot servo is providing enough resistance to keep it wherever I put it;
I own an SLSA, and haven't built a 12, but i THINK the autopilot only controls the trim tab on the FF stabilator.
Nope.
The pitch servo is connected directly to the control column that your sticks are bolted too.
BTW, the primary purpose of the tab on the back of the stabilator is as an anti-servo tab.
By making its attach mechanism adjustable, it also does the job (secondary) of a pitch trim tab.
I stand corrected.
Thanks for the information.
I'm amazed at how small the servos are, for a full scale plane I expected substantial servos, but they are no bigger than the model plane servos I use in my model planes.
During my demonstration test flight, before buying mine, while in autopilot, I felt the servo bumping back against my control inputs when it was on, and it was explained to me that that was the autopilot.
Still though, such dinky little servos. Not sure if they even have metal gears in them. I know they make some burly model plane servos with metal gears that have huge power, but VAN's knows what they're doing, so I know they've specified the correct servos for the job.