Pete737

Im posting this because I have seen a huge envelope when it comes to deadplay within a flying stab system.

All research done on this subject indicates it is not ok to have any. Of course I have personally found this impossible to achieve.. Even the smallest amount of play (down to the X/100") seems to be augmented producing play at the stab.

I have not come across an all flying stab airplane with no play yet.

I have seen play range from 1/4 to 3/8" measured at TE to believe it or not 1 1/2" to 2" at the TE and everything in between.

Every pilot commanding these planes says its fine. Even the jet I witnessed with roughly 2" of play (YES 2"!!) flew just fine, Or looked to anyway.

I personally have assembled 2 flying stab systems, I have not been able to get them Play Free yet. I typically can sleep at night if I get the play @ or below 1/4" at the TE.

What do you guys think about this?

Pete

powerjets

My Feedback: (1)

2 " play ??!!
what plane was that ?

lov2flyrc

My Feedback: (24)

Pete,
You need to be a bit more specific.... Are you talking about linkage play or stab mounting play? If your talking about stab mounting play, is this fore/aft, up/down????
Some forms play are acceptable (although not optimal) while others can be disastrous. What form of play are you talking about?

Rider-60

My Feedback: (17)

I'm usually happy when I reduce it to the servo gear play, a bit less than 1/4 at TE. You would need hydraulics to prevent any play. I doubt 2" is safe or even flyable as this is roughly the travel I have in most planes....???

LGM Graphix

My Feedback: (22)

In my Firebird there is less than .010" at the trailing edge, I would say anything more than just gear slop in the servo is far to much. You can't do much with the actual servo slop, but linkage slop can be completely eliminated.

Shaun Evans

Hi,

It also depends on the design of the stab, too. As we have unfortunately learned, some of these planes out there have no thought (let alone informed design) put into where the pivot is or any of the other aerodynamic considerations that apply. I've seen well-designed stabs with 5/16" slop which flew at 180mph with no sign of a problem.

invertmast

My Feedback: (23)

I eliminate all the slop up to the servo gear train..

Pete737

Sorry Todd, The type of play I am referring to is everything but geartrain, . I have not seen any play in servo mounts yet, Only in the linkage if not made in properly. Or clevis horn connections.

As far as the jet with 2" of slop, I swear it to be true. I thought to myself, This jet is going to crash! But I had to stay humble, Realizing that the pilot (who looked to be in his 40's) has probably been flying since I was in grade school. Sure enough the flight was uneventful.

Ron S

My Feedback: (2)

I've measured a freeplay of .05" on my flying stab, power off. I measured it at the LE, which is 7.25 inches away from the pivot point. I just deflected the surface up and down, with little load on the surface (trying to not move the geartrain). With power on, I'm sure that number would grow by putting a larger hand load on the surface, where pushrods, servo arms, and everything start buckling or torsioning... So it will be dependent on what kind of load you put on it.

Intentionally adding freeplay to the system is how we test for flutter on aircraft wind tunnel models. Freeplay = bad (and so is flutter [:'(] ). Its importance grows as your airspeed goes up.

Countryboy

My Feedback: (25)

My JL F-4 has about .5 to 1.0 mm in the stab in all three axis. One given is the gear slop in the 8711 servos, and the rest is in the stab pivot mechanism. Having dis-assembled it twice in trying to improve it, I guess I will have to live with it. Hopefully it won't be a problem!

lavi rider

My Feedback: (6)

If one is using two servos for each stab then even the servo backlash can be eliminated ...... setting up the two servos to have their 0 point at the backlash end of each other...

lov2flyrc

My Feedback: (24)

Ok... Linkage play is a serious problem that should be immediately attended to or you will flutter. Gear train play has never really been an issue as flight loads bear on the surface and take up the slack. Mounting or pivot play has also proven to not be much of an issue; again, flight loads tend to take up the slack. Excessive mounting play can cause flutter but not typically seen at our flight speeds. The biggest issue you should be concerned with on mounting play is to make sure the surface cant bind up as flight loads build up on the surface and deflect it to the extent of the play available. Ideally, you want to minimize the play, be it mounting or linkage to the least amount achievable. With simple bushing/shaft configurations I typically remove the bushing and fit a roller bearing of the correct size if possible. Bushings tend to be a sloppy fit to allow space for the lubricant, bearings will eliminate the excess tolerance.