kork

My Feedback: (65)

I built a pica t-26 1/6 scale and installed a os 91 fx. first flite today the horizontal stab snaped off on one side, was able to land but unsure if it was flutter that did it or just to many g's.
my question is when i build the new stab do I build it out of solid 1/4 sheeting like the original or would it be stronger to make a framed up stab? I have flown the plane earlier this year with a 61 fx with no problem.
jason

kork

My Feedback: (65)

fyi, the hinge gap was almost tight so i cant see how flutter would have don that.
jason

Ram-bro

My Feedback: (101)

did you monokotte or glass the plane? What were you doing just prior to and during the incident? Did you hear any flutter?

kork

My Feedback: (65)

the plane is monkote and I was comming out of a dive but nothing crazy. I did not hear anything out of odinary nor did anyone else. The plane leveled off and suddenly shot straight up. One of the 3d guys even said he could never use enough elevator to make his plane do what mine did. After inspecting, i found it stripped the servo even. I had a new hitec 325 hb in it.
i just read buzzo's deal on flutter so i guess that maybe is what happened. so what do i do different this time when making my new stab?
jason

kork

My Feedback: (65)

another reason i think it was flutter is i have a chipmunk i built with a 15cc gas engine and have had it clocked at 115 mph and do everything i can to it and she still flys like a dream with a 1/4 stab also but framed instread of solid.
jason

Ram-bro

My Feedback: (101)

what kind of break was it? The reason i ask about the monokote is that if you trimmed the monokote on the stab and scored the balsa underneath.........

kork

My Feedback: (65)

I thought that also but thats not the case. On a typical arf that could happen but when i cover planes i always run my mono up throgh the inside corner and onto the next surface a 1/4 inch. the break was right at the crotch.

kork

My Feedback: (65)

i did look up my servo and it was a 50 something ounce servo, that should be enough? right? the bird does have alot of elevator surface i guess. compared to other wardbirds. I dont know

3136

I would have thought you would hear it if flutter caused it. Also flutter normally rips the control surface out.
You may have cracked it in transport or a previous hard landing.

kork

My Feedback: (65)

well i am showing a picture of a hanger 9 arf spit that actually has more elevator surafec than my t-28 and is even tappered to less than 1/4 inch on the trailing edge of the elevator . i also did figure out that the side that broke is the non control horn side. so my guess is flutter, but once again which way is stronger, framed or solid?[img]stab 1[/img][img]stab 2[/img][img]stab 3[/img]

kork

My Feedback: (65)

you could hear the engine but i guess i really dont know what flutter sound like. the plane has never landed hard or ever been bumped. there's only  4 flights on the plane.

WacoNut

IMO a framed surface is stronger. You have grain structure running in different directions.
I prefer a framed up stick stab and elevator to a solid balsa sheet.

At least you landed the plane in one piece.
Anthony

kork

My Feedback: (65)

anthony, thanks for the direction. i have the plans on the table and will have it in the air very soon. I know from all your building tips to other guys you have some time under your belt. It was wierd when it happened that with a stripped servo and broken stab you always dig deep to keep your calm and land it like a perfectly running aircraft! i got lucky!!
jason

eddieC

My Feedback: (2)

You were very lucky to get it down!

Whether you go built-up or solid, you might want to put a carbon or hardwood spar in it, and tail brace wires. Belt-n-suspenders.  [8D]

KitBuilder

Does the stab have hardwood leading edge or or other sitffener. Most likely damaged or compromised before you even got it.

dbacque

My Feedback: (3)

The fact that it happened after a dive indicates that speed was up and flutter is a real possibility. G forces or lift forces breaking a surface are rare.

Hinge gap is rarely the cause when it comes to flutter. If it was flutter, the more likely culprit was flex in a pushrod or slop in the controls. If there was any play in the connection, that can be a source of flutter, if you could move the surface against the control rod (pushrod flex), that can be a source of flutter.

I lost a Goldberg Extra 300 to elevator flutter and I'm sure it was due to flex in the recommended pushrod setup. I didn't like the setup when I built it but thought "They've got to know more about this than I do." It was the last time I trusted a manufacturer's recommendations if I disagreed.

Bottom line is, make sure your control set up has as little play as possible and is stiff, stiff, stiff, stiff!!!

If it's not stiff it ain't worth a f***!

Dave

jmpups

My Feedback: (1)

If you built A T28 instead of a t26, the stab would have probable stayed in tack.

SCALECRAFT

My Feedback: (13)

Was the balsa a light weight balsa. Big difference from the hard wood balsa.

I have used balsa slab h-stabs in the past under heavy loads, and I always use a harder balsa for that application.

Never failed.

Steve

kork

My Feedback: (65)

there was no slop in the linkage , but I guess we will try again, I built a vert and horizontal stab today and will have it in the air this week. If it was flutter, maybe just sanding the leading edge different  could change it, but i am just taking a crap shot.

jason

airraptor

My Feedback: (66)

take a pic of the damge to show us. a solid stab will be stronger IMO. all the built up ones on ARF's and some kits will fail in high G turns or pulls out of a dive. I replace all stabs on any arf that will be at the high end of power or over powered. It could be that you servo striped first, went to full up elevator and then ripped that half off....

blw

My Feedback: (3)

Just a gap in hinges won't make control surface flutter, but any alignment error is one of the biggest reasons for it. The differential in air flow all around and thru the gap does it.

wickedpissa

My Feedback: (1)

The leading cause in flutter is not gap but linkage so is you have flutter look to you servos, rods first then gap

blw

My Feedback: (3)

Could be. Either way, most of it is avoidable.

Flutter can cause little to no damage all the way up to massive destruction. I had a model with elevator flutter problems and it sometimes only did it for a couple of seconds. It was always very loud and unmistakeable. Balancing the model nose heavy seemed to avoid it all the time, but it would flutter as soon as you balanced it. This model was known to have a chronic problem with flutter. That was the Fantasy by Major Hobbies. Later, Skyshark bought the rights to the kit and the owner documented the fix on RCU.

I have another plane that had aileron flutter badly on one of the first flights because I left a control horn loose. The damage was extensive but I landed it okay.

kork

My Feedback: (65)

i will snap some pictures tonight, I thought about flying wires but just does not make sense on a t-28. I am going to take my chances and fly it! i did sand the leading edges a litllte different than last time. also added a hardwood spar in the horizontal stab. I will say that i have always used dubro knuck hinges with gorilla glue and was able to do some great testing on pulling apart the old hinges. Not a chance!!!! not one of them on the elevator or rudder would even think of comming loosse with a plier's.even tried to bend and twist them loose to no avail.
jason