Free Bird

Any signs of flutter on the back end? I wanted to get a Rare Bear, but never did because of the stab issues. I don't feel that I should have to redesign the back end to keep it from falling off in flight. If the issue has been fixed in the Navy version, I just might be tempted.

thunder21

My Feedback: (2)

I've done a bunch of full power dives without a hint of flutter. I used the stock elevator control system and used the innermost hole on the servo control horn. I didn't seal the elevator gap as of yet.

I'm using a very smooth electric motor and a four blade APC prop so I'm probably inducing flutter less than the typical glow motor would. No vibrations, lower RPMs and less prop turbulence.

cat5752

My Feedback: (1)

I bought the Rare Bear when it first came out, but never put it together when I read all of the stab issues. I contacted Ace Hobbies, and they sent me a new set of stabs (redesigned), with better carbon fiber tubes. I am thinking that with all the problems the Bear had, they kept that in mind when they built this Navy version. I started building my Rare Bear last night, and over all it is not a bad kit. I am tempted to cut apart my old stabs to see if mine would have failed. I guess when they first came out they were not glued all too well, on top of most people going overkill on the engine, tails didn't seem to stay on long. I have my fire-proof suit on, I'm sure it won't be long before someone jumps on here and bashes ThunderTiger........

thunder21

My Feedback: (2)

My guess is the stabs were coming off due to elevator flutter. The leading cause of elevator flutter is control rod flex coupled with the fact that the elevators are not counter-balanced. I used the stock balsa control rod and a lot of guys said "that's not strong enough, use a CF rod" I got a pretty thich CF rod (7mm) and found it had a lot more flex than the balsa (which was almost as heavy as spruce) So I went with the stock components.

I'm sure the overkill motors don't help the situation.

cat5752

My Feedback: (1)

I have a picture from the Rare Bear thread that showed a guy mounting the elevator servo in the tail, on the tail support webbing. Used the two control rods soldered together, ended up about 4 inches long. That looked pretty viable to me, and I think that is how I will do it.

kev71h

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JoeMamma

Picked up my F8F Bearcat today. The glass fuse is absolutely flawless. This is the first ARF where I won't need to re-shrink any of the covering. It's all nice and tight.

I crashed my Thunder Tiger Rare Bear last year due to elevator flutter in a high-speed dive. Everybody heard the flutter except for me.

I noticed the wood at the retract mounts are much better on the F8F versus the Rare Bear.

I won't be using the supplied mechanical retracts. Instead, I'll be using the air Robart's from the Rare Bear. I will also be using the (undamaged) OS 1.60FX from the Rare Bear. Overpowered?.............nahhhhhh.

Got to find a neat (heavy-duty) way of re-doing the elevator servo controls and mounting. Also, hooking up the tailwheel with those goofy springs......Yikes ! Got to find a better way.

Also got to find an easier way to mount the removable canopy. Didn't like the screws. Magnets maybe ? Anybody got any neat ideas for a quick-release ?

I also want to find a different way to secure the wings to the fuse for easier removal and installation. Some kind of quick-release ?

I'll be scaling mine after a 1947 era Blue Angels Bearcat.

Let's see some of your modifications.

Thanks,

JoeMamma

thunder21

My Feedback: (2)

The problem with doing that is that this bird is tail heavy. Adding weight behind the CG means more weight up front. Mine is totally stock and even though my power system weighs 50 ounces, I had to add 10 ounces to get the CG where I felt comfortable flying the model.
I don't feel that anything needs to be changed to get this model to fly at the speeds mine does (100 MPH level) Faster speeds may need some elevator mods. The best thing to do is to counter balance the elevator. If I encounter any fluttering, that's what I'm going to do.

The kit supplied wheels are a joke. I upgraded to H9 Pro Lite wheels and they work well.

JohnVH

My Feedback: (38)

a sweet bird, did you get your speeds off a radar gun?

kbrd

Hello All,

I have a K&B Sport .65 that I would like to put on the TT F8F. The promos all call for a .91 but I don't intend to race it, and Rare Bear shows a .61-.91 range for that ARF. Has anyone tried a .65 on this ARF. I want to fly it as a Fun Scale, so I don't want to overpower it.

Regards,

Jack

thunder21

My Feedback: (2)

The problem with using a .61 motor on this model is that the model WILL end up at around 11 pounds (to achieve the proper CG). A .90 sized 2 stroke is not really overpowering an 11 lb model. It would probably fly OK on a .60 motor but you wouldn't have much low end available. And if you get into a difficult situation at slow speed, the model is going to stall. I've seen video of a few RareBears get into that situation. It's not pretty.

I ran a doppler analysis (WaveOSScope) which determined the speed.

cublover

My Feedback: (47)

Hey Thunder,,,got mine together,,going to put it in the air in the morning,,heres a couple of pics,,,hell of alot weight added to mine..your Vid looks awesome..I put KMP retracts w/robart air support in it and kept the tail wheel the same..lots of mods to it,,but will post the outcome tomarrow afternoon...I also balanced mine at 5 inches,,,good to see you did the same..now mine has got to fly...LOL

cublover

My Feedback: (47)

PS..power is a 150 saito,,not shooting for 100...but 80 would be coollllllllllllll!!!!!!

Richard L.

My Feedback: (24)

How much weight did you have to add to the nose with the Saito 150?

thunder21

My Feedback: (2)

A Saito 150 should get the F8F well beyond 100MPH! The manual calls for a 1.20 four stroke.

Good luck with the maiden. Keep the speed up landing and use the amount of flaps specified in the manual. At around 11 lbs, mine is easy to land but my club's rough field keeps flipping it over on it's back.

The Raven

subscribe....sorry folks.

Elsiebird

I had a f-8-f as of 1-14-07 and on its first flight with a os 1.20ax the first dive i put it into i heard fluter and the elevator quit responding the plane crashed so i dont belive they have all the bugs worked out but i am going to buy another one anyways and defenitly chage the elevator linkge maybe put the servo near the tail or beef up the control rod

thunder21

My Feedback: (2)

Elsiebird, did you use the stock elevator linkage? Did you use the innermost hole on the control horns? What servo did you use?

cublover

My Feedback: (47)

Hey guys,,,I have a tip for you on this build,,,,you have the fuse, wings and tail section in the box,,,,build it the way you fly...not the way the kit decribes,,and this goes for any ARF...I dont even open the book anymore,,,I look at everything and start building,,as far as the balance,,I figure it out!!!!.,,,just like they do with the real ones,,,pretty hard to put a full scale bearcat on your fingers and hold it up....LOL,,,I know I might get bashed on this,,,but I cant remember the last time I lost a plane from NOT using my head when I build a plane..I build it so I can fly it,,,and not worry about it,,,,the ply in this kit is UNREAL,," so much",,I only used 1 piece to build it,,thats the former that goes in the fuse behind the cockpit..the rest i'll use for mixing epoxy I guess,,or ill just throw them away,,guess all im say'n is use your head when building ANY ARF and make them stronger,,,if you use the standard push rod for the elevator in this kit,,,,your plane WILL go down,,that has got to be the biggest disaster in this kit...just my 2 cents,,,,but worth a millon if you use what I tell you...mine will fly for seasons...have a wonderful day....Rod,,,,,,,,,,,cublover.....PS......I'll get some pics for you guys on what I did,,so you can get an idea

thunder21

My Feedback: (2)

The standard pushrod seems plenty strong to me. It's much less flexible than a CF rod. I've done a bunch of high speed dives without any flutter. But then again, my F8F is electric so it may not be as fast as a glow model and certainly doesn't have the vibration.

Weak servos and sloppy/incorrect linkages can cause flutter just as much as weak stabs.

cublover, did you have to add much weight in the nose to balance the model? What's your RTF weight?

f15iceman

I keep hearing about elevator flutter on these airplanes and the I read the engine that people are putting in them. So if you hear there are problems with elevator flutter why would you put a much larger engine than the manufacturer calls for. The airplane calls for a .90 so you put a 1.20 in it and proceed to do a long dive. That just sounds genius. The major problem is the size of the elevator in comparison to the stab. When the elevator is larger than the stab is or the same size the stab that will cause flutter. They should make the size of the elevator smaller so this would cure the problem. Granted it won't be exact scale but if you want exact scale than you should build one yourself. So people if you don't want to run into flutter problems listen to manufacturer recomendations and NOT double the size of the motor.

cublover

My Feedback: (47)

Like I said..just my 2 cents,,,but at my alt., that would not be enough engine....you have to remember im at 6000 ft....need a little more engine up here...,,and besides that...you could put a 220 saito on it,,if you just add a little more "beef" to it...there is nothing wrong with building and ARF by the book,,,but it wont last long,,"that is a fact",I dont care what anyone sais,,,for instance,,,there is hardly any glue on the landing blocks...one hard landing,,,and your fixing a wing,,,no thanks..you have to remember also,,that thundertiger HAS upgrades for RareBear,,as a freind of mine called them and said he had a bear that had substandard "or old style" tail feathers,,,,,,he had new ones in white a week later,,,now if they can do it,,,so can we...just make this plane fly-able for you...not the way it sais in the manual,,youll be fine...a 90 2 stroke is = to a 120 four stroke,,,and i have a 150 saito,,,,i dont think that is a pile load of MORE power,,do you???

cublover

My Feedback: (47)

hey thunder,,,,,,,,,,,you know,,im sitting at 13 pds w/fuel,,,I looked at your post and watched you fly it,,,awesome job!!!!! cant wait till mine gets in the air,,should be sunday,,,hope and keeping fingers crossed that the weather holds out...and yes,,I had to add a ton of weight to the front end of it,,but I built an alum. box, "that bolts on to the engine mount,, and the weight is bolted to that...you were REAL close with the balance of this model as well..I came up with 4 7/8...so 5 is on the money...you did a hell of a job on it,,,hope mine looks as good in the air as yours does!!!!....Rod

cublover

My Feedback: (47)

welllllllll,,,,I flew it today,,,,we tried to get a radar on it,,but I would bet it got a 100,,,wow!!!!!!!!!!!!!,,awesome plane,,,fly's like its on rails,,,little tough on landing,,,but i'll bend the gear back a little and i'll be ready to go again.....flight was a little shakey at first,,but when I got the trim in,,,,WOW!!!! it was awesome,,,here are some pics of it in the air,,the 150 is perfect on this plane,,,,............next project please....LOL

Photos taken by Roger Mayo..thanks Rog,,,real nice

thunder21

My Feedback: (2)

Congrats on the maiden;-) Your Bearcat looks great in the air!!!

Get some video and I'll measure the speed with a doppler tool.

At 13 lbs with fuels your wing loading is a little high, somewhere around 40 oz/sqft. But crank down those flaps and she drops down nicely. I've learned to keep the bottom of the back fuselage parallel with the ground. If I pull the nose up too high it stalls. I've done it a couple times and the gear blocks seem to be holding OK. I did dribble some thin CA on them in addition to shimming the back mount to get the wheels forward.

It's a great model. I want to fly mine badly, but winter has finally set in to MD.