Hello all,
Ok, I have a fibreglass CMP Yak 54 50 size. There are lots of complaints about the snap tendinces of these plains. Mine balanced out just fine....no lead...just a way too big engine.... 61 to be exact. I have about 7/8 inch up elevator and it will still try and snap, even if I'm slow to apply it. My question is will the use of flaperions or spoilerions help? I'm a little reluctant to try it without some imput from someone who has tried it. Be it a different plane or what not... Just some experance. Thanks.

G'day Mate,
An elevator induced snap, is caused by flying too slow, & using too much elevator, which stalls the wing, & the tailplane, ( horizontal stabilizer) & once these are stalled, the engine torque makes it snap roll to the left, because the prop drag is trying to stop, the prop, & have the fuselage spin or just using too much elevator, causing the same thing.

Take the airplane up and at about half speed, do an inside snap roll. If it does it, then try it with the elevator at low rates if you've setup dual rates. If it does it on low rates, then you've got way too much elevator throw rigged. Nothing wrong with the model other than your setup of it. Yak's are supposed to be aerobatic, and snaps are part of the performance envelope. But a very sensitive elevator doesn't have to be. Simply adjust the elevator rigging. Move the pushrod connection in one hole on the elevator servo arm and test fly again. Or if the pushrod is already connected to the inner most hole (which is very doubtful), move the elevator horn connection out one hole and test fly again.

Simply assembling an ARF by the Chinese instructions doesn't complete the job. Even ARFs deserve proper flight tuning before making the final judgement of their "flying qualities".

I'd suggest that you also use geistware's online application to see where a sensible CG would be for your specific model. It's quite easy to do. All it takes is a yardstick. Measure the 7 measurements and plug them in. It's way more correct than even the mfg's manual's information. Then go test fly and see what throws the elevator really needs.

The mfg's suggested throws aren't sacred. Matter of fact, they're very often incorrect.

An elevator induced snap is about the easiest problem to solve that we face. And very often, the solution for many fliers is simply to program some exponential into their TX.

In the meantime, put a couple more clicks on the TX throttle stick when on final, and don't firewall the airplane on takeoffs. Give it a chance until you can tune it. Dance with who you brought to the dance.

What does your model weigh? Based on their web site, they claim 2800 g on an area of 33 dm/2. That would be a rather portly 28 oz/sq ft which is a lot on that sized model.

It's about 6 and 3/4 pounds. My scale isn't the greastest... Yeah, it's really heavy for it's size. I think this might have a lot to do with it's poor flying quality. It's all in the fuse which is fiberglass. The wings are nice and light aswell as the stabs and control surfaces. From what I understand these models are all tail heavy to start with. Some people add weights to the nose... I added engine...
I'm going to look for an old thread on here somewhere that goes into this model a little more indepth.

[link]http://www.rcuniverse.com/forum/m_4139101/anchors_4174833/mpage_1/key_/anchor/tm.htm#4174833[/link] Thats the one. There is links to more disscusions on there too. Anybody know is SFG or stall strips might help? Keep in mind that this model is not a 3D model at all. It's a scale plane.... But it's performance is not so good. Snap rolls, rolls and even hammer heads are great. It's just the elevator snap that makes it a pig. I could turn it down to the point that it would never snap but then it wouldn't be able to do a loop at all or even have enough throw to get out of trouble if need be. It's a known problem with CMP yak 54 50 planes, but there has got to be a solution that doesn't kill it's performance completely.
Da Rock, I'm going to check out the CG calc a little later this afternoon. Thanks!

You can add all the aerodynamic devices known and reshape the wing using any tricks -(twist to add washout etc,) but here is the cold hard truth
most small ,scale aerobatic models simply can't be made light enough for easiy controlled , slow speed aerobatics
the wing loading simply is too high.
the very best you can do short of starting over -is to balance no more than 30% of MAC -then insure all surfaces respond and travel identically .
Seal hinge lines to prevent any difference in lift effectiveness from one side of the model to the other .
observe control at lower speeds and learn control inputs which keep you out of trouble.
adding inboard stall strips etc., is really futile.

Unfortunately I have no answers for you.

I do have a comment though----I have never owned, flown or seen a decent flying aerobatic (scalish) model in that size.
Going a bit further, I have drawn a 'personal line' of 650sq.in.. That is THE smallest I will even build.

The difference made by that last 100 sq.in. is hard to believe. But trust me it is there!

I do wish you luck however-----'cause short of a minor miracle that is what it will take.

33 dm^2 is 511 sq in or 3.55 sq ft of wing area. That weight places the wing loading at 30.4 oz/sq ft, throw in a full fuel tank and you are nearly 34 oz.

This is typical of many ARF's that are lead sleds. It would be a great flying model if it's weight were in the 4 1/2lb. range.

Ok, I've reduced the throws to around 7/16. We will see... I have also programmed in a bunch of stuff and a systematic schedule to try everything. Expo.30%. Spoilerons and flaperons, both very conservetive. It's nice to have a bunch of free switches! Also, a buddy of mine suggested that I seal the hinges which I have. Da Rock, good call on the geistware's online. My CG was just shy of a half inch to far back.... Might have a lot to do with it. I'm still pretty new to RC planes... Been flying helicopters for awhile and control lines on and off for twenty years. It's a litte different.... We let you know if I got it dialed in. Thanks

The reduced throws may help but in the end I'd have to go with the rest and say that it's just way too heavy to fly the way it's intended to fly.

well, yeah.... It's a little pig..... The thing that gets me about it... and is ultimately my fault.... Ok, I had a funtana X50 that was totally awsome untill I stuffed it. Then I went down to the hobby shop to ask the experts.... Who recommended the CMP Yak 54. Being a fan of the Yak I jumped on it. Should have done my homework, it's a major POS. After the fact, I ended up asking the guy at the hobbie shop some questions and he was shocked and then played it off that it was fiberglass.... and that it was a scale plane not a 3D plane at all. So far I'm really disapointed in this plane. Which really sucks because I was happier than a clam when I first took a look at it. It's a really pretty plane but a total dog. I figure if I can get it to fly half way well, I'll just hang on to it and enjoy it. If I can get it to do a half way decent loop I'll call it good. Other wise I'll sell it to a buddy that, 1 really likes the looks, and 2 only flies around in big circles. HAAHHaAHa. No really, I'll give it to him. I won't sell an ill flying hunk of junk like this to anybody. But if I can fix it! Oh how grand that would be! With really, really lite touch I can fly it around doing snap rolls and hammerheads, but if I can get it to behave! Cuban anyone? It's just the super hypersensitivity to elevator imputs that make me really dislike this plane.Yes, I have plenty of EXPO...but know I have more. 50%. Besides, just the fact that several hundred dollers of my stuff is flying around in the little tank.... I want to make it behave. Which in my honest opinion is not a lack of skill on my end, I haven't stuffed it yet... If it flew fairly decent it would be a great scale plane, not a flying tank.

G'day Mate,
Please excuse my stupidity, but what makes everyone believe, that exponential on the elevator is going to fix a plane with too much elevator throw.
EXPO does not reduce the throw, it only makes the stick less sensitive around neutral, the more EXPO used, the further out from the centre the stick is desensitised, but when you get to the end of the EXPO setting, you will get linear movement, & if that is too much & causes a stall, BANG she snaps.
You must reduce your throws, & the easiest way is to reduce your rate settings.
Then fly it & see how it performs.
I would almost guarantee that it is not a dog if flown the way it was designed, I don't believe this particualar plane is designed for 3D.

Everyone doesn't believe that. But some do believe that expo helps fly an airplane that's got an overly sensitive elevator.

It's been suggested that he reduce the throws, and he adjust the dual rates to have a low rate that's tuned to the airplane, and he add expo. It's also been suggested he fly this particular airplane faster.

Right on about the expo. When you give full throw, it's going to snap whether it has expo or not. On a meany like that I start doing very large loops, then gradually tighten them up to the point where it snaps. then back off on the next one till it doesn't snap. Judge that position, say half back stick. Land the plane. Give it half back stick. Now you know where to set the throw without snapping. Many high wingloaded planes are just as happy to snap at high speed as well. Used to have a Yellow Cap 10B was notorios for snapping, yet it was the best aerobatic plane I've ever had. Would do two perfect Lomcevecs one on top of the other and if you held it in it would go into a perfect knife edge spin. But if you did a high speed flypast and give el. alone it would do the quickest snap you've ever seen. Had about 1/2 of el. travel on a 1/4 scale plane. I have another one almost finished.
Gord.

ABSOLUTELY !!! Exactly the truth about this topic.

Aerobatic airplanes REQUIRE elevator deflection that can and will stall the wing. And that means you have to fly loops and such with less than that deflection. That's one of the primary reasons Dual Rates were invented.

It's not an error in design or a failure of the airplane that some of them tend to stall out of loops or stall off on one wing when landed too slowly as many inexperienced flyers instantly assume. It's the pilot using too much elevator and/or trying to steer with ailerons when the steering should be accomplished with the rudder.

Tune your elevator throws. Tune your dual rates. Tune the CG location. Then tune all three again. Then tune your flying skills.

Ditto. da Rock speaks da Truth!!

Know thy airplane!

I've been flying mine for a couple of years now and she's a little B*&%ch , but I love her to bits, she does'nt half keep you on your toes, if at any moment you put in to much elevator , she's snap like a cajun camen !

I would't swap her for the world, and I manged to smash her up good , more times than I care to remember, mainly on landing and coming in too slow, you definitely have to "fly" her in !

Nick