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.

take your low rate elevator setting down to about 7/16" and see if it still snaps

Yeah, that will help with the snap but then doing a loop is out of the question. I can keep it from snapping being really easy on the elevator and catching it with the aleirons but I still need about 100 feet going in to the loop and end up damn near dragging the ground... not really a good feeling. I would like to pull a tight loop and end up and the same elevation as I started.

if you want a tigher fun fly loop program the radio on a switch to use up or down elev. with up or down ailerons. you should still be able to do a small loop wiht 7/16" of elev. throw.

To help tame the snap a bit you can try to:

i. make the plane slightly nose heavy
ii. raise the ailerons by 1/8" and not leave it at level
iii. mix in some spoilers with the elevators, I think QQ does that for his Yaks too, I vaguely remember reading it somewhere, might be wrong about QQ but it does help with a snappy plane. Mix it so what when you pull max ELE the spoilers are raised but about 1/8".
iv. sell the plane and buy the CMP Katana, she is such a sweet plane to fly!

I flew one of the Global Raven 40, everyone told me it was a lemon, the plane will not even get off the ground/will snap when you loop it/snap as you come in for landing, I was happy with it, flew it like nuts and it never snapped on my until the end when I tookher up high and pulled hard loops, that was when I learnt how nasty the plane was. I did raise the ailerons by 1/8" and that might be why I had fun with the plane.

hi samtech

Please keep it in mind that these type of models are designed to snap to a certain extent.
Taming them too much could kill the performance.
Every Cap, Extra, Sukhoi etc, that I have ever flown, snapped if large elev was introduced.
When the model is no longer going in the direction that it is pointing, (because it is changing direction too quickly) the airflow over the wing will break up and it will snap.
To me this is a good thing not a problem.

Piroflip explained it very well, this model will not allow you anything but sweet and slow elevator inputs. Mine was only comfortable with 5 mm up and down elevator travel (3/16") and was able to do nice (and big) loops.

Is the CG set correctly? Sounds like it's nose heavy. Maybe move the CG back then dial down your throws.

Mike

A snap is nothing more than a stall. A stall happens when the load the wing is carrying at the speed the airplane is flying needs lift that requires the wing to pitch to an AOA that's beyond the stall. Speed affects it, load affects it, and your ability to hold the correct amount of elevator affects it.

Adjust the elevator rigging and it'll be easier for you to fly as tight a loop as the airplane can fly. Then you'll have a clue if redesigning the airplane would be sensible or worthwhile.

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.

A bunch of excellent posts on this issue.

I was also going to suggest toning down the elevator throws to tame the snap tendancies.

As noted the higher 3D rates on planes of this type make them prone to snap.

Very true.............

3D models are supposed to have great big throws. And they take either an experienced pilot or a lot of learning by pilots who aren't experienced. And the experience required is not so much to do the 3D stuff, but to fly the airplane with the slight touch required to do the other manuevers, like loops and landings, without stalling.

You know, the last few days there have been a number of guys wanting to rework aerobatic airplanes to be easier to fly. Sometimes it's a lot more sensible to choose an airplane that matches the pilot's skills than it is to try and redesign an existing airplane.

That one deserves a permanent place in the RCU beginner's guide to RC planes.

"You know, the last few days there have been a number of guys wanting to rework aerobatic airplanes to be easier to fly. Sometimes it's a lot more sensible to choose an airplane that matches the pilot's skills than it is to try and redesign an existing airplane".

I'll second that, a Yak should be a Yak, not an aileron trainer.

IMHO I will say any plane that uses less than 1" throw for its elevator because of snappy habits has 'problems'. Leaving aside a plane that flies at 200 mph etc. 7/16" is not much throw at all for any sport plane. Yes, some planes are designed to snap and they have their purpose but snap with little throw and all would mean just a relatively bad design. The big CMP Yak is the same, my friend flew one and dumped it after the maiden flight ... he loves to fly hard 3D and all with his QQ 50cc and QQ 100cc but that big Yak from CMP is very snappy. Seems in the ARF thread the flyers only used 7/16" throw on the elevators. Its sad for such a nice looking plane.

That's a pretty encompassing statement.

Many smaller planes ( .60 and below and in some cases larger ) have recommended high rate throws of less than 1".

If I dial up a several planes that I have that high, they WILL snap hard. The measurement is relative to the size of the plane and control surfaces. 1" on one plane is not the same as on another.



I also have the CMP 1.40 Yak 54.

It will snap all right, but if you dial in the rates to the recommended there is nothing that I see unusual.

If you fly it at high rates the snap tendancy may catch you during a slow speed approach turn....

But that's really pilot error IMHO. Other similiarly sized and constructed Yaks are no different.

I have yet to fly a YAK. So far for me all the planes I have had have flown with more than 1" throw on the elevator, not had any snappy plane before other than my Global Raven. I don't mean just 3D planes but also planes like Laser 200, Extras, SU 31, Super Chipmunk etc. I hardly 3D but I have flown them hard and I must say with that much throw they have been very good to me.

It's all relative to the size of the plane and the size of the control surface.

On a plane with a short control surface, 1" can represent extreme movement of the surfaces....

E.G. on an Alpha 40, this is a tremendous amount.

On a plane like the Laser, 1" might be small enough for a "lazy" or loose loop.

It depends upon the plane.


The Yak is built for 3D manouvers with high rates....

Being able to snap it hard, is part and parcel to how it is supposed to fly... but this can cause problems for the pilot if they forget about it, or try to fly it like a trainer...

On a Yak, letting the plane "settle in" to a landing is a good way to assure that it will snap.

Coming in under power will prevent this.

opjose - I see what you are saying ... it is relative, just that planes like my Pac Aeromodel Laser 200 has a big elevator and so does the Super Chipmunk. Come to think of it the SU31 is the same too but they were not snappy at all with a lot of throw. Maybe I have been lucky in my choice of planes too ...

Mine is no 3D plane. It's a scale plane only.

Sam - the CMP Yak is lovely but so many tell of its snappy tendencies. The CMP Katana 50 is a very nice flying plane, I like that one. Its so smooth and I like it for aerobatic flying with less throws. She will perform manuevers very nicely.

That will make it snap even worse. NEVER go aft CG when you have this kind if issue.

Sell it!

Good advice.

The OP also stated that he had an oversized engine... which probably added to the wing loading of the plane.

A heavily loaded Yak will be all the more prone to snap.

I'd like to know which engine he used?

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opjose, it's a supertigre g-61 ABC with a bisson muffler. It was either add engine or add lead.... Some people have tried building a battery mount up front next to the engine and putting the throttle servo up there too. These planes have a really bad rap for being tail heavy. I just put the biggest engine I have in it. Balanced out right on the money.
I'm going to try out some different programing tomarrow.... Flaperons and spoilerons allong with reduced throws. I'll post the results tomarrow evening. Oh yeah, some have suggested speed will cure it.... I'm taking a couple of differnt props with me.