RE: Nasty elevator induced snap
 

IMHO you did it right!

I'd increase the prop pitch as you've indicated to avoid overly slowing the plane.

You'll want to come in hot and slow the plane down only once the wheels are just over the threashold and as low as possible.

The reputation of that plane is at least partially deserved. It has a smaller wing, so it is easy to snap... but then so does my much bigger version too....

RE: Nasty elevator induced snap
 

Hi samtech,

I watched one of these CMP Yaks go in hard at the SAMs field a couple weeks ago late on a Sunday after one of our race sessions.

The pilot had a dead stick on his test flight after very little time to get acquainted with the planes handling and on the last bit of the pull to line up with the runway he ran out of all the essentials for flight, airspeed and altitude for the bank angle and wing loading of this particular plane.

The plane hit pretty hard and yet it was still very repairable. They make a tough little Yak.

The one thing I wonder about with this kind of problem, is how many of the pilots that complain of this type of problem are transitioning out of the low wing loaded electric 3D style planes and into a more scale performing type plane.

You seem to understand the difference. But I have seen other cases where the person involved needed a short explanation of how wing loading and wing design will effect a planes performance. The CMP Yak I observed looked like it would fly just fine when setup properly.
You HAVE to remember though, the double tapered wing style wing is going to be more prone to a sharp departure into a stall and snap as opposed to a constant chord or single taper style wing.

By the way if chances happen to be such that I was watching your plane that day, hang in there and keep at it.

RE: Nasty elevator induced snap
 

Tommy gun. Yeah, that was me. I've been back out there a couple of times and flew it. Really was a simple repair. Cowling got a little chewed up and the landing gear broke.... other than that it was fine.
I'm going out there today. It's a little windy but not to bad.

RE: Nasty elevator induced snap
 

I kind of thought it was a big coincidence that you were in Elk Grove and posted this thread.

I was the nut job with the white chevy truck bed full of war birds.

Glad to hear you stuck it out. Did you get rid of that fueling valve? Or was there some other issue that caused the dead stick.

I'm on the way the RC Country right now. And will be flying tomorrow AM. Maybe I'll see you out there.

RE: Nasty elevator induced snap
 

Tommy gun. Kept the fueling valve. The problem was my tank pressure was to low. I pluged up one port on the bisson muffler with a set screw. No more problems, runs great.
Speed... still need more. I'll try a 13x6 next week. Spoilerons.... not so good. Flaperons... major improvement. I can still snap it at will but it behaves much better. It's almost predictable. Still lands really hot. I think I'll try a full spoiler setup next week. Touch down and then spoilers. The problem I had today was that I could come it fast enough to keep it controllable, touch down in the first thirty feet of the runway start turning like crazy and be at the end of the field before it was slowed down enough to turn around without tipping and dragging the wing. None the less, it flies much better. It's just really over weight, having a time getting used to it. My funtana weighed in at 5 1/2 pounds and was a good deal bigger. This little pig is 6 3/4 pounds. Glides like a bowling ball. But hey, it looks great.

RE: Nasty elevator induced snap
 

Samtech-
I'm glad you started this thread because I have this plane myself (still in the box) Can you tell me what your CG location is and what throws you ended up with? How much flaperon did you use?
I am reasonably sure that this plane will be way above my skill level so I will probably let it stay in the closet, but the info will come in handy when I do decide to build it- if I don't sell it first, I'm a little scared of it now.:D

Thanks
Jason

RE: Nasty elevator induced snap
 

Sowega flyer, Nothing to be scared about... but something to be conservitive with. It's no 3D plane but it will do some really great snap rolls and hammerheads. It's just snappy. What engine and gear to you plan on using? Hope you can build yours a bit lighter than mine. I'll post the throws and relations a little later this evening. The CG is right at 3.25" ish. From the leading edge right up againest the fuse.

RE: Nasty elevator induced snap
 

I've heard before that these planes are extremely tail heavy so I figured, like you, that I'd put a big engine on it to even it out. I have a .61 (its a Lincoln "redhead" from e-bay..it runs great) but I also have a GMS .76 thats fresh off the break-in bench. I may go with that since the weight is about the same and the extra power will be nice. I don't want to hammer it into the ground though... My radio will support the use of flaperons, so if they work to stabilize the yak, thats all the better. Whatever it takes to keep from adding weight...I'll try to lighten it up during the assembly. I was a little concerned about the figures when I bought this plane- I knew it was heavy for its size and that the wing loading would be high.

RE: Nasty elevator induced snap
 

Ok, here's the throws. Elev low 5/16 up and 1/4 down. Elev high 7/16 up and 9/16 down. I have 50% expo on both. Flaperons low 1/8 down with elev up. Flaperons high 5/16 down with elev up. Spoilers...not worth the trouble but low 1/8 and high 1/4. Rudder low 1 1/4 and high 2 1/2. Alerons low 9/16 up and 11/16 down. High 1 1/2 up and 1 1/4 down.
Ok, with the alerons high this sucker will roll over twice before you know what happened... at least at speed. Its a little touchy with that much throw. I have it in there so I can get it spinning fast and throw it into a flat spin without losing to much altitude. Just flying around I leave it in low. Rudder, it handles all I can throw at it. I might see if I can get a little more out of it. Knife edge flight is a little tricky. More speed might help that. I can get it to sail across the field in a knife edge but can't make it turn without losing alitude fast.
Ok, the elevator.... in low it's real pretty easy to fly around but if you get yourself in trouble you don't have much to work with. In high you need to really work with it to get it to do what you want. It will snap pretty easy but it's flyable. Also, I have heard...but I haven't had this problem. There are reports that some people couldn't get it to fly level. It was either climbing or desending... I haven't a clue. Maybe just hyperactive sticks???
Landings are real hot. Mine being a tank will stall and nose down still going pretty fast. Today, I was landing near half stick. Any slower and it falls out of the sky. Any faster and it would roll right off the end of the runway. Thats with supertigre g-61 spinning a 13x4.

RE: Nasty elevator induced snap
 

Great info, Samtech- I appreciate it!


Jason

RE: Nasty elevator induced snap
 

samtech: Thanks for posting all of this info. I just bought this plane and plan to use an OS 61 FX in it. So I will set it up initially to the same specs that you have laid out here.

If there is any other advice you can offer (perhaps things to look out for during the build) then I'd love to hear it.

Thanks again.

RE: Nasty elevator induced snap
 

That's not really an "oversized" engine.

Let us know how the flight goes.

I'd start with at least the "X"x6 or "X"x7 prop...

RE: Nasty elevator induced snap
 

Funny I was reading through this and it brought to mind a Great Planes RV4 40 size I bought used.
It was advertised, and someone else bought it, then sold it to me, warning me of the tendency to snap with too much elevator.

It was a simple fix; the two elevator halves had two separate pushrods to one servo, and the two halves were not lined up with each other,
acting as a sort of permanent aileron on the tail.

Easy fix, just adjust the pushrods to line up the elevator halves.

(I've seen this too at the field, a newbee with two elevator servos not mechanically lining them up)
(who buys a Funtana as a second plane?! I did.)

RE: Nasty elevator induced snap
 

And tune the elevator throws so that when on low rates, the elevator doesn't move far enough to stall the wing. Set high rates to let the elevator stall the wing.

Then you have the best of both worlds. When you want snap rolls etc, flip the elevator to high rate. When you want safer flying, flip on low rates.

RE: Nasty elevator induced snap
 

Glad i went ahead with the Great Planes CAP 27%...........it's great.