Hi all,

I have a BME Yak-54 with a DA-50cc, 22x10 prop. My problem is whenever I attempt to Hover from a Harrier the wings will start rocking from side to side violently, so I keep fighting them with no luck.

What coud be my problem? Too small diameter prop? To much/too little throw on elevator/ail? too nose heavy?

Any help would be much appreciated.

Thanks,

David

There are several things that could be getting in the way, up to and including the design of the tail. Moving away from that let's look at a few things. Everything below assumes that all the basic trimming out work has been done over the course of a whole bunch of flights. Things like balance, engine offset, up and down line trimming, etc. Going from harrier to hover requires a quick pull of max elevator, correct rudder input to offset torque and P-factor, and a good blast on the throttle to pull the nose around and push the tail down. Think about wing and tail position when you hit the throttle and you may find the problem. Here's some others.

Consider a c/g that's a little too far forward.

Wing weight imbalance. You need to balance both statically and aerodynamically between the wing halves.

Trim differences between ailerons and or elevator halves.

Wrong type of prop.

Operator unknowingly holding a small amount of aileron. This is a BIG one.

Rudder trim or offset. Incorrect rudder input by operator.

Everything he said, plus all planes have their "sweet spot" aingle-of-attack, which can sometimes be greater than 45 gegrees, so it could be elevator throw or just a throttle/elevator management issue as well.

Going back over the original post I have a thought that the prop is part of the problem with a 10 inch pitch. My opinion is that an 8 inch pitch would be better.

Here's something else to try: add a little more expo to your rudder in 3D mode. Awhile back I discovered, by accident, that sometimes I could hover/TR better in normal mode than 3D. What it turned out to be was, I was overcontrolling the rudder and then having to chase it. Once I reduced the effective rudder sesitivity at mid stick, I was able to let things settle down. Once I got confident at these moves it didn't matter, because I could anticipate what was going to happen.

Have you ever noticed how in a nice harrier, when you raise the nose but don't add power the airplane descends, in an elevator? Try entering your hover in the same way. Establish a nice smooth harrier, then pull the nose up. Let the nose begin to smoothly pitch up and then smoothly add power to counter the descent. You'll find yourself in a nice, controlled, stable hover. If you come in with the power too soon, the airplane will begin to climb and you'll have to throttle back to maintain altitude. By waiting a bit, and I mean just enough to let the nose start to come up, you will be carrying a bit of power into that hover, which will give you more control (moving air over surfaces) and make the airplane more stable. With a little practice you can make the whole thing look like its happening in slow motion. When entering your hover from harrier in this way, you'll find there is less flopping around to correct for. Hope this helps!

Dave

Dave, I typically enter the Hover the exact way as you describe. I simply transition from a Harrer to a Hover. Problem is, during the Harrier my wings will not stop rocking. AT this time, no aileron nor rudder input on my behalf, just throttle and elevator. I only correct when the rocking takes the model to a dangerous position requiring immediate correction. Once the model is pointing up, the rocking stops and it hangs, but I have very hard time positioning the model on the runway centerline becasue of the non-stop movement of the wings. That is, I cannot control the Harrier laterally.

I'm thinking along the lines of prop size. I will try with a 23x8 or 24x8.

Ah, I get it. So the problem is with harrier wing rock which is messing with your transition to hover. I would check your lateral balance and make sure its on. Then make sure all your surfaces are even. Bottom line, though, wing rock in harrier can be controlled. You just have to really stay ahead of it, correcting with the ailerons this instant the wings start to roll. The quick, little correctings required soon become second nature, and so fast nobody really sees you correct or the wings rock. learned to do it in G2, which I was told was a great way to learn because if you could harrier in that program, a real model would be a piece of cake. Anyway, its something to practice. Try just getting into your harrier with the plan of making one or two corrections and then flying out. Do stay in it until it becomes a mess. You'll master this quickly and then begin to lengthen the time you can stay in harrier. In time, you'll develop a feel for it in straight lines and turns.

best of luck,

dave

The speed with which you make the transition has a large impact as well. To slow a transition from the somewhat horizontal to vertical and the remaining lift the wings are generating becomes an issue. A fast transition passes through that transitional lift period quickly enough so the wings do not have time to make an impact. An item of note is that the smaller aerobats are much more susceptable to this.

excellent point.

Silversurfer is talking about that most dangerous of times, the transition from flying "on the wing" to true high alpha, 3D. That's when you can really get into trouble and the need for a fast transition, as he says is very real. I often use a wall to get through it as quickly as possible. Once you're in a true, high alpha harrier, the wing really isn't lifting much. And once you can control the rock the transition from harrier to hover can be wonderfully slow. I have a video I shot jasut recently of this very thing using a little slimer I designed. But I don't know how to post it and provide the link. Its not much of a video, I'd actually be embarassed to show it. But the point is from a stable harrier with the nose up about 45 degrees, I slowly increase the angle of attack until I'm in a hover and then a torque roll. If I couldn't have controlled the rock, it would have been a mess......

Its a YAK. Yaks typically do not have significant issues with wingrock, as a matter of fact they are probably the most stable 3D platform there is, IMO. I have had Edges, Extra and Ultimates but have not owned a Yak, however I have flown my friends misc variations. The Yaks to me are as stable as you can get.

I would check and make sure that your lateral balance is good and form there its just a matter of sticktime. The plane should basically be trimmed out for normal flight and coupling issues that could not be corrected by setup should probably be mixed out. Yes, coupling effects the plane in every plane, not just on knife edge. SO the mixes will subtly correct some problems you are having transitioning from harrier to hover.

My bet is that you are behind the airplane a little. All planes wingrock some, but you cannot tell when a pilot that has mastered the harrier is flying because he/she is subconsciously correcting before the problem ever starts. If you are looking at his sticks, the corrections are so small that you cannot see it usually. If you ever get up really close to a "pro" 3D pilot, you will be amazed at how little the surfaces move when they settle into a harrier or hover. It looks like the plane is just hanging there motionless, and it is, but that is because the corrections are way ahead and therefore they are VERY subtle. I have actually had a pro fly my Extra and although I wrestle with it some, in his hands it looked to be an absolutely perfect and stable plane. It would hover motionlessly inches above the grass like it was hung from a string. Practice makes perfect guys.

Think of it like riding a bicycle. You are CONTSTANTLY making tiny corrections to keep the bicycle upright without even thinking about it. When you 1st start you either over correct, or do not correct soon enough and the bicycle is all over the place. Eventually your brain figures it out and you ride the bike without ever realizing you are correcting, much less seeing visible corrections. In time you will just do it. You will harrier and hover the same way.. Just keep doing it and eventually it will be second nature.

Mike,
didi you read my post? That's exactly what I said.....

Yep, just reaffirming your postion.[8D]

cool! Safety in numbers

I think you need to work the aileron and rudder to stop the rocking. Once you get the rocking stopped, it will "lock in" and the harrier will stabilize. Only thing I've flown that didn't need working on aileron and rudder priop to stabilizing is foamy shock fliers.

You have a pretty good point with the foamies. They always seem to just hang there and pivot with the wind some.

Well I don't get it guys. I've been flying 3D for a while. My last model was a H9 27% Cap and it never rocked the wings like my Yak is doing, and is a Cap!! As a matter of fact, that Cap was very easy to Harrier and move around the runway, inches from the ground. I purchased the Yak thinking that it would be even easier with it.

I don't think correcting is going to do it, the rocking is too violent and if it was controllable I think I would have handled it by now. My Cap rocked the wing very little and yes it was totally predictable.

Lateral balance is not likely either. The airplane is pretty much "trim less". Perfect uplines, perfect downlines, very little trim required when inverted, and very explosive on high rates. I can Flatspin this sucker without loosing any altitude. I have mixes for Knife Edge and Idle to 1% downtrim. No coupling issues so far. Rolls are as axial as could be.

Could anyone tell me if my prop size seems right? The model is 30% scale, DA50, BME 22x10. My gutt tells me to move to a 23x8, or a 24x8. I'm thinking I may not have enough prop wash over the ailerons.

Did I mention that the wings will rock side to side? Not just left or right.

Thanks for your help guys, keep it coming.

What kind of prop would you recommend? My Yak is 16lbs, with a DA-50. It has a decent vertical (enough for Sportsman), and Harriers (well or I try to anyways) at about 25-30% throttle. I can actually hold a Harrier for a while, until the wing rock gets too violent then I go straight up. It hovers with no issues.

There is one thing that you might be overlooking.

weight

I have had a flown a few planes of the same design where one was pretty heavy and it had a wing rock something fierce while the other was smooth as silk.

Falconwings,
It seems to me you have a handle on all the elements of this, and that you have learned to control wing rock in other planes. i bought this little slimer, a Great Planes UCD that rocked rediculously. I never could get it right. I think trying the bigger prop would be a good bet. You've got me stumped....

Oh not at all Dave
I appricate all the input. It's just that when I encounter porblems like this I'd rather ask the people that do this everyday rather than trying to figure it out on my own and loose a $2000 perfectly good model.

I've noticed on the BME website that the Yak video shows some small wing rocking, but not as bad as my model. I initially thought it may have been the wind but no fat chance, I tried it ona d dead calm day with the same results.

David

Some planes rock,some dont. Ive seen Caps and Extras that lock in and never rock, like a foamy. Even if you never did a harrier planes like that make it easy to do,too easy. Sounds like to me you got used to the way the Cap harriers and the Yak needs something. I myself have never had a plane that didnt rock some,the best was EF Yak(68" wing),it did rock but so gently you could ignore it,I chose to correct it with right aileron. I would hit right ail just as the right wing tip was about to come up, this would stop the rock for a few seconds,the more wind,the more often you need correction. I would try the Yak in the least wind possible,in the AM or PM,get it down in light winds first,then you'll have it down when its not optimum conditions. You might even need full right ail or continuous ail,what ever it needs. I used to hold full right aileron at times,being in HA,it never snapped out on me,just enough authority in that attitude to correct the rock,if you drop the nose suddenly,then it could be a problem. On the other side,if you were lucky enough to have a plane that doesnt rock,keep it.

So now I'm thinking of what BodyWerks said, about the sweet spot being possibly greater than 45 degrees. I had a plane like that. I would start in a stable hover and slowly relax the nose. The airplane would move offstill almost in a hover. Gradually I got better and better at it and in time was able to harrier it around like normal, though still at a pretty high AOA. I'm still thinking, too, like Mika and I said, there may be a level of correcting you might need to slip into. Really fast anticipations of what its going to do. Like I said, I learned this in G2 and if you've every flown that sim, the airplanes rock so violently they sometimes snap and go inverted. By now I can harrier the sim planes around upright and inverted, so when a model tries that on my I say, "no you don't!" David, I'm in no way minimizing your problem, just looking for ways out. Do you have a practice plane? I always work out new stuff on something small and cheap. Silversurfer calls 'em slimers which i thought was funny so I have been too.... I'm thinking of something that isn't as sublime as a Mojo, but like a Flip 3D, or an Extreme 330. Something that's going to give you a bit of a hard time. Ok, now you can tell I'm bored because I haven't stopped writing yet. In the early 1980's I really liked WWll fighters. Most of the models being flown at that time were 60 sized, with very high wing loadings. If you could fly one of those ships weighted down with epoxy paint, etc, you were doing something. So I built one but had never flown a high wing loading plane. So I took my 25 powered little stick and rubber banded hand tools (piers, crescent wrenches, etc) on the wing and practiced. I had to be sooooo careful just turning this thing. By the time I was comfortable the maiden of my Corsair was no problem. I flew that thing all summer and had a wonderful time. In the fall I sold it. The guy crashed it on the first flight. Too high of a wing loading.

Dave

I do not have G2, I use IPACS Aerofly Deluxe and to date I haven't seen a model as difficult to Harrier as my Yak.

The Cap would rock some but it was controllable, enought to be able to get it close to the ground and move it along the field with total directional control. Sure it neede some rudder, thr, ail, and elev worked but nothing extraordinary (man I wish that Alitalia was still around!!).

My Harrier is way higher than 45 deg, probably closer to 65 deg, but doensn't matter as it behaves the same. I don't think it should be that difficult to Harrier a model, if indeed my Yak is such a pain then is not a fun model.

I think you're right. I had that CAP too. Sweet flyin plane.