Can't get my 72" Yak to "settle in?"

Can't get my 72" Yak to "settle in?"
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Can't get my 72" Yak to "settle in?" - 6/5/2008 5:40:42 PM

dmccormick001

Posts: 121
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
Status: offline

I have an older QQ Yak-54, I think it's a 72". Even though I just bought it, it is still brand new. I bought it complete with motor, a YS140 Sport, because the 2 previous owners couldn't get the motor to idle correctly. I had to drill out the hole in the carb barrel, among other things, but the engine is now purring like a kitten. It still isn't really broken in fully. But I've made several short flights already, and the plane seems to fly incredibly well. Very sharp and responsive, but not squirrelly or difficult to predict. I think I'm going to love it, but I have one small problem that I'm not sure what's causing it. I have the plane balanced exactly on the recommended CG, and trimmed for level flight at about 1/2 throttle. When I slow it down to land, it seems to want to climb slightly, so that I feel like I'm having to actually give it a little down elevator to try to get it to the ground. It doesn't ever settle into a landing attitude like I'm used to with other planes, i.e. slightly nose high and losing altitutde slowly. My YS is idling at 2000-2500 RPMs, but it seems to wait until it is ready to stall before it drifts down at all, and once it stalls of course it drops like a brick. Is my CG too far back, regardless of the recommeded location? That's what my common sense and experience tell me, but I'd like some advice from someone who's flown these planes before. Inverted the plane only requires a touch of down to keep it flying level, it doesn't climb as if it's tail heavy.

BTW this is my first giant scale 3D plane. I have smaller 3D planes, and also fly warbirds a lot, including a couple of giant scale warbirds.

Post #: 1

RE: Can't get my 72" Yak to "settle in?" - 6/5/2008 6:23:37 PM

randy racer

Posts: 1287
Joined: 4/7/2005
From: mayfield, KY, USA
Status: online

if your c of g is right you need to check your engine trust line. if you have to much down thrust you will need to use more up trim under power and when the power is off the nose wants to climb. mine did the same thing and i added a little up thrust and it was perfect. this is a great little plane you have so enjoy it.

randy

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RE: Can't get my 72" Yak to "settle in?" - 6/5/2008 6:26:24 PM

octanehuffer

Posts: 693
Joined: 7/15/2006
From: Lakeland, MN, USA
Status: online

Sounds like its flying perfect to me! Sounds the all the other QQ planes I have. You could however, make it more tail heavy to have the tail drop upon landing. If that suits your flying style.

ADam

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Post #: 3

RE: Can't get my 72" Yak to "settle in?" - 6/5/2008 6:31:11 PM

Walter_Mitty

Posts: 22
Joined: 6/24/2006
From: CAMBRIDGE, UNITED KINGDOM
Status: offline

Hiya,
it seems to me that your CG is about as perfect as you could get,for a mix of precision, and 3D.The test i always do is:get really high,power off,und go vertically down. Then let go of the sticks! If it pulls out to the canopy,it's a foreward CG.If it pulls to the U/C,then the CG's too far back.Every aeroplane is different!

. I have 4 Yak 54's (I kind of like them!!)Each one handles slightly differently!
As for all of mine, (sounds like your's too) Try a switched mix for landing, 2-4% down elevator at idle for landing,this works for me on all of mine!!

(in reply to dmccormick001)

Post #: 4

RE: Can't get my 72" Yak to "settle in?" - 6/5/2008 7:13:14 PM

dmccormick001

Posts: 121
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
Status: offline

Thanks guys! That's what I needed to know-if anyone else who owns this plane has had a similar experience. The thing flys so well that I didn't really want to change the CG. I might try sticking a couple of shims under the engine mount to see what that does, but I don't know how many degrees of down it's supposed to have, so I have no way of checking it.

quote:

ORIGINAL: Walter_Mitty

Try a switched mix for landing, 2-4% down elevator at idle for landing,this works for me on all of mine!!

Now why didn't I think of that?? That would be too easy. I could activate it with a switch instead of the stick, so if I'm at idle and want to do a harrier or elevator I'll still have that nose high attitude.............. OK, now I just need to make it to "quittin' time"!

Thanks guys. You've been a big help, as usual.

David

(in reply to Walter_Mitty)

Post #: 5

RE: Can't get my 72" Yak to "settle in?" - 6/6/2008 1:25:58 AM

randy racer

Posts: 1287
Joined: 4/7/2005
From: mayfield, KY, USA
Status: online

if your thrust and C of G is right you won't have to remember to pull a switch to land on any of the QQ yaks and i have had 5 of them so far. 72" 73" two 102's and the little electric one. i would rather a plane fly right and save the switches for other stuff.

rr

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Post #: 6

RE: Can't get my 72" Yak to "settle in?" - 6/6/2008 2:13:37 AM

dmccormick001

Posts: 121
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
Status: offline

Well, my CG is right, so take that out of the discussion. Now you keep mentioning my down thrust not being correct, so let me ask you this. The down thrust is set by the firewall that comes pre-built and pre-set. How do I (or you) know if it is or isn't correct? I've built kits, so I know all about setting right thrust and down thrust per the kit's specs, but on an ARF that is built with pre-manufactured parts to the designer's specs, how am I supposed to know the correct degree/s of down thrust? It isn't published anywhere. I have an incidence meter and can check it, but if I don't know what it is supposed to be, how do I know if it is wrong? Did you just use trial and error on your engine mount? What did you do, place washers or something under the bottom of your engine mount? How many did it take to fix your's? I'm reluctant to change something like that unless I have some reason to believe it is wrong in the first place, and it's hard for me to accept that the plane could be manufactured with the wrong amount of down thrust, you know what I mean? I'm not arguing with you, since it seems to have worked on your plane/s, but I just wanted to hear from some other people who've had this same plane and see how they dealt with it. The idea that the plane's trim settings could be a little different at slow speeds isn't hard for me to accept at all, I've had other planes that did the same thing to a lesser degree.

Remembering to "pull a switch to land" isn't a big deal. I use dual rates, so I flip switches a good bit anyhow, and I fly several warbirds with retracts and flaps, so a lot of times I'm busier when I get ready to land than at any time during the flight. Got wingtip lights and landing lights on some of my planes, too. Looks cool at dusk to flip on a couple of high-output LEDs mounted near the gear to help keep you oriented as it gets dark.

David

(in reply to randy racer)

Post #: 7

RE: Can't get my 72" Yak to "settle in?" - 6/6/2008 4:37:13 AM

ctnic

Posts: 58
Joined: 11/14/2003
From: Grand Rapids, MI, USA
Status: offline

dmc,

The down thrust on the engine is 0 degrees. My first 73" yak from QQ had about 1.5 degrees of downthrust. I just made wedges from some thin carbon fiber panel then trial and error to bring it back in line. The one I have now was perfect out of the box.

Remember, these are factory made and sometimes things get off a tad. Not only was the downthrust off but the horizontal stab measured +1.8 degrees. Not hard to fix but I only new it was off because it was so obvious. I could not find any info on it either at the time so a quick call to QQ Aircraft got me the info I needed. On the 73" the engine downthrust and wings are 0 degrees with the horizontal stab 0 to .5 degrees using the fuse canopy area as reference. I would assume the older 72" version is the same.

Chris

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Post #: 8

RE: Can't get my 72" Yak to "settle in?" - 6/6/2008 12:36:27 PM

randy racer

Posts: 1287
Joined: 4/7/2005
From: mayfield, KY, USA
Status: online

my 72" would fly power on level and when i chopped the throttle it would pick the nose up ( balloon ). the vertical test also will tell you if the thrust is wrong. if you are going up full power straight and then coming back down off power your plane pulls to the canopy adjust your thrust up. do this with washers under the engine mounts.
it is hard to beleive that a jig built , lazer cut plane could be off but it happens. some times it's not so much the plane as motor choise, how the engine mount was drilled, and prop selection. when you get the thrust adjusted up/down and right/left on a very well designed plane like QQ yaks they will grove so take the time to check it out.

randy

P.S. to trim a plane out right it take me several days at the field and a bunch of flights but it's worth it

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Post #: 9

RE: Can't get my 72" Yak to "settle in?" - 6/6/2008 3:06:24 PM

dmccormick001

Posts: 121
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
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OK, looks like this weekend I'll be checking incidences. I appreciate all the help and info.

I've got to get this thing landing right, it's hurtin' my reputation. The last three or four times I've landed it have been sorta "rough", if you know what I mean. Hard to land one smoothly when you have to hold down elevator just to get it to come to the ground.

David

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Post #: 10

RE: Can't get my 72" Yak to "settle in?" - 6/6/2008 3:43:20 PM

sethslasher

Posts: 50
Joined: 6/18/2005
From: New Holland, OH, USA
Status: offline

All of QQs planes that I've flown (102", Python, 85"

none have had this tendency. As said before, check your thrust and see if that is off BEFORE you make a mix. Try and get the plane flying as best as it possibly can by experimenting with things like thrust. For IMAC stuff, it sometimes takes me most of the year to get my airplanes trimmed out, so just have patience with it!

Seth

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Post #: 11

RE: Can't get my 72" Yak to "settle in?" - 6/7/2008 2:30:08 PM

dmccormick001

Posts: 121
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
Status: offline

Well, you guys were right. I checked my downthrust, and I had about 1.25-1.50 degrees of down. While I was at it, I checked my horizontal stab, and it was perfect. I guess that isn't a surprise since the plane flys so good. I've put a large fender washer under the bottom engine mount, and now it's right on the money, so as soon as I can leave work and go get the truck loaded, it's off to the field to see what a difference it makes. I'll let you know how it works.

Thanks again guys!

David

(in reply to sethslasher)

Post #: 12

RE: Can't get my 72" Yak to "settle in?" - 6/7/2008 9:59:21 PM

randy racer

Posts: 1287
Joined: 4/7/2005
From: mayfield, KY, USA
Status: online

great, now get out there and fly that thing. haha! let us know how it goes,

rr

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Post #: 13

RE: Can't get my 72" Yak to "settle in?" - 6/11/2008 11:53:33 PM

Dessie

Posts: 3
Joined: 9/16/2007
From: gorey, IRELAND
Status: offline

Hi David,
I had the exact same prob with my 73 inch, had to fit washers to the bottom of the engine mount, mine flared up about 30 degrees when i dropped power on landing, scared the sh.. out of me and i tore the undercarriage off. what prop are you using as i am having some probs slowing it down to land using a 16 x 11 APC, thinking of changing to a 18 x 8 standard or is this too much prop for this engine????

Dessie in Ireland

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Post #: 14

RE: Can't get my 72" Yak to "settle in?" - 6/12/2008 12:51:52 PM

dmccormick001

Posts: 121
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
Status: offline

I'm using a 16 x 6 Vess prop on a YS 140 Sport. I've also tried a 16 x 6 APC, and can't tell any difference in performance with either one. The 16" prop looks too small with the big, round cowling on this plane, so as soon as my LHS gets some 18" in stock I'm going to try one. The maunal on my engine says you can use several larger size props, so I don't think an 18" will be too much, but the only way to tell for sure is to try one and check the engine RPMs. The 11 pitch on your prop is definately going to speed it up, you might try less pitch.

The washers under the engine mount seem to have helped the ballooning some, but haven't eliminated it. I may try adding another, although I checked the incidence with a laser meter and I thought I had it right on 0. The plane still doesn't settle in like I expected, but some of my flying buddies with experience with giant scale are telling me that's kinda' normal, and that I need to learn to manage my decent during the last few feet with throttle, not elevator. I'm having to break some old habits and learn to do that, and it seems to be working. My landings are good, but they take a lot more concentration and effort than I'm used to. I can't just line it up, cut the power, and feather it to the ground with the throttle. Once I chop the throttle it floats for several feet and then tends to drop too quickly if I don't give it just a touch of power to stretch it out. I've changed a couple of things trying to get it dialed in, so I'm going back this weekend and re-checking my CG to make sure it isn't a tad nose heavy now. All of this will require lots of test flights! Oh Darn!

David