I was out flying my QQ Yak 85 today and was re-checking the CG in that I had done some repairs and was out of commission for a while.

I have seen videos that indicate your CG is good when the plane starts fall towards its back when doing a 45 degree inverted upline (excuse me if that's not the correct terminology). Anyway, my plane just kept climbing inverted at a 45 degree angle with NO down elevator.

SO everything is telling me the plane is significantly tail heavy which is a b*tch because I almost have everything under the engine cowl right now and I don't want to add more weight. This is an issue with all of the QQ 85's that was fixed with the 86. Perhaps I can creep the ignition box to the front of the engine box along with the ignition battery.

MY questions are:

Would this tail heavy condition be what is causing ridiculous wing rocking when flying upright slow harriers on high rates? Some wing rocking would make sense, but right now it is beyond control

Could this be what is also causing hovering (not torque rolling) to have such wing rocking as well. Obviously the CG the way it is now helps it stay on it's tail but the wing rocking seems beyond normal.

Any insight would be appreciated...

-Brad

By the results of the test you have described you are tailheavy. (barring some crazy incidence problem) Wing rocking in a hover is just new to me. Are you sure you are hovering, and not just a very high angle harrier ? It is a lot easier to hover nose down a bit - basically still harriering. If you are truly hovering tail down the plane will want to torque roll without massive aileron correction. But it should not want to rock.

If you need to bring the CG forward, you can space the engine forward accordingly. Because of the big round cowl, you want the prop at least 1/2" forward of the front of the cowl, preferably 5/8" or so.
Wing rock in a hover doesn't exist. If you are truly hovering, the wing isn't generating any lift and therefore cannot rock.
Other indications of a tailheavy plane would be tremendous tuck toward the belly in knife edge. This is because a tailheavy plane requires down trim to fly straight and level, so when the plane is in knfe edge the stab is now your rudder and that down trim causes it to tuck.
Also check your lateral balance, that will contribute to wing rock. Do this by flying the plane on an extended downline with the engine at idle and then pull to level flight, rather swiftly. The plane's wings should stay level. Of course, make sure your elevator halves are traveling perfectly equal prior to doing this...

Thanks for the input guys...I was referring to wing rock when not completely hovering...ie..a very high angle harrier I guess..when the plane is perpendicular to the ground it will torque roll for days..no problem there..

As is, the engine is already a good distance from the firewall. I"m going to try to move the remaining stuff forward first.

I'll check the lateral balance as well. Could bad lateral balance also be seen popping into a normal wall from level flight?

Tail heavy makes a plane more sensitive to control inputs. It will also allow you to hove better in most cases. But on any of mine if it's tail heavy it doesn't roll very well.

I'll experiment this weekend and see what I come up with.

Brad,
Your airplane does not sound that tail heavy to me. When you pull to a 45 upline and then roll inverted, a correctly balanced model will continue on that line for a moment and then slowly fall towards the canopy. A tail heavy airplane will pitch toward the belly in the same scenario. If your model continues on the 45 with no down elevator you are pretty close. Your wing rocking sounds like radio setup. Start troubleshooting by taking out some elevator throw. You should see some improvement with less rocking back and forth. Another thing you'll want to look at is your expo. Be sure to have a minimum of 35% on the elevator as a starting point. Good luck.

Stan,

I didn't consider that too much elevator might be the culprit in terms of what is going on. I didn't know that could cause that problem but I'll give it a shot. I think I've got that much expo but I'll take a look.

Thanks

Originally Posted by FixedWing172

Brad,
Your airplane does not sound that tail heavy to me. When you pull to a 45 upline and then roll inverted, a correctly balanced model will continue on that line for a moment and then slowly fall towards the canopy. A tail heavy airplane will pitch toward the belly in the same scenario. If your model continues on the 45 with no down elevator you are pretty close. Your wing rocking sounds like radio setup. Start troubleshooting by taking out some elevator throw. You should see some improvement with less rocking back and forth. Another thing you'll want to look at is your expo. Be sure to have a minimum of 35% on the elevator as a starting point. Good luck.

I'm not saying your wrong, but I am curious. Why would too much elevator throw cause wing rock? Also, why would you have to have a minimum of 35% expo to prevent wing rock? I have not experienced this, although I am flying a 40% Carden Cap, not a Yak.

In my experience wing rock is normal to some degree. Excessive wing rock is caused by a high wing loading. Correct me if I am wrong.

I do agree with you on the c.g. It is very close to where it should be. It is pilot preference once you get it as close as he has it now.

Hey Brad,
Glad to hear your still flying my old plane, it was the first 85"er released and flown with a DA 50. Stan is right, it sounds like your almost perfect with the cg, if it was climbing on the inverted 45 I would say it's tail heavy but right now your about neutral. I had everything mounted on the motor box including all batteries and found it to be just right, just slightly nose heavy. Is the wing raock worse than when you were flying it before?

Lee

Brad here is a picture of my install. In this picture I had a nickle medal battery in the box also for extra weight but it removed after the maiden because it wasn't needed.

Lee

Lee,

It just seems that the wing rocking is excessive enough that I can't counterbalance much with stick movements with the plane tilted up high on 3D rates doing an upright harrier down the flight line. Therefore, if I want to come down low to hover, I alway pop up into a wall and ease it back down.

The wing rock isn't unmanagable doing an elevator, just on that one move. It could be my skills but ironically moves harder than that don't phase me that much. I've had crappy glo planes be more stable doing this manuver so I want to make sure it isn't something in my setup. I'll keep experimenting.

I did take your lead and I have the ignition, ign. battery and 2- 2600's up in the front. Still, I could move the ignition and ign. battery up and flush with the inside part of the firewall...that and move the regulators on each side of the gas tank and bring the receiver forward.

Anyway, had to re-do the firewall from one hard bonk on the nose, after that repair the plane is just as strong as ever and I have about 98 flights on her. My DA-50 is nice and broken in as well...very nice!!!

You ought to come down the PGRC IMAC Aug. 25-26th. I'll be out of town on the 25, but was considering heading out there on the 26th.

-Brad

I have a 30% YAK 87'' 16 lbs. and when I do a harrier and get a little wing rock I give it more elevator and get the nose up and it stops the wing rocking. Mine is a little tail heavy for rock solid hovering. I had a Areo Works 85'' Yak 18 lbs. It was hevy and would wing rock bad, caused by a high wing loading !

My planes is nose heavy by a long shot!! every time i hover it goes nose down

my planes nose heavy so every time i hover it goes nose down