After many builds with never a problem... I have two airplanes in a row that do the same thing which makes me think I somehow have lost the formula when setting the firewall angle, CG or maybe the manuals are wrong ??

Here is what I have on an Aerotech Extra (DA50) and a Columbo Anderson Extra (3W-75i) they are the lastest planes I put together and they both do the same thing..

Fly plane at full throttle... chop throttle.. plane does not climb or dive, tells me incidence and up/down thrust are OK
Fly plane straight up plane stays straight even at WOT - tells me right thrust (mixed in with rudder) is dead on
Fly plane in down line, it pulls to canopy slightly, mixed out with down elevator (pretty normal )


CG on Columbo - dead center on tube, right where manual says. 19 pounds 14oz FUW.
CG on Aerotech - in the third fifth of the range (i..e if range was 1-5 I'm at 3) 16 pounds 9oz FUW
Incidence on both planes are zero/zero.

The planes FLY very well with no bad tendencies whatsoever. Where I am having problems is on landings. I come in on approach, and all looks great until I get over the runway. When I reduce and/or cut the throttle the plane balloons up way to high to land. I have to feed in down elevator in order to compensate, which usually ends in overcorrection and a missed landing. Add any headwind into this equation and its very hard to get the plane on the ground. The plane cannot land hot, it will continue to fly, so something is definitely up.

To try to reduce the sensitivity of the elevator, I have enabled a landing flight mode - the elevator throws are very low (15%) and 40% expo. The elevator still seems a little sensitive but not hypersensitive as it was with no expo and higher rates. Again, in normal flight everything is fine and even on high elevator maneuvers the planes do not snap.

So.... does this sound like a CG issue or could it be I need to add some up thrust ? The CA Extra has some upthrust built in. The Aerotech has none.


Honestly, these planes should be easy to land yet they are harder to land than some of my previously (and much smaller) planes. I battled a 20 mph head wind yesterday while flying the extra and on about the 7th attempt to land it I drifted slightly off the runway and caught the gear on the edge of the pavement. I tore out the gear block when I hit a rough spot in the dirt. I was very lucky as it was a clean break with no other damage to the plane. The plane is already fixed (beauty of a kit) but I really don't want to go through that again.

One last thing. Early in the day before the gale whipped up, I did an intentional dead stick landing (i.e. lined up with the runway and cut the ignition) it was a LOT easier to land and came in very predictable.

I'm thinking upthrust... anyone else??

DP

Sounds tailheavy to me.

It could be a tail heavy problem. My 38% CA was balanced at the front edge of the wingtube.

DP - before I would change any of the hard stuff ( CG or
thrust) I would try spoilerons in your landing mode. If you
have JR, use the landing system on a 3 position sw and
set two values for spoilers, eg, 10 and 15 degrees. Next
time out play with it up high to see what it does. Should
dirty the airplane sufficiently to allow you to fly it in
with power (pulse the throttle) and keep the nose
down.

That would work but it doesnt fix whatever problem he is having.
Those planes should not need spoilerons to land.

I would say tail heavy too. My Sukhoi did the samething. I move some weight foward and it stopped balloning on landing with no change in 3D or sequence flying.

You told us about several flight trim checks except inverted and if any elevator input is needed.

Tail heavey from me too. My Wildhare Giles has a DA50 in it and it does the same thing. In the air it isn't too bad, but come time for landing and you have to push down elevator.

Buzz

If you can land with only 15% throw and 40% expo, I also bet you are tail heavy. Sensitive elvators = tail heavy...

That is strange as you stated that the CG is good per the manuals of the planes.

Do you have good servos for your elevators ??

Inverted flight no input needed... Usually in my big planes I have to hold some down elevator to keep the plane from sinking.. so it looks like the consensus is the models are tail heavy at the current CG. They are in the middle of the recommended range, but that does not mean much. One man's balance is another's tail heavy!!

I have looked all over for "real" CG locations here and elsewhere.. no one seems to have any good numbers for either of these planes. The manufacturers are useless, they just say balance on tube or give a range. Since neither of these planes are out there in large masses or have fallen out of popularity... I guess I will experiment with each by shifting some weight forward and see what happens.

I have usually had great luck balancing by gut feel and/or using MAC. In this case neither worked!
Thanks for all the input guys! I'll let you know what the results are in a few days..

DP

If you need no elevator input when inverted then you're definitely tail heavy.

I would agree with eveyone else that has said CG. Flying straight and level with just enough speed to keep it straight and level, as you SLOWLY back off of the throttle, don't touch anything else and see if the nose goes up or if it is actually the tail dropping.

I did some experimenting with an OMP 80" profile. With a rearward CG, I could get it to act as you are saying yours has. When i slowly let off the throttle, I could see the tail drop.... At one point, The CG of my plane was at the aileron hinge line......boy was that a fun ride!!!

Made the suggestion directed at the landing issue because he said:
"The planes FLY very well with no bad tendencies whatsoever. Where I am having problems is on landings. "

I am using 8611s or 5945s all around. I re-checked the balance on both planes this AM.. they are closer to the aft limit than to the forward limits and my hypothesis from reading some of the posts here on RCU is that the CG numbers on both these planes were "not so good" in the manuals. I am in the process of moving some weight forward. Looks like the gale is moving back in again.. high winds the next few days.. so it might be next week before I fly again. I don't mind some wind, but they are taking 20-30mph tomorrow!

The past few planes I have put together have been 33% - 40%. I find them much more forgiving to balance. Since they also were all H9 ARFs 1 Comp-Arf and 2 Cardens their manuals and/or designers have the CG and thrust numbers dead on. Mike M and Dennis gave me starting points and I never had to change them after the first flights. Comp-Arfs are hugely popular so I got those numbers here.

I have not found anyone who has built an Aerotech Extra, and what few people built the Columbo's all moved on to other stuff!

Again, thanks for the info.

DP

I had the same problem with two of my planes and it turned out both were tail heavy. I would say from all I have read here is it's CG.

ten pillows

I set the balance by flying a 45 degree upline at full power, 1/2 roll to inverted and let go of the sticks. If it heads to the moon, it's tail heavy. If it heads to the Earth, it's nose heavy. If it keeps on tracking on the 45 line....it's just right. If you fly a lot of 45 lines in your sequence, this will minimize "too much thinking"....

I agree that it is tailheavy. With what you are saying especially the way it flies upright and then NO down elevator to fly inverted it definitely sounds tailheavy. Do you have any down elevator trim in it? I would be you would need it to get the plane to fly level hands off, which is why you would not need down elevator when inverted.

Hey Ted,

You going to Clinton in a few weeks?
Advanced this year?

I am still figuring out my H9 Sukhoi. There is much debate about where the CG should be on my plane, but I suspect mine is a bit tail heavy because my experience is similar to yours -- flies great in all modes, then a real handful to land.

The post that caught my attention in this thread was the one about elevator input needed for inverted flight. I too, need virtually no input to maintain inverted. If that fact equals tail heavy, then I may experiment with moving my batteries around to see if I get any improvement.

im not sure but it should fly where pointed, rather than having to mix in contolls, does the fuel tank being less full affect this more that other planes?

SBR brings up a good point. If the tank is forward and the CG flight tests are done at the beginning of the flight they might not be valid.

I built a tank mount in my Sukhoi and now my tank is over the CG. I did have to remove the canopy brace that was over the tank. No problems with that though. Of coarse there's not much wood left in my canopy hatch anyways

I try to install all my tanks right on the target CG.. or as close to it as I can. Usually that means the middle of the suggested range, or on the tube if that is the suggested balance point. In the case of the 28%, it was impossible to mount the tank on the tube or at CG, the center of the tank is mounted slightly forward. I balanced the plane empty and full to see what the difference is. Not much with a 20oz tank, the cg shifts about 1/8"

I have reconfigured a few things and shifted the CG up a full 1/2" on both planes - fortunately I was able to do this without adding weight.
I guess I will see how they fly and go from there.
DP

Hey Wayne:
I'm planning to be at Clinton as long as I can get "clearance from the tower"..
Still working on Intermediate.

Sandbagger.