mchadwick

My Feedback: (1)

I have spaced the engine out up to 3/8" to help with balance issues. It sounds like you are already about where you want to be. The DLE 55 will give you very noticeable improvements in power and will be a direct swap if you find it is still light on power. Redwing RC will sell the engine pre-run so it is tested plus the carb is wet and ready. My 55 likes a 23-8 Falcon or Xion Carbon Prop.

Truckracer

My Feedback: (19)

Going back to post 5, I knew as soon as you mentioned you had a Slipstream plane and you were using their recommended CG .... you had a problem!

Good job getting some weight out of that plane! Sounds like you're well on to your way to resolving the issues. As others have said, don't discount the improvements the DLE can offer if you still need more power.

grosbeak

Yes, that is a Xoar 23 x 8. And thanks... I like the way it looks too.



A123 - 6.6V, 2500 mAh

Thanks again for the help. The removal of the extra weight certainly seemed to make a difference.

sensei

I think you may have misunderstood what I was saying. Moving things around in the fuse first is a given and does not need to be said because if the designer does their homework this is the standard method to obtain the proper C/G and always has been. Adding useful weight to an aerobatic airplane is only what is needed to fly the airplane in the first place, adding anything extra to compensate for design errors that blow out the C/G is not useful weight at all. Anyway I am happy everything worked out for you and you took some weight out.

Bob

grosbeak

Gotcha. Thanks - I'm happy too!

grosbeak

I put it on the scales in the shop this evening and changed the specified CG in the spreadsheet from 150 mm from the leading edge (Slipstream's spec) to 173 mm (centre of wing tube). I entered the readings from the scale and was surprised to find that my changes at the field had only moved the actual CG back from 150mm to 159mm. I thought back to when I bought the plane from its previous owner - at the time the receiver battery was mounted just aft of the wing tube, so I moved it there too. The result - another 10 mm back... 169 mm from the leading edge. Still a little nose heavy if we're judging by the wing tube.


In the process I removed the landing gear reinforcement and standoffs (I may reinstall it if I think it's warranted), the BatShare, and the mounting plate, hardware and straps that held the receiver battery to the motor box, for a total savings of 210 g (nearly half a pound). Note the new weight in the upper right corner, down from 19.8 lbs.





We'll see how it goes at the next flight. If it's too much I'll move the receiver battery forward and try again.

Truckracer

My Feedback: (19)

Grosbeak, you should start a new thread in a more appropriate forum regarding your CG changes and experiments. I think many people could learn from what you are going through with the SBach.

Another point that might interest you .... while many use the 45 degree inverted climb as one test for proper CG and it is a good check, I also look very hard at how precise the plane can do snap and spin entries and exits. Once a plane gets so far into the aft CG range, it can be very difficult to control these two maneuvers. Not a big deal for 3D as these planes rarely do real snaps anyway (yes I said it) but a major problem for anyone trying to do precision maneuvers such as in IMAC. Proper CG is just the location that is the best compromise for the individual airplane, it's purpose and the pilots comfort among many other factors.

grosbeak

I often have a hard time finding the correct forum here in RCU; if I were to start a new thread, do you have a suggestion as to where it should go?

As for spins and snaps, I'm planning to use this plane for IMAC. I'm still firmly rooted in Basic so I will be doing spins this year... snaps may come later. I'll keep your advice in mind.

Truckracer

My Feedback: (19)

I think the forum you're in here would be fine, just bring the CG information into a new thread with a different title.

Zeeb

My Feedback: (41)

Oh come on now, there ARE guys who can do real snaps in IMAC competitions, you just have to have the correct name on the entry form..... lol

speedracerntrixie

My Feedback: (29)

I have to agree with Truckracer here and i have had the conversation with quite a few judges and CDs. A competitive IMAC airplane is so lightly loaded that it simply will not stall unless you go really deep into the snap and then your heading will be off and points will be lost. The typical IMAC snap roll is a blip of pitch deviation followed by aileron and rudder. I naturalize the elevator about 1/2 way through the snap and hold rudder a little longer then ailerons. Spins are another challenge, I never let the airplane stall but the judges can't see it. Hold nose up about 10-15 degrees with elevator. Just before the airplane starts to mush let off the elevator and the nose will drop. Just as the nose hits horizontal give full rudder to the direction you want it to go and after the wing on that side drops follow in with aileron and elevator. It's a way of flying through the spin entery that actually looks like the airplane stalled.

Truckracer

My Feedback: (19)

Zeeb and Speed, I agree with your comments but was referring more to 3D airplanes not doing snaps than IMAC. At least the IMAC guys do a far better job of making their maneuvers look like snaps and spins than the 3D guys. I hear 3D guys calling some of their maneuvers snaps when they don't look anything like snaps.

At any rate, the point was that at an extreme aft CG, when the airplane does finally stall such as in a snap, it can be very difficult to stop it on point. I usually find that aft CG point where stopping snaps and spins becomes difficult and move the CG slightly forward from there until the airplane is predictable.

I use to train judges some years back (quite a few years back!) when IMAC was in its infancy and trying to teach the fine points of snaps and spins was one of the hardest things to get across. Easily spent 1/3 of our training time on these two maneuvers. We got quite good at detecting guys that were just doing vertical snaps on a down line and calling it a spin! I would bet it isn't much different today. We always encouraged that flyers discuss their low scores with the chief judge when they thought they should have scored much higher.

daveopam

My Feedback: (9)

You are getting there on the weight. As a comparison. My 50cc AW Extra 300 is 84" span. It comes in at 17.5 pounds with a DA-60 and pitts muffler. Your canister is maybe a little heavier? I do have a heavy IGN battery. it is a 5xsub "C" NiCad cells. RX battery is a 2S lipo on a reg. I am a little surprised you are a pound heavier than I am, but I have no time on a plane from your manufacturer.

Other thing I was wondering about. You are trying to get your CG on the wing tube. Is the wing tube centered under the main spare? Many are just aft of the main spare so please be carful and sneak up on your rearward CG. Most of the time you will be OK because you are starting with a full tank. Just pay attention as you fly. If the ELEV trim starts get off (the plane climbs as it burns fuel) or the AILEs start to feel funny(reacting slower from level or not centering after a roll) set it down and go back the other way.

Keep us posted on your progress.

David

Truckracer

My Feedback: (19)

The human body has this little area that tells the brain when the CG has gone too far into the tail heavy range. That little spot is located just rear of center and between the legs. Some people have been accused of clinching so tightly they could have made diamonds if a lump of coal was inserted in just the right place!

daveopam

My Feedback: (9)

This sphincter you speak of will keep a John Deere from pulling a tooth pic out of it during landings with a CG too far aft.

Jetdesign

My Feedback: (8)

I recently got a plane that most people are adding a ton of nose weight to. I refuse to add lead to an airplane. Out of the box I found nearly 1/4lb worth of weight to remove behind the CG, a lot of it in the tail wheel. Using a super light tail wheel, light elevator servos, and light elevator linkages (including turning the servos such that the linkages are as short and light as you can make them) will go a long way to reducing lead in the nose. My next step is to build a servo tray further forward to mount the rudder servo more forward. No one says you have to put the servo where they tell you to.

If you use the 1oz in the tail = 3oz in the nose, the 1/4lb I saved in the tail is 3/4lb of lead in the nose. Guys were adding about 6-8oz so I think I'm doing pretty good!

The plane is an Aerobeez Sbach, which is basically the same as Redwing Models, Peak Models, etc.

grosbeak

When this is sorted I will do that.

David, I will definitely keep you posted on the progress. Thanks for the tips about the CG - I'll keep that in mind for sure.

grosbeak

I got my next flights in a week ago - It was an improvement but I think I've gone a bit too far the other way. It was a little tail heavy so I have moved the battery to just in front of the wing tube.

Spent the day at the field yesterday and got a lot of flying in. The CG - 164 mm behind the LE - is now perfect. And I'm noticing much better performance, especially in vertical uplines, since I shed all that weight.

Thank you for the help and encouragement.

daveopam

My Feedback: (9)

That is great news! I suspect the original owner of the plane is now wishing he had tinkered with the CG.

David

grosbeak

I wouldn't be surprised!

Truckracer

My Feedback: (19)

Grosbeak, thanks for coming back and posting your success. So many times people just go away and nobody knows if the suggestions helped or not.

How much weight did you finally remove from the plane and how did that translate to the CG? How much did you move the CG back from where you started?

grosbeak

In total I've removed 1.2 lbs from the airplane, most of which was in the lead ballast and second ignition battery on the motor box. This reduced the weight from 19.8 to 18.6 lbs.

The CG was moved back 14 mm; it started at 150 mm from the leading edge of the wing and moved back to 164 mm.