grosbeak

I have a DA 50 in my 87" Slipstream SBach 342. The plane is heavy - nearly 20 pounds - mostly due to the location of the CG and the need to add weight to the nose for balance.

The DA50 is connected to a canister - it's a sweet combination but I'm testing the waters for more power. I'm wondering about a bolt-in replacement with more displacement - something that would preferably use the same standoff spacing and the same muffler flange. I understand that shorter standoffs may be required.

Feedback welcomed.

speedracerntrixie

My Feedback: (29)

I would focus more on weight reduction.

Zeeb

My Feedback: (41)

Well a DLE-55 should bolt right in but that's not going to gain you much. As noted, you need to put that thing on a diet, not only is the performance lacking but with wing loading like that it'd feel more like a Warbird than an Aerobat....

grosbeak

Thanks for the tips, fellas, but that's not real helpful.

As mentioned it needed plenty of nose weight to balance because of where Slipstream specified the CG - 23mm in front of the wing tube. I'd rather have useful weight than ballast - adding a second RC battery and strapping all three of them to the motor box helped, but there's still lead left and the weight of a bigger engine is just the ticket to replace it. The weight (and, therefore, the wing loading) will not change.

Truckracer

My Feedback: (19)

I can't speak for the Sbach but other Slipstream (and their brothers under different company names) are notorious for having their CG shown way too far forward. You might try removing weight a bit at a time, slowly moving the CG farther back. The plane may fly better and you'll get rid of some weight in the process. Certainly worth a try and it will cost you nothing but time. Most aerobatic planes have a very wide CG range.

As for the DLE / DA, I noticed quite a bit of power difference between the DA 50 and the DLE 55 so don't completely discount that exchange.

grosbeak

About the CG - very interesting. Thanks for the tip - I'll give that a try.

speedracerntrixie

My Feedback: (29)

I agree with Truckracer here. I too think you are running the CG too far forward and if you got into the mindset of removing and/or reconfiguring things to shed some weight you would have a much better performing airplane. Calculate where your CG is now. Ideally for that airplane you should be at 30% to 33% of MAC. Getting to that point would drop most if not all the dead weight out of the nose. If not there are lots of things to get weight out of the tail. Take some detailed pictures of the entire airplane inside and out and I can come up with at least 25 things to drop some weight.

grosbeak

I'm not familiar with the term MAC - could you please elaborate? Yes, shedding an extra A123 and some lead would definitely lighten things up. And I might take you up on your lightening offer.

thepamster

MAC=Mean Aerodynamic Chord.

http://www.airfieldmodels.com/inform...amic_chord.htm

grosbeak

Gotcha.

What I am actually going to do is remove a little weight from the nose, test fly the plane and repeat... working the CG back a bit at a time until (a) I reach the wingtube or (b) I'm at the point where the flying characteristics are just where I want them. For now I will pursue this option instead of a larger engine. I think I might be able to remove two or three pounds.

speedracerntrixie

My Feedback: (29)

So there are a few things you can do to see where you are CG wise. I always tend to set it at a safe forward location for test flights and then tune. I have never had an airplane come out perfect the first time. First thing to think about is when you test flew, did it require up trim? If the wing, stab and engine thrust are set to zero and it required up trim then you are indeed nose heavy. Other signs are needing more then 1/4 back stick for landing flare, nose dropping as speed bleeds off, pulling towards the canopy when in knife edge. I am more then willing to share set up and trimming knowledge with anyone who is willing to give it a try. The problem is once you fly an airplane that is truly trimmed well you will never accept anything less. For me it takes about 50 flights with an aerobatic model.

grosbeak

I can state with confidence that the CG is at a forward location!

I'm the third owner of this plane. After a winter of working on it I first test flew it last spring and I last flew last August - I didn't fly very much at all last year so I don't remember whether or not up trim was required during the (re-)maiden. I don't know what the wing, stab and engine thrust angles are - stock to the airplane as designed by Slipstream (whatever that is) would be my guess. I can't recall how much back pressure was needed to flare, but I can tell you it likes to land fast and yes, the nose tends to drop as speed bleeds off. I don't know about knife edge - this is an IMAC and I haven't done any 3D with it.

I'm not much help, as you can see! But I do appreciate the assistance. And I completely agree than one the airplane is trimmed properly I'm not going to want to fly one any other way.

cessnaflyer54

My Feedback: (68)

If the plane is landing fast, you are nose heavy. I agree with everybody else here. Reconfiguar your CG, I'll bet you will find that you will be able to move it back at least an inch if not more. Do you have a rudder servo in the tail? If so go pull-pull and move it as far forward as possible. That will eleminate a bunch of weight in the nose.
Just some thoughts.

grosbeak

Yes, agreed - I have set aside the idea of a bigger engine, at least for now. And as it happens this plane already has a pull-pull rudder setup.

grosbeak

When testing the CG, is it a good idea to fly inverted to see if the nose drops?

daveopam

My Feedback: (9)

If the CG is perfect the plane will fly hands off inverted. Wont drop at all. If it is tail heavy it will climb and nose heavy will make it dive. It is however a delicate balance. I have a AW Extra 300 that is DA-60 powered. With a full tank it has a slight dive while hands off inverted. After the tank is 1/2 empty it has a slight climb. Somewhere during the burning of fuel it achieves the perfect CG for a short time :-) I should also say this CG setting is a little far aft for most peoples comfort level. If your plane starts to climb hands off inverted think about landing. The plane will tend to balloon with the slightest of ELEV inputs and if it's like my Extra you will need to push the nose over a little to get it on the ground. That's not a comforting feeling BTW.
You have gotten some great advice above. Glad you decided to tinker with the CG. BTW you can mount lead ballast to the standoffs. This will put it a little further forward than the firewall and require less weight.

David

grosbeak

Good info - thank you.

Zeeb

My Feedback: (41)

As noted, a neutral CG is not for everyone's taste. The usual CG test for an IMAC (precision aerobatics) bird is to pull a 45 degree climb, flip it inverted and when it's stabilized let go of the sticks. I should continue at the same climb angle for several seconds and then the nose should start to drop very gradually. I prefer to set mine up so that when you let go of the sticks, it continues on the same angle or climbs very slightly. This setting will require some down elevator on level inverted maneuvers but it will fly sequences better and be much nicer to land.

If you want it further back, it is a time consuming project to set at neutral and as noted, if the fuel tank isn't on the CG the flight characteristics will change as fuel is burned. This is true of any CG setting where the tank isn't on the CG but it's not nearly as noticeable if it's forward or aft as it is when it's on the CG.

Truckracer

My Feedback: (19)

+1

As stated, a CG so far rearward that the plane flies hands off in level flight when inverted is truly NOT for everyone. In fact many airplanes will not permit a CG this far back. An extreme rearward CG also makes the elevator extremely sensitive! Most of us prefer a CG that allows for a good compromise between stability and maneuverability and allows the pilot to relax a bit.

sensei

I have moved the wing tube and anti rotation plates in several ARFs before, now that is just me but I refuse to add dead weight to an airplane, it makes no good sense.

Bob

grosbeak

I don't completely agree - when trying to get to the specified CG my preference are, in order: (a) move things around in the fuse; (b) add useful weight; (c) add dead weight.

grosbeak

Thanks for the tips, everyone. I went to the field today for a few test flights and a little weight removal.


Flight 1 - unchanged. During inverted 45º upline nose dropped immediately.
Flight 2 - removed the last of the lead weights - 258g. During inverted 45º upline nose dropped more gradually
Flight 3 - removed 1 of the 2 rx batteries - 188g. During inverted 45º upline nose dropped very slowly


Just short of a pound (!) removed for a big improvement. Not only for the upline, but landings were easier too.




Cowl off, before removal of lead weights and lower RX battery on right).

daveopam

My Feedback: (9)

Good deal! I never heard you say what prop you are using. I see a Xoar in the pic, is it a 23x8?


david

daveopam

My Feedback: (9)

GREAT looking bird BTW

speedracerntrixie

My Feedback: (29)

What size RX and ignition batteries are you running?