n00bs Gonna Build a Carden

[why_fly_high]

	Quote: Originally Posted by tommy321
	I'm no expert, but everything I've been taught would score that snap as a zero. If you unload the snap before it's finished (i.e. let go of the elevator), the judge can deduct 1 point for every 10 degrees of roll that you unload. Not to hijack the thread or anything? Tom

OK to completely hijack this thread, that is wrong. It is acceptable to unload a snap and is pretty much required for most snaps, particularly vertical. What can nail you is getting out of the rudder and "rolling out" the last part of a snap. Some fullscale planes will push down after starting the positive snap to really unload it.

Dan

[gareth.ky]

I find that when I don't "unload" the snap, particularly on downlines, I end up exiting the snap with the nose high. I can do a pretty decent snap in the sim and once I get it all dialed in I'm sure I can transfer that to the real thing. I was laying a few down on Saturday and they didn't look that bad. I was seriously over rotating though, the roll rate is just a hair too fast.

[mflander]

Too much rudder is a common cause of over rotation also.

[whaturi]

Yeah, the rules do not call for the pitch deviation (elevator) and autorotation (rudder and aileron) to be TOGETHER. Since that is not required, all top IMAC pilots have seperated the two, resulting in better scores. Of course "aileroning" the end of the snap is a .5 per 5 degree deduction.

Glad you already have a handle on it Gareth. I should have known you would after all the planning and dedication you have shown on this build. Speaking of the build, back to the plane! Keep us informed of your setup and subsequent flights. Also, a video wouldn't be objected to here.. hint hint.

[gareth.ky]

Video... we'll see if I can get some video this week.

I spoke with DA on the phone and explained the situation. Here is what I got form them:

• The factory default needle setting for both the high and low end is 1 1/2 turns out
• DA tests the motors on the KS-95 in the shop
• The canister can't be whats causing the starting issue
• They haven't seen an 85 start with the low end needle set any leaner than 1 1/4 turns out
• It's not "flooded" unless gas is pouring out of the cylinder.

So I set the needles back to the factory setting and headed to the back yard. I got the motor to start with no problem maybe a dozen times. I had it in my head that I was leaning out the high end and richening the low end between runs but in fact I had the needles confused! I was making the low end leaner and the high richer. Somehow this was improving things.

So it was consistently hot starting at 1 1/8 turns out on the low end and the high end stayed at about 1 3/4. I want to try and cold start it with these settings but I ran out of daylight. The acid test is, does it start cold. 1 1/2 is too rich on the low end, it bangs hard at idle and it smooths out as it goes leaner. It does start easily like that though.

It was bogging down when I tried to transition to full throttle and as I adjusted it went away. It wants to die when the throttle is rapidly closed. I can get a good sounding idle going and then throttle up (transition sounds fine) and down and it will four cycle and die. I thought that meant the low end was too rich???

I changed two things that could explain the good starts:

• I replaced the throttle pushrod. Carelessness and metal fatigue killed the first one. V 2.0 has no exposed threaded rod. This could have caused inconsistent throttle settings for starting.
• The 4 screws on the bottom plate of the carb went ever so slightly tighter. The puddle of fuel that usually collects on the spacer, that I thought was normal, isn't there so I think I found a leak.

At least a few people on these forums report that low = 1 and high = 1 1/2 is the setting they ended up with. Its pretty clear that the motor will start like that, at least when its warm. Judging by my results tonight I'm headed in that direction too.

[gareth.ky]

OK, took it by Mike's Models and had him listen to it. At first it wouldn't start so we richened the low end to 1 1/4. Started with no problems then. He went in on the high end a bit till it stopped "burping" at wide open. Time to go fly!

[gareth.ky]

The motor is starting like a Swiss watch again. I'm getting some of that world famous DA reliability. It sounds good on the ground but it seems to be too rich in the air. When its inverted it sounds fine. I'm tweaking the high end leaner with each flight.

It was a really good day to go flying. I had to set up a point mix with 5% at the first point and 8% at the end point to eliminate the pitch coupling. Now it will do a nice flat rudder turn with nearly no corrections. In Knife edge it wants to pitch to canopy a bit. The C.G. probably need to go forward a bit more to really make it neutral.

The Yaw -> Roll coupling wasn't as tricky to mix out. I have a 13% linear mix that seems to have eliminated it.

I took about 15% rudder throw out and the snaps are stopping much better now. There is still enough rudder authority for stall turns. Thanks for the suggestion mflander.

With that stuff mixed out I give it an 8.5/10 right now. It's smooth, light, graceful and slow on the down-lines. I have more time to think that I know what to do with. Switch the canister & add wheel pants to get the CG more forward it will probably be a 9.5.

[mflander]

Gareth: On my DA 85, I had the needle set at 1 turn out, and it started fine on every occasion. I'm glad your getting your worked out! It really is a strong motor when it is running right.

[gareth.ky]

Yea, lots of people report the same thing. I don't know why mine wont start that lean.

Maybe that's a break in thing. At 1 1/4 it pops in 1 or 2 flips on choke and then starts in 3. Hot starts are on the first flip. I turn the prop through 3 cycles first to prime it. The idle sounds pretty good once its warmed up. Transition is clean on the ground. It just starts to burble in the air.

The high end is set at about 1 1/8 which is leaner than most report using. The low end affects the high end so my richer low end means my high end can go leaner.

[whaturi]

Gareth, quick question on setting the wing and stab tubes to level and square.

How do you set this if the holes are already drilled in the truss sides long ago? Are they drilled large allowing shimming and adjusting? Are you not so much setting them but more just checking?

Thanks

[gareth.ky]

The motor box sides and the lite ply pieces that mount to the truss sides are drilled exactly the right size for the tube. All those parts are CNC cut from Carden. All you have to do is make sure they end up in exactly the right place.

If you build the motor box square then those holes will line up correctly. For the truss sides you want to make sure the socket support is square, rotated the right way and in the position shown on the plans. Use a square and measure the distance from the end of the truss carefully.

When I assembled everything the socket just slid in. Just measure everything 10 times 4 different ways.

I never checked that the wings were level. There isn't much you could do about it. You would need an accurate jig to make that measurement. Measuring and squaring the parts earlier in the build is much easier than trying to adjust it later on.

[edgewise]

Gareth,great writeup on the Carden build, I am going to be build one this winter and all the information you gave will definately help. Thanks