The actual set-up per CARF instructions were to block the chin parallel. Actually the tail post was made perpendicular first (side view), which required a little more shimming to the chin area to get the post vertical. The stab CL would then be set at 150mm above the surface, if I remeber correctly. Don't hold me to the 150 mm refernce, I don't remember what it was.

That set-up required a 33.5mm block under the post to get it right on. I had to get the fin and stab CL's perpendicular to each other first and then refernce the wing from that arrangement. The wing tube marks, as it turned out, wwere off. I used one mark as the refernce mark and adjusted the other side as needed to get the wing placed correctly in the fuse.

I never reference anything off the wingtube. It doesn't take much to build in a misalignment. I always make certain the tail post and stab are located properly then work the wing in

Hope that helps you,

MattK

Mmmmmmmmmmmmm.


[sm=spinnyeyes.gif]

Andy.

OK Andy, you have to elaborate on that just slightly, what does "Mmmmmmmmmmm" mean?

BTW, can you elaborate on my question regarding the difference in the method you took and the one Matt described. Or am I just missing something?

Thanks,
Keith

Hi Keith,

When I set up my incidences I started by setting up the fuselage like this.

The F1 sits at 90% to the trust line, the thrust line is 0%. If you pack the rear of the fuselage up so that the chin cowl line is level (0%) you then have the correct attitude for the fuselage flight angle. On mine when set up this way, the stab spar tube & anti-rotation pin marks ( indents ) where in the correct place to achieve 0% incidence on the stabs. Whether or not that relates to a 33.5mm packer under the fin post being correct, I'm not sure. My advise would be to assume nothing until checked! MTK was right though in as much as the main wing anti-rotation pin indents may not be in the right place, mine certainly were not ( worked out to be -1.5 degrees incidence [:@] ). Although these models all pop out of the same mold, that dosen't mean that they are all exactly the same, small differences make a big deal!
I can confirm though that the method I've chosen worked for me and the model tracked perfectly in all attitudes, including knife edge! It should also be noted that the 2 degrees of side thrust stated in the manual wasn't enough on mine. 3.5 degrees is the sweet spot using YS 140lm 15 x 12 APC & Wildcat 3DLV 30% fuel.
Check www.composite-arf.co.uk, Mark has started a thread on there which shows the method with pictures!!!!!!!!!!!
Hope this helps,

Andy.

Hi Andy,

What are your incidences after all? Are they parallel with the instructions (wing +,25 stab 0)? You said the 2.5 right trust stated on the instructions was not enough. How about the down trust? How much down trust do you have for the perfect tracking?

Thanks

Alp.

Hi Alp,

Yes the incidences are, wing +0.25, stabs 0, right thrust 3.5, down thrust 0.

I do have around 1mm of down trim on the elevators but that is all.

Hope this helps,

Andy.

Thanks for the info Andy. If you noticed before the instructions suggests 2-2.5 down thrust. However this did not seem to be compatible with the wing incidences.. Last but not least what is the location of your cg?

BTW anybody heard about the rudder flutter problem for the impacts. Couple of impacts lost their tails. The reps are sending emails telling what to do to overcome the design problem. It seems that some kind of bracing which binds the fuselage sides from the rear anti rotation pins all the way to the stab tube is necessary..

Alp.

Yes, we have heard about that one. I and several others have been discussing on the various IMPACT threads, what to do to fix the tail problem for the past 3 months. Go back on any of the threads and review the various discussions.

Composite ARF needs to fix this at the factory. It's really a simple fix.

AND for the models already produced, CARF should give a discount to all who have purchased the first runs in addition to replacing the broken ones free of charge to their owners.

One man's opinion. Anyone else out there agree with me?

MattK

But of course... makes sense!

Hi everyone, usually I stay away from contributing to the site, I just read it, but in this instance I would agree Impact owners should be compensated in some way due to the numerous complaints and problems. But being the devil's advocate I would say instead of asking the company to make it right, just do like we always do and talk amongst ourselves at competitions and on the web and the weaker products will become obsolete because the market for them will not exist.

I have two planes from comp-arf one 2.6 extra and one impact (which is under construction now) Also I have a close friend with a 2.3 extra. The reason of my impact purchase (making full payment in advance and waiting for three months to receive the kit) was the quality, parts fit and prefabrication level I saw in the extras. I should admit that they worthed every cent I paid.

Now I have two criticisms about the impact.

1. I think it's way overpriced. If you look at the prefabrication level, parts fit, supplied hardware and size, it should not cost the same as 2.3 extra. It would be the same price as their 2x2 extra which is 550 usd. Perhaps this only marketing and stands on the belief that the competition pattern kits should be priced starting around 1000 usd.

2. When I first heard about the rudder flutter problem in the impacts I tried to find some discussions on the rcu about the issue. To my surprise what I found was tail cracks of revolution pro because of the rudder flutter. What I cannot understand is how comp-arf came up with a second pattern plane having exactly the same weakness in design with its predecessor.

After the necessary reinforcements I am not quite sure that the plane will balance around back of the wing tube with the servos in the stabs. As an rc modeler who is trying to save every once in the kit spending extra money for the lightest engine and accessories possible, this reinforcement issue really makes me sad as it will put quite a weight in the tail area because of the necessary bracings and epoxy.

I surely agree that comp-arf should fix the problem in the factory change the weight specs of the kit accordingly, and somehow compensate the early kit owners. As a comp-arf fan who was trying to decide which comp-arf plane will be next project, this is what I expect from this company.

Alp.

I am using the MK bellcrank with my Impact and with all the bracing that had to be done, my battery pack is a 6 volt pack and balances right behind the wing tube, with the battery behind the firewall. I was a little bit pissed because I wanted to use a lighter batteyr pack but I need all the weight of the 6 volt pack just to balance it. I am not much for *****in but if my rudder or elevator flutters after all the stuff I have done to it, I am not going to be very happy!!

Does anyone know how to secure the stab servo leads to the side of the fuse as is pictured in the Impact instruction manual? They don't say anything about it and I can't tell how they are secured.

Thanks,
KeithB

Hi Keith,

This is how I have done it in my ZN Synergy, should work fine in the Impact as well. The black paper tube is from Gator RC. I glued it in with a small bead of Polyurethane glue, which foams up when curing. Weighs very little.

[link=http://www.gatorrc.com/gator/fl%20servo%20tube.htm]http://www.gatorrc.com/gator/fl%20servo%20tube.htm[/link]

I used packaging tape to secure the servo wires to the fuse side. This lasts awhile but might have to be redone periodically.

Hello,
I'm building an Impact for a friend. It's going to be an electric conversion using a Hacker C50. I've built about 11 models over the last 3 years but this is my first pattern and composite model.

I've got the instructions downloaded from the C-ARF website and have been following them pretty much accept for the anti-rotation pins for the wing. I'm using the 12mm short tubes as the pins and not using the long 10mm diameter tube illustrated. Jason Shulman does this with his Impact. The reason I did that is my hardware kit didn't have the correct parts in it. I was missing the 12mm CF stab spar tube and the stab spar tube wasn't a tube but a solid CF rod and it was about .7 ounce. The wing anti-rotation 10mm tube was another 10mm solid rod weighing about .7oz. When C-ARF sent me the new parts, it took over a month after I was notified they were shipping to reach me, the wing anti-rotation pin tube was not included and I didn't want to wait another month for the part.

I've installed the cowl, the landing gear formers and struts, the tail stab former reinforcement and mounted and epoxied the wing tube an stab tubes

I'm documenting my build on EZone at

http://www.rcgroups.com/forums/showthread.php?t=305894

I'm confused where the datum line is. The instructions state 37mm down from the center of the stab tube yet the build thread on the C-ARF UK site says its 30mm.

OK, time for a stupid question. How are you guys drawing a straight line on the masking tape from the cowl joint all the way back to the tail? I've only got a 10 foot metal tape and a 3 foot metal yardstick. I was thinking of getting out my chalk line and seeing if I could lay a temporary line and then make some permanent marks.

Thanks for any help.

Kelvin

Hi Kelvin,
I'm working on my Impact and going through all the same problems. I was missing the same tubes and I'm waiting for a new package. Hopefully it will be complete.
I don't think you really need a datum line and it really doesn't matter how high or how low it is. The main thing is that it is parallel to the stab. My plan is to follow their instructions and level up the stab and put the wing at plus .25 degrees. From what I've heard the down thrust is proper if you line up the spinner back plate with the front of the fuselage.
I'm a little concerned about using the top of the vertical stab to align the wings. It sure looks like the top of the vertical is warped a little. I think I will try to measure to the bottom of the vertical.
I've got the added bulkhead tacked in the tail and am trying to figure out how to get glue on the front side of it. A long tube I guess. I'm also planning on a crutch from that bulkhead forward to the trailing edge of the wing.
Keep up the good work. If I had read your thread earlier I would have saved some time putting in the landing gear support. I bet I had it in and out 25 times before I got it to fit.
Regards, Jim O

re the missing 12mm tubes, if you're going to put in gator or similar wing adjusters, then the ones that go in the wings become surplus. You can then sand and join them to use as the stab spar tube in the fuse. Re the fin, I split it along the seam a the top and gently moved and reglued it. Also ditched the factory tail post (heavy) and stripped off the front of the rudder and replaced it with balsa so I could use "normal" hinges. With the MK tail wheel, the rearmost hole is great for doing trianulation measurements for the wings with one of Sam Turner's KISS wing alingment devices. Had to move the right side 30mm hole back about 2mm for correct measurement.

Just another set of data points on the Impact.

Kelvin, one way to get your datum line is to use a lazer leveling device that lights a horizontal beam. Shim your fuse accordingly and when happy with the alignment, mark the red line with a semi-perm marker.

Getting the horizontal ref line on the money will determine to a large extent whether your model needs any pitch mix in knife edge flight so its a good idea to get the line as close as you can.

I didn't do it that way tho since it is a little cumbersome, even with a lazer level. I have outlined what I did with the one I have set up in an earlier page of this thread, so I won't write that again.

MattK

Thanks everyone on the advice. I'm using the Robart's incidence meter. I have their standard rod and extended rod. I notice when I try it on the left stab that I must have the anti-rotation pin hole a little too big and there is movement in the needle that is why I think I need to know the datum line.

Why is a crutch needed from the tail reinforcement former to the TE of the wing?

I wasn't planning on putting in wing adjusters. I've seen them on Central Hobbies. Is there a link to the Gator devices? I can still mod the wing to accept these I suppose. I can set the incidence any time during the build. I may hold up on doing it until last. I've read some use these adjusters and others don't. I doubt the owner will be flying this in any competitions

I just read the comments of the rudder. I thought it looked a little off, now its confirmed. So I have to split the tail at the top and rejoin? Do I use CA to tack it then some epoxy underneath?

Thanks

Kelvin

I haven't looked at the latest instruction manual to see what the current modifications are -- it sounds like a crutch from tail to TE of wing.

From the analysis of failures it is clear that C-ARF are not fans of anyone leaving out the cross fuselage brace/wing anti-rotation pin. There is certainly suspicion being thrown on models where that cross brace has been left out and wing adjusters put in instead -- this is regarded as a departure from recommended practice and not a good thing to do!!

I cannot tell from Kelvin's post above whether the mods effectively mean the cross brace has been left out -- but sounds like it may.

David

Yes, I left out the anti-rotation tube because they sent me the wrong part. It was a solid rod and weighed .7 ounce. Jason Shulman uses the short 12mm tubes as anti-rotation pins in his Impact. I was going to build it stock but I wasn't going to wait another month or more to get the anti-rotation tube from C-ARF. When they ship parts from Thailand they must ship them on the slowest boats from China. When I waited for the replacement hardware they sent me an email on December 28 and I didn't receive the parts until February 6. Not the fastest customer service.

I checked the stab fin on my Impact. I taped on the rudder and set it straight and eyeballed it and set a square along it and it appears to be staight.

Thanks.

Kelvin

Hi David,

If we put the receiver/switch/battery tray in such that it replaces the brace, it would solve that "problem". I'd much prefer to have the trimmability of adjusters than not, but that's just my preference.

Yep -- Thats close to what I did. Adjusters, but with the servo/receiver tray acting as the brace -- and I used the DEPs system so had both elevator and rudder servos on the tray. And I will do it again on the second one I am building!

On the first one I just put in adjusters at the back of the wing. On the second I will put on front and rear adjusters as the front of the wing was a little freer that I would have liked.

David

David,

When you put in the tray to replace the cross brace did you raise it up in the fuz to come close to the orginal cross brace position or did you leave it down on the balsa rails already fixed in the fuz?

I am powering my Impact with a Hacker setup and although I am fitting the rear bulkheads I am not keen to install the horizontal crutch as it does restrict access to the rudder pull pull setup. Does anyone have an opinion if the reduction in vibration etc of the electric setup reduces the likelyhood of a failure without the crutch?

Also can anyone running the Hacker setup give details of their air cooling outlets? The manual gives a suggested outlet size on the fuz bottom but suggests it could be bigger for the Hacker setup.

Thanks in advance.

Malcolm