Composite-ARF Impact: What I have found -Long message

Mon Sep 13 12:46:24 AKDT 2004

I am posting this to help any one that might be getting one of these
planes.  I copied the info from my posts on RCU.

These are the few things that I have found with the kit. 

Wing: 
The wing tube is not perfectly round like say a PBG tube. With this in mind
it looks like the phenolic sockets in the wings and the one that goes in
fuse were made by wrapping glass around the wing tube. The reason I say
this is that the wing tube fits better in one direction then the other. I
also had to do a bit of sanding in the phenolic tubes to get the wing tube
to slide in. I also found that the phenolic tube that goes into the fuse
was slightly loose on the wing tube. You can use tape on the tube or put a
bit of epoxy/micro balloons in the phenolic tube and sand for perfect fit. 

Stab halves: 
They use a carbon tube for the tail. It was a tight fit into the tail
halves and needed to be sanded to fit. They use a piece of carbon rod to
set the incidence and act as anti-rotation pins. The problem I see is that
the directions tell you to set the wing at 0 and the tail at negative .2 to
.3 degrees. If you do it this way, once you have the plane finished with
the tail post glued in it would take some serious work to change the
incidence on the tail. So you have 2 choices. Fist is set the tail at 0
degrees and set the wing to positive .2 to .3 degrees. (Same as setting the
tail at negative .2 to .3 degrees). It will be much easier to change the
incidence on the wing after the plane is built if you find out you need to.
The second choice would be to adapt a set of tail adjuster to the plane to
allow incidence changes to the stab. I opted for option 1. I didn’t follow
instructions on the mounting of the elevator servos. I decided to mount the
servos inside the stab half instead of the stock way were you need to cut a
big hole for the servo case to fit into the fuse. I took this idea from a
German website that has build pictures. You will find it really useful.
http://www.weinig-web.de/impact.htm 

Rudder:
I made the rudder removable which was pretty easy since they use Robart
hinges. This will allow me to ship the plane. I can get some picture and do
an in depth here if people want me to. 

Landing gear: 
I verified that the mold marks in the fuse for the gear exits were equally
spaced. Cut these out before sanding and fitting the gear formers. My
formers needed a bit of sanding to line up properly. 

Firewall: 
The firewall is not a perfect fit. I had pretty good sized gaps between the
fuse and firewall at the bottom and where the fuse bulges on the sides. I
am putting in a Hyde ARIAS mount so I needed a bit beefier firewall then
what was included so I cut a new one out of ¼ end grain balsa carbon. If
you are going to use a soft mount with a separate nose ring the included
firewall will be strong enough. Basically you will fit the stock fire wall
and use some ply to fill in the gaps. 

Control Horns: 
The stock control horns will work if you are comfortable with using
standard metal clevises. I figured it will eventually get sloppy and they
do not recommend using ball links on the stock horns because of twisting.
So I ordered some .074 Uni carbon from Aerospace Composites. I cut out new
horns and they should be more then stiff enough to handle ball links. 

The engine compartment: 
The engine area is marked for suggested cut out. I cut the area out as
marked and found that with my motor/mount combo the left side of the
firewall came into the opening. I am running a Mintor 170 with a Hyde ARIAS
mount. My suggestion is that you leave a bit more material in the left
corner and trim it out after the firewall is glued in. 

Header: 
I also found that I need 60mm rise header for my Mintor 170. So keep that
in mind when you are ordering your parts.

Only other thing I’m doing different is that I’m using carbon pins and a
4-40 bolts to hold the canopy and chin cowl instead of their method. If you
have any more questions I will be happy to try and answer them. Go to the
German website because for me a picture is worth a thousand words. If you
want some pictures of mine I would be happy to do that as well.

As far as weight goes I weighed it this morning ready to fly minus wheel
pants and its coming in at 9.8. I usually don't put wheel pants on because
I am always flying on a grass field. So even with the wheel pants I would
be sub 10. I could have reached 9.5 by going with a different mount. I am
running the Hyde ARIAS mount that weighs about 6.5 oz. If I would have went
with the AR mount and nose ring I could have lost about 2.5 oz plus the
weight of the beefed up fire wall for the ARIAS. I could have also saved 2
oz by using JR 9411 in the wings and JR Mini digitals in the tail and a
micro digital on the throttle. I am by no means an expert and this is only
my third pattern plane, and first composite. The first 2 were bought from
other flyers almost ready to fly. All in all it was a pretty easy build. I
am glad that I had the expertise of a very kind and generous FAI flyer. He
helped me set the wing and stab incidences and was there to answer all my
stupid questions. Below is the equipment that I have used. 

Composite-ARF Impact (Impact Paint Scheme) 
Mintor 170 w/ 60 degree rise Header/ Mintor New Aluminum pipe 
2@ DB Pipe mounts 
Composite-ARF 3.5in Carbon Spinner w/ APC 17x13 
Dubro 20 oz fuel tank 
3@ Hitec 5975 HB Corless digital/Composite gears (Ailerons,Ruddder) 
3@ Hitec 5245 Mini Digitals (Elevators, Throttle 
2200 ma Li-ion battery with Jacco regulator/switch 
JR Ball links w/ titanium pushrods on all control surfaces. (I made new
control horns out of .074 Uni Carbon to handle the load of the ball links) 
MK tail wheel assembly 
DB Light wheels.

Well, the Impact has been flown. I got about a dozen flights on it this
weekend. All that can be said is wow. Things I have found with my setup. 

Incidences: Tail/Motor at 0 degrees Wing at .25 degrees positive.
Recommended (Tail at .2 to .3 degrees negative – Wing/motor at 0) I opted
to do the incidence change on the wing so that if it needed to be changed
it would be easily accessible. If you do it the manufacturer’s way it makes
it pretty much impossible to change without a butcher job. 

CG: Set at the front on the recommended CG range (1/2 to ¾ behind wing
tube) right at ½ behind the tube. The plane flew tail heavy and I needed no
down when inverted. So I shifted some things around and got the CG just
behind the wing tube. The plane flies much more solid there and requires a
small push when inverted. 

Mixes: Right now I have no mixes and I’m not sure if I will program any.
There is a very slight tuck to the gear in knife edge. And I mean very
slight. Up lines and down lines are very straight. 

There was a pretty good crosswind yesterday and the plane seemed to handle
it very well. I just applied the proper corrective rudder for a straight
line and the plane just grooved. 

My throws are as follows. 

Aileron: High Rate 1in up 1.25 down – Low is 65% 
Rudder: High 2.75 in - Low is 50% (Rudder is very/very effective) 
Elevator High Rate 5/8 Up ¾ down – Low is 60%

If anyone has any question about the plane or setup I would be happy to
anwser them if I can.

Michael Laggis
NSRCA 3618

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