Hi Guys,
Been following this thread for ages as I build/Finish the assembley of an Impact.
For what it's worth, I chose to use the engine cowl horizontal edge to determine my zero attitude line. If you do this, you will find that the pre-determined marks on the rear of the fus for the stab joiners and anti-rotation pin will result in the tail incidence relation will be zero degree's, then just slide the main wings on to the carbon joiner and set the incidence for them at that junture! I am currently setting them at .25 degree's for the first flights, can anyone reflect on this set-up regarding the up/down lines when flown?

Where are the laser incidence available in the US? What brand name?

[link=http://www.buddengineering.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=P]Budd Engineering LMS[/link]

See also [link]http://www.rcaerobats.net/LMS_Info.htm[/link]

Unfortunately it's sold out, maybe it will come available later.

ini

Greatplanes do one which I've heard is good....

http://www.greatplanes.com/accys/gpmr4020.html

Rgds,
Mark

thanks guys

I personally would not trust using the GP laser incidence meter to set a fixed stab incidence. I strongly suggest getting Bob Noll's tape "Perfect Airframe Alignment". This is Volume 1, No. 1 of the "Absolute-Accuracy" series. There are many factors and measurements in setting the stab and wing tube correctly and this tape covers them extremely well. This operation is probably the MOST critical operation in building a pattern plane.

Bob is one of the top master builders and this tape allows you to learn his secrets. You won't regret it.

You can order the tape by calling 610-746-0106.

Good luck,
KeithB

PS. I'm not associated with Bob Noll, I'm just a very appreciative customer.

A clarification to my last post:

I too use a GP incident meter when I set my wing incidence. My prior comment was in regards to "mounting" (i.e. gluing/permanently affixing) the stab or wing tube. The actual mounting of the wing and stab tubes is best done on a flat surface making precise measurements. The incidence meter comes into play when adjusting the wing adjusters (if you use them) after the stab and wing are set. It's also useful in measuring/adjusting the engine incidence.

I have two GP incidence meters. Personally I'm not very happy with them because the free-swinging laser doesn't seem to consistently come to rest at the same location. If I tap it slightly it will swing back and forth and sometimes it comes back to the same location, other times it doesn't. Maybe mine just doesn't have a very smooth pivot arm, but I can't be confident from measurement to measurement that I will get the same reading.

BTW, the Budd Engineering LMS device is for checking equal elevator deflection, not for incidence.

KeithB

DavidGibbs,

PM'd you!

Rgds,
Mark

Keith, Do you think the GP laser meter is better that the Robart's?
Tom

I have used the GP Laser meter and I thought it was very good. I didnt have the problems KeithB described.

The GP unit is much more accurate and repeatable than the Robart unit.


Peter

I haven't used the Robart.

How are you guys going with CG

I will be using a YS140DZ in my Impact. Do I need to be careful about the amount of weight I put in the tail. At this stage I plan to use Futaba 9650 servos in the tail.

Any more flight reports out there?

Thanks,

Peter

OK thanks, I just ordered that video. Not a bad $20 investment.
thanks Tom

I have also the same problem of Keith
"the free-swinging laser doesn't seem to consistently come to rest at the same location"
Also use the Robart, but for so accuracy need to .25º or .3º angles they are not very good
For +/- .5º they are acceptable, but for more precise angles aren't.

I know some guys have created a more precise incidence meter by taking a digital level accurate to +/- .1 degree and fixing it to the Robart beam. The Robart beam ends are kind of sloppy, dont know how repeatable this might be.

For me I have measured to the surface of a flat table and made the leading and trailing edge of the wing equal to achieve 0 incidence. Same w/ the horizontal stab. If you use adjusters you can do some math and turn the screws to achieve other than a 0 incidence. Of course this presumes a 0 incidence for the stab and wing.

This may not be precise enough for some.

What I would say, having aired my paranoia on what you can trust on alignment, is that the fuz markings/indents on my Impact for stab tube, stab anti rotation pins, wing tube and U/C legs proved to be pretty much exactly in the right place after all my checking and double checking. I am not so sure about wing incidence/anti-rotation -- but I didn't them anyway.

This is a refeshing outcome and well done to C-ARF.

I had one of the early Arresti III's and that was . . . well . . . a disaster on this issue!

Re: Building jig.

David Gibbs, or anybody else.
In post #220 there is a picture of a building jig.
Is this jig available commercially?
Thanks,
Magne

I think Gator RC used to do a jig -- not sure who else.

I took the saw bench to a piece of ply one weekend and a couple of hours later had the jig you see in the Impact shots earlier. Attached photo gives a slightly better view -- it is easy enough to copy if you have the inclination.

One day I will get around to drawing a set of parallel kines along the base!

David

Hi Guys!
Byoung466 is dead on with the use of a flat surface and getting fore and aft stab or wing measurements to match (assuming you want 0 degrees incidence). I used to use the incidence meters and found them inconsistent and in some cases misleading. If you don't have a flat surface almost as long as a 2 meter fuselage, get an aluminum I beam type level (of reasonable quality -- sort through the stock at the store, sighting down the level for straightness) that is 6 ft long. Set the fuselage so the centerline (some might call it the thrustline -- but not to be confused with downthrust for the engine) of the fuselage is parallel to the top of your flat surface (in this case the top of your level). Now you can measure and repeat your measurements. In conjunction with this I have also used a block of wood that has an arrow shaft of the right length pressed into it. A variety of different height holes are drilled to accept a sharpened piece of music wire. Adjust the height of the pointer to the aft center line of a stab, for example, move it to the leading edge and see what needs to be done. I have found this to be more repeatable than using a ruler -- the pointer in the center of the centerline means you are right where you want to be (assuming the centerlines are accurate). Try it -- you'll like it! I have used this system now for several years maybe 10 -- since I got burned with the incidence meters twice in a row. For sure on 1 USA Star, an EMC2, and two Prophecies (one of which got a second set of wings after trying to land through some trees in Chicago...The last model, a Temptation, got it also but I had wing adjusters on it and ended up using them to increase the incidence (from 0) a turn and a half positive -- probably to where the drawings called for... some people learn the hard way. The previous ships were happy at zero.

My Impact showed up yesterday so lets keep the thread alive and keep those pictures and discoveries coming! At first look everything looks great. I have not checked for things mentioned earlier in the thread like wing twist -- we'll see.

Now if I can figure out where the center line of the Impact is...

Hope this helps.

Later, Tom

Tom,

Exactly[:@]

I'm not sure if this is the best way to do it but I have set the fuselage on my workbench and propped up the tail end so that the nose ring of the fuselage (i.e. what you would align the spinner back plate to) is at 90 degrees to the bench. I assumed that would simulate the model in 'level flight' - the fuz also looks quite 'level' like this.

Next, I measured from the workbench to the flat part of the fuselage where the cowl fits. This was 216mm (I have the U/C on it!). I drew a line along the entire length of the fuselage at a height of 216mm from the workbench and assumed this would now be my 0 degrees datum reference for everything else.

As the datum was parallel to the workbench I set up the GP laser level to be 0 degrees when sitting on the bench, transferred it to my stab and it read 1 degrees []

Now this is when I get dumb and lose the plot!! What I don't understand is this. With the stab at 1 degrees I guess I would need to file the anti rotation pin holes until the stab sat at 0 degrees?? BUT, if I alter the height of the fuselage slightly at the tail - maybe only by 1/2", the level sits at 0 degrees - so voila the stab is at 0 degrees with no filing/sanding?! So, how do I know what is right?? Are the stab pin indentations correct and my way of levelling the fuz wrong or is my levelling spot on but the stab pin holes way out???

I don't know if that made any sense or if you see what I'm getting at. The wife has shouted at me for getting so wound up with it [&:]

Rgds,
Mark

To the guys that got thier impact, a fellow flyer pointed out to me that fuse towards the rear of the plane -- it looks the rudder area has a slight 2 or maybe 3 degrees of left. Has anyone else seen this on thier Impact? If you pick up the fuse and put it to your eye level and look at it, it appears that it seems to be a bit off!!! Can you guys please look and report your findings please

Hi Mark,
If you go to page 8 of this thread you will see my posting on how I set my Incidences, also if you follow that method the stab incidence will be zero and the fuz will also look as though it's at the correct flight attitude. Hope this helps.

Andy.

Impact flyers unite -- where is this damn horizontal reference line??

On mine, Andy P's approach would have worked as well as the approach I took (and been quicker!!). The stab tube/anti-rotation pin marks on the fuz were close to the consistent with the datum line I ultimately used.

For reference, the datum line I used runs from the flat bit the engine cowl sits on to 30mm below the centre line of the stab tube hole. On the pre-painted model this is the bottom of the blue stripe (with the caveat that there is about 3 to 5 mm difference in where the paint line it is on both sides of the plane). Assuming all the Impacts are coming out the same mould/moulds, and that you accurately open the stab tube and anti-rotation pin holes, that would be the quickest way to get a sensible result. Alternatively draw the line from cowl mount flat plate to 30mm under stab and use that.

A couple of other thoughts from Mark and others comments:
1) The one thing I didn't trust on mine was the alignment of the front of the fuz (whathever that bit is that the spiinner backplate sits relative to) -- mine has about 2.5 degress down thrust in it (Mark, if you hence used it as a refernce for setting the fuz up, it would be the source of your error). It is not the recommended 0 degrees incidence starting point. I will end up with uneven gaps between spinner backplate and fuz.
2) Right thrust at the front of the fuz was closer, but the holes pre-drilled in the firewall are more consistent with about 5 degrees right thrust -- they were 12+ mm off centre rather than the 6 ish required for 2 degrees.
3) I am not sure on the fin alignment -- I have had a couple of looks and I think it may be out a little, but given light and reflections etc. I am not absolutely sure. I will check later -- along with possible wing twists.
4) I did try to see if I could keep the stab anti-rotation pin in one piece -- making the stab mount more rigid. Ultimately I cut it in two as the retainers for it in the stabs in mine were not quite aligned -- and it made getting everything squared up too hard

David

David,

Build thread on the site has been updated to show progress as requested! - www.composite-arf.co.uk

Rgds,
Mark

Good effort Mark -- keep it coming!!

David