MTK

Andy, let me suggest that you build a new, lighter rudder. The stock item weighs in at a hefty 80-90 grams so the balance weight amount you are quoting isn't surprising. The lighter rudder will require less balance weight and if you are careful in the build, you could come out with a balanced rudder weight to equal the stock part.

What I have generally done with larger third scale models is to balance about 2/3rds the weight of the surfaces, to save weight and reduce servo workload. Larger models require an addition of around 10-12 ozs to partially balance all surfaces this way, but the added weight is well spent.

The concept of partial balancing may be applied to pattern size, since weight is always a concern for us.

MattK

PeterP

Hi Matt,

I weighed my stock rudder over the weekend and it weighed 52grams. Basically as it came out of the box. At 80-90grams are you including the horn, hinges and rudder post?



Regards,

Peter

MTK

Peter the rudder I'm referring to was on friend Brian's Impact, the one that broke a tail. I removed the stock unit from the broken fuse with composite horn, and half the hinges attached (the other half was left in the tail post). There was no tail or rudder post attached to the rudder. It weighed 84 grams if I remember correctly.

Your rudder at 52 grams is reasonable, almost 2 ounces.

My built up rudders of this size usually weigh in at 30-32 grams and finish out at around 40-44 grams in paint, including horn but excluding hinges (I use Kevlar hinges normally which weigh nextto nothing)

Matt

dapan

My Feedback: (2)

hello all!
i am writting from Greece and just start building my new pattern plane Impact.
i have one question. I was build some planes and patterns(not 2x2) but i never use gator Plug in Wing Adjusters so i want your opinion iff i must used this. and please inform me if i must order only the gators Plug in Wing Adjusters or i must add and the wing tubes set.
thanks for your time.
Padelis.

pbrantuas

My Feedback: (3)

Hi Padelis,

I have the gator wing adjusters on my impact. They come in a set of 4. Two for the right wing and two for the left wing.
I like have them so I can play with the wing incedence, but once its set you will probably never touch them again.

No need to buy anything else.


Pedro.

ERichard

Andy,
Ditch the stock rudder! It is way too heavy and the hinging is awkward. Building up a balsa one is far easier than you think...I put one together in about an hour and it came in at about half the weight....most of that mass is close to the hinge line. As has been discussed earlier, the stock (80+ gram) rudder has much of the mass aft of the hinge line...a bad situation and a receipe for flutter.

-Erik

ERichard

Peter,
Check your scale again. If you have a stock rudder at 52 grams then you are the exception. I have weighed three Impact rudders right out of the box (i.e no horn, no hinges) just unwrap it and put it on the scale...the minimum mass was 78 and the max was 83 grams. A friend of mine had one that was 92 gr!!![:@] If you have one at 52 then that is telling me that there are some pretty inconsistent layups occurring at C-ARF.
-Erik

Andy P.

Hi Guy's

Thanks for the replies, nice job on the built up rudder Erik you've made me think again!
Did you cut the core from foam or is it built up from balsa?

Regards

Andy.

Rune

Hi
i made a buildt up rudder for my temptation!
weight 26 gr.
it should be almost the same size as the one for the impact i think!

MTK

Rune, you are correct, the rudders are very similar in area. The Impact rudder is a little taller but narrower. The rudder design you show is the better choice over a fully sheeted, composite type, because the CG of the rudder is closer to the hinge line. This is important because inertial concerns are minimized this way, so the rudder will be far less prone to flutter. And should you decide to statically balance the rudder, it will take less weight to balance it. BTW- a statically balanced rudder will eliminate flutter, not just minimize the possibility

MattK

ERichard

Andy,
It is built-up (see pic below). As Matt and others have said/shown you should be able to get them to come out around 30-40 grams if you are careful. I wasn't too worried about getting it super-light so mine came in a bit more...I added a bit more material for the hinge post and the counter balance can be made a bit lighter. I lost a few grams after shaping the counter balance and beveling the hinge line, but will put that back plus a bit after I finish the rudder ( Haven't decided yet whether to MonoKote or glass and paint...leaning toward just MonoKoting it). Another thing to do is put the horn above the horiz stab...straighter shot for the pull-pull.
Cutting one from foam should work just as well....it is a fairly straight taper.
-Erik

Rune

hi!
i used Ora Cover on mine and it was pretty stiff i think .. not as stiff as if it was fully covred but!
Rune

Andy P.

Matt, Erik, Rune,

Thanks for your input guy's, I have decided to build a new rudder & will post some pic's soon!
Can't wait to get it back in the air !!!!!!!!!

Regards,

Andy.

PeterP

Hi Guys,

I thought I would show you some photos of what I am doing during the assembly of my IMPACT.


Firstly,

I did recheck my rudder. I was out slightly but my rudder weighs 60grams. I checked my scales by weighing a Futaba S151 and it weighed 49grams as per Futaba specs. So I am confident in my scales. It is nice to know I have a light one. Here is the photo to prove it.


I have also decided to use MK BB fittings througout this model. I was told that the supplied horns are too flexible - agree, so I decided to try and laminate the existing ones instead of trying to make new ones. The results are fantastic- extremely stiff - bling[:-] and only added a few grams. and a total of 1 hours work.

I have made my internal brace out of balsa / depron / carbon -total weight is 19grams . The carbon / light ply laminate is there so I can mount my rudder servo to it. I am relocating the rudder horn above the tailplane. I dont like the suggested position because no one would see my nice carbon horn - joking I just felt it would be a pain in the ass when it comes to clean up time.

PeterP

I also decided to invest a few hours in assembling a jig to assist me in all the critical stages of assembly of a F3A model. Believe me guys it is worth it spending some time here. A straight model requires a lot less effort to fly.

The jig consists of MDF 16mm for the surface and 2.5in x 1in for the rails. Everything was screwed together with tek screws. I also used a 1metre length of 1/4in threaded rod as well as a stock of 1/4 in nuts and washers.


The jig holds everything in place and postions the fuse level so that the wings and tailplane can be postioned precisely. The use of threaded rods gives you infinite adjustment in getting the fuse level. I am wrapped with the results.

The idea is to get this jig perfectly flat. I then take all measurements from here. You will see that I used threaded cup head bolts at the feet. I tapped 1/4in holes in the rails so now I can screw or unscrew the bolts to raise or lower the jig. I used 6 bolts in this case.

When everything is level I use this device for scribing lines along the fuse. I simply put an exacto knife in it to scribe super fine lines. When it comes to designing paint schemes I replace the knife with a soft pencil to drwa perfectly straight and symentrical lines on the fuse. I simply run this device also the smooth surface of my jig.


Hope this helps some of you.

PeterP

Here are more photos

PeterP

I have decided not to go the wing adjuster route. Not worth the extra effort if your confident that you can position the wings exactly were you want during construction. I have added an adjustable tailplane to fine tune elevator trim. Servos in tail after a lot of thought.

Andy P.

Great work Peter!

Have you decided yet how to finish the colour scheme?
One of your photo's shows the stern post & I noticed that the fin base former isn't installed, you might be aware but thought I'd mention it!
Your building jig looks brilliant [sm=cool.gif] sure will make life a lot easier for modellers now!!

Good luck with rest of the build and keep us updated .

Regards

Andy.

MTK

Peter,

MARVELOUS WORK!!!!

I just love the simple yet supremely effective fixtures. The super simple "height gauge" which uses an exacto knife as scriber, is genius. This device is a "must-get" for everyone wanting precision (been using mine for 25 years and I find more uses for it than you can shake a stick at). I really hope everyone studies your photos and gleans as much as is possible from them. There are many more complicated ways to accomplish the job, but none more effective.

The carbon cloth laminate on the horns is also a great idea, one I hadn't considered!

K.I.S.S. mate!!!! (A little play on words, but quite appropriate methinks!)

Mattk

PeterP

Hi Andy,

The stern former hasnt been installed along with the depron brace. I only fitted the brace temporarily for the photo. I am currently setting all my incidences which are now perfect. It has taken some work as I found that the markings on the fuse are a fair way off.

Even the advice they gave about the 37mm below the centre of the tailplane tube does not result in a line that is directly in line with the engine cowl flange. The jig allows you to check everything perfectly. I would not reply on the seam line at the front of the fuse as being centre. I found it the be of to one side by 3.5mm. By having a centre line directly down the centre of the jig, you can position the fuse exactly by marking certain points along the jig base. Run a set square along the fuse and measure the distance to the centre line. Do this to both sides and make the distance equal.

I am happy with the alignment now but it would not have been possible without the jig. Hopefully I can glue everything up tomorrow.

I have also replaced the supplied wing tube with a PBG unit Frazer Briggs sent me. This new tube is 34grams lighter and much stronger. He also supplied a outer tube which will replace the part which is glued into the fuse. They are a perfect slide fit which will eliminate most of the slop.

I will be painting the IMPACT exactly like my Alliance except replacing silver with gold.

Here is a photo of the alliance.

PeterP

Hi Matt,

I am back home after returning from a business trip and powering to get this model finished for our state champs. I know it will be a much better model than what I am flying as long as the tail doesnt flutter of. I think the brace will lick the problem [sm=lol.gif].

The height gauge was something I stumbled on in my workshop some time ago. The base assembly has a magnetic base which can be purchased from machine tool shops. I simply removed the extendable arm which was replaced with my exacto knife. It works even better than it looks.


Thanks for the compliments.


Cheers,
Peter

Eric.Henderson

I went conventional on the elevator to get a good CG to vary with the Li-ion ballast. At least as conventional as I could :-)

Eric.Henderson

How the ends look....

OhD

Peter, thanks for the post. I was getting ready to bond in the sleeves for the wing and stab tubes but after reading your post went out and started measuring again. The real trick is to figure out where the center line of the fuse is. I finally decided it should be half way between the wings and through the center of the vertical. When I did this I found the seam at the spinner was way off center as you said.
I would be happy to pay more money if the tubes were factory installed in a jig which seems like it would be easy once you had the jig. Then again maybe they don't think they can provide the accuracy we want. All I know is I've spent a lot of man hours measuring and I still don't have the tubes in.

Regards, Jim O

MTK

Peter, mine is a standard height gauge with a carbide scriber. It allows true digital measurement (.001" accuracy) as well as analog, comparative measurement. Available from all measurement tool manufacturers (Mitutoyo, Starrett, Sharpe, and several others).

I have found that the scratches it makes are too fine for my bad eyes to see without some aid, so I pencil the marks in and leave them on the models for reference. Clearcoat right over them.

This is without doubt one of the two most indespensible tools in my shop during set-up. The other is the large triangle I have made out of plexiglas, which aligns stab to rudder post center line, and also fixes the parts while the epoxy cures.

Jim O, consider using the height gauge to scribe your zero lines for stab and wing, on both fuse sides. These will be as parallel as your reference building board is flat. Of course, on the Impact you are at the mercy of the factory installed tube sockets but for your own custom work, it serves extremely well.

regards

MattK