How did you guys mount your rudder, I am not happy with the way they have done it? I don't like them hinges. Is there anyway to use standard ca hinges or radio south pro hinges?

Also what did you guys do with the wheel axels I don't like their setup?

1 more thing anyone of you guy have problems with denting? I know they said composite is soft I didn't expect it to damage this easely, Is there any was to get these dents out. Maybe water and a hairdryer, I heard this workd with balsa. Would it work.



Any help would be appreciated,

Thanks Guys

I saw one where the guy added a balsa face to the rudder and added a solid tail post and used CA hinges. MTK, mentioned building a new rudder at a much lighter weight also.

If you are painting it you can fill the dents, otherwise they are there for good I imagine.

There is a neat/convenient way for mounting wheel pants describedd here:
http://www.rcaerobats.net/Wayne'sWheelpants.htm

CArfs method works, used it on my Rev Pro. Im trying the above on my Impact.

I share the concern about the hinges -- it is very easy to nudge the bottom one slightly loose (sideways) if there is any binding at all, and given it takes most of the force of the rudder horn, once it becomes loose there is room for movement. IMHO it needs to be under continuos watch. I also have a concern over the 1/2" or so of exposed hinge shaft -- I know it is tough and there is probably ne reason (and I am not having a go at anyone) but it still worries me. While there is much discussion on the damage flutter can cause on these fuz's, and how to minimise impact of it, the engineer in me wants to remove any possible weak points or possible causes. I am not sure, but I think the Impact may be one of the few/only C-ARF planes with the rudder done this way.

I am just starting builidng a second one (cos I really like how they fly), and am going to replace the provided rudder with a foam/balsa sheeted one, put in a new tail post extending past the back of fuz, bevel the edges of both, and hinge it the proven way (I tend to use Hayes hinges) where there is as little as possible scope for movement. I guess the counterbalance will need to be carved from balsa -- and given it is the Impact scheme I may need to do some paint matching and air brushing! Other than the painting it should be very straightforward.

I may also (once I am set up to do it the way above) have a go at trimming the front of the provided rudder (the round, glass section at the hinge line) and replacing it with a balsa leading edge as suggested above -- it is good idea, but I would like to compare relative weights.

On the u/c and wheel pants I also made some mods. I fly off grass usually and found those big tough bits when the mowing wasn't perfect would get stuck between the pants and the leg, and there really isn't much strength in the very end of the leg -- and one very big tough bit broke the axle out the end of the leg (fortunatley right at the end of the roll-out on landing)! So I shortened the leg 10mm, put a fillet on the end so it snugged right up to pants without any gap to catch things in, and haven't had any issues since. I am using Dave Brown lite wheels on the NMP axles as they are so simple to mount -- but I replace the provided 4-40 screw provided with a standard 4-40 hex headed bolt as I kept stripping the heads on teh provided ones.

David

FWIW I do have a Rev Pro which uses the same hinging on the rudder as the Impact and it still works fine.

No issue here -- there are many Rev Pro's and Impacts with thousands of flights on them and they are all fine. If they didn't have confidence in it I am sure C-ARF wouldn't supply it.

My understanding of the (relatively) few failures there have been (RP's and Impacts) is that sloppiness in the bottom hinge may have played a part -- hence the emphasis in the new instructions on that hinge and the formers in the back to prevent major damage/inhibit flutter if whatever causes it happens. I do note that is a building issue rather than a design issue!

The rudder set up (and the fact the bottom is the fatest part) does mean that any binding at all (whether when setting up throws, or even at the time of fitting and checking movement) places pressure on that hinge and could work it loose. The 1/2" exposed/unconstrained part of the hinge shaft on the fin side gives a decent sized lever arm if there is binding -- and can loosen the fin side joint unless it is really solidly glued.

Perhaps my occassional lapses into enthusiastic flying without due care and attention on maintenance between outings make me more nervous . . . . .

Hi David,

Is your model still flying with a little down elevator?


I am about to set the incidences on my model so I would be interested to see if anyone has refined the settings.


Regards,

Peter

Hi Guys,
I too didn't like the rudder for the Impact. My stock rudder straight out of the box was 82 grams! (and that is without all the hinges and post). I decided to experiment with building an all balsa one and just bevel the hinge line and use CA hinges, then seal the gap. It is still a work in progress but here are some of pictures of what I've got so far.
So far I have saved about an ounce (the all balsa rudder is 54 grams...before shaping and beveling). Based on several other Impacts I've seen in the area, I decided to move the rudder pull-pull horn above the stab, a position that allows for straighter and more convenient rudder servo installation.
Anybody else have any weights for their redone rudders?

-Erik

Nice work Erik! I will try to do the foam cut for mine over the next week and see where I come out on weight.

I will also likely change the location of the rudder horn as you have done -- and I know a couple of others plan to do the same.

David

Hey Brian did you use ball links for your elevator connection? I saw that Jason use them in his, and I was wondering what people are planning on using. I nkow that Comp ARF said not to use the ball links, however it seems like Jason has used them without issue! Everyone chime in and let me know your thoughts?

Im going to use clevis's. You can twist the horn a little with your fingers, thats probably what the concern is by CompArf, the horn will be more stable with the control force in the middle.

I am using ball links but I am not using the phenolic control horns. I picked up some uni-directional carbon fiber from Aerospace Composites and cut out all new horns. They are extremely stiff and I have had no problems. The other thing you could do is set up the Impacts controls like the scale aerobatics guys do. They order a second set of control horns and mount them side by side with a gap between them big enough to get the ball link between them.

I am a strong proponent of building a new tail components for the Impact and have written about this before. The stock parts are much too heavy. Good job!

MattK

Message posted erroneously -- removed by author

Another thing to keep in mind when running the pull pull cables for the rudder, the hinge line is not 90 deg to the thrust line of the fuzz. If your cables are ran parallel to the thrust line of the fuzz { as mine were } the cables will not be 90 deg to the rudder hinge line { off by about 10 -12 deg. }. This will make rudder control kinda spongy around center and another possible cause for flutter on this surface.

Brian did you get the new one flying yet?

Almost Matt, I am hoping to fly her next week end, after our last talk on the phone I did decide to go with the ladder assem. from the rear former to just behind the canopy and carbon push rods for elev. control and got the elev. servo's out of the tail. My ladder I built came in at 1.2 ounces with the glue and the elev. control rod assem was about 1 ounce without clevises. The hold up was waiting for all the stuff to arrive from central. All I have left is installing new leading edge on the old rudder, close up the back of the fuzz and hinge. I am looking at how easy it looks to build a whole new rudder { pics in this thread } I may just build a new one. I will give you a ring tonight.

Yes, the rudder is very simple to put together from sticks. I do that all the time. That size rudder should come out at around 45 grams ready to install. That's more thean 1 1/4 ozs saved on the tail, which will compensate for the ladder considerably

The other major factor is the actual flying of the lighter rudder. Much longer servo life and quicker actuation and damping.

Matt

Hey Brian,
Can you describe this "ladder assembly"? Or better yet, post a few pix! I have an idea of what your doing, but at 1.2 oz...I must be thinking of something different.
-Erik

I will try to describe it as I have never learned how to post pics here. All i did was cut an 1/8 thick sheet of balsa length wise into 3/4 inch stripes. Two of them were used as the sides of the ladder, they were long enough to go from the rear former to just behind the canopy. The ends were capped to make kinda of a long triangle shape the width of the fuzz. Now just fill in the center with cross pieces similar to building a built up control surface. I spaced the cross pieces to contact the sides every two inches. The whole assem. is glued in place with probond and can be inserted through the canopy opening. Hope this helps. I was surprised at how ridged the assem is when done and when glued in place made the rear part of the fuse VERY stiff. If someone can tell me how to post pics I would be glad to get some on here.

Thanks Brian,
That's what I thought you where talking about......this is what I call a fuselage "crutch", same thing
Do you think that this is necessary? With the rear bulkhead in place and the pipe tunnel floor installed, I find that the fuse is plenty stiff. I can imagine that there will be some torsion during hard snaps, but overall, I think it is better than most "vanilla" fiberglass fuses. Granted, 1.2 oz is not much and you do gain a lot of stiffness.
To post picutres, just go to the bottom of the reply window where it says "File - Click here to upload" and download your photo's ...I think there is a 3 Mb limit (or something like that)....the photo's may not show up when you preview your post, but they will show when you submit.

Thanks,
-Erik

Yes it appears that it is necessary. There are people out there with broken tails regardless, after installing the rear bulkhead

MattK

Matt,
I am curious to know just how many people are breaking their Impact fuselages in flight. Can you be certain that these failures were not due to some other contributing factor? (e.g. improperly installed bulkhead, rudder post or stab tube? or possibly prior damage?)
I know of several Imacts that have had no trouble (one doesn't even have the rear bulkhead installed!) and these guys are flying them hard, even surviving the Reverse Avalanche in Masters '05[:@]

I realize that you can fly a plane hard enough to break it, but that is certainly not going to happen flying the sequences with proper throttle management and smooth inputs. Unless there is a manufacturing defect, I find it hard to believe that the Impact fuses are suffering compression buckling due to flight loads....Is this the type of failure that you see happening?

As you know, it is easy to build a model that is strong enough....however, in pattern, we always strive for a model that is JUST strong enough. From what I have seen, the Impact meets this requirement without significant "sturctural" modification.

If it turns out that there really is a structural problem then this needs to be communicated to every Impact owner....and then it would be wise for Comp-ARF should issue some "AD" to correct the problem. As I said, I am interested in seeing the data...how many are failing?, what are the conditions causing the failures?, are there any "common denominators" that stick out?....e.g. production batch number, Engine/mount choice (i.e vibration problem), etc.?

ERichard, I think the answer might be, ".... one is too many..." to the owner of the one that broke.

I can't really quote total numbers of failures, that number is unkown. I know of four definite broken planes, all failed in similar way, some with the bulkhead installed and some without. There is possibly a fifth as yet unverified. That's out of how many planes flying?? I would guess around 30 planes worldwide, actually flying. There are probably 100 under construction.

I also know that my friend Brian's model broke on its maiden flight, as he was pulling out of the Sportsman split ess.

As far as what we strive for in pattern models structurally, I respectfully disagree. We strive for light as possible, and for maximum strength we can afford. There is also such a thing as the right kind of strength in the right places.

regards

MattK

FWIW I am also aware of the four -- on flights 1, 2, 4 and 19.

Mine was on flight 19 back in December. The manufacturer was responsive etc., and given it was flight 19 I ultimately took it on the chin and hoped (for all of us) I had just been unlucky. It didn't have the rear former. IMHO I had built it solidly, well, and to instructions, and it had had no 'incidents' in flight (or ground contact!!) -- I would regard myself as a competent Expert level competitor and this was F3A plane number 5 I have built. One of my colleagues had flown most of the F schedule with it the flight before, and there were no signs of damage. But given it was flight 19 you never know -- the manufacturer (especially their local rep) were very professional and responsive, and there are so many different things outside the manufacturer's control through building, equipping and flying that I erred on the side of not taking it broadly public at the time. I have a number of colleagues who are flying them with no issues at all (and flying them hard!).

The failure was more severe than the first two in the that the whole tail section broke off in front of the fin/stab while pushing into the outside loop section at the start of the triangle rolling loop. The view is it had to have been flutter to cause such extensive and sudden damage. What caused it is unclear -- is it fin/rudder aerodynamics, the bottom hinge (which had worked very slightly loose -- not in glue failing, but in the balsa around it softening and allowing some minor movement under force)?

One thing I will note (and I am not an expert in composites) is that the Impact construction is more like an egg shell than other models I have -- in that when in its normal shape it is very rigid/strong, but when compromised it fails easily. The outer and inner 'layers' that sandwich the core are very light and somewhat brittle -- and are very easy to both pull off and tear by hand with little force. This is quite different to the very 'tough' combination of Kevlar/Poly foam/glass cloth of my Hydeaway -- which survived a mid air that removed a wing and put it nose first into a dry swamp. There was some compression failure in the foam centre of the sandwich on one side of the rear where the tail had clearly swung round on impact -- but the inner and outer cloth were intact and it was quite fixable. Unfortunately the same could not be said of the Impact -- but it did go close to straight into hard ground from 400 foot (bent crankshaft, stripped servo gears etc.).

I have since become aware of one that failed in almost the same way -- except it had the former and had been built by a very talented and experienced builder in full knowledge of the warnings around rudder hinges etc. While I remain happy to take mine on the chin given its larger number of flights, I will aim to eliminate all possible risk areas on the second one I am building (so replace rudder, traditional hinges, ladder in fuz), and would suggest others do similarly until there is a clear explanation for these incidents. I won't take the risk again. I am also glad I was flying at an isolated field and no where near a populated area.

Tough and light are achieveable in F3A building!!

David

Matt,
I absolutely agree that one is too many....even for the guy that doesn't own the plane. I hate to hear about these kind of crashes, especially like the one that happened to Brian. I think that you will agree that the Sportsman split ess is not a particularly violent maneuaver, so something was definitely wrong. I now see why Brian is beefing his second one up...I don't blame him one bit and would do the same.
If your estimates about the total number of Impacts flying is correct (which I would agree with, maybe 50 at the most) then these are abo****ely unacceptable statistics......13% failure rate! And that just includes the ones you know about. I am going to try to investigate this further....but if anybody out there has experienced an impact failure like Brian's, then please chime in and tell us about it.

As far as my statement about just strong enough, what you are saying is implied in my context....they key phrase in your statement being ..."that we can afford". We all want our planes as light and strong as possible, to a point. I (like many) spend a lot of money on this hobby/sport/disease, but I'm not Boeing or Lockheed Martin so I'm not going to spend a fortune on exotic materials that will make my bird light and withstand loads that it will never experience...that's what I meant by just strong enough. I think at least in spirit we are saying the same thing...if not then okay, so be it.

Back to the Impact problem....Did you witness Brians failure? If so, can you describe what happened? For example, do you think something (rudder or stab) fluttered? I suspect that it was probably all over in an instant, so it is hard to tell. However, inspecting the damage after the fact may have some clues....any ideas?

-Erik