AJsToyz

Looks like that OS can swing a pretty good size prop. I like to fly mine with a 17" at our field. The grass gets a little tall and she tends to want to nose over on landing. Broke my Vess second flight.

Stick 40

Hi,

are you talking about the same twin in the same plane???? If you are what pitch prop are you using, that was the next thing I was going to start looking for. you said 17 inch but 17x??

thanks

sticks

geetarjoe

My Feedback: (7)

Darjen38,

I see youre building the 75-91 version like i am. did you find that the turnbuckles were hard to install in the wing? I think the ones that were included with my kit were either the wrong size, or the blind nuts in the wing were the wrong thread. Upon screwing the first couple in i fellt that they were a bit tight.. the next one got half way then POP! snapped right in half.

this is a beautiful airplane but its definitely a pain to put together.. shouldnt be this way for an ARFin this price range.

AJsToyz

I have a 30cc in my 1.20 with a 17" prop. I had an 18" and was able to break it do to the plane wanting to nose over in the long grass. According to the engine specs on the OS it seems to be able to handle a 20" prop. Just suggesting to stay with a higher pitch smaller diameter for ground clearance.

Stick 40

I was really hoping you had the same engine, oh well.

The instructions with the engine list, 15x8 16x 6-8 18x 6-8 and 20x6. I may go ahead and get one each of the three smaller ones and check the pulling power, with my fish scale.

It will be awhile before I get too it, but will get back down the road.

sticks

darjen38

Yes I had the same problem. and like you had a real sod of one . But well worth it in the end..

SkyPilot101

To cure the loose fit from the strut clevis to the brass attachment points, I soldered up the holes (which were oversize} and re-drilled them out @ 1/16". This tightened up the clevis fit and cured the rattley struts.

ahicks

My Feedback: (2)

Another gas powered Decathlon was offered up to the flying gods yesterday, and arriving back home on terra firma safely, despite very windy conditions! Thankfully they were blowing right down the runway. There was enough wind on a couple of landings to permit a 20-30 foot roll out! The RCGF 20 was proven to have plenty of power, offering unlimited vertical, though maybe not enough for all out 3D. Using an APC 17x6, but not tached yet. Plenty of ground clearance. The engine was very easily dialed in and the second tank of fuel was spent in the air. Suggested CG has proven fine, maybe a hair nose heavy. Suggested aileron throws for low rate not quite enough for me, but fine for the test flights. Knife edge coupling, holy cow, had forgotten how bad they really are. Going to take while to figure out all of what needs to be done there! 4 tanks of fuel with it has let me do a little engine tweaking, a little fiddling with the radio, and the plane is already settling down into what I think is going to be a great little flyer. Very happy with the plane overall. -Al

eclipse3g

My Feedback: (5)

I’ve just finished repairing her. A test flight is coming soon.

ahicks

My Feedback: (2)

Have quite a few flights on the RCGF 20 powered Decathlon 120 now, and the "nose heavy" tendency noted during the test flying stages has proven to be very noticeable now that it's dialed in a little more and I'm pushing the plane into more aerobatic flight. I'm saying it's nose heavy as there's a major trim difference inverted vs. upright, apparent even just by looking at the elevators, which are very obviously set to help hold the nose of the plane up. 45 degree inverted climb out results in a plane dropping it's nose right away. The plane will knife edge easily, but that up elevator trim required for level flight REALLY becomes apparent (coupled big time!) when you roll the plane over onto it's side. Most planes will turn towards the gear when you do this, but this plane wants to turn towards the windshield big time! I put a stick of lead under the horizontal to see if that would improve things, and I think it did, but only have a couple flights on it since. It appears it still needs more? Planning on moving at least the rudder servo to the rear already.

So really, my question is have any of you made any kind of attempt to balance this plane - regardless of the suggested CG (which seems to leave the plane as described above). If so, how successful were you? Am I wasting my time?

As nose heavy as it is, still love the plane when it's flown in a scale manner. Just hoping it's capable of much more....

AA5BY

A high wing plane has a drag couple that plays into knife edge flight. Stick planes are often pretty good at aerobatics, but not so good at knife edge pulling hard to the canopy if they had one for the same reason as the Decathlon.

I'm not sure the inverted 45 deg upline test is a good indicator of proper CG for the Decathlon nor is inverted comparison with an elevator trim that is out of neutral.

Personally, I would balance it on the prescribed CG... then trim the decalage for neutral elevator... then re-balance for proper glide slope.

Are power on/off trims now the same... I ask because often when significant elevator trim exist, they are not.

ahicks

My Feedback: (2)

I haven't taken the time/trouble to set the plane up and get the incidence meter set up on it. That's likely an excellent idea if for no other reason than to make sure I have the struts set right! They're currently set so they're the right length and there's no static twisting load only (they aren't forcing anything anywhere).

Haven't built anything other than ARF's in a long time, trying to get my head wrapped around which way to go with the wing to neutralize the stabilizer/elevator (w/obvious up trim)? Trailing edge to go up or down? Used to setting per plans and forgetting it - probably a good thing!

Re-balance for proper glide slope? That's something I don't ever recall doing?

Regarding power on/off trim, the plane is currently trimmed for near WOT (call it 3/4 speed?). Slower speeds (less power) will have the plane descending, and of course enough power application will check the decent? That doesn't seem too unusual on this plane, though the climbing under WOT is noticeable. Everything else I'm flying usually fairly neutral after trimming. Hadn't thought of that regarding the way this elevator has obvious up elevator trim. Would adding some down thrust be a good option/plan compared to messing with the wing incidence if that becomes necessary?

Thanks a ton for your thoughts! Will get back after seeing what the incidence meter has to say. Hopefully I'll be able to find something to zero out the fuselage without too much trouble! -Al

DougC1

Although I don't think this bird is intended to be a "Neutral Plane", the link should at least provide some base-line concepts for trimming, particularly for CG and engine thrust line.

http://www.pongo-air.com/flightguide.html

Doug

AA5BY

If there are more than a few clicks of up trim in the elevator, it can mean that the plane is significantly nose heavy or has a decalage issue (incidence mismatch between wing and stab). If it is balanced on the prescribed point and doesn't have an elevator authority issue when landing, I'd suspect a decalage issue.

To adjust an up trimmed elevator toward neutral, the plane needs more lift. This can be gained either by trimming the stab more negative or the wing more positive, whichever is easier. Make changes in small increments of no more than 1/32. I've done that simply by cutting a sliver of 1/64" plywood and gluing to the top or bottom of the dowel holes that establish the incidence and filing slightly on the other side with a round file.

Most of the time, a neutral elevator (with proper plane balance and engine thrust) will produce a good off power glide slope and be a pleasure to land. If the slope is not proper with a neutral elevator, then it is time to think further.

ec121

My Feedback: (2)

I put a CRRC 26 on my 120 decathlon, and it still needed the battery in the windscreen to balance at the proper spot. The short nose moment take s a lot of nose weight or I have some really heavy wood in the tail.

ahicks

My Feedback: (2)

Thanks for the link Doug. Not looking for a Decathlon pattern plane, just assurance this thing is trimmed as well as possible? The knife edge coupling is what's REALLY bothering me. It's just crazy. Would like to get rid of all/most of the elevator up trim to see if that doesn't have a big effect on it. Some of that chart is familiar, but there's plenty of new ideas as well. No way I'm going to remember them all, will print off that chart and have it with me next time out.

AA5B- The plane will land very slowly. Seems like plenty of elevator authority, maybe too much (need to be very carefull on take off run with this engine). The stabilizer is epoxied, so thinking my only option is to lower the trailing edge? It's set up with a dowel, so I can do as you mention - filling and filing.

Thanks for the help! -Al

CAT POwer

My Feedback: (61)

Al, what do have your CG on ?

AA5BY

If the glide slope is too shallow and the plane is slowing too much during landing and assuming proper CG, it is likely a product of the up trim needed for level powered flight. Spell that condition D-A-N-G-E-R because unless you apply some down elevator when landing, the plane will want to slow too much with a too shallow of glide slope.

There are two ways to deal with that condition... first you could mix some elevator down trim at low throttle and second is to perform the incidence change on the wing, giving it a slight bit more positive so as to reduce the up elevator trim needed for powered flight.

ahicks

My Feedback: (2)

Cat Power - CG is on the rear of the new spec. 3.5"

AA5BY - I'm used to flying with a heavy tail, actually prefer it that way. 2 of my other planes are setup for 3D (not that I'm any good at it!), another is a Great Planes Giant Sportster that was landing WAY long - all are generally on or to the rear of the suggested CG range. Giving "down" on short final nothing too new here.

CAT POwer

My Feedback: (61)

New spec ?

ahicks

My Feedback: (2)

The original CG spec. listed in the earlier manuals was further back. Not sure how far.

MinnFlyer's build/review of the plane (http://www.rcuniverse.com/magazine/a...rticle_id=1152) mentions this in a couple of places so I was watching for it. Turns out the manual included with my kit has the correct dimensions.

ahicks

My Feedback: (2)

Ok, this morning I dusted off the old Robart incidence gauge. Dusted again after realizing the numbers on the gauge have gotten a LOT smaller than the last time I used it. 20 years ago those numbers seemed fine!

Anyway, I used the bottom of the side windows for a "water line"/reference point. I shimmed the plane to zero that line out. From there I measured both wings at the root and again at the tip - everything measured +1 degree. Same thing on the horizontal stab. +1 degree there too. Measured the engine and it's -1 degree. All this - best I can tell. Like I said that thing's getting hard to read, but after this measuring it seems Seagull's builders are spot on!!

Bottom line, I didn't see any cause for concern anywhere. The down thrust on the engine is likely there to help compensate for the semi symmetric airfoil? Thinking about it, that may not be enough. We'll see what this testing tells us.

The weight I had on the tail has been removed, and CG confirmed at 3.5" from leading edge. Out to the field soon to put it through some troubleshooting runs (per the link above) to see what they can tell me. Be interesting to see how it does there?

CAT POwer

My Feedback: (61)

Never mind

ahicks

My Feedback: (2)

That's working in the right direction to what I was thinking originaly. Where did you find that info?

CAT POwer

My Feedback: (61)

In the manual on the Horizon website