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Dymond F8F Bearcat ARF

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Old 09-28-2004, 09:43 AM
  #51
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Default RE: Dymond F8F Bearcat ARF

I just ordered a GWS retract servo from [link=http://www.balsapr.com/]Balsa Products[/link]. It was $24.50 and it has 111 ounces of torque. I plan on installing that servo, along with the GP .60 size retracts that I am ordering from Tower today.

Richard, have you gotten to the pull-pull cable installation on the rudder yet? There is a balsa reinforced section near the bottom of the rudder that I assume is where you should thread the pull-pull hardware through and attach to rudder. The only problem I see, is that if you mount the hardware that low on the rudder, it seems like it will interfere with the elevator. Any thoughts you might have would be appreciated. Thanks.
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Old 09-28-2004, 09:45 AM
  #52
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I haven't gotten to the pull-pull cable installation on the rudder. I think I will glue in the rear stab and install the elevator pushrod first.
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Old 09-28-2004, 09:59 AM
  #53
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Richard, the only advice I have against doing it that way is this: Having that large hole on either side of the fuse (for the horizontal stab) makes it much easier to fish around those pull-pull lines and thread them through. Once you glue in the stab, you will lose those large openings and threading the cables through will be more difficult unless you can fit your arm down into the fuse. Just my 2 cents.
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Old 09-28-2004, 11:10 AM
  #54
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Default RE: Dymond F8F Bearcat ARF

I will cut slots on the side of the fuse just large enough for the elevator pushrods to slide through. I might not do pull-pull for the rudder and install a single pushrod instead.
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Old 09-28-2004, 05:07 PM
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Default RE: Dymond F8F Bearcat ARF

This Bearcat does look good from the pics.
I didn`t need anymore warbirds, but after seeing this post about the new Bearcat I had to get one.
Should be here soon.
RICH. and others, if you have any pics. of your elevator and rudder set up, or anything on this Bearcat that you changed or fixed for the better, please post.
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Old 09-29-2004, 07:32 PM
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Default RE: Dymond F8F Bearcat ARF

I have been working on mine this afternoon.
I have one retract in . I used a set of Robart mechanicals
I opted for the 85 degree 609 retracts with the 3/16 inch wire.
It seem a little overkill, but sometimes having agood flying session
cut short due to retract failure is more of a buzz kill.

As Richard did I want to go with 3 to 3.25 inch wheels.
I also fly off of grass.

For the elevator I bought a sig heavy duty control horn.
part number SIGH554
It is a prebent "u shaped control horn. That way I have all internal
control hook up, and it is a center pull so no more adjusting y pushrods.

Thats all I did for today
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Old 09-30-2004, 02:13 AM
  #57
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Default RE: Dymond F8F Bearcat ARF

I got the tail feathers glued in place and the slots cut out for the elevator pushrods.
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Old 09-30-2004, 12:54 PM
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Default RE: Dymond F8F Bearcat ARF

Well i got mine assembled and put GP .60 retracts and standard servos and one retract servo . With everything on the plane except the engine and one pound of ballast added inside the cowl the plane weighed in at 6 lbs 4oz and was still tail heavy so i am going with an OS .70 4 stroke which will add another 4oz for a total of 6lbs 8oz with a wing loading of 29.97 ! This plane is a pig, i hope it flies well .

Barry
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Old 09-30-2004, 01:26 PM
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Default RE: Dymond F8F Bearcat ARF

"bear9236"-Did you balance it with the Eng. installed when you got 6lb. 4oz., if so what Eng. did you use when balancing??
Did you go with the pull pull rudder?
Did you run into any truoble with anything when building or changed anything??
Thanks.
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Old 09-30-2004, 01:57 PM
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Default RE: Dymond F8F Bearcat ARF

Sounds like I am going to have to do some shifting and weight adding myself. I am using a saito 82, which weighs 17.6 ounces, so i may end up tail heavy too. I am also using GP 60 size retracts.

I installed my rudder pull-pull today. Went very well. I criss-crossed the cables and came out just above the horizontal stab. I epoxied in a pair of white great planes pushrod exits to clean the installation up a little. There will be no interference with elevators. This weekend, I hope to install horizontal stab and elevators. Still waiting on my servo and retracts to come from tower.
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Old 09-30-2004, 01:57 PM
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Default RE: Dymond F8F Bearcat ARF

No i balanced it with one pound of ballast in the cowl and the plane weighed 6lb 4oz . When balanced with one pound of ballast in cowl the cg was 1 1/2" behind 100mm so i am going to need the extra 4 oz that the OS .70 weighs to get the cg correct .
I put a single push rod for the rudder .
Nothing else was changed . I did have to recut hinge slots and redrill the holes for the tail wheel wire . The plane is a value at $139 but there are a few things that were not done properly at the factory .
If you have assembled arfs before most are not perfect but this one is not for the beginner and instructions are lacking .
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Old 10-01-2004, 07:45 AM
  #62
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Default RE: Dymond F8F Bearcat ARF

We're looking at 20 ounces of engine weight to balance this thing. YS .63 would get you closer than my Saito 56 or a Saito 82. A Saito 100 will be a good candidate on balance and power, but question whether the structure is up to the task.

I will see how the .56 goes, but it's looking like I am going to have a high wing loading and balance concern with this engine. Cannot justify the new price of a Saito 100 right now, but a Magnum 91 might do just as well... Just thinking out loud.
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Old 10-01-2004, 08:17 AM
  #63
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Default RE: Dymond F8F Bearcat ARF

The new YS 63S is pretty light at 17.8 oz total weight. However, a YS 63 with aluminum engine mounts might do the job. A Saito 91, Magnum 91, or OS 91 might be a better choice. I'm going to stick with my YS 63 and stock nylon engine mounts. However, I plan to build a baffle to direct air through the engine cooling fins, and that should add a few more ounces to the nose. The cowl has too big of an opening, which will slow the plane down. Too bad the plane doesn't come with a dummy radial.
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Old 10-01-2004, 09:58 AM
  #64
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Default RE: Dymond F8F Bearcat ARF

I`m putting the wings together now.
The wings are at 53", its listed on the web. site as 57". I`m still planning on using a OS .61FX with pitts.
The Elevator. Stab. where it goes threw the fuse. looks like it will need more mounting area in the fuse to glue and hold it better.
Not much area in the fuse to glue it to!
RICH- did you use a push rod for the rudder(any pics.)?
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Old 10-01-2004, 10:25 AM
  #65
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Default RE: Dymond F8F Bearcat ARF

I did not use a push rod for the rudder. I have cut out slots in the fuse for the pull-pull cables so I will give them a shot. This will be my first pull-pull installation, and it looks pretty straight forward. A push rod will add more weight to the tail, and we want to keep the tail as light as possible.
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Old 10-01-2004, 10:55 AM
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Default RE: Dymond F8F Bearcat ARF

I installed the pull-pulls already and they will work fine. I would recommend crossing the wires though, rather than running each one straight back on the same side. The reason, you will notice, is that if you don't cross the wires they will rub on the wooden inside rear fuselage brace until they eventually break.
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Old 10-01-2004, 12:16 PM
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Default RE: Dymond F8F Bearcat ARF

I have done a small modification to my bearcat.
I removed the servo tray and also the rear bulkhead.
I do not know how much weight I saved but EVERYTHING is going
to the most forward it will go.

Also anybody tried this?
To save on length could I mount my fuel tank sideways?
I plan on using a different fuel tank.
That way I may be able to move the servos farther forward.

The only other bearcat that I have built was a little smaller
with a OS 52 and it was also a cg problem.

I hope this pig flys better than the build.
Greg
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Old 10-01-2004, 12:53 PM
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Default RE: Dymond F8F Bearcat ARF

The OS .70 Four Stroke was still not enough weight , i am one inch behind recommended CG . Does anyone know how to figure out CG on tapered wings to see if the instructions are correct ? I put a single push rod for the rudder i am going to pull that out and see if it helps any .
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Old 10-01-2004, 01:01 PM
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Default RE: Dymond F8F Bearcat ARF

Here is a thread on how to find the CG: [link=http://www.rcuniverse.com/forum/m_2147265/anchors_2153782/mpage_1/key_/anchor/tm.htm#2153782]CLICK ME[/link]
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Old 10-01-2004, 01:06 PM
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Default RE: Dymond F8F Bearcat ARF

I drew and cut out a piece of partial rib on light basswood to replace the one that I trimmed away:
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Old 10-01-2004, 01:08 PM
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Default RE: Dymond F8F Bearcat ARF

Here is the new piece glued in place:
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Old 10-01-2004, 01:37 PM
  #72
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Default RE: Dymond F8F Bearcat ARF

has anybody figured out the square wing area yet?
also mine measures 53 inches
I am guessing that it was a misprint.
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Old 10-01-2004, 01:50 PM
  #73
Richard L.
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Default RE: Dymond F8F Bearcat ARF

The wing is made up of two trapezoids, so is pretty easy to calculate the wing area although I have not done it yet.

Here is the wing area: A = 1/2 * (root chord + tip cord) * wingspan.
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Old 10-01-2004, 01:55 PM
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Default RE: Dymond F8F Bearcat ARF

I finally found my cg calculator and the suggested cg in the instructions is on the spar or 100mm which is at 31% of the MAC . 33% of MAC is at 107mm or 4 3/16" , i don't know if beyond this would be stable .
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Old 10-01-2004, 03:03 PM
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Default RE: Dymond F8F Bearcat ARF

Even after removing all possible aft weight,
I hung a os 70 with heavy hub on the nose it is STILL AFT CG!
That is with no servos or battery just engine hung on the airframe.

Not sure what to do now, I will not add lead,
I don,t think this plane needs a OS 90 for power.
Any other weight savings you guys have in mind?
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