rc bugman

My Feedback: (30)

Hi,

I decided that I needed a kit to build for this past winter and I selected the GP 330 - 1/3 scale (100" ws). It was a wonderful kit to build, very relaxing.

Now the problem:

Even though I built the kit with "building light" as a focus, the plane came out tail heavy. The only servos in the tail are the 2 elevator servos with the rudder servo as far forward as possible in a pull-pull configuration.

Originally, I built the motor box for a 3W-85 which is a very short engine and weighs the same as a 3w-106. After the box was complete, it was obvious that the cowl would have to be hacked up too much due to the short nature of the engine. So, I went to the shelf of "idle engines" and retrieved a 3w-106, shortened the engine box and mounted it. Since the engine box is shorter and the 106 weighs the same as the 85, the tail heavy condition is much worse.

It appears that it will take about 2 lbs of nose wt to balance the plane with a 106 on the nose. That included the radio batteries as far forward as possible and the ignition battery right behind the firewall. I hate to add dead wt.!!

So, I go back to the "idle engine" shelf and find that there is a 3w-120, 3w-140 and 3w-150 sitting there and each of those engines weigh 1.8 lbs more than the 3w-106.

Now the question?

Which engine do I use? and How much power is too much for the air frame?


Elson

krayzc-RCU

My Feedback: (31)

wow nice selections of motors lying around.

Hopefully Tim Mills will chime in here as you use to fly that same plane for years.

Tired Old Man

My Feedback: (1)

Elson,

I'm well familiar with the plane and a 3W-100 is more than enough for it. The 106 would have been killer. For those reasons it would get the 120 if it was mine. I agree about never having too much power but it's nice not to the cut the engine in order to land I prefer the taxi back to going after it...

Cryhavoc

My Feedback: (46)

I built one of these about a year and a half ago after seeing Tom's posts. You're 100% correct. Very enjoyable build. I used a 3W106 on mine as well and I outfitted it with a choke servo and a smoke system. I put the dual servo rudder setup right behind the CG and all my electronics just forward of the CG along with the batteries, (except ignition which was on the engine box). When I maidened her she only needed two clicks of up elevator and a click of left aileron and would fly hands off at half throttle. Most people I've seen with this model have use 80cc engines. I know that the 106 is more than ample to pull this plane around and do anything you want with her. I never weighed the plane but I'm sure it's heavier than most and it flys great. Here's a couple of pics. Hope this helps.

rc bugman

My Feedback: (30)

cryhavoc,

Nice looking plane. Did you also have to add nose weight?

I am also considering rebuilding the horiz stabs out of much lighter material. I built them according to plans using the supplied material and they seemed heavy and very durable.

Elson

BTerry

My Feedback: (8)

Elson, is there any way you could remove weight from the tail? If you could you drop 10 oz you would eliminate the need for 2# of nose weight. You might be able to accomplish this by fabricating a new stab, elevator, and rudder from 1# white foam and 3/32" contest balsa. How heavy are the existing stab, elevator, and rudder? Maybe adding a CF stab tube would save a couple of ounces.

The plane looks great, btw.

3D Joy

Very nice plane.

Thats quite interserting about your CG.

Mine uses a ZDZ 80 RV and 2 servos in the tail, rudder servo in the back of servo compartment. I use a canister (weight closer to CG) so it does not help in the CG. Mejzlik 26x10 (heavy) with Petes models CF spinner (very light). Batteries are on the CG, ignition battery on the motor box and throttle and choke servos in front of the tank. Really nothing special. Carbon tail wheel but no carbon tail tube, it was never needed. In fact I once put a copper tube instead of the aluminum tube (almost 2 oz heavier) and the plane flew good. My motor box is full of holes and I used only one 1/4 plywood for the firewall, the kit calls for two.

My CG is about at the wing tube but I don't know exactly. The plane weight 24.2 lbs, about in the middle of the range in terms of weight.

IMO, the 3W106 is already overkill so I would sure never go with anything bigger on that plane.
As you said, rebuilding the stab before adding 2 lbs of weight in the nose is a good idea. May be a lot of work but...

JoeAirPort

My Feedback: (41)

Use phenolic control horns and CF push rods for elevators, the lightest tailwheel you can find. CF stab tube. Like you said re-build the stabs to be much lighter. All this will help minimize the nose weight required. Titanium bolt for rudder horn?

ddennison

My Feedback: (15)

FWIW,
I had mine with 4 tail servos and a BME 100 a few years ago. It was alittle tail heavy which was nice for #D. I simply added a little lead up front for those IMAC and windy days. The 100 was plenty of power. I also had one battery up front and the other over the gear.
All batteries were NIcad...at that time.

DD

RC AV8ER

Why not move the wing back? Think it would be a lot less trouble than rebuilding the tail? You might rebiuld the tail and still not balance. I have the same kit I think when I build it I will put an extra wing position in it (like the Wild Hare).

Cryhavoc

My Feedback: (46)

I really didn't add any nose weight. It was my first giant scale build so I paid particular attentention to virtually everything I did. I took pics along of the build as well and it matches most everything you see on RCU. I have though quite abit about your tail heavy issue and was awaiting your reply with further info and can't understand why yours is so tail heavy other than the fact that I used a smoke system and a choke servo positioned to offset the balance. My issue worked itself out because I installed all servo's and linkages then installed the fuel and smoke tanks along with the batteries, all the while balancing and testing. I really think if you'll relocate a few things, you may have to add a little nose weight, (not much) but with the 106 you'll be very happy with the way the plane flys. It really depends on what you intend to do with it. It's a great IMAC plane but not a 3D machine. I made no mod's regarding the wing tubes on either end and pretty much built it stock except for the cockpit which I modified the bejesus out of. Gets alot of compliments, (the pics are from prior to maiden, I rerouted the leads, etc., for a more apealing look). I didn't spare anything on building regarding sturdiness and actually built heavier than I should have due to my newness to giant scale. I was guided by Tom's work along with a whole lot of others and didn't do anything extrodinary. This plane builds pretty close to where it should with few mod's like others. PM me if there's any pics of my plane's internals that I can send you that will assist.

Let me know if I can assist/help.

Chris

rc bugman

My Feedback: (30)

Chris,

My tail heavy condition may be an accumulation of a few little things. The servos I used on the elevators are a little heavier than normal. They are 150 oz analog servos. They are a bit overkill. I need to look and see if I can replace them with a lighter servo in the 75 oz range. I was also planning to use a Hitec sail winch servo for the rudder rather than dual 150 oz servos and even though that servo is only a couple inches behind the CG., it weighs 6 ozs. I also have not added the wheels which will help a little with the balance or the canopy which will increase tail wt. So, I need to work on the little things and it should help a bit.

As the plane now sits, it weighs 24 lbs.

Thanks Elson

3D Joy

The canopy alone weights more than 1 pound, wheels hardly do anything to balance... I guess you will be even more tail heavy after you add missing items.

A 150 oz analog must be a standard servo. I would not put anything smaller than a standard back there. You don't need 2 servos for the rudder. One good 2 oz standard servo is plenty.

When you checked the CG, you put the prop and everything? A good CF prop with 5 inch tru turn weight more than a lb.

Cryhavoc

My Feedback: (46)

I used Hitec servo's throughout, except for the choke. I have 5945's on all surfaces. The throttle and choke servo are as far forward as possible. I reduced the weight on the canopy by using the canopy pattern and just making a frame with crossbraces. I then painted it and installed a custom made dash with working I4C digital voltage indicator embedded.