ogm

Hi Guys,

My Great Planes PT-60 came out super tail heavy. I need to add 13oz to the nose in order to properly balance this plane at the 4-1/8" or 105mm mark from the leading edge. This is my third trainer. In the mid 80's, I built a Sig Kadet Senior and the older Trainer 60 from Great Planes. Neither one came out tail or nose heavy and both flew perfect. I followed instructions to the letter.

I have positioned the battery right under the tank, touching the firewall. I also moved the servos tray as forward as it will go. BTW: I am using the ultra light receiver from Futaba-R617FS.


Here is what I have on this plane.

-Saito 72AAC with Muffler ( Total weight 16.12oz)
-Top Flite MonoKote
-Plastic spinner made by Great Plane & wooden prop by Top flite
-Great Plane Treaded rubber wheels, front 2 3/4" and rear 3". (I may have to considering their ultra light wheels for the rear. However, I do not know yet how much lighter are their 3" foam wheels. I will be surprised if they make a difference.


I saw a few complaints at this forum from other people claiming that their PT-40 & 60 also came out tail heavy. But one of the guys said that he only added 4 oz to the nose to balance his PT-60.


I doubt I have done something wrong such as using too much glue or Epoxy to contribute to this problem. I wrote to Great Planes's technical support for assistance. But I have not receive a reply yet. I think they will reply with some suggestions very soon. However, I would like to hear your opinion also.


Best Regards
Otto

KitBuilder

The wheels will make basically very little difference when your talking about needing 130z in the noze. The rear wheels are located generally near the CG so whether you save an ounce or so with lite weight wheels won't do much for your situation. (are you sure you didn't leave a pair of plyers in the rear end or sometihng ). I have never built one, but the kits I have built so far have all generally come out corre t. I had to put a quarter in the tail of my Tower Hobbies 40 kit when I built that due to a nose heavy condition. If built properly I have no explanation for such a tail heavy condition other than a bad design.

TFF

90% of every model plane out there has had to add nose weight. I am not saying that it cant be built without nose weight but I have only built 2 out of about 50 planes that balanced without any work. Also you have a lightweight engine in it. Power wise you are fine, although a .72 4 stroke is considered a high powered .40 size engine. A OS .61FX is 23 oz with the muffler. A true 60 size 2 stroke engine weight is what you are missing.

GaryHarris

Whats the total weight of the plane?

ogm

Okay, based on the engines weight alone, it is starting to make sense to me. As I said before. I built a Great Planes Trainer 60 back in the 80's. That planes was very similar to the PT-60. I had an older OS .61 SF on it. Engines was a bit lighter than the newer 61 FX. I do not know weight of old muffler. I will calculate muffler weight to be close in weight to what come on the FX.

This is what I get:

Base line:
61 FX without muffler= 19.4 oz
61 FX muffler= 3.6 oz
61 FX with muffler= ~23.00 oz

Installed on my Old Trainer 60
61 SF without muffler= 18.88 oz
61 SF muffler= ~3.6 oz
61 SF with muffler 22.48

Installed on my new PT-60
Saito 72AAC with Muffler =16.12oz

Saito 16.12 oz - OS 61SF 22.48 oz = 6.36oz
Saito 16.12 oz - OS 61FX 23.00 oz = 6.88oz

TFF is correct. My 4 stroke is a much lighter engine. If I had a 60 2 stroke, I would only need to add around 6.12 oz to the nose. This is closer to what the other guy I mentioned added to his PT-60 (4 oz). Plus it makes more sense to me since I was able to balance my old Trainer 60 by moving servo tray and battery pack. Not to mention the receivers back then were a lot heavier than the tiny Futaba-R617FS.

Bottom line. I will have to end up adding the freaking 13 oz to this plane.


Hey KitBuilder. Leaving a pair of pliers in the rear???? HeHe. I don't think so.
Gary, I have no taken the total weight of the plane yet. But I will.

smithcreek

My Feedback: (25)

I used a OS 65-LA and needed to add about 7oz, so yeah, your number sound right about the same as mine. It flew great, way better than any ARF trainer I've seen at the field since I started. If I'm not mistaken the fin and stab are solid balsa. I think it would be easy to drill or cut some large holes in the fin, stab and sides to get rid of enough material to balance it with no weight in the nose. Some day I'll be turning mine into a float plane and plane on doing those mods.

TFF

It might not be as pretty but you might be able to make a stand off and put the engine forward so not to have to add as much weight. 1" could help a bunch. A heavy front wheel and foam ones in the back cant hurt either. A friend I worked with built a nice pt 60 and I test flew it and gave him some instruction before he moved; nice plane. Also it is tolerant of a somewhat aft CG so you might be able to hedge that too.

NM2K

My Feedback: (14)

I knew a guy that used to cast his front wheels from lead when he needed nose weight. It worked. Would not have been nice if his wheel collar fell off along with his wheel while flying. But they never did.


Ed Cregger

DavidAgar

My Feedback: (108)

Just ad the weight and fly the plane. Once it is in the air, you will forget all about the added weight in the nose. I have had many PT planes over the years and there is weight in the nose of everyone of them. Just the nature of the beast, as they say. Good Luck, Dave

carrellh

Both of mine needed a fair amount of nose weight.
First one had a Fults dual strut nose gear, heavy Robart "scale" wheels, and TT 61 Pro with a fairly heavy 3"b GP aluminum spinner. I think it needed about 6 ounces but cannot remember for sure.
Second one is a tail dragger. Dubro plastic gear and the Robart wheels from the first one, Magnum 91 FS, no spinner. It needed less lead than the first one, again I don't remember the specifics.

There is so much wing area that you can add quite a bit of weight and still fly pretty well. I've seen one of these planes with a 'bomb drop' box under the fuselage at the CG. The pilot would put a baggie full of flour in the box and try to drop it on the runway. It was probably close to a pound of extra weight. When the baggie hit the groud it would break and the dust would fly.

Darklotus

My Feedback: (4)

Only time I've ever added tail weight in a PT, was when I mounted a 61fx to the front end of a PT-40... (Ask me how it landed) LOL

stevenmax50

My Feedback: (1)

Just saw this thread. My PT 60 is tail heavy also. I cut lightening holes in the vertical and horizontal stabs. I also used a heavy dome spinner nut. I didnt have to add any weight after that. The plane flys great like this. I do not remember the weight of the spinner nut as I did this some time ago. I have the OS 65 LA and my batt is mounted aft of the fuel tank. My covering is fabric and paint. My total weight is exactly 8 pds.