Parkzone T28 Trojan – Center of Gravity?

[Forge]

All,

I flew my Parkzone T28 Trojan this weekend for the first time. Does anyone know where the center of gravity is optimally located on this plane? The instructions don't show it.

I am relatively new to flying and the nose appeared to want to go up without input. Should I add weight to the nose? The plane appeared to be trimmed correctly.

By the way, great site. I've been flying a Flyzone 4ch Piper Cub since Christmas, and the T28 blows it away! It has awesome power and maneuverability, and it was only in low servo control the whole flight. It was too windy to stay up long, but I got it back on the ground quickly and in one piece with a controlled landing!

Finally, all the suggestion about using a Flight Simulator really paid off, I've been using G4 for the past few weeks and it has helped significantly.

Thanks

Forge

[cbatters]

2Q

1. What makes you think the COG is not correct? (One of the advantages of RTF planes is that for the most part, they are shipped properly balanced from the factory. Unfortunaltely, most do not include COG balance info.)

2. Can you correct the "nose up" problem with a couple clicks of down elevator?



Clint

[Forge]

Clint,

I'm not sure, and the COG may be correct from the factory, but I was just looking to confirm that it was set right.

I haven't been flying that long, but from what I've read the COG can have a significant impact on flight performance. My 1st flight was so short due to the wind that I really didn't have enough time to adjust the trim of the plane after I took off. All I could think about was turning it around and getting back on the ground safely.

[cbatters]

Sounds like high winds may have been the primary issue with the nose up operation of your plane. (Fairly common for a plane to nose up in high winds. )


Several thoughts about COG (center of gravity) and COL (center of lift)

1. COG behind COL will make the plane difficult to control if not unflyable

2. COG = COL will make the plane very responsive

3. COG too far in front of COL will make the plane less responsive.

4. Normal to trim a plane with COG slightly in front of COL.

5. You can document curent COG by noting where the plane balances with two pencils or dowels under the wing. Useful if you have to do a repair or modification and want to maintain current balance.


Clint

[Sparky Paul]

I flew mine the first time today, with the c.g. more or less where it comes out with everything in place, about the recommended 2-1/2" back.
It was tail heavy.
Flyable, but a bit twitchy.

[Destroyer of airplanes]

Parkzone left the CG info out of the instruction manual, but they did publish a Bulletin. "2.5" behind the leading edge, measured 1 inch out from the side of the fuselage". Get it even close and it will fly fine.:p

[Forge]

Thanks for the speedy replies guys! I will measure it and balance it out later tonight.

Forge

[jg95762]

I just bought my second T28 and flew it this morning. This is my second RC plane, I also spent a month or so on the simulator before plucking up the courage to fly the T28. I had the first T28 for about 4 months before a hard crash last weekend in the wind.

The new plane seems quite a lot faster which is probably due to the amount of epoxy and hot glue that ended up on the old plane. But the problem, which brought me to this forum was that it was very nose heavy. When I left the elevator alone it would start diving at about 15 degrees. Quite a handful to land. I tried putting up elevator trim but that didn't help much - and it seemed wrong to have to put a lot of up elevator to make if fly level.

After reading this thread and a few others I built a C of G balancer out of dowels and eraser heads. The only way that I could get the plane to balance at the prescribed 2.5 inches back was to move the battery all the way back so that it was touching the receiver. This seemed a bit extreme but I went out and flew it this evening and it was better, but still would drop it nose more than my original T28 when I took all power off and came in to land. The speed was a fair bit faster than my old plane but once I got my heart rate under control it was actually easier to land. It seems to penetrate through the air better which is easier to flare out to land gently.

So, I am thinking my original T28 might have had the C of G to far back. I used to try to land faster but often had too much lift, or would be going too slow.

However, having to move the battery back that far seems extreme. I was wondering if anyone else has had to move the battery back this far or has other input.

I am also scratch building the Scratch plane that was in May's issue of Fly RC and have transferred the servos and ESC from my old T28 to this plane. The plane is not complete yet and it may be a while before I have the courage to fly it. Understanding C of G and C of L will be important for this plane, so I really want to use the T28 to get my head around how this all works.

[cbatters]

What makes you think this is a COG problem and not just an elevator trim issue. (i.e. why don't you jst add a couple clicks up elevator on the transmitter to have slower/shallower glide.)

COG is about balance of airplane not glide slope.



Clint

[jg95762]

Thanks for your feedback. The reason I thought it was related to C of G was because the C of G was forward of where Parkzone recommended and the plane dropped its nose considerable when I took the power off, which was very different to the behavior of the previous plane. Also, I tried trimming the elevator and had more than a couple of clicks and it still didn't make much difference. From visual inspection the elevator is level (horizontal) when the trim is neutral.

I admit that I am a novice from a flying standpoint as well as trimming the plane. I moved the battery back and it seemed to make a difference, but perhaps I was just adapting more to the characteristics.

I will experiment, and read up, some more.

[cbatters]

You should have been able to dial in enough up elevator to get the desired glide slope even if the CG was set too far forward.

Also, do not put too much emphasis on having elevator level with horiziontal stabilizer.

I generally trim horizontal stabilizer for dead stick (no power) good glide slope. (so if the motor kicks out the plane is already gliding as best it can.)

Note: Glide slope on T-28 is going to be steeper than an electric glider due to higher wing loading.


Clint

[jg95762]

Thanks Clint. I flew this morning with the up elevator trim one click from max and the glide path was pretty much level. However, this T28 still seems to glide (power off) a fair bit faster than my original T28. In some ways it is easier to fly because it penetrates through the air better. I think I just need more stick time, and spend time tinkering with the trim and paying more attention to how the plane reacts. Again, thanks for the input.

[kimeza]

So regarding your last post, at that time did you position your battery to satisfy the 2.5" CG or did you shove the battery all the way forward?

I'm about to launch my maiden flight and don't know if I should go with Parkzone's CG or listen to some of the posts and just shove the battery forward all the way.

[Destroyer of airplanes]

Originally Posted by kimeza

I'm about to launch my maiden flight and don't know if I should go with Parkzone's CG or listen to some of the posts and just shove the battery forward all the way.

Shoving it all the way forward put my plane in the correct cg. A little nose heavy isn't a bad thing with this plane. A little tail heavy is.

Good luck with your maiden.

Paul

[kimeza]

Ok. All the way forward. Damn the manufacturer's 2.5" specs.

I'm lanching in T minus 1 hour!! :p

[Destroyer of airplanes]

A little trick I use to locate the CG is to glue a 3/8" square piece of balsa wood at the CG location. Now all you have to do turn the plane over and you can feel the correct balance point.

[Destroyer of airplanes]

I even found a picture.:p

[jg95762]

I hope the maiden flight went well.
I have now gotten comfortable with the balance of my second T28 and can fly it much better than the old one. I have the battery pushed all the way forward which puts the CG forward - seems to handle well. I think my original T28 must have had the CG too far back and I was too inexperienced to know it.

[kimeza]

Maiden flight went great with some exception.
After reading several posts, I discovered the same confusion. I found a post on rcgroups: http://www.rcgroups.com/forums/showt...39#post9601239 which shows several people believing the battery should be further back.

I hot glued a balsa platform to the inside fuselage and put velcro on top to begin my experience.

I tried stock battery all the way forward. T-28 took off no problem, flew like mad. I need to bring nose up when throttle is cut and nose down when I accelerate. At full speed, I'm porposing and the plane would nose up and do loops if I let go of the stick.

Next was a 2100 Lipo all the way forward. Still same up/down issues as above but not as pronounced.

Next was stock battery using the 2.5" CG. Nose up upon take off, instability then crash into some cushy bushes. No damage.

Next was lipo batter halfway between 2.5 CG and all the way forward. Nose up (tail heavy) not as bad, very instable but was able to turn around and land. Left landing gear pulled out of wing (later in the evening the right pulled out). Tape solved this problem.

I flew the rest of the evening with the batts shoved all the way forward but never got rid of the porposing.

My last flight, I was coming head in on 10 -15 mph winds power off. At first glided nicely down the slope but just over some bushes lost control and had a mild crash. Broke the foam just behind the two pins that are under the rear center of the wing (connects into fusel).

Tonight, after the wife fell asleep, I had a date with a hot glue gun (for the LG) and CA (for the wing support).

Hope this helps you nebies to the T-28.

[kimeza]

2nd day out, I flew with the stock 1800, 2100 and the 2500 lipos shoved all the way forward. After proper trimming flew great all day.

Needed down stick at full throttle and nose pointed down with no throttle. I suppose this is normal.

At this CG, into the wind lands like a dream.

[yossarian]

Originally Posted by kimeza

Maiden flight went great with some exception.
After reading several posts, I discovered the same confusion. I found a post on rcgroups: http://www.rcgroups.com/forums/showt...39#post9601239 which shows several people believing the battery should be further back.

I hot glued a balsa platform to the inside fuselage and put velcro on top to begin my experience.

I tried stock battery all the way forward. T-28 took off no problem, flew like mad. I need to bring nose up when throttle is cut and nose down when I accelerate. At full speed, I'm porposing and the plane would nose up and do loops if I let go of the stick.

Next was a 2100 Lipo all the way forward. Still same up/down issues as above but not as pronounced.

Next was stock battery using the 2.5" CG. Nose up upon take off, instability then crash into some cushy bushes. No damage.

Next was lipo batter halfway between 2.5 CG and all the way forward. Nose up (tail heavy) not as bad, very instable but was able to turn around and land. Left landing gear pulled out of wing (later in the evening the right pulled out). Tape solved this problem.

I flew the rest of the evening with the batts shoved all the way forward but never got rid of the porposing.

My last flight, I was coming head in on 10 -15 mph winds power off. At first glided nicely down the slope but just over some bushes lost control and had a mild crash. Broke the foam just behind the two pins that are under the rear center of the wing (connects into fusel).

Tonight, after the wife fell asleep, I had a date with a hot glue gun (for the LG) and CA (for the wing support).

Hope this helps you nebies to the T-28.

This kind of porposing might be normal. More air speed means the nose will come up unless you're on the trim. It is especially pronounced in tail draggers, you can expect the nose to come up some if you gun it and like wise, if it's trimmed out for cruising and you chop the throttle, the nose will come down. Pilots flying real plane are almost constantly adjusting elevator trim during acceleration and deceleration, especially if you're trying to maintain a certain altitude or climb rate.

SO what that means for us is when you get on the throttle, simultaneously add down elevator to maintain level flight. You'll get a feel for exactly how much elevator you need for your various planes. They will all behave a little differently of course.

[Homer_Simpson]

Hi all!

After reading thousands of posts here and on RCgroups I still wonder HOW all of you are able to fly this thing (keeping radio glitches aside for now)

My problem is CG, if I try to balance it acc to recomedations from Parkzone (2.5 inch/6.3 cm from leading edge 1 inch/2.5 cm away from fuse) this plane is so grossly nose heavy that it's imposible to hold it on balancing scale.

I have T-28 RTF so I have no means of adjusting CG beyond shifting battery by about 1 inch (2.5 cm) backward, after that I'm stopped by canopy (big square mold at the bottom preventing battery to shift al the way back).

I tried to put big fishing lead sinker at the tail which ALMOST balaces it out even after taking off nose wheel!

Now thanks to Kimeza - a lot of thanks for sharing your CG empirical tests I have even more doubts of what is going on

Final lesson for me now is that if you make this plane to balance out at Parkzone's recommended CG point, which is so far off that you have to seriously modify your plane to achieve this you WILL crash your plane!!!???

What is wrong??
Data about CG posted by Parkzone is just a typo or "creative" way to increase sale

Please help so mayby I can try to fly it this weekend as this "RTF" haha has so many issues but this will be subject for totally separate story

Regards
Homer

[Homer_Simpson]

Hi!

Following CG tests initiated by Kimeza I took my T-28 RTF to my local field with no plans to fly it, only to practice taxiing and handling it on the ground as coming storm made winds so strong that sometimes it was impossible to keep it going in straight path and few times wind just flipped my plane over. I think it was at least 25MPH in gusts.

Anyway during one of fast taxiings into the wind, sudden gust of wind made it airborn and lifted it to about 4 feet above tarmac, in sudden panic trying to save my plane from possible ditching it into the hard surface I put full throttle and it simply rocketed into the sky.

Battery was all the way back as far as canopy wall allowed. Flight was short and very erratic , turning it into the wind was making it almost vertical but amazingly no stall, more like helicopter hoover. To have a chance to land it I trimmed full down elevator and gently tured it into the wind. Succesfully landed on the grass. After that I've instantly moved battery all the way forward.

During second try with battery all the way forward T-28 behaved better during my landing approach I simply glided into the wind and landed in perfectly but even with battery full forward during high speed turns into the wind T-28 still kept strong tendency to rocket upwards insted of keeping altitude

Final lesson: DON'T try to balance your T-28 @ 2.5" from leading edge, especially for your 1-st flight. You will crash it in case of casual pilot and anything but perfect flight conditions (no wind)

2.5" - It may work especially for 3D pilots trying to push T-28 to its limits or mayby it gives best gliding path and flight characteristics of a "real thing" with engine no less than about 1/4 throttle to make it fly as scale as possible.

Well thats my 2c. Hope it will help save you some initial crashes

Regards
Homer

[kimeza]

I agree. I've been flying a lot since with batteries from 1800 to 2600ma. Bottom line forget factory CG. Just shove the battery all the way forward, secure it with velcro, trim at cruising or full speed and have fun.

I also cut out the bottom of the canopy to accomodate the larger batteries and electronics.

[Karnsy]

I am thinking this thread might be so old but I just purchased a Park Zone T28 and I have read much about the CG. I was hoping someone might read this and help me out. I intend on my maiden flight to put the battery all the way to the front as the book says however,

I can have the battery in to the point it hits the small 1/2" foam at the bottom of the wall that divides the motor area from the battery area or I can continue to push the battery so it rides over the small piece of foam on the bottom and butts up against a plastic brace over the ESC. A difference of about 1/2" or so.

I was hoping someone would let me know which has worked best for them and has anyone afixed some velcro over or onto the battery.
I am guessing if PZ thought it was needed they would have installed it like they did the supercub. I just think the battery could move backwards changing the CG during flight. Any help would be great !!!