Parkzone T-28 CoG

[Tim Kearsley]

Hi all,

I recently bought a Parkzone T-28 Trojan.  This is a RTF model, complete with 35 MHz radio, LiPo, motor ESC etc.  I took the 35 MHz Rx out and replaced with a Spektrum AR7000.

I took it up for its maiden flight a couple of nights ago.  I've not installed the undercarriage as I'm flying in a field with longish grass, so belly landings are fairly gentle and cushioned.  It flies beautifully and is fairly nippy.  One thing I noticed though is that it seems very sensitive to elevator.  The CoG is stated to be between 2.25 and 2.5 inches back from the wing leading edge, measured at 1 inch out from the wing root.  I found to achieve this I had to add a little weight to the tail.

Do you think the elevator sensitivity is down to a CoG which is too far back?  The plane was quite flyable though I also noticed that I had to put in quite a bit of down elevator trim to achieve level flight.  The elevator throw doesn't look excessive.  Inverted flight needed just the slightest hint of down elevator.

I'm still fairly inexperienced, so opinions from the experts are very welcome!

Cheers,

Tim.

[Tim Mackey]

If inverted needed only " the slightest hint of down" then it sounds about right, however excessive down trim to achieve level flight sounds like tail heavy, or thrust line problems - I should just remove the lead, let it balance on the forward point of the range mentioned, and see how you like it - wont hurt. COG is something which you need to experiment with on many models, and different flyers like different setups. Most models can tolerate abit of adjustment - except flying wings which often are VERY hard to control if its wrong - ask me how I know !

You could also try adding in some exponential, I often use as much as 70% on some of my faster stuff

[Tim Kearsley]

Thanks for a very prompt reply Timbo.  You've confirmed my own thoughts on this.  As I understand it, a forward CoG is "safe", if not conducive to sparkling performance.  I think I'll remove the lead I added to the tail and see what the effect is.  The thrust line is built in to the model and looks reasonable, i.e. a bit of down and right.  I think I'll re-read Andy Ellison's excellent "In Trim" article as well and check these aspects out in the methods he recommends.  I shall also set up some exponential - there's nothing at the moment.

Tim.

[Tim Mackey]

Welcome....

[BB]

Timbo knows too much   lol.

I was thinking Tim K of adding a Trojan to my hangar. Can you let me know how you get on with flight times, power etc using those li-po's. Ta a lot

 

[David Ashby - Moderator]

Tim - I added about 50g to the nose of my T-28 as like you, mine was too sensitive on the elevator. Flies great now.

[Tim Kearsley]

Hi Basildon,

Yes, certainly will do.  As well as the supplied 1800 mAh LiPo I'm also using some 2100 mAh batteries I've got.  I added a strip of Velcro to the floor of the battery bay in the T-28 to hold the batteries more securely.  I've only had three flights so far, but first indications are that using on average about 3/4 throttle results in flight times of around 8 - 9 minutes at least.  Power seems adequate and the T-28 will pull nice large loops quite nicely.  Rolls seem fairly axial and inverted is no problem with only a touch of down to hold it level.  As I said earlier, at the moment I'm flying without undercarriage.  I presume performance would be slightly poorer with the wheels fitted due to the increased drag.

More when I've had a few more flights.

Cheers,

Tim.

[Tim Kearsley]

Hi David,

That's interesting.  Without undercarriage, I found that I had to add lead to the TAIL to achieve a balance point in the stated range (2.25 to 2.5 inches back, measured at 1 inch from the wing root).  I'm going to remove that weight and see how she performs.

Tim.

[David Ashby - Moderator]

Yup OK Tim, I'm at work and so can't re-check my model at the moment but she always felt tail heavy and twitchy on elevator till the nose weight went in.

Great little flyer though 

[Tim Kearsley]

A bit more feedback on this topic now:  I've just returned from a flying session with the T-28, this time with the tail weight removed.  It flies better now, at least to me.  I also applied the test Andy Ellison mentions in his excellent "In Trim?" article, whereby you get some height, put the aeroplane into a vertical dive, then let go of the elevator stick and note the tendemcy.  In my case, the T-28 showed a slight tendency to pull "upwards", indicating a slightly forward C of G.  It was slight though, so I reckon it's somewhere near correct now.  The elevator still seems quite sensitive, but not quite as twitchy as before.  I'll check the throw and also put in some exponential.

I had a great session anyway - the T-28 is a VERY nice flier!

Cheers,

Tim.

[BB]

Thanks for the feedback Tim, much appreciated . S'pose I'l be checking all the usual places for pennies now, back of sofa etc etc LOL

[Tim Kearsley]

Well if you buy one Basildon, you won't regret it - it's a lovely plane to fly!

Cheers,

Tim.