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Feb 08, 2012, 03:21 PM
RC pilots do it in the air
marke14's Avatar
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Discussion

Questions on maidening my UM T-28


Hello everyone,

New guy here - I recently posted about my experience as a new flier learning on my HZ UM Champ, which is now on its second (and hopefully final) replacement wing and has a nice SF Designs light kit installed. I bought a DX6i tx to have full range and model memory.

I have learned so many key things about flying RC on this forum, things like orientation, flying in the wind, overcontrol and - a revelation for me - using the throttle to control altitude and to some degree, attitude.

Needless to say, the Champ flies like a champ, is very forgiving, etc. I've progressed to the point where I am comfortable flying in light to moderate wind ("light to moderate" relative to the Champ, that is!), night flying with the aid of the lights, and doing the limited aerobatics that the trusty Champ is able to do, like loops and a little inverted flight. Good stuff!

I recently rewarded my lack of crashing by stepping up to the UM T-28. I bound it to the DX6i and set up the model memory. I am getting close to maidening it, but I want to preserve this aircraft longer than the Champ lasted (or the original wing, I should say ... everything else on the Champ is original).

My first question - the T-28 makes quite a racket when powered up, at zero throttle. To me it sounds like more than servo chatter to me; certainly it's several magnitudes louder than the Champ's idle chatter. Unlike the video in the post linked above (or my Champ), there is an underlying whine in there, and a bit of crackling almost. Do I need to worry that I have a defective ESC or receiver or whatever? The last thing I want is a fire situation on my hands.

Secondly, unfortunately (in my view) the landing gear must be removed in order for the T-28 to fit into its box. The main gear seem to click in and out fairly easily, however the nosegear requires some force to extract from the housing. Being as it moves (in order to steer), is that going to break off at some point, when trying to remove it? I am thinking of flying sans-gear just to avoid damaging it from installing and removing the nose gear every time I fly.

My last question is less specific - just, does anyone have any general tips for people moving up from the HZ Champ (the little one) to the UM T-28? Presumably the T-28 is less apt to right itself after turns, and to return to a level attitude in general right? It requires more "on the stick" handling as opposed to the Champ? I also assume that its glide characteristics are less spectacular than that of the Champ, and that it has a faster stall speed?

My LHS guys also said that roll-wise, it will tend to barrel roll as opposed to aileron roll, because of the dihedral in the wings - any comments on this aspect?

Any general tips are very much welcome. Thanks!

p.s. - here are a couple of pics of my little fleet, including the battle scars on the Champ and my rubber band wing "mod" - ha ha. The one where they are stacked piggyback is just showing the relative size and wing area differential.
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Feb 08, 2012, 04:32 PM
DX5e fatal flaw- PM me!!!!
BEE-DEE-DIP-DIP-DEE-DEE-DAH-DAH-BIP-BIP fairly loud is normal, the whole plane is a sounding board.

You can cut the styrofoam under the wheels and it fits in the box gear-on.

Make sure the control surfaces are neutral before maidening.

You can pretty much ignore the rudder, just fly the throttle and the right-stick.

The big differences:
- it is much faster to bank a lot of you hold the right stick left or right
- it will not self-right (banking) if you return the right stick to neutral
- if you just turn with the ailerons and bank it without then feeding in a little up elevator, it won't turn much and it'll dive a bit

It is not quite as tough as the champ, but you really only need to avoid hitting the ground in a power-dive or an obstacle at high speed.

Don't be afraid to land it in the grass with the gear on, it doesn't care as long as you get the speed low.

Dave
Feb 08, 2012, 04:40 PM
Registered User
ausf's Avatar
You're doing everything right so far.


I'd mix in about 20% up elevator and 15-20% rudder with the ailerons. That'll help protect against the tip stall you may encounter with the T-28 that you wouldn't with the Champ. Set it up with 60% dual rate and about 30-40% expo. Bench test all of that to make sure it's right before you fly, you want the elevator going up with either aileron direction, but the rudder turn with the turning direction (one rudder value will be negative).

I'd also try it gear off over grass in a big field with zero wind at first. It is faster and it may be hard to see at a distance, but make no mistake, it is a real blast to fly.

I learned on it (should have got a Champ first) so I crashed the heck out it. Once I bought the DX6i and set it up, it flew like a dream and allowed me to really start learning to fly. After you get some stick time, you can turn off the mix and do it by hand.
Feb 08, 2012, 04:48 PM
RC pilots do it in the air
marke14's Avatar
Thread OP
Excellent tips from both of you, thank you!

Dave:

I am glad to hear that the loud sounds are normal.

I will indeed trim the foam beneath the gear areas, and try to fit it in w/ the gear (though I like the look w/o the gear much better of course).

Roger that on the coordinated turning w/ up elevator.

ausf:

I will attempt to learn the mixing stuff on the DX6i. As I'm sure you guys are aware, the "manual" that comes with the tx is, shall we say, "very light on detail" ... I had to Google how to bind aircraft and set up model memory! I will Google the mixing stuff as well, or perhaps copy the T-28 model and experiment with the mixing on the duplicate model memory.

I was going to maiden it, wind-permitting, during my lunch break today (at the beach - we've had such a warm and mild winter here even by SoCal standards), but I went out to lunch with a coworker who is visiting the office today instead. So, probably tomorrow, or Friday, as I have a couple of days off!


Seriously, great tips - thank you for sharing.
Feb 08, 2012, 05:43 PM
L'enfer c'est les autres
H2SO4's Avatar
You're obviously methodical and I have no doubt most of your planes will lead long and happy lives

That noise from the integrated "brick" in the T28UM is really something else, isn't it? When I first heard it I actually removed the battery straight away and placed the plane back in its box, because I was convinced the unit must be defective. From memory I then asked the same question - "does it always sound like something's cooking in there?"

I'd like to reiterate the suggestion to fly over grass - the longer the better. Stay high. Height is safety. It's sometimes harder than it sounds, and there's perhaps a tendency to subconsciously want the plane down low where it intuitively feels safer, so I suggest repeating the "height is safety" mantra before your first few flights.

If you get into trouble, cut the power - that's another thing which is frequently more difficult than one might think. Without power, the T28UM can glide down for a safe belly landing (on grass) from absolutely any height. The only way it can be significantly damaged, assuming you're not about to start doing low-down aerobaticts just yet, is to power downwards into the ground.

Read up on "harriers" and how they are done with aerobatic planes. Although the T-28 is a gentle sport plane, and not a hard-core 3D machine, it can in fact do continuous low-angle harriers, and thats the best, slowest, and safest way to land.

The gear is IMHO next to useless, unless you're specifically looking for that scale takeoff and landing look. The wheels are far too small for rolling on anything rougher than a putting green, so using them really implies flying on asphalt or concrete, and that's the best way to shred the plane during those first few nervous landings and disorientation mistakes.

I'm surprised the store guy was troubling you with the distinction between barrel and axial rolls. It's completely irrelevant at this point.

As others have mentioned, dual rates and expo can make a lot of difference. It's important to understand what they do, and to practice finding the relevant toggle switches without having to look down at the Tx - that may be an unattainable luxury, especially during the first few flights. The manual is indeed kinda awful, but in a way you don't need it. Once the principles of low rates and expo are understood, it's just a matter of sitting down with the plane and watching the effect of the various settings on the way the control surfaces move.

Best of luck. I'm sure you'll do well
Feb 08, 2012, 06:25 PM
Registered User
I started with this plane. Took the wheels off, belly landings are better in grass. I used 60% DR and 20% expo IIRC and could glide down to a landing power off and full up elevator if I wanted, if you tip stall you are just plain flying too slow.

A couple of times I just plain Dumb Thumbed it and as long as the power is off and you don't fly into something solid it will be fine. Having said that one time i did power in hard enough to wrinkle the lower portion of the cowling and it still flies fine.
Feb 08, 2012, 10:50 PM
Registered User
Quote:
Originally Posted by H2SO4
Read up on "harriers" and how they are done with aerobatic planes. Although the T-28 is a gentle sport plane, and not a hard-core 3D machine, it can in fact do continuous low-angle harriers, and thats the best, slowest, and safest way to land.
How do you do this with a fullsize T-28?
Last edited by Micheal81; Feb 08, 2012 at 10:58 PM.
Feb 09, 2012, 12:02 AM
L'enfer c'est les autres
H2SO4's Avatar
Quote:
Originally Posted by Mike81
How do you do this with a fullsize T-28?
The principle is always the same, but some planes are much harder to harrier than others. Gliders, for example, are almost impossible to harrier, at least in my experience. I've never flown the big (Parkzone) T-28, but from what I hear its handling is very similar to the UM, and the little one can indeed harrier at a moderate angle of attack (AoA from now).

When the plane is flying straight and level, the wings provide lift, and ideally the prop thrust is horizontal. As the AoA increases, the prop starts providing part of the upward pull/thrust, but initially the wings are still doing their bit. At a certain point, the airflow separates from the wing surface - the wing stalls - and the amount of lift provided by that portion of the wing decreases drastically. However, on planes with very powerful drive systems, the prop may now be providing sufficient upwards thrust to prevent the plane from falling out of the sky like a brick.

As the angle continues to increase, the portion of lift coming from the prop increases, while the wing's contribution decreases. The endpoint is a "hover" - a maneuver commonly done by 3D planes whose thrust-to-weight ratio exceeds 1:1. They're able to literally "hang the plane on its prop", so that the plane is essentially standing still with its nose pointing directly upwards into the sky. All lift now comes from the prop, and the wing is doing nothing at all (except counteracting torque, but that's another topic).

Somewhere in between horizontal flight and "hovering" is the harrier. The plane is pointing upwards, and some of the lift is being provided by the prop, but the wing is still contributing as well, so that the altitude is not necessarily changing despite the nose-up posture. Depending on their design, some planes will start to "wing rock" in this situation, as each wingtip stalls, loses lift, drops down, speeds up in doing so, recovers lift, rises up again... very unnerving. 3D planes are frequently measured by their ability to harrier without significant wing rock.

To get into a harrier, give the plane some up-elevator until you notice that it's pointing upwards without flying upwards. A certain combination of elevator deflection and motor power is required, and it's different for every plane. With practice, harriering can become one of the most entertaining and useful maneuvers. It makes the plane's speed drop, and that's obviously good for landing. In fact, a 3D plane can usually harrier at walking speed, or anywhere between a hover (no forward movement at all) and full horizontal flight speed. It's just a matter of varying the throttle and elevator input.

The T-28 can't quite get past a gentle harrier (not enough thrust + control surfaces are too small for drastic post-stall maneuvers), but it's fun to kick it up into a say 10 or 15 degree angle, and to watch it fly around very slowly and without any nasty wing rocking tendencies.

BTW, it's also best to steer with the rudder when harriering, and to use ailerons only to counter-act any tendency to roll away from wings being level with the ground. That's another advantage of learning to harrier - rudder technique gets a real boost.
Last edited by H2SO4; Feb 09, 2012 at 12:08 AM.
Feb 09, 2012, 10:11 AM
DX5e fatal flaw- PM me!!!!
BTW, learning to do nice landings on pavement with the UM T-28 (once you get the hang of the basics) will go very far in teaching you how to land a trike-gear trainer.

Dave
Feb 09, 2012, 11:44 AM
'tis nothing
shunyata's Avatar
Quote:
Originally Posted by marke14
...

Secondly, unfortunately (in my view) the landing gear must be removed in order for the T-28 to fit into its box. .
Cut out the box foam where the LG goes and it will fit into the box with the gear on just fine..

Don't worry about crashing. Tape and CA. You should see mine, it should be called the T-28 3M instead of UM.
Feb 09, 2012, 03:44 PM
Standing Athwart History
roo_ster's Avatar
I went from the Champ to the PZUM T-28 with little drama. I taped up the nose & wings before my maiden, but have not landed all that hard on either, so it still looks good.

It will dead-stick land all day long, so no need to power in for landing.

One thing: it is not as good in the wind as the Champ. Get a 240-260mah lipo for wind.

Best hop-up/mod is good quality high-C lipos.
Feb 09, 2012, 04:21 PM
RC pilots do it in the air
marke14's Avatar
Thread OP
I had my first two flights today - success! I am glad to report that, against all odds, it looks the same now as it did when I took it out to the field.

It was very unstable in flight - it would pitch up very easily, and seemed to roll all the time. Some trimming is definitely in order, and I had a few crazy loop-arounds and near crashes while I found the sweet spot for the LiPo to velcro on. However, I was able to fly two batteries' worth of time, did some tight turns, outside loops, and rolls! Good stuff. I had one less-than-graceful landing, but all landings were more or less horizontal and power-off (I've learned with the Champ!).

I also flew one battery in the Champ, oh man how easy and stable it seemed compared to the T-28! I am getting better with my inverted flight with the Champ, I really just can't say enough great things about this little airplane. The field where I fly near my house has an Astroturf-covered strip that is used for cricket, and I use that as my little runway. I did some RoG takeoffs with both planes, and several *perfect* landings with the Champ! Man, that is fun! You know you've hit it just right when you flare at the last moment, and the thing plops down gently and rolls out - you can hear the little squeak of the wheels as it rolls.

When I brought it home, I found that when at rest, one of the wingtips on the T-28 is higher off the ground by perhaps between 1/8 and 1/4 of an inch. I really don't know how to adjust this. I think this explains the tendency it has to roll, and contributes to the instability. Any suggestions on how to correct this, to even out the dihedral?

Afterwards, I played around with the DX6i and figured out the mixing - that took some doing (assisted with the "monitor" function in the menus), and I will be looking forward to trying that out. I mixed 15% up elevator and rudder with the ailerons, as someone suggested.
Feb 09, 2012, 04:37 PM
L'enfer c'est les autres
H2SO4's Avatar
Quote:
Originally Posted by marke14
I had my first two flights today - success! I am glad to report that, against all odds, it looks the same now as it did when I took it out to the field.
Congrats! It's quite an accomplishment to bring your first low-wing 4ch plane back home in one piece
Feb 09, 2012, 05:16 PM
DX5e fatal flaw- PM me!!!!
I have bent my UMT28 wings and tail and fuse horrifically, and I have always been able to trim it stable.

It will roll much better one way than the other, though.

Part of what may seem bad behavior is probably the degree of twitchiness the T28 has compared to the champ.

Also, any turbulence or gustiness in the wind will show up like someone yanking the controls, I have had mine roll quite a bit in a gentle breeze but with some turbulence.

Dave


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