Parkzone T-28 rebuild

[Gabe]

So I decided to rebuild my monster T-28. Bought all the foam and a new Power 25 motor. I bought some hinge tape and some cf spars for th elevator. If you recall, the elevator ripped off in mid flight last time.

Well, the hinge tape saved me this time. I actually ripped the elevator in half this time. Had enough control left to land it in the grass. Broke the motor mount in the tall grass, but other than that no damage. Turns out when I glued the spars to the elevator, I left a space right in the center because the clevis mount was in the way. Well, that became the weak point.

Note to self, run the spar the full length of the elevator with one piece next time.

[19000rpm]

Apr 13, 2010 7:55:55 GMT -6 Gabe said:

So I decided to rebuild my monster T-28. Bought all the foam and a new Power 25 motor. I bought some hinge tape and some cf spars for th elevator. If you recall, the elevator ripped off in mid flight last time.

Well, the hinge tape saved me this time. I actually ripped the elevator in half this time. Had enough control left to land it in the grass. Broke the motor mount in the tall grass, but other than that no damage. Turns out when I glued the spars to the elevator, I left a space right in the center because the clevis mount was in the way. Well, that became the weak point.

Note to self, run the spar the full length of the elevator with one piece next time.

You might want to consider using wood for the horizontal stab and elevator with that monster motor.

[Gabe]

Good point. I've never used wood before. Do I need to cut it out of balsa? Hinges?

[19000rpm]

Apr 13, 2010 14:00:54 GMT -6 Gabe said:

Good point. I've never used wood before. Do I need to cut it out of balsa? Hinges?

Yes, Balsa will work. I'd use either CA hinges or hinge tape on both sides. Use dope for paint. It will soak into the wood and make it harder.

I think you might want to add CF spars to the wings too and a piece in the verticle stab with more hingle tape on the rudder and ailerons.

[Gabe]

I'm with ya. I'll look into this on my next trip to my LHS. Still waiting for the motor mount and elevator to get here. It will be a few days.

Thanks 19K.

[19000rpm]

Sure thing Gabe.

Another way to strengthen the balsa, that I've heard about, is to paint it with a mixture of epoxy and alcohol. Maybe your guy at the LHS has some specifics on that.

Once you strengthen one area of weakness the stress gets transfered somewhere else.

Some other things would be to Gorilla Glue the Firewall and use an aluminum motor mount. If you just GG the firewall and use a plastic motor mount any break from a frontal impact will likely be in the motor mount. Which wouldn't be all that bad since they are cheap to replace. If you add the aluminum motor mount the break may go into the fuse someplace around the wing fuse joint but it will take a lot more force to break it there since there is plenty of foam to absorb the stress.

I've seen the aluminum motor mounts on ebay somewhere.

If the wing is at all loose consider GGing that as well. The pegs and screw attachment can come apart when you stress it in a big loop or roll at WOT.

[Gabe]

All good tips. I used epoxy on the wings last time in addition to the bolt. There's just too much flex for me to be comfortable. I think I will do that again this time. She's a beast, that's for sure!

[Gabe]

The elevator and the motor mount came in the mail today from Horizon. I opted to reinforce the elevator with cf rods instead of going with balsa (for now), only because I'm anxious to fly this puppy.

I went ahead and super duper carbon fiber reinforced the elevator. This is truly the weak spot, just like I thought. The center of the elevator has a small "V" cut in it so that it can pitch up or down around the vertical stab and rudder. Its extremely weak.

So I glued some CF to the elevator as before, but also put a piece across the center:





Then, I attempted to stabilize the flex in the elevator a little more by placing two small cf rods along the trailing edge of the V-cut:



I also put two cf rods on top of the elevator running perpendicular. I'm not sure if this helped, but it seemed to eliminate a tiny bit of the flex:



Next, I marked out wings on top for CF tubing. I used my soldering iron to melt the epp away. Man it melts quick and easy. I then laid a nice thick bead of CA in the grooves and set the rods. I added a little activator, and then finally hinge tape just to hold it all down:





Finally, the plank was extremely nose heavy from the Power 25 motor. I offset this a tiny bit by taping a large hex wrench inside one of the cheater holes and along the bottom of the fuse. The CG isn't perfect, but its a lot better. You can see it in one of the first pics I posted above.

I gotta say that there is virtually no flex in the wings at all. Oh, I epoxied them to the fuse too. I'm thinking I should all a little CF to the horizontal stab too.

Well, the winds are at 20-30 still and I got a local show to go to. I will report back tomorrow morning.

[19000rpm]

That's looking stout Gabe. I vote to add some CF to the horz stab and also the vert stab.

Glad you're addressing the CG. I assume you've moved the battery as far back as possible. I saw the wrenches and I'm concerned they're on tight enough. The G forces are going to be huge. Tape may not be enough.

Winds are ferocious here too. Rain mixed in. No flying since Sun. I'm in withdrawl. Boo, Hoo. Fortunately I've been saved from complete insanity by working on the new "Super Corsair".

[Gabe]

Thanks 19K. Actually, there's only one wrench and its in the first pic. Its HUGE. The small bend in the wrench goes up and inside the cheater hole (not shown in the pic). Its on the bottom of the fuse.

All the cf spars on the elevator are CA glued to the elevator. They also have hinge tape over each one just for safety's sake.

I did move the battery back as far as possible too without making any mods. It really needs to go back so far that it would be past the battery hold. I'm trying to think of how to mod the plane. Perhaps velcro straps like the habu has - but I'm not sure how to attach the velcro to the fuse and get it to stay.

As far as CF on the horizontal and vertical stabs go - its definitely going to happen. They are really the weak points right now. I may end up epoxying the vertical stab to the fuse to. Right now its connected by a few screws (similar to the Habu), so even if I put CF on the horizontal and vertical stabs, the weak point would then move to the joint on the fuse.

Its interesting tracing these issues down - kind of a fun little science project.

[Gabe]

UPDATED CF ON STABS:

I burned notches for and installed the CF tubing on the horizontal stabs. I ran out so I didn't get to install it on the vertical stab either:

Here's a few shots:






I also epoxied the horizontal stab holder to the fuse. That removed quite a bit of flex:



Since I was short on CF tubing, I thought I would center the spar on the stab. I think this may be a bad idea because all the force is now directed at the base of the stab when its deflecting - ultimately causing it to be a weak point (see pic below). I should have just run in from the base outwards as far as it would go. I'm still gonna test fly it, but I will need to pick up some new CF, remove the spar from the stab and go the extra distance:



----------------------------------------------------------

And just for kicks, here's two pics of the 12x5 prop on the plane. The other pics don't show how incredibly huge this prop is:

[19000rpm]

If you can, run a piece of CF through the center of the horizontal stab overlapping the other two pieces. It's going to want to break at the edges of plastic piece supporting the horizontal stab.

Check to see if you can get one of the battery holders that have the strap on it and glue it to the fuse. The use them in the P51. Then run a strip of velcro on the fuse running through both sides of the holder with the opposite side of the velcro on the bottom of the battery. You could also make the holder out of plastic.

Wow that's a big prop! Landings are going to need to be real good.

[Gabe]

Man it was good times today with this baby. I saved the full throttle punches for straight aways and babies her the rest of the time. She's a lot of fun. With the spoilerons on, high alpha is really a snap. As it starts to tip stall, a quick punch of the throttle and she's cruising again.

As before, the nose gear connection is really weak and snapped on my first not-so-smooth landing. A little glue and I was off. Totally greased the next one but it didn't hold. I epoxied it earlier today, I'll se how she holds tomorrow.

[19000rpm]

Apr 16, 2010 17:24:23 GMT -6 Gabe said:

Man it was good times today with this baby. I saved the full throttle punches for straight aways and babies her the rest of the time. She's a lot of fun. With the spoilerons on, high alpha is really a snap. As it starts to tip stall, a quick punch of the throttle and she's cruising again.

As before, the nose gear connection is really weak and snapped on my first not-so-smooth landing. A little glue and I was off. Totally greased the next one but it didn't hold. I epoxied it earlier today, I'll se how she holds tomorrow.

Sounds like fun. Only using WOT for straight and level should help to keep everything together.

Since your T-28 is a lot heavier with the bigger motor and battery the nose wheel is going to be overloaded. You'll probably want to re-engineer the mounting at some point.

What kind of speeds do you think it's doing?

[Gabe]

Yup yup. It will definitely need a little modification. As far as speeds go, I'm thinking 50 or so on the straightaway, but there's really unlimited vertical. The motor is so strong compared to the weight of the plane. Its really a fun little bird.

I'm also thinking about ordering two cheap gyros from Grayson and plugging them into the ailerons and then using the one I have from my Blue Ray for the rudder. High alpha would be a snap at that point. I've never used gyros on planes so it would be a cheap and fun mod - I think.