T-Rex

[Ed Keller]

Has anybody done a summary of the mods done to the T-Rex, so that all of the changes for strength & safety are in one place?  Ed

[Mike Callas]

From March 2010
I believe this is from Mr. Walker

"I was talking to Steve Fitton the other night on the phone and we got to talking about what I would do to take the T-Rex to the "next level" considering the way the first production run went (it was really much better wood than I anticipated).  If I were to take the standard ARC to "Nats" level what would I do?  It was a pretty short list really".

1.  Add the ply doubler extensions at the trailing edge if your version does not already have it .  The latest versions will have this installed.

http://stunthanger.com/smf/index.php?topic=16383.0


2.  Thoroughly soak the fuel tank area (all of the joints) with thin CA.  Paint the entire area with thinned epoxy.  Glass the F2 joint to the side walls or fillet with epoxolite or similar.  Also do the BACK of F2 (on the wing side the same).  Add 1/4" lite ply tripler to the back of F2 at the top of the wing airfoil (to butt strengthen F2 from the top).  Soak all that in CA.
3.  Thoroughly soak the end grain of the lite ply F2 all along the radius that will eventually be the bottom of the plane.  Just keep soaking it until it will not take any more CA.
4.  Add 1/32" ply for 1" at the flap root over the flap horns.  Sheet the stabs and elevators (as is) with 1/32" light balsa (per Bob Reeves).  Sheet one side at a time, allowing the flaps to dry on a flat board while the whole thing is weighted.   Butt join ply to new sheeting.  Glass the horn area with 3/4" glass at ply and balsa joint.
5.  Soak the flap and elevator control horn holes with CA and re-drill hole slightly oversized (so the horn is a little loose).  Join flaps and elevators on the flat board before assembly.  Use Gorilla glue as it will fill the hole and gets glues to steel better than anything.  The slop in the hole will make it easy to get everything flat.  Weight it down while it dries.
6.  I would buy new pre bent control horns and pushrods (complete with turnbuckle link in the back) from Tom Morris.  Buy the SHORTER 1.25" horn for the front and the matching slider horn for the back.  Tom has all the dimensions I have been told.
7.  Place each wing half on a flat board and weight down the trailing edge (or clamp down using a full length piece of hardwood on top).  Add vertical shear webs to the trailing edge full length and to the high point of the wing spars out about 5 bays.  After this the wing will now be straight and locked in straight.
8.  Join the wing halves in the same manner on the flat board per typical foam wing joining (I use masking tape to join and then lay the whole thing on a flat board and weight it down until the joint is dry.  DO NOT USE THE JOINERS!!! Glass the wing joint after gluing with 1" glass tape as per foam wing (go right over the bellcrank mount and nut).  After installing the wing in the fusealge use several layers of 3/4 oz glass faired out out (larger to smaller and smaller) at the cradle joints (some carbon tow inline to the fuselage over the joint might be even better). 
9.  Take the unfinished stab and note if it is flat.  If not, give one coat of Polycrylic and wait until it tacks off (it will take about an hour or less).  Place on teflon sheet, wax paper, or old Monokote backing on a flat board and place non stick surface on top.  Weigh the whole thing down.  Let it dry a week.  When you remove the stab it will be hard as a rock and flat as a board.  Finish as normal with whatever you like.  If you use film you may have to put a few coats of Balsarite over the PC.  Do not film on the PC, especially high temp film.  All other paints will stick great to PC.
10.  Re-bend new gear wires from US music wire to suit my propeller size.
11.  Use Dave Brown nylon engine mounts, or better yet OS Max aluminum mounts.  Use Sullivan hard 6 or 8 OZ tank only.  Cock the tank a minimum of 1/4".  Mount the tank as far inboard as possible.  I use velcro to mount the tank.
12.  Glass the nose 3" past leading edge with 3/4 oz glass.  Do two layers on cowl hole.  WRAP THE GLASS ALL THE WAY AROUND TO THE INSIDE OF THE ENGINE COMPARTMENT.  This is for the finger abuse the nose opening takes choking the engine.  It is not for strength.
13.  I would really like to get a magnet cowl retaining system like Bob Branch used for his electric but I am not sure this would work for IC engines.
14.  Cover all open bays with SLC film.  The film only needs to be about 3/4" larger than the open bay.
15.  Cover whole plane in 1/2A silkpan and nitrate dope (I might use Sig Plyspan again, it is so smooth).
16.  Spray two coats of nitrate with zinc stearate from Randy Smith and a little talc.  Sand.
17.  Use one coat of Sherwin Williams Ultra Fil on spots that appear to have trouble (fillets and such).
18.  Paint to preference.

That's about it.  Not a lot of work or extra expense really.  Should add about an extra 2 oz.  I see no need for other mods.

PS:  If you do not accurately measure the CG you cannot trim the plane. Period.

[Ed Keller]

Thanks Mike - For some reason, I could not come up with that post in the archives. Also, it seems that there is, or was, some differences in strength &/or quality from kit to kit, enough to cause an internal wing failure in a coulpe of these.  Regards, Ed

[W.D. Roland]

Shear webs and any extra spar material you can add is a must do!
Webbing the T.E. is a good idea also.
Go out past the landing gear attachment points with the beefing up.

The T-Rex is a good flying airplane that seems to want to do consecutive maneuvers in exactly the same place with little help form the pilot.

[Gerald Arana]

Here's me 2 cents on the T-Rex (Sorry Bradley) 
I think that ship is the WORST airplane I have ever put together.  In the first place you can't work on the engine.................Period! If I were to put together another one (And that'd be when hell freezes over) I'd cut that nose off and make a fiberglass cowl that attachs with screws so I could get to the engine. I didn't like the way the tank went in and YES I know these are all small problems but still; Why should it be like this?
 Also the rudder is to small............why not just put a P-47 rudder and be done with it? Looks like a P-47 anyway.

Jerry

[Steve Fitton]

Here's me 2 cents on the T-Rex (Sorry Bradley) 
I think that ship is the WORST airplane I have ever put together.  In the first place you can't work on the engine.................Period! If I were to put together another one (And that'd be when hell freezes over) I'd cut that nose off and make a fiberglass cowl that attachs with screws so I could get to the engine. I didn't like the way the tank went in and YES I know these are all small problems but still; Why should it be like this?
 Also the rudder is to small............why not just put a P-47 rudder and be done with it? Looks like a P-47 anyway.

Jerry

Ya know, that isn't very productive criticism you've got there, and some of it makes me wonder if you really had a 'Rex or not.  The cowling worked fine,  I had plenty of room and the tank installation was easy.
It doesn't have a P-47 fin and rudder because it isn't a P-47.  Its Brad's fin and rudder.
Whatever the plane's flaws, the cowling, tank compartment and fin and rudder would be down at the bottom of that list.

[Mike Callas]

Uh Hmmm....If I may,
The T-Rex with a few mods builds just fine. The engine compartment is huge. You can install a 2S, 4S or electric. Probably any motor combo will fit.

The sheer webbing in the wing is a quick fix. The doubler in the fuse is a quick fix. I added 2 diving boards to sandwich the fuse where the cockpit false floor is. I do not like interrupting the load path along the top of the fuse. I checked it across my knee (I know, very scientific).

As in any plane, check the wing incidence as if your life depended on it. I modified the saddle until I was satisfied with the wing stab relationship.

While my version came out heavy (69 oz with an Evo 60) it flies way better than I do.

I think most people will be satisfied with this plane. For a very small outlay, a few hours modifying some things, you will have a plane that casts a large shadow at the field, and leaves you with no excuses.

Best regards

Mike

[don Burke]

I think you hit the nail on the head about the "top and bottom".  To prevent the 'up down' failure due to the loop loading the best fix strength of materials wise is to add material to the top and bottom of the cross section.  Think of an I-beam, it's got most of it's material in the top and bottom flanges and a thin web holding them apart, i.e. the top and bottom of the fuselage.  Apparently in the case of the T-rex there's not much there with o-too-soft balsa turtle deck and a big split on the bottom.  I would add fore aft grained top and bottom plates balsa or CF plates that extended fore and aft of the wing TE.  Cross grain doublers would be adding zero bending strength IMO.  Also adding doublers to the fuselage sides is just reinforcing the web of the I-beam, helps a lot in lateral bending, but not so much in vertical bending.

[Dan McEntee]

  One question I have is why not use the wing joiners?  I don't have this kit, but if it was an engineered in part fo the original construction for strength and alignment, I don't see how a little fiberglass can replace it?
  Type at you later,
   Dan McEntee

[Mike Callas]

 One question I have is why not use the wing joiners?  I don't have this kit, but if it was an engineered in part fo the original construction for strength and alignment, I don't see how a little fiberglass can replace it?
  Type at you later,
   Dan McEntee

My guess is the wing joiner may place the wing halves in "less than-optimal" alignment. They are not very robust either.
And do not poo poo fiberglass. It keeps my Q500 wings together and they see a few Gs.

Why, right as I'm typing this, epoxy is curing the fiberglass wrap on my Shark 35 wing while in the background, Tyrone Power is bombing Berlin, singing "I've been working on the railroad".

Mike

[W.D. Roland]

The wing joiners that came with mine were about the strength of Styrofoam. serious!

The failure on mine came on a bounced landing. I heard a pop and figured it was the landing gear blocks knocked loose.
NOPE
The top spar, sheeting, 3/16 vertical web and L.E. cracked outboard of the outboard landing gear.

The wing incidence and the Motor(engine) mount on mine were way out of whack and needed work to bring all to zero.

As far as flying the T-Rex is damned good when out of trim and excellent when trimmed.
An excellent design suffering from Chinese production.

You can make the rudder larger but one day when the wind hit you just right you will be looking at the prop nut coming your way.
You can make a P-47ish rudder within a square inch of stock by shortening the rear of the fuselage about and inch
and closing the ends back up'

[don Burke]

  One question I have is why not use the wing joiners?  I don't have this kit, but if it was an engineered in part fo the original construction for strength and alignment, I don't see how a little fiberglass can replace it?
  Type at you later,
   Dan McEntee

Go back to my comment about the I-beam, or box beam.  The joiner or fuselage side is the web of the beam, the skins or top and bottom, the outer flanges, anything you add to the flanges is a lot more effective, mathematically the square of the distance from the neutral axis of the beam.  So fiberglass across the joint on the skins is going to help a lot.


 

[Steve Fitton]

Thats funny, I was watching Tyrone Power deliver a Havard to the RCAF earlier last nite, before I went back out in the shop to glass the center section of my new Dreadnought stabilizer, and Power went on to join the RAF.  It was fun seeing all those warbirds brand spanking new!  The details like loading the ammo cans for the .303 brownings was awesome  for the scale modeler!!

I didn't see how the T-Rex wing joiners could help in the wing structural areas that fail.  The wings I saw collapse failed just outboard of the center section sheeting, which is outboard of where the joiners terminate, assuming you used them at all.  The picture shows that the joiners go a good way, but notpast the center section sheeting.

The second picture shows where the trouble arose.  Note the (silkspan) covering rippling just outboard of the center section sheeting, including the leading edge sheeting moving independently of the center sheeting.  That plane is a friend of mines and I can assure you there is no dip or pucker in the juncture of the le sheeting and centre section sheeting of the wing when the plane is at rest.  The reinforcements and shear webbing described are to prevent the wing from bending at that spot.