Estes T25 Centurian REBUILD

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
George, thanks for your input. A few responses:

PITCH TRIM ISSUES - My problem tended to be flexing/kinking of the cable, which resulted in poor elevator response. Tended to be near the elevator or near the elevator servo. I used various guide tubes and gluing solutions, which helped. But none were as good as an improved elevator cable.

FLAPERONS - Thanks for the info. Was thinking of using them when very close to landing (about 1 foot off the ground), to slow the model down.
 
Now let's make a hole for the elevator servo:

m_IMG_0660.jpg m_IMG_0661.jpg

My finger is pointing to my first choice for servo location, but I found a spar! The second, large hole that I made was all foam.
 
And the Futaba 3114 servo, hot glued in place:

m_IMG_0664.jpg m_IMG_0665.jpg

Note that I cut a tab off the sevo, for it to fit at the right height above the boom:

m_IMG_0662.jpg
 
And looking underneath:

m_IMG_0663.jpg

3M Blenderm tape being used again. The hole in the fuselage is a bit large to allow the servo connector to pass through.
 
Ok, let's put the elevator back on.

Oh yeah! So glad to see you're going back to using the elevator and servo.

Defiinitely the original "S" snaking of the pushrod was a terrible thing, it is a wonder anyone who did it that way was able to fly it very well.

The servo in the wing, yep, prettier than the model I showed a pic of, with the servo outside on the boom. My concern was for possible weakening of the wing by cutting a hole for the servo. But as long as you don't use some crazy engine power in it to being the wing close to flutter speed, it ought to be OK.

So, I think you have a much better chance of this model flying well, for boost and glidem now that you've gone back to the original tail configuration with elevator servo.

See what you can do about setting separate boost and glide trims with your transmitter, sing a toggle switch (I like to use the Gear switch, forward/away for boost, towards me or "up" for glide) And possible changes to servo arm or control horn distances to the pushrod geometry as well. So as to allow for a wide range of trim travel while still allowing for plenty of control range (running out of up motion for glide sucks, as does running out of down range for boost. Any yes I've been there more than once).

When you are ready to install the pushrod, test fit first, tape the sleeve in place, attaching the pushrod to the elevator end. Then by hand, test for how easy or difficult it may be to slide. If it is not smooth and easy, try a different larger radius for the sleeve or possibly taping in a different location. When you find the smoothest/easiest, then glue it in place. I test for that with just about all my R.C RBG models, even when the pushrod run is mostly straight.

A model like this..... it's just not very effective to try to slow up with flaps. It'd need something like 2/3 of the center span for flap area, and 1/3 of the outer wing for the ailerons. Don't think it'd be worth the work or the extra mass, and in no way seriously suggesting doing so. What it does need is to land wings level so as not to snag a wingtip and ground loop. If someone built a new one....that would be an extra benefit of adding some "V" dihedral, tips raised higher so less chance of snagging a tip on landing (of course the aerobatics would not be quite the same).

Or, add some 1/16" music wire "whisker skids" to the lower fuselage sides (or along the wing roots at the fuselage junction) , about where one would mount main landing gear a bit behind the CG, but just using the wire skids and not wheels. Those could help the model keep a wingtip from digging in once a skid contacted the ground.

I was surprised to read of Mr Matt's message #30. For one.... that it sounds like he was the actual buyer of the Strato Blaster kit I auctioned years ago. The other, that the "tail blew off" when he let it get too fast by letting it fly horizontal a good bit on a G12 boost. Never thought about it. But it sort of makes sense given the possible flutter of the middle of the horizontal stab, with the speed that a mostly horizontal G12 boost might achieve. I never considered that possibility. But then I'd try to keep the model mostly vertical on boost anyway (or 60 degree climb).
 
Last edited:
From what I see it doesn't need to be a S curve control line. The top curve can be removed if the control rod is attached to the elevator via a ball link or link stopper placed some distance out on the elevator. That would give it only one kink in the line, half the resistance and better trim characteristics.

I may not be seeing it right in the pictures so let me know if so.


Richard
 
From what I see it doesn't need to be a S curve control line. The top curve can be removed if the control rod is attached to the elevator via a ball link or link stopper placed some distance out on the elevator. That would give it only one kink in the line, half the resistance and better trim characteristics.

I may not be seeing it right in the pictures so let me know if so.


Richard

You are correct. The new servo location eliminates the need for the "S" cable mechanism.

To defend Estes, these small servos did not exist when the T25 was developed as a kit.
 
Moving right along, let's install a Gold-N-Cable to control the elevator on the T25:

m_IMG_1321.jpg

"How do porcupines make love? Very carefully..."

The same thought applies to installing a Gold-N-Cable: Easy to install, and easy to screw up. Be very careful.....
 
Attaching a coupler to one end of the cable:

m_IMG_1323.jpg

Clevis is top left center; coupler (by itself) is top right center; bottom center is a coupler with the cable inside it. I attached it with 5 minute epoxy, but I need to go back and crimp it.
 
Let's figure out where the tube needs to be located. Here is the servo control arm, with the Gold-N-Rod clevis and coupler attached. I have the servo arm at the location that I want for the "centered" elevator.

m_IMG_1324.jpg

Next, I moved the servo arm fully to the back, with full trim adjustment. I want to figure the maximum movement:

m_IMG_1325.jpg

Once I located full aft movement of the servo, I marked the spot witha thin Sharpie marker.
 
Per the Gold-N-Rod instructions, the tube (that holds the cable) needs to be within 3/4 inch of the coupling.

m_IMG_1332.jpg m_IMG_1326.jpg

Then I taped the cable in place with 3M Blenderm. (By the way, oriented 2nd pic correctly on my computer. Don't know why is uploaded like that.)
 
Now let's work on the back section. First thing I did was sandwich the stabilizer and elevator between two sheets of plywood with a clamp. This holds the elevator still, without damaging the blendern tape hinge.

m_IMG_1327.jpg

Next, I attached the other clevis and coupler to the elevator control horn. I cut the tube to a distance I thought was right, then I installed the cable.

m_IMG_1328.jpg

Now I can cut the cable with enough spare length to fit inside coupler.
 
Keep in mind that the elevator servo is in the center position during all this.

m_IMG_1332.jpg

Next I put light amounts of epoxy on the cable, and inserted it into the coupler.

m_IMG_1329.jpg m_IMG_1330.jpg

Dang, look at all the propellant residue!
 
About time for me to do something Stupid, again..... :kill:

Ok, I misread the instructions. I used epoxy instead of crimping, and now my couplers won't crimp to the cable.......because of the epoxy (?). And I don't want to exert too much pressure while crimping, for fear that I might cut the coupler/cable.

I feel very confident that the epoxy will hold.

There, I said it; I feel better. :blush:
 
From what I see it doesn't need to be a S curve control line. The top curve can be removed if the control rod is attached to the elevator via a ball link or link stopper placed some distance out on the elevator.

You do not have the luxury of seeing the original plans and instructions.

The orginal it had the elevator servo inside the front of the fuselage. The elevator pushrod ran straihgt back near the wing root, then entered the wing and curved sideways inside of the right wing, then curved the opposite way ( "S" ) still inside of the wing, and exiting at a shallow angle from the airfoil near the top of the wing (parallel to the wing bottom) to go straight back inside the boom , and then the curve "UP" along the right rudder to connect to the elevator. So actually originally it was three curves, an entire "S" horizontally and then a shallow curve up. That played absolute hell with trying to get a smooth free-sliding pushrod as is necessary to avoid having problems with hysterysis.

So, eliminating the whole horizontal "S" curve from front fuselage to exit out the right wing for the boom, by locating the servo in the wing (or boom) is a major control system improvement. Leaving just the easier single upwards curve to deal with. Or a direct-drive servo on the stab, though that adds tailweight and with today's lighter radio gear the model needs noseweight to begin with.

Ok, I misread the instructions. I used epoxy instead of crimping, and now my couplers won't crimp to the cable.......because of the epoxy (?). And I don't want to exert too much pressure while crimping, for fear that I might cut the coupler/cable.

I feel very confident that the epoxy will hold.

Well, I would not trust crimping alone anyway (If I crimped, I'd put thick CA in it then crimp before it cured. Or if crimped dry, carefully apply thin CA and use accelerator before it could seep towards the pushrod sleeving). What I often do with that .030 Sullivan cable and threaded brass coupler is to solder the coupler to the cable. Using some good flux, and making sure not to get the threads messed up. But that has to be done first, can't do that with the pushrod installed as the heat would melt the pushrod sleeving and a slip of the soldering iron could damage other things close by. The epoxy probably will hold OK. You have not tried to crimp after the epoxy cured, right? If you did, then you might fracture the epoxy, or break the bond, and then it could slip. Sometimes when I do not use solder to bond the cable to the sleeve, I use thick CA, being careful to be sure to spray accelerator on the cable side of the coupler to be sure no CA ends to getting into the sleeving.

Do remember, nobody ever makes mistakes while building. The model I showed photos of, there is absolutely no 3/16" burn/melt hole near about an inch or so back from the tip of the fuselage nose, from a momentarily misplaced soldering iron. Nope, nope, nope..... :)

Key thing is to catch the potential flight safety/control/structural issues and fix before flight. Seems like you are OK.

Another bit of advice, I think I mentioned it earlier. When you are done and close to flight, do a lateral balance test to find out which side is heavier. Which on this model should be the side that has the servo and pushrod, the "heavier" side will have the wingtip dipped down from level, lighter wing higher up. Then add some weight to the wingtip on the other side (the high one), until it balances out evenly (horizontally). I usually use solder for the weight. Now, this is not actually a tip specifically for this model so much as a universal tip for all R/C models fabricated in a manner where both wings are not likely to weigh exactly the same (like built-up wings or vac-bagged composite wings), or there is some asymmetrical fabrication such as in this case the servo, pushrod, and even electrical wring running on one side but not the other. But this model definitely is going have one side heavier than the other and require it.

I do not recall if the original instructions mentioned that. It should have. Even with the servo in the fuselage, the mass of the "S"-ing pushrod system and patching back over the nasty "S" trench left on the top of the wing skin to provide access for the pushrod sleeving. And the fact that the home-skinned (weighted, or pressed, or vac-bagged) wing panels were not likely to turn out of equal mass.
 
Last edited:
Thanks for the explanation George. I had assumed it was similar to my Sophisticated Lady's T tail which has a bend up the fin then bends again to the horizontal. The horizontal bend explains Crawf56's comment about the servo location taking care of the situation. :wink:


Richard
 
Another bit of advice, I think I mentioned it earlier. When you are done and close to flight, do a lateral balance test to find out which side is heavier. Which on this model should be the side that has the servo and pushrod, the "heavier" side will have the wingtip dipped down from level, lighter wing higher up. Then add some weight to the wingtip on the other side (the high one), until it balances out evenly (horizontally). I usually use solder for the weight. Now, this is not actually a tip specifically for this model so much as a universal tip for all R/C models fabricated in a manner where both wings are not likely to weigh exactly the same (like built-up wings or vac-bagged composite wings), or there is some asymmetrical fabrication such as in this case the servo, pushrod, and even electrical wring running on one side but not the other. But this model definitely is going have one side heavier than the other and require it.

I do not recall if the original instructions mentioned that. It should have. Even with the servo in the fuselage, the mass of the "S"-ing pushrod system and patching back over the nasty "S" trench left on the top of the wing skin to provide access for the pushrod sleeving. And the fact that the home-skinned (weighted, or pressed, or vac-bagged) wing panels were not likely to turn out of equal mass.

Yes, I was thinking about lateral balance. My 3114 servo (in the wing) weighs 7.8 grams. Added a 7 gram weight to the other side, in the same location. Added a little hot glue, to try and give a similar contour for airflow.

m_IMG_1336.jpg m_IMG_1337.jpg
 
Also taking advice (from Frank and George), and programming my radio for a switch for "up" elevator:

m_IMG_1338.jpg m_IMG_1339.jpg
 
Putting velcro on the back of the 1s (3.7 volt) batteries. Originally using a 350 mAh Lipo; moving up to a 700 mAh Lipo.

mAh = "milli-amp hours"

This is a measure of the duration that the lipo battery can supply electricity.

m_IMG_1341.jpg m_IMG_1340.jpg
 
Last edited:
Well, an interesting day. :(

Here I am at the RC field, with my toys. Note my T25 and Pegasus rocket gliders at center left of the pic.

m_IMG_1379.jpg

And here we go, launch time for my T25. I am using as Estes E launch pad with a 1/4" diameter launch rod.

m_IMG_0678.jpg

I am using a D11-P with a D12-0 booster. I have used this setup about 20 times; works well.
 
So, LAUNCH!!! [Note the rocket shadow in the 2nd pic]

m_IMG_0679.jpg m_IMG_0680.jpg

The launch went perfect. The D12-0 did its job, then ignited the D11-P. Up and up, got to apogee, and I hit my switch on my radio to move the elevator to "glide" position.

I was stunned at how well the T25 was gliding. Then I made a critical error...........:eyeroll:
 
Ouch:

m_IMG_1383.jpg

What seemed to happen was that, everything was going fine, and then my T25 just spun in!?!

I was stunned and perplexed. How could a moment of beauty just turn into disaster? Oh, yeah, it's called "aerodynamics".

When I hit apogee, I was somewhat downwind. So, I turned into the wind, gliding great. So I turn to come back....and now I have a tail wind.

What I should have done was gone into a slight dive to gain airspeed. But I kept moving calmly along, until I slowed down enough that the tailwind took away my lift.

I am still a little perplexed that I could not pull out of the spin. But I was not that high above the ground, hence the damage being bad, but not horrific.

As bad as it looks........it's not that bad. I will consult with Dr. Frankenstein...... :flyingpig:
 
As I say to myself all the time, it's airspeed not ground speed:) Tail wind doesn't steal anything, we just let our airspeed get too low and stall because we are looking at our relative ground speed and don't have a stall buzzer....That's a total bummer though, tough day with the pad fire....
 
Last edited:
Man, so sorry to hear about the crash after solving the boost and glide control issues.

There are turns that happen to be made down wind, but the "downwind turn" thing is a myth.

If you were in a hot air balloon at 1000 feet and threw your glider outward to fly it down, and if the wind was 10 mph, to your perspective in the balloon you would be flying your model in calm. There would be no upwind or downwind. Meanwhile, the ground below is sliding by at 10 mph.

Some assumptions to that are no wind gusts, and no "wind gradient" (wind is stronger higher up, slower closer to the ground).

What usually happens is when standing on the ground and the model is downwind, your perspective of what is going on is not so good and the model accidentally ends up being slowed down too much and stalls. And IIRC that bird glides sorta fast so in a downwind situation it might be easy to let it get too slow airspeed-wise because the relative speed along the ground "looks" fast. Or, you bank and yank to try to make it turn quickly (not get farther downwind) and the angle of attack not only adds more drag to slow it more, but brings the wing closer to an angle of attack where it will stall at a faster speed than it it was at a lower angle of attack. The side-slip from a banked turn also could help trigger a tip-stall

Remember what I said about tip-stalling? What you describe sort of sounds like that. Try adding turbulator strips as I described before. Not a sure fix but more likely to help than to hurt.
 
Last edited:
To begin, I have decided that I should pay more attention to what George is writing. Turbulator tape has been purchased....

OK, the rebuild of the rebuild has begun:

m_IMG_1386.jpg
 
"Gentlemen, we can rebuild him. We have the technology."

And the epoxy. Especially the epoxy.......Z-poxy 15-minute is my weapon of choice in these cases.

By the way, always pick up ALL the pieces after a crash. It is amazing what can be epoxied back together.

m_IMG_1388.jpg m_IMG_1389.jpg

There is no way to "clamp" the nose back on, so the tail is sitting in a garbage can to help get the correct angle to keep the nose in place, while the epoxy dries.
 
Back
Top