E-flite T-34 Mentor 25 ePTS RTF; An instructor's point of view
By Ken Myers
July 30, 2008

     The following is what I posted and what the link in the title will open.

From the Manual:
"It is recommended for your first flights to search out the assistance of a qualified instructor, who will help you through your first flights and assist you in the basics of Radio Controlled flight."

I am that "qualified instructor". I have read all 37 pages of this thread so far, and wished I had read them before I recommended this plane to a person who became one of my most recent students.

This plane has been a "pain" since our first outing at the field.

On the first day, there was no flying of the T-34 because the ESC would not arm, and on the very, very rare occasion when it would, it did not function "properly" and at WOT could only turn the prop at 5300 RPM. (Bad ESCs were noted in this thread.)

Thanks to a very accommodating manager at Rider's Hobby Shop, the whole fuselage, including a new speed control was "switched" for the defective one. The original fuselage, as received, had a hole in the side of the covering, as well. They did the whole switch and setup in the store. Great Service Riders!

Unfortunately, the second trip to the field had several problems as well, and ended with no stick time on the T-34 for the student.

The student kept the same canopy/hatch and it absolutely does not fit on the new fuselage. No, it is NOT the cowl that is keeping it from fitting, as noted in this thread. The black stripe on the front of the cowl does not line up with the one on the fuselage, which was only an indication of the &qot;real" problem. The canopy/hatch magnets do not line up and the canopy/hatch will not stay on the aircraft. His original canopy/hatch is slightly longer than the one that must have been on the new fuselage.
We did a field fix and used some rubber bands and a hook and loop strap to hold on the canopy.

The first time I took it for a "trim flight", I could do no trimming. The student had the flaps fixed at the maximum deflection and the wing has the droops on. Shortly after takeoff, and with the plane not at full power, it was climbing at what I perceived as a precarious angle. At first I thought it might be very tail-heavy. I had checked the CG against the recommended CG in the manual, which he had thoughtfully brought to the field, and the CG fell within the recommended range, but it sure was flying "tail-heavy." I tried to add some down trim, but I could not find the elevator trim lever/button. Somehow it did not naturally fall where I expected it to be, and with a "handful of plane" I could not look for it. I landed the plane to take a look. The battery had shifted a bit towards the rear. The battery was still under the provided strap, but there was no hook and loop fastener on the battery and the battery tray. We used an object that we had available to "hold" the battery in the farthest forward position.

On the second "trim flight" I made sure I could "find" the elevator trim lever. We also moved the flaps to the second position from maximum deflection. With about 10 clicks of down trim and a couple of clicks of aileron trim, the plane felt a bit more under control, but still felt like I was flying a balloon. It was very unnerving. While I had little confidence in the plane, it did nothing really odd, but just felt odd on the sticks. After that couple of minutes of flight, I landed and we checked the CG once again. It seemed okay and the battery had stayed in place with our field modification.

I took it up for one more "trimming flight", but it still had a "funny" feel to it. We decided to call it quits and see if we couldn't get some of the problems taken care of before our next session.

I told my student that I would check RC Groups and see what I could find out about this plane.

I found out, in this thread, that the default setup for this plane includes "Expo". Ah, the flying a balloon was explained. I'm not a huge fan of Expo and never use it, but I can understand, sort of, why the supplier might have set up this plane that way. At least now I know why I can't stand the way the plane reacts in the air. It is not the airframe. It is the transmitter setup.

We are now faced with a HUGE obstacle. I have absolutely no way to buddy box my student, and he will need it to successfully fly this plane. Our club does have the JR training box/Tx and trainer cord, which work with the Spektrum system, but the buddy box has none of the features that his Spektrum, by default, is setup with. I could get the appropriate trainer cord and patch cord to use my Hitec Eclipse 7, but that doesnÕt seem like a good option, since he won't be flying "his" transmitter and learning the "feel" of it.

For the time being, I can see the only solution to the problem is to set up his Spektrum as a "straight" radio with no Expo, dual rates or anything else that may not be available on our buddy box Tx. Therefore, I believe it would be better if the initial setup of the included Spekrum were set to a default of no Expo and no dual rates.

If I purchased a Spektrum system, I suppose that it would help, but I would never purchase a Spektrum radio. While I know they are extremely popular, I have very little respect for a company that knowingly markets a radio receiver that can "shut down" due to low voltage and not reboot in time to keep a plane from crashing. Yes, I know that is supposedly fixed now. I would never purchase a radio that has a fuse in it that is not noted in the manual and causes folks from all over the world to have to send their radio in to have a fuse changed, simply because it was never documented. Spektrum also marketed a transmitter charger that could not charge at the "expected" C/10 rate in the usual 12 to 14 hours and actually took (may still be taking) about 20 hours to charge. This led to many transmitter batteries being "under charged."
I have no idea whether the "fuse problem&qut; or charger problem have been "fixed", but they certainly help to demonstrate that this system was not ready for "primetime" when it was released.
I also realize that Futaba had a problem as well, and I wouldn't own one of them either, so I'm not "picking on" Specktrum/JR.

No, I'm not living in the dark ages, and I do realize that 2.4Ghz is the future, but not yet for me. Yes, I highly recommended the purchase of 2.4Ghz technology to those entering the hobby. I think it is a wise move. Unfortunately, it is kind of backfiring on me, as I will soon be working with another student who has just purchased a Futaba 2.4Ghz system.

As I type this, I believe that maybe the best solution would be for me to purchase a "trainer" receiver. I would put my "trainer" receiver in the student's plane, create a trainer plane in my Eclipse 7 memory, and use the student's 2.4Ghz as the buddy box. Just a thought. I'm kind of wondering how other instructors, who do not have 2.4Ghz systems, plan on solving this "problem." Maybe it is not a problem for anyone else as I may be the last troglodyte instructor left on the planet.

There is a problem with his charger. It appears to be working okay, sort of, but his does not have the alligator clips that are currently shown on the Horizon Web site for the supplied charger. His has a plug that goes into a "cigar" lighter socket in a vehicle! When I saw him charging his battery on the seat of his $30,000 plus SUV I couldn't believe it.
We have now gone over how to safely charge Li-Po cells. He's going to add some alligator clips to the charger and charge outside his vehicle in a "safe" container. I just can't believe it came with the "cigar" lighter type connector attached to it.
I noted that the supplied charges seems to be "working okay" because when his charger says the pack is full, my CellPro 10S indicates 94% charged. I guess this is a "conservative" charge, set by the supplier of the supplied charger.

I realize that many of these issues are MY issues, but I am still not very happy that I recommended that he purchase this system. It hasn't started "working" for us yet.

Fortunately, my student has gotten many flights on the EasyStar RTF that I bring with me to the field whenever I'm working with new students. He's doing very well with it now, and not lost total interest in this hobby, yet. I am determined to make this T-34 work for him/us, but the frustration level for both of us has been quite high.

Still, any day at the flying field is better than any day anywhere else.

The following links are responses to my post, as well as follow up posts that I made.

Sort of agreement

Agrees about quality control lacking at Horizon Hobby

Couldn't understand the buddy box problem

Didn't understand the buddy box problem - says some less than helpful things

Thinks its fine plane but not a trainer - had same ESC problem

post by me stating what is in the manual for the supplied radio

I restated what manual said and asked poster Smacka why he'd not respond to some of my comments

Still talking about the buddy box problem.

Discussion of problem with the NiCad charger for the DX6i

Poster Smacka responds that my comments were an "absolute crucifixion" of the T-34 PTS


Before I continue with the saga of trying to use this plane as a "trainer", I am inserting these comments on September 15, 2008.
1.) Almost all of the comments in the thread regarding the design and "flyablity" of this plane are very positive, but over 95% of the "flyability" comments to not relate to this plane being used as a trainer. Most folks are flying it as a stand-off sport scale plane.
2.) Read through the whole thread and you'll find instance after instance of poor quality control; failing ESC's, holes punched through the fuselage by a loose battery during shipping, prop adapter/spinner problems, hatch/canopies that depart the plane in flight, and lack of repair parts.
3.) It appears to be a "good" plane/design with teething problems.


In one of his posts, Smacka suggested, "I would like to see you step back and give it a week or so for you to calm down. Then read your post again. I'll bet it will change."

That's what I did.

On Saturday, August 2, Jim Young took up the plane for a flying CG checkout and trim flight. 4 oz. of nose weight had been added and hook-and-loop fasteners added to the battery and battery tray to hold it securely in position, as it should have been in the first place. It should be noted that the battery tray broke loose from the airframe in one place when the hook-and-loop fasteners were pressed into place. Some CA took care of that problem at the field.

Jim flew the plane around a bit to get the feel and then performed the dive test to check the CG. With the battery as far forward as physically possible and 4 oz. of nose weight it appeared to be just about neutral with an ever so slightly tail heaviness, not exactly the best for training. Several more dive tests were done, with the same results. Remember that the flaps are fixed and the droops on.
If you are unfamiliar with the CG check using the dive, it is describe here by my flying buddy and friend, Keith Shaw www.theampeer.org/shaw/SHAW4.PDF and can be found on the fourth page, in the right-hand column.

I believe that flying the plane with the flaps extended, as suggested in the manual for a beginner, changes the relative CG, and this was not taken into account in the design and equipment placement for good "balance". The NACA droops do compensate for what happens, but it makes the plane a bit harder to control, especially for a beginner.

After noting that the CG was "better", and with a fresh charge on the battery, I took the plane up, got the feel of it, and my student got a few seconds on the stick several times. The wind had come up a bit after our second flight, so we decided to hold off on the training using the T-34.

On Sunday, August 3, I met my student at the field in the morning and we had two flights where HE determined that the plane is too much for him right now, since we can't buddy box it. We continued to "train" on the EasyStar RTF.

The buddy box still continues to be an issue for ME.

On Tuesday, August 5 at 11:18 a.m. I sent an email titled "Spektrum DX6i Buddy Box Question" to productsupport@horizonhobby.com


I tried calling tech support with this question, but that was a bust. That is some horrible, loud music you have on that line while a person is on hold! Guess that is just to keep folks from holding too long.

Hopefully someone will have an answer via email.

My RC student has an E-flite T-34 Mentor with a Spektrum DX6i. In the radio manual it says that it can only be buddy boxed to another DX6i. Is that correct?

If not true, what other transmitters can it be buddy boxed to? What buddy box cord(s) can be used?

Thank you,

Ken Myers"

Yeah, I know, that part about the music was rude, but if youÕve ever called Horizon Hobby tech support, you know what I mean! The music is so loud that it was overdriving the little speaker in the earpiece of my regular house phone. I know, take a breath, count to 10. You can catch more bees with honey than vinegar.

No response yet on Thursday, August 7 after 11:18 a.m., which is 48 hours later. I know they receive the email, as I received an automated response from their system.

In post http://www.rcgroups.com/forums/showpost.php?p=10263290&postcount=589
Smacka said,
"So, with tongue in cheek, your post is an absolute crucifixion of the Mentor T-34 PTS. I believe (my opinion only) it to be exaggerated and unfair. You recommended that your student purchase this plane. Something made you recommend the purchase. Then, you took the entire release of the aircraft personal because you believe it to be beneath your standards...to the point that you were regreting endorsing the plane to a brand new student."

Everyone is entitled to his or her opinion, and I sincerely respect his, really, but I do not believe that what I stated was an "absolute crucifixion" of the Mentor T-34 PTS.
My original recommendation to my student was based, somewhat, on how the plane was advertised and my students desire to purchase that plane. I had misgivings, and they've proved themselves to be true.

Here is a summary of what I said in my original post
1. ESC would not arm - taken care of by local hobby shop by swapping for new fuselage with new ESC - others have noted problems with the ESC
2. Original fuselage had a hole punched in it during shipping due to the unsecured battery hitting it - fuselage replaced as noted above Š- others had noted problems with the loose battery causing damage
3. Original canopy/hatch would not fit correctly on new fuselage - again, hobby shop replaced with canopy/hatch from second fuselage and all was well. While this is NOT the canopy/hatch problem noted here by others, I mentioned it because it shows a problem with duplicating parts that I thought others might be interested in.
4. I had a problem locating the elevator trim tab on the Specktrum radio. I own and fly Futaba, Airtronix, and Hitec radios. I've flown several off brands with and for other students. I was just noting that the trim was more difficult for ME to find than on other radios, and it might be for others.
5. I thought there was a CG problem when full flaps are deployed for flying, and from our recent tests, this seems to be the case.
6. The battery could move when only the provided strap was used. It could, and we fixed it with hook-and-loop fasteners.
7. The default setup for this plane includes "Expo". While others in this thread have said this, I did find this to be NOT TRUE with our example. There was no Expo preprogrammed in this example. Sorry - I was wrong with this one.
8. We are now faced with a HUGE obstacle. This was in regards to the buddy box "problem", which has still not been resolved.
9. I gave my reasons why I would not purchase a Spektrum - just my opinions. My unwillingness to purchase a Spektrum DX6i is exacerbating the buddy box problem. Maybe I should or should not have shared my feelings, but I feel that there should be views given about products and others can take them of leave them as founded or unfounded.
10. There is a problem with his charger. I've provided a photo of his charger. I still believe it to be a serious problem.
Other posters haven't brought up the safety issue with the supplied charger but they have noted that it is not very good at charging their packs. I usually need to "top" and balance my student's pack after it has been charge on his supplied charger using my FMA CellPro 10S, so that is most likely a true statement.
11. I am determined to make this T-34 work. I still am, it will just be a while.

Again, I say, I don't believe I have crucified this model, I've simply pointed out several facts, one of which I noted was in error, and I have given my opinions.

I am not a dealer or hobby shop owner and I don't have any connection with Horizon Hobby. I have no axe to grind with Horizon Hobby or E-flite. I have never been "done wrong" by anyone connected with either organization. I have nothing to gain or nothing to LOSE by letting others know what I believe that I have learned about this plane and its use a trainer for a beginner.

I believe the videos, and posters when they have responded, showing and telling how well this plane flies. All I have been trying to point out is that it is not working for us as a basic trainer with an instructor, as advertised.

On August 21, 2008 I did receive a reply from Horizon Hobby about the buddy box. It read, "Thank you for your recent email.

The DX6i can be buddy boxed with any computerized JR or Spektrum transmitter using a Spektrum or JR trainer cord. If you have any further questions please feel free to give us a call at 1-877-504-0233.

Chris Puckett
Horizon Hobby
Product Support Team"

September 15, 2008 Update:

Chuck and I finished setting up a flap servo yesterday in the T-34. We are anxious to get this bird back out to the field and try it again. We may also have a buddy box to use as one of my other flight instruction students now has two Spektrum transmitters.

Update, Sept. 17:

Back on July 30th I posted how I felt about this plane as a trainer. (see comments at beginning of this article)

We've been able to take care of the buddy box problem that I mentioned because one of my students now has two Spektrum radios, so we can borrow one to use with the student who owns this plane.

Very few of the posters in this thread have used this plane as a teaching tool and tried to use it with the fixed flaps and droops. The majority of the folks are flying it as a "sport" plane and they've noted how well it flies.

We finally got a flap servo installed, and I must absolutely agree that this plane is delightful to fly!

I still feel that flying it around with the flaps "fixed" makes this plane much harder to fly and train on than with the flaps up. Of course, that's just one person's opinion. The bottom line is that we are going to be able to now progress using this plane.

The only "problem" that we have now is that it takes so long for my student's Li-Po to charge on my CellPro 10S, which is much faster than the supplied charger, that we can't get many flights at the field during a given flying session. That little glitch should soon be taken care of as I'll be making him a 4S "A123" pack for this plane. Hopefully Horizon Hobby will take care of the real "teething" problems with this plane soon, as it is a "winner".

The Saga of the E-flite T-34 Mentor 25 ePTS RTF Continued
October 2008

     As I mentioned in October 2008 issue of the Ampeer, one of my flight students has this plane. He decided that he wanted to use the 2300mAh cells from A123 Systems, Inc.
     I brought the plane home to build him a pack. It was the first time that I had spent a lot of time with this plane, besides at the field, trying to fly it.
     The first thing that I discovered was that the bottom two bolts from the motor mount were protruding into the battery compartment. They protruded into the battery compartment about 5/32". In the event of an unanticipated arrival (crash), folks using Li-Pos might have wished they had looked before they crashed and punched in their battery with a protruding bolt! A few minutes with a cutoff wheel and grinder shortened the offending screws.

     Next, I made an adapter for the power leads of the E-flite 40-Amp Pro Switch-Mode BEC Brushless ESC so that Anderson Power Poles (APP) and the original connector provided by E-flite could both be used.
     I also mounted the electronic speed control (ESC) switch on the outside of the fuselage so that it wasn't just dangling inside the airframe. It is quite a bother when they provide a switch but no faceplate and screws!

     The next task in converting to a 4S1P "A123" pack was to get the correct center of gravity (CG). We had added 3.67 oz./104g of lead stick-on weights to the top of the motor mount box, and the plane was flying "sort of okay", but I wanted to try and get the lead out by using the heavier cells and knowing the correct center of gravity (CG). The supplied 3200mAh Li-Po pack weighs 8.78 oz./249.05g and the new "A123" pack 11.34 oz./321.5g.
     I drew half the wing plan form onto some paper and calculated the CG. Using the mean aerodynamic chord (MAC) I found the CG to be between 4" and 4 3/8" back from where the front of the wing leading edge protrusion seats in the wing saddle. The provided manual says that the CG is 4 3/4" to 4 7/8" from that point. No wonder that on the first flight of this plane it went up like a rocket. It wasn't just that the flaps were in the fixed down position. (To read about the initial flights and problems with this plane, see http://www.theampeer.org/t34/t34.htm or the October 2008 Ampeer.)
     Once I knew the CG that I wanted to use, I could then decide on the configuration of the 4S1P "A123" pack for this application. Wanting as much weight forward as possible, I chose a 4S1P side-by-side.

     The "A123" pack uses VelcroTM on the bottom of the rear cell and a balsa wedge to hold it in place. There is very little room in the battery area for the cells to move side to side. That means it is a TIGHT fit!

     Drive Calculator (www.drivecalc.de) did not have the supplied E-flite Power 25 BL Outrunner Motor, 870Kv motor in its database (I've since added it), but I used another typical outrunner of about the same weight and Kv that E-flite says the 25 has to estimate what prop I might want to use. It looked like an APC 12x7 sport could work with the supplied 40-amp ESC, especially if I lowered the timing of the electronic speed control (ESC).
     I mounted an APC 12x7 sport prop and then balanced the plane. The plane balanced just slightly back of the 4 3/8" point, so I had gotten the lead out and the CG about where I wanted it. Unfortunately, the APC 12x7 sport prop that I had on hand had already been reamed to 8mm, so I had to purchase a new prop before I could test the power system using that prop.
     While it doesn't sound like I did much, it took a full day, 9 to 5, to get the plane to this point.
     The next day I went to the local hobby shop and picked up an APC 12x7 sport prop and an APC 12x8E prop. I already had a new APC 12x6E, which is the prop that Jon and I are using on his E-flite Cub with the same power system.
     After I returned home, I balanced the three APC props and the supplied E-flite 12x8 prop. I was very surprised to find that the supplied prop was the most out of balance of all four of the props. It has usually been my experience that APC props are more "out of balance" than other brands.
     I changed the timing to the lowest possible (timing.htm) and the low voltage cutoff (LVC) to allow for the "A123" pack's lower LVC on the provided ESC. I found that the lowest timing available was 5-degrees and lowest LVC setting was 70% of the starting voltage. After downloading and reading the directions for the E-Flite 40-amp Pro, it took a while to catch on to the fact the E-flite 40-amp Pro uses the center throttle position as the "menu" and full on throttle position as the selection control. Changing the LVC proved challenging as the selection starts at 3 tones for a 3S Li-Po and continues through 6 tones for a 6S Li-Po. It was supposed to be 7 tones for the 70% cutoff, but it played a "jingle", not 7 straight tones. Maybe it was 7 tones, but it was very hard to tell, but I believe that I got it. There is no confirmation of the LVC setting when the ESC is activated. We have not experienced any premature cutoff to date.
     I did not want to remove the motor from the airframe, so I did not do my usual drill press test to find the Kv. To test the motor, I did my usual 5 captures of data on my Emeter and used the averages to put into Drive Calculator to create the motor data that is now available in Drive Calculator.
     Some Things to Keep in Mind When Looking at My Data, or Anyone Else's Data
1.) When using brushless motor systems, the motor and ESC used cannot be separated for efficiency claims. The specific ESC and selected timing is part of the motor.
2.) The ESC brand, amp rating and timing all affect the outcome of the observed and recorded results.
3.) The altitude of the static test site, ambient temperature and other local weather conditions affect the results.
4.) Props vary. APC has changed their props over time and not noted it to the end user.
     The bottom line is that your results WILL vary.

     This motor was static tested on a sunny day with the ambient temperature being about 70-deg F/21-deg C. The elevation here is about 980 ft./298m above sea level. The ESC was the supplied E-flite 40-Amp Pro Switch-Mode BEC Brushless ESC was set to a 5-deg advance. (The standard timing is 15-deg.) The numbers presented here are averages for five captures approximately 5 seconds apart.

No Load 1: 9.924v, 2.09 amps, 8688 RPM
No Load 2: 12.512v, 2.516 amps, 11022 RPM
E-flite 12x8: 10.646v, 37.002 amps, 7302 RPM
(Used fully charged 3S1P 3200mAh 15C supplied Li-Po)
APC 12x7 sport: 11.218v, 35.558 amps, 7878 RPM
(Used fully charged 4S1P 2300mAh "A123" pack)
E-flite 12x8: 393.97 watts in, ~73% sys. eff., Pitch Speed ~ 55.3 mph, 73.4 watts in/lb.
APC 12x7 sport: 399.23 watts in, ~74.5% sys. eff., Pitch Speed ~52.2 mph, 74.6 watts in/lb.

     The following day I did the weights and measures and came up with the following information.
Wing area (without droops): ~555 sq.in.
RTF weight (w/supplied Li-Po): 85.88 oz./5.37 lb.
RTF weight (w/4S1P "A123"): 85.65 oz./5.35 lb.
CWL (w/supplied Li-Po): 11.32 oz./cu.ft. (typically advanced sport)
CWL (w/ w/4S1P "A123"): 11.29 oz./cu.ft. (typically advanced sport)
Wing Loading (w/supplied Li-Po): 22.24 oz./sq.ft.
Wing Loading (w/ w/4S1P "A123"): 22.18 oz./sq.ft.

     The weights and power are just about equivalent and produce a stall speed of about 17.5 mph and a pitch speed to stall speed ratio of about 3 to 1.

Chuck's T-34

Some Final Thoughts

     From the threads on RC Groups about this plane, it seems that most of the folks purchasing this plane are not using it as a trainer.
     If I were to purchase it for sport scale use, then I would most likely use the Scorpion S-4020-12 power system that I reviewed October 2008 Ampeer.
     Using the noted power system would increase the RTF weight to about 103.3 oz./6.46 lb. The CWL would be increased to about 13.65 oz./cu.ft., which is still typically advanced sport. According to my data for the Scorpion motor from last month, a 6S "A123" pack would provide a little over the following for an APC 14x8.5E; 16.65v, 38.3 amps, 7500 RPM, 638 watts in. The watts in per pound would then be 98.76, with a pitch speed of 60 mph. The stall speed would increase to about 19.2 mph, still giving it about a 3:1 pitch speed to stall speed ratio, but with the larger, more efficient, diameter prop, the vertical maneuvers would increase in size and duration.

To Reach Ken Myers, you can land mail to the address at the top of the page. My E-mail address is: KMyersEFO@theampeer.org
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