75ax on Reactor 46?
 

I have a 55ax on the GP Reactor 46 but the engine does not seem to have compression randomly, mostly when it gets hot (at running temperature, set half a turn back from peak rpm with now cowl) and cuts at some point in flying. Now, why the engine doesnt have compression is another issue and I will fix it later by replacing the piston-liner set (engine hasnt been opened, most likely it wasnt run-in properly). For the time being I want to continue running the airplane with a 75ax. That specific engine is an older engine which did give me problems on another airplane but those could be tank height issues. I plan to achieve 2 targets b y using the 75ax- find out whether the 75 is reliable and continue flyng this airplane with a bit more power and throttle management in 3D

My question is - is the engine too big for the Reactor or should I go ahead and make the swap?

Ameyam

RE: 75ax on Reactor 46?
 

I wonder...if the engine cuts out on you in flight.....and it is turned rich 1/2 turn from peak.....how is the cowling? is your air exit big enough...at least 2 times the entrance...3 times better.....sounds like you may have a heat issue.......
Is the 75 too much...maybe......depends on the weight and ground clearance for the prop

RE: 75ax on Reactor 46?
 

I think the 75AX would be a good match for the Reactor. It is only about 5 ounces heavier. The Reactor has a low wing loading and will handle the extra weght with ease. i think the only issue would be how to mount it with the required large two stroke muffler. it would probably work well mounted at a 45 degree angle.

RE: 75ax on Reactor 46?
 

Running my 55 without cowl. Heat is not the issue. It loses compression when hot and after a few seconds regains it. We didnt run-in her properly last year, that could be the issue. I could rebuild with a new piston-liner but that would be expensive

My 55 is already mounted at the 45 deg angle, so mounting the 75 that way is no prob. The airplane can take a larger prop- 14x4 in its stock config. I was running a 13x4 on the 55 but had tested the 14x4. If a larger prop is required I will put in a set of larger wheels than the 2" Dubro rubber I am currently using.

I am also thinking, how about a 65ax? I dont have that engine- I have

1) 55ax- if I rebuild with a new piston and liner
2) 72a- it was meant for another airplane and was bought box damaged. It could be a little under powered as it would be equivalent to a 48 size engine
3) 75ax
4) FS91sII which is a very reliable engine and currently in another airplane. Its lighter than the 75ax (by 2.26oz or 64g) and has a little less power. It will require a rebuild of the Reactor becaust the throttle servo will not be in the correct place

So if the 65 is required, I will need to order it. Else I will need to take a call and put the Reactor into storage and take out the Phoenic Extra 60" with the 120ax which I am preparing for quite some time


Ameyam

RE: 75ax on Reactor 46?
 

I would try the 75AX before ordering anything new. I think it would be real easy to drop in the 75 and take it for a spin. Prop clearance will not be an issue. I am running a 16x8 on mine right now and it is fine with 2 1/2" wheels.

RE: 75ax on Reactor 46?
 

In the duplicate thread ( http://www.rcuniverse.com/forum/fb.asp?m=10397133 ) you mentioned that the 75AX was problematic on a different model, possibly due to improper break-in; and possibly due to tank height. Before installing it in any other plane you need to bench run it to be sure it runs correctly with a proper tank configuration.

I'd try that before spending $100 to repair the 55 or $210 to buy a 65.

RE: 75ax on Reactor 46?
 

I have already benched the 75ax when I took it out of that model. Only thing someone else did it in my absence, so I dont have the peace of mind that it ran without problems.

I agree with what you are saying, carrellh. I contemplated over it during the day and decided that the best thing to do is to put in the 75 on the Reactor and try it out. If it is still cutting out in this airplane, I have a $ 250 repair on my hands (that what it costs to obtain piston-liner assembly for both the 55ax and 75ax thru Indian customs) in which case I will put the slightly lighter and lot more reliable FS91SII in. And they all have the same mounting dimensions. That is still cheaper than getting the 65ax at $350 landed and there is the possibility that the 75ax may work in the first place so I dont need the spare parts or to pull the 91 out of its home. Thus I can skip the 65ax alltogether. So lots of possibilities, but I need to start with the 75ax anyhow

Ameyam

RE: 75ax on Reactor 46?
 

I think you are just not used to ABC type glow engines.

When the cylinder gets hot, the engine may indeed feel like there is little to no compression as the piston will slide far more easily in the cylinder.

You should feel some pushback because of the trapped air in the cylinder head, but this is still considerably less than when the engine is cold.

FYI: I have one well worn .75 Tower engine that feels like it has absolutely NO compression even when cold, but that engine remains a STUMP PULLER.... a very powerful engine.


The 55AX is perfect for that plane, you should NOT be trying to fix one problem by introducing another.

Fix the fact that the engine cuts out.

You likely have plumbing or pressurization issues, or you are still running the engine too lean in spite of what you may think is the proper setting.
You'll need to find what is to blame and deal with that.

RE: 75ax on Reactor 46?
 

taching it is the only way you'll find out if the motor is up to par. compare it with other's rpm readings..... if i recall correctly i was getting close to 13k with a 13x4 apc using a modified stock muffler with out baffle, and drilled out stinger(exhaust tip) and cut it slightly shorter

RE: 75ax on Reactor 46?
 

I have been grappling with this problem for over a month now. I have already replaced the fuel lines thrice and this time around I pressure tested the lines for leaks before I put them in and on the tank. So pressurisation problems can be ruled out.

No compression means no compression. I found that at that critical temperature, the prop simply turns over by finger. You dont even get the push-back you are talking about. Let it cool a couple of seconds and the compression returns. Loss of compressio seems to be happening a bit randomly. Remember I have already got black oil in the exhaust two or three times within 3 weeks and I have already checked to ensure that everything is as tight as feasible. When I take-off, it runs for a couple of circuits and then deadsticks. This is with the needle set rich and with the stock muffler and with a 13x6S2 prop doing only level flying. Both times this weekend I could tell that the engine was about to deadstick because I could hear the rpm wavering in the air. And everytime I heard the waver, the engine cut-off in less than a few seconds.

Think I have eliminated most of the variables. Please suggest if I have missed something, I will try that out as well. Point is, I want to replace the engine while I still have the airplane intact.

Still, if I do put in a 75 or a 91, I will use a lower pitch prop- 14x4 or so. I dont think a 15" will fit. And I am planning to use a Dubro anti-vibe beam mount I already have to prevent too much vibration stress on the airframe. In any case, I never use full rpm on my airplanes even at take-off as it is simply unnecessary- if you have sufficient take-off run it will lift itself at 60% throttle.

Ameyam

RE: 75ax on Reactor 46?
 

No it can't.

I've heard a bunch of people make exactly the same arguement with exactly the same "engine dying in flight" problem...

But I've found plumbing problems in about 60% of those situations... things which the pilot was SURE is correct, but it turns out there is a leak or some other problem.

Don't rule out ANYTHING until the engine is running correctly.

When warm you should feel some resistance at TDC if not, check your cap screws on the cylinder head.

I'll bet what is happening is that as the engine is getting ( overly ) hot ( because it is too lean ), the head expansion is letting air blow past the cylinder head, resulting in the low compression.

Get the engine to the point it does this then tighten down the cap screws.

It's normal to have to do this after the first few flights. The cap screws get VERY loose at first.


Which may mean you are burning too much oil, though some black oil in the exhaust is not unusual dependant upon the fuel you use.

What are you using? Synthetic or Castor?

A 13x6 on a .55 AX seems a bit big to me. I run 13x6's on higher power .75 2C engines. My .61's use 12x6 props.

Step the prop size down to what is recommended until you've resolved ALL problems.


While it is very likely running too lean, or leaning out in flight, it does not sound like the cylinder is seizing because of the heat.

Again check your cap screws when the engine is hot, all of them, but particularly the head screws.

Also did you rebuild the head at some point?

Is it possible you put things back together incorrectly?

Famous words often spoken right before a crash... you MAY have but never assume so until the problems are gone.

Another famous line is "Watch this!".... crash... :D

Until you've discovered the problem, introducing a new one ( e.g. a new engine ) may just make things worst.

The AX is a good engine and should not give you these problems unless something is amiss.

BTW: Look for nipples that have broken. Remove the nipples clean them and put a bit of thread lock on before re-installing.

Be VERY careful not to overtighten. They go on snug, but they strip very easily.

Also check the muffler nipple. Often it can become clogged with sludge, killing tank pressure and causing what you are seeing.

Put a smaller prop on the .55 AX. This will reduce the load and the heat build up. You may simply be running it too hot.

I use a laser temperature guage to make sure I'm not overloading my engines.

If the temp climbs above 310 degrees around the plug after WOT for 5 minutes, I KNOW I'm either running the engine rich or with too much load.

RE: 75ax on Reactor 46?
 

I already have a bubble-less clunk in the tank and the tank is well padded.

This time I tested the fuel lines both in the tank and going to the carb muffler and filler. Basically, I held them underwater and blew as hard as I could into the tubing with one side closed with a fuel dot. The tank does not have any leak.


Its not warm, its hot, sufficiently hot to burn your fingers when you try to choke. At that time there is no resisteance. I did tighten the head screws when I got the black oil. But I did that when it was cold. Any tighter will either strip the threads or slip the head bolt. This is not a new engine, must have already a couple of gallons through it.

The factory set for the HSN is 1.5 turns out or so. We rere running at 2-2.25 turns out. I was watching out to prevent it from running too lean. It goes out with a nice smoke trail

For a couple of weeks I was using plain castor because synthetic wasnt available. When flying last year, I was using Klotz 200 plain synthetic. This last weeks I was using klotz 100 which contains 20% castor blend. I have mainly used klotz based synthetic fuel all the time, used plain castor only one week

The manual recommends 12x8 or 13x6. I broke-in with a 12x8 but I cant hover with it. Then I moved to a 13x4 and was using it for the longest time. This past week, someone suggested that the 13x4 may be causing over-revving so I put in a 13x6 purely as an experiment. They are all MAS

Havent touched anything other than tightening it

Safe flying here. I wont test out any fancy moves unless having tested on the sim first and then will do them at good height



I had removed the carb a couple of weeks back and cleaned by blowing through the nipples. I used a tubing to blow through the nipple under plain alcohol. Then I removed the HSN and pushed the tubing into the hole and blew through that as well

I will try out the screw tightening bit, will just heat the head with a hair drier and then tighten. I will give it another last chance this sunday as one of the more experienced members on the field has offered to help me out to try and resolve the problem. I am sufficiently frustrated anyeay [:@][:@] If not, I will replace the engine

Ameyam

RE: 75ax on Reactor 46?
 

Try a 12x6 prop on it. See if that cures the deadsticks.

If it does tackle the hovering issue separately.

RE: 75ax on Reactor 46?
 

I did the remaining things- atrificially heated the head with a hair drier till the point I couldnt touch it. There was no loss in compression, it does that randomly. But, I tried to turn the screws, none turned, only the allen wrench slipped on the screw head (I am going to have fun opening it)

I replaced the fuel tank (as per the club member's suggestion) to a Sullivian 320cc tank (I had bought it last year after the deadsticking started). It is larger than what I was using so the CG will go off but if it works its worth adding a bit of tail weight later. I also put in an OS bubbless clunk as you suggested. Since the tank is soft, I was able to add extra padding everywhere so the tank is snug now (not that the earlier tank wasnt). This is now my most expensive tank setup yet.

I ran it at idle, thats about the most I can do at home. Its now nearly 12.30am, this is most likely the 10th or 15th consecutive day that I have sat up this late to set it up, I can do no more of this.[:@][:@]

I dont have a 12x6[&o]. Since the recommended is 12x8- 13x6, I have 11x9, 12x4, 12x8, 13x4, 13x6 and for other engines 14x4, 14x6, 14x8, 15x4, 16x8, 17x4, 18x6. Guess the remaining are too big. I had tried the 12x4 on an earlier 55ax engine and it screams (I dont have the baffle in, no scope to put that in now). There is no 12x6 in stock anywhere locally and I cant order from Tower or Singapore just yet. There is a 13.5x4 MAS Formula series, a 12.25x3.75 APC 3D prop, 13x6 APC pattern prop, thats it. So please suggest which to put in.

Ameyam

RE: 75ax on Reactor 46?
 

Opjose,

so should I get any of these props?

Ameyam

RE: 75ax on Reactor 46?
 

Try the 12x4.

The engine will rev higher, but the plane will seem to fly slowly to you.

Put in a flight or two and see if the engine deadsticks or produces the low compression you mentioned.

Thus far everything is pointing to an overheating engine.

The "black oil" is burnt synthetic or castor.

The loss of compression may be the result of too much expansion of the cylinder sleeve because of heat.

The engine should get up to about 280 degrees F, which will feel hot to you, but if the engine is properly cooled the prop shaft will only feel warm.

If the prop shaft feels hot, the engine is running far too hot.

If the 12x4 does not deadstick but you find the plane does not pull out of hovers, then try the MAS 13.5x4.

BTW: What is the all up weight of your plane fully fueled?

RE: 75ax on Reactor 46?
 

I have a 12x4, I will try that. Dont think there is much point in the 13.5 x4, remember I am flying with a 13x4 and now a 13x6. With the 12x4 my engine will positively scream but let me see.

I frankly have no idea what is the fueled or unfueled weight of the airplane, I dont have a weighing scale for that

Ameyam

RE: 75ax on Reactor 46?
 

a 13x6 is a pain in the rump to tune on that engine.....because that engine cant turn a 13x6..it overheats.....i bet that 12x4 will solve all of your problems
your engine wont scream on a 12x4....14000-15000 rpm isnt screaming, 16000+ is screaming
you should prop that engine around the 13000-16000 rpm range...the perfect seems to be about 13500-14500 on the ground to get the most amount of power
you will also have a huge improvement in fuel economy

RE: 75ax on Reactor 46?
 

Actually it makes a difference.

The lower pitch puts less load on the engine, which is what we are trying to accomplish!

A lower pitch will drop the load on the engine, but a smaller diameter drops it even faster....

So a 12x6 versus a 13x6 will present less load on the engine than a 13x4 versus a 13x6 prop.

As I previously said 13x6 is IMHO too large for that engine. Even my .75's will bog down with that size prop, which is just about right for a .75 and definitely not for a .61 let alone a .55AX as you have. All of your symptoms are consistent with too much load on the engine.

As Jimmy says if you want 3D capabilities try the 12x4. That will produce more thrust but less airspeed.

BTW: Get yourself a fish scale. Knowing the weight of a plane is a useful measure especially when evaluating or correcting behaviour.

A cheap fish scale will do fine, nothing fancy is needed.... you can also use them to measure thrust too!

RE: 75ax on Reactor 46?
 

i have a .55AX and it turns a 13x6 no problem. I use a 12x6 on it and it runs great.

It sounds ot me like there is a muffler pressure issue.  Which muffler are you using?

RE: 75ax on Reactor 46?
 

Hmm...

The OS .55AX is rated optimistically by O.S. for 1.75HP @ 16000 RPM... a figure that is impossible to achieve with the 13x6 prop.

A 13x6 prop spinning @ 11266 RPM would achieve the same HP rating.... something that is a bit unrealistic on the ground.

I wonder what you are turning with the 13x6?

Never-the-less he SEEMS to be having HEAT issues from what you can see in his above posts.... note the "compression" posts.

My first query was to his plumbing and he's already gone over it several times. He's using the stock muffler too which should be fine.

RE: 75ax on Reactor 46?
 

Its the stock muffler. When refitting the Sullivian tank on Tuesday, I accidently switched the muffler and carb lines, so when I went to pump in fuel, it came out through the exhaust, meaning the miffler nipple isint clogged. I pushed a piece of wire in any to clear it and it didnt seem blocked either

I am currently hunting a 12x6 prop (no one seems to have). If I dont get it, I will use a 12x4 and check. BTW, Sunday is "Holi" day (its the festival of colors), so I am not sure I willl be able to reach the field without getting painted myself. Let's see

Ameyam

RE: 75ax on Reactor 46?
 

Now if you could just get the plane to dump colored chalk on everyone! :D

Hobby-Lobby sells just such a thing with chalk "smoke" cartridges of different colors.

RE: 75ax on Reactor 46?
 

Opjose,

nice day of flying today. Had two flights didnt take the third to be a bit conservative because wind was picking up. Before the first flight, the club expert I was talking about tightened my cylinder head and the screws turned about quarter turn. I hadnt done this last bit of tightening because I was worried it would strip. Anyway, he did it and replaced the glow and put in a 12x8 I had and it remained operational throughout the flights till I cut it, so engine is OK.

Now that that the engine is sorted, I want to know of the setup. I hadnt set the CG and the 12x8 was too fast for landings. I also couldnt hold the nose up in hover. Even at full throws and the nose would fall forward. So which prop should I put in -13x6 or 13x4? Remaining things -cg, larger wheels etc I will handle and will report the dead weight as well soon

Ameyam

RE: 75ax on Reactor 46?
 

Glad you got it fixed. The 13x4 will definitely hover better and give you better pullouts to vertical. It will limit your top speed though, so if you want to fly any traditional aerobatics with the plane or fly in significant wind you will like the 13x6 better.