ameyam

This refers to my earlier post where I had similar problems with a 55ax.

I have a 75ax in a Reactor 46 with a 14x8 prop. I am running klotz 100 (synthetic-castor 80-20 blend) with 10% nitro (basically, 1 bottle of the klotz which is about a litre mixed with 3.5l of methanol and 500ml of nitro). The engine in question was out of use for quite some time, its been run-in and then washed in plain alcohol and thoroughly oiled before it was put into storage and runs fine otherwise. Am using a 240cc generic make tank with a single normal clunk and 3 line system. Using Dubro regular tubing which I have pressure tested beforehand to eliminate tank problems. The manual recommends 2-2.5 turns for the HSN and 1.5 turns for the LSN as rich for starting.

Couple of weeks back I started with the 14x6 with the needle 3 turns out for the HSN and 1.7 turns for the LSN. The idle was quite OK, I left it there. I found that the peak RPM was about 2.5 turns of HSN so I set it about 2.8 turns for the HSN. When flying without cowl I didnt experience too many problems but I did very little hovering, mostly pattern at that time

Didnt fly last week

This week on Saturday after refitting the cowl, I noticed it lost power in vertical every time I tried to hover. Ultimately I had a deadstick and had a hairy-scary landing but no damage.

Though the cowl has a lot of cooling holes (both inlet and exit), I decided to fly without cowl anyway today. I tuned the engine with a colleague holding it vertical (I couldnt do that yesterday) and it tuned at 3.2-3.3 turns out. Again, I lot a bit of power in vertical but it didnt deadstick and I did the 10min flight. Someone suggested to give it a tank of run-in on the ground just in case. When doing that I went in and out with the HSN from upto 4 to 2.8 turns. After a couple of minutes at full throttle when I idled, she cut. I immediately noticed that there was no compression (or very soft compression). We realised the thing was very hot, you could feel the radiant heat sitting in front of the model even though there was a good breeze and it was too hot even to touch. Interestingly, I had exactly the same problem with the 55ax. I didnt have the instrumentation to measure the temperature today

Do you think that 10% is too much nitro? My colleague is flying with 4% nitro and his airplane flies OK but his batch was finished, so I couldnt test it today. This was actually my 4c mix which I am using on all my engines. Outside conditions are at about 38 Deg C so its very hot to begin with

Point is, I have about a litre of fuel left in this batch. The next batch I can drop the nitro content. Or I can brew a fresh batch with no nitro and add in this remaining fuel which will give me about 2% nitro effectively. Alternatively, I can brew a whole seperate batch with about 2-4% nitro so as to elminate all problems. Please suggest

Ameya

jester_s1

If you are losing power in the vertical you are too lean. That would also contribute to the heat. To help with cooling, you may need to put some baffles in your cowl to direct the airflow over the cooling fins of the engine.

ameyam

No, it overheats even now when I am flying it open

Ameyam

TexasAirBoss

My Feedback: (22)

I run an APC 13X6 on mine. Runs great, stays cool. I think a 14X8 is just too much prop.

HighPlains

My Feedback: (1)

Way way way............................................... .................................................. .................................................. ...........................way too much prop

vertical grimmace

My Feedback: (1)

Yep. reduce the load.

ameyam

this is a 75AX. The manual recommends 13x10, 14x6, 14x8, 15x6

Ameyam

jester_s1

Have you measured the RPM with your prop? You should be able to get 12k or so to get into the engine's powerband. Less than that and you're lugging it which will create more heat and also hurt your overall performance.

HighPlains

My Feedback: (1)

It would take engines in the .90 to 1.20 size to run those props.

I don't know why OS recommends these ridiculous props sizes for engines. Either it is a way to make low noise requirements or a very silly marketing strategy. With people checking specs on engines, they may think that saying they operate on the big props must mean they are stronger engines. Pure bunk. If they were torque monsters then they would have very long strokes and small bores, known as a "under square" design.

ameyam

Issue is couple of weeks back when I started I was thinking exactly the same. Hence I started wit a 14x4 and after I took off, we could hear the high pitched sound of the engine overrevving. My 14x6 is on the FS91SII so I put in a 14x8. Dont think that the prop will make that much difference. Remember, I have the very same problem with the 55ax before this and I used all props from 12x4 to 13x6 (12x4, 12x6, 12x8, 13x4, 13x6) but couldnt resolve it. Was using the same batch of fuel though

Ameyam

Hydro Junkie

Sounds to me like you're running way lean. You have to remember that the fuel does three things, it lubricates, it burns AND IT COOLS THE ENGINE. If you're getting that hot and using a smaller prop overrevs the engine, richen it up and try again. You could also add some alcohol and oil to what you have and try it as well. By adding enough oil and alcohol to double your quantity, you will reduce the fuel to between 3 and 5%.

ameyam

Hydrojunkie,

thats the idea except that the Klotz based fuel is very expensive to do trial-&-error with. What I am contemplating is making a batch of fuel with no nitro what-so-ever. If I continue to have overheating problems with that, the problem is somewhere else. I can always add in nitro later if I want.

No ways I am running rich. Like I wrote, the LSN needle is supposed to be rich at 1.5 turns out from carb closed and this is at 1.7 turns (intentionally). The HSN is supposed to be rich at 2.5turns out. But I have had this problem of overheating at 4 turns out, so neither of those are the reason. I am considering flushing my carb with fuel just to get out any grit that is stuck. Again issue is one of the screws that holds the carb has stripped and I dont want to risk the other. As yet there are no air leakages, engine cuts when the kill switch is pressed

Again its not under propped, 14x8 is the manual recommended prop.

Will test out the non-nitro fuel and then report. May be one of my fellow fliers has fuel with no nitro

Ameyam

Mr Cox

If your engine even runs with the main needle at four turns out, you most likely have an obstruction of fuel-supply somewhere, or a too low tank etc.

You should always set the needles by listening to the engine, the factory recommendations does not mean anything as you have just proven. If the engine runs hot, then it is set too lean for the prop and fuel that you are using.

ameyam

Thats what I was thinking too. At work right now, will go home and open up the HSN carb side and clean it out with a thin wire. I will also hold it under alcohola nd blow hard into it. That should dislodge anything that is stuck. It is very unlikely that anything that is stuck is a recent problem. For the last couple of years I have been using a bubble-less clunk and an inline filter on my fuel pump but this engine was last run before that time

By the way, the needle ended up four turns out specifically because I was setting it by ear

Ameyam

Gray Beard

My Feedback: (-1)

When you had the 14X4 prop on it and you heard it over revving with your mark one ear ball how did it run? Was it over heating? Some prop makes and sizes make different sounds so you really can't go by the noise being made. Needle settings are done differently from engine to engine but factory settings are usually pretty close but can change a lot depending on the fuel mix. Using FAI fuel usually means having the needles open a bit more then normal. Usuing FAI fuel usually makes the engines run cooler. You may want to tune your engine with a tach to see what you are really getting in the way of RPMs.

jester_s1

People in the US run all the OS engines with 10-15% fuel all the time, even in the South where temperatures are about the same as in India. Your nitro content is not the problem. Everything you describe sounds like a lean engine, especially considering that it overheats even with the cowl off. Checking it out with a tach will remove all the guesswork from engine tuning. You can tell if your prop is appropriate to the engine, if your fuel delivery is good enough, if your nose up mix is right, and if you're ok with a low tank. I don't use a tach every time I tune, but I do use one always with initial setup of a plane and whenever I have a problem. It has saved me hours of frustration.

ameyam

I just cleaned the carb out. Dont think there was too much goop but I did all the stuff- I put tubing inside the HSN cavity and on the carb connection, then held under alcohol and blew as hard as I could. Did this with both the carb closed as well as open and with one tube plugged as well as open. I pushed in some throttle wire inside the carb as well as HSN hole gently to dislodge anything stuck. I blew in air in all directions. That is about all I can do. Did this with both the LSN all the way in as well as out.

I then set the LSN to 2 turns out, HSN at 3 turns out and ran the engine a bit at idle. I had a lot of dark brown and a bit of black oil in the exhaust. Finally, I again set the LSN back to 1.7 turns out, cleaned out what oil landed on the floor and ran it again. This time I just got some burnt castor. Ran it at idle only, cant go to full throttle in the appartment. It did get a bit hot but I wont know by touch.

I will put a tach and temperature gauge on it on Sat-sun when I can head to the field. I will also use plain-castor-no-nitro mix that a fellow flier has and see the difference. Will report then

By the way, I am using MAS K series throughout, both 14x4, 14x6 & 14x6 so sound behaviour is likely to be consistent

Ameyam

Gray Beard

My Feedback: (-1)

PM me your email address and I will send you a file so you have a bit better understanding of fuel and what things like nitro are doing. K series is also a four stroke prop. Just an FYI.

Rudolph Hart

Or if he wants to lower his frustration level temporarily he could just drink the alcohol and stare at the engine,which can be satisfying too

Gray Beard

My Feedback: (-1)

Done that more then once!!!!!!

ameyam

I dont drink (atleast no alcohol)

Ameyam

N429EM

As you mentioned, one of your carb screws is stripped, I'd be VERY surprised if you don't have a vacuum leak causing the engine to run lean.

EJ

ameyam

N429EM,

that would imply that the engine will not cut-off when the baffle closes, right? Well it doesnt happen

The screw threads have slipped a bit, it screws in but doesnt stop turning when tightening. I have put in some teflon tape and put it in. It still wont tighten but wont come out either

Ameyam

Mr Cox

When you close the throttle barrel you will also close of the fuel supply and the engine stops as it can not run on air alone. It can take a while to empty the crankcase from fuel but then it stops.

A stripped carb screw will give and engine that runs too lean, so that should be the first thing to fix before looking at other things.

ameyam

I can put some silicone sealent around the carb but that isint going to help much. Remember, both the o-ring around the neck and the screw are still there

Ameyam