siclick33

I recently tried to run my OS 91 VRDF in a Jim Fox Hawk (Ramtec fan).

The engine is second hand but started fairly easily. It is fine up to about three quarters throttle. If I open the throttle further it dies. If I reduce the throttle at this point it wil continue running but if I leave the throttle open it will quit completely. It seems to have quite a bit of power just before this happens. I tried a brand new McCoy no 9 plug and it is exactly the same.

I am using a remote needle so this may be a mixture problem. It is also in front of the fan so I am a little wary of adjusting it a high RPM. I will probably replace this with a servo controlled valve.

My question is:

This is my first DF engine. Where else should I look as a cause to this? Does it need particulary wide bore fuel lines? May this cause the problem? Could the engine be faulty? How far open should the needle be (I know this is difficult but do remote needles have different characteristics to normal needles)?

Sorry this is vague but I am desperate to get my new model flying. She looks good but I don't dare fly like this!

patf

My Feedback: (4)

sounds like you need to richen the mixture. if this does not help there are probably bigger issues..

siclick33

I've tried it really rich. What are the bigger issues? My though was that at high throttle maybe the fuel lines were not big enough to allow enough fuel through.

I think I am using standard fuel tube (about 3mm i.d.)

patf

My Feedback: (4)

when mine was not coming up past 3/4 sloppy rich, i took it apart and it looked line metal shavings had been dumped inside, everything was scored.

back to your issue. have you checked all of your fuel lines, try leaving the glow plug battery on while bringing up the throttle. if you have a spare needle valve, try using that and bypass your existing one.

you have not mentioned what fuel you are running either.

siclick33

Thanks for your help. I will try your suggestions.

I don't think you get the fuel in US.

I am using Model Technics Formula Irvine 10% (10% Klotz Super Techniplate oil and 72% methanol). This is what the previous owner used and does come recommended.

I am also using a hopper tank. I will bypass that and see if it helps also.

JimBrown

My Feedback: (2)

The OS .91 VRDF generally likes a lot of oil. The Wildcat Jet-A DF fuel I use in mine is 23% oil, 5% nitro.

You may also want to try large fuel tubing throughout the fuel system. I use 1/8" ID fuel tubing, brass tubing, tee's and the clunks are drilled out to 1/8".

Regards,
...jim

jetfreak

My Feedback: (9)

My starfire did the exact same thing. Brand new OS .91 VRDF DROVE ME NUTS. Your first thought is that it is running extremely lean as PATF stated. Everytime i richened it up, It got worse. Finally I decided to try and lean it out and it come alive.

1. Is it blowing alot of smoke at 3/4 throttle?

2. At 3/4 throttle. Try leaning the top end about a 1/4 turn and see if that makes it worse or better. If you have the mixture valve in a bad spot to get to....then take it out and temporarily mount it until you get it real close.

3. What ending up working for me was that I was able to get it running at about half throttle with out quiting. From there i started leaning the mixture out a lil at a time. Eventually I was able to open the throttle up and fine tune it from there.

If the motor is sloppy rich, It can't get up on the pipe.

PS. You WILL NEED a servo controlled remote needle valve. When you have full tank of fuel, the weight of the fuel helps push it through the fuel lines. As you burn off fuel during flight the engine will start to LEAN OUT on you. Without the weight of the fuel it is causing the engine to have to draw it a lil harder therefor causing the lean scenario. YES even with a hopper tank. ASK ME HOW I KNOW [8D]

If your thinking you can just run it a lil rich so that by the end of the tank it will be right. WRONG. You can use the supplied remote needle valve, I still use it on my starfire. There is one small problem. The threads on that needle valve are very fine thread. Meaning it takes alot of turning to make much difference. BVM remote needle valve has a more course thread. Allowing you to have that much more control.


Hope this has helped


sean

renegade pilot

Hi,
I have been operating OS91/Ramtec fan combinations for the last 8 years.
The standard remote needle works fine with no need for in flight mixture unless you are trying to get every last bit of power under all circumstances.
All of my set ups have always been with saddle tanks to a 2oz header then feed the engine. You have not mentioned if you are running tank pressure. On the ramtec the pitot pressure works fine but if you are not running pressure then the fuel flow may not be enough. The starting point for tuning your engine, for the standard OS remote needle, is to close the needle and then open 2 1/4 turns. This should be within about a quarter of a turn of where the optimum will be. Once the engine is running you need to let it warm up with the power to the glow plug left on until you are getting good throttle response, maybe 10 to 15 seconds. Once you get the engine to run at full throttle then gently pinch the fuel feed to the engine slightly, if the engine speed does not increase or the engine cuts out then the engine is to lean. Adjust the needle until you note a slight increase in engine speed when pinching the fuel line, at that point the engine will be tuned slightly rich and should not go lean during the flight.
You said that the needle is located in front of the fan and you do not like to adjust it at high speed. The fan should be fully enclosed within the ducting and the needle should be outside of the ducting with no possibility of getting fingers anywhere near the fan!!
Finally have you checked for any dirt in the needle which may be restricting the flow.
Hope some of this helps.

Russell

Jet Doctor

Hi

As suggested you need to ensure that your fuel lines are big enough and clunks are drilled out(including hopper!). To simplify matter you could try a seperate tank or just the hopper(but it obviously won't last long!) to feed the motor as this will give posetive pressure to the carb. It sounds like you are running out of fuel, this can only be confirmed by leaving the glow on while trying to run it up. If it were rich or very rich it should still run but with lots of smoke. If you can achieve this you are winning. If you then pinch the tube and the motor spins up, you know to close the needle. If you cannot achieve the rich running, you need to check for blockages right through to the carb.

What pressure and tuned pipe are you using? 2 of your components are an excellent combo, to complete, add BVM mixture control and BVM pipe. Make sure you are also using the Ramtek shroud pressure fitting. This provides the most reliable combo avaiable for DF. Pipe pressure makes the motor very difficult to set up and you could have mid range flooding due to excess pressure from the 25000+ rpm! Fuel is also important, 23% oil and 5-10% Nitro. Mccoy no9 is also the best plug you can use. If the motor has been standing for a long time you might also consider changing the bearings. Remember this motor is running on the ragged edge of piston powered engines and needs all the help it can get! The final test you need to do is the idle test - 1 minute at idle and then open the throttle- if you can keep it running, you will have the most reliable setup. Another tip is when you get to flying, once you have taken off, push youe idle to max and only come down on your landing approach.

Good luck and don't give up

Zane

razorice79

My Feedback: (1)

ok, lots of good info here.. heres a another question for ya.. I purchased a used os.91 vr-df, had to change out rear bearing.. i did that put it back together ran it today on test stand.. and also I changed from JMP pivot pressure to pipe pressure because of my 2 tank locations below the engine.. and have large fuel tubing through out system.. didnt drill any clunks out.. bvm needle value/dynamax fan. well I started it up runs great at mid-low idle will not quit, has very little/if any smoke in low range.. but when i open the throttle after mid-low idling it will hesiate before going full throttle.. but if i drop it back down to mid-low range then back up to full throttle it starts to almost scream.. i have alot/good amount of smoke coming out from mid-full range.. do i have this setup to lean or to rich? my low speed screw was at 4 turns out when i bought the engine.. i went on OS website and retreived at factory setting of 2 turns out on that.. my bvm mixture is 1/2 turn open on the mixture arm and the needle screw setting on the bvm mixture is 2 turns out... I also removed my ez-fueler from system and fuel filter.. (i think i had to much plumbing before for the jmp pivot pressure to do its job) so I went back to the basics! I know its probly rich but, want to make sure im doing this right, (cant afford another engine)..well guys let me know what you pros think about my setup!![:-] thanks a bunch for your time and knowledge...

razorice79

My Feedback: (1)

ohh forgot to add, im using wildcat premium blend 10%nitro 18% oil (80%syntheic/20%castor) airplane glow fuel.. and i added 5oz klotz benzol racing castor oil.. mccoy 9 or os #8 glow plugs. macs 15cc tune pipe and panthers rubber coupler.. (wildcat DF is unavailable in my area, i would have to order 4 gallons plus shipping to get that fuel) is this fuel mixture im using good enough?