I went out a put a few flights on my new Kaos today.

Only bad thing... two deadsticks. Both happened the exact same way. I was up high and started a Running 8 by slowly pulling back the throttle and pushing over. Before I even reached the bottom of the loop the engine would start to hiccup and was dead by the bottom. I plan on re-plumbing the enture fuel system to eliminate anything obvious. Is this a symptom of an upright mounted engine, a setting or something? Could the low power setting and the negative G's cause the fuel to fly out of the carb instead of being inducted? I could fly all around the field inverted and the engine ran like a top. But the high negative G pushover kills it. Flying from inverted and pushing a half outside loop, it's fine (at full throttle). It's just the outside loop from the top while retarding the throttle. I'm perplexed.

The Evolution .60NT is a pretty simple motor to run. Gobs of power... just this one problem during this maneuver,

Any advice would be appreciated.

Hi Dave, it's amazing how a fuel tank setup can work perfectly in every situation except one. I Had the same experience today with my new Hangar9 Phoenix7. I rebuilt the tank floor from the factory setup to get perfect tank position and today while test flying the plane my buddy and I both commented about the very consistent needle setting from full to empty and every attitude, we flew every type maneuver to check the tank position and it worked perfect except for the last quarter of the slow roll. It will consistently hiccup but keep running. It does not hiccup on the eight point roll!. Conclusion, the clunk weight is to light and not keeping up with the fuel when the attitude changes slowly. you may have a similar problem. Oh BTW I love the Hangar9 Phoenix7, I flew the original in contest in the 70's. Good Luck

Thanks Ron. Hopefully re-plumbing and putting on a bigger/heavier clunk will do the trick! Glad you like the 7... I considered one for a while and still may go for one!

Just wondering if the combination of slowly closing the throttle and pushing the nose over causes the fuel to move to the front of the tank, but there's still enough throttle up to run out what's left in the lines.. Chopping it back to idle before pushing the nose over could reduce the fuel demand and mask the issue? A hopper tank might help IF this is the problem.

I've never seen a clunk that will fall to the front of a tank, but most of the time my nose is pointing down, I'm well off the throttle and have really long fuel lines (tank over COG).

YS sell a foam clunk for their DZ fourstrokes as little bubbles play havock with the positive displacement pump arrangement in their injected motors. The foam cluck keeps out the air and acts like a mini fuel cell when the cluck is exposed..

I will check that out that clunk as well. Hadn't thought of the fuel position. Thanks!

Dave, I'm curious what brand tank are you using?

During an outside loop, the fuel level moves around and relocates just like during inverted flight respect to the carb's height.

I believe that the engine cannot just hold more than few seconds at idle while inverted, when the muffler pressure is minimum.

If the centerline of the tank is too far from the needle height in normal position, the carb feels a dramatic change in fuel level when inverted.

If that is your case, and relocating the height of the tank is not practical, a compromise in tuning the low end between upside down and right side up may be a solution.

Sullivan seamless.

Thanks! I'll give that a try also.

Ed,

When we see the side view of a Kaos we see the tank already has a low position related to the spray bar and that can give some troubles. (red arrows picture 2) Too rich fuel /air mixture ratio inverted.

When I look at the pictures of your Kaos (picture 3), it looks like you also did make the nose longer and did mount the engine in a more forward position, see the grey sketch and orange questionmark in picture 2. Maybe because of the back plate mounted mixture needle valve?

Can you make a sketch showing us the distances and dimensions? Especially the distance between the front side of the tank and the back plate of the engine. (blue arrows)

When you do not use a fuel pressure regulator or pump it is important to keep that distance as short as possible.

If not, I think the engine can get too much fuel in nose down going directions as result of the hydrostatic pressure. (of course until the moment during flight the clunk will be above the fuel level and the line is empty in short time!!) Remember you adjust the engine in nose up position so the mixture ratio already will be rich in horizontal ATTITUDE.

Also for this problem a regulator is a solution, first the mixture will always be optimal, not too rich, second the chamber of the regulator does contains an extra amount of fuel.
My Taurus has the spray bar also above the centre line of the fueltank because this engine is much larger than the engine the plane was designed for, see picture 4.

Maybe you can use this information.
If your dimensions are as on the plans, I would check them with the original dimensions.

Cees

Thank you! I'll take a look at all of this. Which regulator would you recommend?

I actually built the planes to plans and didnt modify the nose at all. maybe the Tower Kaos is different.

That was wrong, Dave, not Ed.

Dave,

On the pictures the nose seems to be long and even you see the backside of the tank near the LE of the wing. See the picture. Is it possible to shortem the distance between the tank and motor?

Most important to try in the first place!!!!


If the distance between the backplane of the engine and the front side of the tank is short than you haven’t much to do in the first place. Maybe adjust the low needle and another plug (with a bridge?). A lot of idea’s to try.

A pump does make the layout more complicated so if it is needed in the end we can write some posts about that. Let me know and I will show you.
Some brands: Cline, Iron Bay, Webra and in the past there were the Jim Walker regulators.

Success and I will follow the process.

Cees


Edit in the picture:
Dave would it be better tom reduce the deflection of the nosewheel and safe/protect the sudder servo.
Compare the picture with your real situation.
Have fun,

3 quick things about this engine/carb:

A: make sure yout throttle barrel isn't moving side-to-side (side play) during flight. I have found that if it moves, especially during a near idle position, it can cause the engine to cut out. This might be happening during your maneuver. Making sure the linkage puts a gentle side pressure helps with consistancy, at least on these Evo carbs.

B: Back pressure. This engine (and the 1.00, too) is especially sensitive to muffler pressure, and IF you have an aftermarket muffler you will have to reduce the outlet area. This will help make your low end rock solid, along with A and C.

C: This may sound crazy, but bear with me- I have fiddled with several of these Evo 60's for a long time. Hook up a temporary on board glow, and see if it fixes the problem. I have found difficulty in getting the 60NT to run well CONSISTANTLY when mounted inverted, especially at low throttle conditions. I know, I know, most two strokes are a bit more irritating when inverted. However, I have had many success stories with inverted mountings, but this engine is different in some mysterious way. Lean or rich, it didn't matter. Tank position was good, with nice & short tubing. This is my theory and opinion, but I think there is a connection with this and the glow plug position in the head (evolutions are canted towards the back somewhat) and poor reliability in some attitudes and throttle settings... maybe fuel droplets in the intake charge... heck, I don't know. You may try to verify this by doing some other negative G maneuvers at low throttle or idle and see if it does the same thing. I could adjust the engine to a perfect low & high mixture when sideways or upright, then turn it over and it wouldn't idle well and the problems would start. Different brand 60 did not have the slightest problem with the same plug. I know your engine is upright, but perhaps your negative G maneuver is bringing out this trait in your situation? Just a guess, but I will bet a 6 pack on it- IF your plumbing is right!

I put an on-board glow on this engine and the problem of quitting stopped, and the engine ran like a scalded dog inverted. I later repositioned to a side mounted engine configuration and took off the on board glow with success as well. Runs awesome to this day!

Just my observations, folks! Don't flame me! [8D] I still do love all of my Evilution engines! They pull hard.

EDIT: others have mentioned the fuel tank level(a plumbing item)... I second those observations also.

WOW all great stuff! I do use a Jett muffler. How would i go about reducing the output area? Suggestions?

Well, I don't know if I would do it with a Jett muffler... you will lose your top end more than likely. A good way to experiment would utilize a tube that you could constrict, like a rubber muffler extension. Now that I know you have a Jett muffler, maybe you should try a perry pump or a regulator instead as others have suggested, since the whole back pressure deal is purely a fuel delivery thing. You really should try the onboard glow. Just a quick & dirty setup you can remove easily... maybe that and a little leaning of the low end.

I often wonder... would putting a check valve between the pressure tap on the muffler and the tank vent line crate a situation where the tank would hold pressure even when the throttle is pulled back? Sort of a weak YS pressurized pump setup. After shutdown I'd have to relieve the tank pressure (like a YS) if there were any left.

Fourmost products makes one just for this purpose... never tried on, however.

Dave,

It sounds to me like the engine is running lean atlow throttle when performing the neg G maneuver. The conditionyou and Firepower are experiencing sounds like what happens when the throttle barrel bore of the carburator is to large for the engine. e.g. not enough air speed past the carb venturi to drawfuel into the carb.

Have you been able to verify if the engine is running rich or lean during the inverted portion?

If lean the following may help to understand what is happening.

The OSMax7D carb has this problem on the 61FSR when the brass insert is missing form the throttle barrel of the carb. (see insert pic) The 7D was offered 3 different ways depending on which engine it was used on. When the 7D was used on the 61FSR thebrass insertutilizedmade the throttle barrelbore 8.5mm. On the 90 FSR a larger insert was used for 9.5mm throttle bore. The last 7D carb I purchased from my LHS was labeled for use with the 108FSR and had no insert for a throttle bore of 10.5mm. Point of all this is it sounds like your engines carb throat is borderline on the large side and the problem only shows up when doing negative G maneuvers.

OS Max's solution was to use a pump on the engines with too large of a throttle bore to keep the fuel flowing during low throttle conditions and too give a nice boost of performance out of the engine. I've got 9 flights on my Kaos which has a 50FSR and a perry pump and have positivefuel draw in all flying manuvers. I wanted to make sure I could concertrate on learning to fly pattern maneuvers and not have fuel delivery problems during any of those maneuvers. See pics for pump locationand plumbing.

I called Perry Pumps and asked the best way to hook up their pump and they suggested that you use a T-fitting as close to the carb as possible and runa return line back to the fuel tank or back to another T-fitting between the pump and the fuel tank. (See pump and bypass system pic fromp the Perry Pump website.)

Also when using their Pump you just vent the tank to air. No muffler pressure to tank.

If you have access to a pump try it and see if this solves the problem.

Dave,
Impossible.
The tank pressure is related to the power level of the engine on any different moment. Idle, low pressure, full power higher pressure.

The tank pressure has to be released to the muffler in idle situation in all positions, that’s why the location of the tank in the fuselage is important. To prevent the engine gets too much fuel in nose down idle situation. Because the hydrostatic pressure can be high related to the (low) sucking pressure of the engine in that situation.

A check valve I use combined with the fuel pressure regulator so I do have enough pressure also in nose up situation to feed the carburetor.
So my Taurus can have a nearly unlimited time in nose up and nose down position after idling the engine.
When using a check valve you will measure a much higher pressure level than with the “uncheckvalved” connection but the carbs all are designed to work without a check valve!!!!


Cees

I have a Taurus with a Veco .61 and Perry carb. I had problems with a muffler pressurized tank, it was very sensitive to needle settings and would quit. I replumbed the tank to be vented to atmosphere and used the third line as a fill. The problem went away, it will suck the tank dry and not miss a beat at all power settings, tank level and flight attitudes.

Very interesting post, Roguedog!

For tanks located way off the centerline of the spray bar, the attached schematic shows how the influence of the height of the fuel reverses for each case.

If the loop is tight enough to generated 2g's of acceleration, the weight of the fuel doubles.

The outside loop may put more static pressure on the spray bar, making the mix too rich for steady idle.

An uniflow layout may be a good solution in this case:

http://www.fraserker.com/heli/uniflo...flow_works.htm

Michael,

This thread is about the Evolution 0.60 NT and the carbs of these are all designed for normal muffler pressure and not an higher pressure stored in the tank by a check valve. That was why I did write
When using a check valve you will measure a much higher pressure level than with the “uncheckvalved” connection but the carbs all are designed to work without a check valve!!!!

About the Veco 61, but so “off topic”.
The Veco .61 was provided with an exhaust baffle not a muffler. First versions with a VECO carburetor and later also with a Perry carburetor. The dimensions of these carburetors were not based on tank pressure IMO, think for example about a small throat of the barrel or the range ability or characteristic of sleeve and/or needle valve(s)!
When mounting a muffler on such an engine can give some adjustment complications when using the pressure connection. Much easier to do of course is trying to run the engine without using the muffler connection. A good solution for the Taurus because the distance between tank and engine can be short.
Only point not to forget, the (Top Flite, MAN) Taurus was designed for up to 0.45 engine, so the carb of the 0.61 Veco will be on a higher position.

Cees

You forgot to deduct the muffler pressure lostin the outside loop.Because the muffler vent is at the top it is reduced by the head of the fuel. With this arrangement the correct tank placement is with the center line of the tank below the spraybar. But usually less than 1/2 inch.

I put in a Uniflow setup as I had all the parts and seemed like it would significantly change SOMETHING. Next I'll look at a pump I suppose.

All great advice and I thank you!

I suspect the problem might be engine related. Dying in a dive is usually after a long dive. I takes a long time to use up the fuel in the line at idle. What is more typical is that as fuel is burnied in the line air is drawn in after the fuel. Then when the plane is at the bottem the line starts to pick up air behind this air and so there is a large bubble or a lot of medium bubbles. So then the engine leans out or dies on the upline.

Maybe a hotter glow plug would help?