I have quadra 75 in a ziroli corsair has a Menz 22-12 prop and the highest rpm's I am getting is 6500. I have flown this plane seven times and everytime it flew after 4-5 minutes it dropped RPMs/power in the air and I had to land. I then changed the fuel tank and all the lines. I also checked the diapram and the screen. It has a simple two line system with a vent and T-line. The fuel tank is wrapped in foam. The highest I can get is about 6500 with the 22-12. After running on the ground for 1 minute it surges for a second a couple times like its getting air bubbles. The transition is flawless. It also has plently of cooling in the cowl.

The needles right now are 3/4 high end
2 low end.

Any suggestions??? I am about to unbolt and send to b and b for a check up...

Thanks
Peter

Have you flown that Menz 22-14 with success in the past? In other words, is this a new problem with a known engine / prop combination. That seems like quite a load for that engine. I've flown the Q 75 quite a bit but always with something like a 23-10 or 24-10 and even then the 75 turned those props in the high 6800 to 7200 range if memory serves me well. I'm not sure you have an engine problem or maybe its just overloaded with too much prop.

I currently fly the Q 75 in a Z Skyraider.

No I intially flew it with a 24-10 as well and was having the same issues. I had a lot of people reccommend using that prop. Wouldn't it be able to turn higher rpms with the 22-12?
Thanks
Peter

You might try a 22-12 as that would be less load than a 22-14 but that engine should run fine on a 24-10. Exact engine RPM will depend on how the individual prop loads the engine. If that engine is in good condition and you feel that carb issues have been dealt with, you might try looking at the reeds. A leak there would cause problems. Sorry, I don't want to be overly negative, but my friends Q75 went back to B&B twice and a simple problem was not solved. I don't have a lot of confidence there.

Is the engine cooled well ... that is air directed through the fins and not just around them?? Big round cowl planes can cool well or poorly ... depending on airflow. Scale modelers are famous for not having enough cooling inlets or outlets ... much less flow direction in between. Do you have a scale engine in front of the 75? I lean towards your engine being both overloaded and poorly cooled as the problem. Wish it was here so I could look at it!!!

I must apologize for the mistype in my first post it was a 22-12 on there. I have just put a 24-10 back on and will retry it. What RPM's roughly should expect with that prop? Because part of the problem was the highest rpms I could get were just barely 6000. this was before I changed the tank and lines. There is no baffles in the cowl and no scale radial. It sits in an open cowl with the head just barely sticking out. It has a big hole cut for the muffler. and plenty of air exit between the cowl and fuse.
I wish you were here too! You really know your sh$t on quadra's! Thanks a milliom for the replies! Much Appreciated!

Peter

The Q75 is equivalent to a Sachs 4.2 and we always ran 22-12 on those. I would expect roughly the same rpm with a 24-10 or 22-12 and would
agree that a 22-14 would be a pretty heavy load for the 75. I think 6500 would be a reasonable figure for that engine to turn. As for the performance
drop after a few minutes in the air, that is an odd one. I agree that the reeds would be a good thing to check but they, like the carb, usually work
or they don't so doubt if that's where the problem is. However I learned a long time ago to never say never. You might also check the carb block to
make sure it isn't warped a bit and that the gaskets are good as this sounds more like a heat related issue.

I had a Quadra 75 in a 1/4 scale ME109G and with a Bolly carbon fiber 21x12 it would turn about 7300 on the ground. I would expect a Menz 22x12 to be a little less than that, perhaps around 6800-7000.

The drop in rpms is interesting. I assume that he carb has been checked and that it is tight on the engine? It sounds like it is heat related if it doesn't do it until the engine gets warm.

-Ed B.

Ran the quadra 75 today with the 24-10.
I set the low end at 1 and had the high end from 3/4 - 1 1/2 best RPM was 6200. The surge/quick 150-200 drop occured every 45-60 seconds when ran wide open but would last for a second. The engine fired every time, never stumbled or cut out. I did not see any air bubbles in the line or see any fuel around the carb. What is a strange is the low end was just as good at 1 turn than at my orginal setting of two it never seemed to make a difference the transition was still flawless...

Hi Dolittle,

You might try running the engine without the cowling to see if there is a change. The regulator diaphragm of the carburetor is subject to the whims of cowling pressure and this could be causing your troubles.

Another carburetor fluke is that some walbros and possibly tillitsons have a governor built into them. When the engine reachs a certain rpm induced harmonic. the check ball in the governor unseats and allows an extra amount of fuel to enter the engine and slows the engine down until the harmonic stops. The governor is what keeps chains saws from overspeeding when the throttle is held WOT.

Some models never see the critcal harmonic and run just fine. Others due to the airframe characteristics hit the key harmonics and go rich in the air no matter how you set the needles on the ground.

Hope these little tidbits help

Carlos G.

Thanks Carlos I am going to the next step in my "work up" I am going to order a new carb and replace the gaskets in between the carb block and the engine and the carb and the block.....