AeroVee performance issues

[Fastcapy]

I will get yelled at (again) by admins if I go into it, so all I will say is good luck and that I and others have felt/feel your pain.

[n502pd]

Have you degree wheel checked the cam for actual lift and duration? you will need dial gauge for lift measurments. Did you do the rebuild yourself? When I set the cam timing I took a picture of it as proof!! What you describe really sounds like a retarded cam, or a mis-ground one, one way or the other.

Have you compaired the thrust from your plane to another identically equiped plane, using a scale tied to tailwheel and a tree? this way you can change things and test for more or less thrust without flying, and wasting your nerves. Feel free to PM me if you need more info. :)

[gammaxy]

Your speeds and climb performance seem to indicate you are getting about 80% as much power as I am. Have you checked recently that the throttle is free to open completely? Is it possible for there to be some slop or stretch in the system so that when the engine is running the throttle hits a different stop before opening completely? Ever experimented with a less-restrictive air filter?

What compression ratio and combination of shims did you use when rebuilding the engine?

I'm really hoping you figure this out soon.

[radfordc]

- Ever since then I usually average about 4.5 gph. So to me, 4.09 gph is too lean and may be part of my heat problems. It can't hurt to check so I'll richen the mixture a bit and do some tests.

The very least fuel burn I ever saw was over 4.75 gal/hr in cruise flight at altitude with the mixture leaned severely. Making power I always saw over 5 gal/hr.

[nwawingman]

I agree with your numbers Charlie. I personally run my AeroVee just lean enough to run smooth. Lean anymore than that and I see my temps climb. I find that the cylinders heads are much cooler that way and I average 5 gal/hr.

[wlarson861]

You may have alluded to one of the problems. When I got rid of the Nikasil cylinders I think it took about 30 to 40 hours for the temps to get back to "low" They would still hit 400 to 410 on climb even solo on really hot days. When I was normally aspirated 390 was a good day climb temp at 80 OAT. Solo climbs were still around 600 fpm though with a Prince prop. Another thing I did was look at the bottom opening and realize the engine mount crosses the firewall right above the exit, I added about 1.25 inches to the opening to compensate for this and saw a slight reduction in temps. I think I suffered from too much anxiety over some things that breaking in the engine fully solved. Trying to cool a new(er) engine is just impossible until it is ready. As far as the climb performance I bit the bullet and went turbo. All My problems with cooling and climb went away and I rarely see climb temps above 380 now. It's a $4000 fix but to me was worth it, the Jab was a lot more than I was willing to go at the time.

[SonexN76ET]

Mike,

Here are a few other items for you to check:

1. Make sure your flaps are not too far retracted. If they are too far in the up position the aircraft will mush through the sky and not climb well because the wing is developing insufficient lift. Both climb and airspeed will be poor. On the other hard if they are set too low they will increase lift but also cause additional drag.

2. Make sure you have an accurate slip/skid indicator ball. The Sonex demands that the ball be perfectly centered to get maximum climb and cruise performance.

3. When you had the issue with your valves burning with your first engine build, a more likely cause than running too lean was that your valves were not fully closing. The manual states setting the valves to .006 in one are and to "between .006 and .008" in another. If you can just barely squeeze in the .006 feeler gauge, it could be that you have less than .006 and your hotter valves will not be closing fully and will allow carbon and lead deposits to form and then start to burn.

4. I would also go to an airport with a long runway (6000 plus feet) and try different takeoff techniques. With my Sonex, I have to accelerate in a flat attitude after liftoff to at least 80 mph before I can start comfortably climbing. Anything slower than this and my climb rate is poor.

5. Check your wheel pants to ensure that when in flight they are not oriented where the wheel wells are pointing into the slipstream even a tiny bit.

6. Perhaps smooth fairings for your gear leg intersection would help too.

I look forward to hearing your solution. Please be safe out there with your test flights.

Jake

[nwawingman]

Excellent advice Jake! I especially agree with #4. There is a lot to be said for how we fly and getting the most performance out of our aircraft. I raise the tail around 40mph and rotate at 55 mph. Level out to build speed before I start my climb out about 80 like you referred too. It always seems to help my climb rate. I have watch others try to climb off in a three point attitude and it looks that there climb rate suffers. At full gross I will add a notch of flaps.

[mike.smith]

Your speeds and climb performance seem to indicate you are getting about 80% as much power as I am. Have you checked recently that the throttle is free to open completely? Is it possible for there to be some slop or stretch in the system so that when the engine is running the throttle hits a different stop before opening completely? Ever experimented with a less-restrictive air filter?

What compression ratio and combination of shims did you use when rebuilding the engine?

I'm really hoping you figure this out soon.

8:1 compression, running on AvGas. I cc'd the volume in the heads so I know I have a solid 8:1 ratio. I have the big K&N air filter. The throttle moves to full throttle.

[mike.smith]

- Ever since then I usually average about 4.5 gph. So to me, 4.09 gph is too lean and may be part of my heat problems. It can't hurt to check so I'll richen the mixture a bit and do some tests.

The very least fuel burn I ever saw was over 4.75 gal/hr in cruise flight at altitude with the mixture leaned severely. Making power I always saw over 5 gal/hr.

Sonex says their factory planes average 4 to 4.5 gph, so my usual numbers seem to be in line with that.