AeroVee performance issues

[mike.smith]

I used to have the ground adjustable prop. Now I have the recommended 54" Sensenich. With both props my climb performance has been anemic and quite scary, especially at gross weight. I don't know if there is anything anyone can suggest but let me tell you what kind of numbers I'm seeing and perhaps you will think of something.

I've rebuilt the engine a couple of times (replace Nickasil cylinders with cast iron, and after replacing the crank and bearings from a prop strike). All 3 versions of the engine have run with the same numbers. While always seeming to under perform a bit compared to some other AeroVees, the numbers appear to be within specs, so I think I've built the engine well and haven't done anything to compromise performance. I have the wheel pants and gear leg fairings (tail dragger) installed.

My #1 cylinder always runs hotter than the others. EGTs often run about 100 deg higher than the others (even #3). CHT also run hotter, often around 50 degrees. This has been true in all three engine builds. I have installed a metal deflector in the cowl opening to deflect some air away from #2 and back to #3 but that has not seemed to do much if anything. My cowl seals are all tight and the super tin and baffles are in good shape and installed where they are supposed to be.

The #1 and #3 cylinders have always run leaner than the front two, which is easy to see when you look at the insides of the heads and at the spark plugs.

During run-up, turning off the secondary ignition yields an rpm change of 0-20 rpm. In flight if I turn off the secondary ignition I don't see any measurable change in temperatures.

After the winter I richened my mixture. During my last flight the engine was running a bit hot, and the #1 cylinder is what dictated how I climbed and how I adjusted the mixture. Since it was running hot I kept the mixture close to full rich most of the time. When I got back home and put gas in the tank I had burned 9 gallons for 2.2 hours of flight, so my fuel flow was 4.09 gph. So I think I'm still running too lean. I'm going to richen the mixture another 1/8 turn and see what happens. But if I run full rich on takeoff I often get an rpm drop, so leaning the mixture at least a little seems to give the best rpms.

There were times on this last flight where the #1 EGT was at 1380+ but the CHT was at 365. I usually see 390+ on the CHT if the EGT is correspondingly high. So I'm not sure what to make of that. But it wasn't consistent like that.

The climb with the prop is still pretty anemic. I now tend to get off the ground, build up speed in level flight, then pull back the stick and climb past the 60' trees at the end of a 2,700' paved runway (at 270' MSL). I've altered my first fuel stop on the way to OSH this year so that I won't be taking off toward Pennsylvania mountains like last year (and scared the crap out of me!). I have been keeping track of my performance numbers. On my last flight:

Climb out = 3,150 rpm at about 200-250 fpm
- Weight 961 lbs (Plane 655 lbs, me 190 lbs, full fuel 102 lbs, smoke oil 3 lbs, tool bag 11 lbs)

Climb to altitude:
3,030 rpm, 250 fpm, 72 kts, 68 deg OAT (took me 20 miles and 20 minutes to climb to 5,500')

Cruise 1:
3,130 rpm, 5,500', 93 kts indicated, 63 deg OAT (if I bumped up the rpms my #1 cylinder temps went up, but if I richen the mixture maybe I can bump a little more out of the rpm and airspeed, but 93-96 kts is about all I can get right now. With my old prop I was at 105-107 kts but the climb was just as bad.)

Cruise 2:
3,160 rpm, 5,500', 96 kts indicated, 57 deg OAT

Maximum RPMs in level flight, if I ignore the high EGT/CHT numbers, is about 3,250 rpm.

Another AeroVee owner noted:
I see around 600 to 700 fpm when flying solo with full fuel at around 80mph on climbout. I don't have the tool bag or smoke oil but am at 667lbs empty so it should be about the same.

So I don't know what might be up, but flying at gross weight is downright scary, as there is very little climb performance. Often I see 3,150 rpm and 100-150 fpm, and my #1 and #3 cylinders are all bumping up into the red.

Any insights would be appreciated.

Mike

[radfordc]

I used to have the ground adjustable prop. Now I have the recommended 54" Sensenich.

On my last flight:

Climb out = 3,150 rpm at about 200-250 fpm
- Weight 961 lbs (Plane 655 lbs, me 190 lbs, full fuel 102 lbs, smoke oil 3 lbs, tool bag 11 lbs)

Climb to altitude:
3,030 rpm, 250 fpm, 72 kts, 68 deg OAT (took me 20 miles and 20 minutes to climb to 5,500')

Cruise 1:
3,130 rpm, 5,500', 93 kts indicated, 63 deg OAT (if I bumped up the rpms my #1 cylinder temps went up, but if I richen the mixture maybe I can bump a little more out of the rpm and airspeed, but 93-96 kts is about all I can get right now. With my old prop I was at 105-107 kts but the climb was just as bad.)

Cruise 2:
3,160 rpm, 5,500', 96 kts indicated, 57 deg OAT

Maximum RPMs in level flight, if I ignore the high EGT/CHT numbers, is about 3,250 rpm.

I know I'm just telling you what you already know....You're numbers are far out of whack with "normal" that I can't even guess what is wrong.

You're engine is turning the correct rpm on takeoff (3150) but is at least 200 rpm low at max level flight.

You're rate of climb is at least half of what you should see turning the prop at 3150 on takeoff. You're cruise speed is at least 5-10 kts slower than it should be at the rpms you're turning.

At 1200 lbs gross my Sonex would still climb better than 250 fpm.

You're sure of the instrument indications?

[rizzz]

I'm no expert but from what I gather it is the choice of camshaft that determines at what RPMs your engine will output the most torque.
Maybe you have an incorrectly ground camshaft, or perhaps Sonex accidentally shipped the incorrect type? I believe the one they normally ship with the AeroVee is a CB Performance Eagle 2234, this is very similar in lift/duration to my Engle W100 and as I'm told a good choice for engines running the sort of RPMs we do.
The race car guys will use totally different camshafts as they run much higher RPMs...

[radfordc]

While the engine could be the problem there is still something strange. If you have two identical planes turning the same prop at the same rpm, they should perform the same...no matter what engine is installed.

Mike's plane is climbing slower and has slower cruise speed than "normal" Sonexs do. At the gross weight and rpm's he is seeing the plane/prop should have more performance.

The fact that his engine seems to develop normal climb/cruise rpm, but doesn't give full max level rpm is also strange.

I'm stumped.

[JohnF]

Mike,

Have you verified the accuracy of the tachometer?

Just a thought,
John

[achesos]

Hey Mike,

I'm interested in your solution since I'm about to complete first flight with an AeroVee taildragger that is 667 empty too...

As much as we want to believe these are all the same, I wonder if your 80.0 HP engine has the same output as my 80.0 HP engine? My point is that they won't be exactly the same - the odds are against us that they can be exactly the same. I believe that this will also apply to the airframes themselves too - no two exactly alike - only approximations of the design/plans with some measurement error and tolerances all stacked together into the final assemblies.
So I agree that it makes sense to check your instrumentation, but it seems to be a fact that you want better climb performance no matter what some of the other gauges indicate.

I'm not smart enough to design a plane, so I stick to the basic principles smart people have identified for me. I vaguely remember that the enemy of thrust is drag...
Not to cast stones, but I wonder about rigging and other parasitic drag issues being a problem? Maybe a little fitment here and there or a gap seal somewhere special will clean things up and make it perform more typically? I stare at mine and wonder: "Is this good enough?". At this point, I'm still simply hoping that mine will fly straight and fast (okay, reasonably fast in the not too distant future).
Please keep us updated on what you identify, test, eliminate and confirm. Good luck.

Sean

[n982sx]

My take on your numbers.

First some actual numbers from one of my latest flights for comparison.

OAT
Ground 600' msl 82, 2900' msl 70 Gross Wt 990

Climb
RPM 3170
IAS 78 kts
FF 6.9 gph
Rate of climb 448 fpm

Cruise 2900' msl
RPM 3150
IAS 103 kts
FF 4.4 gph

These are nominal numbers for me at about 30 pounds heavier - 990 - than you. At max gross - 1150 - I recently climbed direct to 5500' msl with the following set of numbers. Maybe not quite the same climb profile as you but, close enough.

OAT
Ground 650' msl 84, 5500' msl 66

Climb
RPM 3150
IAS 80 kts
FF 6.5 gph
Average rate of climb 290 fpm for 15 minutes
Initial two minutes of climb 420 fpm at 74 kts

I have an MGL unit that records all my flight data and it includes a fuel flow meter. I also am running the standard 80HP Aerovee and prop, the same as you.

As you can see, on initial climb out, at the same RPM, but at max gross I'm getting just over a 400 fpm climb. I usually lower the nose a tad just for cooling after the first 400 feet, but I have no mountains to hit around Chicago, so I don't worry too much about climb rate after that. I usually reach 400' between 35 and 55 seconds, depending on temperature and weight. >600 fpm is common below 55°oat and just me in the plane.

Looking at my cruise data, you may be right in thinking that you are running too lean. I don't know how reliable you feel your fuel flow numbers are, but I run richer than you indicate. Have you performed the 100° EGT temperature drop test in the air? If so what are your results?

I also don't know how many hours you have on your Aerovee, but I never could get the prop to turn faster than about 3250 in level flight for the first 75 hours or so. The engine seems to gradually loosen up over time. Recently I was cruising along at 118 kts at 3380 rpm and 5.5 gph. I've been able to achieve these numbers since after about the first 100 hours or so. I'm up to 395 hours now.

Since your rpm's don't seem that off let me ask an obvious question. Are you running with gear fairings and wheel pants installed. Your numbers are more like I might expect if they were not. If you are, I would suspect your rpm indications are higher than actual, other than that I can't come up with what might be wrong.

[gammaxy]

Any chance you have a clogged static port? It might have an effect of causing you to think you are slower than you are on climb out and climb at a shallower angle while simultaneously indicating a low climb rate. Seems unlikely that this would be the problem, but if I were in your position, I'd probably test it. Connect a tube (or syringe?) to the static system and roll up the end and verify that the system responds faster than you could possibly climb.

From your description, it does sound like you are tuned leaner than I am. I do have to lean a bit to get full RPM on climbout, but if it wasn't tuned that way, then when I level out and the RPMs increase, the engine will become too lean. I do have a different propeller, though, and get closer to 2900 rpm on climbout and 3150-3200 in cruise. FWIW, I never have to limit my throttle in cruise to keep temperatures down.

Your old 105-107 knots in cruise at 5,500 feet doesn't sound too bad to me. My airplane gets slower the higher I get and I do around 120 knots at 1500 feet or so. Once correcting for altitude and temperature, your number seems reasonable. I really wish I understood how Sonex gets 150mph at 8000 feet.

[Corby202]

I do not know the full facts but if this engine was mine the first thing would be to confirm the indicated rpm was correct. Assuming that is correct, can you get at least 3000-3100 rpm static if not and everything on the engine is correct, it could be to much pitch on the prop. This would also account for the higher temps.

[mike.smith]

Hi, everyone:

Thanks for the input. Knowing what numbers others are seeing certainly helps figure out where the issue might be. I really have two issues that are, and are not, related: HEAT and CLIMB. Here are some bullet points based on all your comments:

- My pitot static was just checked when I did my xponder check, and they were dead nuts perfectly calibrated.
- I have the wheel pants and gear fairings installed. I have since day one.
- I have rebuilt the engine twice. Overall it has 160 hours on it. With the new cylinders and bearings it has 20 hours. Maybe in another 20 or 30 hours things will improve?
- But climb performance has been poor for the whole two years I've been flying.
- I've never found anything out of rig or trim. I'm happy to have others look, but there is certainly nothing obvious. I've never experienced any off center ailerons or draggy flaps. I have the fairings at the roots of the flaps so the flaps don't travel upward. If I look out at the wings during flight I don't see anything at the flaps or the ailerons that looks out of place.
-Having taken to heart much of what Mike Busch has written, I do try to use the EGTs as more of a guide than an absolute. It's the CHT's that I take great care to keep under 400 deg at all times. Except for #1, my other 3 cylinders usually run in the low to mid 300's.
- When I look up inside the cowl openings on the ground, all the baffles seals are tight to the cowl. I suppose it's possible that the forced air could lift the cowl during flight. I think only a camera inside the engine compartment could show me that.
- I was pretty much a stickler for following Sonex's instructions. I followed the measurements for inlet openings as shown in the AeroVee manual.
- I used the recommended 12.5"x4" outlet with the aluminum dam at the leading edge.
- When I first built the engine and ran it, things were running hotter than I would have liked, but still in the green. When I was checking my fuel burn I was down at 3gph or a little more. This was way below where it should have been. I messed around with the needle settings but things started running rough. I changed to another needle and have been running very well ever since. But I spent the first 50 hours or so running way too lean. When I did my first annual my compression was awful, so I removed the heads and took them to a shop. They showed me how the valves were burned from running too lean. I suspect that all happened in the first 50 hours. 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.
- As a rule, #2 and #4 run very close to one another, and are way in the green. #3 is hotter than #2/#4, but still about 30 or 40 degrees cooler than #1. I have checked for induction leaks many times. The only thing I have not tried is squirting flammable fluids around the areas prone to induction leaks. I suppose that's next.
- My empty weight hasn't changed measurably since I weighed it 2 years ago. I measured it on calibrated scales from my EAA chapter. I got rid of the Nickasil cylinders so gained some weight there, but then I replaced the lead acid battery with a Lithium battery, so got much of it back. I've added a fuel flow transducer but that added only several ounces. Other than that I haven't changed anything. If I'm off in my current empty weight I would guess it's only by 5 lbs or so. Nothing drastic.
- Regarding my posted climb numbers at 72 kts, If I get slower (because the nose is up) then my temps increase. If I lower the nose for the temps, then my climb decreases to less than 200 fpm. It's my temperatures that are keeping me from pushing up the throttle and pointing the nose up a bit more.
- I would currently never get 3,250 rpm at gross. Only with me in it and below 1,000 lbs. But maybe that's because the temps have kept me from even trying. At gross I often have to step climb. Climb; temps go up; level out; temps go down; climb a bit; temps go up; level out; temps go down, etc, etc.
- When I had the ground adjustable prop I had to set it to the finest pitch (0 - zero) to even get my rpms up to 3,000. Most of the time I could not get the rpms past 2,950, and my climbs and gross weight performance were just as they are now: awful. So I never got any satisfactory numbers during tests. They were anemic and within a very small range. What has changed since I changed to the cast iron cylinders is that I still have scary small climb numbers, but now with the added issue of hot cylinders. The only thing different about the ground adjustable prop was that even at the finest pitch setting I was getting 105-107 kts in cruise.
- At gross, when I take off, to clear 60' trees that are a fair distance beyond the end of the 2,700' runway I have the airspeed in the 60+ kt range, and I often see them dipping into the 50's. My fpm climb is in that 150 fpm range. I can't pull the nose up any higher and I can't flatten my trajectory. I just have to hold the stick, hold my breath, and pray there isn't a hiccup in the engine. If I'm that draggy then I would think those issues would be patently obvious to even a casual observer.
- It feels like I need 2" of extra prop, and an extra 200-300 rpm to swing it.
- Sonex acknowledged that at one time some incorrect cams had been shipped, but they said my engine kit was some 200 kits beyond that known problem, and their shipping information shows I had the right one.
- When I had the Nickasil cylinders I had NO problems with heat. None at all.