Building an Experimental PA11

After flying some more hours and doing some manuvers, takeoffs, landings, etc....here is where I'm at....
Overview: Experimental PA11 w/J3 (zero thrust) Mount and O-200A
Prop:Catto 76-36
Trim: elevator Tab type
Tail: Balanced typ
Empty Weight 842
Fuel: dual 36 Gallon wing tanks
TK1 Monster Shocks and 26" ABWs

I get 2550-2600 rpms on take off @60mph which is lower than I'd hoped for, but feels pretty solid. I could use a little flatter pitch when I go on floats...The Catto is nice, but I'm jonesing for a ground adjustable Sensenich....I'll fly awhile before I get too crazy.....another 100 or so Rpm might be nice.
I get consistanly 93 MPH cruise once trimmed for cruise @2500RPMs
Stall: 38 MPH indicated (no surprises)
I rigged it the old fashion way with string and bubble and it came out perfect (no adjustment required)
I have both right and left upper swing up doors and I bought the Piper Cub upper door latches from Univair, and they don't hold the door up very well.
This thing is a joy to fly, and I'm having a blast....Phase 1 @ 25 miles from home base kinda stinks (only one other airport in the box)
Standard Scott masters with Cleveland single puck brakes are a little on the weak side....It gets better as pads wear in though. Probably need boosters when I go to 29s
My aluminum struts turned out nice....they only ended up a few pounds lighter than the supercub struts I have but I really like them..I made cable fairleads out of 1/2" PVC conduit /and drilled the flat on the trailing edge of the extrusion and tapped with a #4 to attach. I'll let you know how they hold up. ...on a J3 or an 11 you could get away with all 4 struts being the smaller profile to save some weight, but I like the bigger front struts that I have just fine. I'll keep it as is.
Nothing earth shattering here in the STOL department, but I have a nice honest, sweet flying Cub that I'm proud as heck to have built myself. Those who have said an 11 is a great flying plane were right. I can imangine what it would be like if I would have shed 50 lbs or so. It's really nice to fly now though, and I'm happy with most of my decisions made throughout the build.
The rubber windsheild strip is really nice and seals right up....widsheild is very solid and I love the look....I've read threads on here about it and I hesitated at first....but it's all good. I like it.

My Catto 76-36 won’t spin up enough....2300 static, not quite 2400 @60mph on takeoff . I’m going to try my Sensenich 76AK-2-40 on for size so I can send my Catto for a re-pitch. I saw some time back that Roger Peterson used 76AK on his O200 with good results...I think it will still be too much prop to get past 2600 rpms. I’ll let y’all know.

Dan you might check out TCDS 1P2 for the 76AK-2-40. Sensenich didn't approve that model vibration wise for the O-200. Stated limits are, if I read it right, 135 HP and 2600 RPM Max Continuous. I'm not saying it will blow up but you may be in little known territory when exceeding 2600 or with that particular engine. I've used that same prop and dimensions to success on two C-90's (the current one is a C-85 Stroker with C-90 cam and lifter bodies). If you want more torque at current rpms you might consider installing a C-90 cam. The O-200 likes to rev up more I assume driven by camshaft lift and timing.

Edit: I looked it up and mine will static 2440 and exceed 2600 if allowed. I'm careful to maintain limits.

Gary

Thanks....This is the prop I currently have on my C90 Taylorcraft...it’s in for some maintenance so I thought I’d try it out. I will see what I get for static and if I fly it, and it happens to look like it could exceed 2600 rpms, I’ll back off. It’s THE prop for my C90-12F on my Tcraft though...I’ve tried others and this is the one. Thanks for this info Gary!

Yes it's installed on my Taylorcraft now as well (PA-11 w/C90 previously). If not already done try static rpm with your current air filter and then without. I find a Donaldson P10-7150 does better than any others (Challenger or Brackett) ~20+ or more than the latter.

Gary

BC12D-4-85 said:

Dan you might check out TCDS 1P2 for the 76AK-2-40. Sensenich didn't approve that model vibration wise for the O-200.

Gary

Click to expand...

Gary,
Just because the 0-200 isn't listed doesn't mean anything. It only means the prop wasn't tested for vibration purposes on the 0-200. It may be just fine.

skywagon8a said:

Gary,
Just because the 0-200 isn't listed doesn't mean anything. It only means the prop wasn't tested for vibration purposes on the 0-200. It may be just fine.

Click to expand...

Sure. Let's flip a coin. Winner flys the prop?

Gary

BC12D-4-85 said:

Sure. Let's flip a coin. Winner flys the prop?

Gary

Click to expand...

Not that at all. They just never did the testing. That doesn't mean it's unsafe. If they had done some testing and found a discrepancy, it would be noted on the TC.

Actually now that we are talking about this, my Catto has a strange harmonic at about 2375 as I’m just transitioning from liftoff to climb out ...only for a few seconds then it goes away. Anyone have that before?

I'd fly the AK76 within the specified HP and RPM limits noted on an Experimental aircraft. The major changes between the C-90, C-85 Stroker, and O-200 are the cam...timing, duration, and lift, plus ignition timing. Carbs vary by P/N. The rest like displacement, compression, major components is similar as far as I know. The Stroker uses O-200 components like crank, rods, and cylinders.

Dan's thread.......back to it.

Rough spot with Catto? Might see if it happens with RPM deceleration too then contact Catto? Might be airspeed-rpm related as well.

Gary

I could only get 2200 static with the 76AK. That’s 100 less than the Catto

Dan Gervae said:

I could only get 2200 static with the 76AK. That’s 100 less than the Catto

Click to expand...

Please try w/o the air filter as well. The cam and ignition timing of the O-200 is different than for a C-90....made more for higher rpm horsepower with short C-150 prop, I suspect. Specs are in the overhaul manual for each. C-90 max rated 90 hp at 2475; 95 hp at 2625 5 min. O-200 100 hp @ 2750, etc. You have a C-90 on the "T". What's the static on that with that prop?

However, JimC used to report good things about the O-200's here and elsewhere. He developed a graph that I have that showed the O-200 mo betta' at all rpms. Guess it all depends on prop-carb-ignition timing-compression-cam-intake-exhaust. The Piper exhaust may be more restrictive than say a C-150 exhaust for example. Same for air filters.

Gary

Make sure your carb heat is fully off and flapper leakage minimal. Make sure your throttle throw is fully open. Confirm magneto timing is correct. Try static w and w/o air filter. Compare static to your C-90 as mentioned. It would also be nice to confirm compression and check if valve timing and lift is per specs with a degree wheel on the crank. In other words make sure the O-200 is sound before chasing props. The C-90's are a torquey engine. The intake valve closes a few degrees earlier than the O-200 which helps some.

Gary

Same result without air filter. Anyone know the best setup for a Marvel carb on an O-200? Like a start point and then fine tune. The idle mixture may be slightly rich as I occasionally get a stumble on takeoff...usually on a touch and go or full stop and then go again....any pointers on optimizing this?

compressions are 77,78,78,76
timing is 24 degrees (old serial number cylinders).
engine has 300 Ish hrs on top and 30 on lower (new bearings after tear down and internals magnafluxed and yellow tagged) I can get over 2800 on full throttle in cruise.

0200 is like a 2 stroke bike, needs to rev. I had a 7636 catto on my 0200 cub and got about what you got. The 7440 1b90 was worse, my stroker will turn the Mac 2550 on takeoff

Glenn

Dan Gervae said:

Same result without air filter. Anyone know the best setup for a Marvel carb on an O-200? Like a start point and then fine tune. The idle mixture may be slightly rich as I occasionally get a stumble on takeoff...usually on a touch and go or full stop and then go again....any pointers on optimizing this?

compressions are 77,78,78,76
timing is 24 degrees (old serial number cylinders).
engine has 300 Ish hrs on top and 30 on lower (new bearings after tear down and internals magnafluxed and yellow tagged) I can get over 2800 on full throttle in cruise.

Click to expand...

Stumble sounds lean?

Glenn

Best to compare the C-90 to O-200's performance with that AK76 prop.

Accelerator pump has three adjustments. See MA-3-SPA Manual for troubleshooting and options. Page 2-3 and Fig. 4.

Edit: Install a manifold pressure gauge. Note the indicated ambient pressure prior to takeoff. Note it WFO near the ground as safe. Should be close like within 2" or even less if the engine's volumetrically efficient. Note at idle. Should be low around 10"+- if the engine is tight internally and intake leak-free. Also good for setting power and detecting carb ice early.

Gary

https://msacarbs.com/carburetor-troubleshooting/

I feel like the Engine is fine...just need to turn it faster. I wasn’t surprised that the 76AK Was too much prop to spin fast. I would like to try the adjustable Sensenich....I wish I had bought one....at the time I was buying my Catto there was all that stuff about vibration/harmonics on an O-200...it was the 72” version then. The 76 adjustable sounds intriguing....but I could wrong. I love the ideas so far. I remember Glenn telling me a while back that he had not been happy with the 76-36 on his O200. I tried and seems like the same results he had. Nicole at Catto said you get 30-40 rpm per inch on static and 50-60 rpm per inch at max.....She can move it up to 3”...so the full 3” should get me 2390-2420 static and I’m thinking I’d gain 120-150 rpm on takeoff which would change my takeoff performance quite a bit

The C-150 seaplane w/ O-200 swinging a 1A90/CF75-35-38 range wants to see 2400 to 2500 static. That Sen AK76-2-40 I can run 2440+-15 static with the Stroker and max just over 2600. Apples and fresh oranges of course. I'd consider the Sen adjustable.

But.....If I had a Taylorcraft C-90 capable of speed and a PA-11 O-200 capable of STOL I might swap engines. You have a beautiful plane that you're figuring out what it's for and how it's going to be used. My PA-11-90 on floats flew upper 80's - lmaybe ow 90's at the same 2400 rpm and prop (AK76-2-40) as my Taylorcraft now goes over a hundred. Fun choices Dan.

Edit: How about 8.5:1 pistons and cylinders to put some lead in that pencil?

I was born in Escanaba and lived in the UP 14 yrs. Nice place.

Gary

If you haven't already done so, you might want to check the tachs for accuracy too.

supercrow said:

If you haven't already done so, you might want to check the tachs for accuracy too.

Click to expand...

good point. I’ll borrow my buddies digital tach. I ran a static check on the C90 with the 76AK-2-40 and it statics around 2300. That’s 100 more than the O200 will spin it. Provided either of my analog tachometers are accurate. I do know that the plane performs fine (for an electric equipped 840 lb cub)....it’s been in the 90s here the last few days with DA nearing 4000’ so early mornings are when I’ve been flying. I just know when I put this thing on floats I’ll need to get more RPMs on takeoff for sure. That won’t happen until next year, but I’d like to get it sorted out. Again, my mission starts to point towards. Ground adjustable. I’d sure like to try one out. Anyone out there running a stock O-200 with the Sensenich 76” ground adjustable? I’d like a pirep before I make such a purchase.

Dan Gervae said:

......so I can send my Catto for a re-pitch.......

Click to expand...

As I understand it, the Catto prop is wood with a composite covering.
How do they repitch it?

They remove material from one side and add to the other, then recoat as I understand it. That's as far as my understanding goes though. Appearently it is fairly easy.....But I would sure like to see it done just to satify my curiosty.

Dan I’ve had two Sensenich 76” ground adjustable props, an early one on my C-90 (first of the new design) and then again on my O-290.
Compared with the props used prior the C-90 took better advantage and really shined, but I was very happy with both, and would highly recommend it.

On my C-90 it literally felt like I added 20-30 hp during the ground roll due to the rate of acceleration.

Note : these two engines use two different props - the c85/90/o-200 uses a sq tip 76” and the o-290 was two blades from a 3-blade design that was more of a tapered ninja blade.

After flying 20 hrs on my new plane, I then installed Stolspeed Vortex generators on my wings. After flight testing I noted the following:
the wing comes to life faster on takeoff….it was noticeable. My stall speed decreased about 4 mph indicated….stall doesn’t break anymore…just mushes and recovers over and over…ailerons stay responsive.
seems to indicate 3-4 mph faster in cruise.
as I said though…most noticeable was on takeoff. I could feel it create lift sooner. Very typical results yes. Bottom line….stolspeed vgs are cheap improvement.
mill install them on horizontal next after a little more flight testing

What % of chord station did you choose?

Gary

BC12D-4-85 said:

What % of chord station did you choose?

Gary

Click to expand...

directions said between 8-10%, then they said calculate 7% from leading edge, run your string line and place the front tips of the vgs at that location. This puts the high spot of the vgs at approx 8.8%

I tested a few different VG locations on my flapless 11-like wing (Wag Aero leading edge is slightly rounder like the Husky leading edge so my milage my vary). I found I preferred the VGs slightly forward of the suggested installation station line. This was most noticeable during landing/stall attitudes, although they worked wonders during takeoff as well as you noted already.

It is entirely possible the rounder leading edge on my wing caused this variance. However, I somewhat suspect our the lack of flaps and our AoA (relative wind) during flare is slightly higher thus requiring the VGs to be slightly forward to be able to vortex the air before the laminar flow interruption creeps up the rear of the wing.

Update: I really suggest adding the VGs under the horizontal stab. That, and elevator gap seals helped immensely in a variety of ways. Your mileage may vary, but they work real well for me.

I landed last night at 38.6 hrs…all was grand. Plane has performed flawlessly…went to go tonight to fly the last of the 40 hrs off and as soon as I started I knew I had stuck a valve. I pulled the valve cover and # 3 exhaust valve was stuck open…I freed it with a rope, but now I’m trying to decide if I pull the jug and ream the guide, or try shoving the valve into the barrel with floss on the end and ream it out….I’m leaning towards pulling the jug. Stuck valves never fix themselves. Ugh! Wondering if it’s something I’m doing ? Over leaning??? Maybe it was morning sickness. Either way….gotta do something .

From above "Maybe it was morning sickness"

6/8-21:
#279 "Actually now that we are talking about this, my Catto has a strange harmonic at about 2375 as I’m just transitioning from liftoff to climb out ...only for a few seconds then it goes away"
#284 "The idle mixture may be slightly rich as I occasionally get a stumble on takeoff...usually on a touch and go or full stop and then go again"
"...engine has 300 Ish hrs on top and 30 on lower (new bearings after tear down and internals magnafluxed and yellow tagged)"

Maybe it was talking to you earlier?

Edit: If I were out in the bush and had a stuck valve - I'd apply Kroil or spray brake cleaner and tap it with my rubber hammer. They have it removed and repaired when back in town.

Gary