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RV-7 N117TR

I am in the process of replacing my fuel lines due to over flaring and over tightening, details here:
http://www.vansairforce.com/community/showthread.php?t=123689

I did add some "pip" pins to the canopy,
http://www.mcmaster.com/#98404A008
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Whew, new fuel lines from the tanks to the gascolator complete. I used approximately 24 feet of 5052 to make roughly 6 feet of fuel lines. Leak check, ground run and an hour flight were leak free.
I wasn't able to appropriately bend the 5052 as a 1 piece line like I could the 3003 so I used a union and 2 pieced it. I went back and forth between the 5052 and the extra joint or 1 piece of 3003. I found 3 1/2 turns of my Rigid flaring tool gave me good consistent flares and 75 inch/lbs with a crows foot was about 3/4-1 flat after my "finger tight."
I wanted to follow the recommendations in this thread:
http://www.vansairforce.com/community/showthread.php?t=81499&highlight=Fuel+valvee
So I wouldn't have to cross the fuel lines but everything was already setup the plans way so...

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My homemade AOA port seemed to calibrate fine, but the AOA was flaky in the pattern. More playing needs to be done.
 
Sooooo instead of flying I've been working on the RV again, long story short the rings never seated and the excessive blow-by caused a sticky exhaust valve. More details in this thread:
http://www.vansairforce.com/community/showthread.php?t=124324&highlight=engine+stumble

In addition to the cylinder inspections, I've had several sets of hands and eyes on the bottom end. I originally wanted to pull it all apart but was advised to leave it together.

I was originally going to clean up cylinders/pistons, re-grind valves/seats (slightly pitted), check and ream valve guides if needed, replace rocker boss bushings, and put it back together with new rings and seals. After adding up cost i found I could purchase factory new lycoming steel nitrided cylinders with everything but rockers (even seals/gaskets) for about twice the cost of fixing my current channel chrome cylinders. I opted for the new cylinders, I've spent over 10 years working on it I'm ready to fly for a while. The new cylinders showed up last night in my driveway....

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I had 1 intake leak on my first flight, I found the intake tube clamp was bowed. I filed it back flat, installed a new gasket and flew for 100 hours leak free. While cleaning up the intake tubes/clamps I wanted to see if the other clamps were as bowed as the one I filed. It was pretty easy to find the one I had previously filed, the other 3 looked like this when placed on my back riveting plate.
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Although filing the clamp flat did "work," it didn't leave the proper amount of material for the flange of the intake tube. Luckily a college buddies dad needed a little project and since he has the tools and know-how he is re-machining my intake clamps for me. He sent me a teaser photo, man I wish I had all of his tools!
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I also sent my rocker arms off to have new bushings installed. I'm meeting an A&P friend tomorrow to look over my new parts and hopefully install them on Monday.
 
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My A&P suggested I leak check the valves before installation by pouring fuel (I used jet fuel) into the intake/exhaust chambers and make sure nothing leaked into the cylinders. As one would hopefully expect, no leaks. You can see the fuel in the right port in the pic.
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No leaks on the inside, everything is still shiny and pretty.
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More general cleanup on the push-rods and tubes etc.
 
Cylinders torqued per the Lycoming Overhaul Manual and Service Instruction 1029D.

When I did a baffle repair several months ago I noticed the lower cooling fins were eating into the lower baffles. I made "pads" out of the Van's black baffle material and glued them to the lower baffle wraps. There was more wear than I expected on the black baffle material on the lower wraps, I'm going to copy DanH's work from here (post 39):

http://www.vansairforce.com/community/showthread.php?t=37835&highlight=baffle+mod&page=4

As expected my composite workmanship still has a ways to go, on a good note there was no mess to speak of. The front cylinders have always been cooler than the rear cylinders, I extended the baffle wrap a little higher on the front cylinders.

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Between the heads I used short pieces of the Ultra Black infused 9 Oz fiberglass, than I ran a bead of sealant between the 2 pieces from underneath. I also used Ultra Black along the edges of the wraps that I could get to.

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I have the oil cooler mounted behind #4, I made the wrap a little longer slightly overlying the top of the cylinder. I wanted to see if this would help keep the air in the cylinder fins instead of exiting through the cooler, at least that's my intent.

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On the backside of #3 I made a small piece of wrap that started slightly below the minimal cooling fin depth area. Previously had a washer between the cylinder and the baffling, I may add a small bump to increase airflow.

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The shop that overhauled my engine previously ground the numbers off the pushrods and made "custom" shorter pushrods.......
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Thanks to McDoogle for the borrowed ride, I was able to buzz around and pick up the proper pushrods. An A&P friend walked me through the procedure for checking the dry tappet clearance, quite a handful by yourself!
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After I got the airplane back together it took me an hour and a half to put tools away and clean up to ensure I didn't leave any tools in or parts off. I rolled it outside and did a test run. I can't believe it started on the first blade, everything ran up normal and shut it back down in 1 minute.
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I gave it a twice over and cowled it up and pushed it most of the way to the runway. I reviewed my flight plan and emergency procedures and possible scenarios, ready as we'll ever be! My spinner gap looks great!
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Startup and runup were normal, full power on the runway showed gauges green and a normal static RPM of 2080. No issues on a 45 min flight besides high CHT's(400-450) at full power. Very short descent and taxi in to the hangar for de-cowling. Everything looked good, a little leftover oil from assembly but not oil on the usual spots from the breather. She's all buttoned up and ready for the next flight at 16.5 GPH...I'm just happy to be flying again!
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As expected my composite workmanship still has a ways to go, on a good note there was no mess to speak of. The front cylinders have always been cooler than the rear cylinders, I extended the baffle wrap a little higher on the front cylinders.

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Remember, the forward side of #2 has the same "no fin depth" issue as the back side of #3.

Between the heads I used short pieces of the Ultra Black infused 9 Oz fiberglass, than I ran a bead of sealant between the 2 pieces from underneath. I also used Ultra Black along the edges of the wraps that I could get to.

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Don't forget to seal between the outside of the glass wrap and the inside of the aluminum wrap.
 
Cowling Inlet ReShaping

I recently sent my prop back to Catto, I've been watching it closely since hitting a rubber cone at OSH. I found that the scratches in the prop from the cone haven't grown lengthwise but one scratch started to open up slightly when I twisted the blade with my hand.
While the plane is down why not turn a small project into a big one......

I would like to re-make/redesign my stock air inlets for:
-better cooling
-less cooling air leakage
-easier cowl removal and installation
-retain the same basic shape of the Van's cowl inlets

Step 1: Order plenum from BillL

Step 2: Remake the cowl inlets into a divergent shape instead of converging and a female notch to hold a rubber intake diffuser.

Ste 3: Make rubber Inlet diffusers to fit baffling and plenum and the cowling inlets with a male notch to hold the front in place.

The stock inlets converge and seem to choke off airflow, the opening gets smaller before it gets bigger. The outboard portion of the outlet seems to be angled the most.

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The inboard portion isn't as bad, and it has to go around the ring gear.

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Looks like Its best to cut the entire flange off the inlet, glue in foam-sand to desired shape with a female notch for the diffuser to fit in?
Best way to make the notch so it is repeatable on the rubber boot diffuser?
 
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Pic of my left inlet ramp, I glasses in the inboard portion to give the baffle material something to push against. The left hand forward baffling is removed in this pic, lots of room between the top of the cylinder and the curved top of the cowl.
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Right side has the top of the cylinder squeezing together with the bottom of the top ramp, I should have cut some material off the top ramp and moved the curve forward.
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I'm planning on cutting both ramps out and using a diffuser boot instead.
 
I'm not sure of the angle I should make with the bottom of the inlet. The existing inlet points downward, the metal baffling points back to the middle of the cylinder. Should I leave the downward angle initially then angle towards the middle of the cylinder as the top of the new diffuser boot can expand on the top side?

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I roughly measured my right inlet with the more restrictive upper cowling ramp in 3 different places, front-middle-aft end of inlet. Due to the shape and access, the cross sections are basically square and I used pieces of paper to gauge the size and measured the papers. Almost the same vertical dimensions with expansion sideways. The top page is the side view and measurement of the inlet in inches. The bottom page shows the inlet from the front-black, middle-red, and rear-purple with rough total areas denoted in their color square.
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I've made no progress in trying to pick an inlet, I'm trying to decide between making a smoother larger diffuser shape behind the Van's inlet or make a new round inlet and diffuser. The Van's inlet is harder to seal and make a diffuser for, the round inlet involves reshaping the front of the cowl.

Here's a 5 inch circle mounted in the center of the Van's inlet, I think for asthetics and diffuser shape it should be moved above the cowling split line and outboard toward the outside of the cowling.

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Good start...measuring, playing with shapes and locations, and thinking.

As velocity ratio (velocity through the inlet divided by freestream velocity, Vi/Vo) goes down, duct shape inside the inlet becomes less critical. As velocity ratio becomes higher, internal diffuser shape becomes more critical.

You've measured the stock inlet and find it to be 21.29 sq in. A 5" diameter round inlet would be 19.625", only slightly smaller. Assuming no other changes (notably exit area) there would be no appreciable difference in Vi/Vo. Any gain in conversion of dynamic pressure to static pressure would have to come from an improvement of the internal shape.

Bill Lane obtained a good text when we were talking about ducts earlier this year. Here's a snip, the first paragraph of the chapter on diffusers, credit Applied Fluid Dynamics Handbook, Robert D. Blevins:



Note the part about boundary layer. Any large, stable separation results in less static pressure, as does a shape or separation that results in jet flow. Again, from Blevins; you want #1 or #2, the latter resulting in the highest Cp. #3 works OK. #4 and #5 are bad news:



So how to apply this very basic knowledge to your application? First realize the stock Van's inlet is sized for moderate Vi/Vo, as would your new round inlet. A lot of the diffusion (conversion of dynamic to static) is happening out in front of the inlet, and actual velocity through the inlet is significantly lower than aircraft velocity. That's why we can get away with the crappy duct shapes...the sharp angles, edges, and steps that would trip a faster flow. I would expect only moderate improvement in pressure recovery with improved duct shape alone.

Still, we'll take all the pressure we can get. Once you settle on which Vi/Vo scheme you wish to pursue (the size question), the inlet shape and location largely depends on what is best for duct shape and sealing. Do all you can with shape, but since here the low velocity ratio makes shape less critical, sealing is where you can probably make a significant improvement. Let's face it, the typical flap sealing around a GA inlet is truly awful.

Bottom line? At this inlet size, simply avoid big pro-separation duct errors, and let seal design be the primary driver of the inlet shape and position.
 
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To add to what Dan has stated one thing you can do is move the inlet as close to the prop as you can. This lets you make a slightly longer "diffuser' duct, which will help in keeping with a smooth flow.
If you have a constant speed prop you can turn the blades by hand to get the full coarse condition and then set your inlet 1/4 to 1/2" aft of the blade edge.
Moving the duct closer or farther away from the prop hub might also get you a bit more length due to blade width.
 
Andy,

Previously I wrote "At this inlet size, simply avoid big pro-separation duct errors, and let seal design be the primary driver of the inlet shape and position." You can, however, select other inlet sizes and shapes. Let's explore a bit, from the standpoint of design and fabrication.

As noted previously, as you go smaller, you'll need more and more attention to internal diffusion. If you go larger, you'll eventually arrive at a place where you need nothing more than a hole in the front. The advantage is design simplicity. With mere holes, you no longer need to seal around individual inlets. All that remains is to divide the upper cowl volume from the lower cowl volume, the actual sealing being simple enough that leakage is reduced. That makes a plenum lid unnecessary; it is just a sealing device.

The Mooney Acclaim and Cessna TTX are good examples. Below, I've posted the Acclaim baffling. The Continental has no front alternator, which simplifies the under-the-propshaft tinwork, but it can be adapted to a Lycoming. Look up some photos of Sean Tucker's engine baffling for an example.



Here's an interesting one-shot illustration, Fig 5 from AIAA 80-1242R, which tells a lot about big holes in the front of a cowling. (The paper is available at the NASA documents server: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980214918.pdf)



The researchers set up an entire engine nacelle and wing section in a NASA Ames wind tunnel. They tried three different inlet sizes (41, 61, and 107 sq in total) while measuring upper cowl pressure recovery (Cpu), and the variation in drag (Cd). None of the inlets had any sort of internal diffuser. The climb condition was about 100 knots (and 8 degrees AOA), while the cruise condition was roughly 160, close to typical RV speeds. Wc was an arbitrary 3 lbs per second mass flow, the right ballpark for our Lycomings, set by throttling the flow downstream of the inlet as necessary. The scale across the bottom is inlet ratio, 0.2 being (for example) an inlet area 5x the area of a 3 lbs per second stream tube...a very low Vi/Vo inlet.

There are a number of interesting observations to be made, but here I'll stick to just two key points. First, without good internal diffusers, pressure recovery (Cpu) takes a dive as the inlet ratio is increased. In the 0.6~0.8 range it's is truly awful; the addition of internal diffusers is mandatory at those ratios, and here you see why. However, look how good Cpu is at low inlet ratios, with a very steep rise for the climb condition between 0.4 and 0.2. That performance comes without internal diffusers to complicate design and fabrication, just big holes.

Take a beer:30 survey on any flightline, and you find the usual objection to big holes is drag. However, take a look at the lower plot; the Cd lines are almost flat across a wide range of inlet ratios. For the same cowl and mass flow, inlet size actually has very little relation to drag.
 
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Dan,
Thanks again for taking the time to explain this, I understand parts of the conclusions in the studies but still wrapping my head around it. I'll have to grab my notes.......

I get the 3 lbs per second mass air flow, I believe it comes from the lycoming cooling air requirement charts. It's hard to interpet scale but 2 lbs per second mass airflow keeps CHT's in the 400's.

Just putting some thoughts on paper:
-The 3 lbs per second mass airflow will keep things cool wether through large or small inlets.
-The mass airflow of 3 lbs per second is driven by the pressure differential between the upper and lower plenums.
-Large inlets externally slow the air and provide good pressure recovery with lots of sins in inlet/diffuser shape.
-Small inlets have higher velocity air that need very good inlet/diffuser shape to provide good pressure recovery
-Poor pressure recovery may provide less than 3 lbs per second mass airflow and high CHT's

How do you calculate the size of a tube required to flow 3 lbs per second mass airflow at 160 knts? I'm trying to find the formula of how big an inlet is needed to provide .2 Vi/Vo.

So with the inlet size Vi/Vo in the study at cruis of 160 knts the inlet velocity for the different inlets was:
107 sq in = 32 knts
61 sq in = 64 knts
41 sq in = 96 knts
 
More thinking out loud......

At sea level, standard temp and pressure at 90 knts the theoretical inlet size required to provide 3 lbs/sec of cooling air at a Vi/Vo of .2 =____Area of inlet____.

Vi=18knts (Vi/90knts=.2)
Vo=90knts
90knts=151ft/sec
Volume of inlet=151ft * inlet area

So for the volume of air is it 14.7 psi and interpolating this chart (http://www.engineeringtoolbox.com/air-temperature-pressure-density-d_771.html)
at 60 degrees (close to std) interpolating 10-20 I get .154 lbs/ft3.

I'm having trouble converting/figuring out the volume of 3 lbs of air per second, probably going about it all wrong. Dan, what formula did you use to derive your inlet size of 6 inches?
 
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Just putting some thoughts on paper:
-The 3 lbs per second mass airflow will keep things cool wether through large or small inlets. Don't really need 3 lbs/sec for a 360
-The mass airflow of 3 lbs per second is driven by the pressure differential between the upper and lower plenums. Right
-Large inlets externally slow the air and provide good pressure recovery with lots of sins in inlet/diffuser shape. Without sin...larger inlets make diffusers less critical. Very low Vi/Vo inlet doesn't need any diffuser at all.
-Small inlets have higher velocity air that need very good inlet/diffuser shape to provide good pressure recovery But they work just fine if you get it right.
-Poor pressure recovery may provide less than 3 lbs per second mass airflow and high CHT's Yep.

How do you calculate the size of a tube required to flow 3 lbs per second mass airflow at 160 knts?

Initially design for the most difficult cooling case; full power, slow airspeed. You realized that in your next post, but 90 knots is unrealistic; check dynamic pressure (Q) for 90 knots to see why. At 90, the maximum available Q is 5.28" H2O on a standard day, and per the chart 0-360 chart 3 lbs per sec would require about 12.5" drop across the baffles. Although propwash will push the available Q a little higher (see below), you can't get 3 lbs per second at 90 knots.

120 knot standard day Q is 9.38" at SL, and it doesn't drop below 8" until 5000 feet. With good inlets you might get a Cpu (ratio of upper plenum static pressure to available dynamic pressure) as good as 0.8, so 9.38" available means 7.5" in the upper plenum. The Lycoming cooling air chart says 7.5" will give you about 2.4 lbs per second mass flow. Better start there, as it's what you have.

BTW, you may be thinking "But will that be enough to keep CHT in line?" Well, no guarantees, but there are a few things that can boost the end result.

One, the Lycoming cooling chart data is emperical data, meaning it's what they recorded using whatever they considered to be standard baffles. We don't know exactly what those baffles looked like; that information seems to be in a Lycoming book you can't get. However, judging from the state of standard GA baffle tin design, or even Vans baffle tin, it wasn't anything fancy. We can do things to improve heat transfer at the baffles. For example, I see you've already been busy with glass wraps.

Two, in the climb power regime there is some boost in Q due to propwash. Exactly how much varies with propeller design (notably the shape of the blade roots near the spinner), and the intake location/shape (notably how far outboard and how much radial deltaP across the inlet face). For the BA Hartzell and outboard, low Vi/Vo inlet I use, the difference between 100 knots IAS level flight (low power) and 100 knots IAS climb (full power) at 3000 ft PA was:

low power: upper 6.0 lower 2.5 deltaP 3.5
high power: upper 9.0 lower 3.75 deltaP 5.25

Note that even in the low power case, propwash is boosting Q a bit, as standard Q for this altitude at 100 knots about 6", and no inlet can achieve 1.0 Cpu if the plenum has an outlet. (An inlet with no outlet would be an airspeed pitot.)

In the high power case, propwash is boosting the available Q quite a lot. If I assume a Cpu of 0.8, then available Q was about 11.2", equivalent to about 137 knots.

These numbers should not be treated as accurate in an global sense (because I was using IAS rather than TAS to make the climb airspeed target easier to hit), but the concepts are correct.

I'm trying to find the formula of how big an inlet is needed to provide .2 Vi/Vo.

Whoa hoss...first things first. I've seen data taken with a stock RV-8 inlet, and pressure recovery was actually pretty good. Don't you want to determine what you have before launching off into big time glass work? If pressure recovery is good, the design goal becomes improved sealing and heat transfer, not intake design.

I saw piccolo tubes in your photos. Go fly at 120 knots and determine your current Cpu. You need PA, temperature, and upper plenum pressure.
 
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Prop is in California, but I did get temps and pressures before I pulled it off. Notes are at the airport, should get there tomorrow.

Here's some historical pressures from a while ago, more detail in this thread:
http://www.vansairforce.com/community/showthread.php?t=112941&page=6

"I made 2 flights 4 hours apart at approximately 2000 Pressure Alt. and 78*F with plenum pressure differential measured between static pressure in in/H2O. Here's the rough averages:
115 knts IAS-upper plenum 7.5 In/H20-lower plenum 1.4 In/H2O
130 knts IAS-upper plenum 9 In/H2O-lower plenum 1.5 In/H2O
160 knts IAS-upper plenum 13.25 In/H2O-lower plenum 2 In/H2O"

"Whoa hoss...first things first. I've seen data taken with a stock RV-8 inlet, and pressure recovery was actually pretty good. Don't you want to determine what you have before launching off into big time glass work? If pressure recovery is good, the design goal becomes improved sealing and heat transfer, not intake design."

Yes, my original plan was to use the Van's inlet with a plenum/diffusers and better sealing to the cowl inlets. Reading the different studies has me slightly rethinking the use of a round inlet. I've been very hesitant about "ruining" any of my current parts leaving me an easy out to put it back the way things were........too late.
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Either inlet will still require me trashing the current upper cowling inlet ramps and forward baffling. The thought of major glasswork/re-shaping of the front cowling has had me stalled, I'm currently taking it slow and trying to think through the options. I'm not sure if the simplicity of sealing the round inlet along with reshaping the front cowling outweighs the complexity of sealing the Van's inlet. My equally important goal is easy cowling removal and installation.
 
We can do things to improve heat transfer at the baffles. For example, I see you've already been busy with glass wraps.

Yes, when I installed new lycoming nitrided cylinder assemblies I also made some silicone baffle wraps similar to yours. Really easy to apply with everything off the engine. I really liked the flexibility/durability of the material and they stuck VERY well to the cylinders.

As I was breaking in the cylinders I kept waiting for the CHT's to stabilize at my old CHT temps. Old cylinder CHT data here: http://www.vansairforce.com/community/showthread.php?t=112941&page=5)
Anywho the oil usage stabilized around 8 hours but at 25 hours the new cylinders where about 40 degrees hotter than the old ones. Filing the casting slag on the cooling fins between the valves was worth about 10* cooler and removing the baffling wraps from the cylinder barrels between the cylinders was worth about 10* as well. I also removed the remainder of the baffle wraps from #1,#3 cylinder with no change, I previously had used Van's black baffle material between the curved baffling and lower aluminum baffling. At 50 hours the new cylinders are still 20 degrees hotter than the previous ones, mixture distribution seems to be way different as well.

Since things were apart and I don't have baffle wraps on #1 and #3, I was also thinking about changing the baffling a bit as described here:
http://x-jets.com/Design_for_optimum_cooling_efficiency.pdf
Lots of stuff in the way underneath, but if I could stick the baffling wraps to the baffling around the inlet/exit curves and also design an outlet duct with a different capture system than the rod.
 
"I made 2 flights 4 hours apart at approximately 2000 Pressure Alt. and 78*F with plenum pressure differential measured between static pressure in in/H2O. Here's the rough averages:
115 knts IAS-upper plenum 7.5 In/H20-lower plenum 1.4 In/H2O
130 knts IAS-upper plenum 9 In/H2O-lower plenum 1.5 In/H2O
160 knts IAS-upper plenum 13.25 In/H2O-lower plenum 2 In/H2O"

Convert IAS to TAS, then determine dynamic pressure for that TAS and density, then divide upper plenum pressure by available dynamic pressure to determine upper plenum pressure coefficient. Check my math, but I get:

115 IAS = 121.0 TAS = 8.66" H2O 7.5/8.66 = 0.86
130 IAS = 136.7 TAS = 11.0" H2O 9/11.0= 0.81
160 IAS = 167.9 TAS = 16.7" H2O 13.25/16.7 = 0.79

Even if the inputs are off a little (for example, uncalibrated IAS), it doesn't change the big picture...the stock Vans inlet is pretty good in this level flight condition. Although level flight Cpu might be tweaked for a gain, the real reason for a change (for example) might be to improve Cpu in a high power, high AOA condition, or because it provides a mechanical path to better sealing, or for drag reduction.

Two observations.

Those lower cowl pressures are quite low. There's nothing very restrictive about your exit.

In the other thread you listed 5.5 " H2O for 100 knots IAS in low power level flight, and 6" H2O upper plenum pressure for a full power, 100 knot IAS climb. If that climb condition is apples to apples with your level flight measurements (notably same OAT and altitude), you're not picking up much boost in dynamic pressure due to propwash. That's interesting, given that climb cooling is a big deal. Let's look at that.
 
I put this in a separate post, as it deserves a disclaimer. This where we get experimental...I don't have any supporting documents on this subject, so the following is theory and opinion until proven. Comments please.

Oh yeah, Andy, before we get going too much, was that climb condition measurement in fact apples to apples with the level flight measurement?

Dug up a photo of your prop:

http://www.vansairforce.com/community/showpost.php?p=832884&postcount=198

The Catto has good airfoils at the blade root, as I would expect. So why is that airfoil not increasing inlet pressure at full power?

My guess is twofold. One, it might rise if the inlet was closer to the prop. I think Tom and I have the same opinion here. On my own cowl, I moved the inlets forward to minimum clearance at coarse blade pitch

Two, the slot inlet is subject to significant radial flow across the length of the inlet, i.e. pressure at the outboard end of the inlet is significantly higher than at the inboard end. Such flows wastes pressure. Craig might have some sort of calculated pressure map of the outflow that we could look at. The outflow illustration in CR3405 says there is a considerable radial pressure gradient. If true, a round inlet moved as far outboard as possible would have a major advantage in the high power climb case. FWIW, I've recorded a 33% gain (6" vs 9") with such an inlet.

BTW, it wouldn't matter if such a reshaped, relocated inlet was high or low Vi/Vo.

Stock and relocated inlets side by side:



 
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"There's nothing very restrictive about your exit."

Nope, my plan was to play with the exit after the inlet/plenum side. I was trying to change 1 thing at a time so I could have a better idea what the changes were doing.
Since I was eventually going to reshape the outlet I did cut the aft edge of the stock Van's exit forward approximately 3/4-1 inch in an effort to reduce CHT's while I was playing around with the other things. CHT's were unchanged, lower cowling pressure lost about .5 in H2O and I lost 2 knots. The airspeed loss was noted from my TAS on the EFIS, 4 leg NTPS shows my TAS readout to be just under 2 knots slow.


"Oh yeah, Andy, before we get going too much, was that climb condition measurement in fact apples to apples with the level flight measurement?"

Yes, I took all the measurements on the same flight.
 
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Since I was eventually going to reshape the outlet I did cut the aft edge of the stock Van's exit forward approximately 3/4-1 inch in an effort to reduce CHT's while I was playing around with the other things. CHT's were unchanged, lower cowling pressure lost about .5 in H2O and I lost 2 knots. The airspeed loss was noted from my TAS on the EFIS,..

Loss of low cowl pressure = loss of exit velocity = drag increase. Nicely matches theory.

...4 leg NTPS shows my TAS readout to be just under 2 knots slow.

Not nearly enough to skew conclusions. Two knots = Q of less than 0.01" H2O

Yes, I took all the measurements on the same flight.

Yeah, but did you grab the upper plenum pressure very close to when you passed through 2000 PA in full power climb?
 
Andy, returning to your stream tube question, and intake area ratio...

First establish known parameters. For this example we'll assume that we're climbing at 120 KTAS through 2000 feet on a standard day, and mass flow (from the Lycoming cooling chart) is expected to be 2.4 lbs per second.

120 KTAS = 202.53 feet per second
2.4 lbs per second / 2 inlets = 1.2 lbs per second per inlet
Standard density 2000 ft = 0.072098 lbs per cubic foot
1.2 lbs / 0.072098 = 16.6440 cubic feet

The necessary math is based on the usual formula for volume:

volume = area x length

or

volume = radius^2 x pi x length

We know the length of the stream tube (202.53 feet) and the volume (16.6440 cu feet), so just flip it around and solve for R^2:

volume / pi x length = R^2
16.6440 / 3.14 x 202.53 = 0.02617

That's radius squared, so its square root is the actual radius of the stream tube...

sqrt of 0.02617 = 0.1618 feet

Two times radius is diameter, so:

0.1618 x 2 = 0.3236 feet

And last, 0.3236 x 12 = 3.8832 inches stream tube diameter for one intake.

We're interested in area ratio, i.e. stream tube diameter / intake diameter, so we need area for each. Here I'll assume a 6" diameter inlet ring, since I don't yet know what you might choose:

(3.8832 / 2)^2 x 3.14 =11.837 sq in
(6 / 2)^2 x 3.14 = 28.26 sq in

11.837 / 28.26 = 0.4188 area ratio, which is the same as Vi/Vo

Yes, I've put it into a spreadsheet and sent it to you.

Plug in different altitudes and airspeeds. You'll see that Vi/Vo changes with each change of input. For example, at 175 KTAS the stream tube is longer for the same volume, so diameter is decreased, and area ratio becomes 0.2871.

Take particular note of the converse; area ratio rises when airspeed is reduced. It means for a high Vi/Vo inlet, low airspeed makes diffuser quality more critical...which is why some small inlets don't cool very well at low speed and high AOA. Any little design error or condition that pushes the inlet flow into separation tanks the Cpu value.

As always, ya'll check my arithmatic ;)
 
Dan,
That's exactly what I was looking for, I still have more homework to do to wrap my head around it. I think I was having more trouble keeping the units straight than anything.

As far as the plenum pressures taken at 100 KIAS level vs full power, those numbers were taken a year and a half ago and I honestly cannot remember for sure. I believe I was at 1800 level for the 100 KIAS where I took my readings, I then transitioned to a full power climb at 100 KIAS starting at 1800 pressure altitude but I'm sure it took at least 500-800 feet to get a stabilized airspeed and pressure so the pressure readings were most likely taken passing through 2500-3000 pressure altitdude. Next time I will start the climb low enough I can be established on airspeed and pressures passing through my target altitude.
 
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Next time I will start the climb low enough I can be established on airspeed and pressures passing through my target altitude.

Never hurts to repeat a test. For now it's not a big deal. The difference in available dynamic pressure due to air density reduction is only about 0.10" per 500 feet.

For example, you previously listed level flight upper plenum pressure as 5.5" H2O for 100 knots IAS in low power level flight at 2000 PA, and 6" H2O upper plenum pressure for a full power, 100 knot IAS climb. If you were in fact passing through ,say, 2500 PA when you recorded the 6.0" figure, maybe it would have been 6.1" at 2000. Doesn't change the big picture; you're not getting much of a pressure boost due to prop outflow in full power climb.
 
Pressure and temps from a month ago with the aft edge of the cowling exit cut forward and a temp probe in the lower cowling. The lower cowl temp may be off a tad, on the ground the EFIS OAT was 49 with the cold lower cowling 54.

Level flight
Pressure Alt 3500
OAT 32 *F at 3500PA

100 KIAS
Upper Plenum 5.8 in/H2O
Lower Cowl .81 in/H20
Lower Cowl Temp 107*F
CHT 294-302

160 KIAS
Upper Plenum 15.4 in/H2O
Lower Cowl 1.16 in/H2O
Lower Cowl Temp 108*F
CHT 348-382

100 KIAS = 103.5 KTAS = 6.56 in H2O 5.8/6.56 = .88
160 KIAS = 164.9 KTAS = 16.65 in H2O 15.4/16.65 = .93
 
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The plenum I received from BillL fit my standard Van's baffling like a glove once I removed my black baffle material.

6760A36B-265E-4A79-AA2F-AFAE461CD564_zpsyljk15ag.jpg


3A5187CD-400B-4E70-9E2C-6579142C65F1_zps0b9maqf6.jpg


Unfortunately there seems to be some difference in the vertical position of the front of the plenum. My baffling for the Van's cowling is trimmed to a tight 1/2 inch all the way around, that leaves about 3/4 inch of metal baffling above the front corner of the #1 cylinder. Seems the Sam James cowling must have more vertical clearance in the area, Bill was nice enough to send me a template of his front baffle for the #1 cylinder which is approximately 3/4 inch taller than mine. In order to keep 1/2 inch clearance from the top cowling I had to lower the front of the plenum.

5EDCB063-08E3-47FC-911A-3A01E021DE8F_zpss7zq7qo6.jpg


The piece of paper shows the bottom of the top cowling with a 1/2 inch clearance line, the plenum is well below that.

E3A9E715-9969-450E-ADDD-54D1B8275AE9_zpsu8xow81p.jpg


I was hoping to possibly trim the outboard front corners slightly, but I think there is just too much variation in the shapes between the Van's and Sam James cowling.

20B1E42B-FD6B-489C-9D06-1633E8108BC4_zps1sv1aiae.jpg


5761B62C-A0DB-4ECD-B4C3-23133C210513_zpssjmw7l1q.jpg


Although this doesn't look like it's going to work for my installation, I think BillL's Plenum is a great product for anyone installing a Sam Jame's cowling. His product, price and service was unbeatable.
 
More destruction, man I was so proud of those ramps. I used foam/glass to continue the spinner curve of the cowling onto inlet ramps so the black baffle material had a nice smooth transition to push against. I didn't have the heart to throw them away...

9E0AE698-8DB2-4065-817B-A37155503C44_zpsfvutmn9t.jpg


The top cowling is cleaned up and block sanded, I never smoothed the surface originally and just roughed it up and covered it with epoxy. I'm thinking of using the top cowling as a mold for making a plenum but it's going to take some work first. I would rather build the plenum over the existing baffling, but I can work with the top cowling at home in a semi-heated garage (and in the house next to the woodstove when the wife is at work!). Here's a pic before the first thin coat of filler/micro.

32C3E87C-BD60-4266-B6C0-BCACEDC6C807_zpsbyrtp9vf.jpg
 
Andy,

You're welcome to borrow a little room from me. I normally keep the shop around 60 degrees. I'm guessing I'm 20 - 25 minutes north of you.

I'm just starting on a 14. Could use a bit of advice, tutelage, and would share a cup of coffee.

Shop%202015.12.2.jpg


Send me a PM if you're interested.

Fred
 
I figured the inside of the cowling would be a good test bed for trying drywall mud as a pinhole filler, I figure the extra heat should help expose anything and if it does the areas will be under the cowling. The inside of the cowling was coated with raw epoxy but never properly block sanded, I added a thin coat of filler and sanded smooth. I then spread drywall mud on with a rubber scraper, I added a second coat later just smooshing it around the surface with my hands. As expected it sanded of very easily, it seemed to fill the little scratches, small and large pinholes well.
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9D1B1CAA-E24F-4E88-BA9D-EC04E2B615A8_zpsfnxy0pgf.jpg


I carefully cleaned it up and squeegeed on a coat of epoxy primer. I wet/block sanded this and then sprayed a coat of epoxy primer that I also wet sanded.

F008C7B7-A9C9-41BB-8ACF-674C15B684C7_zpskw60w5qx.jpg


3D3D0BB8-F223-4D5C-9262-DF5A22561454_zpsoz9cpf5o.jpg
 
I buffed on a layer of wax, and a couple coats of PVA. This was my first time using PVA and I sprayed my first coat on too heavy, I had some runs and drops on the vertical surfaces. I used AEROPOXY and laid up 4 layers of 9oz glass, so far this is one of my better fiberglass pieces. I covered the layup in peel ply and topped it off with scrap glass to soak up any extra resin,l. I tried really hard to squeeze out all the extra epoxy and air bubbles while it was between sheets of plastic before I applied the epoxy infused glass to the cowling.
1C2CB955-E028-4EFD-8CBF-13A0A1DE22C8_zps5npgalex.jpg


It half cured in the garage at 65-70 last night .I'm trying for a 110* cure with my wood stove and instant read thermometer.

7571098D-5447-402E-A682-C4D07F1022DE_zpscmwswfdh.jpg
 
Andy,

You're welcome to borrow a little room from me. I normally keep the shop around 60 degrees. I'm guessing I'm 20 - 25 minutes north of you.

I'm just starting on a 14. Could use a bit of advice, tutelage, and would share a cup of coffee.

Shop%202015.12.2.jpg


Send me a PM if you're interested.

Fred

Fred...:eek: Does that extend to Canadians? I'll come use your shop!!!:D
 
Another RV guy swapped me BillL's plenum for an RVBit's plenum, it fit the Van's cowling slightly better but still too flat on the outboard edges to suit me.

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2AECE0FB-5D09-4A99-A759-A00C5B6B4D02_zpsq1df3xgv.jpg


I wish I could fit this on the airplane, but this lets me work from home so to speak. I roughly trimmed the plenum to the metal baffling, now to try to make some flanges. The aft baffle sits at an angle, I marked/sanded this angle on some foam and glued it with micro in place on the cowl to hold the correct shape. I also formed additional foam blocks for the forward flanges. This stiffened my floppy plenum up considerably, it may still require additional strength.

C73B3381-FC15-412F-86E7-D1EED5494424_zpseljnsz4c.jpg


1543C120-DA46-4D02-80B9-8081913767AE_zpspi6xdlt6.jpg
 
I'm playing around with making my own round inlets for the front of the cowl. Time to fire up my Wife's router for the first time, It was her not so popular Christmas present several years ago.......go ahead and laugh I really should've known better....
I ordered a circle jig and several router bits, the first cut was on the circle jig itself to make room for a 7/8 core box bit.

DB3C1647-0F56-4CBE-B258-7AB2D8C351CB_zpsu17gspoy.jpg


I also ordered a chunk of HDPE plastic to route shapes into, fairly cheap and nothing is supposed to stick to it. I cut my first groove, Man this thing makes a mess!

C5C5C311-4CEE-40AE-B667-039EE1F4D66D_zpsz6isfbmk.jpg


I filled the grove with a wet mixture of West Systems and Flox topped with a single ply of 8.9 oz scraps, I set a cheap plastic cutting board on top weighted down to try and flatten things out. It worked pretty well, nice flat surface and just a little bit of prying popped it right out.

32C4099C-AA37-4D5C-A5A9-542656EE9DFC_zpsjlsx0okr.jpg


929A0292-1545-4836-A956-2DF6562DCD97_zpsuvqk2qzo.jpg


My original impression is that the ring is too large for my cowling, 6 inch inner diameter is just shy of 8 inch outer diameter. I want to play with making a smaller radius on the inside of the ring and maybe a 5 1/2 or 5 3/4 diameter opening.
 
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Andy,

I tried to make flanges like you have and it did not work well - the cause was the engine twist. The engine is twisted to the right side, although the crank flange is in the center.

The baffle width is 31.5" wide and parallel. The sides are perpendicular to the back baffle too. But the engine is twisted.

If your current path does not flow well, You might consider taking the insulation and fastening it to the baffles, then placing the cover over the top, when it fits in place, you can check the clearance to the cowl, then glue to the insulation.

If your path works, then. . . . (like Roseanne Rosanna-danna ) never mind.
 
BillL, in my best New York accent.....
"What are ya tryin' to do, make me sick?!:D

I believe you are right in fastening the foam to the baffles and then gluing the plenum top to the foam, I wish I would have thought of that first. As it is I'm hoping to see how it fits or doesn't fit tomorrow. Oh well it's only fiberglass, I can always grind it off make a mess and do it all over again.
 
Andy,
Two thoughts...
1. Does your wife's router have a shop vac fitting? If so, you can buy her a nice shop vac for Christmas...to go with the router of course... :D
Seriously, a vac would help with the mess. If the router has no vac fitting, you could get one of the girls to hold the tip of the vac near (but not too near) the router as you make the cut to suck up the scraps. Getting the oldest girl to help would be best, and I'm sure she would love to help Daddy work on the plane.

2. The 6" diameter on the inner lip may seem too big, but if you do the math it will give you just about the same area (28 sq. in. each side) as the standard Van's cowl inlet (25 sq. in. each side). If you then throttle the exit per Dr. Dan's previous posts, you should have plenty of cooling for just about any flight regime without creating speed/drag issues.

Regards,
 
Cripes, if my wife gets on here and finds out you got your wife a router, that racheting wrench set sitting under the tree I got for her is going to look sad.

Thanks a lot, pal.
 
Unfortunately BillL was right, there is a bit of a twist in the baffling. Seems the right front of the baffling is 1/4-3/8 inch lower than the left front. I'm sanding off the foam I glued to the fiberglass plenum and gluing foam to the baffling instead.
8FCC3538-10CA-445A-8064-2FFFB78B620E_zpsoznmsr1i.jpg


I think I've finalized my inlet shape and size. I originally planned on using the existing inlets, but to better my odds of more cooling I decided to:
-make the inlet area larger
-move the inlets outboard
-move the inlets forward
-use round inlets

I ended up with 5.75 ID per inlet with 25.97 sq in versus my stock size of 21.29 sq in, SJ large rings have 16.8 sq in per inlet. Being fixed pitch I generally climb out at 130 knts as a compromise between horsepower, climb rate and cooling. At 130 knts my stock Vi/Vo should be .54, with the new larger inlets it will be .45. At 90 knts the stock Vi/Vo should be .77 with the new larger inlets at .65.

I used a 7/16 outer lip and a 3/16 raduis inner lip for the ring I plan on bonding to the front of the cowl. I routed a 7/8 core box into some HDPE then routed the middle of the groove out.
230DA8E2-74F9-49C6-BC63-775C99603B8A_zpsrf7stdc2.jpg


I routed out another disk to fit the hole and then used a 3/8 core box bit to make the inside radius. I used a finish nailer to tack everything to the bench.
742A7A38-0C01-4F2D-911E-AD6651FEB40F_zps8gvm4opf.jpg


The new ring with the smaller inner radius next to the full 7/8 diameter ring I made first, the OD of the smaller ring is .75 inch less.
EE7490BE-82B9-4165-91BA-02BDE23F5676_zpsvf1nih1q.jpg


The 3/4 inch smaller outside diameter of the new ring appears to be easier to blend into the existing cowl, just my uneducated opinion.
B039EA5B-64C5-4E6F-AE8C-272A7D7A7FE1_zpsteqc3i2s.jpg
 
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2. The 6" diameter on the inner lip may seem too big, but if you do the math it will give you just about the same area (28 sq. in. each side) as the standard Van's cowl inlet (25 sq. in. each side).

Michael,
Just curious if the inlet area quoted was from a smooth horizontal induction Van's Cowl. I found my vertical induction on cowl inlets were considerably smaller than a friends RV7 with the smooth bottom horizontal induction cowl. Just curious if all the smooth bottom cowls have a larger inlet area than the vertical induction. I did some glassing to get the inlets to match up while fitting my cowl, I think I inadvertently decreased my inlet area while doing this.
 
I lightly peened the outer surface of the prop flange bushing in several places with a center punch and pressed it in with some all thread as recommended by Saber, I also used some red loctite. I'm not positive it will hold and will test tighten with some scrap tubing in case it comes loose. The availability and price of oversized bushings leads to having someone with a lathe turn down an indexing bushing to the size I need as my next option.

5D37904F-CCC5-4B5E-AE8A-094C2A8E7BF4_zpszbqgyjtg.jpg


I mounted the prop to find my clearance from the back of the prop blade to the front of the inlets, since the spinner portion of the cowl is flat and equidistance from the prop I used it as a reference.
The inboard right side is 1 1/8 inch aft of the prop blade, the left side is 1 3/32 inches. The outboard side is harder to measure accurately due to the blade sweep and lip of the inlet but the left outboard side is about 15/32 further aft than the right outboard side.

0DBF8A17-0FD6-445D-BF0E-131E4B805CCE_zpssockmahq.jpg


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I mounted a yard stick to the split line of the cowl and hot-glued some foam to represent the closest point of the rear of the prop blades. I marked center lines on the round cardboard with some vertical tick marks to play with different locations, I also made some marks on the spinner portion of the cowl for outboard/inboard measurements.

DE3C3D53-CC9C-44D3-9EE1-D472BFFA1AC8_zpsr2xrmvok.jpg


This moves the inlet out quite a bit from the original location, I'm shooting for 3/8 inch aft the prop blades on the inboard side of the inlet.

266AF94A-BBC9-4E47-A53F-08144BC2F40D_zpsiudguv6i.jpg
 
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Best build session I've had all year.....last couple of months included! Mr. Baby is down for a solid nap while the oldest 2 are actually interested in learning how to apply math with tape measures, ratios (mixing epoxy) and power tools while the 2 year old plays in the bucket of soapy water......
Here's the blank slate so to say, its been the front of my plane for 2 flying years and attacking it with 60 grit and sloppy epoxy has been the biggest hang-up of this project.

4677763A-C2ED-48C4-9844-74139692995A_zps5gmuwawm.jpg


The girls and I figured out how to measure and scribe an arc in some foam and the 5-1 ratio of epoxy to hardener. They painted on some dry micro and we stuck our foam blanks onto the cowl.

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While we were waiting for the cowl to dry my oldest daughter and I made some templates for the flanges of the plenum. After gluing the plenum top to the foam on the engine baffling I sanded the edges down to make up for the width of the fiberglass, we'll see how it fits.

FBCD7B11-6644-4772-AF01-B5F52333DAE8_zpsmvmkgxhr.jpg


80FDA5FD-4149-4C1D-844B-CDCA35A5AB26_zpsc8dpbj7z.jpg


A0BE798D-3737-45FC-931E-064AE7F89E38_zpshbglplsq.jpg
 
I whacked the excess foam off with a drywall saw.

AEF90A0D-DC2C-4B0B-98C2-E0587911B7A0_zpsfe7me3un.jpg


When I originally fitted the cowling I used a 3/16 inch gap between the spinner and the cowling, I'm using the flat face of the cowling behind the spinner as my reference plane. I used a 1/4 inch piece of Masonite over the flat spinner area to give me the proper height, I used a flat piece of oak with some sandpaper glued to it to sand the foam down. I used an 1/8 inch piece of cardboard to further cut down the right side which was slightly closer to the prop. The

BC556EBF-D07E-4612-9635-08ECA1DCFE07_zpsbl9k3xq9.jpg


6180CAA5-C95F-4062-87F4-BCA8AE2395EA_zpsbx3erpyp.jpg


It left me with about 11/16 gap between the flat spinner area of the cowling and the front of the rings, the left side foam height is 3/8 inch higher than the right side. The aft edge of the prop is about 1 1/8 forward of the flat spinner area of the cowling giving me about 1/4-3/8 inch clearance between the prop and inlet rings....I hope.

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Inlet rings epoxied in place.

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Looking Good Andy! Don't forget about prop blade clearance. I don't know about Cato, but others can come back even with the back of the spinner (or more for the older Hartzell composite CS). The right side is closer due to the engine angle. (I see you knew that!)
 
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