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catto vs constant speed

R

Reheat

Active Member
A lot of you have expressed interest in the Catto prop vs a constant speed propeller. There are many of us flying behind a Catto. In fact the endorsements from this group are what convinced me to try the propeller in the first place. It is simple, LIGHT WEIGHT, smooth, relatively inexpensive, has no harmonic issues and provides GOOD performance. Does it perform as well as a CS prop? No, it does not. The constant speed prop will give a higher rate of acceleration as well as a higher rate of climb. How much so depends on how well the builder kept the weight down.

Allow me to attempt to illustrate with the following graphs (My RV-8).

Graph 1 shows power available vs power req?d for fixed pitch and C/S AT THE SAME WEIGHT. The vertical distance between pwr req?d and pwr avail at a given airspeed is EXCESS POWER. This stuff is addictive. It is crack-for-pilots. The more you?ve got, the more you want.


powernz3.jpg



Graph 2 shows rate of climb comparison, again AT THE SAME WEIGHT

clicompareql6.jpg




Since MOST C/S machines are a little heavier than their fixed-pitched cousins,
Graph 3 shows rate of climb comparisons with the C/S ship weighing 100# more than the Fixed

100lbseb1.jpg



The bottom line is that I love my Catto. For an old fighter-pilot it provides me with a very lively airplane with minimum weight and complexity. If you are an EXCESS POWER junkie, I understand... 10:1 pistons, C/S prop, and shoot the nitro to it! Just gimme a ride in it sometime.

I hope that maybe this sheds a little more illumination... more food for thought for those of you who are still contiplating a propeller.
Cheers!
 
Nice Chuck.....

.....now do a max cruise speed graph of the two, with the Catto at 7500' and 2700 RPMs:D

Thanks,
 
Hi Pierre. If you look at the top graph you'll see that the two pwr avail lines come together where they cross the pwr req''d line at about 180ktas. The data point for my airplane at 75%/7500' is about 175ktas, and I would assume that the C/S would run close to that as well, given that the two prop efficiencies were similar. Since this data is derived from flight testing, cafe reports, and a Hartzell computer program, and good ole curve fitting, don't pay as much attention to the absolute numbers (they're as close as I could get em) as the comparison of the two types of props. Everyone's aircraft will have a slightly different drag polar and Installed Power number and results will vary accordingly. I should add that the fixed pitch curves are for a GENERIC prop with a max efficiency of .84, but feel it represents my Catto pretty well.
 
Where's the Beef?

I'm probably missing the point, but to me the charts just make me wish I could afford a Hartzell. I thought you were going tell us about Catto props. Do you have one that shows Sensenich vs. Cato vs. Hartzell?
 
Sorry Jon, didn't mean to be misleading. No intension of trying to sell you on the Catto. I just thought some graphic illustrations between Fixed and C/S props might be helpful to some. I do not have the where-for-all to give you a comparison between the Sensenich and the Catto. Both are good propellers, I'm sure, and I expect their performance to be similar. The Sensenich has some harmonic issues, weighs more, but is impervious to rain.

The basic physics (and the whole point, I suppose) is that there is no magic in the Catto that would allow it to perform like a C/S prop. I really like mine for its smoothness, light weight, and lack of moving parts and am willing to give up a little acceleration and rate of climb. Craig nailed the data point I gave him which was 75%/8000'/2700 rpm/200mph(175k). I did not ask for more speed so that TO/Climb could be as good as possible given the pitch of the prop.

The graphs definitely show the superior performance of a C/S prop. It's the "how much difference" I wanted to illustrate. My apologies if there was any confusion.
 
I really like my Catto

I've put about 100 hours on mine so far and I really like it. Smooth, quiet, light weight, NO MAINTENANCE, and the performance is good enough.

I have completely lost the urge to fly behind a CS prop. For me, the extra performance is not worth the hassle.

Also, the drag is much lower at low airspeeds. This was a pain in the pattern until I got used to it. During an engine failure, however, it becomes a life saving feature.

When I want to come down fast I keep the TAS up around 160-to-170 and pull the power. It comes down really fast.
 
Nice!

Chuck,
I certainly appreciate your time and effort in putting this info together. Even though I went with a Hartzell it is a bit eye opening to see the bottom graph which highlights the effect of the weight diffence . It would be interesting to know the actual weight of my installation when you include gov., cable control, oil lines, added oil, and brackets. I'd be surprised if it was a 100# but 60 wouldn't surprise me at all. In any case it certainly has its penalties and evens the playing field some. More important to many, would be the hard hit on the wallet & cost of maintaining the CS. Thanks again for posting this.
 
Steve Brown said:
I have completely lost the urge to fly behind a CS prop. For me, the extra performance is not worth the hassle.
Click to expand...

All depends where you live and fly, I suppose.

Out here in mountain country, we try to convince all that are still "sitting on the fence" to go with a C/S; even with the difference in cost.

Why......... because I don't know any RV owner around here, who wouldn't prefer a C/S over their fixed pitch prop, if money and engine limitations weren't of concern; especially if they've flown both for comparison. With high density altitudes, and quickly rising topography at various airfields, the C/S is amazingly different, performance wise. And that includes getting out of the airport, as well as getting in.

L.Adamson
 
It looks like from your plot that the CS peaks in efficiency at 150k/173mph and the Catto at 172k/198mph, right? Seems to me your CS needs to be re-twisted to get it to peak at a higher speed. Notice that those two efficiency peaks are reasonably flat over 10k-20k, so the prop could be designed to deliver its peak at the higher speed and still deliver good performance if the drag was later reduced.
 
I would suggest that you people at the higher fields have your props designed to deliver rated rpm at summer density altitudes of 14,000' to 15,000', baro altitudes of 11,500' to 12,500'. That way you'll have plenty of power for your high-hot takeoffs, plus you can cruise reasonably fast at the higher altitudes where the traffic and turbulence is reduced. I've flown with a friend out of Casper, Wy, about 6000', 25C, for a density altitude of about 8500' at 1550 lb. My Lancair has 77 sq.ft. area, and SL 125HP at 2800rpm. I designed the prop to give me 2800 rpm at 10,000' dalt, so it gives me 2230rpm static and 2410rpm in a climb at 110mph IAS for a ROC of 1450-1550 at 1000' dalt, 1350lb.
 
Paul your observations are correct. I do not pretend to be in the same league with you guys who design these things. The C/S curve was generated from a DOS program that Hartzell sent me some time ago when I requested propeller efficiency curves from them. I Graphed the data for sea level operation and have since lost the program when my old computer dumped. The acft was sold and I do not recall which specific propeller it was. The curves were meant to represent general FP and C/S props designed for RV's to show the basic performance differences. If you feel they are mis-representative in some way, I think we all would like to know so we can have a more acurate picture of what is going on. Perhaps the C/S would be better represented if the peak was skewed to the right a little. I seem to recall that the Hartzell peaked at .86. Your comment on the flat part of the curves has already shed some more light on the subject. Anything else you would like to add would be appreciated.
 
Reheat said:
Sorry Jon, didn't mean to be misleading. No intension of trying to sell you on the Catto. I just thought some graphic illustrations between Fixed and C/S props might be helpful to some. I do not have the where-for-all to give you a comparison between the Sensenich and the Catto. Both are good propellers, I'm sure, and I expect their performance to be similar. The Sensenich has some harmonic issues, weighs more, but is impervious to rain.

The basic physics (and the whole point, I suppose) is that there is no magic in the Catto that would allow it to perform like a C/S prop. I really like mine for its smoothness, light weight, and lack of moving parts and am willing to give up a little acceleration and rate of climb. Craig nailed the data point I gave him which was 75%/8000'/2700 rpm/200mph(175k). I did not ask for more speed so that TO/Climb could be as good as possible given the pitch of the prop.

The graphs definitely show the superior performance of a C/S prop. It's the "how much difference" I wanted to illustrate. My apologies if there was any confusion.
Click to expand...


Chuck,
Are you running a 2 or 3 blade catto?
What pitch?
 
Nice Job

Chuck, I apreciate your input and that, though you mention the graphs may not be perfect, I am willing to bet they are not only "in the ball park" but probably close to home plate. They give an excellent idea of the performance differences and how relatively insignificant they are (high density altitudes aside). Thanks, George
PS: I also have a Catto and except for the rain factor I like it. (I know that I would be over 2600 RPM with a Hartzell too frequently in my 160 HP Lyc.)
 
Excellent Report

Thanks for the report, Chuck. Lots of good info here.

This is one I am saving to a pdf file for future reference.
 
I'll stick with a FP

L.Adamson said:
All depends where you live and fly, I suppose.

Out here in mountain country, we try to convince all that are still "sitting on the fence" to go with a C/S; even with the difference in cost.

Why......... because I don't know any RV owner around here, who wouldn't prefer a C/S over their fixed pitch prop, if money and engine limitations weren't of concern; especially if they've flown both for comparison. With high density altitudes, and quickly rising topography at various airfields, the C/S is amazingly different, performance wise. And that includes getting out of the airport, as well as getting in.

L.Adamson
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My airport (KPAO) is so close to sea level that half the time my altimeter reads below sea level at the airport. On the other hand, my daughter lives in Littleton and I've flown the airplane out of KAPA on a hot day. Performance is obviously significantly degraded form sea level, but is also significantly better than my last airplane (1981 M20J) which had a CS prop. So, it depends on what you compare it to.
If I wanted to use even higher elevation and potentially shorter strips, with obstacles, I might be tempted to go CS. My first inclination, however, would be to address the problem with horsepower rather than CS prop. I'd rather add the pounds putting more CI under the cowling, if possible, because it doesn't add complexity in terms of maintenance or flying.
Just my preference.
My reasons for preferring FP are only tangentially related to money. I'm not a great mechanic and don't have lots of time to spend maintaining the airplane. So I put a very high value on keeping things simple. Also, I consider myself a decent IFR pilot, but I fly better IFR with fewer knobs to yank.
I'll admit that if I lived in high country my views on FP verses CS could change.
 
rain concerns

What are the rain concerns with the catto prop and what do most folks do to compensate for the condensate when IFR?
 
Rain?

I've been flying my Catto for over 4 years and haven't found rain to be a problem.
Now to be honest, I don't like flying in rain anyway. When I get into rain, I pull back on power and head for the "bright spot".
I do have "prop guard" leading edge tape on mine.
 
Dan, I am running a 66 dia / 76 pitch 3 blade.

Bugsy, Craig Catto says that if you keep the revs below 2200 then you will be ok in the rain. I haven't tried it, but I think some of the other guys have.
 
Slow down

Bugsy said:
What are the rain concerns with the catto prop and what do most folks do to compensate for the condensate when IFR?
Click to expand...

Rain usually means bumps. The RV9 has a VA of 100kts, so slowing down is a natural part of flying in rain anyway. For me that has meshed well with the RPM "limit".

I have flown in rain, but not heavy rain yet. I don't particularly like flying in heavy rain, but if it happens I'll slow to VA.
 
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Rain

I have flown in rain and throttle back to 2100 to be on the safe side. Even with that I still have a little rash on the first 5" or so of the leading edge. I do not have the prop guard tape and sort of wish that I did. The damage may have happened early when the rain was very light and before I pulled the power back.

Is there much, if any, loss of efficiency with the tape?
 
L.Adamson said:
All depends where you live and fly, I suppose.
Out here in mountain country, we try to convince all that are still "sitting on the fence" to go with a C/S; even with the difference in cost.
Why......... because I don't know any RV owner around here, who wouldn't prefer a C/S over their fixed pitch prop, if money and engine limitations weren't of concern; especially if they've flown both for comparison. With high density altitudes, and quickly rising topography at various airfields, the C/S is amazingly different, performance wise. And that includes getting out of the airport, as well as getting in.
L.Adamson
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Not quite a prop item, but I designed a set of wingtips for Jim Smith's RV-6. They increase wing area from 110 sq ft to 115 sq ft and AR from 4.8:1 to 5.8:1. This should make high altitude flight a little faster, and keep the nose attitude further down up high. Let's see how these test out and what performance gains, if any, Jim sees. These might be the answer for you "uppity" people! If you want to contact him about his three-blade ELIPPSE prop, his OAT and TAS testing travails, or just to encourage him in his wingtip experimentation, his e-mail is: Jim Smith, [email protected]
 
Side by Side

Reheat said:
Since this data is derived from flight testing, cafe reports, and a Hartzell computer program, and good ole curve fitting, don't pay as much attention to the absolute numbers (they're as close as I could get em) as the comparison of the two types of props. Everyone's aircraft will have a slightly different drag polar and Installed Power number and results will vary accordingly. I should add that the fixed pitch curves are for a GENERIC prop with a max efficiency of .84, but feel it represents my Catto pretty well.....

The C/S curve was generated from a DOS program that Hartzell sent me
Click to expand...
The data you got from Hartzell was most likely older F7666 blade and 74" dia data. Top speed wise 74" is a little slower than 72" and the F7666 verses the BA is also a little hit on top speed.

Good info, but how did you mix empirical data (actual flight data) for your Catto and theoretical/derived data for the Hartzell. I'm just asking. I'm guess you derived some empirical aircraft drag data. How did you derived that aircraft drag data? Any way, good effort, love the math and graphs.

A side-by-side with another RV-8 (with like engine, weight, fit and finish) with a Hartzell, to check the data, would be cool. I'm a big fan of the SBS comparisons, and throw a Sensenich and other fixed props in there as well.
 
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gmcjetpilot said:
The data you got from Hartzell was most likely older F7666 blade and 74" dia data. Top speed wise 74" is a little slower than 72" and the F7666 verses the BA is also a little hit on top speed.

Good info, but how did you mix empirical data (actual flight data) for your Catto and theoretical/derived data for the Hartzell. I'm and just asking. I'm guess you derived some empirical aircraft drag data. How did you derived that aircraft drag data? Any way, good effort, love the math and graphs.

A side-by-side with another RV-8 (with like engine, weight, fit and finish) with a Hartzell, to check the data, would be cool. I'm a big fan of the SBS comparisons, and throw a Sensenich and other fixed props in there as well.
Click to expand...

All things considered (weight, complexity, cost), the fixed pitch propeller is an good alternative to the constant speed units at this level of flying without pages of numbers to back it up.

When I came into the RV world, Tom Lynch checked me out in the 6A and later the 6 - one was CS the other FP. I was impressed with the CS operation but the FP was no laggard. It took a bit more runway to get airborne but climb out and cruise was most acceptable. I do not have SBS numbers but the impression from the left seat was good. The overall performance of FP compared to CS was more than just OK.

The item that least impresses me with CS other than cost and weight is glide range. It just does not exist. Unless the system provides for feather or near feather, the airplane will come down much sooner than later.

Missed your ugly dog, George. Welcome back. :)
 
Hi George. Your assumption is correct. This all started with a quest to come up with an estimated Equivalent Flat Plate drag number for my airplane in order to compute the Drag Polar. Sounds easy enough, but… Maybe not! I was intrigued by Jack Norris’ Zero Thrust Glide (ZTG) method. I found the CAFÉ report they did on a RV-6A (FP) using this method. They computed L/D Max using the glide data, but had to admit that as hard as they tried, finding perfectly still air was a problem. There was also the CAFÉ report on the RV-8A, but the ZTG was not used. Still, the RV-6A report gave me a place to start and I knew that their numbers would be closer than anything I could come up with glide-wise. I had a book on Flight Testing of GA acft by Ralph Kimberline and that was also helpful. Neal Willford’s articles in Sport Aviation provided some of the Propeller Data, as well as, performance formulas that allowed me to determine that the ones I learned 35 yrs ago were still valid. Since gliding was out, I decided to use cruise data to determine the drag. My acft consistently hit 179-180 ktas WOT at 7500’ at 75% pwr. Here’s where the hallucinating begins. There are no dyno numbers on my engine, but Mattituck placarded it at 185HP, so that’s what I used. I picked a max prop efficiency of .84 based on some of Neal Willford’s numbers backed up by an Aero textbook. I then juggled with the Installed Power Reduction until .93 seemed to be reasonable. From there it was
185 X .75 X .93 X .84 = PWR AVIAL = PWR REQ’D. Divide by the Velocity and you get DRAG. Next, Calculate the Induced Drag at the data point and separate it out and you are left with the Parasite Drag. This yielded a Flat Plate Area of 2.2. The CAFÉ boys came up with 2.32 for the RV-6A, so I felt I was in the ballpark (yeah, and the left field wall is 400’). So… the data represents SOME acft with a Flat Plate of 2.2 and at least gives a graphic demonstration of FP vs C/S over the Velocity spectrum. This is sorta like standing in front of everybody naked (heaven forbid). I keep expecting Kevin Horton to stand up and shout BULLHOCKY or some other equivalent.:p
 
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Reheat said:
Next, Calculate the Induced Drag at the data point and separate it out and you are left with the Parasite Drag. This yielded a Flat Plate Area of 2.2. The CAF? boys came up with 2.32 for the RV-6A, so I felt I was in the ballpark (yeah, and the left field wall is 400?). So? the data represents SOME acft with a Flat Plate of 2.2 and at least gives a graphic demonstration of FP vs C/S over the Velocity spectrum..:p
Click to expand...

In my computer programs I use for prop design, one of the things I get is an estimate of the equivalent parasite drag area (not to be confused with flat-plate drag area) using the performance data I get when someone does TAS testing using one of my props. I got numbers of 2.2 +/- 0.05 for Jim Smith's RV-6 which seems ballpark to the C.A.F.E. number of 2.32. 'Guess the difference might be due to the nosewheel. One of the interesting things that came from my program is that to get a good data match between the computer model and the actual flight data is that I had to tell Jim that his O-320 was only putting out about 150HP rather than my assumed 160HP. He said that's right, it is a 150HP engine! Did you also notice the high induced loss of the -6 at higher altitudes and slower speeds? This throws in an extra term when considering performance, since a higher HP -6 will have more speed and less induced loss, so that you can't estimate speed solely by (HP)^1/3!
 
Some heretical houghts about it

Reheat said:
... Since gliding was out, I decided to use cruise data to determine the drag. My acft consistently hit 179-180 ktas WOT at 7500’ at 75% pwr.
Click to expand...

IMHO 7500 dalt gives an RV at 200+ mph much more than 75%. Mine gives 75% at about 9500 dalt as explained in my recent posts.

As to finding best L/D speed and drag polar, I stumbled on this and I think that Kevin Horton says it's close to accurate (KH - sorry if I'm misinterpreting you). You can find the minimum sink speed for a given atmospheric condition and loading by finding the lowest power that will sustain level flight. The ratio of minimum sink to best L/D is always 1.316. In other words, if minimum sink is 76 kts, best L/D is 100.

If you know the weight of the aircraft and the minimum sink speed, pull the power, hold that speed and observe your vertical speed. Now compute the horsepower that was required to keep you up there. Ditto for best L/D if you like. It's not quite as precise as the zero-thrust thing, but you can do it inexpensively and come quite close to the truth. Closer, I think than you will get by using 75% assumed at 7500' dalt.

What this does not do is to distinguish engine HP from prop efficiency; it only measures net power as experienced by the aircraft.

Ok, let the flaming begin..
 
Heck Evan, no flaming, there are a lot of ways to skin that cat. Checking your website and your performance numbers, it all seems to add up. Your prop would appear to have less effective pitch than mine and you are running higher rpms which should account for the higher pwr%. What did you get for Drag numbers using your method?

Paul, thanks for your numbers. Let us know how your wingtips and increased aspect ratio work out.
 
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I don't really have the drag numbers, but..

Reheat said:
Heck Evan, no flaming, there are a lot of ways to skin that cat. Checking your website and your performance numbers, it all seems to add up. Your prop would appear to have less effective pitch than mine and you are running higher rpms which should account for the higher pwr%. What did you get for Drag numbers using your method?

Paul, thanks for your numbers. Let us know how your wingtips and increased aspect ratio work out.
Click to expand...

I get 75-80 kts IAS for minimum sink, but I go by the Lift Reserve Indicator, not airspeed. If I'm turning 2800 instead of 2700 then my extra HP would be approx. 3.7%. More of my "extra" power is coming from ram air and a good induction system. Next time I fly, I'll hold it to 2700 and see what I get. I never did the rest of the numbers on this airplane, but have used that method on cars and a Cessna. When I get my Catto prop back it should be able to test this better because it will have more pitch.

When I used this idea on the Cessna I was trying to find total HP by adding the sink rate and the climb rate. I think I ended up with about 30 HP available for climbing and the rest went for drag.

If an RV with 180 HP at 1800 pounds climbs 1500 fpm for example, then it is using 82 net HP to climb and the rest to maintain. If it sinks at 900 fpm, for example, it needs 49 HP for minimum sink. The problem here is that the minum sink is at 75 and climb is at 110, more or less. So there's 82+49= 131 leaving 49 for the speed difference and the prop losses and losses for density altitude, etc. It would be good in these computations to test the sink rate at the same speed as the climb but I haven't done that. This is a simple framework which limits our errors to the basic performance parameters that can be measured. While it's not perfect, it is designed to contain the errors within a known zone. So, it's a good cross check.
 
Roger Roger Over

David-aviator said:
All things considered (weight, complexity, cost), the fixed pitch propeller is an good alternative to the constant speed units at this level of flying without pages of numbers to back it up.4.
Click to expand...
Roger that, I agree 100%, no put down on fixed props at all, Pos and Cons. Regarding weight, the RV7 does not mind weight on the nose; it almost needs it, but a light RV4 or RV6, with a light weight fixed wood prop and 320....is a pure joy.
Reheat said:
This all started with a quest to come up with an estimated Equivalent Flat Plate drag number for my airplane in order to compute the Drag Polar. Sounds easy enough, but… Maybe not!
Click to expand...
Roger that, very nice number crunch-in. Thanks, that explains your methodology; I was just curious. You explained it very well, and I followed your logic. I see nothing wrong. I know still air is hard to find for flight test. That's why I like side-by-side "normalized" flt tests between two like planes simultaneously; it's easier and takes some variables out; all those numbers makes my head hurt, :D but your numbers are interesting and a useful starting point. Cheers Dudes.
 
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hevansrv7a said:

IMHO 7500 dalt gives an RV at 200+ mph much more than 75%. Mine gives 75% at about 9500 dalt as explained in my recent posts.
..
Click to expand...

According to Lycoming's data on their O-320 and O-235, the MA carb gives about 1.5" drop at sea-level rating, and I think an injected system will have a drop of about 0.5", just a WAG. When calculating your power using MAP, it should be as a percentage of MAP/28.4" for carb, or MAP/29.4 for an injected engine. However, according to several sources, you should also reduce power by the density ratio, DR, raised to the 1.135 power, or (DR-0.15)/0.85. Then you also have to consider induction temperature, TI, since each 5.2F increase over 59F will reduce power by 1%! So try this for HP percentage:
100 x MAP/28.4 X (459.7+59)/(459.7+TI) X (DR-0.15)/0.85 where DR is
(1-6.88E-6 X dalt)^ 4.56. I agree that your power when you're toolin' along at around 200 mph TAS will be more than 75% at 7500' dalt unless you have big induction losses. Around 9000' dalt works for me, too depending on TAS.
 
Not sure that's right, FI & Carb are about the same

elippse said:
According to Lycoming's data on their O-320 and O-235, the MA carb gives about 1.5" drop at sea-level rating, and I think an injected system will have a drop of about 0.5", just a WAG.
Click to expand...
Not sure this is about props but are you sure? Do you have references.

1" to 1.5" hg to just go through the carb sounds too high. I doubt a CARB v FI are that much different. Most of the drop is in the air box and plenum / induction tubes. Pressure drop through a Carb and FI servo TB should be close, my guess within in a 1/10th inch H20. 1" to 1.5" hg sounds like the P-drop for the whole system, not just the carb throat. Your P-drop likely includes the air box, carb and induction plenum and tubes.

1.5" hg loss just to go thru a HOLE (in the carb) with a venturi and an butterfly open valve just sounds high. I could be wrong. No offense. The Gent from AFP posted a P-drop for FI servos/TB. May be he will chime in. I recall the P-drop diff between carb / FI is not that great.

Speaking of pressure drop, FACTORY planes have lousy air boxes when compared to Vans filtered air box (FAB). Typically (carb or FI) RV's have about 1" to 1.5" more MAP than a Cessna. Of course some of that higher MAP is due to more RAM at 200 mph verses 120 mph.

FI may make a pony or two more, due to better fuel distribution but not a full 1" of MAP worth of power. Its a popular belief that FI makes lots more HP, all things being the same, but the physics does not back that up. Fuel and air is fuel and air, regardless how its delivered. FI is more efficient, because distribution to each cyl is better controlled, so it can make a little more power but not wholesale increases. Some people I have talked to thought the HP change between a IO360 (200HP) and O360(180HP) was all due to the FI. Its of course really higher compression and the angle valve heads (and 30lbs more of engine).

Cheers


PS: An urban legend is a fwd facing induction makes more power? Well IMHO the air has to make a 90 degree turn at some point! There is little difference if you make the turn in an air box or in the plenum. The reason Lyc made fwd induction was for the airplane makers of light twin engine planes; the engine nacelles where not as tall, as the cowl on a single engine plane. A bottom induction was in the way. If you look at HP of 320's, 360's and 540's with vert or horz induction, everything else being the same, there is no HP difference (per Lyc specs).

The HIGH performance fwd facing COLD inductions are making more power, but its because they are not heating the air. They also probably have a better plenum / spiders (induction runners).
 
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gmcjetpilot said:
Are you sure? Do you have references. 1" to 1.5" (h20) to go through the carb sounds too high. I doubt a CARB v FI are that much different. Most of the drop is in the air box and plenum / induction tubes.
Click to expand...

Textron Lycoming Specification No. 2283-G, October 6, 1994 Detail Specification For Engine, Aircraft, Model O-320-D1A, -D2A, -D2B, -D1C, -D3C, -D2G, -D3G, 160 Horsepower direct Drive, Curve 13381, Marvel-Schebler MA4SPA, 1.24" drop at 160HP, STP.
Avco Lycoming Specification No. 2499-G, 5 February 1982, Detail Specification For Engine, Aircraft, Model O-235-L2A, -L2C, 118 Horsepower, Direct Drive, Curve 13265-B, Marvel-Schebler MA-3A, MA-3PA, 1.48" at 118 HP, STP.
Contact! Magazine, Issue 62, P.2, Towards an understanding of CARBURETORS, Clare Snyder.
My O-235 L2C with 9.7:1 CR shows over 1.4" drop below ambient pressure at full throttle, 2230 rpm. I have a bypass valve around my K&N 4" X 10" filter which shows no MAP change when it opens, since I have no perceptible filter or manifold drop.
 
Thanks, what I thought + Air box magic, Air filter myths

elippse said:
Textron Lycoming Specification No. 2283-G, October 6, 1994 Detail Specification For Engine, Aircraft, Model O-320-D1A, -D2A, -D2B, -D1C, -D3C, -D2G, -D3G, 160 Horsepower direct Drive, Curve 13381, Marvel-Schebler MA4SPA, 1.24" drop at 160HP, STP.
Avco Lycoming Specification No. 2499-G, 5 February 1982, Detail Specification For Engine, Aircraft, Model O-235-L2A, -L2C, 118 Horsepower, Direct Drive, Curve 13265-B, Marvel-Schebler MA-3A, MA-3PA, 1.48" at 118 HP, STP.
Contact! Magazine, Issue 62, P.2, Towards an understanding of CARBURETORS, Clare Snyder. My O-235 L2C with 9.7:1 CR shows over 1.4" drop below ambient pressure at full throttle, 2230 rpm. I have a bypass valve around my K&N 4" X 10" filter which shows no MAP change when it opens, since I have no perceptible filter or manifold drop.
Click to expand...
Carb and FI have about the same Pressure drop
Thanks for the info. That is what I though, we're on the same page. The loss you quote (1.48") is not JUST the carb (on a flow bench), its the whole system from the air box, carb up to the MAP gauge. 1.48" hg makes sense. Of that 1.48" the carb throat it self is only contributing a few 1/10ths. So even if a FI throttle body had less pressure drop, it would be only a small part of the total induction loss. The air box, plenum, induction tubes and cylinder head are where most loss comes from as well.

Also keep in mind these Type Cert papers are on an engine stand. An engine on a test stand has no RAM air pressure recovery to feed the induction. Also I wounder what kind of air box do they use? I don't know. The installation affects the total induction loss because the intake / air box is a big player as well as the planes speed.


Why RV's are better than Factory Planes
RV's in high speed cruise can get MAP equal to ambient pressure. That means the air box is making up for that 1.5" loss. Some RV's even see a little over ambient pressure. I have heard of 0.3" hg higher than ambient. That is with out a turbo!

Why do RV's have 1.5" hg more MAP than a Cessna, with the same engine, carb or FI? Air speed and better way better air box.

Cessna's and Piper's have terrible air boxes. Cessna just plastered the filter face on the cowl. Than the air box is a shallow little square metal thing with a butter fly valve (for the carb heat). As the out side air tries to make its way in, the high speed air just spills over the filter. There is no pressure recovery. Actually there's lots of pressure loss and external drag (with plume/interference drag). Than it hits the lousy air box.

With Vans air box, the air comes though a small low drag scoop and slows down symmetrically around a round filter directly below the carb/FI-TB. As the air slows, pressure builds per Mr. Bernoulli, and than goes through the filter. Externally there is no air spillage from the scoop. So we have low drag and high pressure recovery. The down side is carb heat is not as good.

A RV going 200 mph has 1.5" hg RAM air pressure to use. A Cessna going 120 mph has only 0.5 RAM: So the RV already has about an extra 1" hg pressure to recover for the induction. The Vans FAB has a positive pressure recovery and the Cessna is neg. Since RV's often have ambient MAP at WOT, it means they are recovering most of the RAM. No I don't have a picture of Van in my wallet and send Christmas cards, but he did a good job with all his filtered air-boxes.

FILTER MYTHS
As far as filters, like in vans filter air box (FAB), a K&N is used. The filter helps! It straightens out the flow to enter the Carb or TB in a smooth even manner. K&N filters have very, very, very low pressure drop, about 0.05" hg at full rated CFM flow. A common miss conception is a bigger filter is less loss. That is NOT true. First you are talking about 1/2 of nothing, as far as loss. Sure a bigger filter might change loss 0.01". The filter is rated for and at a recommended CFM, and as long as you are less than that, you are fine. The advantage of more filter area is cleaning intervals are less. Of course you have to keep it clean. You want more HP and speed, than keep your K&N clean. :D
 
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Its not urban legend

gmcjetpilot said:
........
PS: An urban legend is a fwd facing induction makes more power? Well IMHO the air has to make a 90 degree turn at some point! There is little difference if you make the turn in an air box or in the plenum. The reason Lyc made fwd induction was for the airplane makers of light twin engine planes; the engine nacelles where not as tall, as the cowl on a single engine plane. A bottom induction was in the way. If you look at HP of 320's, 360's and 540's with vert or horz induction, everything else being the same, there is no HP difference (per Lyc specs).

The HIGH performance fwd facing COLD inductions are making more power, but its because they are not heating the air. They also probably have a better plenum / spiders (induction runners).
Click to expand...

Putting the air intake in a high pressure area has the possibility of increasing MP. Normally this would be forward facing. A high pressure area indicates drag, so the ability to increase MP may be inverse to good aerodynamics.

Mooney's used to have "ram air". Which basically allowed you to open a door (which looks very much like the carb heat door on my 9A) which opens to the front, bypassing the air filter.

Opening the ram air on my 1966 M20E would increase MP by about 1". On my 1981 M20J it was less than about 1/2". The difference, I think, was improved cowling on the newer airplane.

The newest Mooney's don't have ram air at all from the factory. An after market cowling for Mooney's (LoPresti) has significant RAM air

I think the ram air effect on my 9A is significant, but next time I fly I'll give it a try. at cruise speed I'll pull the carb heat and see what happens to MP.
 
Some RV Data

Hi Guys,

The following is provided in response to George and Elippse's posts and is data captured on MP loss in the FAB equiped RV "a" models with carbed 320/360 engines and fp props.

Two years ago after completing my 9a I had some induction problems and requested some comparative test data from RV drivers on the Matronics list.

The Test: On RV6-7-9's with carbed 320/360 engines, FP props, Vans stock cowl/FAB system and electonic mp guages, I asked for the pilots to check their mp guage after power up but prior to engine start and note the mp. Then check the mp at wot just at lift off and note the mp. Determine the differential and let me know. I believe I got this procedure from Kevin Horton as a way to determine induction efficiency by measuring the mp loss through the induction system.

I recieved feedback from (speaking from memory here) 15 RV drivers from the Matronics list. I also personally conducted this test on 5 local RVs for a total sample of 20 aircraft.

The overall average was 0.8" of mp loss on carbed/FAB equiped engines in RVs.

BTW, my brother recently started flying his Superior powered RV7a and now has around 6 hrs on it. His engine is the IO360 M1B clone with forward facing FI, Vans snorkle induction (no scoop-induction air pickup from the left cooling inlet like a Mooney M20J), and the stock K&N filter. He did the same test as above once--result--.8" of mp loss. I should note that he has a Hartzel CS prop so the rpm was higher than the aircraft in the fp test above.

I was told by the guys at Eci that a loss of less than 1" under the above conditions was a pretty efficient system.

As alway YMMV!!

Cheers,

db
 
Net MAP gain after loss

I don't know what the losses are in my system (SJ cowl and airbox, K&N filter, vertical FI) but my net MAP is around an inch over ambient. I don't have any good data preserved on this, but can collect some when the WX improves a little here in Michigan. I did find this old one..
DA=6933
RPM=2660
TAS=158 kts
MAP=22.4
Pwr=72% (not WOT)
GPH=10.3
Ambient=23.91 (per calculation from DAlt)

My MAP has been calibrated by the same technician who certified my altimeter for IFR.


 
Good points, my reply

Steve Brown said:
Putting the air intake in a high pressure area has the possibility of increasing MP. Normally this would be forward facing. A high pressure area indicates drag, so the ability to increase MP may be inverse to good aerodynamics.
Negative Steve. Van the man wrote a series of articles on this back up by test. Now I kind of agree but we WANT ram pressure. If the scoop is designed well than external drag minimized. And to agree with you the RV7/8 no scoop intake van sells (Horz air box) has less drag, est about 1 or 2 mph by Van, while still getting good pressure recovery. As you know it takes the air from the left cowl intake. The air as already slowed and there is pressure recovery there. Further there is a nice bell or trumpet shaped plenum. The problem with most FWD facing inductions is lack of room to develop a good diffuser, a place to slow air down and make pressure. We want pressure. Last an engine does not SUCK continuously like a jet. It starts and stops. So the plenum volume acts like a reservoir.

Mooney's used to have "ram air". Which basically allowed you to open a door (which looks very much like the carb heat door on my 9A) which opens to the front, bypassing the air filter.
Click to expand...
I am familiar.


Opening the ram air on my 1966 M20E would increase MP by about 1". On my 1981 M20J it was less than about 1/2". The difference, I think, was improved cowling on the newer airplane.
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You have been tricked. The 1" is more a "relative" indication of how poor or less than optimal filtered path is, than how great the RAM air is. If the filter is not a low loss type like K&N than bypassing the filter can help. I am not saying having a unfiltered fwd facing throttle body does not help, but its not the panacea or pot of gold. Part of that 1" is just relative to a so so filtered system. The change from Vans filtered air box and RAM is only may be a few 1/10ths. I think Dan said he got 0.30" more? Part of that was he had to compromise his existing Van's system to install a valve to select between filter and RAM. It's like everything in aviation, there are trade-offs and No free lunch. The KISS method says HAVE one good filtered system. However if you want a two way filter/RAM system, than go for it. But the corollary to the wisdom of KISS is not KISS-ing will tend to add weight, cost and time. Is the benefit worth it. You decide.

The newest Mooney's don't have ram air at all from the factory. An after market cowling for Mooney's (LoPresti) has significant RAM air
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I am not sure what you mean by "significant RAM" air", and I am familiar with both. I am not saying ram air has NO benefit, just the benefit is relative to how good or bad the filtered system is. If you have poor mediocre filtered system then RAM air will look pretty good. If you have a Van's filtered system you will not see that much difference. Also a 1/10th or two more MAP is worth a HP or so? So is it worth it. Do you have a separate RAM scoop, that will add a little drag all the time, negating the benefit? For (most) RV'ers I say leave it off, since the gain is small over the stock system. Also no filter and a straight can CAN and has brought down planes from blockage, like a bird (unlikely but documented) and even wet snow. Of course Mooney say close the RAM air in precip.

You name dropped Roy LoPresti, who passed a number of years ago. I have long admired his career; he was a very talented aero designer. His Son is running the company now. I talked to him once. More significant than some of LoPresti's aftermarket cowls having RAM air, is they used round inlets, like the Barnard/James cowl, both based on the NACA funded Mississippi State data. Not a put down of LoPresti's design only that they had to certify it and sell it commercially to General Aviation pilots, so they could not push the envelope. The theories & concept of the "round inlet"(1) are better exicuted on with the Barnard/James cowl/plenum. RAM air or not. [(1) there is a lot more to it than just a round, as discussed else; see NACA / Miss-state reports.]

Its all about design, fit, form & function. If you have a filtered system like Van's FAB, adding all the RAM stuff adds complexity, weight and cost, for little return. Again how much is 0.10" hg of MAP worth? 0.30" hg MAP? A HP or two. To get that will cost you. How much speed does 0.20" hg buy? 2/3 rds of a MPH. How much will a NASA / Miss State cowl buy you? +6 mph

I think the ram air effect on my 9A is significant, but next time I fly I'll give it a try. at cruise speed I'll pull the carb heat and see what happens to MP.
Click to expand...
Depends on your definition of significant. IF you want to test you need a DATUM a standard to test from. The datum should be ambient pressure. The problem with doing test at altitude is you only have an est of ambient so here is the test (I got from Van in RVator article):

Read baro on the RAMP, in-hg. With engine off the MAP gauge and Baro should match, say 29.92" hg. Now start up, take off and make a LOW HIGH SPEED PASS OVER THE RUNWAY, wide open throttle (WOT). What is the MAP? This is where you can brag you had 0.10" over ambient. If you have VERT induction and Van's air box your MAP will be at ambient baro. THIS IS FANTASTIC, because it means the RAM air + Air Box is overcoming the rest of the loss in the Carb/FI-TB and induction and cylinder head, which we est. to be 1" to 1.5".

My opinion is, fwd facing induction is more pain and cost than worth. However if you want want it, than its the right choice, but folks with vert induction should not have Horz induction or RAM air envy, the stock setups are pretty good. I will say the Horz set-up that Van offers (no scoop cowl looks good) is a TAD better than the FAB for Vert induction over all. However there are trade offs (as always). The down side is you need to use the stock cowl. I like the James/Barnard cowl which adds 6 mph, more than making up for 0.10" more MAP and a mph less drag the Horz air box gives.

Good luck, fly safe.
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Just a minute.

gmcjetpilot said:
Steve Brown said:
Read baro on the RAMP, in-hg. With engine off the MAP gauge and Baro should match, say 29.92" hg.
Click to expand...
If you are talking about the altimeter setting, they will only match if you are at sea level. The altimeter setting is based on a sea level pressure. For example, if you are on the ground at Denver, the ambient barometric pressure will be noticeably different from your altimeter setting.
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Yes but it does not matter

Mel said:
gmcjetpilot said:
If you are talking about the altimeter setting, they will only match if you are at sea level. The altimeter setting is based on a sea level pressure. For example, if you are on the ground at Denver, the ambient barometric pressure will be noticeably different from your altimeter setting.
Click to expand...
Good point, you are right the altimeter baro (per atis or awos) is corrected for non standard conditions. Altitude, sea level or Denver, does not have anything to do with it, std conditions (temp, humidity) does. The MAP gauge is a pressure gauge and will read close to baro, regardless of altitude, at std conditions.

So forget the Baro and altimeter comment, I was just making a general statement, the MAP gauge is a barometric pressure gauge with the engine shut off.

Let me correct, for the test NOTE the MAP gauge with the engine OFF on the ramp. Forget the altimeter or baro setting (good idea to make note of it for flt test). The engine off MAP gauge reading is your reference data point, NOT the Baro. Good catch Mel
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My data

I am kind of interested in this induction loss stuff because I modified my system for the worse last year. I have an RV-6 with the standard updraft carburetor setup with the undercowl inlet on an O-360. For a couple of reasons unrelated to this topic, I trimmed the rubber seal so it no longer overlaps the fiberglass inlet tube. There is now about an 1/8" gap there.

Before startup, today, at about 3,275 feet MSL, my MP read 26.8 inches. On initial full-throttle climb, at about 110 knots it was 25.9 inches. I then did a fairly low pass, although I had to keep a slight climb to stay away from airspeed readline. At 178 knots IAS the MP was 26.5 inches at full throttle. Figuring I was about 50 to 100 feet above my hangar elevation it looks like only .2 inches or so below ambient pressure. I can live with that, with the hopes that with less engine to cowl contact I won't have so many airbox cracks.
 
Mel said:
gmcjetpilot said:
If you are talking about the altimeter setting, they will only match if you are at sea level. The altimeter setting is based on a sea level pressure. For example, if you are on the ground at Denver, the ambient barometric pressure will be noticeably different from your altimeter setting.
Click to expand...

I think what he meant to say was to set the altimeter to read zero feet and read the field pressure in the window. 'Course, that only works on airports up to a certain field elevation, above which you cant set it to zero. In this case, take the SL baro and subtract 1" X field elevation/1000. Or to be more precise, multiply SL baro by (1-field elevation X 6.88E-6)^5.256.
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Need a brush up, we'll talk

elippse said:
I think what he meant to say was to set the altimeter to read zero feet and read the field pressure in the window. 'Course, that only works on airports up to a certain field elevation, above which you cant set it to zero. In this case, take the SL baro and subtract 1" X field elevation/1000. Or to be more precise, multiply SL baro by (1-field elevation X 6.88E-6)^5.256.
Click to expand...
We long left the prop subject, ha-ha. :D I don't want to get in trouble with Doug. Setting zero field is "QFE". That was not what I was trying to say, I think. Now you are throwing exponential equations with engineering notation at me; now I am confused and want to cry. :D. All this altimetry discussion is making me hypoxic. I need a beer.

Altimetry is one of my favorite subjects I knew and taught fwd & backwards, at one time. Now I'm rusty. After I brush up, I'll write you a Pvt mesg, when I can discuss it with you. Take care, I'll go study now professor. :D

n5lp said:
I am kind of interested in this induction loss stuff because I modified my system for the worse last year. There is now about an 1/8" gap there. I can live with that, with the hopes that with less engine to cowl contact I won't have so many airbox cracks.
Click to expand...
Good for you, -0.20" hg, not bad. Of course the seal would get you back to net or positive.

Air box cracks: Yes I hate them to pieces. Pieces because that is what you end up with. A couple of suggestions. to Keep the box from cracking (they all do) while having a seal:

-A strut from the engine to the forward part of the air box to take movement out. If its at a slight side angle you can tale a little side load out as well as up & down. Most of the damage is from the box flex up and down, IMHO.

-You are right a tight seal that does not flex works the box harder. Cut the air box back and add new seals again. It will have more give. I had a two peice seal. The shape is flat at top and a "C" facing up. I had one flap at the top and one wrap around the bottom "C". So there where two seems at the top corners. It no doubt leaked, but it was more forgiving. I would think it would be less leaky than a 1/8" gap.

-I made another top plate (the one that cracks that bolts to the engine) out of thcker 6061 aluminum. It's stiffer and has better fatigue qualtity than the 2024 I think they used..

-Last, I added a doubler to the metal top of the air box (that rivets to the fiberglass). I put it inside the box. It was built like a tank. I think if the engine mount failed, the engine would stay in the plane by the stout air box. :rolleyes:
 
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Catto vs Constant speed

Hi All
As far as catto vs constant speed my experaince has been. 2 RV6a's with 180hp constant speed is no match for my Catto 3 blade 0320 RV4. I out climb them I am faster and better looking to boot! Never mind the fact that my Rv4 is 250lbs to 300lbs lighter the said RV6a's ( whats a few pounds )
 
It could be something else

Dayton Murdock said:
Hi All
As far as catto vs constant speed my experience has been. 2 RV6a's with 180hp constant speed is no match for my Catto 3 blade 0320 RV4. I out climb them I am faster and better looking to boot! Never mind the fact that my Rv4 is 250lbs to 300lbs lighter the said RV6a's ( whats a few pounds )
Click to expand...
My RV4 with a 150hp and hartzell ran rings around many RV's with 160 hp and 180 hp, so not sure its all the prop. The RV4 is a great plane and light does count. The old saying's are: "there is no free lunch" and "you can't violate the laws of physics". Catto being made of wood has thicker blades, efficiency in general, apples v apples, a metal prop (Hartzell or Sensenich) will be more efficient than wood. With that said, there is nothing like a light RV with a wood prop; it's a special experience. Not taking anything away from your RV4 or prop, there is no clear winner or all Pro no Con anything in life or aviation. Cheers :D
 
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Weight a minute...

Back in 2003 my ANG unit had 9 of us F16 Drivers owning RV4's and one RV8. It was so cool I wrote an article in Sport Aviation about it.
We had in attendance 4 -180 C/S Hartzells, 1- Art Chard built 190HP/Hartzell beauty with RV6 wing tanks unpainted 940 lbs. 1- 180HP Aymar Demuth wood, my 150 Catto 2 blade The Bandit, a 160HP Catto 3 blade and a 230HP C/S RV4 monster called No Fear. All had carbs except No Fear and the 180HP AD. 4 had Electronic ignitions and one mag. 2 Jeff Rose and two Lightspeed. We flew each others airplanes alot and went cross country and did alot of dogfighting.
What was the best overall RV4 in performance, fuel economy over a given distance, best dogfighter? Hands down Brian Wolf's 190HP(9.0:1 comp) lightweight Hartzell masterpiece. It consistently was the overall best flying RV4 of them all. However comma, my little 150HP was close in all the categories. My Catto 2 Blade was always slightly faster and better climb than the 160/3 blade Catto. (Craig built me the first Catto for an RV4 back in 98'). The 180 Aymar Demuth cruised exactly the same speed and power setting as my 150 Catto 2 blade, not very efficient but did very well in acro. For aerobatics and dogfighting I liked mine the best as the nose was lightest with my Narrow Deck 0-320. Over a given distance they all burned roughly the same fuel at the same speed except the 180 Aymar Demuth and No Fear. The 180 AD had an Airflow Performance FI with full inverted system and always had better mileage. No Fear also did very well on fuel with his Bendix FI. Obviously flat out No Fear could blow all of our doors off but only beat the 190HP beauty by a smidgeon and also suprisingly the FP 180HP RV8 with metal sensy 85 pitch who could almost hang with No Fear turning 2900 RPM with his FP prop! The 180 and 190HP airplanes however cost on average $10-20K more in going in costs which buys alot of 100LL.
In overall bang for the buck my RV4 was the lowest going in cost, lowest maintenence, lowest HP but not lowest top speed, suprisingly. It was also the lightest of all of them. I ran auto gas most of the time and operated off a grass strip. I finally sold the Catto 2 blade after installing a 170HP wide deck 0-320 and Gary Hertzler prop. The Hertzler prop BTW was the best of all of the FP props I ran over 10 years. Sadly, I sold my RV4 last summer. (I bought a Rocket, woohoo!)
The perfect RV4 engine/prop combo? If you have the money, a Hartzell adds value and efficiency, period. It does make for a heavier nose, more moving parts and weight but doesn't erode in rain and allows more efficient use of all the HP. However comma, I think a Catto or Gary Hertzler 2 Blade on a 190HP lightweight with a AP FI system would be the best flying of them all.

I haven't flown an RV4 I didn't like...but I really like the Rocket!

Smokey
 
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Nice prop v prop write up

smokyray said:
In overall bang for the buck my RV4 was the lowest going in cost, lowest maintenence, lowest HP but not lowest top speed, suprisingly. It was also the lightest of all of them. I ran auto gas most of the time and operated off a grass strip. I finally sold the Catto 2 blade after installing a 170HP wide deck 0-320 and Gary Hertzler prop. The Hertzler prop BTW was the best of all of the FP props I ran over 10 years. Sadly, I sold my RV4 last summer. (I bought a Rocket, woohoo!)
The perfect RV4 engine/prop combo? If you have the money, a Hartzell adds value and efficiency, period. It does make for a heavier nose, more moving parts and weight but doesn't erode in rain and allows more efficient use of all the HP. However comma, I think a Catto or Gary Hertzler 2 Blade on a 190HP lightweight with a AP FI system would be the best flying of them all. Smokey
Click to expand...
Nice write up. If you read Vans writings through the 80's and early 90's you will see Van resisted c/s props like crazy, it was not in line with his light, simple (dare I say) cheap overall "total performance" mission and philosophy. Van of course finally gave in and thus the RV-8 with a IO-360 (200HP) and c/s prop. He had to admit that more HP and c/s prop was nice. Van fought it for a decade, but the marketplace demanded it. He also said he NEVER would he make a 4-seater, because there where good ones out there like the Comanche or Bonanza that could be had for $40k. Well he gave in to that as well. Partly because those fast 4-seater's where getting old and partly again because of market.
 
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Ditto: Nice prop v prop write up

SmokeRay, very interesting to see your experience with the diversity of the same model (RV4) and the differences in Prop/Hp combo's.
Thanks
 
Prop edge protection tape

Several comments about prop edge tape in this thread and no responses from Paul Lipps who, when these postings were posted, perhaps did not have a definite opinion on the subject. When I met him in 2010 he most definitely did have some thoughts on the subject, which I'll pass on here.

I had bought a new Prince in 2007 and noticed after my first encounter with rain that the outside third of the leading edges were in bad shape. This . . . after paying Lonnie for "extra edge protection". I think what he meant by extra edge protection was perhaps spraying on an extra coat of epoxy . . . dunno. All I knew was I didn't like what rain had done to my otherwise beautiful prop and since I don't go out of my way to avoid rain I wasn't happy with the situation. I sent it back to Prince for refinishing (for which I was charged something substantial - $300- $400 I'm guessing, plus shipping) I considered the damage to be a defect in manufacturing (especially since I'd paid extra for the "extra protection" and was slightly miffed at being made to pay for the repair work.


When I got the prop back, it seemed like it might be a good idea to cover the outside third to a half of each blade of my newly refinished prop with some "prop tape" I'd heard about. I hadn't been using it very long by the time I flew up to Santa Maria to meet Paul Lipps and do a balance job on his Lancair. I also wanted his opinion regarding my "prop tape". By this time (2010) he had apparently formed an opinion regarding this solution and he most certainly didn't think much of it. He explained that the tape edge, slight as it is, "trips the flow" of the air going through and past the blades. He did a much better job of explaining just how that works than I'm doing explaining it here - so I won't try. Short story is I took the tape off there and then and, since the prop was in virtually new condition following its refinishing, I sold it for not much of a loss. I replaced it with a Sterba. Sterba urethane edges hold up very well in rain. I've had two of them of different pitches and lengths. Can't say enough good about them. Sterba will be missed.

Anyway . . . point is, leading edge tape is not a good solution. What IS a good solution is to buy a Sterba (if he's still in business - don't think so - retired) or buy a Catto with the blended-in stainless (I think) metal protection that provides an indiscernible (to the touch) border between where the metal and the body of the prop come together. Sensenich does this (using rivets I think). I'm sure it's just as sturdy, and they DO make a beautiful prop - but in that particular aspect of smoothness where the two materials are joined, Catto seems superior. Whirlwind does this well too. To my eye, it's as smooth as Catto's work.

Catto, for anyone who may not know, worked closely with Paul Lipps in achieving Paul's prop design work. Sufficiently so that Phantom took first many times in many races - Reno and otherwise. The plane was (I suspect) temporarily retired following the death of Lipps (cancer) and the plane's owner and racer, Tom Aberle (cause of death unknown). But Phantom will surely rise again - if it already hasn't. I don't keep up that much.


**********************

Old subject I know, but may be of interest to someone. My point primarily is, unless someone has come up with some remarkably better prop edge protection tape in the years since I was interested in all this, my thought is tape is not the way to go.

Mike Stirewalt
KSEE
 
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