catto vs constant speed

[gmcjetpilot]

[quote=Mel;195179]

Originally Posted by gmcjetpilot

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.

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

[n5lp]

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.

[elippse]

[quote=Mel;195179]

Originally Posted by gmcjetpilot

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.

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.

[gmcjetpilot]

Originally Posted by elippse

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.

We long left the prop subject, ha-ha. 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. . 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.

Originally Posted by n5lp

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.

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.

[Dayton Murdock]

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 )

[gmcjetpilot]

Originally Posted by Dayton Murdock

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 )

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

[smokyray]

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

[gmcjetpilot]

Originally Posted by smokyray

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

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.

[TGRV7]

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