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Cruise speed - 360 with a Fixed Pitch Prop?

moespeeds

Well Known Member
Friend
For the guys running fixed pitched props with a 360, what kind of cruise speeds and climb rates are you seeing?

Anyone running a 3 blade FP?

Asking for a friend.
 
I'm running a O-360 with a Catto 3-blade on my 8A. I bought a used "RV-4" prop, design specs from the dataplate:
Diameter: 66 inch Pitch: 76" RV-4
Engine O-360 Design PM 2800
Prop Red Line RPM max 3200

For max speed I get 165 KTAS at 8000 MSL and 2800 RPM. But since the redline on the engine is 2700, I usually run it at 145-150 in cruise. 145 KTAS at 8000 MSL comes out to 8.5 gph.

On climb I get around 1250 fpm, that is also at 8000 MSL. The ground around here is 5000, so I did my climb testing up that high. I estimate I should get about 1400 fpm down at sea level, if I ever take my plane there.
 
"Asking for a friend....."

Hahahahahahha

Love it.

Fit a C/S prop and enjoy the full fun that an 8 can provide :D

I'll get my coat.....:rolleyes:
 
"Asking for a friend....."

Hahahahahahha

Love it.

Fit a C/S prop and enjoy the full fun that an 8 can provide :D

I'll get my coat.....:rolleyes:

There's always that one guy.... :)

I'm quite happy with my Whirlwind 200RV. I really am asking for a friend.
 
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If your fixed pitch prop is pitched for cruise (2700 RPM @ WOT), then your top cruise speed should be the same with both props - both being limited to 2700. The fixed pitch might have a slight speed advantage because of its lighter weight. That’s what I found out when running against two O-360 powered RV8’s with carbon fiber Hartzells in my RV4 with it’s carbon GA Sensenich at WOT at about 1,000’ AGL. I was 1-2 knots faster. The trade off was in takeoff distance and initial climb. I could still get off the ground in less than 500’, and climb to pattern altitude by the end of our 5500’ runway, but the CS RV8’s could get off a little shorter and initial climb was better. Cruise climb at about 135 KIAS was about the same at WOT, the fixed pitch being at a lhigher RPM/ lower MP. The biggest difference I’ve seen in my airplanes is that for a given percentage of max power (ie. 65%), the fixed pitch will be running at a higher RPM - with a corresponding lower MP, because you can’t run WOT at 65% unless you are relatively high, and then you’ll likely see something close to 2700 RPM. There’s nothing wrong with this. Lycoming says you should be able to run this engine at 2700 to TBO without problems.
 
My specs are:

Engine: Superior IO-360-M2S with dual PMag

Prop: Catto 3 blade, 68" diameter, 76" pitch

75% Power:
@3000ft: 2510rpm / IAS 156kts / TAS 165kts / 24.4" MP / 8.9 usg/hr
@6000ft: 2610rpm / IAS 159kts / TAS 174kts / 22.8" MP / 9.1 usg/hr

55% Power:
@3000ft: 2220rpm / IAS 136kts / TAS 144kts / 20.1" MP / 6.8 usg/hr
@6000ft: 2220rpm / IAS 134kts / TAS 152kts / 19.1" MP / 7.1 usg/hr

Those are measured values of my flight testing... But not yet lean of peak.

Then also the climb performance as well as takeoff and landing performance. But they were done when I did not yet had to much experience (below 30 T/O and LDGs in total) thus they may could be improved.


Regards,

Yves Heller
 

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Frugal Cruise

fixed pitched props with a 360 - cruise speeds and climb rates

I flew and RV-8 with an O360 and a Catto 2-blade pitched for cruise.

The initial climb was 2000fpm at sea level and it tapered to 1500 rpm by 4000ft.

It would "frugal cruise" at 160kts. Above 6500ft the fuel flow was 8.5gph or less as altitude increased.
 
Rv-8, Titan IO-370, WW GA prop, 1032#, WOT @ 7750’ measured with auto-pilot and 4way GPS runs avg. 179kts@2780rpm, 22.8”MP. Goes faster down low. Have not measured climb but it is sufficient. Engine is low CR on Mogas, Slick and SDS, AFP FI on cold air slump, 4pipe exhaust.
 
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RV-8 with IO-320 FP

I know the thread was asking about 360 cruise speeds with a FP prop....but just a data point.

My RV-8 with an IO-320, W-W ground adjustable prop cruises at 155 kts true airspeed at 65% power (as computed by the Dynon SV) at 7.5 GPH rich or peak. 75% at 8.5 GPH is 163 kts true airspeed, WFO at 7500" DA is 173 kts true airspeed at 13.5 GPH. Reducing drag and weight are the keys to speed and climb. I have my W-W pitched for best climb (1200 fpm at 115 kts Indicated airspeed through 5000 DA), but this leads to slight prop overspeed at WFO. I have pitched the prop for best speed and made it to 177 kts true airspeed with a significant drop in climb performance. Yes, a C/S prop would be nice, but my engine isn't plumbed for a prop governor, so sometimes I just happy to have an RV-8 and the ability to go fly...
 
would I buy a car with only one gear? Think not...
Having a total performance RV with a speed ratio of 3.67 (factory figure for the 180HP version) and a FP prop just doesn't do justice to the design. Guess financing a every square inch available glass panel was prioritised, choices choices ;)
 
My specs are:

Engine: Superior IO-360-M2S with dual PMag

Prop: Catto 3 blade, 68" diameter, 76" pitch

75% Power:
@3000ft: 2510rpm / IAS 156kts / TAS 165kts / 24.4" MP / 8.9 usg/hr
@6000ft: 2610rpm / IAS 159kts / TAS 174kts / 22.8" MP / 9.1 usg/hr

55% Power:
@3000ft: 2220rpm / IAS 136kts / TAS 144kts / 20.1" MP / 6.8 usg/hr
@6000ft: 2220rpm / IAS 134kts / TAS 152kts / 19.1" MP / 7.1 usg/hr

Those are measured values of my flight testing... But not yet lean of peak.

Then also the climb performance as well as takeoff and landing performance. But they were done when I did not yet had to much experience (below 30 T/O and LDGs in total) thus they may could be improved.


Regards,

Yves Heller

I think Yves gave an excellent response (including documented results) to the original posters question.

But the question begs asking "What is CRUISE speed?" when applying it to a fixed pitch prop. Is it W/O throttle, Partial throttle, % power, max rpm at ? altitude?? Seems everyone has a different definition of what CRUISE is.
 
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Thanks Ralph.

Yes its somehow important that we all talk about the same thing to compare.
Such as is speed messured in mph or kts and indicated or true? And also as you mentioned at what setting.. Otherwise its quite difficult to compare.
 
A properly pitched FP prop for top speed or other specific configuration has two advantages. Weight is the obvious one, and no prop governor. I'm sure the governor isn't taking huge amounts of power, but it's not zero either. It would be interesting to know it's exact requirement.
 
Actual cruise numbers: RV4 rather than RV8, but relatively similar - O-360, standard compression, fixed pitch Sensenich carbon fiber prop pitched for 2700 at wide open throttle, so cruise setting I guess. In the pic below, 2560 RPM, 19.7”, 64% power, 9,500 feet, 8.8 gph, 172 KTAS. This is not at wide open throttle. WOT at this altitude would still give me 2700 RPM.

24DF0CE3-4C1F-4600-BEA3-9536772D081F.jpg
 
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Actual cruise numbers: RV4 rather than RV8, but relatively similar - O-360, standard compression, fixed pitch Sensenich carbon fiber prop pitched for 2700 at wide open throttle, so cruise setting I guess. In the pic below, 2560 RPM, 19.7”, 64% power, 9,500 feet, 8.8 gph, 172 KTAS. This is not at wide open throttle. WOT at this altitude would still give me 2700 RPM.

View attachment 18489

I can't wait to fly my to be finished RV8. The flight school rental barely files faster than 100kts.
 
A properly pitched FP prop for top speed or other specific configuration has two advantages. Weight is the obvious one, and no prop governor. I'm sure the governor isn't taking huge amounts of power, but it's not zero either. It would be interesting to know it's exact requirement.

Also, a C/S prop is the most expensive single item on your aircraft to maintain, if maintained i.a.w. the manufacturer.
 
Yup

Also, a C/S prop is the most expensive single item on your aircraft to maintain, if maintained i.a.w. the manufacturer.
Yup, this is why I went with fixed pitch Catto. Except for showing off on climb out, my flying doesnt entail 500 foot strips with 150’ trees at each end. But I am sure once I visit Johnson Creek with my new plane, that will change. ( Bring on the -15!)
 
Cross country cruise in RV8 with Superior IO360 and Catto 3 blade I get 162 ktas at 2460 rpm and 8.2 gph at 5000 density altitude. 2700 rpm equals 178 ktas, more if I'm willing to exceed 2700 rpm. First photo is 178 ktas at 16000 density altitude. Second shows 30 + statute mpg at about 12000 density altitude. Don't buy the one gear thing. My turf airfield is at 155 feet msl and when I'm light, I can go from standstill to 1500 feet in one minute, more when temps are cool and less in hot summer temps
 

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Cross country cruise in RV8 with Superior IO360 and Catto 3 blade I get 162 ktas at 2460 rpm and 8.2 gph at 5000 density altitude. 2700 rpm equals 178 ktas, more if I'm willing to exceed 2700 rpm. First photo is 178 ktas at 16000 density altitude. Second shows 30 + statute mpg at about 12000 density altitude. Don't buy the one gear thing. My turf airfield is at 155 feet msl and when I'm light, I can go from standstill to 1500 feet in one minute, more when temps are cool and less in hot summer temps

What do you mean “Don’t buy the one gear thing”? Are you talking about fixed pitch props fly like you only have one gear? Because they do! A CS prop totally transforms the plane! It climbs better and lands shorter, and makes formation much easier.. but fixed or CS, they all cruise fast and are a blast to fly either way, but don’t knock CS on the RV.. it’s really the way to go on a -8 imo.
 
For the guys running fixed pitched props with a 360, what kind of cruise speeds and climb rates are you seeing?

Anyone running a 3 blade FP?

Asking for a friend.

Putting a FP prop on a plane with a performance envelope like an RV Is like driving a corvette stuck in 3rd gear. Sort of fun, but you sure are missing a lot.
 
Placing a heavy c/s prop on an RV 3, 4, 6, 7, or 8, makes your RV handle like a dump truck.
 
Placing a heavy FP prop, gadgets, or fat pilot/pax on an RV 3, 4, 6, 7, or 8, makes your RV handle like a dump truck.

And cruising at 2600 RPM iso 2300 or 2000 gets you tired quickly, not even touching the single speed efficiency here…
 
Placing a heavy FP prop, gadgets, or fat pilot/pax on an RV 3, 4, 6, 7, or 8, makes your RV handle like a dump truck.
...
I have never driven a dump truck, but now I want to give it a go, if it's as fun as my RV-8! :D
 
24 posts on this thread and no one has mentioned nose gear vs taildragger and its relation to prop selection.

Choices and opinions are what makes Experimental Aircraft the best Aviation.
 
I'm not knocking constant speed props. There are some advantages. Like better climb for the first sixty seconds of flight. CS and FP climb the same after about 120 knots. If you need CS to slow down, perhaps your energy management needs some attention. What I object to is the old saw of "stuck in one gear". CS allow you to cruise at a lower rpm. My fixed pitch Catto runs turbine smooth and quite efficiently at all rpm, not tiring at all. I recall a comment in the RVator that switching from FP to CS felt like a broken motor mount. And being 40 lbs lighter allows the full feel of the design to shine through. These planes just feel best when flown light. So if your mission is mainly cross country, you may want CS. If your mission is total performance, you can't go wrong with a well matched FP. As Van's used to say "build it light and keep it simple".
 
As someone who started out with a FP prop (RV-8A) and replaced it with a CS prop (Hartzell BA), I can report that putting a FP prop on that plane was the one big mistake I made on that build.

If you want a plane to fly for the $100 hamburger then it makes little difference. If you are looking for efficient cross country, the choice is obvious.

Carl
 
I primed of all my parts with rattle can primer!!!!! and it made no difference in how fast I can do!!!!
 
Placing a heavy FP prop, gadgets, or fat pilot/pax on an RV 3, 4, 6, 7, or 8, makes your RV handle like a dump truck…

Quite curious how the RV 3 handles with a fat pax? :D I'm sure it would be fine with the weight of a nose gear, a constant speed prop, but no primer.
 
Drifting

The OP is looking for real world numbers.
Answers to the original question will help someone make an informed decision, including myself.

With the recent 13% increase in engine cost it’s conceivable that may have blown the build budget for many. The previously planned C/S prop is the place to make a big cut.
 
The OP is looking for real world numbers.
Answers to the original question will help someone make an informed decision, including myself.

With the recent 13% increase in engine cost it’s conceivable that may have blown the build budget for many. The previously planned C/S prop is the place to make a big cut.

Generally speaking, one of the greatest challenges around here is getting your actual question answered...
 
Generally speaking, one of the greatest challenges around here is getting your actual question answered...

From memory so don’t hold me to it.
- RV-8A with Sensenich FP prop, 180hp IO-360, 2600 RPM at 4500’, 165 kts. I limited RPM to 2600 so it could go faster if I tolerated the excessive RPM.
- Same RV-8A with Hartzell CS prop, 2500 RPM at 4500’, 175 kts (and about a GPH less fuel burn LOP).

Carl
 
Antisplat east exit bar

AgE 76, RV6A 180/fixed, installed to ease entry/exit of self and wife of same age.
Love it! Significantly easier now.
Easy to install and well engineered product. Planning on more purchases.
Bill Hall
 
Climb differences

From memory so don’t hold me to it.
- RV-8A with Sensenich FP prop, 180hp IO-360, 2600 RPM at 4500’, 165 kts. I limited RPM to 2600 so it could go faster if I tolerated the excessive RPM.
- Same RV-8A with Hartzell CS prop, 2500 RPM at 4500’, 175 kts (and about a GPH less fuel burn LOP).

Carl

Hi Carl,
Thanks for the numbers. Did you notice a significant difference in climb FPM performance?

For example, loaded near gross and climbing to 8000 to 10,000ft
 
I think there is a whole lot more than just speed to make the prop decision. I have a Cato 3 blade prop and am very happy with it. The speed I am getting is about 5 knots less then what others reported which is probably due to the fact that I don't have wheel pans on (I am going into pretty rough fields and got tired of banging them up) so as you can see speed is really not my main concern.

As for cruise speed. If I do fly cross country I put my throttle on full and leave it there till I start my decent. On the climb up I lean to keep the EGTs constant and when at cruse (which is typically above 7500) I lean to 2700 RPM lean of peak or to highest RPM I can get if I can't reach that. As others said the Cato prop feels really smooth there. Feels better to me then running it at 2400 RPM but maybe that's just because I am so used to it.

Now in terms of cross country advantage in terms of time. As I do the maintenance I take a total time approach to this. If you have somebody else do the work you might look at it differently.

Lately I am only flying 60 hours a year down from about 100. Let's go with 100 hours for this exercise as its more favorable to constant speed props. So if I spend 1 hour of additional maintenance my effective speed (time I spent with the airplane vs distance flown) goes down by about 1%. Most people I know spend at least a couple of hours on extra maintenance on their constant speed prop not counting the days they can't fly at all because of something needing investigating... . So using that math a constant speed prop makes you actually loos time for most of us and reduces the days the airplane is available for flying. Now if you flew really a lot 100s of hours a year and you have a paid for professional maintenance team that math might change but most of us don't.

Don't get me wrong if you want a constant speed prop by all means get one but I am not sure you can make a honest time argument for it.

Oliver
 
I'll be posting some results later this week as I go from the Sensenich 2 blade metal FP to the Catto 3 blade carbon FP. I have been happy with the performance of the Sensenich, but it's a bit heavy and the Catto just looks so sexy. Before I get any comments on why.... I bought the plane with the Sensenich installed and the Catto boxed up for refurb. I sent the Catto to them for refurb and the cost just made sense. I LOVE the way the 3 blade looks, I wouldn't mind shedding some weight and from the folks I have talked to the carbon 3 blade runs so smooth.

If weather permits I'll fly out to Catto tomorrow for the switch or if the fog sticks around, later this week. I'll get performance number on the Sensenich on the way out and the Catto on the return flight. Should be interesting to compare the 2 back to back.
 
Hi Carl,
Thanks for the numbers. Did you notice a significant difference in climb FPM performance?

For example, loaded near gross and climbing to 8000 to 10,000ft

The short answer, climb after installing the Hartzell BA CS prop was noticeably better than the FP Sensenich prop across all flight conditions. But shoot fire, any RV climbs well regardless of what prop you are using. The prime reason I made the switch was to gain cruise efficiency (as in MPG at ~170kts). This design target drove the engine and prop decision process for the next three RVs as a well. Your mission profile may be different so establish your own design objectives.

The current RV-8 has 260 hours on it over the last 18 months, 90% being cross country. A few long runs have been at gross weight (up to 14K’) and while I could see the weight effect it made no difference in how I operated the plane. I did lose a couple of knots when at gross, but for two 3.5 hour legs back to back up to Denver this was in the grass.

One last comment on considering prop weight. While I’m a firm disciple of Van’s built it light principle, I evaluate total impact when looking for weight reductions. For example a nice, composite FP prop might shave off 20-25 pounds, will the trade offs of to get this reduction improve overall performance or not? W&B is not really an issue as this is part of the “where do I mount stuff” process.

Shoot fire, I would be much better off shaving 20-25 pounds off of me - win/win.

Carl
 
I'll be posting some results later this week as I go from the Sensenich 2 blade metal FP to the Catto 3 blade carbon FP. I have been happy with the performance of the Sensenich, but it's a bit heavy and the Catto just looks so sexy. Before I get any comments on why.... I bought the plane with the Sensenich installed and the Catto boxed up for refurb. I sent the Catto to them for refurb and the cost just made sense. I LOVE the way the 3 blade looks, I wouldn't mind shedding some weight and from the folks I have talked to the carbon 3 blade runs so smooth.

If weather permits I'll fly out to Catto tomorrow for the switch or if the fog sticks around, later this week. I'll get performance number on the Sensenich on the way out and the Catto on the return flight. Should be interesting to compare the 2 back to back.

Just a reminder switching props will require you to go back to phase 1. (at least with my ops limitations)... .

Oliver
 
Took a while to get the weather to allow a nice long flight. Here is what I have gathered not scientific, but as good as I can get.

Note this is installed in an RV6A not an RV8

Before:
IO-360, 200 HP - Metal Sensenich 2 blade FP - @ 8500 ft, best economy (LOP, 2450 RPM) 1 saw 151 KTAS @ 59* OAT - best power (ROP, 2650 RPM) I saw 170 KTAS

After:
IO-360, 200 HP - Catto Carbon 3 blade FP - @ 8500 ft, best economy (LOP, 2450 RPM) 1 saw 156 KTAS @ 39* OAT - best power (ROP, 2650 RPM) I saw 177 KTAS

Since the Catto is small in diameter and much lighter the feel in the plane ground or flying is much smoother. Start up is not as violent of an event, idea is VERY smooth. Cabin is quieter in flight as well. Take off and climb performance are at least as good, although I felt I was off the ground a bit sooner that with the metal prop. I put 65 hours on the Metal prop and only have 2 on the Catto so I will reserve final judgment for a later date after a couple XC flights of greater that 2 hours in level flight. The Catto prop is pitched for cruise, I cant get it to exceed 2700 RPM if I'm able to get that high. The Sensenich required me to pull power back once level to keep the RPM under control.
 
That would be a really awesome car though. 1 gear and can drive up to almost 200 mph at only 2700 RPM.
 
Simply NOT accurate from my experience!

Placing a heavy c/s prop on an RV 3, 4, 6, 7, or 8, makes your RV handle like a dump truck.

I have been flying my RV8 which I built for 10 years. I had a Catto 3 blade for 7 of those years with a 0-360 180HP motor cruising 170 knots at 2500 rpm. I now have a BPE built IO-360 200HP angle valve motor with the Hartzell 2 blade composite constant speed prop cruising (2400 rpm) 190 knots usually at 6500-9500 msl.
My CG was very far aft with the light Catto prop as it was hard to load without the CG moving very close to the aft limit with a passenger and baggage. Between the motor and prop I added 66 pounds to the nose with the heavier angle valve motor and constant speed prop. I now add weight (25lbs) to the aft baggage compartment when flying solo.
In my opinion the airplane is much more stable with the forward CG. It is also much easier to load with a passenger and baggage and the CG ends up in the middle of the envelope. An added benefit of the more forward CG is the airplane lands much easier in my opinion.
My plane absolutely doesn't fly like a dump truck! Ridiculous statement in my opinion!

Kevin
 
I have been flying my RV8 which I built for 10 years. I had a Catto 3 blade for 7 of those years with a 0-360 180HP motor cruising 170 knots at 2500 rpm. I now have a BPE built IO-360 200HP angle valve motor with the Hartzell 2 blade composite constant speed prop cruising (2400 rpm) 190 knots usually at 6500-9500 msl.
My CG was very far aft with the light Catto prop as it was hard to load without the CG moving very close to the aft limit with a passenger and baggage. Between the motor and prop I added 66 pounds to the nose with the heavier angle valve motor and constant speed prop. I now add weight (25lbs) to the aft baggage compartment when flying solo.
In my opinion the airplane is much more stable with the forward CG. It is also much easier to load with a passenger and baggage and the CG ends up in the middle of the envelope. An added benefit of the more forward CG is the airplane lands much easier in my opinion.
My plane absolutely doesn't fly like a dump truck! Ridiculous statement in my opinion!

Kevin

Very true! The EIGHT never should have been on that list. How does it handle without the 25lbs in the aft baggage?
 
I had the CG all the way at the front of the envelope before I put a Cato prop on that moved it back.

I found 3 point landings and spins more difficult but doable with the CG in the front now both are substantially easier but you have to pay more attention with heavy passengers and luggage. I guess you can’t get everything in a tandem configuration. Luckily the 8 has a forward luggage compartment you can use to balance things out.

Oliver
 
FP vs CS

It's more than fixed pitch vs Constant speed, because not all FP props are the same. I have a cruise prop, 160hp RV-6.
A buddy that I fly with a lot, for coffee or burgers, has a 180hp RV-8 CS.
He has to run 25/2500 to stay with me, unless I throttle back....
But, he blows my doors off on takeoff/ climbout...
 
Plane handles like a dream!!!

Very true! The EIGHT never should have been on that list. How does it handle without the 25lbs in the aft baggage?

I couldn’t be happier with my current set up! I know the Hartzell Composite prop price is a deal killer for many! I’m fortunate to be able to pull it off! However I can’t imagine an 160hp RV 6 out running my RV 8 with the Catto prop cruising 170 knots!
 
I couldn’t be happier with my current set up! I know the Hartzell Composite prop price is a deal killer for many! I’m fortunate to be able to pull it off! However I can’t imagine an 160hp RV 6 out running my RV 8 with the Catto prop cruising 170 knots!

Sorry realized your question was without the weight…very nose heavy on the front edge of forward CG. But dead center loaded for x-country. Not ideal without the weight added.
 
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