Rebel Performance

[karl hipp]

My 150 HP Rebel on bungees with 26 inch fat tires trues out at 92 kts at 8000 feet.
I question the efficiency of my modified off brand prop.

My inquiry is ---does anyone have experience and advice on another prop that might give me a significant bump in speed?

Karl Hipp

[Walter Klatt]

What "off brand" prop are you using?

When I had the 150 hp 320 in my amphib Rebel, I found the "name brand" 2 blade metal Sensenich 74 X 54 prop to be the most efficient. My static rpm was 2500 and top speed, full throttle straight and level was 2720. Top speed was 125 mph, and cruised at 105 mph (65% power).

Because it turned 2500 static, was able to make good power for take-off and climb, yet did not overspeed at the high end. So was pretty well the perfect prop for that plane. I also did a lot of side by side tests with other identical Rebel amphibs with other props, and beat them all in take-off, climb, and top speed.

Here is a very common mistake people make with prop selection. And that is they over prop it (too much pitch) and the engine is robbed of power. They have lower static rpm, and can't make max rpm at WOP straight and level. You might as well have a cheaper, lower power, lighter weight engine, if that is what you have.

And then there are props (eg. a very popular composite) that need low static rpm pitch just so they don't over rev in cruise and WOT on our Rebels. They are fine for slower planes like the Supercubs, because they can pitch them for a higher static, and they still won't over rev due to that plane's overall high parasitic drag. But that is not the case with our Rebels.

I did a lot of testing with props, and could not find a better prop for the Rebel on amphibs (your big tires would have high drag, too) than this Sensenich 74 X 54 prop. And this includes the 160 hp 320. One of the local guys, again with the identical Rebel amphib (except he had 160 hp) had a 74 X 56 prop. In side by side tests, I was able to beat him not only in take off on the water, but also in climb, and top speed. The problem was that with 56 pitch, it reduced the power available from his 160 hp to less than my 150 hp. He had it repitched to 54, and it was like a new engine, as he then had good performance as was expected from the higher hp.

Probably the best example with my side by side tests, was with a wheels 160 hp Rebel using a Mccaulley prop. When I told him my climb and speed numbers, he wouldn't believe me. So we did some inflight tests, both of us with a pax, but mine also had the extra weight and drag of the amphibs. To his great surprise, I beat him in climb, and top speed. He didn't doubt me after that...

I could tell you more, and have posted in the past about the Senenich props vs others.

[karl hipp]

thanks for all that info Walter.
The reason I call it off brand

It was made by PROPS INC in Oregon. I had to cut it down to 70" just to get 2500 rpm flat out.

I asked the guy to make me another one and he didnt even know the pitch of the one he had already made for me.

[karl hipp]

I went to the PRINCE website--I know there is a lot of talk about the prince props.
I entered the info on their "prop calculator" and they came up with a 76/58 prop for $2,148

Certainly for that kind of money for a wood prop I would like to get it right the first time

I dont doubt your numbers on the 74/54 Sensenich Walter. The prince website form doesnt have a place to consider floats or big tires.--- so I am more confused than ever now

[Washington Rebel]

I talked to Lonnie Prince and he recommended a 76x56 for my plane
200 HP with big tires
I just got it.
It is beautiful and hopefully will be on the plane soon if I get the wiring done.

[irishfield]

How much HP do you have Karl.... I'm running a 74/44 Prince that was built for a 160 and I can't fully spin it up with my 150HP Lycoming.

[Walter Klatt]

Karl, you can't compare diameters and pitches between different prop manufacturers. Blade shape/airfoil also matters. I am just giving my experience, and which prop I found to be the best for that engine on a Rebel amphib.

[Walter Klatt]

How much HP do you have Karl.... I'm running a 74/44 Prince that was built for a 160 and I can't fully spin it up with my 150HP Lycoming.

Looking at the Prince website, their recommendation of a carbon fiber p-tip on a Rebel is the 74-46, which is even more pitch than you have!!?? What static and WOT top speed RPMs are you getting with the 44 pitch? Are you sure your engine is producing full power? And what ever happened to that Senenich prop you got from me? And did you try the VGs yet?

[karl hipp]

I am running a 150 HP Lycoming. I guess I am currently getting about the same speed as walter. 92 kts--which is about 105 mph at 2400 RPM.
The Prince prop that was recommended in wood is a "P" tip 76/58

A buddy with an O-290 on 6 X 8 tires gets 120 mph with a 72" Sensenich. I don't know the pitch. But he is 15 HP less and drives right past me.

I have had the VG's on for some time. They dramatically lower the time and distance on the ground.

Since my runway is at 6,500msl, I never cruise around at much less than 9,000 and often higher.

It is my experience that the VG's slow you down less as you get higher with negative drag effect at 12,000 feet and a speed gain as you go up from there because they decrease your aot

[Rebel541]

My 150 HP Rebel on bungees with 26 inch fat tires trues out at 92 kts at 8000 feet.
I question the efficiency of my modified off brand prop.

My inquiry is ---does anyone have experience and advice on another prop that might give me a significant bump in speed?

Karl Hipp

G'day Karl !


( I've been away for the past week - so my reply is a tad slow - sorry )

PRINCE props will swap a propeller if it isn't right too ya know ! ..... so don't fear getting caught out with the wrong one !!!

Yes - they are "pricey" - but boy - do they WORK

FULL RPM on takeoff - so you get THE best climb performance possible - and then it automatically coarsens up in flight as you back the power off - so it becomes a cruise come SPEED prop !

Plus - they are THE "smoothest" running propeller I've ever flown behind too .....

95% of the performance of a Constant Speed prop - with a fraction of the weight, complexity and COST !

AND - if you get their "P-Tip" version - you'll gain an extra 2" of ground clearance as well

What more could anyone ask for ?!?!?!?!?!?

[irishfield]

There seemed to be a lot of issues in the early days of pitch variance Walter. I had the 74/44 here from an aircraft buy that came off a 160 x H2AD. Mark Morin ordered a prop for his 150 (your old one) O-320 and they sold him a 74/46. We were left scratching our heads, so we tried both on his at the time and the 46 spun up higher... so yah my 44 is coarser than his 46 in our case anyhow. Possible this prop was made a 44 and was sent back and made coarser.. and just wasn't rebranded! My motor is making power.. as I can turn it 2500 on take off.

VG's... there in my flight bag somewhere. Got the glue.. but no time with everything going on.

Your prop.. I bought it back from Mark... it's safely stored under my work bench for a rainy day ! :shh:

[Rebel541]

Karl, you can't compare diameters and pitches between different prop manufacturers. Blade shape/airfoil also matters. I am just giving my experience, and which prop I found to be the best for that engine on a Rebel amphib.

G'day Walt / Karl !

My Reg 35 (Aircraft Design Engineer WIZZ buddy) has lent me various propeller design books - by design engineers from the 30's & 40's (when the last "definitive work" was done ON wooden propeller design) ....and also by the German - Edward Weik - who, by all accounts IS "THE" last expert on wooden props ........

My buddy (Steve) has designed (amongst many other things) the 25 ton carbon fibre sonar domes on billion dollar submarines (his "specialty" is CF and composites) many military aircraft modifications, light, ultralight aircraft designs, gyrocopters - and lots more ....... (he's a seriously bright boy :thumbup:)

Steve keeps telling me that - "If you take a set of numbers (diameter, pitch and blade section data) to 100 different propeller manufacturers - you will get back 100 TOTALLY DIFFERENT propellers !

Seems that EVERYONE is "an expert" - and have THEIR OWN methods to calculate what is needed to make those numbers convert into a usable prop'
(and added to that - are the multitude of variable in regards to "what sort of engine" - and it's condition - are driving said propeller !)

I have a pantograph - (it's like a HUGE rotary key cutter) ..... and I can make copies of ANY propeller (or just about any shape - period) ..... and have made around 30 propellers - so far ..... each one supposedly "improving" on the last one / design ....... but it just ISN'T "that simple" ........

It's somewhat of a lottery I've found ....... but that is also WHY I really like PRINCE's policy of swapping the propeller - until they get THE right one that suits YOUR application .... AND - once you've flown behind a "self adjusting - almost constant speed, lightweight propeller" - you will most likely never go back to whatever you were using - before !

[snowyriver]

Since we're on this prop discussion I thought I'd chime in. Walter, you know what prop I was using, it's a sensenich 76-54. Or I should say it was. A few months back I flipped my plane over and the prop did not survive (don't tell Dennis lol). No human injuries so that was good but I did need to find a new prop. I decided to give catto a try. I know Dennis had a poor experience with his catto prop, ultimately ditching it for another sensenich but I'm hoping for a different outcome. Craig Catto said that with my rebel plane specs, weight, and the 180 hp eng I needed a 82-46. He said the 46 pitch should keep the top end about where it was. I'm very interested in what the low end will do because honestly, it already felt like a rocket on takeoff! I should be back in the air in a month or two and I will give a full report.

Since I let the cat out of the bag, let's name it: it was almost entirely due to flying without weight in the tail. I usually keep my survival gear back there (34 lbs) but was flying w/o it. Not a very technical landing at all but while managing it the tail started coming up and before I knew it-bam. Happened fast. I won't do that again. Also, the lighter prop, about 20 lbs lighter should help. CW

[irishfield]

You know SJ gives out hats for that eh Craig ??!!!

I came close once... but thankfully was on skis. Was just stopping a slide when the skis decided they were done sliding but the airplane wasn't. Tail went up as high as it could and the thing that saved me was the rear ski check cables stopped it from going any higher, but I sure got a good view of the ground from that angle. When the tail came back down I drove my tailspring up into my rudder. So if you get in that situation... put one rudder pedal to the floor.. to at least save the rudder!

[Walter Klatt]

[quote="snowyriver"]Since we're on this prop discussion I thought I'd chime in. Walter, you know what prop I was using, it's a sensenich 76-54. Or I should say it was. A few months back I flipped my plane over and the prop did not survive (don't tell Dennis lol). No human injuries so that was good but I did need to find a new prop. I decided to give catto a try. I know Dennis had a poor experience with his catto prop, ultimately ditching it for another sensenich but I'm hoping for a different outcome. Craig Catto said that with my rebel plane specs, weight, and the 180 hp eng I needed a 82-46. He said the 46 pitch should keep the top end about where it was. I'm very interested in what the low end will do because honestly, it already felt like a rocket on takeoff! I should be back in the air in a month or two and I will give a full report.
quote]
Well, good luck with your Catto. When Dennis tried it with his O-375 Elite amphib, it had lower static rpm (thus making less power) and still revved out at the top end. Yet he had less top speed than with his old (yours) O-360. And on his first take-off and climb-out he thought he had an engine problem, the performance was so much less than with his old engine.

Having said that, you could put a 2 X 4 on the front of an O-360 powered wheeled Rebel and it will feel like a rocket. So am sure your new Catto will still be more than adequate. I still remember my very first flight in a Rebel with Robin in their factory 80hp Rotax test plane. I thought it performed pretty well!! Of course back then my only comparison was a Cessna 150.

To keep the tail down for landing, do you have the VGs on the underside of the hor stab?