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RV4 Fixed Pitch Questions

Scott Hersha

Well Known Member
I have an RV4 with an O-360-A1A / 180 hp, and a Sensenich 72 X 85? prop. My airplane is fairly light (980#) and it performs quite well with this setup in most areas. However, I can?t use the power that I would like to at anything above about 5,000? without over speeding the engine. At 7,500? DA, with wide open throttle, I?m turning 2880 RPM, and seeing 182 KTAS. I don?t run it like that, except for a test purpose. I would like to see 2700-2750 at WOT, and the same TAS as I have now.
My options as I see it are:
1. Repitch the Sensenich to a higher pitch
2. Buy a ground adjustable - Sensenich 2 or 3 blade, or a 2 blade Whirlwind
3. Buy a constant speed, either Hartzell, or Whirlwind. This would involve removing my engine to modify the firewall to make room for a governor, cost 2-3 times more than option 2, and negatively affect my current light weight handling qualities.
Option 1 costs about $400 at a reputable prop shop in Sellersburg, IN. There are warnings on Van?s website about re-pitching metal Sensenich props, but I?m guessing that is for DIY re-pitch jobs. The prop shop has a pitch table meant for this purpose.
So my question is - does anyone have any experience with either re-pitching their Sensenich prop, or the use and performance of either of the above mentioned ground adjustable propellers?
I do fly formation and it has been an interesting challenge compared to my previous CS RV?s, requiring a much higher level of anticipation to stay ?welded wing? in some situations. Pitch outs for an overhead landing is really an interesting challenge. The 3 blade GA prop would help a little in these situations. If anybody has experience in this area, please tell about it.
Thanks,
 
You left out one option. Call Craig Catto. He can fix you up with the proper prop.

This will also reduce your overall weight.
 
Yes, forgot to mention Catto. Nicole is recommending a 3 blade 64? X 80? prop. This runs just under $5K not including shipping and lead time is 3-4 months. The price is the high end of my non-CS options, but I am concerned that if we got the pitch wrong, I?m stuck with it. And the wait time puts me in to fall. If I go that way, I?ll re-confirm my performance numbers with my current prop to try to get a Catto that is right.
 
Yes, forgot to mention Catto. Nicole is recommending a 3 blade 64? X 80? prop. This runs just under $5K not including shipping and lead time is 3-4 months. The price is the high end of my non-CS options, but I am concerned that if we got the pitch wrong, I?m stuck with it. And the wait time puts me in to fall. If I go that way, I?ll re-confirm my performance numbers with my current prop to try to get a Catto that is right.

Craig is REALLY good at hitting the numbers. If he has your current data, he will get it right!
 
Sensi re-pitch

I had a metal sensi repitched for my old Pacer. told the shop how many rpm i wanted and it worked like a charm. check the prop section for feedback on the Sensi/GA ground adjustable props.

on the Catto, depending on which prop extension you have, you may be spending another $800-1000 to get the correct size with enough bearing surface up front for the Catto.
 
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Gil,
I was told that the factory doesn?t re-pitch, or do any servicing of their props anymore. They use a network of approved prop shops for that. I?ll probably go that way to begin with because it?s much cheaper, and I can get it done in 2 days. Sellersburg is a 2 hour drive for me. I will still most likely either go with a Catto, or one of the GA composite props - all of which is lighter than my metal Sensenich. There is plenty of favorable reports about Catto. I haven?t heard performance reports from anybody that has tried the GA props.
 
Gil,
I was told that the factory doesn?t re-pitch, or do any servicing of their props anymore. They use a network of approved prop shops for that. I?ll probably go that way to begin with because it?s much cheaper, and I can get it done in 2 days. Sellersburg is a 2 hour drive for me. I will still most likely either go with a Catto, or one of the GA composite props - all of which is lighter than my metal Sensenich. There is plenty of favorable reports about Catto. I haven?t heard performance reports from anybody that has tried the GA props.

Well that's interesting. I contacted two of the prop shops in AZ and was told they did not re-pitch the RV props because they were too thick at the base. One said his repair technician would quit if he had to re-pitch another RV prop. :)

This was about two years ago.


PS, they were both listed as Metal Prop Repair Facilities for AZ
 
This article from my build log is ancient history but probably still interesting for those considering a repitch of the metal Sensenich:

http://home.hiwaay.net/~sbuc/journal/fairings.htm#repitch

pants-14.jpg
 
Thanks Sam. That scares me just a little. Two big beefy boys on a long pipe seems a little crude. I?ll contact my prop shop tomorrow to see what their re-pitch method is. Maybe call Sensenich to make sure they don?t do this anymore, like I was told (by a prop shop in my state-Ohio). I also suspect there is an error in my claimed 85? pitch. I borrowed pitch gage from a friend today and I?ll check it tomorrow. This gage measures pitch in degrees from a datum - the front face of the hub - so I?ll have to figure out the angular relationship to pitch in inches.
I flew today to test some of my numbers, and I?m still convinced I need something with more pitch -
7500? DA at WOT = 2900 RPM; 181 KTAS
9500? DA at WOT = 2880 RPM; 183 KTAS

It was a warm day in Ohio, so 9500 DA was about 7600? PA.
 
I agree with earlier remarks: Call Catto!

The RV4 that I used to co-own had a three-blade Catto prop on it.

160 hp. Not a very clean airframe (with some fairings not quite fairing), not a particularly lightweight airframe either. And yet, we also hit the same 182 kts that you did. Only at 2650 rpm.

I've just bought an RV3. It will have a Catto. Period.
 
It is very crude but the way props are repitched if the hydraulic apparatus isn't available. My prop has been flawless for nearly twenty years following the repitch.
 
I'll be the odd guy out on this one.

On my 360 -4, this spring I went from a Prince FP to a Hartzell CS. I was initially concerned about the extra weight, but in the -4 it actually helped. My back seat is finally useful! Makes Formation easier, you get full power for TO, and my new personal favorite, cruising at 2300rpm is soooo smooth.
YMMV
 
I will be even more odd (typical).... What is your mission Scott???

It sounds like low density altitude operation with some formation mixed in.

Asking as I have found the Sensenich GA to be a wonderful "alternative" to a constant speed prop. I frequently operate from high density altitude short backcountry airstrips - takeoff/landing at 10,000' DA and 2600' dirt airstrip with trees is not uncommon (example here, good stuff starts at 7:15). Having the ability to adjust the pitch of the prop to match my mission for the day is fantastic. Yes, a constant speed prop would be far better - but that option is also far more complicated/costly (as you have noted).

Regarding formation. I have found the opposite. Formating with a finer pitch setting (climb) results in the aircraft being "quicker" to respond to power changes - so easier to stay in position when maneuvering. I have no idea if that is typical or just me and my setup.

I have been very impressed with the Sensenich GA. It was smooth out of the box - so smooth that I've never bothered to dynamically balance it. It performs better than the last fixed pitch prop I had installed (older Catto) though I don't have super good numbers to back that up. It affords the adjust-ability mentioned above. I suspect the latter is of no use to most folks as many of the other owners I have talked to seem to find the setting they like and then never make another change.

I had a fixed pitch Sensenich adjusted on my RV-3. The shop said they bent it as far as they were allowed (some sort of Sensenich limit??). It made a difference but not as much as I needed. I don't know how all that works but maybe worth checking before you decide to have your existing prop adjusted.

Not trying to sell you on any one option... just trying to give more to think about. ;) Hope something in there is helpful...
 
JD,
Thanks. That?s good information and exactly the kind I was looking for. If I have my metal Sensi re-pitched, I?ll ask the limits if they have any. I was told by one of the prop shops that an inch of pitch change on a Sensenich is worth anywhere from 25 to 50 RPM. That?s a big range and makes me think they are guessing. If I need to lower my WOT RPM by 200 (I do), I would need to have it bent to an 89? pitch and that?s if the change is 50. If it?s 25, I doubt they could get there.

The GA Sensenich sounds interesting, and if I got a 3 blade, it would help in formation flying. Nicole at Catto told me the 3 blade prop slows the airplane down noticeably faster.

I have a McCauley hub from a Whirlwind 200RV constant speed prop from my last RV8 that bit the ground (By former partner). It is probably in good condition and only has about 50 hours on it, but will still need a tear down inspection. There are definitely blades available if I wanted to reblade it. The holdup on getting a Whirlwind CS seems to be the McCauley hub. Jim Rust (Whirlwind ?inventor?) is trying to clone the McCauley hub, but I don?t know if he?s there yet. Anyway, that would be a possibility if I could get it done and not have to spend $10K + for a new one.
 
fit and finish...

One thing to note if you go the Sensi GA direction. I looked into this for my early -4 (Serial 715) and my airplane has the cowl for a 12" spinner. Sensenich ONLY makes that spinner in a 13" (Later -4 cowling).

I've seen a few 12" cowled -4's with 13" spinner and it's just not for me. That's my only reason for not pulling the trigger on the Sensenich prop.
 
Justin,
Mine is an early one too (#530), but it wasn?t completed until 2005, so the builder must have bought the cowl near the end. I have a 13? spinner on my Sensenich now and it lines right up.
 
Right - good point! I have one of those. I care more about flying than looks so it didn't bother me for long - as you can tell from the unpainted spinner!! ;)

2018_12_23_RV4_SensenichProp1.jpg


When seen from this angle, it isn't even noticeable. :D

DSC04739.jpg
 
Right - good point! I have one of those. I care more about flying than looks so it didn't bother me for long - as you can tell from the unpainted spinner!! ;)

That's right! Go out and fly the snot out of it... That's why we bought them, right? I bagged 150 hours on mine last year and on track to do even more this year. They're fun airplanes.
 
One thing to note if you go the Sensi GA direction. I looked into this for my early -4 (Serial 715) and my airplane has the cowl for a 12" spinner. Sensenich ONLY makes that spinner in a 13" (Later -4 cowling).

I've seen a few 12" cowled -4's with 13" spinner and it's just not for me. That's my only reason for not pulling the trigger on the Sensenich prop.

Sensenich does indeed have a 12" spinner. I have one.

I didn't care for the improper fit of the 13" spinner on the old style cowling. Sensenich was VERY HELPFUL and provided a 12" spinner. The profile is slightly different, but I like the looks more than the 13" which was just too big.

Sensenich-prop-12-24-19-1-scaled-e1577334255295.jpg


Sensenich-prop-12-24-19-2-scaled-e1577334179421.jpg


Sensenich-prop-12-24-19-3-scaled-e1577334324308.jpg


I'm still tweaking the pitch, upward, but so far the prop has been performing well.
 
Catto prop

Hi Scott,
I have the Catto three blade on my 4. (Old photo on my VAF signature) While it is smoother than the Whirlwind ground adjustable 2 blade that it replaced, I would differ with Nicole that you can slow down faster than a two blade. No difference in that area between the two.
Also at wot, I will pass the recommended max rpm for the prop. Catto's props are works of art but in my case he did not quite nail it. I could have sent it back for a rework to get it perfect but did not elect to do so.
Mark Wyss
 
Thanks Mark. That?s what I am afraid of happening - missing the pitch setting. Plus the 3-4 month wait for a new prop isn?t what I?m looking for. I just ordered a new GA Sensenich carbon fiber prop. I ordered the two blade after talking to Don Rowell at Sensenich and he confirming what you said about the three blade not slowing down any better than a two blade, due, at least partially to the two blade having a wider cord. They should be ready to ship it to me in 3 weeks.
 
Same problem

Scott,

I was in the excact situation as you. Lightweight RV-4 (about 970 lbs) with an O-360 which probably puts out about 185 HP due to using dual PMags. Overall the performance with the metal 72 x 85 Sensy was good, but I didn't like the amount of vibration, but in fairness to the prop I have a conical mount engine. And also like you, I had a lot of throttle left up at 7,000 - 8,000 feet. Going WOT would get me around 2,800 - 2,850 RPMs, so I was leaving performance behind.

I agonized for years on what to do (search my posts for the same questions you had). How to balance cost, performance, maintenance, etc. A lot of recommendations to get a Catto, but like you, I feared getting the pitch just a little bit off. Finally bit the bullet and bought the Sensenich GA prop from someone here who converted to a WW C/S prop. If money, time and everything else were not an issue, I'd go with the WW C/S, but the Sensenich GA is a GREAT compromise in my opinion. I like the way the plane handles with the CG more aft, but to each his own.

Here are my unscientific observations on the metal vs the GA. Started at pitch setting "4" but changed to "5" after two flights. "4" put me in the same situation as the metal Sensy. GREAT climb rate but was hitting 2,800+ at cruise.

Initial acceleration - HUGE difference. The GA prop gave my takeoffs the WOW factor I've been looking for. The initial acceleration (first 5-6 knots) is not as good as a C/S but it quickly catches up. My wife occasionally goes with me, and is not a pilot, but she even noticed a huge difference on takeoff.

Climb rate - I'm guessing I get about 200 FPM more (at same IAS) with the GA. I routinely see 2,200 - 2,400 FPM (or more) for a couple of thousand feet at 110 IAS when solo. Yesterday, solo with half fuel I was holding 1,800 FPM at 140 MPH (about 52 degrees outside). I do sometimes wonder if my engine is putting out more than 180-ish HP but it has never been dyno'd.

Cruise - At pitch "5" I lost about 2-3 knots TAS with the GA prop at my normal cruise RPM of 2450 or so. That being said, I will re-pitch to 6 or maybe even 7 for long trips. Was going to do this for OSH but that is on hold. At "5" I still top out just a bit above 2,700 (maybe 2,750 or 2,760?) at WOT.

Smoothness - much better with the GA

Deceleration - seems a bit better with the GA, but still not C/S worthy.

Looks - I LOVE the looks of the carbon fiber GA prop and the blade design. Not sure if the clear coat carbon fiber look is still available but I think it is cool

Negatives? - The only thing I can think of is I found the metal prop is easier to start if you have a weak battery - get the prop moving and the momentum of the heavier prop helped it continue through the compression stroke until it catches.

Also, I knew the metal could probably take some heavy rain with little to no worries. GA with metal leading edge? Remains to be seen. Would be the same concern with a CATTO. I try to avoid rain showers but I do live in the PNW!
 
Rick,
Thanks. That?s really good information. I have some pretty detailed data on my current setup, so looking forward to testing the new prop when I get it. It sounds like wee have a similar aircraft, except mine is a standard Lycoming O-360-A1A, so most likely 180 hp. I do get 2880-2900 RPM at 8,000 DA and 182 KTAS. My current prop has 85? pitch, 71? long. The new GA prop will also be 71? long. I?m looking forward to the performance enhancement that you have experienced. I?ll post what I find out about mine when I get to that point.

Thanks
 
Sensenich does indeed have a 12" spinner. I have one.

That's good to know! Game changer maybe for us 12" cowled guys... My information was from Oshkosh 2018. I spoke with their booth and they didn't have one at the time (I was told...)
 
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