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Lose 5-10 knots with a 3 blade prop on a 10?

Subwaybob

Well Known Member
Spoke to Vans support today. They (one guy) thinks I'll lose 5-10 kts with the Hart 3 blade prop over the two blade. Is this true? My RV10 will have a Thunderbolt 260hp and POSSIBLY a 3 blade. I sure as snot don't want to lose 10 kts! Any truth to this?:confused:
 
Data please

I am very skeptical that there is a 10 knot loss with a 3 blade compared to the two blade. I would believe 2-3 knots...maybe.

If you have definitive, not anecdotal data, please share it...
 
I am very skeptical that there is a 10 knot loss with a 3 blade compared to the two blade. I would believe 2-3 knots...maybe.

If you have definitive, not anecdotal data, please share it...

Absolutely correct. Couple of knots at most. Verified by racing my 3-blade MT against 2-blade Hartzells at last year's Race for Rhinos. At one stage I spent the best part of an hour 100m or so behind a 2-blade. Tried everything I could to close the distance but couldn't. Eventually he just drew away - maybe 1/2kt. There were a total of 6 -10s at the race and I was the only 3-blader, Results showed us all within 2kts apart from one who was about 4-5kts faster than anyone else - no-one could work out why (supposedly stock aircraft ;)). He ended up on the podium.

On the plus side - super smooth and (supposedly) better TO and climb performance. Plus the cool factor ;):D Only real downside is getting the lower cowl on and off. Some mods needed to the lower cowl. After a while, you get the hang of it.
 
Posts like Paul?s above mean nothing; there?s too much variation from plane to plane. The only good test is A-B on the same plane. I?ve only seen one such post; that owner put his 3 blade up for sale after trying a 2 blade and gaining 5 knots, iirc.
 
Posts like Paul?s above mean nothing; there?s too much variation from plane to plane. The only good test is A-B on the same plane. I?ve only seen one such post; that owner put his 3 blade up for sale after trying a 2 blade and gaining 5 knots, iirc.

A little harsh, I think ......

It was a reasonably sized sample so I think the comparison has merit. Again, apart from the one aircraft, not only were we within a knot or 2 of each other, we were also within a knot or 2 of our handicap speed.

Having said that, 2 knots would be worth some 2 minutes over the race. I'd like to try a 2-blade to see what benefit it gives and then swap out for the next race. Full time though, I wouldn't want to give up my MT - love it.......
 
+1 to harsh :p

Our 3 blade MT 7 will keep up with a 2 blade Hartzell without any issue.

Besides, how often are you running flat out ?

Ultimately, you look at what you want out of your aeroplane and look at the pro's and con's of 2 or 3 blade props. 3 blade is smoother and in our case, the MT has phenomenal acceleration and deceleration, it's smooth and quiet and I cruise just fine at 145kts at 23/23.
 
To each their own. :)

Saying the other airplane was faster because one had a 2 blade and one had a 3 blade means nothing.

The only way to verify for sure is to take the same airplane, at the same weight and power settings, and fly it under the exact same atmoshpheric conditions (pressure/temp/altitude, etc). Period.

BTW, we did that with my RV-10 (swapped props) and noticed no measurable difference in speed. We even took my RV-10 back to the mothership and let Van fly my airplane right next to the factory RV-10, with both Van and I in mine (Van doing the flying) and Ken Krueger flying the company RV-10. At 8500' and full throttle, we were neck and neck. The GPS's on each airplane were within 1 knot of each other. Everyone was surprised. :) Without swapping the props it still didn't mean anything except it put to rest all of the hullabaloo that the MT is 10 knots slower.

There are advantages and disadvantages to each prop. one might be smoother, have more ground clearance, and better climb performance. The other might be more durable on unimproved runways, easier to get cowling off, cost less, etc..

Racing is a totally different arena. :)

Build the airplane for you. :)

Vic
 
Then...

"...Posts like Paul’s above mean nothing; there’s too much variation from plane to plane..."

Then you also have to conclude the same about posts like David's...
 
The MT is virtually a maintenance free prop. Maintenance manual lists no required service other than visual inspection. Sealed maintenance free bearings do not require greasing. These props are not prone to slinging grease. First 10 hrs. on my -7 I was amazed how smooth the MT was and figured it wouldn't need dynamic balance. But I figured what the heck, turned out to be .38 out of balance. Got it balanced to .02 and it is now almost turbine like smooth. There is a lot to be said for engine/prop vibration and its long term effects on the entire airframe and components. To each his own, and say what you will about the MT, but IMHO it's one sweet prop!
 
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To each their own. :)

Saying the other airplane was faster because one had a 2 blade and one had a 3 blade means nothing.

The only way to verify for sure is to take the same airplane, at the same weight and power settings, and fly it under the exact same atmoshpheric conditions (pressure/temp/altitude, etc). Period.

BTW, we did that with my RV-10 (swapped props) and noticed no measurable difference in speed. We even took my RV-10 back to the mothership and let Van fly my airplane right next to the factory RV-10, with both Van and I in mine (Van doing the flying) and Ken Krueger flying the company RV-10. At 8500' and full throttle, we were neck and neck. The GPS's on each airplane were within 1 knot of each other. Everyone was surprised. :) Without swapping the props it still didn't mean anything except it put to rest all of the hullabaloo that the MT is 10 knots slower.

There are advantages and disadvantages to each prop. one might be smoother, have more ground clearance, and better climb performance. The other might be more durable on unimproved runways, easier to get cowling off, cost less, etc..

Racing is a totally different arena. :)

Build the airplane for you. :)

Vic

...... and there we have it. Won't stop the myths though. Perhaps there should be a new section in "The Never Ending Debate" section ;)
 
Well, maybe


I also removed an MT 3 blade and installed the 80" Rocket version of the Hartzell BA 2 blade. Substantial increase in speed as a result - 'almost stock' TCM 550. Mike - you need one of those on your nose!

Could be the design points for the Rocket P/N MT are optimized wrong - I spec'd economy cruise 2100RPM at FT/10000MSL, and it works great at that setup. So, it might be overpitched, or have a bit too much area? Dunno, but I still have that smooth operator upstairs - gonna try it on a higher HP version - with supercharger and RG. That testing will be interesting to say the least.

MT wants the data at several altitudes before they produce different blades, but they did agree to work with me. I think a Hartzell BA can still out-perform the MT (might take new - and more - blades to get there), but that sure is a lotta bux to let lay around...
 
Does MT or Hartzel prime their props?

Was trying to take another never ending debate and if we combine them...maybe they will both be solved:D
 
Paul (and others),
I apologize for sounding harsh - that was not my intent. But please re-read your own post. ?The winner was 5 knots faster for unknown reasons?. If the winner had chosen to run a brand X prop, lost 5 knots and run even with everyone else, would the correct conclusion be that brand X was just as good? You need to vary the prop, and only the prop (same airframe, wx, etc) to reach a supportable conclusion.
 
Since Van's sells MT and Hartzell I have no reason to favor one over the other, but another point of consideration that might be of interest to some....
Investigate what the service and overhaul intervals and costs are of prop you are considering.
Years ago when there was a 3 blade MT on the prototype RV-9A (which all the pilots loved, BTW) it came time for an overhaul. Because of the costs involved in shipping it to/from an approved repair facility, and the quoted cost of the work, it was found to be close to the wholesale cost of a new Hartzell, so the MT went into storage (still there to this day) and a new Harzell was installed in its place.

That may not be the case any longer (was 10 years ago), but something that discriminating shoppers might what to investigate.
 
To each their own. :)

BTW, we did that with my RV-10 (swapped props) and noticed no measurable difference in speed. We even took my RV-10 back to the mothership and let Van fly my airplane right next to the factory RV-10, with both Van and I in mine (Van doing the flying) and Ken Krueger flying the company RV-10. At 8500' and full throttle, we were neck and neck. The GPS's on each airplane were within 1 knot of each other. Everyone was surprised. :) Without swapping the props it still didn't mean anything except it put to rest all of the hullabaloo that the MT is 10 knots slower.

There are advantages and disadvantages to each prop. one might be smoother, have more ground clearance, and better climb performance. The other might be more durable on unimproved runways, easier to get cowling off, cost less, etc..

Racing is a totally different arena. :)

Build the airplane for you. :)

Vic

Vic, could it be that your plane was only 1 mph slower than Vans because you had another 50 hp under the cowl? Was your plane making 310 hp when you did this test? I would really like the MT, but.... I want you to tell me that it wasn't making that much hp so I can buy one and be quiet and cool for the same speed!

http://forums.matronics.com/download.php?id=14897&sid=9ac23f2ae3f1c23fb487b704c83f7e5e
 
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How about service and support from MT vs. Hartzell?

I have not heard any positive or negative thing about Hartzell but know of at least two unhappy people with MT, in relation to warranty/support.

They also did a poor job dealing with the prop governor issue a couple of years back.
 
No

No, his airplane was not making 310HP during the test at 8000+' DA...but Van's wasn't making 260HP either.

As stated in the article's conclusion, the 2 bladed prop is more efficient. That is no surprise as the theoretical calculations indicate this. Problem is with two different aircraft, as the article stated. Too many different variables between the aircraft to get truly definitive data.

The only way to get better data is to fly the different props on the SAME aircraft...
 
Last night I was seeing

174 TAS, 24.5", 2300RPM, 14gph LOP, 2700' DA, 5500' MSL, 2?F.

Thunderbolt IO-540, Hartzell c2yr-1bfp/8068d (I think that's the number, from memory)

Just a data point for you.
 
Randy Leverold tested the Whirlwind two and three blade props on his RV-8. The three blade prop was two knots slower. Climb, acceleration and deceleration were all better on the three blade.
 
Why not have the best of both worlds and install the MT 2 blade prop like I did on my 182.

2v1xbg5.jpg
 
2 vs 3 blade discussion has been going on in the Mooney world since they started retrofitting 3 blades to them. The consensus is that 2 blades are faster on Mooney's. I will be putting a 200 HP Mooney engine and 2 bladed Hartzell on my F4 project.

Cheers,

Phil
 
Paul (and others),
I apologize for sounding harsh - that was not my intent. But please re-read your own post. ?The winner was 5 knots faster for unknown reasons?. If the winner had chosen to run a brand X prop, lost 5 knots and run even with everyone else, would the correct conclusion be that brand X was just as good? You need to vary the prop, and only the prop (same airframe, wx, etc) to reach a supportable conclusion.

No offence taken Bob ........

I didn't get a chance to check out the prop on the faster -10. Could be he had some fancy Scimitar, blended etc etc. As I said, I would love to borrow a 2-blade and see what it could do but it would be a huge amount of work to try and prove a point - and I certainly can't justify spending $10k just so I can get an extra couple of knots in a once-a-year air race - especially as my wife isn't complaining about me building a Bearhawk :D

In my opinion, the MT 3-blade is an excellent prop. Super smooth and great looking. I get 155kts TAS (178mph) at 9000', 60%, 10.5 usg/hr - that'll do me .........
 
Spoke to Vans support today. They (one guy) thinks I'll lose 5-10 kts with the Hart 3 blade prop over the two blade. Is this true? My RV10 will have a Thunderbolt 260hp and POSSIBLY a 3 blade. I sure as snot don't want to lose 10 kts! Any truth to this?:confused:

Yes, the do indeed.

I have just been test flying a new -10 with the Hartzell 3 blade and it is heaps slower. 10 knots possibly.

When I get a chance with some known to be good data, I will try to remember to come back and post it.

From a single photo the other day with verified static, I had at 5500' 163KTAS at 25.2"/2320 76 LPH. This thing is a pig LOP, or was, we are correcting that, but my RV10 would be TAS 164 on 44-45LPH. My guess is about 7 knots, but that is a guess for now. But it sure is not 2.
 
Yes, the do indeed.

I have just been test flying a new -10 with the Hartzell 3 blade and it is heaps slower. 10 knots possibly.

When I get a chance with some known to be good data, I will try to remember to come back and post it.

From a single photo the other day with verified static, I had at 5500' 163KTAS at 25.2"/2320 76 LPH. This thing is a pig LOP, or was, we are correcting that, but my RV10 would be TAS 164 on 44-45LPH. My guess is about 7 knots, but that is a guess for now. But it sure is not 2.



I hate to say it again, but comparing TWO different airframes is not a valid test in any way.

Somehow we keep missing that through this thread. Randy did some testing, I did, and I think that is about it.

Vic
 
Last night I was seeing

174 TAS, 24.5", 2300RPM, 14gph LOP, 2700' DA, 5500' MSL, 2?F.

Thunderbolt IO-540, Hartzell c2yr-1bfp/8068d (I think that's the number, from memory)

Just a data point for you.

14 GPH is LOP?... seems kinda high for LOP
 
I hate to say it again, but comparing TWO different airframes is not a valid test in any way.

Somehow we keep missing that through this thread. Randy did some testing, I did, and I think that is about it.

Vic

Vic, could you look at my post quoting you on page 3? I'm curious what your thoughts are. I hear you have a new Thunderbolt engine from Jeff at Lycoming but I'm wondering about the article. Thank you.
 
Vic, could you look at my post quoting you on page 3? I'm curious what your thoughts are. I hear you have a new Thunderbolt engine from Jeff at Lycoming but I'm wondering about the article. Thank you.

So, I was annoyed at that article, quite candidly. The engine manufacturer, which had a reputation for exaggerating HP, claimed 310 HP at 2800 RPM. Most of our engines will make a lot more than 260 HP at those RPM's. That's what the racer's do, and they take a pretty good life out of the engine doing just that.

From the numbers I saw cross-referenced to Lycoming power charts, using fuel flow/MP. etc. mine may have made 5 HP more at most due to the 9:1 pistons. The reality is that during that flight, fuel flows, and power settings were matched. My airplane was actually heavier, as we had all of our luggage in it.

BUT, and I say a BIG BUT, it still didn't mean anything as we had 2 DIFFERENT airframes. We did not swap the prop. The only thing, if anything, we learned that day was that just maybe the MT prop wasn't 10 or more knots slower. :)

Vic
 
So, I was annoyed at that article, quite candidly. The engine manufacturer, which had a reputation for exaggerating HP, claimed 310 HP at 2800 RPM. Most of our engines will make a lot more than 260 HP at those RPM's. That's what the racer's do, and they take a pretty good life out of the engine doing just that.

From the numbers I saw cross-referenced to Lycoming power charts, using fuel flow/MP. etc. mine may have made 5 HP more at most due to the 9:1 pistons. The reality is that during that flight, fuel flows, and power settings were matched. My airplane was actually heavier, as we had all of our luggage in it.

BUT, and I say a BIG BUT, it still didn't mean anything as we had 2 DIFFERENT airframes. We did not swap the prop. The only thing, if anything, we learned that day was that just maybe the MT prop wasn't 10 or more knots slower. :)

Vic


Vic's observations are very much correct. Data between two airplanes flying side by side doesn't mean much. My initial comments are from 10+ years of flying with a few (very few) side by side comparisons. The last one was a couple of years ago when flying alongside a friend that has an airplane that is very similar to mine, but has the 2 blade Hartzell and I have the 3 blade MT. At the same altitude, similar weight, and the same fuel flow he had about 7 knots on me as I recall. Maybe his airframe is just faster than mine, but we don't know that for a fact. Actually, my LOP numbers are pretty close to many of those mentioned in these posts. Again, different airframes. If I had it to do over, I would probably go with the Hartzell, but not because of performance. I have the Flightline AC air conditioning system which adds weight aft, and I could use the extra weight on the nose. Also, I have a certified IO-540-C4B5 but I have one Lightspeed ignition and one mag. That means the powerplant is not certified and MT will not honor the warranty on the prop. They told me they were not aware of any certified prop manufacturers that would warranty with a non-certified ignition system. I will also add the MT has provided outstanding support and customer service to me over the past 10 years. It's a great prop, but probably not the best for my application.
 
BUT, and I say a BIG BUT, it still didn't mean anything as we had 2 DIFFERENT airframes. We did not swap the prop. The only thing, if anything, we learned that day was that just maybe the MT prop wasn't 10 or more knots slower. :)

Vic

I don't even mind giving up a little, (but not 10 :D). My understanding is that that MT prop is smooooooth as silk on a new baby's butt. Some even say almost turbine smooth. I think I'm just going to have to do it...
 
So, I was annoyed at that article, quite candidly. The engine manufacturer, which had a reputation for exaggerating HP, claimed 310 HP at 2800 RPM. Most of our engines will make a lot more than 260 HP at those RPM's. That's what the racer's do, and they take a pretty good life out of the engine doing just that.

From the numbers I saw cross-referenced to Lycoming power charts, using fuel flow/MP. etc. mine may have made 5 HP more at most due to the 9:1 pistons. The reality is that during that flight, fuel flows, and power settings were matched. My airplane was actually heavier, as we had all of our luggage in it.

BUT, and I say a BIG BUT, it still didn't mean anything as we had 2 DIFFERENT airframes. We did not swap the prop. The only thing, if anything, we learned that day was that just maybe the MT prop wasn't 10 or more knots slower. :)

Vic

Vic,

You can say it until you are blue in the face, but the data does not stack up in your favour. The OP asked about a hartzell 3 blade did he not?

You claim no difference with an MT......I am not even going to comment on what that might be as i have never flown one on a -10. But I can tell you that the stretched RV8 down here has a MT 3 blade and it is dreadfully slow, borrowed a 2 blade hartzell and it was 14 knots quicker. The prop was given back and the plane dropped back to its original slower speed.

Now back to RV-10's. I have 4 of them at my disposal for data collection. In terms of weight and A/C systems , one of the 2 blades has the same a/c and similar weight as the 3 blade Hartzell machine. So as close as you can get as apples to apples. Same builder too. The other two are 2 blade and similar in spec except one is a fraction lighter.

To a knot in terms of TAS and litre in terms of fuel flow, thats 1/4Gallon close, the 2 blades ( all three aircraft) are all the same speed. Data and side by side testing.

As I said previously if I remember and can be bothered I will get back here with some real data.

And by the way this is on verified static (minimal error on GPS box) and correct OAT, as the TAS is OAT dependent.

If the MT 3 blade for the RV10 is knot for knot, everyone wanting 3 blades should go that way.

Can you detail the pro's and cons of that MT Vs the others? It might be beneficial for everyone in the shopping mode.
 
Respectfully, what is the explanation for those that have performed an actual change from a 2-blade constant speed to a 3-blade constant speed on the same plane and only report 2-3 knots degradation? Is everyone fooling themselves, too prideful to admit the truth, or wishing it to be different?



Vic,

You can say it until you are blue in the face, but the data does not stack up in your favour. The OP asked about a hartzell 3 blade did he not?

You claim no difference with an MT......I am not even going to comment on what that might be as i have never flown one on a -10. But I can tell you that the stretched RV8 down here has a MT 3 blade and it is dreadfully slow, borrowed a 2 blade hartzell and it was 14 knots quicker. The prop was given back and the plane dropped back to its original slower speed.

Now back to RV-10's. I have 4 of them at my disposal for data collection. In terms of weight and A/C systems , one of the 2 blades has the same a/c and similar weight as the 3 blade Hartzell machine. So as close as you can get as apples to apples. Same builder too. The other two are 2 blade and similar in spec except one is a fraction lighter.

To a knot in terms of TAS and litre in terms of fuel flow, thats 1/4Gallon close, the 2 blades ( all three aircraft) are all the same speed. Data and side by side testing.

As I said previously if I remember and can be bothered I will get back here with some real data.

And by the way this is on verified static (minimal error on GPS box) and correct OAT, as the TAS is OAT dependent.

If the MT 3 blade for the RV10 is knot for knot, everyone wanting 3 blades should go that way.

Can you detail the pro's and cons of that MT Vs the others? It might be beneficial for everyone in the shopping mode.
 
Data point

"...But I can tell you that the stretched RV8 down here has a MT 3 blade and it is dreadfully slow, borrowed a 2 blade hartzell and it was 14 knots quicker..."

I would like to see some hard data on that one...14 knots is a bunch...and some quick napkin calculations do not support that much of a difference with everything else being held constant...

Is the 3 blade slower in cruise? The math says yes. How much slower is the issue. When the anecdotal evidence does not reflect the theoretical calculations, you have to ask why...
 
props

From Hartzell's website FAQ's. Highlighted for discussion.

"...
If 2-blade propellers are more efficient, then why don’t all propellers have 2 blades?

The short answer is because efficiency doesn’t propel the airplane, thrust does. The most efficient propeller blade count for a particular aircraft is a function of the aircraft mission and a number of other factors. These include the amount of engine power, operating RPM for the propeller, diameter limitations, aircraft performance requirements (high speed cruise, takeoff, loiter, etc), noise requirements, and others. Depending on the combination of these parameters a 2-blade propeller may be most efficient, but as power increases additional blades are generally required to efficiently utilize the increased power..."



"...How much faster will my airplane go with your prop?

Generally, it requires a large increase in propeller efficiency to produce a small increase in cruise speed on an aircraft. If the propeller was well matched to the engine and airplane performance on the original installation, it may not be possible to increase the cruise speed by a significant amount. However, this is not always the case, and in some installations there have been measurable speed gains with Hartzell propellers. Check with the TC / STC holder to see if there has been any accurate performance tests conducted on your specific installation.."


So, on the RV-8 with a 14 kt difference, is it possible that the 3 blade prop was not properly matched to the application and the 2 blade was? That would explain the large difference.

Also note in the second paragraph the statement that about large increases in efficiency versus small changes in speed..and finally "some" applications result in "measurable" speed increases. "Measurable" implies a small increase...14 kts is a huge increase.

This is basically stating what the math proves. You need a larger increase in efficiency to effect a small change in speed. Therefore, you would need a MUCH larger increase in efficiency to effect a relatively large (14 kt) change in speed. Each company attempts to optimize their prop aerodynamics using the same physical laws. It is therefore unlikely that the difference in efficiencies between two properly matched props would be a very large number. Given that small number, a large difference in speed due to prop efficiency, is unlikely as well.

At the speeds we cruise at, a difference of around 5 kts would be reasonable. I am skeptical of a 14 kt increase... (due to prop efficiencies)

"If it sounds too good to be true, it probably is"
 
At the speeds we cruise at, a difference of around 5 kts would be reasonable. I am skeptical of a 14 kt increase... (due to prop efficiencies)

"If it sounds too good to be true, it probably is"

I saw this from a company doing Cirrus props. Most of the gains can be attributed to the MT being 37 lb's lighter than the 3 blade aluminum Hart. It's a pretty close comparison on both 3 blades. Cirrus only puts 3 blade props on their planes. Maybe they know something...

http://www.midwestaircraftrefinishing.com/blog/?p=41
Also:
https://www.mt-propeller.com/en/entw/stcs/cirrus_3.htm

All I really want is to NOT lose anything. I don't care if I gain over the numbers. Van's numbers suite me just fine!
 
I think...

I think, realistically, around 5 kts loss in cruise would be reasonable; the math supports that for the 3 blade versus two blade.

That said, if you read the boards, most people are flying around at 155-160 LOP and accepting the minimal leg time difference in exchange for the fuel economy. This really makes the couple knot difference in maximum speed a moot point, as you aren't operating there anyway...
 
"...But I can tell you that the stretched RV8 down here has a MT 3 blade and it is dreadfully slow, borrowed a 2 blade hartzell and it was 14 knots quicker..."

I would like to see some hard data on that one...14 knots is a bunch...and some quick napkin calculations do not support that much of a difference with everything else being held constant...

Is the 3 blade slower in cruise? The math says yes. How much slower is the issue. When the anecdotal evidence does not reflect the theoretical calculations, you have to ask why...


Bob,

I do not have the data now. This was almost a year ago. It was sent back to MT, they said nothing was wrong with it. I assume you understand the expense and seriousness of sending a 3 blade prop from Australia back to MT and return. This was not just on a whim, funny enough it was a bit better when it returned, despite denials. But not massive amounts.

But lets not get distracted with that as a odd machine in the fleet.

Today we get the replacement battery from Earth X after the original gave up playing nice, so I will soon have some RV10 data on this new one with the 3 blade. Before I commit to numbers here I want to be sure the static and OAT are pretty darn close to accurate. Many folk do not realise how much error you can create with these two being off the mark.

All the best :)

PS, appropriately LOP, the RV10 with the two blade will TAS at 164KTAS +/- 1-2 knots. Get up in the FL130 range and that drops a bit, in the 155-160 range.
 
Respectfully, what is the explanation for those that have performed an actual change from a 2-blade constant speed to a 3-blade constant speed on the same plane and only report 2-3 knots degradation? Is everyone fooling themselves, too prideful to admit the truth, or wishing it to be different?

Rob, that is a very reasonable question to ask.

I suspect you are onto part of it. Now some props play better than others. So for example we had one experience with a MT 3 blade on a -10 reporting only a small loss. Assuming this is all valid data, and the poster seems confident it is, then great. That might be the pick of the bunch.

The hartzell 3 blade we have here at present is yet to be confirmed but on initial observations, it would appear twice that amount. I will know more later this week.

It is important to remember that unless the instruments (which are normally very accurate) are fed with valid data (static and OAT) you can have errors that are huge.

I had this experience recently with a Lancair IV. It would TAS 12-13 knots faster than reality, and the static error was only 2-3 knots of that, the rest was OAT. I am acutely aware of these things and even I was fooled by my own complacency in trusting the data.

As the great man Ronald Reagan would say.......Trust, but verify!
 
Just another point of interest in this discussion about numbers of blades- the Phantom biplane racer at Reno gained over 30mph going to a 4 blade Paul Lipps design compared to the original 2 blade. Absolutely huge.

This shows that with proper design, more blades does not always have to be slower.

I submit that some of the 3 blade props available for RVs could be improved upon.
 
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