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  #1  
Old 09-06-2007, 08:22 AM
Kahuna's Avatar
Kahuna Kahuna is online now
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Default MT 3 blade vs Hartz. 2 blade performance

I finally got around to publishing my data on my head to head flight test of the MT 3 balde vs the Hartzell paddle blade 2 blade.
A lot of work went into the flight testing data captures and the resulting data and graphs. The nut of it is this. The 3 blade is smoother, but much slower. Enough so that I pulled it off. AND I was able to ge the 2 blade smoothness in line with the 3 balde. Thought you rockets guys might like this info.
Performance comparisons here
How I solved the 2 blade smoothness by clocking the prop

Best,

Last edited by Kahuna : 09-06-2007 at 08:22 AM. Reason: typo
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  #2  
Old 09-06-2007, 09:43 AM
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rv6ejguy rv6ejguy is offline
 
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Nice data. What do you Rocket guys have to say about this?
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Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW- 384.3 hrs. on the Hobbs, new ventral rad installed, new systems and mods, flight testing now
Twin Turbo Subaru EG33, Marcotte M-300, MT, RV10- Tail is on, stalled by life and work.
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  #3  
Old 09-06-2007, 09:46 AM
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Default 3 blade clocking??

So, I guess someone has to ask this, did you "clock" the MT to get the smoothness, or is it just a "bolt it on and go" fact of life that the MT will be naturaly smoother??

Thanks,
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  #4  
Old 09-06-2007, 12:11 PM
Tom Martin Tom Martin is online now
 
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As a rocket guy it is obvious from Mikes data that if both planes had the same prop then the F1 would be 10 knots faster :-)
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  #5  
Old 09-06-2007, 12:21 PM
Bill Dicus Bill Dicus is offline
 
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Default Prop vibes and performance

Kahuna: This is great data and obviously took a lot of effort. Thanks for that and for making it available to the rest of us. Bill
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  #6  
Old 09-06-2007, 12:51 PM
Steve Sampson Steve Sampson is offline
 
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Default 2 blade MT?

Did you ever think of trying a 2 blade MT? That should be faster and smoother. Steve.
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  #7  
Old 09-06-2007, 01:32 PM
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Kevin Horton Kevin Horton is offline
 
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Quote:
Originally Posted by Kahuna
I finally got around to publishing my data on my head to head flight test of the MT 3 balde vs the Hartzell paddle blade 2 blade.
A lot of work went into the flight testing data captures and the resulting data and graphs. The nut of it is this. The 3 blade is smoother, but much slower. Enough so that I pulled it off. AND I was able to ge the 2 blade smoothness in line with the 3 balde. Thought you rockets guys might like this info.
Performance comparisons here
Mike - that is very interesting data, and quite depressing for anyone who wanted to run that particular MT prop on a Rocket or Super RV. Thanks for sharing it with us. I appreciate the effort you have made to measure the performance of your aircraft.

Prop efficiencies vary with power and TAS (among other variables), so it isn't clear how applicable these results would be to MTs and Hartzell props that would be run on RVs, at power outputs produced by engines typically seen on RVs. But, it certainly suggests that Hartzells are probably a better bet than MTs, if level flight performance is considered important.

A few comments/questions:

"Ind TAS" - Your graphs are labelled "Ind TAS". What is that? I assume that it is a TAS indication on an EFIS, which while labelled TAS, would not be corrected for instrument error, static source position error and OAT error. This would certainly be a useful indication of performance changes, so I understand why you would record it and report it. It is much more practical to do a single run at each condition, and record the TAS indication on an EFIS system, than it is to do four legs at each condition. Only having one test point at each condition leads to a bit of error, as you can see from the waviness in the graphs. But the overall trend is quite clear, and that is what you are interested in here, rather than the exact performance at any one condition.

TAS vs average ground speed - Looking at the spreadsheets, it seems like you did a cross check by taking GPS ground speeds on the four cardinal headings, averaged the results and compared against the "Ind TAS". A lot of people like to average four GPS ground speed that way, and it certainly is simple, but there are a couple of errors that can bite you. First, the average of those four ground speeds will only equal the TAS is the wind is zero. The error is small if the wind is light, but the error can be several knots if the wind is strong.

I played around with a spreadsheet to look at the effect of wind on average ground speed on the four cardinal headings. The error introduced varies a bit with the wind direction, but you can make a rough correction for the effect of wind by taking the standard deviation of those four ground speeds, dividing it by the average ground speed. Then, subtract the following values from the average ground speed for a rough wind error correction:

std dev/.....error
ave GS
5%..........0.1%
10%..........0.4%
15%..........0.9%
20%..........1.6%
25%..........2.6%

For example, if the std deviation of the ground speeds is 15% of the average ground speed, the actual TAS would be about 0.9% less than the average of the four ground speeds.

Heading error - Also, small errors in the actual heading can have a significant effect. If your compass is out by a few degrees, or you don't accurately fly the cardinal headings, the average ground speed could vary by several knots. For example, for the condition where the std deviation of the ground speeds is 15% of the average ground speed, a 5 degree error on two of the legs would change the average ground speed by over 0.5%

NTPS Spreadsheet - If you are going to go to the trouble to fly four legs and record data, I strongly recommend you also record GPS track. Then you can use the NTPS spreadsheet to calculate TAS, and not be affected by winds or heading errors. Use the "Four legs" tab of that spreadsheet.
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  #8  
Old 09-06-2007, 02:36 PM
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I think the Hartzell is so superior in this test that any small potential errors in TAS are irrelevant. We are not talking a few knots here, we are talking lots of knots. In any case by taking so many readings, errors are likely to mainly cancel. Occam's razor Effect here.

I'll say again in flight testing, I use IAS at the same altitude and close OAT for comparisons. Way quicker and it avoids all the posts on how you came up with TAS figures from GPS or from glass, whiz wheel etc.

I personally prefer the side by side flight comparison method for true performance testing of modifications and welcome Kahuna's inclusion of that data here as well. This negates other variable such as humidity and hp output- something which can have significant effect and which is rarely measured.

Thanks for posting your real world results and impressions. Also interesting was your clocking trials. I've always wondered if I could get my package even smoother or if I'd be wasting my time.
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Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW- 384.3 hrs. on the Hobbs, new ventral rad installed, new systems and mods, flight testing now
Twin Turbo Subaru EG33, Marcotte M-300, MT, RV10- Tail is on, stalled by life and work.

Last edited by rv6ejguy : 09-06-2007 at 02:51 PM.
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  #9  
Old 09-06-2007, 02:51 PM
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Kevin Horton Kevin Horton is offline
 
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Quote:
Originally Posted by rv6ejguy
I think the Hartzell is so superior in this test that any small potential errors in TAS are irrelevant. We are not talking a few knots here, we are talking lots of knots. In any case by taking so many readings, errors are likely to mainly cancel. Occam's razor Effect here.
I agree 100%. I was not suggesting that the potential small errors in the data invalidated the conclusion. Those potential errors are probably on the order of one or two knots, which is much, much smaller than the difference that was observed between the two props.

Quote:
Originally Posted by rv6ejguy
I personally prefer the side by side flight comparison method for true performance testing of modifications and welcome Kahuna's inclusion of that data here as well. This negates other variable such as humidity and hp output- something which can have significant effect and which is rarely measured.
This is a good approach, if you have another closely comparable aircraft to test against, and no changes are made to the other aircraft. But, if one aircraft had a Lycoming, and the other had an alternative engine, it is possible that the two engines may have different variations of power with ambient conditions, which could possibly pollute the results.
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  #10  
Old 09-06-2007, 03:07 PM
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I'd bet if you were comparing the MT against the Hartzell with 8475D-4 paddle blades, or the new 8068 blended airfoil blades which are more efficient at Rocket speeds, there would be an even greater speed difference.

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