Van's RV-8A "Tweety" Performance

Bill Palmer · May 10, 2006

RV-8A Builders/Owners/Pilots,

Last Thursday, after I read the May 2006 Sport Aviation article "Reciprocals Rotaries Nose to Nose" by Van's Ken Scott, I e-mailed Van's regarding the apparent poor performance (relatively speaking) of Van's 200hp RV-8A "Tweety." I questioned "Tweety's" inability to approach Van's published performance specifications and, particularly, "Tweety's" inferior performance in a one-on-one fly-off with "Dilbert," a 180hp(+), FADEC-engined RV-8. Today, I was pleased to receive a response from Ken Krueger, Van's Aircraft Engineer, as follows:

"Bill, you are not making correct comparisons between numbers."

"When Van's quotes a number for 75% cruise, it is for operation at wide-open throttle at 2700RPM at 8000 ft Density Altitude. We ran the side-by-side cruise tests at 8000 ft Pressure Altitude but the temperature was warmer than standard. Also, we ran at 2500 RPM as opposed to 2700 RPM as in our 75% cruise scenario. Finally, the side-by-side ground speeds do not account for the effects of wind. The GPS ground speed was strictly for comparing different aircraft flying under the same atmospheric conditions."

"When Van's quotes a number for rate of climb, it is for operation at wide-open throttle at 2700 RPM at Sea Level density altitude. We timed the side-by-side climb test from brake release to 8000 ft. This means that your calculated rate of climb to 8000 ft includes time for take-off and acceleration to best rate of climb speed. Also, your calculated rate of climb is an average climb rate which reflects the fact that climb rate diminishes with density altitude. Finally, we ran the side-by-side climb tests at 2500 RPM as opposed to 2700 RPM as in our "quoted" max rate of climb scenario."

"The engine in "Tweety" has a lot of hours on it and it is definitely not putting-out rated horsepower. The engine in "Dilbert" is FADEC-equipped and, if anything, is putting out more than rated horsepower. Also, the prop on Dilbert is one of Hartzell's "Blended Airfoil" propellers which is very efficient indeed."

"I think that what you are seeing in "Dilbert" is an aircraft that performs better than our published numbers. What you are seeing with "Tweety" is an aircraft that, when new, performed up to our published numbers. The numbers you derive from the side-by-side fly-off are NOT valid for comparison to Van's published numbers for the reasons I have outlined in the previous paragraphs of this response."

"Ken Krueger, Engineer, Van's Aircraft"

My personal "take-aways" from Ken's response is that I'm definitely equipping my 200hp, angle-valve engine with electronic ignition on at least one set of plugs, building as light as I can, and installing a blended-airfoil, constant-speed Hartzell propeller if, or when, the propeller is approved for angle-valve engines. I wish I was already flying so I could challenge "Dilbert" to a duel, but I'm still many months away from first flight. Is there anyone on the list who has a strong, light 200hp RV-8A to challenge "Dilbert" now?!

Best Regards,

Bill

CraigC · May 10, 2006

Tweety numbers

He says that operation in cruise is at 75% at wide open throttle? What? A lot of what he said if said verbatim is not right.

mdredmond · May 10, 2006

If I did my quick math right, full throttle at 8000' should yield about 75% power in a normally aspirated engine.

22" / 30" = .733 = 73.3%

Surely I could be wrong.

That begs a question. I know virtually nothing about c/s props and high-performance engines.

When Van's refers to 55% or 75% power, are they referring to a percentage of sea-level power (as I assumed above) or are they talking about a percentage of available (considering density altitude) power?

Ironflight · May 10, 2006

When people talk about 75% power, they generally mean 75% of rated, sea level HP....

Paul

mdredmond · May 10, 2006

Thanks, Paul. So a normally-aspirated engine puts out 75ish% of rated power at 8000' if firewalled, but burns less gas because we've leaned it.

That makes sense.

-matt

rv72004 · May 11, 2006

If you lean past peak HP you also produce less power. MP and RPM alone do not account for %HP . Mixture plays a big part as well.

Ironflight · May 11, 2006

mdredmond said:
So a normally-aspirated engine puts out 75ish% of rated power at 8000' if firewalled, but burns less gas because we've leaned it.

-matt

Well, partly right...fuel burn (assuming you have leaned to perfection, however you define that) is proportional to power output. If you are putting out less then 100% power, then you'll burn less fuel. It's not burning less fuel at altitude because you leaned it, it's burning less fuel at altitude because it is producing less power. If you turbo-charged it to put out 100% at altitude, it would burn more fuel - even leaned to "best power" or "best economy".

My favorite chart in the Lycoming Operators manual is the single line that plots minimum fuel flow for percent power. If you have a percent power meter in your plane, and you lean by EGT, you'll end up very close to this line when you check your fuel flow.

Paul

Chickenlips · May 11, 2006

The only contribution I can make to this thread is a very simple thing I use all the time to estimate the % power my engine is running... so simple, that I can do it and still fly the plane.

If you want to know (roughly) how much power your engine is producing then you simply add the manifold pressure in inches to the rpm in 100's and if the total is 48, then you are at 75% of rated power output. This works for the small Lycoming engines.

EXAMPLE:

If your manifold pressure is 23" and your RPM is 2500 then:

23+25=48 and you have 75% power being produced.

Additionally, for every difference of 3 in the total you get a difference of 10% power:

EXAMPLE:

If your manifold pressure remains at 23 but you reduce RPM to 2200 then:

23+22=45 and you have then 65% power being produced.

EXAMPLE:

If you reduce manifold pressure to 20 and leave RPM at 2500 then:

20+25=45 and you again have 65% power being produced.

Admittedly this probably only works for the 65-85% range but it is so simple and so close to the graphs from Lycoming that it quite useful.

Kevin Horton · May 11, 2006

Chickenlips said:
The only contribution I can make to this thread is a very simple thing I use all the time to estimate the % power my engine is running... so simple, that I can do it and still fly the plane.

If you want to know (roughly) how much power your engine is producing then you simply add the manifold pressure in inches to the rpm in 100's and if the total is 48, then you are at 75% of rated power output. This works for the small Lycoming engines.

This is wonderfully simple, but it only works in a very narrow range of conditions. For one thing, it does not account for altitude. For example, with an IO-360-A, 2500 rpm and 23" = 69% at sea level and 74% at 5000 ft (all these should be 75% according to your rule).

2500 rpm and 20" = 57% at sea level, 62% at 5000 ft, and 65% at 8000 ft (all these should be 65% according to your rule).

2300 rpm and 19" = 48% at sea level, 52% at 5000 ft and 56% at 10,000 ft (all these should be 55% according to your rule).

If the temperature is 20 deg F warmer than standard, you can subtract 2 - 3% from the above percent powers.

My conclusion is that this rule of thumb might be within 5% if you are at full throttle, and the temperature is close to standard, but it may have significant errors if you are less than full throttle, or if the temperature is much different than standard.

N674P · May 11, 2006

This thread reminds me of something I've often wondered - does someone make a Percent Horsepower gauge? Or is this a figure an EFIS can display?

Ironflight · May 11, 2006

Efis...

N674P said:
This thread reminds me of something I've often wondered - does someone make a Percent Horsepower gauge? Or is this a figure an EFIS can display?

The GRT EFIS displays it - it's not a hard computation to do, so I suppose most EFIS system's with integrated engne monitoring can do it - but I don't know for sure about any but GRT.

Paul

Kevin Horton · May 11, 2006

Ironflight said:
The GRT EFIS displays it - it's not a hard computation to do, so I suppose most EFIS system's with integrated engne monitoring can do it - but I don't know for sure about any but GRT.

It is easy to display a power number. The hard part is displaying the right number.

Paul - Do you have any idea how accurate the GRT EFIS power display is? Have you compared it against the Lycoming power charts?

1. Does it have different curves for different engine models? The power curves for the parallel valve engines differ from the angle valve engines. And there are small variations between the curves even within an engine family (i.e the family of parallel valve engines, or the family of angle valve engines).

2. Does it account for non-standard temperatures?

3. Does it account for mixture setting, or does it assume the mixture is set for best power?

chrispratt · May 11, 2006

Paul:

I'm impressed. There's actually someone who can read a Lycoming chart. The ones in my manual look like they've been photocopied and reduced so many times it's hard to tell what's on them. They may even date back to the days of carbon paper.

And of course for my engine, O-360-A1A, the charts are also very dark so you really can't tell what they say. Makes me appreciate the job the airframe manufacturers do in presenting nice clear charts.

Chris

Ironflight · May 11, 2006

Kevin,

In checking the numbers I got during flight testing, the EFIS-computed %power was always within a percent of what I could get from the tables in post-flight data reduction - which, to be honest, is probably as accurate as you can get with the sensors involved. Let's be honest - we are not using multi-thousand-dollar, lab-calibrated MAP, pressure, and temperature sensors in these airplanes. Or at least I'm not! When you consider the potential sensor error, I'd be happy to see numbers within a couple percent.

As to specific engines - yes! There is a process that the manual takes you through to build data points from the engine manufacturer's tables (and Chris - it helps to have some young engineering students with good eyes who blow the tables up on a copier to get the data!!), and then feed those numbers into the EFIS. I suspect it is is a curve-fit type solution, not just a linear calibration curve. Of course, if you call Sandy up at GRT, she has already figured out the right numbers for most popular engine models, and she'll give them to you so that you don't have to strain your eyes!

Temperature calibration? Well, temperatureappears to be part of the solution, but wait a couple of months till we get to the steamy part of summer here in texas, and I'll be able to tell you if the EFIS still matches the ook. Most of my testing was done durign the winter, which (down here) closely matches the standard atmosphere.

None of the data systems and sensor components are calibrated to standards that I would use to drive variable-stability control laws during an atmoshperice re-entry, or decelerating flight from the hypersonic down through landing....but that's not what I'm trying to do in the RV! I'd say that the numbers I see are at least as accurate as what most folks can read from those Lycoming tables !

Paul

Ironflight · May 11, 2006

chrispratt said:
Paul:

And of course for my engine, O-360-A1A, the charts are also very dark so you really can't tell what they say.

Chris

I've got the same engine Chris, except mine was made my Mattituck with ECI parts, and has a "TMX" serial number. Surprisingly enough, however, the Operator's Manual they gave me still says "Textron Lycoming" on every page...

Fortunately, mne sems to be a pretty good original - Figure 3-35 is actually legible!

Paul

jcoloccia · May 11, 2006

Ironflight said:
I've got the same engine Chris, except mine was made my Mattituck with ECI parts, and has a "TMX" serial number. Surprisingly enough, however, the Operator's Manual they gave me still says "Textron Lycoming" on every page...

Fortunately, mne sems to be a pretty good original - Figure 3-35 is actually legible!

Paul

I'm kinda' curious, Paul. What made you decide on an O-360 vs. an IO-360? It's a relatively small price differential (less than $500 difference) so I'm thinking that something else drove the decision.

Ironflight · May 11, 2006

jcoloccia said:
I'm kinda' curious, Paul. What made you decide on an O-360 vs. an IO-360? It's a relatively small price differential (less than $500 difference) so I'm thinking that something else drove the decision.

John,

In a word - simplicity! In a few more - it met my requirements.

My short answer when asked that at the airport is "I can fix a carburator in a cornfield if I have to!" I just have no experience with injection (except listening to people talk about all the tuning and troubleshooting they did to get theirs going!)

While I can fly negative-G aerobatics, I really don't enjoy them - positive-G sport Acro is pretty much what I like! So I didn't need to add Injection for that (along with inverted oil, high pressure fuel pumps, return lines, sniffle-valves, etc...). Add to that the fact that I've worked on carburated airplanes most of my life, so building and fixing the thing was a lot easier for me. Talking with numerous folks who'd "been there, done that" during the early days of my project, it became apparent to me that I simply didn't need the additional 20 horsepower bad enough to add the rest of the complexity. I did my firewall-forward install (less baffles) in about a week - I just know my way around that kind of stuff well enough. Injection would have taken me a lot longer, with more to learn.

I'm certainly not going to tell anyone that chooses the "IO" that they made a bad choice - because everyone's requirements and consequential choices are different. Mine pointed to the Carbed 180, and I am really happy with it!

Paul

jcoloccia · May 11, 2006

Thanks for the reply. You echo many of the thoughts that have been going through my head lately. I'm getting ready to order a fuselage and ideally I'd like to order the finish kit at the same time so choice of engine is starting to get me thinking. My current feeling is that I will build my tanks with flop tubes and a return (since it would be a HUGE pain to retrofit), but I'm WAY undecided on engine. I share your sentiments with the simplicity of the carb setup, however I do like hanging upside down from time to time, and maneuvers like Hammerheads can get pretty exciting (read MESSY) without inverted oil.

My current thinking has me leaning towards simplicity: efis, minimal IFR support, carb on the engine. Get it done fast, quick, and reliable. That will free up time for the next project: the Pitts

pierre smith · May 12, 2006

Carbed too

Hi John,
We think alike as well. Our 0-360 with a homegrown overhaul and factory overhauled carb sure is sweet! We have a late model 6A QB with the tall tail and at 8000' and 2650 RPM, we consistently see 200 MPH. Hard to beat for rapid simplicity. If had it to do over again, I'd still have at least 180 HP but maybe a new roll your-own 360 built under supervision at their factory.

Kevin Horton · May 12, 2006

Ironflight said:
As to specific engines - yes! There is a process that the manual takes you through to build data points from the engine manufacturer's tables (and Chris - it helps to have some young engineering students with good eyes who blow the tables up on a copier to get the data!!), and then feed those numbers into the EFIS. I suspect it is is a curve-fit type solution, not just a linear calibration curve. Of course, if you call Sandy up at GRT, she has already figured out the right numbers for most popular engine models, and she'll give them to you so that you don't have to strain your eyes!

Interesting. Do they have you pick off power values for specific conditions, or do they want the end points of the various lines on the graphs?

I'm down in Brazil right now, and have spent my spare time on the last two days hacking together some Python code that calculates power for the IO-360-A series engines. The code replicates the method used by the Lycoming power charts. I'll use it to automatically calculate the power for each of the time slices in my recorded flight test data.

Ironflight · May 12, 2006

Kevin Horton said:
Interesting. Do they have you pick off power values for specific conditions, or do they want the end points of the various lines on the graphs?

QUOTE]

It picks off intermediate points from the lines Kevin, not just the end points. I'd really love to see what you come up with when you're done, because I'm sure it would help with data reduction from our GRT Decode files as well. Knowing your background, I bet your method will be pretty accurate!

Paul

Kevin Horton · May 13, 2006

Python power script for IO-360-A

Ironflight said:
I'd really love to see what you come up with when you're done, because I'm sure it would help with data reduction from our GRT Decode files as well. Knowing your background, I bet your method will be pretty accurate!

I've put my IO-360-A power python script in the Downloads section of my site. It replicates the Lycoming power chart as closely as I can make it. I've validated it against my IO-360-A spreadsheet, which was validated against the Lycoming power chart, plus various POHs from aircraft with these engines. It isn't perfect, but it is as good as I can make it in a reasonable time frame.

It has three functions:

1. calculate power from rpm, MP, altitude and temperature,

2. calculate the MP required for a desired power, given the power, rpm, altitude and temperature, and

3. calculate the rpm required for desired power, given the power, MP, altitude and temperature.

The first function could be useful in data reduction. I intend to use it to automatically insert a column of engine power in my flight test data.

The last two functions could be useful to produce power tables.

The zip archive also includes standard atmosphere calculation, and unit conversion scripts that I wrote to support the power calculation script. I'm a python neophyte, so I haven't yet figured out how to write a setup.py script to automatically install them, but they work from wherever they are put on your hard drive. There are probably bugs, so please let me know if anyone finds one.

I've got a similar script for the O-360-A and -C series engines, but I haven't properly validated its outputs yet. If anyone wants it, I'll send it to them.

zkvii · May 13, 2006

GRTDecode options / Power output

Hi

I'm lurking ;-). A few questions,

Does the logic / math work for all lycomming or is it specific IO-360 (180hp) - excepting the lookup tables will vary?
Does the prinicple work for non lycomming engines?
Do people want the just the pwr value in the XML GRTDecode output?
Is it easier to do this inside excel later?

Kevin: Looks good to me, my understanding of the code is to:
normalise the input to std units
get sea level power (table look up)
correct pwr for the actual vs std day temps

If Kevin is OK with me copying the logic and the want it there I could add this fairly easily.

Regards,

Carl

Ironflight · May 13, 2006

I'd love to see you add it Carl, if Kevin approves...I unfortunately don't speak Python!

Paul

Kevin Horton · May 14, 2006

OK to use for any purpose

zkvii said:
Does the logic / math work for all lycomming or is it specific IO-360 (180hp) - excepting the lookup tables will vary?
Does the prinicple work for non lycomming engines?
Do people want the just the pwr value in the XML GRTDecode output?
Is it easier to do this inside excel later?

Kevin: Looks good to me, my understanding of the code is to:
normalise the input to std units
get sea level power (table look up)
correct pwr for the actual vs std day temps

If Kevin is OK with me copying the logic and the want it there I could add this fairly easily.

The logic and math would work for any engine, if the manufacturer has provided power charts in the standard format. The values in the lookup tables are specific to each model engine.

The code normalizes the inputs to standard units. Then it finds the power for the actual rpm and manifold pressure at sea level standard conditions. Then it finds the altitude required to get the actual MP at full throttle, and the power under this condition. If this differs from the actual altitude (which it almost always does), then it interpolates between the full throttle altitude and sea level to get the power. This interpolation is done using density ratios. Finally, the power is corrected for non-standard temperature.

This is the exact same method that the Lycoming power charts use, so the accuracy is only limited by how accurately I could pick the values off the power charts. Of course, it is only accurate with mixture set for best power, and it cannot account for engine-to-engine variations.

I have no problem with people using this code for any purpose. I have updated the files to add a copyright statement, with a BSD style license. This allows the scripts to be used as-is, or in modified form, for any purpose.

osxuser · May 14, 2006

Is this for the IO-360A series (angle valve) or the O-360A series (parallel valve)?

The IO-360B series is Parallel valve as is the M series. The O-360's are all parallel valve.

Kevin Horton · May 14, 2006

O-360-A power script now available

osxuser said:
Is this for the IO-360A series (angle valve) or the O-360A series (parallel valve)?

The IO-360B series is Parallel valve as is the M series. The O-360's are all parallel valve.

I see that I screwed up the description on my site, so I understand the confusion.

The script that I posted yesterday is for the 200 hp angle-valve IO-360-A series engines. I just finished checking the script for the 180 hp parallel-valve O-360-A series engines, and it is now available on my site.

200 hp angle-valve IO-360-A power script
180 hp parallel-valve O-360-A power script

The scripts allow many useful things to be done, including creating custom power charts. For example, the following python code creates a power chart similar to the O-360-A power chart on the VAF Home Wing site:

Code:

#! /usr/bin/env python

import o360a as O
import std_atm as SA

# column widths
col1 = 8
col2 = 6
cols = 6
full_width = col1 + col2 + 12 * cols + 15

diff = 0.75 # amount the MP must be less than the atmospheric pressure.  
            # otherwise it is assumed that full throttle is reached.

print '-' * full_width

piece = []
piece.append('Press.'.center(col1))
piece.append('Std.'.center(col2))
piece.append('100 HP -- 55% Rated'.center(cols * 4 + 3))
piece.append('117 HP -- 65% Rated'.center(cols * 4 + 3))
piece.append('135 HP -- 75% Rated'.center(cols * 4 + 3))
full_line = '|'.join(piece)
print '|' + full_line + '|'

piece = []
piece.append('Alt.'.center(col1))
piece.append('Alt.'.center(col2))
piece.append('Approx. Fuel 7.8 Gal/Hr'.center(cols * 4 + 3))
piece.append('Approx. Fuel 9 Gal/Hr.'.center(cols * 4 + 3))
piece.append('Approx. Fuel 10.6 Gal/Hr'.center(cols * 4 + 3))
full_line = '|'.join(piece)
print '|' + full_line + '|'

piece = []
piece.append('1000'.center(col1))
piece.append('Temp.'.center(col2))
piece.append(' '.center(cols * 4 + 3))
piece.append(' '.center(cols * 4 + 3))
piece.append(' '.center(cols * 4 + 3))
full_line = '|'.join(piece)
print '|' + full_line + '|'

piece = []
piece.append('Feet'.center(col1))
piece.append('deg F'.center(col2))
piece.append('RPM & Man. Press.'.center(cols * 4 + 3))
piece.append('RPM & Man. Press.'.center(cols * 4 + 3))
piece.append('RPM & Man. Press.'.center(cols * 4 + 3))
full_line = '|'.join(piece)
print '|' + full_line + '|'

print '-' * full_width

piece = []
piece.append(' '.center(col1))
piece.append(' '.center(col2))
piece.append('2100'.center(cols))
piece.append('2200'.center(cols))
piece.append('2300'.center(cols))
piece.append('2400'.center(cols))
piece.append('2100'.center(cols))
piece.append('2200'.center(cols))
piece.append('2300'.center(cols))
piece.append('2400'.center(cols))
piece.append('2100'.center(cols))
piece.append('2200'.center(cols))
piece.append('2300'.center(cols))
piece.append('2400'.center(cols))
full_line = '|'.join(piece)
print '|' + full_line + '|'


for alt in range(0, 16000, 1000):
	piece = []
	piece.append(str(alt).rjust(col1))
	temp = SA.alt2temp(alt, temp_units = 'F')
	temp = int(temp)
	piece.append(str(temp).rjust(col2))
	press = SA.alt2press(alt)

	pwr = .55 * 180
	for rpm in range(2100, 2500, 100):
		mp = O.pwr2mp(pwr, rpm, alt)
		if press - mp < diff:
			piece.append('FT'.center(col2))
		else:
			piece.append(str(round(mp,1)).center(col2))
		
	pwr = .65 * 180
	for rpm in range(2100, 2500, 100):
		mp = O.pwr2mp(pwr, rpm, alt)
		if press - mp < diff:
			piece.append('FT'.center(col2))
		else:
			piece.append(str(round(mp,1)).center(col2))
		
	pwr = .75 * 180
	for rpm in range(2100, 2500, 100):
		mp = O.pwr2mp(pwr, rpm, alt)
		if press - mp < diff:
			piece.append('FT'.center(col2))
		else:
			piece.append(str(round(mp,1)).center(col2))
	
	full_line = '|'.join(piece)
	print '|' + full_line + '|'

print '-' * full_width

This produces an output like:

Code:

-----------------------------------------------------------------------------------------------------
| Press. | Std. |    100 HP -- 55% Rated    |    117 HP -- 65% Rated    |    135 HP -- 75% Rated    |
|  Alt.  | Alt. |  Approx. Fuel 7.8 Gal/Hr  |   Approx. Fuel 9 Gal/Hr.  |  Approx. Fuel 10.6 Gal/Hr |
|  1000  |Temp. |                           |                           |                           |
|  Feet  |deg F |     RPM & Man. Press.     |     RPM & Man. Press.     |     RPM & Man. Press.     |
-----------------------------------------------------------------------------------------------------
|        |      | 2100 | 2200 | 2300 | 2400 | 2100 | 2200 | 2300 | 2400 | 2100 | 2200 | 2300 | 2400 |
|       0|    59| 21.0 | 20.3 | 19.8 | 19.3 | 23.5 | 22.7 | 22.1 | 21.6 | 26.1 | 25.1 | 24.5 | 23.9 |
|    1000|    55| 20.7 | 20.0 | 19.5 | 19.0 | 23.3 | 22.4 | 21.8 | 21.3 | 25.8 | 24.8 | 24.2 | 23.6 |
|    2000|    51| 20.4 | 19.7 | 19.2 | 18.8 | 23.0 | 22.1 | 21.6 | 21.1 | 25.5 | 24.5 | 23.9 | 23.3 |
|    3000|    48| 20.2 | 19.4 | 19.0 | 18.5 | 22.7 | 21.8 | 21.3 | 20.8 | 25.2 | 24.2 | 23.6 | 23.1 |
|    4000|    44| 19.9 | 19.2 | 18.7 | 18.3 | 22.4 | 21.5 | 21.0 | 20.5 | 24.9 | 23.9 | 23.3 | 22.8 |
|    5000|    41| 19.7 | 18.9 | 18.5 | 18.0 | 22.1 | 21.3 | 20.8 | 20.3 |  FT  | 23.6 | 23.1 | 22.5 |
|    6000|    37| 19.4 | 18.7 | 18.2 | 17.8 | 21.9 | 21.0 | 20.5 | 20.0 |  FT  |  FT  | 22.8 | 22.3 |
|    7000|    34| 19.1 | 18.4 | 18.0 | 17.6 | 21.6 | 20.8 | 20.3 | 19.8 |  FT  |  FT  |  FT  | 22.0 |
|    8000|    30| 18.9 | 18.2 | 17.8 | 17.4 | 21.4 | 20.5 | 20.0 | 19.6 |  FT  |  FT  |  FT  |  FT  |
|    9000|    26| 18.7 | 18.0 | 17.6 | 17.2 |  FT  | 20.3 | 19.8 | 19.3 |  FT  |  FT  |  FT  |  FT  |
|   10000|    23| 18.5 | 17.8 | 17.3 | 17.0 |  FT  |  FT  | 19.6 | 19.1 |  FT  |  FT  |  FT  |  FT  |
|   11000|    19| 18.3 | 17.6 | 17.1 | 16.7 |  FT  |  FT  |  FT  | 18.9 |  FT  |  FT  |  FT  |  FT  |
|   12000|    16| 18.0 | 17.3 | 17.0 | 16.6 |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |
|   13000|    12|  FT  | 17.2 | 16.7 | 16.4 |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |
|   14000|     9|  FT  |  FT  | 16.6 | 16.2 |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |
|   15000|     5|  FT  |  FT  |  FT  | 16.0 |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |  FT  |
-----------------------------------------------------------------------------------------------------

gmcjetpilot · May 15, 2006

BA Hartzell for IO360 available

Bill Palmer said:
My personal "take-aways" from Ken's response is that I'm definitely equipping my 200hp, angle-valve engine with electronic ignition on at least one set of plugs, building as light as I can, and installing a blended-airfoil, constant-speed Hartzell propeller if, or when, the propeller is approved for angle-valve engines. Best Regards, Bill

I just talked to Hartzell last week,

The BA HARTZELL PROP IS Available for the IO360(200HP) angle valve.

It is not shown in Van's catalog or web site but it came out a month or so ago. It is available. Call to get price.

N674P said:
This thread reminds me of something I've often wondered - does someone make a Percent Horsepower gauge? Or is this a figure an EFIS can display?

They all derive an approximate HP not actual HP from MAP/RPM/DENSITY ALT. For us with manual mixture we are as concerned with not wasting gas so FF and EGT are important parameters. Approx HP is good enough, but one sure way to know HP is know RPM and Torque. Torque is a little tricky to measure on a airplane, but torque is a common feature on turboprops.

Cheers George

PS: I have a O360 and it is simple and you need to add the $600-$800 more for the installation cost, mostly for the more expensive fuel pumps.

Bill Palmer · May 15, 2006

Hartzell Prop Info

Thanks, George

After I posted my original message, Ken Krueger let me know that Hartzell had indeed approved the new blended airfoil propeller, F7497. As a result, I contacted Hartzell to see if modifications planned for my Lycoming IO-360-C1D6 (200hp, angle-valve, counter-weighted crank) would violate any placards, or incur any restrictions, with respect to Hartzell's new F7497 blended-airfoil propeller. Specifically, my planned modifications are: (1) Dual Lightspeed ignition (no magnetos), GAMI injectors, and "A" forward-facing sump. Here is the answer I just received from Hartzell's Product Support:

"Although we have not tested the Lightspeed on the 200 HP counterweighted crank engine with the 7497 blade design, previous testing of similar combinations has shown minimal effect on propeller stress. Also, the GAMI injectors and the sump/injector setup will not have a significant effect on prop stress."

"If you are using the standard cowling, you will need an HC-C2YR-1BFP/F7497, there are no placards and the diameter range is 74" - 72"."

"If you are using an extended cowl, such as the James "Holy Cowl" you will need an extended hub, such as the HC-(F or M)2YR-1BFP/F7497."

Thanks Again - - I hope all the great info on this thread (performance specification clarification, Kevin's power scripts/info, new Hartzell prop, etc.) have been of interest and benefit to everyone.

Bill

Mel · May 15, 2006

One other thing might be worth checking into. Correct me if I'm wrong, but I seem to remember that the "extended hub" Hartzell is not approved for aerobatics.

fodrv7 · May 15, 2006

GRT % Power

Kevin,
I fed information (Derived from your spreadsheet) into my GRT EFIS for % Power and on a short flight yeterday, found that it was under reading about 5% from your figures at a given Altitude.
I suspect that it is taking Temperature into account and so I need to compaare the figures for Density Altitude, not Pressure Altitude.

I am flying Melbourne Brisbane today, >700nm, so I will have a closer look and report further when I return.
Pete.

Kevin Horton · May 15, 2006

fodrv7 said:
Kevin,
I fed information (Derived from your spreadsheet) into my GRT EFIS for % Power and on a short flight yeterday, found that it was under reading about 5% from your figures at a given Altitude.
I suspect that it is taking Temperature into account and so I need to compaare the figures for Density Altitude, not Pressure Altitude.

Using density altitude instead of pressure altitude won't help. It actually will make things less accurate.

For a given rpm and MP, the power increases with altitude (due to lower exhaust back pressure, I think). For a given rpm, MP and altitude, the power decreases with temperature (less air density with the warmer air).

If you look at the warm temperature, and calculate a density altitude, and use that instead of the pressure altitude, the calculated power will increase (due to the higher altitude for the same rpm and MP).

E.g., the following calculations are for an IO-360-A series engine. Let's imagine that the rpm and MP are 2500 and 20" HG, and you are at 5,000 ft, and the temperature is 15 deg C (std temp would be 5.1 deg C). All the following powers are for mixture for best power.

The correct power for those conditions would be 121.6 hp (60.8% power).

If you use the same rpm, MP and altitude, but use std temperature, you get 123.8 hp (61.9% power).

The density altitude was 6150 ft. If you calculate the power for 2500 rpm, 20" HG, and 6150 ft at std temperature, you get 125.8 hp (62.9% power). This is even worse than ignoring the effect of temperature.

Note: the power script files I created include a standard atmosphere calculation script (std_atm.py). This script has a number of useful functions, including the calculation of density altitude, accounting for pressure altitude and temperature, or indicated altitude, altimeter setting and temperature.

A better approach is to record the OAT, and enter that into the spreadsheet. It will then correct for the warm temperature.

Kevin Horton · May 16, 2006

Updated script

I uploaded a new version of the IO-360-A power script . I fixed some errors in the examples (which would have caused failures if anyone ran "python io360a.py" - thanks to Alan Adamson for finding this), updated the readme.txt to better explain how to use the script and added new functions to work with percent power, rather than horsepower.

I will eventually make the same changes to the O-360-A script, but not tonight. Too tired.

gmcjetpilot · May 17, 2006

Yep 3.8 on the fun meter

Mel said:
One other thing might be worth checking into. Correct me if I'm wrong, but I seem to remember that the "extended hub" Hartzell is not approved for aerobatics.

Yep that's right Mel, the extend hub's are limited to 3.8 G's. From the stand point 3.8g's is not 6 g's, the prop is definitely not aerobatic. I am not recommending but just pointing out that most acro (if done properly) is 3g's or less. I know some guy's who do "gentle aerobatics" with their extended hartzell props. My "whifferdale loops" are only 3g's max. (My loop may look like an egg from the ground but they still are fun.) G

Jink3232 · Oct 18, 2015

IO-360B. 180hp

Has anyone used Ken's script to produce charts for a IO-360B (180hp) engine? If so, can I get a copy?

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