B&S 49-series (810cm3/49ci) for aircraft use - TiPi's Q&A thread

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Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
So what size shed is to small?
Getting off topic - should be moved to the small workshop thread but.................. it depends.

For this project it could be accomplished in something on the order of an 8ft square shed if one had room outside to run the engine.

My small shop has interior dimensions of about 9 x 17 ft. It is going to be tight but comfortable for the engine project. I have discovered-confirmed that the 2 foot extension I added to the new roof (overhang) will allow me to get the Quickie canard through the door. I've already started sketching ways to make the wings bolt on rather than glue on. I'll accept the increased weight of the added hard points to be able to resume building after the engine is running.

WonderousMountain

Well-Known Member
Once made an 8' by 8' A frame.
Thicis too small on account of
you are able to stand only in the
Middle, & it won't fit an 4' by 8'
Sheet on either side.

TiPi

Well-Known Member
Log Member
So what size shed is to small?
7x7m with a built-in room for: 2 ride-on mowers, 1 push mower, all the gear to maintain a 2.5 acre property, 1 aircraft in pieces, engine, flow bench, machinery etc. With the extensions it will be just big enough

TiPi

Well-Known Member
Log Member
Some good news
My wife has informed me that some strange men in a truck came to our place today and left a load of material behind. My shed extension is starting to take off. Now we just need some dry weather for a week to get the ground work and concrete done, not looking good for next week though.

blane.c

Well-Known Member
HBA Supporter
I've had to wait for dirt, usually framed some walls and set them aside or built roof trusses/cut rafters and set them aside etc. I mean you know what dimensions you are building to, so no biggie.

TiPi

Well-Known Member
Log Member
Update February 2021

Not much happening The weather hasn't been too kind and my builder is still waiting for the break to do the slab and then put the shed extension up.

I have done some calculations with regard to our new location and engine power/test club impact:
Previous test location: 72m msl, temps & pressure recorded during the last full power test were:
QFE: 1,010mbar, temp 20 deg C, humidity would have been in the 60-70% range
New location: 750m msl, 500km closer to the equator (latitude 17deg 20' S), QFE is between 920-930mbar, temps vary from 10 (winter) to 30 (summer), humidity is dry in winter and 80-99% in summer.

Below is a table of what I have worked out how the new location will affect engine power and test club resistance. My interpretation is that the loss in engine power is pretty much offset by the reduced drag of the test club, so the same rpm should be achieved with the same engine configuration? Or in other words, I should be able to compare any new test results directly with the previous test results, without having to adjust for standard atmospheric conditions?
These calculations are for dry air, humidity will knock off another couple of % from the engine power but not affect the test club. Information that I found indicate 3% power loss at 100% relative humidity at 25deg C. Keep in mind that the whole test procedure has probably a +/-5% error, if not more.

I would appreciate if someone could review my thinking and run these numbers through whatever program you have to validate my results.
Thank you.

Protech Racing

Well-Known Member
Cold , dense air makes more power and will spin the prop faster , due to the engine having compression of 9/1 while the prop operates in only slightly heavier air .

Vigilant1

Well-Known Member
I would appreciate if someone could review my thinking and run these numbers through whatever program you have to validate my results.
Sorry, I'm still working through your table, will give it a try,, I assume your power and air resistance change is relative to your original location at the same temperature?

These calculations are for dry air, humidity will knock off another couple of % from the engine power but not affect the test club.
Not so sure about that, though the effect will be minor. As I see it, if pressure remains the same, then every molecule of H20 displaces a molecule of either O2 or N2.
Power: At, say 100% humidity and 35degC, roughly 5% of the molecules will be water (a VERY humid day), so the number of O2 molecules inducted per stroke is 5% less than in dry air and we'd have roughly 5% less power.
The club: The molar weight of dry air is 29 grams/mole. The molar weight of water is 18 grams per mole. At constant pressure (so, same number of molecules per unit volume), as we introduce water vapor to dry air the density of the mixture decreases, since each H20 molecule has 63% of the mass of each (average) air molecule (primarily heavier O2 and N2 molecules) that it displaces. The lower density of the new mixture will present less resistance to the spinning club. In the example above (100% humidity, 35C) if 5% of the total molecules are H2O and they weigh 63% as much as the average air molecule, then the density of the moist air would be 98.15% of the density of the dry air. I haven't worked out the impact this has on the club's drag, but I suspect it is within your margin of error of the equipment.

Edited to add: If the club's resistance is described by the drag equation (D = Cd * (1/2 (rho * V^2)) * A) and air density (rho) is decreased by 1.85%, then drag on the club is also decreased by 1.85%

If I've got this right, then higher humidity decreases your engine power and also decreases the drag from the club. The reduction on the drag of the club will be about 37% as much as the decrease in engine power, so it offsets the power loss some, but not entirely. More significantly, all the adds and subtracts due to humidity under normal conditions will be within your estimated +/- 5% precision of the measurements.

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Vigilant1

Well-Known Member
TiPi.
For what it is worth:

Quoted:

For the new location, my calculator produced the same DA with those inputs
Also, for the new location and above inputs (zero humidity):
Absolute pressure: 926 hPa (by definition, same as QFE)
Absolute density: 1.082 KG/M3 (.0021 slugs/ft2)

For the old location and 20 deg C, I computed:
 Metric Imperial QNH 1019 mbar (or hPa) 30.19 inHg QFE 1010 mbar (or hPa) 29.83 inHg Altitude 72M 236 ft Temp (DegC) 20 68 deg F Density Altitude 209 M 685 ft Abs Pressure 1010 mbar (or hPa) 14.649 psi Abs Density 1.201 kg/m3 .00233 slugs/ft3

Air resistance of club (based on comparative air density): 1.082/1.201 = .90 The drag equation indicates drag is proportional to air density, so if air density is 10% less, then air resistance is 10% less

Power: The Engine Tuner's Calculator (below) calculates a "Relative Power" figure based on several factors. This is the expected output of an engine run under these conditions compared to an engine run under the SAE J1349 conditions, which are: Air temp 77 deg F (25 deg C), 29.235 Inches- Hg (990 mb) actual pressure and 0% relative humidity.
Disclaimer: I don't know anything about this calculator and can't say if it is accurate or not. I entered 0% relative humidity to get the output below, so the impact of RH differences between the two sites is not included:
Old location: Relative power: 103.5%
New location: Relative power: 92.5%
Expected difference in power at new location: 11% reduction

Anyway, similar to your calculations, my quick review indicates that the reduction in engine power at the new location can be expected to be pretty close to the reduction in drag force on the test club due to the decreased air density. We both found that expected power would decrease about 1% more than the expected aero drag. Since Power = Force * Velocity, if the velocity (RPM) of the club stays the same, then your test results between the two locations should be very close.

References:
QNH to QFE Calculator: http:/www.hochwarth.com/misc/AviationCalculator.html
DA Calculator (also computes absolute pressure and absolute density): Density Altitude Calculator - English/Metric, Relative Humidity
Engine Tuner's calculator: Engine Tuning Calculator - using relative humidity

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TiPi

Well-Known Member
Log Member
Thanks Mark,

This pretty much confirms what I have been thinking. It also confirms that Gustave Eiffel was a lot more clever that we thought He has come up with a simple engine dyno that has a built-in power correction for density altitude. With paper, pencil and slide rule!
When I started this project, I didn't anticipate this move to higher grounds and wanted to use the test club predominantly as a relative measure for the improvements. Now I don't need to go back to a standard engine and start all over again

The humidity impact on power is pretty linear to the H2O vapour pressure (displaced O2) and is at our worst about 3-4% (25-30deg C and 100%). Here is a bit of an overview of different standards for ICE power correction factors:

Most use very similar formulae with only some minor changes in the influence factor for temperature and the reference air pressure and temp. None of them consider humidity as the influence is relativley small in the normal range of atmospheric conditions.

DIN70020 Method
This method for power correction, recommended by DIN70020 standard (DIN, 1986), does not account for changes in air humidity. If changes in the atmospheric conditions are small with respect to a standard condition, then the engine overall efficiency, fuel specific heat and air/fuel ratio can all be considered constants. Taking the engine volumetric efficiency varying proportionally to the square root of the temperature, the following correlation is written:

The DIN70020 method indicates the reference atmospheric condition of p0 = 1.01325 bar and T0 = 293 K.

SAE J 1349 Method
The SAE J 1349 standard (SAE, 1995) recommends the following atmospheric power correction factor (CF2) for spark ignition engines:

The SAE J 1349 method indicates as a reference ambient condition for measuring the engine power in dynamometer tests p0 = 0.990 bar, T0 = 302.4 K, and p0n = 0.013 bar. This correction factor is recommended to be applied in the range from 0.950 to 1.010 bar, and from 288.5 to 316.3 K.

JIS D 1001 Method
The JIS D 1001 standard (JIS, 1993) recommends the following correction factor (CF3):

The reference atmospheric condition for Eq. (3) is of p0 = 1013.25 mbar and T0 = 293 K.

ISO 1585 Method
This method is given by ISO 1585 standard (ISO, 1992), and is also adopted by the Brazilian Society of Technical Standards (ABNT, 1996). The suggested power correction factor (CF4) is:

The reference ambient condition is p0 = 1.000 bar, T0 = 298K and pn0 = 0.010 bar. The correction factor is recommended for utilisation in the range from 0.800 to 1.000 bar, and from 288 to 308K.

Vigilant1

Well-Known Member
Gustave Eiffel's "wood dyno" method is really something. Flexible, cheap, and pretty darn accurate. I'd heard many folks say that it was "self adjusting" for altitude, but it is good to see that idea fleshed out a little.

The humidity impact on power is pretty linear to the H2O vapour pressure (displaced O2) and is at our worst about 3-4% (25-30deg C and 100%).
Just out of curiosity, I put RH figures into the Tuner's Calculator that I used. Going from 0% RH to 80% RH decreased HP by about 2%. I think it can be safely ignored. "One less thing . . . ."

It is probably good that your builder is waiting for good weather to pour your slab. With concrete, you definitely don't want any mistakes.

Mark

Vigilant1

Well-Known Member
Here's a newly offered inverted Vee aviation engine design: http://www.ac-aero.com/wp-content/uploads/2020/05/ac_FALCON_2020_R00_051820.pdf
It is a 2 stroke V4 that supposedly runs on Jet A, diesel, avgas, mogas, or just about anything else. It also has a built in reduction drive and a list price of $25k US ($217 per HP)

Okay, maybe not much in common with the B&S 49 series. Still, it has been awhile since an inverted V has been on offer for aircraft (as far as I know). TiPi's engine will have a big brother.

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tunna95

New Member
Really enjoying this thread, and looking forward to further developments when the shed extension is up and running. In theory, could you take the vanguard EFI to replace the Nikki carb and then use a custom ECU module with an open-loop system? Would this be a better way to get lower idle RPM and also be able to control mixture at higher altitudes? Being in the UK, cold starts and carb ice are a real issue.

TiPi

Well-Known Member
Log Member
Really enjoying this thread, and looking forward to further developments when the shed extension is up and running. In theory, could you take the vanguard EFI to replace the Nikki carb and then use a custom ECU module with an open-loop system? Would this be a better way to get lower idle RPM and also be able to control mixture at higher altitudes? Being in the UK, cold starts and carb ice are a real issue.
EFI is still an option if I can’t get a single carby to work properly (single or dual barrel). The challenge with EFI is to identify and address all possible and likely failure modes while keeping it simple. No point in designing an EFI system that will cost the same as the actual engine.

blane.c

Well-Known Member
HBA Supporter
EFI is still an option if I can’t get a single carby to work properly (single or dual barrel). The challenge with EFI is to identify and address all possible and likely failure modes while keeping it simple. No point in designing an EFI system that will cost the same as the actual engine.
You may be able to work with [B]jbiplane[/B] to develop a EFI.

TiPi

Well-Known Member
Log Member
You may be able to work with [B]jbiplane[/B] to develop a EFI.
I’m following his work, might be an option if he comes up with a simple & reliable system. Speeduino is also on the radar as well as nanoEFI.

karmarepair

Well-Known Member
HBA Supporter
In theory, could you take the vanguard EFI to replace the Nikki carb and then use a custom ECU module with an open-loop system?
I haven't looked at the Briggs EFI system much, but the Kohler system uses the flywheel to drive the crank position sensor. I'm not sure if the "ring gear" for that function is machined into the flywheel itself, or a separate piece, but having to keep a flywheel you don't need, that may actually endanger the crank if you drive the prop from the PTO end, is a big weight liability for no benefit.

Vigilant1

Well-Known Member
I haven't looked at the Briggs EFI system much, but the Kohler system uses the flywheel to drive the crank position sensor. I'm not sure if the "ring gear" for that function is machined into the flywheel itself, or a separate piece, but having to keep a flywheel you don't need, that may actually endanger the crank if you drive the prop from the PTO end, is a big weight liability for no benefit.
The B&S EFI system is just EFI, no ignition. So, the flywheel (with magneto magnets) is still required unless you work out a new ignition system. And, as you know, if you get rid of the flywheel you also need to fit some other starter and alternator arrangements.

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Vigilant1

Well-Known Member
Really enjoying this thread, and looking forward to further developments when the shed extension is up and running. In theory, could you take the vanguard EFI to replace the Nikki carb and then use a custom ECU module with an open-loop system? Would this be a better way to get lower idle RPM and also be able to control mixture at higher altitudes? Being in the UK, cold starts and carb ice are a real issue.
Just to mention it: The "hard" lower limit for idle speed is due to the B&S ignition with fixed advance timing. To get really low idle would require a modification of that as well as the carb.
BTW, welcome to HBA.

TiPi

Well-Known Member
Log Member
BTW, my shed still hasn’t been done
All the materials finally turned up about 5 weeks ago, and then the rain didn’t stop till last week. Concreter is booked for Tuesday, fingers crossed.

There are a couple of options that I want to try out for variable timing:
Honda GX690 coils (retarded by 15deg below 1,000rpm)
Briggs coil with large air gap (could be around 8-10deg over rpm range, might need stronger magnet)