Cruise Speeds
Posted: Sun Aug 23, 2020 10:06 pm
by Direct C51
I have been trying to clean up my Sonex, aerodynamically, in order to gain a few knots. I was feeling like something was off with my numbers compared to the published data from Sonex, until I started doing some calculations.
Sonex Published Cruise Speeds:
Aerovee 80hp - 150 mph.
Jabiru 3300 - 170 mph.
AEROVEE - 44" pitch prop. This prop moves forward 44 inches for every rotation. In order to cruise at 150 mph with 100% efficiency (not possible) the RPM would be 3600!
44 in x 3600 rpm = 158,400 in/min
158,400 / 63360 = 2.5 miles / min
2.5 x 60 = 150 mph
Now, there is no way an airplane will operate at 100% efficiency. Drag and prop slippage means we will see about 85% efficiency. So a more realistic number might be 113mph at 3200 RPM!
44 in x 3200 rpm = 140,800
140,800 / 63360 = 2.2222 miles / min
2.2222 x 60 = 133 x .85 = 113mph
JABIRU - 64" pitch prop. To get the 170 mph cruise Sonex claims at 100% efficiency (not possible) would mean 2800 RPM. The max cruise RPM for a Jabiru is 2750. At a realistic 85% efficiency, and using the max cruise 2750 RPM, the cruise speed is realistically 142 mph.
64 in x 2750 rpm = 176,000
176,000 / 63360 = 2.7778
2.7778 x 60 = 166.6667 x .85 = 142 mph
Let’s not even get started on the 687 mile “conservative, low altitude 130mph TAS” range…
Re: Cruise Speeds
Posted: Sun Aug 23, 2020 11:38 pm
by mike.smith
Different conditions will give different results, but in level flight with my AeroVee I can cruise WOT at 130 kts (burning a LOT of fuel). That’s about 149.5 mph. I don’t generally run like that except for short bursts, or I feel like I’m whipping the “horse” to death. I generally cruise at max 100 kts or 115 mph, at just under 3,000 rpm. My taildragger weighs 673 lbs empty, and I’m running a Prince P-Tip prop. Math or no math, those are the numbers I’ve gotten over the last 6 years and nearly 500 hours.
Re: Cruise Speeds
Posted: Mon Aug 24, 2020 12:55 am
by peter anson
According to the Jabiru installation manual, Jabiru 3300 cruise speed is 2750 to 3100 rpm. I do normally cruise at around 2750 rpm and speed is around 120 to 125 knots - 138 -144 mph. 3100 rpm should push the speed up to around 140 knots but fuel consumption would be pretty high. For range, I don’t think I have ever tried for more than 280 nautical miles, about 320 miles.
Peter
Re: Cruise Speeds
Posted: Mon Aug 24, 2020 11:00 am
by Direct C51
mike.smith wrote:Different conditions will give different results, but in level flight with my AeroVee I can cruise WOT at 130 kts (burning a LOT of fuel). That’s about 149.5 mph. I don’t generally run like that except for short bursts, or I feel like I’m whipping the “horse” to death. I generally cruise at max 100 kts or 115 mph, at just under 3,000 rpm. My taildragger weighs 673 lbs empty, and I’m running a Prince P-Tip prop. Math or no math, those are the numbers I’ve gotten over the last 6 years and nearly 500 hours.
Mike, what pitch prop do you have? I would imagine the Prince is closer to 46” in cruise. What RPM are you at when flying 149.5mph? 3800? I’m not trying to be condescending, but do you find you more often have a headwind when compared to your GPS ground speed?
peter anson wrote:According to the Jabiru installation manual, Jabiru 3300 cruise speed is 2750 to 3100 rpm. I do normally cruise at around 2750 rpm and speed is around 120 to 125 knots - 138 -144 mph. 3100 rpm should push the speed up to around 140 knots but fuel consumption would be pretty high. For range, I don’t think I have ever tried for more than 280 nautical miles, about 320 miles.
Peter
Peter, looks like we are in agreeance and your real world experience proves my math. I predicted 142mph at 2750 RPM and you confirmed 138-144 mph. I agree, 3100 RPM should give you 140 kts/160mph. Is that a normal cruise RPM for a Jab? Still 10 mph less than published cruise numbers.
Re: Cruise Speeds
Posted: Mon Aug 24, 2020 5:23 pm
by mike.smith
Direct C51 wrote:
mike.smith wrote:Different conditions will give different results, but in level flight with my AeroVee I can cruise WOT at 130 kts (burning a LOT of fuel). That’s about 149.5 mph. I don’t generally run like that except for short bursts, or I feel like I’m whipping the “horse” to death. I generally cruise at max 100 kts or 115 mph, at just under 3,000 rpm. My taildragger weighs 673 lbs empty, and I’m running a Prince P-Tip prop. Math or no math, those are the numbers I’ve gotten over the last 6 years and nearly 500 hours.
Mike, what pitch prop do you have? I would imagine the Prince is closer to 46” in cruise. What RPM are you at when flying 149.5mph? 3800? I’m not trying to be condescending, but do you find you more often have a headwind when compared to your GPS ground speed?
54" diameter, 44" pitch. At about 3370 rpm is about all I can get in level flight.
I went back and looked at my flight tests between my Sensenich and my Prince props. The Sensenich only got up to 110 kts at 3,250 rpm. The Prince got up to 125 kts at 3370 rpm. Test OAT was around 76 deg F for both tests. Flying out to OSH last time I was getting 130 kts at times (according to my knee board numbers I recorded), but I didn’t record the rpms.
Re: Cruise Speeds
Posted: Tue Aug 25, 2020 8:18 am
by peter anson
Direct C51 wrote:Peter, looks like we are in agreeance and your real world experience proves my math. I predicted 142mph at 2750 RPM and you confirmed 138-144 mph. I agree, 3100 RPM should give you 140 kts/160mph. Is that a normal cruise RPM for a Jab? Still 10 mph less than published cruise numbers.
I never cruise using 3100 RPM* but recall being at a fly-in some years ago and talking to a guy who had flown down from Bundaberg in one of the Jabiru 230s from the factory. He said that they were running at 3000 RPM the whole trip. I tend to fly by fuel flow using an indicated 21 to 22 litres per hour. Again, the installation manual says 75% power would use 24 litres per hour. I have tried running at higher RPM but the gain in speed didn’t seem to justify the extra fuel consumption.
- I did cruise at up to 140 knots one time when I was worried about reaching my destination by last light but can’t recall the fuel rate.
Peter
Re: Cruise Speeds
Posted: Tue Aug 25, 2020 9:50 am
by sonex1374
Peter,
Talking to the Jabiru USA team they say the 3300 loves to spin up and run at 3000 rpm in cruise. However, like you, I rarely push the engine that fast. I prefer to run at around 2750-2900 burning somewhere between 5.8 and 6.5 gal per hour. I always get the impression that I can lean a little more and save fuel, but it just seems to purr at those settings, so that’s good enough for me. At 2750 down low that will yield around 135 mph, but go up a bit higher or run at 2900 and cruise speeds increase to about 150 mph. The 3300 will do 170 mph but it burns a lot of fuel and just seems hard on the engine so I never do it (probably overly caution, but that’s just my opinion).
Jeff
Re: Cruise Speeds
Posted: Wed Aug 26, 2020 12:35 pm
by markschaible
Hello SonexBuilders.net!
Every few years this topic comes-up, and invariably, folks are dismayed at our published figures because they are looking at indicated airspeeds and/or GPS ground speeds. Please keep in-mind that all of our published cruise speeds are given in TAS (True Airspeed).
Here’s an example of typical cruise data on one of our archived flight test cards for an AeroVee powered Sonex:
Indicated Altitude: 8,000 feet MSL
Altimeter Setting: 30.07
Temperature: 13C
RPM: 3150
Indicated airspeed: 130 mph
True airspeed: 150 mph
Density altitude: 9,425 ft MSL
Pressure altitude: 7,863 ft MSL
Here’s a look at what we typically see with a Jabiru 3300 powered Sonex or Waiex using the same atmospheric conditions to do the TAS conversion:
Indicated Altitude: 8,000 feet MSL
Altimeter Setting: 30.07
Temperature: 13C
RPM: 2850
Indicated airspeed: 150 mph
True airspeed: 173 mph
Density altitude: 9,425 ft MSL
Pressure altitude: 7,863 ft MSL
Get out your whiz wheel, digital E6B or find a good online TAS calculator, punch-in your data and see what you get!
Best Regards,
-Mark
Re: Cruise Speeds
Posted: Wed Aug 26, 2020 1:09 pm
by builderflyer
Possible cruise speed dilemma?
For those flying behind a Jabiru 3300 and wishing to stay within the “light sport” rules (i.e. drivers license medical), it is likely necessary to use a maximum continuous rpm of 2750 at sea level. Fortunately, the manual that came with my older engine specifies 2750 as the maximum continuous rpm but I believe that later manuals call for a higher rpm. Even at 2750 rpm at sea level my Sonex really pushes the CAS limit of 120 kts (138 mph) as specified in the light sport aircraft rules..
The point is that if you have a Sonex (or Waiex) with a Jabiru 3300 and it came with an engine manual that specifies a maximum continuous rpm of something over 2750 rpm, chances are you aren’t flying a Sonex that can be legally operated under the light sport rules (depending, perhaps, upon which prop you may be using). Just my non-lawyer opinion after discussing the matter with Pete Krotje (sp?) formerly of Jabiru USA a few years ago. Others may choose to disagree.
Art,Sonex taildragger #95,Jabiru 3300 #261
(Currently flying under BasicMed but want to keep a driver’s license medical available as an option)
Re: Cruise Speeds
Posted: Wed Aug 26, 2020 1:15 pm
by lpaaruule
I assumed 8000’ referred to density altitude, not indicated, but I see on the performance specs it’s stated as 8000’ MSL. The density altitude in this case is closer to 10,000’ than 8000’. The last time I was at 10,000’ indicated, the density altitude was closer to 9000’, but the OAT was much colder.
Anyway, without knowing density altitude, the spec is a little, hmm…can’t think of the right word. [edit → ambiguous]
Seems like it would take the same fuel flow to get 150mph indicated, no matter the altitude. Other variables besides aerodynamic drag come into play I’m sure.
Interesting discussion though.
Re: Cruise Speeds
Posted: Wed Aug 26, 2020 2:23 pm
by gammaxy
This does come up every few years. It would be cool if someone flying an Aerovee with the Sensenich propeller could meet those numbers at 9,400 feet density altitude. I can dig up plenty of evidence of not achieving them 
I suspect I’m a good 20mph slower.
I averaged 135mph (as measured with an official stopwatch divided by the race distance) at the 2015 Big Muddy air race down low at WOT–my experience has always been I get more power and fly faster down low. http://sportairrace.org/sarl/node/2200
Sonex published a webinar that shows some of their raw numbers that are very close to what I see in practice: https://youtu.be/HQzHaQ-Pk7I?t=5164. The fastest they show seems to be 141mph true at ~2500ft and 3250 rpm. This seems pretty realistic for a clean airplane with fairings installed. I don’t normally achieve it, but I’m confident it’s possible with some care.
I just don’t understand the physics that would allow me to fly 10mph faster at a lower rpm while breathing air that is ~20% less dense at 9400ft. Best case scenario, the reduction of drag will cancel out with the reduction of power and I’d be flying the same speed. But, I also need to increase my angle of attack to compensate for the reduction of lift (the equivalent of throwing an extra 180 pound passenger in the airplane), so I always end up slower.
Now, there is no way an airplane will operate at 100% efficiency. Drag and prop slippage means we will see about 85% efficiency. So a more realistic number might be 113mph at 3200 RPM!
I think your logic is mostly sound and a fantastic sanity-check, but I don’t think multiplying by 85% is fair. Different manufacturers and designs define pitch differently, but one common definition is relative to the bottom surface of the airfoil which should always work out to a lower number (by several degrees) than the pitch of the airfoil chord line. Spot checking the POH for a Cessna 172 and what I see in my experience with the Sonex, I think using 95-100% is actually pretty close at cruise speed. EDIT: I agree that 85% is a reasonable guess for propeller efficiency, but disagree that it can be applied to this equation. The pitch of the propeller is a somewhat arbitrary physical measurement often based on the bottom surface of the airfoil ~75% out from the hub. I think this convention already “bakes in” the efficiency reduction you’re trying to apply.
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 8:01 am
by GraemeSmith
Well don’t forget that the P-Tip prop claims to repitch itself by up to 4" as speed increases.
Prince Marketing wrote:Prince P-tip props are the only wood / composite anti-vortex droop tipped propeller in the world. This propeller is a wood, fixed pitch propeller that relies on the forward pull of the propeller to automatically provide pitch change proportional to the amount of force being applied to the propeller disk. When a propeller operates at a slower airspeed than its maximum capabilities, it has a proportional pull in relation to the velocity of forward motion. At takeoff and climbing condition the propeller has its largest forward pull, due to the scimitar shape. The tip of the propeller cones forward, as the coning angle changes the propeller will lessen pitch providing shorter takeoffs and higher rates of climb. As the propeller increases in forward speed the disk pressure is reduced, forcing the propeller to increase pitch and top speed. This change in pitch is approximately 4“ from takeoff to cruise. The droop P-TIP delays the vortices. The propeller then has smooth air to provide better thrust and a pronounced reduction in propeller noise. Additional benefit of the P-TIP design is the volume of air the propeller produces. When air flows through a standard tip propeller design the airflow at the tip will flow over the propeller tip, as soon as it passes the tip it will tuck down behind the propeller blade giving a cone of air from the propeller smaller than the propeller diameter. A 68” P-TIP will give the same volume of air as a standard tip 72” propeller. By reducing propeller diameter there is less frontal area or flat plate drag of the aircraft, higher top speeds are the result without sacrificing takeoff or climb.
Though it is not clear if this means the 44" prop repitches to 48". Or if the loaded 44" prop pitches down to 40". Assuming it pitches up to 48" that would account for better speeds than OP’s original calculation suggests and Mike Smith (and my) experience shows:
AEROVEE - 44" pitch prop. This prop moves forward 44 48 inches for every rotation.
At 85% efficiency.
48 in x 3200 rpm = 153,600
153,600 / 63360 = 2.4242 miles / min
2.4242 x 60 = 145.45 x .85 = 124mph Which would be 108knots.
–
I tend to cruise at 2,900
So working it again:
48 in x 2900 rpm = 139,200
139,200 / 63360 = 2.1969 miles / min
2.1969 x 60 = 131.8 x .85 = 112mph Which would be 97.5 knots. And that is AWFUL CLOSE to the 98/99 knots I get at 2,900rpm.
So I’ll assume the P-Tips are improving the prop efficiency slightly out towards the tips as claimed.
–
To someone else’s comment about efficiency. The McCauley fixed pitch metal prop efficiency figure I am used to using is 0.8 - a sort of “assume the worst” figure.
If you really want to get into it:
https://www.sciencedirect.com/topics/en … efficiency
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 10:51 am
by gammaxy
GraemeSmith wrote:Though it is not clear if this means the 44" prop repitches to 48". Or if the loaded 44" prop pitches down to 40". Assuming it pitches up to 48" that would account for better speeds than OP’s original calculation suggests and Mike Smith (and my) experience shows:
It means it pitches down to 40". The scimitar shape causes the pressure to be farther back near the tips relative to the rest of the blade and will tend to reduce the pitch. Put your finger out near the tip of the propeller and push in the direction of thrust and you’ll see which direction the blade should twist due to this effect. This pitch change will be most pronounced when the propeller is the most heavily loaded which will be at full throttle at slow speeds (during takeoff). This should allow the engine to turn a little faster and generate a little more power than otherwise.
There’s also a centrifugal twisting moment that tends to want to decrease blade pitch, but it is purely a function of RPM and not loading.
A lot of propellers have some backward sweep near the tips that gives a similar, but probably less pronounced effect. It would be interesting for someone with a high speed camera to actually measure how it compares to the Sensenich. I own both a Sensenich and P-Tip and think they’re both great propellers, but I think a lot of details of the P-Tip are more about marketing. It would be very difficult to set up a test to conclusively show its benefit. In my case, the P-Tip is 46" and the 44" Sensenich allows higher RPMs, so I prefer that one.
To someone else’s comment about efficiency. The McCauley fixed pitch metal prop efficiency figure I am used to using is 0.8 - a sort of “assume the worst” figure.
I agree that propeller efficiency is in that range, but applying it to the math like in this thread is incorrect for the same reason that estimating glide ratio from angle of attack of the bottom surface of the wing of an arbitrary airplane would be incorrect. If you agree with me that your propeller is not actually increasing pitch to 48", you’ll see for yourself that .85 is no longer the right number to get the math to work out.
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 11:41 am
by markschaible
builderflyer wrote:Possible cruise speed dilemma?
You need to be flying a Jabiru 3300L engine: “L” for “Light Sport,” not the Jabiru 3300A if it was manufactured after a certain date. There is an addendum to the Jabiru 3300 manual for “L” engines. Contact Jabiru USA (now Arion Aircraft) for the most up-to-date information about this. This only became an issue after Jabiru increased it’s max continuous RPM specification a number of years ago. Spec used to be 2850 and they increased it to 3300 RPM if memory serves me correctly. We certainly could not understand the logic of increasing their Max Continuous RPM specification to match their Red Line specification – they were just really proud of the engine! When Sport Pilot was released, we conducted low altitude flight tests at 2850 RPM (was the current max. continuous spec of the engine at that time). When correcting the data for sea level, standard day we ended-up about 3 mph under the “speed limit.”
Keep in-mind that Sport Pilot is not a radar gun speed limit. The specification is very specific to sea level, standard day conditions in level flight. There is nothing prohibiting a Sport Pilot from climbing to a more efficient altitude to take advantage of better TAS and efficiency, or from exceeding the maximum speed in a descent. Some monstrously powered bush planes out there prescribe time limits to climb power and have extremely low max continuous RPM specifications (lower than normal for the engine used) specifically for Sport Pilot compliance. A Jabiru 3300 powered Sonex is on much more solid ground with regard to compliance, in our view, than some of the games being played with other aircraft types. The FAA has agreed with our interpretation of the Sport Pilot rules when it comes to compliance of the Jabiru 3300 powered Sonex when it has been questioned in the past.
Anyway, without knowing density altitude, the spec is a little, hmm…can’t think of the right word.
Manufacturers always give performance numbers in TAS at specific indicated MSL altitudes (if they give an altitude at-all, you usually have to look at a POH to find that). The example I gave from our archives happened to be a higher density altitude, however, if you plug the same indicated numbers into “standard day” conditions (8,000 ft indicated, 29.92 ALT setting, 15 degrees Celsius, 130 mph indicated) you come-up with essentially the same TAS (151 mph), pressure alt is 8001 ft and Dens Alt is 9816. If it’s truly standard temperature at altitude, -9C, then you would be truing out at 144 mph if you’re indicating 130 mph, but the colder, more dense air at-altitude will probably allow you to see 135 mph indicated (150 true) without breaking too much of a sweat.
I averaged 135mph (as measured with an official stopwatch divided by the race distance) at the 2015 Big Muddy air race down low at WOT–my experience has always been I get more power and fly faster down low.
Did this race include takeoff, climb, descent and landing, or was the watch started and stopped with the aircraft flying across the line at cruise speed? 135mph is an outstanding average speed for a cross country at low-altitude. Flight planning for a normal cross country would take into account takeoff, climb, descent, pattern and landing so you’re never going to plan a normal cross country (time or fuel-wise) using only the cruise speed and fuel burn numbers at your target cruise altitude. Also keep in-mind that you will see a higher indicated airspeed down low, but TAS will be lower.
The fastest they show seems to be 141mph true at ~2500ft and 3250 rpm
This definitely supports our published numbers: 130 mph TAS at 3,000 feet, which is based-on cruising the AeroVee at 3150 RPM.
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 11:57 am
by builderflyer
markschaible wrote:Hello SonexBuilders.net!
Every few years this topic comes-up, and invariably, folks are dismayed at our published figures because they are looking at indicated airspeeds and/or GPS ground speeds. Please keep in-mind that all of our published cruise speeds are given in TAS (True Airspeed).
Best Regards,
-Mark
Mark,
Do you have the approximate gross weights at which your speed tests were run? I assume the factory aircraft were not loaded up to max gross for the tests or could have even been lightly loaded. This may partially explain why some of the others differ in their test results if their aircraft were more heavily loaded at the time of their testing.
Thanks,
Art,Sonex taildragger #95,Jabiru 3300 #261
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 12:56 pm
by builderflyer
markschaible wrote:
builderflyer wrote:Possible cruise speed dilemma?
You need to be flying a Jabiru 3300L engine: “L” for “Light Sport,” not the Jabiru 3300A if it was manufactured after a certain date. There is an addendum to the Jabiru 3300 manual for “L” engines. Contact Jabiru USA (now Arion Aircraft) for the most up-to-date information about this. This only became an issue after Jabiru increased it’s max continuous RPM specification a number of years ago. Spec used to be 2850 and they increased it to 3300 RPM if memory serves me correctly. We certainly could not understand the logic of increasing their Max Continuous RPM specification to match their Red Line specification – they were just really proud of the engine! When Sport Pilot was released, we conducted low altitude flight tests at 2850 RPM (was the current max. continuous spec of the engine at that time). When correcting the data for sea level, standard day we ended-up about 3 mph under the “speed limit.”
Mark,
Thanks for reminding me about the Jabiru 3300L model engine. I believe that engine is placarded at a max continuous rpm of 2850 because of the trouble Jabiru stirred up in the light sport industry when they raised the max continuous rpm on the 3300A model from 2750 to 3300. My early Jabiru engine is a 3300A model. So when Jabiru raised the rpm limit, they effectively removed my Sonex from the light sport catagory. In discussing this matter with Pete Krotje (owner of Jabiru USA at the time), he suggested that I keep the original manual that came with my engine which specifies a max continuous rpm of 2750. Then, if ever questioned by the FAA, as to the legitimacy of my Sonex qualifying under the light sport rules, I could present the manual along with Sonex LLC confirmation of meeting light sport requirements even at 2850 rpm. This combination should, hopefully, satisfy the FAA with regards to my particular aircraft.
My earlier point, however, was that if a Sonex has a 3300A model engine on it and the manual that came with that particular engine (or the only version of the manual that is kept with a specific aircraft’s documents) specifies a max continuous rpm of 3300, for example, then that Sonex can’t legally be operated as a light sport aircraft. I don’t know if there are any Sonex out there that fit into this status.
Thanks for your response,
Art,Sonex taildragger #95,Jabiru 3300 #261
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 2:01 pm
by markschaible
builderflyer wrote:Mark,
Do you have the approximate gross weights at which your speed tests were run? I assume the factory aircraft were not loaded up to max gross for the tests or could have even been lightly loaded. This may partially explain why some of the others differ in their test results if their aircraft were more heavily loaded at the time of their testing.
Thanks,
Art,Sonex taildragger #95,Jabiru 3300 #261
We’ve been able to get these numbers at various loading up-to and including takeoff at max gross.
Bottom Line: if you can’t indicate 130 mph with an AeroVee powered Sonex or 150 mph with a 3300 powered Sonex at or around max continuous RPM, then something is wrong: Fairings & wheel pants, rigging, engine/carb tuning, propeller, airspeed indicator calibration, etc.
I’ll leave this discussion with this, Kerry’s recent article at: https://www.kitplanes.com/the-one-true-airspeed/
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 3:51 pm
by builderflyer
markschaible wrote:
builderflyer wrote:Mark,
Do you have the approximate gross weights at which your speed tests were run? I assume the factory aircraft were not loaded up to max gross for the tests or could have even been lightly loaded. This may partially explain why some of the others differ in their test results if their aircraft were more heavily loaded at the time of their testing.
Thanks,
Art,Sonex taildragger #95,Jabiru 3300 #261
We’ve been able to get these numbers at various loading up-to and including takeoff at max gross.
Bottom Line: if you can’t indicate 130 mph with an AeroVee powered Sonex or 150 mph with a 3300 powered Sonex at or around max continuous RPM, then something is wrong: Fairings & wheel pants, rigging, engine/carb tuning, propeller, airspeed indicator calibration, etc.
I’ll leave this discussion with this, Kerry’s recent article at: https://www.kitplanes.com/the-one-true-airspeed/
Thanks Mark,
I have a plans built pitot-static system on my Sonex and as built it provided a rather high, unrealistic IAS. After calibration (it was all static system error), I was able to achieve a difference of only 1 or 2 mph between IAS and CAS from 90 mph to 190 mph. So I feel pretty good about any cruise numbers I may report. One correction on your “bottom line”…for the 3300 powered Sonex you said an “indicated” 150 mph at max continuous rpm whereas I believe you meant to say a TAS of 150 mph. My Sonex is reasonably fast but not that fast.
Ok, I’m done.
Art
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 5:08 pm
by markschaible
No, I mean indicated for the 3300. your TAS at 8,000 feet should easily reach 170 mph.
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 5:43 pm
by SonexFactoryTech
Mark brought this thread to my attention and asked me to share my numbers. Numbers are boring, and variable, and not as absolute as everyone wants them to be but I’ll dump mine here and leave ya’ll to it.
Aircraft: Metal Illnes
Polished finish
Tailwheel configuration
Jabiru 3300-powered (engine s/n 170)
Sonex-recommend Senensich glass-coated prop
Fully faired
Empty weight 654 pounds
Gross weight for both flights; about 936 pounds (Plane, pilot, stuff, and 17.2 gallons* of fuel).
(*A legacy Sonex tank vented straight up on a conventional gear Sonex allows about 17.2 gallons of fuel onboard.)
Date of Flights: Jan 2006
Flight One:
Pressure Altitude 8000 feet (Alt set to 29.92)
WOT = 3110 RPM
GPH = 6.9 (6.7 to 7.0 range)
OAT = 10 degrees F
CHT = 246/249
Oil T/P = 193/53
EGT = 1313/1357
IAS = 163
CAS = 164
TAS = 188.75
Endurance = 2.46 hours
Range = 465 mi
MPG = 27.3
Flight Two:
Pressure Altitude 8000 feet (Alt set to 29.92)
2850 RPM
GPH = 4.9 to 5.0
OAT = 10 F
CHT = 247 / 251
Oil T/P = 181/47
EGT = 1392 / 1428
IAS = 146.5
CAS = 148.7
TAS = 169.94
Endurance = 3.4 hour
Range = 577 mi
MPG = 33.9
I also once flew 486 miles in 3.9 hours on one tank of gas, and flight tested a scenario where flying at 100mph IAS at about 2000 MSL I could lean out to 2.2 GPH, giving a no-reserve range of 780 miles.
Blue Skies…
Kerry Fores
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 6:25 pm
by builderflyer
Hi Kerry, thanks for posting your numbers. I’ve seen those before. You’re taking us back to the good old days when none of us could match your performance numbers. We could only be envious. Eric Scheppers comes to mind.
Flight 1 confirms suspicions that you were not using an rpm of 2850 but rather over 3100 rpm and that you were running with a light load, both of which help your cruise numbers. Flight 2 is a bit more confusing in that if that flight were transposed to sea level, it would seem your particular Sonex would not meet the rules for a light sport aircraft…it would appear to be too fast. But then it was a very cold day.
Anyway, I’ll just continue to be filled with envy and have to accept the fact that I built a “dog”.
Art,Sonex taildragger #95,Jabiru 3300 #261
Re: Cruise Speeds
Posted: Thu Aug 27, 2020 11:09 pm
by gammaxy
Kerry, quick clarification, was the temperature 10F or 10C? When I do the math using 10F as written (which seems likely for January in Wisconsin), I calculate 180mph instead of 188mph TAS. Still fantastically fast.