Thrust-To-TOW Ratio

NoWingsAttached

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Please note the change in thread title, after careful consideration of the thoughtful comments and suggestions below.

Please find here a table for the ZeCA (explained below) Ratio for known (and some estimated) gyrocopter types with their respective power plants.

The list will be edited and added to as folks report in, and is arranged in no specific order.

The higher the ZeCA value the better the expected take-off and climb ability.

AC = Air Command
RFD = Dominator
SC = Sport Copter
MB = Monarch
TG = Tango Gyro



Gyrocopter ID & SeatingEngineThrustCalculated HP @~4.3:1 Thrust: HP)Dry Weight ZeCA @ TOW (Dry Wt +225#)
the Wicked, MAC AC IIMAC Yamaha YG4 14060014059536.19
Godzilla, MAC AC IIMAC Yamaha YG4 16068015863038.5
Blue Bee, Hirth Honey Bee 1Hirth 26062856630528.27
Kurtsey, MAC AC, 1MAC Yamaha YG4 1406006657536.87
SC II, IO-360 210, 2Lyco IO-360 Special900210110034.19
Predator, IO-320 160, 2Lyco IO-320690 (calculated)160 (listed)110027.85
TG YG3 120, 2Yamaha Vector 120515 (calculated)120 (listed)600 (est)31.97
TG YG3 135, 2Yamaha Nytro 135 (EFI)575 (calculated)135 (listed)600 (est)34.88
Bensen Mac,1Maculloch 70305 (est)71254 (est)32.49
Jazzenjohn, 1Hirth3207427732.52
MTO 912, 2Rotax 912 100430 (calculated)100 (listed)600 (est)27.53
CavalonRotax 914495 (calculated)115 (listed)630 (est)30.07
MagniRotax 915580 (calculated)135 (listed)600 (est)35.11
AC Subaru, 2Subaru 2.2560 (calculated)130 (listed)75029.87
Sparrowhawk, 2Subaru 2.5690 (calculated)160 (listed)900 (est)31.52

Playing around with numbers, I realized that the first successful Yamaha Genesis 4-cylinder powered aircraft, affectionately known as "The Wicked", my beloved Air Command tandem that I purchased in flying condition from Ora Cook for $4,500 (it was Ora's gift to me back at Bensen Days 2011 after he met my 7-yr-old while we were RV camped next to each other and spent hours chatting), produced 600# thrust and yet only weighed 595# dry. Round up the weight a tick and that is an interesting 1:1 ratio.

SO I trotted out my trusty trig excel spreadsheet and started pluggin in other gyrocopter dry weights and thrust numbers that I knew off the top of my head and arrived at an amusing ratio that is great for overall comparison of ALL gyrocopters ever built. All ya gotta know is your dry weight and your maximum reliable thrust (from a properly done test, of course. No fair cheating with "spiked" test results from hitting the throttle fast and hard. The thrust must reflect steady state thrust after at least three full seconds of waiting for the pull numbers to settle in.)

The basic trig equation is

tan Ø = opp/adj

My excel sheet converts tangent to radians, and then degrees (I couldn't figure out a way 5 years ago to build the thing to go straight from the equation to a degrees output, so it takes three steps. I still dont' know any other way to do it with Excel, to be honest.) You just plug in your weight and your thrust, and read the output angle.

I'm calling it the Zero Climb Angle, or ZeCA for short.

So the higher the thrust, and/or lower the weight, the higher (and better) the ZeCA value.

My Wicked has a perfect ZeCA of 45°, and my Blue Bee at 300# tested with a 60 HP Hirth producing 285# thrust has a ZeCA of 43.53°

An 800# gyro would need to produce a whopping 800# of thrust to hit 45 ZeCA degrees, but I think the best we can expect from a 160HP engine is just this side of 700# (from my most recent tests using Geoff Resney's YG4 EXUP, which I have nicknamed Godzilla). A Subaru 2.5 producing 670# thrust, in a heavier enclosed SxS gyrocopter weighing 850# will have a ZeCA value of 38.25°, and the same gyro producing 700# of thrust on a dry, cool day will have a 39.47 ZeCA.

Geoff Resney's MAC YG4 EXUP Air Command weighs 630# and produces 670-700# thrust, and so the ZeCA value of "Godzilla" is an INCREDIBLE 45.87 - 47.12 ZeCA !!!

Wow. And I'm betting there is at least one MAC 90 Bensen out there that can one up us here. Where is it, and can anyone provide cold, hard facts and data for it?

In 2015 I finished Kurt Carleson's single place Air Command MAC YG4 (I nicknamed that one "Viper") which pushes 600# no matter what day of the year it is, for some reason. It weighed 565# at the time, though it has put on some weight with many alterations and add-ons since. Kurt's ZeCA number, as-built, was 46.97.

Godzilla is my new MAC-built WWF Heavyweight Champeeeen.

The Wicked remains at 45.24° ZeCA these days, dropping to third place behind Godzilla and Viper.

If anyone wants a free copy of the MAC ZeCA Excel spreadsheet, write to me at

[email protected].

I would absolutely LOVE to hear from ANY of you with your numbers so we can rank your hot-rod gyrocopter in an (un) official listing using the ZeCA formula. No cheating, it's no fun if you pad the numbers. There are no prizes, no trophies, just a friendly and fair comparison. Thrust-Weight Comp SHT.jpg

Hope to see you at Mentone 2020, God willing and the creek don't rise.

Yours truly,
Gerg the Monster Maker.
 
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Jazzenjohn

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My single place gyro with an HKS engine has 320 pounds of thrust on a good day and weighs 277 pounds dry. It will do OK with your thrust to dry weight ratio, but not nearly as well at flying weight because the pilot is a far larger percentage of the flying weight than on any 2 seat craft. Mike Gaspard and Gary Goldsberrys Bensens had over 300 pounds of thrust with MAC engines and weighed ~254 pounds. I'd expect the best results would be the Gyrobee with the 618 engine and Mike Boyettes Dominator with the 670 engine. I've seen a light single place with the 100 HP 4 cylinder Hirth engine too.
 

XXavier

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As it may be of help concerning propeller thrust [Propellerschub Fprop], I copy below some relevant pages of a very relevant book: 'Flugphysik der Tragschrauber'. Yes, it's German, but can be understood, with some patience, by anyone interested.

In page 185 (not included) of the same book, the authors state that the maximal static thrust for the gyro they choose for the book (Autogyro MTO Sport, fitted with a 100-hp Rotax, mass in flight 392 kg) is 2000 newton.
 

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JETLAG03

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Surely the thrust is only a small part of the equation, rotor size and drag, unless you want to do only ground based drag racing
 

WaspAir

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I don't entirely follow the significance of expressing this ratio as an angle. An L/D ratio can be converted to an equivalent glide angle, and that gives some additional insight into how it might fly (e.g., a 19:1 L/D is about a 3 degree approach angle), but the angle computed here doesn't appear to me to carry a comparable meaning, adding anything over and above the information of the bare ratio itself.
For an F-15 fighter with 58,320 lb thrust and empty weight of 37,500 lb, the arctangent of that 1.555:1 ratio is 57.3 degrees. Does that tell us something that 1.555:1 does not, or provide further insight about its flight? Maybe I missed something.
 

Jazzenjohn

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Thrust to weight will translate into climb performance but the thrust to empty weight is less useful than thrust to all up flying weight. Whether it is expressed as an angle or ratio doesn't make much difference to me.
 

Vance

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In my experience static thrust and dry weight have little to do with how a gyroplane will perform.

Static thrust is just that, a measure of the thrust when a gyroplane is not moving.

I had a friend pitch his prop for maximum static thrust and he found he had to re-pitch it a lot before he got best performance in the air.

To focus on dry weight rather than takeoff weight can be very misleading and has little to do with actual performance.

Solo The Predator has a takeoff weight of around 1,100 pounds and will climb out at around 1,100 feet per minute.

With full fuel and a typical client she is closer to 1,400 pounds and climbs out around 600 feet per minute.

Her 160 horsepower Lycoming IO-320 weighs 260 pounds or slightly less than 19% of her maximum takeoff weight or 33% of her dry weight of 797 pounds.

The 230 horsepower IO-360 in the Sport Copter II weighs around 280 pounds or 16% of her maximum takeoff weight of 1,700 pounds or 28% of her dry weight of 1,000 pounds.
 

NoWingsAttached

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The purpose of ZeCA is in stating a theoretical "Zero Climb Angle" to the ends of simply stating the ratio of a particular gyrocopter weight (Not a 6 ft, 230# dude compared to a 5-ft 130# lady pilot, and nothing to with fuel on board since all you need in 6-10 # to fly.) to power in way we can all easily and quickly grasp and picture it in our heads, separate from all other variables. The two factors considered are the easiest to quantify by just about anyone who owns a gyro, you can usually find a means to obtain these two numbers on the ground with a bit of help and test equipment like that available at the annual Mentone Convention each year (at least we did this when I was Secretary of PRA).

At what angle will a certain gyro hang on the prop and quit climbing? I don't know, but ZeCA is one way to quantify that shade-tree gyrocopter pilots and builders in Rotorland.

The base line line is simple and the same for every gyro - regardless of pilot, fuel and payload weight; the rotors; and/or how to get best performance by tweaking prop pitch, etc. ZeCA quantifies theoretical performance gyrocopter itself, alone - not it's rotors, props, fuel capacity, pilot, drag, etc.

ZeCA has nothing to do with actual, realized performance, or a true, measured hang angle recorded after perfecting the make, style and size of rotors, and then all the myriad, infinite combinations of prop. You could spend years on that, alone, on a single gyrocopter.

Thanks for the many responses to add your gyrocopter's numbers to the record, please add yours soon!

Hope to see many people at Mentone 2020, damn the torpedoes!
 
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NoWingsAttached

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My single place gyro with an HKS engine has 320 pounds of thrust on a good day and weighs 277 pounds dry. It will do OK with your thrust to dry weight ratio, but not nearly as well at flying weight because the pilot is a far larger percentage of the flying weight than on any 2 seat craft. Mike Gaspard and Gary Goldsberrys Bensens had over 300 pounds of thrust with MAC engines and weighed ~254 pounds. I'd expect the best results would be the Gyrobee with the 618 engine and Mike Boyettes Dominator with the 670 engine. I've seen a light single place with the 100 HP 4 cylinder Hirth engine too.

Two categories, then: Single place and two-place.
 

NoWingsAttached

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In my experience static thrust and dry weight have little to do with how a gyroplane will perform.

I think I'm going crazy. Again.
 
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NoWingsAttached

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Her 160 horsepower Lycoming IO-320 weighs 260 pounds....

The 230 horsepower IO-360 in the Sport Copter II weighs around 280 pounds...

The weights given in the owner's manuals for Vance's IO-320 actually range from 280# to 294, not 260# as stated, and the IO-360 ranges from 288# to 293#, not 280#. I have no other info, and do not pretend to know much about Lycoming engines at all, so if there is something I am missing please post.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++

The Sport Copter II reports that the highly-modified engine used on the SCII is similar to a Red Bull engine, and they have tested it on their gyrocopter pulling an astounding 900# of thrust, in a machine with a dry weight of 1100# and a max TOW of 1750#.

We're all looking forward to Doug Gross flying his new AWESOME, SCII down to Mentone from Michigan for the convention, after having taken delivery of it in Oregon, then flying it home via California and Texas.

Can't wait to get up to Mentone see that beautiful beastie! WELL DONE, Sport Copter! Lycoming 320 Series Weights.jpg
 

NoWingsAttached

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The ZeCA value for the SCII is 39.29

I don't entirely follow the significance of expressing this ratio as an angle. An L/D ratio can be converted to an equivalent glide angle, and that gives some additional insight into how it might fly (e.g., a 19:1 L/D is about a 3 degree approach angle), but the angle computed here doesn't appear to me to carry a comparable meaning, adding anything over and above the information of the bare ratio itself.
For an F-15 fighter with 58,320 lb thrust and empty weight of 37,500 lb, the arctangent of that 1.555:1 ratio is 57.3 degrees. Does that tell us something that 1.555:1 does not, or provide further insight about its flight? Maybe I missed something.

OK, in deference to your post I will drop the degree sign° from the number.
 

Vance

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The weights given in the owner's manuals for Vance's IO-320 actually range from 280# to 294, not 260# as stated, and the IO-360 ranges from 288# to 293#, not 280#. I have no other info, and do not pretend to know much about Lycoming engines at all, so if there is something I am missing please post.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++

The Sport Copter II reports that the highly-modified engine used on the SCII is similar to a Red Bull engine, and they have tested it on their gyrocopter pulling an astounding 900# of thrust, in a machine with a dry weight of 1100# and a max TOW of 1750#.

We're all looking forward to Doug Gross flying his new AWESOME, SCII down to Mentone from Michigan for the convention, after having taken delivery of it in Oregon, then flying it home via California and Texas.

Can't wait to get up to Mentone see that beautiful beastie! WELL DONE, Sport Copter! View attachment 1147595
I weighed the IO-320-B1A in The Predator complete with exhaust and accessories at just under 260 pounds.

The IO-360-B is listed at 270 pounds.

I am not sure what model is in the Sport Copter II and I didn’t weight it so I added a little weight to avoid accusations of exaggerating.

Most of the parallel valve IO-360s I have weighed are around 270 pounds depending on the exhaust and accessories used.

An IO-360 is simply a stroked IO-320 so there is very little extra weight.

The angle valve IO-360 is around 40 pounds heavier depending on the accessories.

The IO-360 I flew in the Sport Copter II is modified by Ly-con and is supposed to make 230 horsepower at 2,700 rpm.

It had the light weight starter, alternator and a very light exhaust so it may well have weighed 260 pounds.

Often the weights in the manual are with a very heavy generator or two, a heavy starter, a very heavy exhaust and a vacuum pump.
 

NoWingsAttached

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I am guessing at the thrust numbers for Vance's Predator, since they are not available yet, but judging by my own thrust tests with Geoff's 160HP Godzilla we can expect 680-700#.

With a given dry weight of 1100# the Predator has a ZeCA value of 31.72 - 32.47

I have found with the many varied thrust tests I have conducted over the years that a ratio of roughly ~4.3: 1 exists between Static Thrust and realized HP, depending largely on prop efficiency due to speed, design and tested pitch.
 

Vance

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I am guessing at the thrust numbers for Vance's Predator, since they are not available yet, but judging by my own thrust tests with Geoff's 160HP Godzilla we can expect 680-700#.

With a given dry weight of 1100# the Predator has a ZeCA value of 31.72 - 32.47

I have found with the many varied thrust tests I have conducted over the years that a ratio of roughly ~4.3: 1 exists between Static Thrust and realized HP, depending largely on prop efficiency due to speed, design and tested pitch.
The dry weight of The Predator is 797 pounds.

I generally round it up to 800 pounds.

Take off weight with one person aboard is around 1,100 pounds depending on the fuel on board.

This appears to be the number Greg has seized on.

I am not able to imagine a reason to use dry weight to predict performance.

Often when soloing someone we add weight so the performance is more like the performance with the instructor on board.

If I am doing pattern work in The Predator for an hour at the end she will climb out measurably faster because of the six pounds lighter fuel load.

I feel static thrust is pointless so I have never checked it.

It is my observation that the propeller has a very large effect on static thrust so guessing at 680-700 pounds seems as pointless as using dry weight to predict performance.
 

NoWingsAttached

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Static Thrust Testing is a universal, easily-measured, and repeatable - and therefore scientific - test which measures a single force in a single direction, or vector, a test of which is affected by a couple of basic factors including HP, and some other not-so-obvious factors such as air density altitude, apparent wind, rolling friction of the gyrocopter from a zero start, and the various parameters of propeller efficiency including tip speed as a factor of diameter and speed of rotation, surface drag, pitch with relation to tip speed, number of blades and design of leading, tip and trailing edges.

Given all of that, we can arrive at a general "given" prop efficiency of 85 - 95% in most cases.

Armed with this information, and given that we all do the test in generally the same manner, we can all arrive at fairly even results across the board no matter where we are, who is doing the test, and what kind of gyrocopter/powerplant combination the test is being done for.

It is not unlike doing a dyno bench test on an engine. Yes, results will vary by as much as 10% from one shop to another on the same engine, but in the end we do get useful data from which to pull interesting results which are acceptable to 99% of the population as being reasonable, and accurate enough for comparative purposes.

As I mentioned above, I have found that it is possible to arrive at a very close interpretation of HP output of a power plant given just two things: Prop efficiency (which is including air density etc) and measured thrust. Having a known HP rating from, say, a dyno bench test, and prop efficiency, we can also turn this around and arrive at an expected thrust number.

And thus we have an apples-to-apples(hopefully no bad apples) look at how a gyrocopter may be expected to perform with respect to just two things: Weight and power (which should come as no surprise to anyone reading this).

Thank you for reading, and thank you especially more for posting your gyro weight and thrust, and/or expected engine HP. The more data, the better the whole thing is in the end, and more accurate. Kinda like "4 out of 5 dentists agree"...it works better if you poll more than 5 dentists.
 

NoWingsAttached

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When discussing the use of real-world thrust number actuals as a comparative index across the many types of gyrocopters one might consider, instead of just reported HP claims and ratings, some great info is contained in this article concerning power loss through shafts and transfer cases.


It is easy to understand that a direct-coupled Lycoming will transfer significantly more power to the prop, and thus produce more thrust per rated engine HP, than, say, a Yamaha Apex with one of Teal Jenkins' three-gear tractor FW gearboxes mounted on it; or that a Mohawk Silent Drive Hy-Vo chain drive is far more efficient than any gearbox at all.

The many configurations of redrives/PSRUs used on aircraft powerplants of all types makes it impossible to nail down a single efficiency number that fits every case.

Therefore to be summarily dismissive of thrust testing as a suitable means of determining power delivery to the prop and predicting aircraft performance is foolish, if not arrogant.

As to the mention in post #17 that a prop can be no more efficient than 60%...I'll leave that up to you to read the paper cited and come to your own conclusions. As for me, what I have tested and found personally over many years of work is what I stated prior. Prop efficiency is a mathematical equation that does not lie. It is a straight-forward trig, physics and real-world measurable of either static thrust or true air speed, with the difference being in generating the propulsion of air from a standing-still, steady state vs forward aircraft motion creating an apparent movement of air through the prop before being propelled by it. In the latter case, prop efficiency is a real-world, hard facts number determined by comparing theoretical distance to be moved over a given time period according to prop pitch compared to an actual, tested, measured distance an aircraft moves over a given period of time, or AS, and taking into account airframe drag.

Using both tests, static thrust plus tested air speed, one can arrive at a fairly decent idea of how much drag a particular aircraft exhibits in flight testing.

Another method we used for testing drag and mechanical rolling friction on my Porsche GT1 race car was to measure deceleration with a very expensive accelerometer in the car while taking my foot off the gas.

You can now do the nearly the same thing for a gyrocopter with a free app on your smart phone to arrive at a pretty good approximation of real-world, measured airframe drag.
 
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NoWingsAttached

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Bottom line to date: Godzilla rules.
 

XXavier

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How do you calculate propeller efficiency? Can you give an example, with your figures?
 
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