How accurate is the technical data for gyros?

ckurz7000

Senior Member
At just so happened that, on the German forum, someone posted something about the Tercel. I followed a link and wound up on their website. Skipping the marketing parts I quickly found myself reading the technical specs and starting to scratch my head. I found some glaring discrepancies between what is on the manufacturer's homepage, what is written in the POH and what my own experience tells me.

Curiosity piqued, I visited the homepages of other manufacturers and got very mixed results. Where available I downloaded the POHs and tried to ascertain the accuracy of technical specs given on the internet.

I do NOT want to denigrate any particular type of gyro. They all have their pros and cons and, across the board, fly reasonably well. However, I would like for other people to become aware of the fact that even technical specs given by the manufacturer need to be taken with a grain of salt and questioned.

Without further ado, this is what I found:

The empty weight of the Tercel is given as 285 kg and the MTOW as 560 kg. Curiously enough, payload is not the expected 275 kg (the difference) but only 240 kg. That's what got me to consult the POH which is available for download off the webpage. Here, empty weight is 295 kg, MTOW is 560 kg and payload is 265 kg, the expected difference between MTOW and empty weight.

Vmin on the webpage is 40 km/h while it is 60 km/h in the POH. Vne is 210 km/h on the webpage and 200 km/h in the POH.

Climb rate is speced at 1200 fpm, the same on webpage and POH. However, from my own (admittedly limited) experience, it would be pretty hard to coax 1200 fpm sustained climb rate at MTOW from a Tercel (at standard atmospheric conditions, of course). A Tercel pilot on the forum surmised that it might be the solo climb rate. That would be more realistic, of course, but still misleading. There are certain definitions for how to measure particular quantities. And climb rate is to be given at MTOW. The manufacturer may choose to give climb rate figures for other configruations, too, but that it is purely optional. If nothing else is specified, a climb rate figure applies to MTWO and ISA.

Landing distance is given as 0-5 m. Here we have another problem with definitions. Landing distance (in the absence of any other modifiers) is to be quoted for a dry, level asphalt surface, at MTOW, over a 50 ft obstacle, windstill and ISA. Clearly, the 0-5 m from the website include only the landing roll. The POH is better in this respect and gives 45-55 m. The question begs, however, which one it is? 45 or 55 m. Still, even this number is quite short and I question if it is really possible to land over a 50 ft obstacle and bring the gyro to a stop in 45 m. The point is, it has to be done using average pilot skills and the procedure set forth in the POH. So no stunts or loading the rotor. Just standard procedure.

Take-off distance is given on the web as 100 m. In the POH it is 115. This sounds reasonable albeit a bit short in my experience. At MTOW, and using the procedure given in the POH I would not want to rely on clearing a 50 ft tree 115 m down the runway. The BCAR Section-T specifies a safety factor of 1.5 for the quoted take-off distance in the manual. I doubt whether this factor was applied (although the manual was not meant to be to Section-T standards).

Next we come to cruise speeds. Before I do, however, I want to stress the importance of properly calibrating the ASI. I have seen deviations of 10% on my MT03. So, while seeing 140 km/h on my ASI, I was really only doing 126 km/h. A similar problem might exist with other gyros. Therefore, in the absence of an ASI calibration curve, I have no way of knowing the calibrated airspeed, which I need to know accurately for my flight planning.

Unfortunately, for the Tercel, no calibration curve is given in the POH. Cruise speed is cited at 140 km/h at 75% power, at a fuel flow of 20 l/h. According to my (limited) experience, these numbers are too optimistic. You may be seeing 140 km/h on the ASI but in actuality I found cruise speeds more in range between 110-130 km/h at 75% power and MTOW. The fuel flow of 20 l/h is that of a Rotax 914 at 75% continous power. The Tercel has a turbo boosted Rotax 912 which outputs a mayimum of 135 HP. I wonder if, at 75%, fuel flow should not be higher than 20 l/h.

-- Chris.
 

ckurz7000

Senior Member
The MTOSport

The MTOSport

Alright, next I looked at the Auto-Gyro homepage, specifically at the MTOSport. The POH is also conveniently available for download, which makes it easy to compare to the specs on the homepage.

I found a mistake for MTOW which is given as 450 kg / 560 kg on the web (depending on specific national regulations), whereas the POH mentions 450 kg / 500 kg. That's a 60 kg difference in MTOW!!

Next, let's look at Vne and climb rate, the only other specs interesting for my purposes.

First off, I did find a calibration curve for the ASI. That's a big plus.

Climb rates are also quoted for three different load conditions, including, of course, MTOW. The web mentions 4 m/s (800 fpm) which is the climb rate at 450 kg. At 500 kg it is 3.4 m/s (680 fpm). So there is a slight ambiguity of interpretation if you just take the plain number on the web.

Vne is 185 km/h, on the web as well as the POH.

In section 5.6 of the POH I find take-off and landing distances over a 50 ft obstacle as well as take-off and landing roll distances. Taking off requires 300 m and landing 150 m over a 50 ft obstacle. Now, these numbers I have a good feeling about. They are easily attainable using average pilot skills and no stunts.

Comparing Tercel and MTOSport, I wonder why it takes 150 m to land an MTOSport at 500 kg and only 45-55 m to land a Tercel at 560 kg. I am going out on a limb and claim it is due to different testing procedures or "rounding errors" in measurements.

What I found sorely missing the MTOSport POH is any useful data for the cruise portion of a flight. No cruise speeds quoted and no fuel consumption either. Is every pilot expected to do his own flight testing??? The web claims 160 km/h cruise speed which is well above what is achievable at a useful cruise power setting of, say, 75%. In my experience it is more like 135 km/h.

-- Chris.
 
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C. Beaty

Gold Supporter
Some of the discrepancies, aside from the hustling aspect, come from the ASI installation.

The only satisfactory static pickup for anything with the range of fuselage attitudes of a gyro is the coaxial type; sometimes called a Kollsman pickup. That way, both static and pitot inputs are at least in the same pressure field.

There is a 1930s NACA report on this subject but I don’t have a link handy.
 

ckurz7000

Senior Member
The DF02

The DF02

I know, this is a rather exotic little machine but since a good friend of mine owns one of the four flying specimen, I was curious and looked. For those interested, the webpage of the DF02 is here.

First off, there is no POH for download.

Vh (maximum horizontal speed) is given at a believable 160 km/h. Cruise speed at 120 km/h. From experience I know that the DF02 cruises faster and climbs better than a Tercel, Xenon or MTOsport. Yet cruise speed of the MTO is allegedly 160 km/h and that of the Tercel is 140 km/h. What gives?

Maximum climb rate is quoted not at the MTOW of 300 kg but at 270 kg at which point it is 1000 fpm. According to my friend, who hat a look in the POH, at MTOW it is 650 fpm. This number seems plausible to me. Yet again, the Tercel climbs almost twice as fast?

Not from the web but from the POH my friend reads take-off and landing distances to me: 90 m take-off roll and 220 m to clear the ol' 50 ft tree. What's even better, there are diagrams of climb performance in the manual which let you determine climb rate at various loadings and density altitudes.

-- Chris.
 

ckurz7000

Senior Member
The Xenon 4 Executive 912-T

The Xenon 4 Executive 912-T

Who in the gyro community isn't aware of the Big Fight between Trendak and Celier. With the dust reasonably settled, there are now two gyros which look like identical twins: the Tercel (Trendak) and the Xenon (Celier). I am sure both manufacturers work hard to make differences apparent but...in all honesty...well...you know those puzzles in the papers where you have to spot the difference...

Empty weight is 295 kg, with a little footnote that says it could be more (according to selected options, of course). How realistic the 295 kg are, I don't know.

"Maximum speed" is 195 km/h. How maximum speed is defined, I don't know. If it is Vne, that I can believe. If it is Vh I am sceptical.

Cruise speed is given at 160 km/h, which I have trouble believing. At 560 kg MTOW I doubt that the Xenon cruises at a CAS of 160 km/h for any useful power setting. In this respect I find the 140 km/h which the Tercel claims much more believable (albeit still a bit on the fast side, but who knows?).

A climb rate of 1200 fpm just like the Tercel, is difficult to swallow. I wonder how it was measured.

Take-off and landing distances both seem to forget about the 50 ft obstacle.

The POH offered for download on the website is for the Xenon 2, even though a Xenon 2 is not offered for sale anymore. No POH for the Xenon 4 is available. But in layout and structure as well as much of its contents the POH reminds me of the Tercel (or the other way around, as the case may be).

Greetings, -- Chris.
 
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ckurz7000

Senior Member
Some of the discrepancies, aside from the hustling aspect, come from the ASI installation.
I agree that the pitot-static system is fraught with errors in many of the current gyro installations and probably accounts for many discrepancies and misconceptions regarding cruise speed etc.

C. Beaty said:
The only satisfactory static pickup for anything with the range of fuselage attitudes of a gyro is the coaxial type; sometimes called a Kollsman pickup. That way, both static and pitot inputs are at least in the same pressure field.
That's what you'd think. But on the ArrowCopter it was different. Initially we tried a coaxial pickup on a carbon fiber rod about 10 cm in front of the nose. We wanted to get clean, undisturbed air as well as static and dynamic pressures at the same location. We were not happy. Results were not as accurate as we had hoped as well as being quite dependent on flight attitude. Next we tried a longer pickup of about 30 cm. Same problem.

So we went back to two static ports, one on either side of the cabin, well ahead of the wing roots, tied together. It took us a couple of tries to find the best spot but now we have ASI to within 2 kts over the entire speed range from 65 to 200 km/h. And much less influenced by flight attitude, too.

Greetings, -- Chris.
 

Steve_UK

Active Member
If you want basic common standard factual data then best not leave this to the manufacturer.

Look at the documents on the link below - six type approval data sheets for different gyrocopters all tested and measured to the same standard. Great.


http://www.caa.co.uk/default.aspx?catid=1419&pagetype=68&gid=1562


Unfortunatley most manufacturers do not put their machines forward for this process.

At the moment only Magni and Auto-Gyro are playing ball.

Arrowcopter are stuck somewhere in the middle of the process - hopefully to be resolved, completed and published soon.

Take care with claims straight from the horses mouth or the horses website marketing brochure.
 

ckurz7000

Senior Member
Here’s the definitive paper on dynamic/static pickups:

http://naca.central.cranfield.ac.uk/reports/1948/naca-report-919.pdf
Yes, that's a mouthful. I actually read this report a while ago. Calibration of airspeed systems has become so much easier with the advent of GPS. But still, it takes knowledge and a certain amount of flying skill. Simply reversing the course and taking the speed average is not good enough.

I admire guys like you and Jürgen who seem to have a vast technical library at their beckon. I know a lot of it is available through the net. But still.

-- Chris.
 
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ckurz7000

Senior Member
If you want basic common standard factual data then best not leave this to the manufacturer.

Look at the documents on the link below - six type approval data sheets for different gyrocopters all tested and measured to the same standard. Great.


http://www.caa.co.uk/default.aspx?catid=1419&pagetype=68&gid=1562


Unfortunatley most manufacturers do not put their machines forward for this process.

At the moment only Magni and Auto-Gyro are playing ball.

Arrowcopter are stuck somewhere in the middle of the process - hopefully to be resolved, completed and published soon.

Take care with claims straight from the horses mouth or the horses website marketing brochure.
I read through some of those reports, Steve. And, yes, a tightly regulated certification process with supervision by the authority is both the nightmare of a manufacturer as well as the best a customer could wish for.

Still, I have a problem with some of the information contained in the POH which are supposed to documents included in the certification process. Reading the manufacturer's information on the web should be data taken straight from the POH, if technical specs are involved. Everything else seems doubtful practice to me.

-- Chris.
 

Vance

Gyroplane CFI
Thank you for bringing this up Chris.

Thank you for bringing this up Chris.

I find it comedic when people want to race what is published in the POH (my gyroplane has a 4kt faster cruise than yours and burns three liters per hour less.)

I have found there is often a disconnect between marketing and engineering.

In my opinion there is no excuse for the drivel that is in some POHs.

I find what is in “Limitations” frustrating and even dangerous.

I would advise any pilot to do their own testing on the machine they fly.

It appears to me that for many manufactures that the POH is just something that needs to get done and the task is often given to the "new guy".

Conditions make such a difference and few people take conditions into account or even understand the process.

It is not just gyroplanes. Last night at a FAST meeting a master CFI advised us to add a gallon per hour to what is in the POH for flight planning (about 15%). He went on to say how accurate his flight planning results were. This was for a certified fixed wing aircraft.
 

WaspAir

Supreme Allied Gyro CFI
It is not just gyroplanes. Last night at a FAST meeting a master CFI advised us to add a gallon per hour to what is in the POH for flight planning (about 15%). He went on to say how accurate his flight planning results were. This was for a certified fixed wing aircraft.
To be fair, a great deal of the discrepancy for certified aircraft is due to aging of and wear and tear on the powerplant, rigging differences and little maintenance issues, and pilot mixture leaning practices. A new Cessna fresh off the line and competently flown will do a pretty decent job of matching the numbers, but most people are flying aircraft old enough to buy vodka or maybe even apply for Social Security.
 

ckurz7000

Senior Member
It would be great to have a gyro testing facility or even only a single person. They would fly different types of gyros and put their test data up on a public place. Kind of like a Consumer Report. Gosh, that would be a fun job to have! Just gotta find someone willing to pay me doing it. ;)

-- Chris.
 

WaspAir

Supreme Allied Gyro CFI
We had a fellow in the U.S. (Johnson) for many years who did real world performance testing of sailplanes using consistent methodology, with results published in Soaring magazine. It was nice to have meaningful results to make valid comparisons. He usually was loaned an aircraft by a proud owner to make the tests, as the models hit the market.
 

loftus

Active Member
As you imply Chris, the only way true comparisons can be made is for all machines to be tested in the same standardized fashion. I think it's fair to say that where some effort is made as with Autogyro, a pretty good ballpark picture can be obtained. Clearly Arrowcopter , with you as their OCD test pilot have gone the extra mile.
For practical purposes, I think 'ballpark' is a pretty good place to start, with the rest being up to the pilot getting to know his machine. I'd also be wary of any manufacture claiming vastly superior performance over 'ballpark' with similarly designed and configured machines. As to cruise specifications, in my gyro I find this to be a pretty wide range based on so many things particularly desired fuel burn and comfort for given air conditions. In my MTO that ranges from 65 - 85 knots. Just changing my prop from the stock MTO, dropped my cruising speed RPM from 400-500RPM for any given speed, and pushed my max level speed accordingly higher.
Chris, just let everybody provide you a gyro to test. They could use it in their marketing 'Chris Kurtz Verified.'
 

All_In

Gold Supporter
It would be great to have a gyro testing facility or even only a single person. They would fly different types of gyros and put their test data up on a public place. Kind of like a Consumer Report. Gosh, that would be a fun job to have! Just gotta find someone willing to pay me doing it. ;)

-- Chris.
Hi Chris
When I 1st came to this site. IIRC Tim O 'Barnstormers' posted he would like to start just such a testing co.
Maybe one day PRA can find a qualified volunteer.
I'll add it to our project list.
 
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