Max speed of gyros?

[rtfm]

Hi there,
While I appreciate that a major part of the 'fun' of flying a gyro is the journey itself rather than the destination - I'm intrigued by the fact that the 'magic' speed barrier for gyros seems to be 100mph, while that of modern kit planes seems to be 200kts. Why is this? Is it because of the inherently high parasitic drag of gyros compared with that of fixed wing aircraft? Or does it have to do with the induced drag of the rotors? Or is the relatively low speed of gyros rooted in something else?

Regards,
Duncan

[StanFoster]

Duncan: Retreating blade stall is the big limiting factor for forward speed. You have an advancing blade which is the one that is going forward and itis going through the air at its rotational speed plus the speed of the gyro. The other blade is the retreating blade and its airspeed is the rotational speed minus the forward speed of the gyro. The advancing blade is flapping up resulting in a lesser angle of attack..while the retreating blade is flapping down increasing its angle of attack. These blades do this automatically acroos the flapping hinge automatically to balance out the forces on each side of the rotor.

There is a circle of reversed flow on the retreating blade side that grows larger as the forward speed increases. This causes the angle of attack to steadily increase on this retreating blade side as the forward speed increases.

The blade starts stalling and it has reached its limit.

This is a very simplistic explanation..but there are all kinds of sources to go into this in very fine detail.

[rehler]

To compare to a fixed wing aircraft to a gyro you should find one with a similar sized engine and aircraft weight with a wing or wings having a total area of 450 square feet. This is the "wing area" in flight of a gyro with a 24 foot diameter rotor (the total disk area). Let's say two wings (bi-wing), each 7' wide by 32 foot long.

There is a LOT of drag by the "wing" of the gyro. Not too unlike a paraplane.

[PTKay]

Comparable UL from Czech I am testing to buy:

Qualt 2000, (see my logo pic)

450 kg MTOW, Rotax 912 80 hp, Vne, 150 mph, Vmax level 140 mph,
V stall 40 mph, Vcruise 75% 110 mph.

It flies really nice, although taildragger.

PTKay

[Harry_S.]

If you want to zip cross country @ 150 kts. fly fixed wing.

If you want to have fun & stir up a little air down low for a couple hours, fly a gyro.

[rtfm]

Hi Harry S
Couldn't resist it, could you? :D I thought I'd made it perfectly clear that I wasn't whinging about the speed of gyros cf fixed wing, but that I was simply puzzled by the very different max speeds of the two types. It was a technical question, not an invitation for folk to state the obvious. Aah, well...
Duncan

[Screw]

Gyros with a small rotor can have faster cruise speed than a gyro with a large rotor because of the stall speed of the retreating blade on a smaller rotor. Therfore, If you had a gyro with two small rotors with enough disc area as single one needed to carry the same wieght, you should be able to go faster. The question is why would you want to.

[RHerron]

Duncan,

You have it figured out. It is the induced drag of the spinning rotor. Remember that the rotor blades (wings) are going very fast through the air although the rest of the aircraft isn't. In a fixed-wing, everything is going the same speed.
This is the essence of Cierva's invention. He didn't want the airframe and wing to have the same airspeed. He wanted the 'wing' to have its own independent airspeed and not depend upon the occupants having to move at that speed.
This did away with the conventional fixed-wing stall/spin issues, clearly a serious problem even today.
And...this gives the autogyro its inherent, special flight qualities which include the ability to fly slowly (safely) and land very slowly. In addition, it doesn't have the mushy feel of a fixed-wing in slow-flight. Furthermore, it is much more pleasant to fly in turbulence (if properly configured).
The tradeoff is that it isn't a particularly fast aircraft and is "power-hungry" compared to a fixed-wing of the same weight and power.
Most anyone who has flown a gyro is quickly hooked on its flight characteristics.
Fixed-wings are the best traveling machines and the gyro is the best sport flyer...my opinion.

[cgmg]

I agree that gyros are the sport flyers of the sky. Ten minutes in a fixed wing on a turbulent day, and I'm heaving my cookies.The constant rolling and yawing in a fixed wing does me in every time. Give me two hours in a gyro in the same conditions, and I'm having a ball.

It's been four years since I soloed, and I still get a rush out of landing in our gyro. And when the crops are gone, I can buzz all over within a 15 mile radius of our strip at 20 feet above the ground, knowing I can land with little or no roll if needed. Try doing that in a fixed wing, and you're guaranteed to plow dirt if your engine quits.

I had my first engine out at 50 hours of experience, and landed in a standing bean field with no damage to the machine. The only real problem was pulling the beast out of the beans to the road, and getting it on the trailer.

If you want to go somewhere fast, fly fixed wing. If you want to feel like you're going fast, even when you aren't, fly a gyro, and fly low when the terrain permits.

Always, always, always, don't fly over what you can't land on if your engine quits.

[PW_Plack]

There used to be a page on the flygyro.com website regarding world records, and I haven't been able to find it today, but didn't Wing Commander Ken Wallis fly a 60 HP gyro at just over 130 MPH?

[mcbirdman]

I may be wrong but I think I read that retreating blade stall is the reason helicopters can't go over 180 or so mph -.
It is apx the maximum amount of forward speed of the aircraft combined with rotor tip speed that would result in the rear edge of the blade actually going backwards compared to apparent wind, thus the stall.

I think that it is not retreating blade stall that dictates why most gyros only top out at 100mph. It is the huge amount of power that it would take to overcome the drag that occurs in these machines. Most of us just don't have the power available to overcome these draggy machines.

[birdy]

After attending the oz nationals on the weekend I was impressed with the diversity of the 23 machines that attended,big,small,powerfull,not powerfull,slow and unfortunately,there was a fast one.I haven't seen many gyros before but I know they are the safest low,slow machine ever invented.
This low hour pilot,with a very high power to weight ratio was flying way too fast,especialy in the gusty conditions.He was scareing the hell out of me,so much so,I couldn't watch after he climed steeply on full power from 20' ,then hit the stronger wind at 100' and almost went over backwards.Thankfuly,he bought a fixwing machine that was for sale at the strip,and hopefuly he will sell the gyro.

Please,gyros are not for speed,they are for low and slow,speed will kill you faster than you can blink.

Horses for courses.

[Doug Riley]

If you think about it for a minute, you'll recognize that the rotor blade that is travelling forward at a given instant has airspeed equal to its rotational speed PLUS the gyro's forward speed. The blade travelling backward has airspeed equal to rotational speed MINUS the gyro's airspeed.

We can accommodate this difference for modest forward airspeeds by using a mechanism that changes the angle of attack of one blade compared to the other as they rotate. At some forward speed, however, such a mechanism gets overwhelmed by the airspeed difference. At that speed, the forward-travelling blade is going so fast that it becomes both unstable and unduly draggy. At the same time, more and more of the back-travelling blade is stalling.

[scott heger]

I can get 120+MPH in a dive out of my SportCopter. Not bad for a Rotax 582. While watching the rotor tach, the blades continue to accelerate past 100 MPH then seem to hold rotor speed. I would not think retreating blade stall is much of a factor in my particular machine, or most single place small engined gyros, just the lack of horsepower to go any quicker. I have been told a SportCopter has hit 140 MPH in a straight down full power decent, but I'm not going to find out.
The biggest problem to me, flying at 100+ is the wind blast in a open frame. It just is not comfortable for very long, and makes you tired quickly. Cruising around at 70-80 is much more fun. My helicopters VNE is 150 MPH, at around 140 , it starts "talking" to you, and at 150, you dont need a airspeed indictator to tell that the thing does not want to go any faster. The cabin gets a hop going and the controls start looseing some sensitivity. Two blade rotor systems normally are worse than 3-4 or 5 blade ones. However I have been in a A-Star350 at 155 MPH , and the thing is as smooth as going muchslower. Just depends on the machine, not unlike many of our gyros.

Scott Heger, Laguna Niguel, Ca N86SH