Gyro History

C. Beaty

Gold Supporter
Here's some material from the book: Cierva Autogiros by Peter Brooks:

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raghu

Senior Member
Many knowledgeable folks, even back in Cierva's time, knew that gyros are not the most efficient aircraft. Cierva of course strongly disagreed and argued that gyros had the potential to perform very close to FW aircraft. In1930, he said Gyros were within 5% to 10% in terms of top speed with FW. Some of the debates on this between legendary Aero Boffin Glaurte and Cierva in contemporaneous literature make for entertaining reading. Today of course we know Glaurte was closer to the truth than Cierva. But how big is the difference in top speed for the same power in the kind of aircraft we fly, say an LSA?

By my estimate a well optimized LSA class gyro the penalty in cruise would be about 25% ( 2 times more drag than a FW LSA). Do any gyros today come close to this value? The Calidus is a closest to a streamlined gyro. Comparing it to a modern FW LSA by flight designs we find cruise at identical fuel flow (4.8 Gallons per hour) is 100MPH for Calidus versus 132MPH, a difference of 32%.

How do we get these numbers? In gyros today the biggest component of drag at cruise is surprisingly not the rotor but the parasite drag of everything else hanging from the rotor. How close can we get to a typical LSA FW performance if we replace wing with a rotor? Assuming the span of the FW and the Gyro rotor are identical the induced drag of both aircraft will be nearly the same. The difference is in the profile drag between the rotor and the wing. A rotor has a L/D of around 8 to 10 and the L/D of a modern LSA FW wing is about 4 times less at 30 to 40, if we consider profile drag at cruise. The wing profile drag at cruise typically contributes about a third of the the total drag. All this means is that the gyro should have about 2 times more drag than a similar LSA FW and at the same power the FW will fly 25% faster at cruise. In reality the numbers may be a little higher as I have ignored mast and hub drag. All in all not too bad and gyros should make practical LSA aircraft.

raghu

Senior Member
It turns out the speed difference for identical power between Flight designs and Calidus is actually a little closer- 27% rather than 32% slower. I had a CAS TAS issue that I have now fixed in the above post. With rotor technology as they stand it is hard to see this improving significantly below 25%. I think scaling gyros to the RV class airplanes- ~1600lbs AUW on 200HP , cruising ~140 MPH would be interesting.

Gyro_Kai

Senior Member
But, as you get faster, don't the scales tip further towards the FW? There is a limit as to how fast you can fly in relation to your rotor blade tip and the faster you go, the more of your retreating blade is useless.

Kai.

anthom

Member
Is it beneficial to have faster turning rotors as opposed to slower ones in order to reduce the effect of retreating blade stall at comparatively faster forward speed than for a slower rotor? My understanding is that induced drag of the rotors will also be less as rotor speed increases. However parasite drag of the gyro would increase. How much would be the overall drag increase?

Example, 24 ft rotor turning at 300 rpm forward speed at 100 mph vs 24 ft rotor turning at 350 RPM at 100 mph. What will be the overall effect of retreating blade stall in both situations? Will it be possible to increase the forward cruise speed in the latter case without penalty?

Thank you.

raghu

Senior Member
But, as you get faster, don't the scales tip further towards the FW? There is a limit as to how fast you can fly in relation to your rotor blade tip and the faster you go, the more of your retreating blade is useless.

Kai.

Yes, absolutely the scales do tip in favor of FW- there are hard limits due to retreating blade stall. Advance ratio (mu) of 0.35 is close to best L/D and 0.5 is where retreating blade stall becomes an issue. However, your typical gyros (euro/bensen clones) cruise well below mu of 0.35 and hence there is opportunity here with appropriately sized rotors. As I mentioned the main reason gyros in our recreational class are slow is because of the enormous parasitic drag contributed by the non rotor components.

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WaspAir

Supreme Allied Gyro CFI
I think scaling gyros to the RV class airplanes- ~1600lbs AUW on 200HP , cruising ~140 MPH would be interesting.
Sounds remarkably like the A&S18A and McCulloch J-2 in size and power . . .

kmtck

Newbie
It turns out the speed difference for identical power between Flight designs and Calidus is actually a little closer- 27% rather than 32% slower. I had a CAS TAS issue that I have now fixed in the above post. With rotor technology as they stand it is hard to see this improving significantly below 25%. I think scaling gyros to the RV class airplanes- ~1600lbs AUW on 200HP , cruising ~140 MPH would be interesting.
Raghu and Chuck, how about partially powering the rotor to lower the overall drag? Is there a path to move from 25% to maybe 10-15%?

Waspair, what do you cruise at in A&S?

C. Beaty

Gold Supporter
Sounds remarkably like the A&S18A and McCulloch J-2 in size and power . . .
And they sold like hot cakes, didn’t they?

Hobycopters are consumer products, no different than tennis sneakers; all depends upon perception and appearance.

I’m content with Walmart’s \$10 sneakers but the “in” crowd will settle for no less than \$100 Air Jordans.

WaspAir

Supreme Allied Gyro CFI
Waspair, what do you cruise at in A&S?
It's much more comfortable at 85 than anywhere near 140. I have business cards that have a logo on the back reading "twice the horsepower, half the speed!" that fixed wing pilots find amusing.

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raghu

Senior Member
Sounds remarkably like the A&S18A and McCulloch J-2 in size and power . . .
yeah, but with half the parasite drag.

Of course recreational aviation is a tiny niche and gyros are a nice within a niche. Its never going to be a mass product. That said CB was of course saying the same thing circa 2000 about the dreadnaught gyros and how they make no sense and then came the euro clone revolution.

You can disparage them as clones, not original, benson copy cats etc., and I do not disagree. But the reality is the euro clones have transformed the gyro world. We have never seen more hours flown by gyros ever in history. And the safety record has matched (if not bettered) the early cierva era. Which is incredible give where we were a decade or so ago. While the US was theorizing/obsessing about thrust line and CG the europeans pragmatically built a reasonable (for recreational aviation) size market and launched a range of attractive (nothing wrong with that) high performing gyros.

PS. And just for CBs benefit ....I have no relationship (paid or otherwise) with the euro folks. Personally I am more of Little wing/tractor guy but you cannot deny the impact of the euro gyros.

anthom

Member
Although the Euro style gyros are Bensen clones, these products have evolved in the last 20 years. They are more streamlined than the original Bensens, are fair cross country machines, have decent horizontal stabilizers, have more instructors for training, and are being manufactured in large numbers driven by consumer demand. IMHO seeing the trend, I'm afraid that in the USA, the days of the small singles and the certified jump take off gyros are numbered due to the appeal of flying under Sport Pilot regs.

WaspAir

Supreme Allied Gyro CFI
yeah, but with half the parasite drag.
That will be a tall order. The tandem 18A isn't stylish by modern gyro standards, but it has well faired gear and engine cowl, and a decent cabin enclosure.

WaspAir

Supreme Allied Gyro CFI
Scanned the back of the business card for your entertainment. Note the unconventional pilot's wings design; the leading edges don't point in the same direction (usually both leading edges are facing up) because, after all, this is ROTARY wing flight, and the wings must be made to spin counterclockwise.

Jean Claude

Junior Member
How about partially powering the rotor to lower the overall drag?
Partially powering the rotor to lower the overall drag is a bad mean. The power gain by the lower drag is about the same that the power put on the shaft.
A benefit appears only if Rrpm is keep unchanged by increasing the blade pitch.
But then, if this benefit becomes significant it requires reduce immediately the pitch blade when engine out because the Rrpm loss is dangerous

Smack

Re-member?
Partially powering the rotor to lower the overall drag is a bad mean. The power gain by the lower drag is about the same that the power put on the shaft.
J.C., do you have any scientific evidence for that statement or is it just 'opinion'?
I'm used to equations from you.
Brian

Jean Claude

Junior Member
This is the result of my spreadsheet, Brian, when I wanted to quantify the expected gain.

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