Ducted Fan Gyro

Hi, I am new here, but I don't understand something.

Matt wrote: "If it weren't for the prop, gyros would all be sleek and "low profile" and not so "gangly" looking. Oh well, maybe someday."

What about ducted fan.

I think I have seen some like this, what happend to them ?

PTKay

[ToddP]

I can guess three reasons:

1. Expense
2. Fuel Burn / Load
3. Slow throttle response

How am I doing here?

Thanks Todd,

but what do you mean by that:

1. Expense

If you are anyway having a tall tail
with it's mounts and fixes why no something round
instead.

Gives prop protection etc.

Also with ducted prop you can run higher revs
so no reduction needed on your engine.


2. Fuel burn

With low, sleek gyro you will certainly have lower burn.
(No high wheels, lower cabin - glider style etc.)

3. Reaction

Of course you sometimes need sudden thrust blow,
but how often ?

Besides of that comment.

Do you know any successful (flying) ducted fan gyro
except for the Canadian device form the 50ties.

PTKay

I found some news on it by Pegasus.

Do you know anything, if they are active at all ?

PTKay

Maybe I am wrong writing "Ducted Fan"

Maybe Ducted Prop will also do with all
the advantages of Ducted Fan and no disadvantages.

BTW Pegasus is:

http://www.pegasusrotorcraft.com/index.html

PTKay

[twistair]

One of the problems with ducted fan is that it is not so simple to build it effective as one could imagine. It's supposed that really effective duct cannot be designed and built without serious science and experiments. I don't know much about details but I talked about it with our TsAGI brainers. Two things which come in mind from these conversations first are:
1) for good efficience the clearance between collar and prop should be some millimetres only (which also adds the problem to make the duct+engine+prop system rigid enough to avoid strikes in flight
2) the collar should be calculated very carefully to reach real efficiency
BTW, I remember that one of such gyros built by individual was described in 'Contact' mag in 1999. It was available in the Net at http://www.geocities.com/eaa108/9903news.htm but seems to be unavailable now. In case it's missed I have this article saved on my comp. (added: I checked it - the page is still available). Attached is one of the subject photos.
Vic Shumeiko built ducted fan gyro in late 80's here but flight testing wasn't long due to some circumstances. He used old Schkoda engine which brought him good numbers in thrust.
As for Pegasus it's real name is Avian 2/180. It was designed in Canada in late 50's-early 60's, some prototypes were built and test flown. It was certified by CAA but never manufactured in series.
This particular aircraft shown at the photo is sitting I believe somewhere in California. It was restored from one of Avian prototypes but not flown after restoration.
I've contacted this old man who owns it. He hopes to get this gyro manufactured again but I'm not an optimist about his chances. BTW there are two good but huge videofiles at his website, they show old Avian flights. Some good photos of Avian prototypes can be found at Hofstra website.
Peter Payne, author of famous "Helicopter Dynamics and Aerodynamics" manual, was one of Avian's designers. Two years ago I've contacted his son who told some interesting details on Avian's story.

Cheers,

Alex

[mceagle]

Propeller effeciency on low speed aircraft drops dramatically with decreasing diameter, ducted or not.
A 24" fan behind 100 hp would not have the push to run over your toe.
However, at 160mph it is a different story.

[ToddP]

PTkay,

I apologize. This morning, before coffee...and thinking, I replied to your post. I got in my head "fan" and immediately thought turbo-fan or turbo-jet like the Williams turbojet engines.

http://www.gasturbine.pwp.blueyonder.co.uk/wr24.htm

I'd still have to go with expense as a problem though. I can't imagine a ducted fan setup wouldn't be considerably more expensive than a conventional propeller and tail arrangement. There would have to be some pretty hefty engineering costs and a very limited market to recoup those costs.

Thanks Everybody,

my comments to you opinions are:

1. There is plenty of off-shelf ducted fans (props)
used by the hovercraft people. Since these machines are far
more popular than gyros I can assume that all the engineering
is already done and well tested. So why reinventing the egg.

2. Regarding speed effectivity, as far as I am concerned
the ducted fan gives solid staedy thrust already by very
low air speeds (see above), that's why they use them for
ground vehicles.

3. I know everyhing about the Avian (and Arrow) history. It's very
interesting and educative :'(
I just hoped that the Pegasus people sucseeded in something...

4. Of course the example of the ducted fan gyro is interesting,
but obviously taking no advantage of this solution.
It's aerodynamicaly "dirty", using transmissions with 1:1, what
for ? just ads weight. With modern, slic plastic constructions
proper fan could add for low profile on ground and good yaw control.

McEagle wrote:

"Propeller effeciency on low speed aircraft drops dramatically with decreasing diameter, ducted or not.
A 24" fan behind 100 hp would not have the push to run over your toe."

I think you are basicly wrong.

The idea of a ducted fan is, that even by 0 vehicle speed
the air speed inside the duct is high, that's the trick...

"However, at 160mph it is a different story. "

Yes, this is a differet story, because even by 10 mpg
ground speed on gyro the air speed in full runnig fan
is the 160 mph mentioned above.

But maybe I am wrong.

PTKay

[twistair]

Of course the example of the ducted fan gyro is interesting,
but obviously taking no advantage of this solution.
It's aerodynamicaly "dirty", using transmissions with 1:1, what
for ? just ads weight. With modern, slic plastic constructions
proper fan could add for low profile on ground and good yaw control.

It's not obvious that the ratio is 1:1. I'd rather say that it apparently has some reduction ratio.
The main advantage of the subject gyro is that it was finally built. After all you have an excellent chance to astonish us with your own - flying - design ;).
It would be also nice if you could fill out your profile with at least your name and location as it is prescribed by this forum rules. People should know their heroes ;D.
As for the existing solutions for ground vehicles they may be simply too heavy for light gyro though aerodynamical solutions apparently should exist. I'm now discussing this with our local guy who is experienced enough in designing different props/fans for years. Since I'm also playing with airboats a little it's very interesting theme for me too. I have a small 160-hp airboat which could be used as a testbed for ducts.

[Screw]

I like the small turbine engines.

[Screw]

not sure how to post a link...http://www.atpcoinc.com/files/Engine2Small.wmv

Hi,

I still insist on maybe "Ducted Prop".

Turbines are gas guzzlers, maybe nice,
but certainly not for gyro.

Of course it is nice to fly on Jet fuel, but you can do do it with piston diesel engines at lower cost.

Alex,

as you probably noticed from other forums,
(PolishCopter, Diesel etc.) I am from Poland, near Warsaw.
I am a total aviatics "amateur", but also freak.
At the moment thinking what kind of flying machine I should
buy or bulid.

Therefore my posts and questions regarding all aspects of flying.

Of course "dirty" means nothing more than "not aerodynamically clean".
Nothing more than that.

Will be happy to share all your experiences on your boat and other developments.

PTKay

[PTKay]

I talked to some hoovercraft people.

They can help if asked.

PTKay

BTW: my profile is updated

[PTKay]

Twistair, Alex,

sorry for not keeping the rules.

My profile is updated.

PTKay

[twistair]

I've also accumulate some info - it's not optimistic. As it was earlier supposed, all this ground vehicles stuff is heavy and doesn't work at higher speeds. To design new stuff is too costly for individual design. Profi told that the duct has sense ewhen you need max thrust at VERY low speed - to push the ground vehicle over the small obstacle or to drive it upward a hill for example. When speed grows the Cd of the duct grows too fast starting from 70-80 kmh. Sure it should be estimated in numbers more carefully to show that the idea is good or bad but it takes a bit more time. I'd leave it for some weeks.

[PTKay]

I found on another discussion a dual prop.

The dual engine machine is owned by GE, of course! Look at the number on the rudder.

Actually this machine was built by Gary Goldsberry and Art Evans. It went thru several iterations and this is the first time I saw it with the two props inline. Counter rotating?

[PTKay]

Another pic

[twistair]

Very transparent duct :)
Seriously, PTkay (I wonder what part of nick is the name :),

if you're just looking what to build then I'd suggest not to sink in to debris. I use to tell our newcomers (almost everybody tries to find the obvious genius thing which he thinks nobody tried before ;D that you should choose first who you wish to be yourself: designer who has a miraculous chance to fly his child years later or the wannabeapilot who wishes to fly himself soon. If your choice is second - stop your research and just take a proven design, build it and fly it. All other (except of buyinf ready to fly one) choices may end in the hungar years later. It is way easier way to jump into the sky. If this jump enjoes you - then you can try to build your own contraption. But you'll already have some real experience, not only Inet photos and talks.

Just from my own experience :)

[PTKay]

Alex,

I agree with you.

As you know from other forums I am seriously in contact with the PolishCopter manufacturers.

It's winter here now (you know it better than me down in Moscow), so before I can test or check anything "hands on" I am just browsing all ideas and possibilities on the web. So to say flying "virtually". It is much easier, warmer and safer, first of all.

I just really dont like this tall legged gyros, like the "Ochotnik", with no cabin. And with cabin you start to get in aerodynamical troubles.

So before I see the PolishCopter flying safe and steady I will keep bugging the forums with some questions.

Maybe this will help the next version of the PolishCopter be just perfect.

PTKay

BTW: The P is for Paul - Pavel ;)

[rfi]

Ducted fans are efficient up to around 125 Mph. Jim Miller tried a ducted fan on his racing airplane, Pushy Galore and found that at 180-200 Mph the duct had so much drag that it actually reduced speed, but in the 0-125 range it is quite efficient.

I talked with an old fellow a few years ago that helped develop the ducted fan on the Avian 2/180. He is a retired aeronautical engineer who lived in Prescott, AZ when I talked with him. He said that they started with around 800 pounds of static thrust with the unducted prop and ended up with close to 1100 after a lot of cut and try work.

I think the best way to maintain the 1/16 inch clearance between the prop (or fan) and the duct is to have them rigidly attached to each other. One would need to use a short constant velocity driveshaft such as one used on the front wheel drive for automobiles and decouple the prop/fan from the shaking engine.

The reasons a properly designed ducted fan is more efficient than an unducted prop are two fold: 1) the duct acts like an infinitely large end plate which eliminates the tip vortex and improves efficiency, and 2) the duct is typically a thick airfoil section that develops a lot of lift. The lift vector is not perpendicular to the chord line but is tilted forward a few degrees which results in some forward thrust. that is the same phenominom that makes rotor blades spin around.
If one spend a lot if time and properly designed a good ducted fan system it would probably be pretty efficient, and since the ducted fan can be run direct drive with a smaller diameter prop it should weigh about the same as an unducted prop system with a reduction drive.

The only advantages would be reduced noise and high thrust at very slow speeds.

[PTKay]

Don,

for me the other advantage is smaller diameter, it means lower legs and normal keel on CTL gyro.

Another aspect is safety, it is safer for the people around and for the propeller itself. The duct is a protection at the same time.

Again a question, I have seen some films and magazines with nice streamlined ducted fan gyros. Can anybody tell me what it was ?

PTKay

[PTKay]

Alex,

(transparent duct)...

it was more about a smaller prop diameter than a duct. With counterrotating dual props you can have the same effect like with ducted fan, same thurst lower size.

Another problem with big props (solved with duct or dual) is roll moment.

I don't know how big this problem is, but for me seems worth discussing.


PTKay

[PW_Plack]

PTKay,

Chuck Vanek, whose company was called Vancraft, tried to develop a ducted-fan gyro in the late 1950s here in the Northwest US. (He still has the shroud in storage above his garage.) Perhaps not coincidentally, he also built an operating hovercraft powered by the popular McCullough drone engine. In any event, he eventually gave up on the duct and removed it from his gyro, leaving him with a tall tail much like those in common use today.

I don't know how many other members of the local PRA chapter tried to build ducts, but several of them wound up flying tall tails like Chuck's in the early 1960s. I'll see if anyone at this weekend's chapter meeting knows any more details.

I've looked very hard at ducted fans, because they seem like an obvious strategy to align center of thrust, center of pressure, and center of mass. The extra weight of the duct shouldn't be more than the redrive it could eliminate. Some attention to the aerodynamics of the engine would probably be needed to reach the efficiency level expected.

Here's the story of an experimental fixed-wing plane whose builder uses a ducted fan with a Mazda RX-7 engine, with no redrive:

http://www.bridgingworlds.com/DUCKT.HTM

[PTKay]

I found it in one book on Ducted Fans:

Autogyros
Although it can be argued that autogyros (rotorcraft whose lifting rotors are not powered) are
not inherently high-induced-drag machines, nearly all the machines currently on the market or
built from plans are designed for low takeoff and landing speeds rather than high cruise
performance. As a result, they need a great deal of static and low-speed thrust from their
powerplants. This already makes them good candidates for ducted fan propulsion, but another
factor is now intruding, namely noise regulations. Autogyros are noisy! Ducted fans allow lower
installed power, lower source noise and faster climb—all tending to reduced perceived noise.

And the biggest drawback for the DF, the limited speed range is no topic for the gyros, they have limited top speed anway, so the range 0-100 kts is more than sufficient, and this is well developed for DF.

So I am still surprised, why so few were designed... ???


PTKay

PTKay

[twistair]

So I am still surprised, why so few were designed...

It's simple: there are no military billions invested in this part of aviation.
As it was summarised above, the proper DF is true complex thing which needs true R&D. Guess, what is an hour rate for wind tunnel? Then take a look at modern gyros design - the real state of art (in professional aviation terms) parts are quite rare in them. The reason is same - cut and try costs. As one of our silverhaired guys likes to tell, "any aircarft design is everytime just known compromise between aerodynamics and budget. This last counts first." It's a good explanation on what we see these decades in gyros designing which R&D budget comes from us ourselves only.
Another saying of the same person is (he is a technical supervisor for experimentals here): "...in this aircraft certain cons outweigh doubtful pros" ;D. This may be an answer on DFs.

[twistair]

This one is at the Russian Air Force service ;)

[PTKay]

Alex,

this is a beauty, exactly how I imagine a practical,
safe and grown up gyro. Do you have any more specs on this one.
;D

I hope it is not top secret russian army development...

Is there a civil version available, does it make jump starts ?

In any case please give us as much information as you can get.

Paul

[PTKay]

Don wrote:

"Ducted fans are efficient up to around 125 Mph. Jim Miller tried a ducted fan on his racing airplane, Pushy Galore and found that at 180-200 Mph the duct had so much drag that it actually reduced speed, but in the 0-125 range it is quite efficient."

It's good for me, I havn't seen any gyro going more than that. ;)

Alex,

you say, "wind tunel time is expensive..."

It seems, that all the gyros that were developed by professionals in wind tunels (the Russian military above and Avian) are ducted prop (mayby let's talk Ducted Prop DP, instead of Ducted Fan).

You can argue, that CarterCopter is developed by pros and no DP, but they aim at speeds more than 125 mph, and braking Mu, so see above...

The drag of in-prop-wash, large H and V stabs suggested on other dicussions (AAI e.g.) is certainly higher, or the same, as the Duct for the Prop, with small yaw steering plate, like the ones on Avian and your image above.

The horizontal and vertical areas of duct are big enough to do the function of all kind of stabs.

The modern composite technology should be good enough to manufacture something like this, not more expensive that the stabs mentioned above. Also the mounting of the duct is nothing more than mounting of the high "cross" stab.

Thats my opinion.

Now we have to find somebody brave (and rich) enough to test it.

;)

PTKay

[twistair]

this is a beauty, exactly how I imagine a practical,
safe and grown up gyro. Do you have any more specs on this one.

I hope it is not top secret russian army development...


Sure it's a big secret so, please, do not tell this to anybody: this device never flown. It's, say, designer built half a dozen of similar things displaying them at different airshows, military parades etc. But no one ever flown. Keep this secret!

[PTKay]

Alex,

it's a pity, it looked so nice.... :'(

Paul

[Brent_Brown]

Paul this is for you.

[Brent_Brown]

It has a Hirth F30 motor and was used as a powered paraplane before they added the blades

[Brent_Brown]

http://www.absaerolight.com/ Here is the wed site I got that photo from

[Brent_Brown]

From what it looks like it should fly OK the big body is countered by the big ducted fan. so if the thrist is good it will fly. looks heavy to me. So let get rid of the body and make it an single sseat open gyro and it would be able to use a smaller motor maybe.
Just wood for the fire

[Brent_Brown]

This is off a hovercraft if we can make the duct light it will work OK

[PTKay]

Thanks Brent.

PTKay

[le-wardy]

Alex,
You mentioned of talking to someone who had some 'Avian' flying footage on their website. Could you post a link to this website, so I can download it to watch it. I am very interested to see how the Avian flew.

Many thanks,
Les.

[Brent_Brown]

the new look