Center line thrust ?

[joeheli]

What is the benefits of a center line thrust beside the other one? I heard that for the Bensen they have the upgrade to make it center line thrust. ???

[Chuck Irby]

Jose,

Primarily, a CLT machine is less prone to PPO and PIO.

You mentioned earlier that you were reading a book. What is the name of it?

[joeheli]

I am reading "Rotorcraft flying handbook" and "How to fly Gyros"

[Chuck Irby]

Jose,
I can't remember if I have read those or not. Do they not cover CLT, PPO and PIO? A good book on gyros should cover these topics in much more detail. Look for it, and if it's not covered, let me know and I'll give you more info.

[joeheli]

Chuck:

Yes, they talk about the topic. About the CLT, can I modify it just by raising a couple of inches up?(3",4",)
corect me if am wrong but the CLT of the gyro is directly
on the middle of engine? ???

[Chuck Irby]

Jose, to make your machine a CLT machine would require a major redesign and rebuild. I don't know, but there may be a kit available for that purpose for your machine.

[joeheli]

Like what?

[GyroRon]

I strongly reccomend coming to Bensen Days and learning all you can.

A stock Bensen with a Mac engine is nearly Center line thrust as it is. If you get rid of the side tanks and use a seat tank it will be real close to CLT and I see no reason for mods. Do add a large horizontal stab though....

[Chuck Irby]

Jose, I agree with Ron. He knows a lot more than I do about this stuff.

Boy, I had a great afternoon of flying.

[GyroRon]

Only reason to mod a Bensen for thrust line purposes would be if you replaced the Mac engine with a engine that turns a larger diameter prop. The Mac engine turns a short prop and turns it at high prop RPM.With the short prop the thrust line, which is the push line from the center of the prop forwards, goes almost right through the center of mass or CG for short.

One way to think of center of mass that is easy to understand - and not totally true for all machines but certainly close enough for this disscussion - Is when you sit down in the seat on the gyro, Where your belly button is located, this is about where the center of mass or CG is. If the props trustline is above your belly button you likely have HTL. If it is at your belly button it is CLT.

If you wanted to replace the Mac engine with a Rotax or Subaru or VW, all those engines use larger diameter slower turning props which would require the engine and prop to be rasied up the mast to allow for prop clearance on the keel. When you raise the prop as a whole you also raise the props centerline. Raise the center line of the prop and you raise the thrustline. If you don't raise the pilot also - which is a significant part of the CG of the gyro - then the thrust line now becomes much higher than the CG and then you have a possible problem and a gyro that is much more likely to hurt you than before. If you raise the prop you have to raise the pilot as well to keep the Cg and thrust line in balance.

That is what was done on my last gyro. It was a Bensen that had a bigger engine and longer prop put on it. To keep it at CLT the pilots seat and all the controls including rudder pedals and stick etc... were raised up the mast to align with the new thrustline. It isn't a very hard mod to do but will take alot of time.

Look at this picture and if you look hard enough you can see a Stock Bensen BM8 under all the mods that were done....

[GyroRon]

And then look at this picture and you will see a newer gyro design that has a stepped lower keel to allow the seat to stay the same distance above the keel in front of the mast, yet be lower in the rear so the center of the prop would still be in line with the pilots belly button.

[GyroRon]

And then this pic shows a machine with even more of a step in the keel to allow a even larger prop to turn yet still be in line with the pilots belly button.

Note.... A Mac powered gyro uses a prop in the 40 inch diameter size range. The Falcon in the second pic uses a 52 inch diameter prop and the dominator in the last pic - along with the black Bensen above - uses a 60 inch prop. The larger the prop, the more the keel has to be stepped or the higher the seat has to be raised.

[Chuck Irby]

Jose, This is some good info for you. Just send your check to Ron Awad.

[gyromike]

Note.... A Mac powered gyro uses a prop in the 40 inch diameter size range...


Not quite Ron.

The smallest prop on a Mac that I've seen is 48" diameter.

I swing a 52" X 26" Tennessee Prop on my 90 Mac.

[Aussie_Paul]

If I remember correctly my dads prop on his Mac in the early 60's was 49".

Aussie Paul.

[Heron]

Just remember that a well design gyro does not want to "do"things on its own, it reacts to pilots imputs.
It is more maneuverable and have a larger envelope for more fun.
Braking with the past is a good thing, we have materials and engines today to build a modern gyro!
Heron

[GyroRon]

Sorry guys :o :o :o I knew it was less than 50 inches in most cases I just didn't know where. That was why I said in the 40 inch range which could be from 40 inches all the way up to 49.99999999 inches! But do tell Bensen experts, what prop came standard on a plans built BM8?

[joeheli]

Thank you Ron , now I understand . And you guys too!! ;D

[bogman]

Ron I'm no expert, but my Bensen with the Mac has a 48" prop.

[Caribean_gyro]

Let me share my 2 cents .
If you learn the correct way, you read, you ask, you internalize all of this how this aircraft work and how we should treat it. We will be on the safe side.

I learn the old bensen way, then a friend died in a aircommand. Reason high blood preasure and sugar level "heart attack" SO wasn't the gyro.

I decide I need more information . So I took aiplane lessons,gyro lesson and soon helicopter lesson. I am alwasy learning with every CFI I fly with and evry person I fly with .

Is there a safe gyro NO. Is there a Safe Pilot NO. I said this becasue no matter how safe an equipment is we humans find a way to screw up.

And no matter how safe we fly again We humans like to impress others.

Have done it. I have been in PPO and let me tell you droping 800 foot is not a happy thing. What save me was "CFI talking in my brain" shut the power pull the stick , calm down. Next step read study more etc.

Any way happy safe flying.
Chuk P.

[Greg Mitchell]

Gentlemen,

I posted this about a week ago for Paul Bruty to comment on OZ forum.

Dr Houston's report re; thrustlines being no more than 5cms plus or minus. I find this to be a dilema. Greg Grimminger theories suggest thrustline needs to be above CofG with neg angle of attack HS. And you and others seem to agree with this, (if I am wrong, I apologise), BUT many in the CLT Camp (and you do talk the CLT thing), suggest the thrustline needs to be on or just below the CofG. Dominator, SparrowHawk, Butterfly/Monarch. I ommit the Aussie craft simply because I don't have enough detail/specs to comment on them, though I would think that Owen Dulls and Murray Barkers craft designs may fall into this group also. I don't know.

Anyway, there is a bloody big spectrum there in that plus or minus figure. 2" or 2 1/2" doesn't seem like a hugh range, but when we look at all the variables, your CLT and my CLT are definitely different. You could help us all out by telling us who you think is most correct given this CLT thing seems to present more questions than answers.

The guys who are looking to get thrustline on or below are trying to remove the PPO effect given rotors are unloaded for whatever reason.
Whilst Greg and the PRA seemed to espouse CLT sometime ago, there appears to have been a very definite shift by Greg and perhaps the PRA toward this Airspeed, Power and G-Load Stability only being attainable with slightly high thrustline and Neg angle of attack HS.

This may account for some of the rank and file clubs in the US wanting to distance themselves from the PRA. Greg makes a powerfull arguement, intelligent and articulate. BUT is he right, or simply trying to justify a high thrustline product??? Everyone, manufacturing or distributing craft will claim there's is the way to go. And yet I am fighting this temptation with respect to the Butterfly/Monarch. I don't want to sell them, they should do that on their own merit, proof is in the testing.....RIGHT.

Thanks Paul,

Mitch.

Any comments re: CLT would be appreciated.

[Aussie_Paul]

Sorry Greg, just been too busy. Aussie Paul. :-[