Engine thrustline

[scottessex]

I have noticed that some gyro's have the engine thrustline in line with the keel.
Some like the sportcopter, have the engine tilted, up in the front.

And bensen plans called for the engine to be tilted down in front. What gives??? ??? ???

[Udi]

The most efficient configuration is when the engine thrust line is in line with the CG, and parallel to the flight path. I assume that the Bensen engine is tilted down in order to get the engine thrust line to pass closer to the CG. This makes sense. The early Autogiros (tractors) engine was tilted nose down, for the same reason. You don't lose much thrust by tilting the engine 3-5 degrees, and it makes sense to do it when the moments about the CG are otherwise not balanced.

The Sport Copter engine is tilted upwards because Jim Vanek found this configuration to work best for his machine. I am not sure that we can explain it from a theoretical point of view.

Udi-

[Douglas Riley]

The engine on the Sport Copter is tilted the way it is becauser Jim Vanek's father, Chuck (a city fireman who "designed" and marketed gyros as a sideline) had been doing it that way since the early 60's. Jim picked up where Chuck left off. Chuck called the business Vancraft.

[Greg Mitchell]

G'Day Gentlemen,
Posted below on Oz forum and would like some more answers if possible. Thankyou. With respect to SportCopter angle thrustline.


The thrustline pushing up ward is providing some of the lift?

Is this part of the climbing out on the prop stuff?

I read somewhere, that not only is the thrustline slightly high relative to the CofG but it's also pushing up over the top of its mass because of the thrust angle. Which in effect makes the thrust CofG offset even greater.

What advantage would be derived from the propblast striking the Horizontal Stabilizer at that angle, will it be helping to hold the nose up, by providing a down force on horizontal tail surfaces?

Is there a difference, in the forward thrust moment, of negative and positive angled thrustlines, pushing the mast forward, further or less? Reference: Bensons 3 degree engine angled down, brings the CofG forward onto or just ahead of the Rotor Thrust Vector. Certainly, this has been described as slight positive stability.

What if the engine was angled up three degrees on the same gyro, Does this push the nose up more, less, the same amount? Perhaps more, I'm thinking the angle of the up thrust keeps pushing the pendulum further forward, because at some point the up thrust would, due to its position or attitude with in the Arc {climbing out position}, be trying to fly out on the prop..........Someone straighten me out.

Fly Safe,

Mitch

[Greg Mitchell]

G'Day Steven,

Mate I didn't post the above to have people rubbish Jim or SportCopter. I am looking for technical info about all types of configurations. I would hope the 'Experts' would attempt to answer my questions without resorting to 'off-handed' comments. Not intended to offend, just looking for answers.
By the way you Disc package was sent Thursday by Air Mail. Hope you enjoy.

Best regards,

Mitch.

[Udi]

G'day Mitch,

I don't know anything about the Sport Copter history. What I do know is what Jim told me when I asked him about the engine angle. Jim didn't try to explain it from a theoretical point of view. He said they have found that the gyro is flying better this way. He also said that the gyro is flying slightly nose down, so with the engine mounted nose up, in flight, the engine thrust line is parallel with the flight path.

From a theoretical point of view, one has to ask the question whether the added nose-down moment resulting from moving the engine thrust line higher than, and away from, the CG, is partly or completely cancelled out by the nose-up moment resulting from the prop wash hitting the stab at an angle.

Here. A whole post without bashing anyone!

Udi

[Doug Riley]

Steve Kozned, the fact that someone is your best friend, an admirable guy, a hero, a brilliant machinist or even an ace pilot does not in itself qualify him/her to design aircraft. Particularly back in the 60's when I got started in this wacky but rewarding hobby, virtually all gyros were eyeball-engineered. A very few people knew how to "run the numbers," but the notion that this was even possible wasn't widespread.

Intentionally raising the thrustline in order to have the prop blow on the HS is a maneuver much like trying to pick yourself off the ground by pulling up on your own hair. It simply adds a bending load on the airframe. The engine pushes down on the nose, the HS pushes back up on it. It's possible to use a HS to compensate for small amounts of thrustline misalignment, but intentionally ENLARGING the misalignment seems unproductive at best.

I'm sure Jim Vanek is telling the truth that his machines fly a bit nose-low. The photos bear this out. (Gyros with high thrustlines that are set up to Bensen hang specs typically do fly nose-low; the nose-low stance increases as you go faster.) To tilt the engine in order to match this stance is to treat the symptoms instead of the underlying problem, however. Why not alter the hang angle so that the frame is level in flight locate the engine parallel to the flight path and arrange the masses so that the CG is located at or near the thrust line? The HS is then still desirable, but its function is much less critical.

[mceagle]

Stephen,
I think that you were being a little sensitive there.
I didn't read that Doug had trashed Jim or his machine but mainly pointed out different design perspectives and his opinions on how to approach them.
However, if an ace pilot has the capability to fine tune an established design to the point of operable brilliance, then he should also have the ability to thoroughly explain his reasons for such fine tuning and the results he recorded doing so.
I left out your comment about "aesthetic brilliance" because beauty is in the eye of the beholder, and many would not consider the Sport Copter to be an attractive design.
Just a further comment - how do you rate "operational brilliance" - and please do not embarass yourself and suggest that it has anything to do looping ability.

[C. Beaty]

Steve, as a hardware design engineer, what kind of hardware do you design and where did you receive your degree in mechanical engineering?

I don't consider any structural design with numerous eccentric load paths an engineering work of art, no matter how aesthetically pleasing some individuals may find it to be.

[C. Beaty]

Obviously, Steve, you know more about computers than I. Only recently did I learn that a gigabyte is 1,073,741,824 bytes (2^30).

[GyroRon]

Steven, Both Doug and Chuck have seen a Sportcopter in person and looked it over real good I am sure of that! Matter of fact both of these people were at Bensen Days and there was a pristine 582 powered Sportcopter there flying at the fly in.

Also how a gyro flys does not make up for a poor design. A RAF2000 in showroom stock configeration is no doubt a VERY poor design not only due to the thrustline offest, but in many many other areas as well. But in the hands of a trained pilot they fly great. I myself have seen a few sportcopter gyros. They ARE very nice, highly detailed, and look to be fine machines all around. I have yet had the chance to fly one so I can't say much about how they fly. I did get to fly a Sportcopter copy called the Soma and it flew good, but there was a lot of differences between the Soma and the Sportcopter so it isn't saying much

[CLS447]

Steve , it seems to be that you are either a Dominator/ Dragon wing user or you are something less ,according to some here. I don't understand this conspiracy against Jim V. / Sportcopter. And I don't like it ! He's making some damn nice stuff & some people would rather die than admit it! Didn't you make it to Dominator Days ? I believe in giving credit where credit is deserved, & Jim V. definitely deserves more than he gets on this conference!

[C. Beaty]

Chris, do you know what an eccentric load path is?

If you grab a gyro by the mast, rock it from side to side and it creaks and groans, you've got 'em. Dominators don't. Bensens don't.

Proper structural engineering is pretty basic stuff.

[scott heger]

Udi, I got the same response when I asked Jim about the engine tilt. On the other conference , several people (hi Chuck) jumped all over me for buying into "junk science" engineering. Well the bottom line is Jim V tried several different engine angles and this one worked the best and was the most forgiving. Now I am about the same size and weight as him. I find my SportCopter completely forgiving, fun to fly and stable either going 15 MPH or 100MPH. Maybe if I weighed 50 pounds more or less, it would not fly as well? Possibly Jim V just got lucky after 30 years being around gyros and guessed what would work best.....ya believe that? Come on guys, he is constantly thinking of ways to improve what he has made so far, and as time goes forward, I think better products, improvements, and new machines will also come from SportCopter. The Vortex was a great buy/value when introduced in 1998 at about $12,000. It also almost put him out of business. Quality cost money. He got the machine right the first time, can RAF make the same claim? If he goes forward on another model, I know it will also be "right" and safe when produced. His delivery schedule is slow, some have complained, me included. Have you ever heard anyone complain about the quality of parts? Not me. He made everything right, including replacement things for free that were wear related from a purchase 5 years ago. He is a gem in the gyro business.

Scott Heger, Laguna Niguel, Ca SportCopter N86SH

[C. Beaty]

Steve, struts and braces terminated with those stupid UL fixed wing Instabushings and "U" hoops almost unavoidably impose a dogleg in the line of force. Tension and compression loads of struts and braces should always be concentric with the tube axis. Also, there should be no cleavage load imposed on bolt heads.

I took a quick lap around the ultralight area of Sun-N-Fun last Saturday, paying particular attention to structural details and was appalled at how poorly many were designed: doglegs in wing struts, bolts in bending, etc. Makes a good case for ballistic parachutes.

Poor structural design doesn't mean something will break but if it doesn't, it will be heavier than necessary with correct design. Bulldozers often attach hydraulic cylinders to the hull casting with "U" brackets made from 1" steel plate and attached with 1" bolts. But bulldozers don't fly.

I also saw a few ULs that had proper structural design but sadly, they were in the minority.

If you want a good example of how struts should be terminated, take a close look at an Aeronca. Everything will be in a straight line.

Just because these UL fittings are in the Aircraft Spruce catalog doesn't mean they're a good option for stuff that flies. Pretty, though.

[Mike Jackson]

Hi Chuck,

Any chance you could provide simple drawings or pics of the do's and don'ts regarding the fitting issues you described? Do any of the EAA pubs address this?

I always "perk up", STS, when someone mentions cleavage. Can you explain this term in the structural context?

Thanks,

Mike

[C. Beaty]

Sure, Mike. Here's a drawing of dos and don'ts for terminating steel tube ends, originally from Federal publication ANC-5 (assuming I can figure out how to attach a picture).

I imagine EAA has some manuals that extract data from ANC-5, the bible of aircraft construction.

Aluminum tubes are difficult to terminate without fancy machined fittings.

When you pry the lid off of a paint can with a screwdriver, you're applying the type of cleavage I meant. Brackets should never be attached to a bolt that applies a prying force to its head.

[Al_Hammer]

Now, here's a landing strut (Apollo 11 lunar lander)
http://www.hq.nasa.gov/office/pao/History/alsj/a11/ap11-s69-31042.jpg

PS: Chuck, are you able to view private messages on the forum? I sent you one.
thanks

[Udi]

For the sake of clarification, we have to separate good engineering practice from safety. Some poorly engineered machines, like the RAF, are clearly unsafe, but I don't think we can say that on the Sport Copter.

I agree with most of Doug and Chuck's comments regarding the Sport Copter. Tilting the engine nose up in order to have it blow on the stab does not make good aerodynamic and engineering sense. Lifting the stab into the prop wash and leaving the engine level would make more sense.

I also don't like the ultralight u-brackets and instabushings. But this is one way to make a simple kit that anyone with a torque wrench can build in a short time. The compromise of using this construction method, like chuck has said, is having to over-engineer the joints so they can take the eccentric loads. This is an engineering compromise, intended to make the kit more user friendly. The Dominator does not have this kind of joints, but the Dominator is not a kit at all. Building a Dominator requires more skill and tooling than building a Sport Copter or an Air Command.

Getting back to safety, I don't know that anyone has tested the Sport Copter for stability yet. It may not be an engineering marvel, but I am not so sure it is unsafe to fly. The pilot is sitting pretty high relative to the engine thrust line, it has a nice sized stab, and the workmanship is impeccable. Sooner or later someone would test the Sport Copter for stability and report the results.

I really think that the Sport Copter line of products had/has the potential to be very successful. If only the Vaneks would take advice from some of the more knowledgeable people in this field.

Udi-

[PW_Plack]

Udi,

I think you make the point well about the compromises inherent in creating an easy-to-build kit. To me, Jim's most significant achievement is in designing an airframe which is very strong, and despite any over-building required to make it that way, makes the 254-pound Part-103 limit with two pounds to spare, even with a Rotax 503, horizontal stab, brakes, and suspension on main gear and nosewheel.

U-brackets may be a shortcut for the builder, but some other shortcuts I see bother me more. I find it difficult to begin a serious safety discussion with a designer who clamps against small, round aluminum tubing without a solid plug inside, mounts a windshield where your forehead will hit the edge if you're thrown forward, or seats the pilot on a plastic bottle of fuel that results in a gasoline bath in a hard landing. Sport Copter does none of those things.

[Steven_Kozned]

Udi,
As always from you, yet another refreshingly unbiased, fair and open minded post.
Regards,

[Mike Jackson]

Thanks for the reply and diagram Chuck. I've also seen a few of the U fittings on ULs including gyros. I have a better idea of what to look for.

Cheers,

Mike

[jucie]

Did you read my mind, Udi? Well said, my friend.