View Full Version : KB-3 axle
09-25-2004, 02:35 PM
I understand the reasoning behind the curved axle on the KB-3 but was wondering if anybody has put a straight axle on with bigger wheels? Is the attitude difference while sitting on the ground going to be a huge problem?
I plan on flying out of some semi rough areas and don't like the idea of having tiny wheels for this. Any advice is appreciated.
09-25-2004, 03:20 PM
I would guess that Ken was trying to save weight by using the smaller wheels. A straight 2x2 axle and 6" wheels is the standard setup and should be fine.
A much more serious issue is that the stock KB-3 (unlike the -2) is lethally unstable. It lacks any horizontal stabilizer at all (again, probably to save weight), has a high thrustline and quite a powerful engine for so light a machine. It's a proven killer and should not be flown without modification to add pitch stability.
I don't mean to rain on your parade, but please let us all know that you've attended to the stability problem. It has been quite awhile since the last gyro fatality and it would be nice to keep it that way.
09-25-2004, 07:43 PM
I had nearly 200 hours on my KB-2 with a Rotax 503 conversion kit and no horizontal stab. I did have a Bensen rock guard on it which did nothing. Infact, I later took that off and had no problems.
I haven't bought the KB-3 yet and was jumping ahead with the questions.:)
Has anybody put some type of stab on a KB-3 for pitch stability? If so, where was it mounted? Thanks.
09-26-2004, 04:43 AM
I had a straight axle with wheelbarrow wheels on mine, I also moved the rock gaurd under the rudder.
But now I am doing a CLT conversion.
See pics under Bensen section, Bensen rebuild and rebuild part II.
09-26-2004, 05:26 AM
Cheapest easiest way to make it reasonably safe, is to add a Dominator Tall Tail to the rear. Call Ernie Boyette at RFD and he can help you get that worked out.
09-26-2004, 05:29 AM
Richard Kennedy of Arkansas modified his KB3 by adding an 8" step in the keel to raise the CG, and added a tall tail made from steel tube and fabric. The stabilizer is in the propwash, and he added adjustable trim tabs to it.
He occasionall posts on the forum. Maybe you could send him a P.M. and get his opinions on the differences between the stock KB3 and his conversion.
09-26-2004, 06:02 AM
I love that conversion. Looks good and I am sure flys rock solid.
09-26-2004, 10:46 AM
WOW, that looks so cool. That looks like the ticket for safe flying.
Ok, now for a serious question. I'm not sounding like a smart a_ _ or anythig but if the KB-3 (or any HTL for that matter) is "a killer", why would they sell them? Like I said, I'm asking this seriously and not because I was planning to buy one. If this is a problem, why wouldn't the company sell a stab as an after thought? I know Air Command did this years ago because my buddy bought one and he said it made a huge difference. This is the biggest reason I was glad to find a gyro forum to hear advice and opinions.
If this topic has been discused before, sorry.
09-26-2004, 11:10 AM
Poor engineering would be my answer (and I'm no engineer.) Ever since Igor Bensen designed his famous gyrocopter (more kits sold than any other aircraft) there have been numerous look-alike's that followed his lead without investigating all the vectors that occur in a gyroplanes flight envelope.
Bensen started in the early 60's, Brock copied and became available in the 70's as did Air Command in the 80's.
Only recently, in the 90's, has the commercially available RFD dominator returned to the design parameters that were known in the 30's.
Luckily, through their example (and Chuck B's 20 years of harping) have copycats started to produce safer machines.
Some manufacturers simply have to much effort and emotional investment in their creations to accept and put forth the effort to change however.
Just my opinion (from a distance through time) but I think Dr. Igor Bensen has killed more pilots than anybody else, through his unwillingness to talk openly and exchange knowledge about gyroplane design criteria.
I also think Chuck B and Norm Jacobsen have saved or will save many many lives by the momentum of the knowledge they have shared efficiently and inexpensively.
Hope that answers your question (in a roundabout fashion.) darrellwittke
09-26-2004, 11:17 AM
When you read all the documentation of Bensen, given with the B8M for example...You can see all what you have to know to fly as safely as possible... But after him, all the knowledge was lost and the designs which followed, were flawed! the teeter rotor is not forgiving!...
09-26-2004, 04:46 PM
Mark, no one but the manufactors can answer that question. It is retarded if you ask me, not to make improvements and upgrades over the years. In the case of the KB-3 I would guess - Only a Guess! - that since the designer is no longer alive that Mrs. Brock and company don't want to mess with his designs. I also had heard - never got the Pleasure of meeting Ken Brock - that Ken was the type of fellow that right or wrong, did things his way and stuck to them.
Another factor that some companys - and pilots and new buyers of a particular machine - use is this type of thinking.... " Well we have X number of machines sold, and X number of machine flying, so there can't be a problem. " Or the " If a person is properly trained, trustline placement and lack of a stab is not important. " Bottom line is if a machine is unstable, if it can bunt over and kill you, Then it WILL if you allow it to. Why roll the dice?
Why these companies such as Brock and RAF will not improve upon their offering and update them to modern standards is beyond my thinking. Some say it is because of lawsuits, that if the design is changed or altered then a lawsuit could be brought forward by a former pilots widow...
09-27-2004, 06:08 AM
"Why would they offer it if it's a killer?" The question contains a couple hidden assumptions -- both of which turn out to be untrue. They are
(1) All gyro designers know how to engineer an aircraft to be safe.
(2) No gyro designer would market a machine that is unsafe.
In fact, many gyro "designers" are skilled mechanics and/or sharp pilots. Those accomplishments do NOT qualify you to do design work, however. They do get you the respect of other craftsmen/pilots -- and that's the problem. A well-liked pilot may come up with an awful design (unintentionally), but he can sell it on the strength of his reputation as a "good stick."
A skilled pilot can handle a quite unstable aircraft. He may not even notice the instability unless he's trained in standard engineering flight-testing procedures. Because of this, he may "pooh pooh" the stability issue, even though stability is an OBJECTIVE criterion, NOT a matter of opinion. IOW, that great pilot may not intentionally market an unstable machine, but he may dismiss the whole concept with an attitude of "I can handle it -- all you need is more training and you can, too."
Same ol' story.
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