View Full Version : Nuebee Builder Questions
06-07-2004, 07:57 AM
Ok you old salts! Time to help out a first-time builder.
Symptom: 2-place side by side. Running full fuel and 2 200lb occupants flys in a slightly nose-down attitude requiring back stick pressure. Trim spring is already stretched way tight.
Of note: My HStap on my tall is NOT exactly parallel with my keel. It is sitting a few degrees up in the front! :mad:
Question One: Would it be OK to instead of making the HStab parallel instead to make it a few degrees down in the front? :confused:
Question Two: Would moving my teeter bolt position on my Dragon Wings have any effect on this or other issues switching from one person to 2 person flight? :confused:
Question Three: Does chewing gum left on the rotors loose itís flavor overnight?
06-07-2004, 08:18 AM
Tim, I will address the most important of your questions first. It depends on the gum, the weather and most importantly, how used the gum is! My opinion is that the HS should be parallel with the keel and you shouldn't have to change the teeter bolt location. Have you done a hang test?
06-07-2004, 09:39 AM
Yes, the chord of the HS should be parallel to the desired stance of the craft in flight if the craft is a CLT machine. If the thrust line is above the CG at all, the leading edge of the HS should be from 1-4 degrees lower than the trailing edge -- again, measured relative to the DESIRED stance of the craft in flight.
This is a simplified version. We'd need to know a lot more about your craft to refine it. In general, however, the HS should be set between a strictly level position and a leading-edge-down position of 1-4 degrees. Leading-edge UP is undesirable.
If, after all this, and assuming that you don't have a thrustline that's significantly above the CG, you will need to alter the hang position of your rotor head by changing the cheek plates. If you DO have a significantly high thrustline, fix that first... don't rely on the Band-Aids of HS adjustment or hang position tinkering.
As you get the machine's in-flight stance more level, you'll need to slack off the trim springs.
Changing the teeter bolt height won't have any effect on the in-flight stance. This adjustment is used to minimize two-per-rev vibrations.
06-07-2004, 09:54 AM
To correct the nose low flying you need to change your cheek plates. Don't expect the HS to correct this.
I know this is a lot of work, but the hang test should be used to locate the rotor head (cheek plates) so it is close to correct (near 11 degrees nose down keel) with one and two occupants.
However ... I suggest you make the cheek plates so it flys level (11 degree hang test) with you alone if this is what is to be done most of the time with only an occational rider (then it will fly nose down with the second person on board). Or, if the gyro is to be used for training and flown with two occupants often, then set it for you and the expected "average" weight of students (then fly nose higher alone or lower with a heavier student).
06-07-2004, 10:05 AM
Ken's post assumes that the gyro does not have a significantly high thrustline. If it does, it will fly nose-down even though the cheek plates are adjusted correctly. The nose-down stance in such cases will get worse as you fly faster than normal cruise and can become quite dramatic (and dangerous).
A HS with negative incidence, located in the propwash, can compensate for small thrustline mislignments. "Small" means in this case on the order of 1"-3". A HS cannot compensate for a 6," 8" or larger misalignment on a pusher gyro. Changing the cheek plates does nothing whatsoever to compensate for thrustline mislignment of any magnitude.
06-07-2004, 10:30 AM
I think there is some confusion here. For example:
1. A gyro with properly located cheek plates (hang test) will fly level regardless of the thrust line to CG offset, with or without a HS. Only a "change in speed" (throttle) will create more or less thrust, which will then push the nose down or pull it up - as the thrust (throttle) is changed.
2. The speed of flying does not affect the "push over" effect of a high thrust line.
3. Flying speed only affects aerodynamics, such as drag or HS pitch. An unusual amount of low drag will pull the nose down more the faster you fly. An unusual amount of high drag will push the nose up more the faster you fly. A HS pitched nose up will push the nose down more the faster you fly.
06-07-2004, 11:03 AM
My gyro does not have a high thrust line offset.
The stab is currently a few degrees up in front, and I hope that is the source of my problem.
The gyro was hang-tested for a single person, not 2-people with extended range tanks. I will re-hang if the HStab does not correct the problem.
Outside of new cheek plates, are there other remedies? Moving the battery from under the seats to under the engine perhaps?
06-07-2004, 11:17 AM
Side View for reference
06-07-2004, 11:34 AM
Well, Ken, a gyro with any GIVEN hang angle will fly more and more nose-down as the thrustline is moved higher and higher above the VCG. This is a by-product of the need for the rotor thrustline to move farther forward of the CG. You can also achieve the tail-heaviness that is required for level flight with a high thrustline by moving the rotor head forward or moving ballast back.
Speed per se does not affect the amount of PPO moment. However, an increase in LEVEL speed above cruise requires more throttle, which certainly does add to the PPO moment (because it produces more thrust).
I agree with Ken that new rotor cheek plates may be required. Tim has mentioned that the problem occures with two people aboard, so apparently it's ok with one person.
Tim, in a two place machine you want the second person to sit close to the location of the machine CG with only the pilot. Suspend a plumb bob from the teeter bolt when you hang test the machine with one person on board. A perfect two place machine will have this line passing in line with the passenger center of gravity.
The best solution is to move the teeter bolt (i.e. cheekplates) forward and then rebalance the gyro so it hangs at 11 degrees with only one person, and not much more with two people.
06-07-2004, 12:05 PM
I still think there is some confusion, at least on my part.
You said: "a gyro with any GIVEN hang angle will fly more and more nose-down as the thrustline is moved higher and higher above the VCG". This does not address the issue, as the VCG does not move up or down while flying a gyro (unless the pilot stands up or does something to change the VCG location).
But you said: "an increase in LEVEL speed above cruise requires more throttle, which certainly does add to the PPO moment (because it produces more thrust)". This is true, but the added thrust is offset by the added drag of the rotor, so the gyro's attitude remains the same doesn't it? It seems that the nose would not go down unless there is a lot of low drag or the HS is pitched noes up.
I don't believe the thrust offset would cause the gyro's nose to go down in steady speed flight.
06-07-2004, 12:33 PM
Ken: I must have timed out. Here's what I tried to post, more or less:
I'm speaking of unaccelerated level flight. Assume a gyro in such flight, at cruise speed. Assume also that it has a high thrustline and that the resulting PPO moment is not fully countered by a down-loaded HS or other aerodynamic device. Such a gyro must fly with the rotor thrustline ahead of the CG in order to hold the nose up against the PPO tendency.
Now assume that the gyro speeds up in level flight by adding power. At higher airspeeds, the rotor flies at a shallower angle of attack. IOW, as the gyro speeds up, the rotor becomes more nearly level. (The pilot experiences this as a need to move the stick forward when power is added to avoid climbing.) As a result of this levelling, the rotor's thrustline swings aft, closer to the CG. If the craft were to maintain its former stance in the air, the nose-up moment caused by the rotor would decrease -- at precisely the time when it needs to INCREASE (because power has been added).
Result? The nose drops, moving the CG down-and-aft relative to the rotor thrust line. This preserves the nose-up moment of the rotor, at a cost of flying quite nose-down at high speeds. The effect is very real, and can be rather scary. You feel like a kid riding in a wheelbarrow who's about to be dumped out forward.
Note that rotor drag doesn't increase as airspeed increases. It actually goes down! Check the graphs in the FAA Rotorcraft Flying Manual or the old Bensen manual. TOTAL drag goes up because of the effect of fuselage drag, but THAT drag isn't applied way up at the teeter bolt, so it doesn't necessarily cause a nose-up reaction.
06-07-2004, 02:30 PM
I would get the HS parallel with my keel or 1 to 2 degrees low and hang it so that it is 9 degrees at the keel solo and 12 gross. I am going to put over 100 pounds of gas in the front of my tractor and plan to do the same. That is 12 degrees max at gross and 9 empty, so with full fuel I can climb out and empty I can still push the nose down to land.
06-08-2004, 06:14 AM
Anyone have a set of alum plates I can use as check plate models they want to sell? :confused:
06-08-2004, 06:24 AM
How significent a difference would you guess moving the battery behind the seats would make?
06-08-2004, 06:26 AM
Tim, moving the battery should make a significant difference.
06-08-2004, 07:53 AM
I could relate in great detail, a personal experience, but time is a factor right now.
I would suggest you level the horizontal with the keel. Neutralize your trim and go fly. I'm pretty sure you will be pleased with the results. Some additional adjustments could be needed.
06-08-2004, 11:57 AM
Thank you Chuck, Harry, and again Brent, Doug, Udi and Ken.
I weather and GF permitting I will make the changes suggested and report back. Remind me at Mentone I owe you guys a beer.
I have ordered the needed materials, I hope they will arrive by Friday!
06-08-2004, 04:51 PM
Ok you old salts! Time to help out a first-time builder.
Symptom: 2-place side by side. Running full fuel and 2 200lb occupants flys in a slightly nose-down attitude requiring back stick pressure. Trim spring is already stretched way tight.This can be quite unsafe if that spring breaks
Of note: My HStap on my tall is NOT exactly parallel with my keel. It is sitting a few degrees up in the front! Not good at all
Question One: Would it be OK to instead of making the HStab parallel instead to make it a few degrees down in the front? possibly
Question Two: Would moving my teeter bolt position on my Dragon Wings have any effect on this or other issues switching from one person to 2 person flight? No
Question Three: Does chewing gum left on the rotors loose itís flavor overnight?Only if you take it out of your mouth!!!!!
I would start by calculating the COM in relation to the thrust line. If the thrust line is a couple of inches above the COM have the stab few degrees down in the front, other wise paralell with the keel if the keel is what you are using as your datum to set hang test, controls, and egine angles.
Conduct the hang test and arrange it within the accepted parameters.
If after this you still have a lot of trim spring pressure that will be a result of the brand of blades that you are using, you will then have to fine tune the torque tube offset. A 1/16" reduction in the torque tube offset has quite a considerable effect ion trim spring pressure.
Just my few rambling thoughts. :D
06-09-2004, 09:54 AM
That is a salty response!
I had to get out my gyro design book to get a grip!
06-14-2004, 07:40 AM
Got lots of work done on the gyro this weekend. A big note of thanks to the Chapter 34 members that helped me. They loaned tools :eek: including this cool digital level ( got to get one of those for myself! ). They helped me winch my gyro up to the roof of the hangar again and again ( boy that is heavy! ).
Ok, skipping the mundane details here is the deal:
Horizontal Stab is how horizontal! :D
Attached cheek plate template and with the gyro on the farthest forward setting here are the results:
400+ish Pounds of pilot and passenger :o ( they feed us well at the chapter )
8 gallons of gas ( Main tanks hold 10, plus I have two extended range tanks that were empty at the time of the test )
Measurement was ... + 12.6 Degrees.
So it looks as if I will need to go out a little farther than my template was made for to get 11 Degrees.
No work next weekend (Fathers Day) :( so hopefully weekend after next I will have a set of cheek plates correct for 2 people and fuel.
06-14-2004, 07:42 AM
Cut-away view :D of template.
Tim - If your Air Command is set up like mine, the hang angle measurement has to be in relation to the mast, not the rear keel! The mast angle has to be between zero, or vertical, with minimum weight (i.e. one pilot, no fuel), to a maximum of 5 degrees nose down with two people and full fuel.
In my Air Command, the rear keel is angled up (there are 3 degrees between the front and the rear keels), so the rear keel is not a good reference for level flight. I don't know if all Air Commands are set this way.
I hope this helps.
06-27-2004, 08:18 PM
Got the new cheek plates.
She flys GREAT. I finally got to fly her properly trimmed. :)
I got a couple of good short flights down the 4I7 runway today. It is a 5000 foot runway so it is a great place to practice.
I feel very gratified that at long last I was able to takeoff, cruse, land completely controlling the gyro myself. :D My instructor was with me of course but now that it is trimmed out and I have got a grip on how she is going to handle I expect to be flying her solo pretty soon.
I don't feel right giving a review of the machies performance just yet as I only have about three flights in where I was the only one on the controls. I will write something up once I have had it around the pattern a few times.
06-27-2004, 08:24 PM
It was a great day at the hanger. Arrived early enough to see the deer cruising the fields.
06-27-2004, 08:31 PM
It was a good day all around. However, my cooling problem is not solved after all. I think I know the problem and should have it fixed next time I get to work on the gyro. Probably in a few weeks.
More great news. A new gyro is born. This just arrived at the club hangar today for hang tests and engine break-in
06-27-2004, 08:33 PM
This is the first Sport Copter I have spent any time with up close. Great quality stuff. Check out this cool FOLDING mast. :eek:
06-27-2004, 08:35 PM
Harlen flew in x-country in his Soob powered V-Tail :cool:
06-27-2004, 08:37 PM
Rodney's bee is a scratch built work of art.
06-27-2004, 08:39 PM
Here is the sport copters pod. :cool:
06-27-2004, 08:42 PM
The Air Command 147 did some great flying today
06-27-2004, 10:10 PM
One last one of Dennys new Sport Copter. Check out the wood prop, very classy. :)
06-27-2004, 10:20 PM
Ok, Yet another nuebee builder question:
Is a trim spring just a regular old spring you get from the hardware store or are they of a certain 'grade'.
06-28-2004, 02:32 AM
Great looking machines, Tim, and great shots also. I am a little hesitant to answer your last question though, as mine came from a hardware store.
06-28-2004, 04:55 AM
I replaced mine with one from a hardware store and it seems to work ok. I still have to saftey wire it but I may go shopping for a shorter one so I can mount my electric trip higher on the mast. It seems like the DragonWings like alot of backpressure!
06-28-2004, 05:04 AM
Tim, that reminds me that I probably have too much back pressure, I think. When I release the stick, even at just 50 mph, the nose comes up. Isn't that an indication that I have too much back pressure? Yes, I safety wire all my springs.
06-28-2004, 05:11 AM
Yes Chuck you got too much pressure. It should go to the airspeed you set it at when you let go of the stick. And I use a hardware store spring on mine too.
06-28-2004, 05:16 AM
Thanx, Ron Boy. What got you up so early this morning?
06-28-2004, 05:24 AM
Don't know. I got a long day of going to the airport and playing with my toys ahead of me. I guess I wanted a early start....
06-28-2004, 11:27 AM
Any good quality spring from Pep Boys Aviation Supply will suffice.
06-28-2004, 11:41 AM
That Air Command 147 looks quite scary. I thought that ill-considered beast had been buried after it killed CFI Jim DiGaetano several years ago.
At minimum, it almost certainly needs more vertical tail surface area. (Remember that the Air & Space has three large verticals and still has yaw-roll problems.) HS power needs very close attention, too.
06-28-2004, 04:43 PM
When I use the term back pressure on the stick, I mean how much back pressure would be required without a trim spring.
If the design of rotor that you are using is not matched to the torque tube offset, then the trim spring requirement can be dangerously high. It the spring should break, and you are lightly holding the stick, the force forward could end up with the pilot having an exciting ride. More so if the thrust line is high.
06-28-2004, 05:12 PM
"Pep Boys Aviation Supply" -Harry you made my day! :) That is what I am calling it from now on!
I heard that such an accident had happened.
This 147 has been modified in a number of ways. From the picture you can't see the tail section very well but it has a greatly augmented HStab that has been moved up into the prop stream. Other changes were made but I don't know all of the details.
It is one of the best looking gyros I have ever seen. :cool: I have not flown in it yet though so I can't give a review just yet. :( If there was a CLT version of this machine I think it would unseat the Sparrowhawk and Magni M16 as my favorite gyro. :D
She is running a fuel injected Soob 2.5, I think the redrive is a RAF, The prop is impressive and sounds amazing. The cockpit is among the best I have ever seen. I'll see if I can dig up a photo but it wont do it justice.
I think of it as a "Rotorway Exec - Gyroplane". If Air Command released a CLT version I would be forced into a second mortgage for certain :eek: .
06-28-2004, 05:27 PM
Fortunately, she is CLT. Is there a way to check for a mis-matched condition other then flying with out a trim spring?
I hope to buy a selection of springs and rotate though them to see what works best. Any tips?
06-28-2004, 07:47 PM
Here are a few photos. I am still looking for one of the cockpit.
06-28-2004, 07:48 PM
View Two, on the runway.
06-29-2004, 05:26 AM
can you get a closes up of the rotorhead for me it looks like cables. if it is how do thet feel.
06-29-2004, 05:32 AM
this is the CLT of that
06-29-2004, 05:59 AM
I have flown a couple of gyros with Morse cables. Could not feel any difference.
06-29-2004, 06:00 AM
Aussie Paul. :)
06-29-2004, 06:22 AM
A good looking bird, Paul, and interesting construction.
06-29-2004, 07:08 AM
Brent, I will try and hunt down some picts of the rotorhead. I thought I had some and some of the cockpit.
I have been checking out the Futura. The BMW engine aspect seems cool.
Paul, Did you see my question for you?
06-29-2004, 09:40 AM
The last change has a 912? in it and new gear
06-29-2004, 11:20 AM
I assume this one is not finished as I don't see any way to control the rotorhead.
Like the 147 it seems alittle shy on the rudder surface.
After reading Doug's recommendations I think I would agree and increase the rudder surface to keep better control in cross-wind gusty conditions.
06-29-2004, 02:51 PM
It looks like the line coming down from the rotor head at 11 degrees runs through the pod with about half the pod area behind the line, so the double tail rudder fins seem to be plenty big. Can't say the same for the 147.
06-29-2004, 05:44 PM
Flying without a trim spring does not give you any indication of thrust/ CoG offset. There are too many other variables in play.
06-29-2004, 07:22 PM
Here's the NTSB report on the 147 crash. Sounds like maybe he got distracted watching the oil and coolant temps and wasn't watching the RRPM.
I wonder who the cited "program manager" for Air Command was. Larry?
06-29-2004, 08:20 PM
Bunt over is what I would call it.
06-29-2004, 08:51 PM
Kev, what if he wasn't distracted and was watching the RRPM? What could he do about it? There's no way the pilot can slow the RRPM to a dangerous level except at the onset of a buntover, as far as I know. Then it's too late. I wholeheartedly agree with Ron as to Jim bunting over.
Jim DiGaetano was a close friend of mine for ten years. He trained my wife and my son in gyros to the point of solo. He was a good pilot and instructor and was very experienced at flying unstable gyros.
The story is that Jim went into a sharp turn after a "whack, whack" was heard which was the rotors striking the vertical fins. After the rotors slowed the ship nosed over and went in vertically. I think he noticed low rotor rpm and cranked the ship into a tight turn in an attempt to load the rotors, but that is just my idea.
The ship had 31 ft. McCutchen Skywheel rotors which have a MAC at close to 40%.
Under certain conditions the rotors could possibly flutter which would cause high induced drag and cause a reduction of RRPM. Jim was a light weight guy as compared to Thomas Gage who was the previous demo pilot for the ship. Jim was "booking" along at a pretty high speed so it is certainly possible that flutter could have occurred.
I talked to an old fellow from Georgia at about the same time of Jim's accident who said that he put a set of Skywheels on his Barnett gyro and the blades got into a flutter and he almost crashed, so it is a possible scenario.
Doug Smith was the one who witnessed the crash.
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