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Author Topic: Changing Stab Height  (Read 1417 times)

Online Ken Culbertson

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Changing Stab Height
« on: January 29, 2022, 11:07:01 AM »
This is one I have never encountered so I thought I would ask those who know.  I have a proven design that I have built several times.  The stab height is 1 1/2" above the wing centerline 3/4" above the thrust line.   I am going to use a logarithmic flap arrangement that reverses the pushrod movement to the elevator.  The Elevator horn now needs to be on top.  Can I safely lower the stab by 1/2" and not totally screw up the planes aerodynamics?  This essentially puts the stab near the thrust line instead of well above it.  Should I perhaps change the stab incidence?  It was to be 1 degree negative (LE Up) with no down thrust.

Plan "B" is to add a direction changing "horn" near the tail.  Extra weight and one more thing to create problems but I could move the adjustments to it and make the elevator horn connection fixed with decent leverage.  Choices.....

Ken
« Last Edit: January 29, 2022, 03:17:29 PM by Ken Culbertson »
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Online Dan McEntee

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Re: Changing Stab Height
« Reply #1 on: January 29, 2022, 01:09:24 PM »
    Just flip the bell crank over and put the short arm facing inboard. This puts the down line in back, and changes the direction of the pushrods. How the horns are arranged stays the same. If this is a profile, the added benefit is the controls are on the inboard side and pushrods and such stay a bit more clean.
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Online Ken Culbertson

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Re: Changing Stab Height
« Reply #2 on: January 29, 2022, 03:53:45 PM »
    Just flip the bell crank over and put the short arm facing inboard. This puts the down line in back, and changes the direction of the pushrods. How the horns are arranged stays the same. If this is a profile, the added benefit is the controls are on the inboard side and pushrods and such stay a bit more clean.
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Sorry Dan but this is a logarithmic that reverses the direction of the elevator pushrod.  Hard to explain but the horn has to go on top.  If I flip it over then I cannot service it.

Ken
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Offline Howard Rush

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Re: Changing Stab Height
« Reply #3 on: January 29, 2022, 06:26:30 PM »
How do you have your logarithmic system implemented?  Here's what Igor does: http://www.netax.sk/hexoft/stunt/the_max_ii.htm  I copied his.  It works fine.  Is yours constrained by your fuselage somehow?
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Offline Tim Wescott

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Re: Changing Stab Height
« Reply #4 on: January 29, 2022, 06:39:11 PM »
How good of a pilot are you?  I know that the absolute top guys feel that there's a difference between the "typical stunter" and a 0-0-0 arrangement, but I'm not sure how much tweaking you need to do for that.

Might want to search around for articles on 0-0-0 stunters -- there should be discussions there on elevator height & its effects on performance.

You might also want to consider a dorsal fin & rudder big enough to house your pushrod, and just leave the stab where it is.
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Online Ken Culbertson

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Re: Changing Stab Height
« Reply #5 on: January 29, 2022, 08:19:53 PM »
How do you have your logarithmic system implemented?  Here's what Igor does: http://www.netax.sk/hexoft/stunt/the_max_ii.htm  I copied his.  It works fine.  Is yours constrained by your fuselage somehow?
It is the experimental one that Mark Wood is working on.  The extra step of combining adjustable flaps into the system has reversed the movement of the elevator pushrod.  I designed the plane around Igor's system.  It has a GeeBee like rear end so there is absolutely room for the flap horn if I lower the stab 1/2" to let the pushrod clear the stab L/E.  I am not thrilled at having an adjustment hatch on the top of the plane either.   As I said in my original post, I have been flying the same configuration for the better part of the last century.  Thrust line 3/4" above wing C/L stab 1 1/2" above wing C/L.  I have had 1 0-0-0 that needed a permit because it hunted so bad, and I have flown some that only had mild hunting but were spectacular in maneuvers.   I don't think dropping it 1/2 is going to create problems but I have never experimented with stab height.  I was hoping to get the advice of those who have.

I really didn't intend to get too deep into the woods over the system since it is Mark's baby and still under development so I will leave it to him to explain.  What got me interested was the adjustability of everything mounted on a removable tray.  I have long thought that differential flaps (opposite of Palmer's T-Bird) with far smaller differential would be better than different chords.  Mark's system will allow for that.

Ken
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Online Ken Culbertson

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Re: Changing Stab Height
« Reply #6 on: January 29, 2022, 08:42:11 PM »
How good of a pilot are you?  I know that the absolute top guys feel that there's a difference between the "typical stunter" and a 0-0-0 arrangement, but I'm not sure how much tweaking you need to do for that.

Might want to search around for articles on 0-0-0 stunters -- there should be discussions there on elevator height & its effects on performance.

You might also want to consider a dorsal fin & rudder big enough to house your pushrod, and just leave the stab where it is.
Tim, When I was in my 30's I was up there with the big boys but now I am about a 550.  The older I get the more the + - factors in.

I mentioned it in my reply to Howard.  I have owned 0-0-0 and flown others.  I loved the way that they flew in maneuvers, but you had to pay way too much attention to them in level flight.  You can make them grove, but it takes all of your attention.  I like to focus ahead to the next maneuver and that is hard when your plane wants to chase birds when you are not looking (sorry, local humor). A good friend has one of the new Russian 0-0-0 planes that I have flown.  I would scrap what I am building now in a heartbeat if that plane was capable of one lap of level flight at the same altitude.  Maybe you need some Vodka to smooth it out!

Ken
« Last Edit: January 30, 2022, 11:02:48 AM by Ken Culbertson »
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Offline Mark wood

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Re: Changing Stab Height
« Reply #7 on: January 30, 2022, 01:35:00 AM »
It is the experimental one that Mark Wood is working on.  The extra step of combining adjustable flaps into the system has reversed the movement of the elevator pushrod.  I designed the plane around Igor's system.  It has a GeeBee like rear end so there is absolutely room for the flap horn if I lower the stab 1/2" to let the pushrod clear the stab L/E.  I am not thrilled at having an adjustment hatch on the top of the plane either.   As I said in my original post, I have been flying the same configuration for the better part of the last century.  Thrust line 3/4" above wing C/L stab 1 1/2" above wing C/L.  I have had 1 0-0-0 that needed a permit because it hunted so bad, and I have flown some that only had mild hunting but were spectacular in maneuvers.   I don't think dropping it 1/2 is going to create problems but I have never experimented with stab height.  I was hoping to get the advice of those who have.

I really didn't intend to get too deep into the woods over the system since it is Mark's baby and still under development so I will leave it to him to explain.  What got me interested was the adjustability of everything mounted on a removable tray.  I have long thought that differential flaps (opposite of Palmer's T-Bird) with far smaller differential would be better than different chords.  Mark's system will allow for that.

Ken

I've just been listening to the dialog. Vertical separation helps reduce the impact of the "wake" from the wing changing the incidence on the wing. The closer to inline with the wing the greater the impact potential will be. How much moving the horizontal down will impact the behavior of the airplane also has a dependence from the horizontal separation of the wing and stab.  Given this, it would be very difficult to say one way or the other whether 1/2 would make a difference. Intuitively, not that much. Another option is to simply swap sides and move the horizontal to 1 1/2" below the wing centerline but that would be kinda weird looking maybe and not exactly fix the problem.
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Online Massimo Rimoldi

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Re: Changing Stab Height
« Reply #8 on: January 30, 2022, 09:56:18 AM »
Hello.
 I have no idea the size of the logarithmic system, but if you flip it over and pop the pushrod out of the bellcrank under the wing maybe the horns can fit between the wing and the stab

Massimo

Offline Tim Wescott

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Re: Changing Stab Height
« Reply #9 on: January 30, 2022, 10:33:54 AM »
...  I have owned 0-0-0 and flown others.  I loved the way that they flew in maneuvers, but you had to pay way too much attention to them in level flight.  You can make them grove, but it takes all of your attention.  ...

Well, I'm embarking on a learning experience then -- I'm just in the preliminary stages of designing myself a 0-0-0 stunter, with aerodynamics shamelessly copied from Chris Cox's F8F and a weird-ass fuselage by moi.
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Online Ken Culbertson

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Re: Changing Stab Height
« Reply #10 on: January 30, 2022, 10:44:43 AM »
Hello.
 I have no idea the size of the logarithmic system, but if you flip it over and pop the pushrod out of the bellcrank under the wing maybe the horns can fit between the wing and the stab

Massimo
Size wise it is slightly larger that Igor's but the flap linkages make it about 1 1/2 times longer. You are right about flipping but this is a removable setup.  Flipping it would require a massive top hatch or moving the canopy which destroys the lines.

Ken
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Online Ken Culbertson

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Re: Changing Stab Height
« Reply #11 on: January 30, 2022, 10:53:33 AM »
Well, I'm embarking on a learning experience then -- I'm just in the preliminary stages of designing myself a 0-0-0 stunter, with aerodynamics shamelessly copied from Chris Cox's F8F and a weird-ass fuselage by moi.
Being big on the moi stuff I would maybe make up a similar dimensioned beater and play with incidence and thrust before framing up your pride and joy.  I know on one that I flew the owner was able to get it under control by going nose heavy and upping the control forces.  I haven't flown it since, but I am willing to bet that it does not maneuver as well as it did.  That may be OK though.  At my age I need that lap to plan, in some cases remember  LL~, the next maneuver.  Can't have it going on a sightseeing trip.

Mark - My aft moment is 19.5.  That may be enough to clear most of the wake.  Un-trimmed with everything at neutral this design turned considerably better outside if that tells you anything.

ken
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Online Massimo Rimoldi

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Re: Changing Stab Height
« Reply #12 on: January 30, 2022, 11:23:36 AM »
Size wise it is slightly larger that Igor's but the flap linkages make it about 1 1/2 times longer. You are right about flipping but this is a removable setup.  Flipping it would require a massive top hatch or moving the canopy which destroys the lines.

Ken

Maybe you can just put the elevator horn down and attach the push rod to the horn where the rod from the bellcrank comes in.

Massimo


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Re: Changing Stab Height
« Reply #13 on: February 02, 2022, 12:55:17 PM »
Hi Ken,
Iíve built many in line (o, o ,o) stunt ships and they all flew really good.  Dropping the stab to be more in-line wonít change it much,  (if any).  I think they all grooved fine and maybe better than most of the other models Ive built and flew.  What I liked about the in-lines models, was how easy they would transition from inside to the outside portions of each maneuver.

Later,
Mikey

Online Ken Culbertson

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Re: Changing Stab Height
« Reply #14 on: February 02, 2022, 02:24:13 PM »
...was how easy they would transition from inside to the outside portions of each maneuver.


Amen to  that.  How did you deal with the hunting?  Incidence?  Nose weight?  Slow controls, Majic spells?

Ken
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Offline Tim Wescott

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Re: Changing Stab Height
« Reply #15 on: February 02, 2022, 04:02:59 PM »
Being big on the moi stuff I would maybe make up a similar dimensioned beater and ...

Nah, I'm going to do what the rest of the junior varsity in the Pacific Northwest does -- I'm going to copy what Paul Walker is currently doing because he's doing it.

Besides, I want to learn the tricks of the big, light, molded fuselage approach, so even if the plane doesn't fly it'll be a good learning experience.
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Online Dan McEntee

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Re: Changing Stab Height
« Reply #16 on: February 02, 2022, 04:41:00 PM »
Tim, When I was in my 30's I was up there with the big boys but now I am about a 550.  The older I get the more the + - factors in.

I mentioned it in my reply to Howard.  I have owned 0-0-0 and flown others.  I loved the way that they flew in maneuvers, but you had to pay way too much attention to them in level flight.  You can make them grove, but it takes all of your attention.  I like to focus ahead to the next maneuver and that is hard when your plane wants to chase birds when you are not looking (sorry, local humor). A good friend has one of the new Russian 0-0-0 planes that I have flown.  I would scrap what I am building now in a heartbeat if that plane was capable of one lap of level flight at the same altitude.  Maybe you need some Vodka to smooth it out!

Ken

       I know you may be putting tongue in cheek with this comment but I don't understand the issue you have with in line set ups? I have two models hanging on the wall now that are in line designs, and both can be flown through a tank of fuel while flying level flight and me looking everywhere but at the airplane, as long as the wind isn't gusting. But then so does any other airplane I have that I may fly in in a contest. I have mentioned in another thread that I always use the set up that Bob Whitely described in an article in Stunt News years ago and that combined with some careful bench trimming and balancing yields a  "eyes off" flying airplane. I even retrim airplanes that way that I inherit or buy off of other people. I haven't had an airplane with a "hunt" in it since I read that article.
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Online Ken Culbertson

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Re: Changing Stab Height
« Reply #17 on: February 02, 2022, 06:51:53 PM »
I always use the set up that Bob Whitely described in an article in Stunt News years ago and that combined with some careful bench trimming and balancing yields an "eyes off" flying airplane.
Any idea what year? Most of the old ones are on the PAMPA site.  I would love to read that article.  Maybe it has something to do with my style.  I come from the "Gieseke school" where a plane is heavy if you can feel it in your hand walking to the car and nose heavy if the CG is ahead of the flap horn.  Seriously, none of my inline planes would grove in level flight till I added serious nose weight which destroyed the "pop" corners we flew back then.  Haven't tried one since the 70's.  I have flown some since and they all hunted.

Ken 
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Online Dan McEntee

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Re: Changing Stab Height
« Reply #18 on: February 02, 2022, 07:19:53 PM »
Any idea what year? Most of the old ones are on the PAMPA site.  I would love to read that article.  Maybe it has something to do with my style.  I come from the "Gieseke school" where a plane is heavy if you can feel it in your hand walking to the car and nose heavy if the CG is ahead of the flap horn.  Seriously, none of my inline planes would grove in level flight till I added serious nose weight which destroyed the "pop" corners we flew back then.  Haven't tried one since the 70's.  I have flown some since and they all hunted.

Ken

   It's been a while but had to have been 15 year s or so or more ago. It was titled "Things That Always Work."  I haven't read it in a while so would do me some good to re-read it also as it was much more than what i mention. I've slept a few times since then. Maybe 6try search the PAMPA listing for article by Bob Whitely. I don't think he wrote very many.
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Online Trostle

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Re: Changing Stab Height
« Reply #19 on: February 03, 2022, 08:39:55 AM »
       
 I have mentioned in another thread that I always use the set up that Bob Whitely described in an article in Stunt News years ago and that combined with some careful bench trimming and balancing yields a  "eyes off" flying airplane.

   Dan McEntee

"Things that always work" by Bob Whitely  -  Stunt News  -  July/August 1998. 

(Only about 23 1/2 years ago.)

Keith

Online Dan McEntee

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Re: Changing Stab Height
« Reply #20 on: February 03, 2022, 09:07:47 AM »
"Things that always work" by Bob Whitely  -  Stunt News  -  July/August 1998. 

(Only about 23 1/2 years ago.)

Keith


     WOW!! That means that I'm that much older also! Disgusting!!!
     Thanks Keith!
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Online MikeyPratt

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Re: Changing Stab Height
« Reply #21 on: February 03, 2022, 09:31:19 AM »
Amen to  that.  How did you deal with the hunting?  Incidence?  Nose weight?  Slow controls, Majic spells?

Ken

Hi Ken,
A few had small hunting problems but for the most part it was easy to fix, on one model it turned out to be a sticky hinge on a flap, I removed the flap and replaced the hinge no more hunting.  Before replacing the hinge I tried everything up & done thrust, side thrust, more nose weight, less nose weight, heavier wheels, removed wheel pants & spats, tip weight & lead-out position, faster & slower lap times, warts on the flap.  I was at the point of giving up on the Magnum Force.

I removed the hinge seals and was cleaning of the tape residue off when I found the the sticky hinge.  Thatís was a good thing because the Natís were only a few weeks away.  After resetting all the adjustments back to where I started, the planets must have all aligned themselves, it flew great!, now I could really practice and get ready for the Natís.

One of the most fun things I did being the contest director for the Sig C/L contest was to help anyone that needed help with their model, Ive flew a lot of the models that were entered and the modeler asked for help.  Every time the modeler said its hunts, a closer inspection showed that something was sticking somewhere.

Later Buddy,
Mikey



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