Appowner

While not a Jet, it was suggested I throw this out here to you guys.

I'm building a 30% scale model of a Piper Cherokee 180 based on the Hostetler plans for the 140. The trick is the real one has a Stabilator or Flying Stab which I want to replicate but Hostetler does not show in the plans. So to that end I'm looking for advice/suggestions as to:
Constructing the pivot so it's solid, serviceable and as light as possible for this size model?
Where to get the parts?
To counter balance or not?
What size servo you guys might recommend for this? Currently considering going with 200 ounce.

Here are the specs for the stab and some basics for the model itself.

Stab:
Simple, straight constant cord fully symmetrical.
36 inches span
9 inches cord
TE of stab has an anti-servo tab (included in above measurements) which travels in the same direction as the stab itself. Just further. It is 1.5 inches wide by 33 inches long.
The stab will rotate a max of 15 degrees up from neutral. Down will be much less but I never really had trouble getting one to come down.
Pivot point is located at the 28% point of the cord. Basically it's on the front side of the box spar.
There is also a counter weight that sticks out from the center of the front of the stab into the fuselage. The stab is then balanced 100% statically. Don't know if I'll use that or not.
Fuselage cross section at the pivot is 2 inches wide by 5 inches tall. Should be enough room. Fuselage behind the pivot will be a two piece, top & bottom fiberglass tail cone.
Right now the plan is for the stab to be a single piece. Attaching/detaching through the removal of the glass tail cone. However, the idea of a 2 or even 3 part stab is a consideration. Plug in outer panels either to each other (2 piece) or to a semi-fixed center section (3 piece). But being in the tail, weight is a consideration and the one piece might be the lightest of the bunch.

The model has a 108 wingspan and will weigh in the neighborhood of 30 pounds and hopefully, less.
Current power choice is the OS 320 Pegasus.
The model will be sub-sonic! Anticipated speed of 65 mph max.

So, with the experience in flying stabs on jets, what can you guys suggest? Here are some pics of the real deal and model plans of one and the way someone else did their Hostetler Cherokee.

Thanks All!

gunradd

My Feedback: (9)

Cool project!

I would not worry so much about the weight and focus on getting the stab 100% balanced. Planes that are bigger like this tend to have light wing loadings but allot of stress on the control surfaces. Even if you have lead in the nose the stab needs to be balanced.

I would go with 400oz servos since they are around the same price and pretty standard now. Make sure you use max mechanical advantage by using the inside holes on the servo. Go to dreamworks RC and you should be able to get a rod and some clamps for a servo horn.

On the tab I have worked on real ones and its a simple piano hinge. You should do the same on yours.

Viper1GJ

My Feedback: (20)

Great project.

I recently discovered parts from Actobotics available from robot supply houses. They have bearing blocks, clamp hubs, and horns that you may be able to use. I recently posted some info here: http://www.rcuniverse.com/forum/rc-j...-elevator.html

Also the AMA LMA document has some info on computing servo forces for flying stabs.

Back in the 1970's I had about a 100 hours in a Cherokee 180 before the Air Force. It was a good flying airplane. Will be a great model.

Good luck on the project. Post some pictures!

Gary

Craig B.

I would have to say that I don't agree on the need for stab balancing in our models. Not one of my jets have balanced stabs. That includes 3 x F16's, 2 x F18's, 2 x F15's and an F14 and 20+ years of flying jets. They all do several hundred K's per hour. What is far more important is to minimise control surface slop and that comes down to tight pivot mechanisms, slop free linkages and powerful precise servos with the correct geometry (longer control horn on the surface and as short a servo arm as possible)

Hope that helps. Flame suit is on.

gunradd

My Feedback: (9)

Greg no need for flames lol.
I too don't balance all my jets. I did not balance the stabs on my F22. It went through two sets of new gears due to wear on 8711 servos. If they where balanced the wear would have been much less. Some I do if I feel they need it. The first few carf mepohestoes where crashing due to elevator needing to be balanced. Saw the tail come off two and one was able to land using thrust vectoring and another lawn dart because he did not have it. They where flying in formation and both got to a certain speed and both came apart almost the same time. Now CARF fixed that problem I understand by balancing the stabs at the factory. Also the BVM F16 got balanced and I understand now its done at the factory. Back when I built Barrys it was not balanced but BVM supplied a kit to balance them because Bob felt it was needed. . I did balance my big F15 and also my F18. They where really big heavy models and the stabs where very out of balance and did not want the extra servo wear.

Now this guys plane while is a flying stab its a straight stab and not like a stab on a jet. I seem to remember a mandatory SB on these stabs on the full scale relating to the counter weights, hinges, corrosion and some crashes. All I know is I have had to spend countless hours in my 20 years as an aircraft mechanic and IA inspector balancing flight controls to manufactures specs. I find it hard to believe its all a waist of time and the aircraft manufactures don't know what they are talking about.

Bottom line
How many aircraft have crashed because some one took the time to properly balance a stab? 0
How many have crashed because they didn't balance the stab and got flutter...…. Lots.

While it might not happen on this guys plane he has a place for the counter weight and its in the same place as the full scale. Why not utilize it? Cheap insurance.

Zeeb

My Feedback: (41)

Your memory is working just fine Kris except that it turned into an AD....

As for the OP's question and Craig's response; part of the issue is that the pivot point on the flying stab is forward of it's balance point by quite some distance. This allows the stab to be mounted further to the rear of the fuselage and since the counter balance can extend quite a way into the rear of the fuselage, it's no big deal to have it there other than the difficulties mentioned that created the AD on the full scale Pipers. That should not be an issue on the model.

The pivot point of the stabs on the scale fighter jet are much closer to the actual balance point with them being slightly tail heavy which is were they should be balanced, so no counterweight is needed unless you have one of BVM's 1/6 th scale PNP F16's as I do, in which case there IS a counter weight installed on each stab in front of the pivot point.....

LN-JET

You should leave the anti servo tab inactive. It is there to give more stick resistance, and lessen the chance of overstressing the aircraft. For a servo this is of no use.
If you want them removable, then maybe go for a square joiner tube, with precise molded sockets .

Lars

YellowAircraft

Hi

I've mentioned this before, and I'm sure this project is long finished, but it's noteworthy that the number of production aircraft in the world with full-flying stabs on which the stabs are static-balanced on the pivot is exactly........zero. This is particularly true for Piper aircraft like the one being modeled. Just sayin...

Zeeb

My Feedback: (41)

Well that's easy to say; Piper no longer exists and hasn't for quite a long time. Hard to compare a Cirrus/Cessna to an old Piper. The Comanches and the early Arrows were some of GA's best efforts at a real, useable by the average person and not too expensive GA aircraft were admirable IMHO.

As for your model; an out of balance control surface can only be made worse by ignoring the issue. It may be a model, but it's still an airplane.....

YellowAircraft

Zeeb

The term 'out of balance' assumes that the balance point is a non-variable, and ignores the loud fact that the plane being modeled does not have a 'balanced' stab. I use air-quotes because I know the stab IS balanced, but not in the sense you mean. This notion that all full-flying stabs should be balanced on the pivot is scientifically absurd... and the best evidence of that is the absence of any examples of this in the [production] full-size aircraft world. The balance point depends on many things--many factors and variables. Go to ANY production full-size aircraft with a full-flying stabs and you will see a stab drooping at the trailing edge. Go to any full-scale Piper aircraft with a full-flying stab and not only will you see one that is NOT balanced on the pivot, but one in which the stabs suddenly 'balances' once you start the engine. Why? The airfoil is designed to balance and 'fly' at a given speed and pressure. So... before we can say a stab is 'out of balance', wouldn't we need to know what the other variables are?

LN-JET

The way I read the manual, the Stabilitor should be anything between neutral balance, to 30 In/lbs tail heavy.

Lars.

olnico

That is correct. Because a tail heavy full flying stabilizer actually provides positive stability while flying.
If the plane encounters an up draft, the stabilizer will tend to rotate leading edge up if its CG is behind its pivot point. This will have a pitch down effect on the plane, which will counter the effect of the up draft.

Auburn02

My Feedback: (1)

Say what?

patf

My Feedback: (4)

I mean the hershy bar wings are gone but you can still buy a piper
https://www.piper.com/models/?ref=homepage-banner

JSF-TC

My Feedback: (2)

This subject feels like it has the same staying power as the mythical 'Downwind Turn' topic............