Roger Shook

My Feedback: (19)

Thanks for chiming in guys!! Two things jump out at me right away.. 1) I will have to read the AMA guidelines, but I am not the that a Byron F-18 fails under the guise of large model aircraft. That being said, 2) I am not planning on using the Byron linkages for this plane. I am purchasing the mechanisms pivot bearings , rods and servo mount assemblies, and hoping to actuate the stabs like most of the newer style kits like Jet Legend, Skymaster, etc. This why I suspected from articles on RC Groups that the pivot might need to be moved. Moving the pivot to the 23 % point will leave this stab VERY heavy at the rear. Which could require lots of weight to static balance and as the structure involved here is Byro foam could get difficult to encapsulate. I am sure I am not done with this adventure at this point. This all comes to bear because of modern EDF motors and fans producing much more thrust than this kit was ever set up for. Just trying to be safe and not wipeout all my work on this conversion!!
Regards, Roger

Art ARRO

My Feedback: (5)

Roger,
Ensure that you are calculating the correct MAC on the Byron stab. I believe there is a method described in the LMA guidelines. Oliver Nicholas (Olinco) also described the method for an F-18 stab in an issue of RCJI magazine a while back. I'll try to locate the issue and can scan it for your reference.

Art ARRO

Art ARRO

My Feedback: (5)

Roger,
To add to my previous post, I'll wager that once you calculate the MAC of the F-18 stab and project the value onto the root you'll be at or near 43%. Just follow the diagram in the LMA-T (for turbine) guidelines. Also consider a strong reliable servo, 150 oz/in torque, to actuate the stab.
I presume you are going to use twin Byron fans converted to E-power. A buddy has done this with his Byron F-16 and the performance gain is fantastic. I believe he used a Hacker motor and 12S Lipos in the Byrofan. Good luck with your Hornet project.

Art ARRO

Roger Shook

My Feedback: (19)

Thanks Art,
I downloaded those LMA guidelines, and will check the MAC this morning. Actually I will be using a single Dyn e max fan or possible an extreme models Ramtec fan which will be fully ducted. I will start out at 12s , based on the performance I saw on Jim Drew's edf Yellow F-15. He has been instrumental in helping me develop my plugs for the ducting. Another fellow,
did one of these a couple years ago , using the stock stab arrangement, and reported flutter on his test flights at fullpower. Thus I am trying to head that off on my development. I am probably over building my stabs (adding too much weight to them). I have cut off the trailing edge foam and added balsa trailing and leading edges. the leading edge balsa also has a thin strip of carbon fiber between it and the foam. Once I determine the pivot point, I will notch into the foam and add a piece of spruce for the control pivot rod to be installed into. And then glass the assy with lite glass cloth. Hopefully I can over come that weight with the batteries up front.

Roger Shook

My Feedback: (19)

Well, after all of that , layed out the the MAC, for this stab and found that the center line of the stock pivot is actually 3/32 of and inch in front of the requested 23% of the MAC . I guess I won't be moving my pivot, and will static balance the stabs. oh if you look at My Gallery you will see a picture of RCAF jet I will be modeling. Thanks guys for getting me on the right track.
Roger Shook

Art ARRO

My Feedback: (5)

Roger,
Good news and your stab beef-up should really work well-much better than an Asian manufacturer of turbine jets. For the static balance, Olnico adds enough weight to the root leading edge to balance- and then removes about 20% of it. Example, add 10 grams to neutral balance and remove 2 grams for the final setup. The e-Dynamax fan should work well in your Hornet. There's plenty of internal space for those 12S Lipos for balance. Again, good luck with your project.

Art ARRO

Flypaper 2

I experimented with the flying stab about 5 yrs ago on a 3D foamy that was giving me trouble where, on a tight loop, it would go around steps, as it it felt like the stab was flying, stalling, flying , stalling etc. Mind you it has about 60 deg throw. At any rate, I went to Google and did much research on the flying stab. I ended up with the recomended pivot point at 25% of the surface area. It will now loop without the steps and loops around the wing CG. No signs of flutter at high speed, which isn't much on a 3D plane. Maybe 50 mph. Pivot in the fuselage is aluminum tubing and the spar into the foam stab halves is close fitting carbon tubing.Getting a bit loose after 5 yrs but still no flutter. I think more because of the proper pivot point. Just a regular small servo as with the erea ahead of the pivit point acts like a booster tab. Doesn't look like much but it works.

Gord.

Rotaryphile

I have tried all-moving horizontal stabs on two models, and couldn't see much difference in performance. A further experiment with an all-moving combination fin/rudder was a total failure - about half as powerful as a conventional fin/rudder of the same total area, despite extreme deflection angles. The stab/elevator or fin/rudder combination acts, when its control surface is deflected, like a cambered airfoil, which can develop far higher lift than any thin symmetrical airfoil that is simply inclined to the airflow.

ByLoudDesign

Look at the modern jet they all use them, but look at their sizes. Much bigger then a normal stab/control surface.

da Rock

For model airplanes, the benefit is slightly less drag for the required lift. The models that gain the most are gliders. Since humans really can't judge airspeed at all (since they can't see wind), gains in cruise efficiency aren't going to be visible. We aren't going to see the difference in performance that is improved. We also have a problem creating a valid test comparison between the two designs.

Flypaper 2

I wonder how many here have actually tried it rather than just theorizing? The flying stab I showed above is the same planform as the stock Flash stab and the same throw. Like i said it would loop almost in its own length. There is no way to compare to the full size plane. In these small comparative sizes the Reynolds numbers also come into affect.

sensei

I have...

Bob

da Rock

Have tried what? A flying stab, or building a model that accommodates both designs so a comparison would actually be valid.

The real problem of comparing two different things is how hard it is to change only those two things. It's screwed even more in this case because seldom can you have the best setup for both designs to operate optimally on the mule airframe. And to prove one detail requires all the rest to match.

For example, a previous post says something about a cambered airfoil can outperform a thin symmetrical one. What has the thickness of one have to do with a difference between the two design concepts. If you want to know which is better, stab/elevator versus flying stab, tests should be done with only that one difference in the two test subjects. Build one test structure different than the other and your test really isn't trustworthy. It would make sense to also test the optimum stab/elevator against the optimum flying stab with area and aspect ratios equal. Unfortunately, without wind tunnel control and instrumentation to give some clue which design works more efficiently, modelers haven't a hope of proving anything.

We can't see airspeed and absolutely can't see or measure efficiency. Good thing is, we'll always have nothing to solve any of these conundrums. So we will be able to discuss our theories forever.

Flypaper 2

The Flash 3D is identical in every respedt other than the flying stab, which is even made from the same EPP foam as the stab elevator. It worked so well I tried it on my Zoombi. Here it is with the flying stab and a booster tab on the rudder to take some of the load off the servo. With the extra rudder throw that the tab gives, it does knifedge loops much tighter. Another point, at these slow speeds that the 3D planes fly at, much stab and rudder area are very essential. Even high alpha takes a lot of throw and precision.

Rotaryphile

I tried an all-moving fin/rudder combo on the same basic design that I have used previously with a normal fin/rudder. It developed about half the yaw angle of the conventional fin/rudder, with the same planform and same total area.

A few years ago, some pattern flyers were touting quite thick vertical fins. I whomped one up from foam, and tried it in a wind tunnel. I could discern very little improvement, if any, from the thick fin, so I stayed with relatively thin fins, with about a 50/50 area split between fin and rudder. The fin/rudder combination evidently can develop, with 45 degrees rudder deflection, about twice the lift coefficient of an all moving surface.

Cessna was forced to add a slot to their all-moving horizontal stab (stabevator) in order to get sufficient downforce for landing with a forward CG. This must have more than nullified any reduction of drag that might be obtained by eliminating the hinge line.

Bax

My Feedback: (11)

Actually, that was in the Cessna 177 Cardinal, and the stabilator had to have the slot added so that it would not stall when at a high "up elevator" deflection. This was a result of them finding out that pilots were doing full-stall landings and winding up with the the stabilator stalling and causing a rapid nose drop while in the landing flare. The slot energized the airflow on the stabilator's lower surface and allowed it to keep working properly throughout the airplane's speed range. Boeing 727 stabilators had vortex generators on their lower surface for the same reason: keeping the airflow attached at high angles of deflection.

UStik

Hm, hadn't the 727 a moving stab for trim and conventional elevators? Of course I agree it had the vortex generators to keep the airflow attached in spite of the sharp kink on the elevator hinge line. The Fieseler Storch even had a slat on the elevator's bottom just behind the hinge line for the same reason. That resulted in both more elevator effect and less stick force.

A full-moving stabilizer (stabilator?) is a mysterious thing for many pilots, at least that is my impression. It must be handled in a different way from conventional elevators. Even during normal landings the deflection needed is quite small. Full deflection (to the stop) is needed only on rare occasions like full-stalled (non-standard) landings when the whole airplane flies with much pitch. In that case, full up stabilator is reached only after slowly pulling more and more during flare. But it's easy to just pull the yoke/stick fully back in a still low-pitch attitude and thus stall the stabilator. That way it is feasible only for the seasoned pilot. Some manufacturers provided kind of trim tabs along the trailing edge which deflect in the same direction to make for both some camber and stick force (which is lacking otherwise). Others try to prevent stabilator stall by slats, slots, or vortex generators. Either way, the average pilot should now be able to handle it.

da Rock

SPOT ON !!

They operate differently. For sure they must be handled differently. The chances of swapping them on the same airframe and not hurting one or the other is slim, very slim. To have a realistic and valid test, you would expect both to perform to their optimum. Something that's just not going to happen by chance.

This is another issue that is way beyond proving on a model field. And assuredly beyond proving by discussion on the internet.

Marty79

The entire Piper Cherokee series of aircraft use a stabilator. from the first PA28 Cherokee built in the early 1960's up to the PA32 Saratoga series. even Piper's "T" tail designs the on the Tomahawk (aka the Trama-hawk) Arrow, Lance and the Seminole all used a stabilator.

From what I noticed there was no real difference in the handling of the aircraft equipped with a stabilator and those equipped a conventional elevator.

UStik

Yes, you're right, I didn't notice any difference in a PA 28 as well. But on the other hand, I was present when the owner of a well-known flying school refused to buy the Tomahawk (what means trama?) because it would drop the nose when an unaware student would flare it. Might have been because the T-tail is not blown by the prop, don't know. Maybe we just don't notice a difference simply because we can handle it intuitively, maybe others can't? And if I was told correctly the Cessna Cardinal is special because they set the cabin forward, the front seats in front of the new cantilever wing, making for an unusually forward C/G position. Besides it's a shoulder-winger so the C/G moves forward (relative to the wing) with more pitch.

Marty79

Sorry I misspelled Trauma

Here's the definition that fits Just like the flight school owner said. The "T" tail Tomahawk would stall much quicker and the nose would fall rather violently. The first time I flew one I was shocked how fast the airplane would stall.

trauma, psychic trauma(noun)an emotional wound or shock often having long-lasting effects

BMatthews

Didn't the Tomahawk get a reversed leading edge slot on the stabilator just to aid in avoiding this sudden loss of lifting power at the tail? It's been a LONG time but that seems familiar.

Marty79

No it didn't I went back ad looked at a couple of my pilot handbooks and I made a mistake the Tomahawk DID NOT have a stabilator. It had a standard stab and elevator. My bad!

But, the Cessna C177 Cardinal did have a slat in the stabilator to help provide positive control at lower airspeeds. the C177A was a poor performing airplane But the C177B was a very nice predictable airplane to fly. Never had the chance to fly the Cardinal RG though.