Author Topic: High or Low tail, what are the pros and cons?  (Read 9789 times)

Offline Frank N. O.

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High or Low tail, what are the pros and cons?
« on: April 21, 2006, 12:29:47 AM »
Now, the discussion about pros and cons about low and high main wing have long been going on, and one of my 2002 plane magazines had an article about it with Beech, Piper, Cessna and a NASA engineer but what about the tail? About one plane I read that the tail was mounted high to be clear of turbulent air from the main wings while operating with extended flaps and planes such as the Commander does have the wing over normal low positions like for instance most Pipers. Cessnas also have low tails, except a variation of the 187 (I still haven't found a picture of it) but their main wings are high mounted and when looking at even the low sleek Cardinal the tail sits a lot lower but is it low enough to avoid turbulent air from flaps? And then the other biggie, something said against the T-Tail namely lack of function during stalls. Of course I'm sure there are many other factors and just how much less control the tail gets is of course also a factor since while some might loose a bit of control it's not necessarily enough to give problems. Note: One of the reasons I wanted my concept to have YF-23-style V-tail elevators was also that at least part of it shoudl always be in clear air, the rudder function was on the main wing btw so not like the V-tail Bonanza.

And speaking of tails, what about the stabilator vs seperate elevator. The original Cardinal had tail-first stall problems that was said to be cured by a adding something at the trailing edge and limiting the downward travel, but that last part doesn't sound smart to me though. How is a stabilator vs convetional elevator in terms of stability, feel/feedback and maneuvering ability? By feel I also wonder if the stabilator might require more force to move depending on where the rotation axis is and how good a feedback it has. I never did change altitude in the Cardinal I flew in, just did some mild turns but it felt nice, apart from the semi-loose yoke (I screw was a mm loose I think from the handle itself to the rod, you could feel a microclonk when pulling in one side of it towards yourself).

I did plan on attaching a schematic with a plane profile and simple lines for airflow but I couldn't find good enough drawings of the planes I needed so I hope you got a good imagination :)

Frank

P.S. I just checked online that my spelling "Manouvrering" is wrong that it should be "Maneuvering", sorry about that, not sure where I got that from except maybe from the other variations between UK and US english spelling like center vs centre and liter vs litre. If I can't remember a spelling of a word I use my natural analytical knowledge of a language to deduce how it's spelled, even if it's a imported word but this time it failed, at least it's a mistake without bad consequences.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline Gulfstream Driver

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Re: High or Low tail, what are the pros and cons?
« Reply #1 on: April 21, 2006, 03:17:12 AM »
Ok, I'll try to tackle at least one of these.   :)

Most T-tail airplanes are quicker than the normal trainer.  Many times, placement of the horizontal stabilizer has to deal more with engine placement than anything else.  Having the tail in the downwash isn't necessarily a bad thing.  In fact, the T-tail Arrow has trouble when it gets slow because the tail is out of the downwash from the wing.  Also, turbulent air from the flaps will help alert you to a stall.  The reason the Cardinal had so much trouble was because the tail was reaching it's critical angle of attack before the main wing did.  So, they added slots to the leading edge to keep the air attached to the bottom side. 

I don't think I ever noticed a difference between a stabilator and an elevator.  In fact, I noticed more of a difference going from a 172 to a 182 than in going from a Warrior to a 172. 

We knew what you ment by "manouvrering".   ;)
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Offline Gulfstream Driver

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Re: High or Low tail, what are the pros and cons?
« Reply #2 on: April 24, 2006, 02:08:58 AM »
I forgot to mention the most important advantage of a T-tail.  It reduces drag. 

All lifting surfaces produce a wing-tip vortex, even the vertical stab.  Putting the horizontal stabilizor at the top of the tail cancels that vortex and reduces drag. 
Behind every great man, there is a woman rolling her eyes. --Bruce Almighty

Offline Frank N. O.

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Re: High or Low tail, what are the pros and cons?
« Reply #3 on: April 24, 2006, 02:26:01 AM »
Aha, that's a nice collection of information there. Makes me want to see that T-Tail Cessna 187 even more.

Btw now we're talking about tails, did I remember correctly that some planes had the elevator-trim moving the whole surface and not just a tab or does that have to be wrong since it would be useless to tirm the whole surface?

Is there a problem with precision with the control when the control-linkage has to be thrue the tail? is there a problem with flexing or is that negligible
 on small planes?

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline Gulfstream Driver

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Re: High or Low tail, what are the pros and cons?
« Reply #4 on: April 24, 2006, 02:41:32 AM »
Bigger airplanes, like transport category, actually do trim the entire horizontal stab.  I forget the reasoning behind this, so maybe someone else can enlighten us.

It's possible that some airplanes have contol cable problems, but that wouldn't be T-tail exclusive.  It would also be fixed by an AD, or the airplane wouldn't be airworthy.
Behind every great man, there is a woman rolling her eyes. --Bruce Almighty

Offline Frank N. O.

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Re: High or Low tail, what are the pros and cons?
« Reply #5 on: April 25, 2006, 09:48:00 PM »
Thanks for the reply :) The control-link was something I didn't want to have problems with but I don't know how precise such parts are and what area could be hard to make work so I wanted to ask now I have the chance to talk to people with real experience about the subject :) Of course I hoped that it wasn't a problem since if it was with a plane less than 8 metes long then how bad couldn't it be on a bigger plane.

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline SkyKing

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Re: High or Low tail, what are the pros and cons?
« Reply #6 on: May 02, 2006, 07:21:33 PM »
I forgot to mention the most important advantage of a T-tail.  It reduces drag. 

All lifting surfaces produce a wing-tip vortex, even the vertical stab.  Putting the horizontal stabilizor at the top of the tail cancels that vortex and reduces drag. 

It doesn't cancel it, it dodges it.  The T is in clean airflow unless you have a really radical AOA.


Offline SkyKing

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Re: High or Low tail, what are the pros and cons?
« Reply #7 on: May 02, 2006, 07:27:13 PM »
Advantages:

The T is in clean airflow, up away from junk kicked up in rough-field ops and out of the tip vortices.  It's better to have all of the airflow from straight ahead, not swirling onto the top or bottom of the stabilizer.


Disadvantages:

Harder to pre-flight

The cantilever-on-a-cantilever design MAY cut useful lifespan of the airframe

Out of the prop airflow, so it takes a little longer to get unstuck in short-field ops


For most people the As and Ds pretty much null each other out.  I like both pretty much equally.




Offline SkyKing

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Re: High or Low tail, what are the pros and cons?
« Reply #8 on: May 02, 2006, 07:30:51 PM »
Bigger airplanes, like transport category, actually do trim the entire horizontal stab.  I forget the reasoning behind this, so maybe someone else can enlighten us.

There is less drag when the entire plane of the stab is tilted than when there are two separate planes, one "flat" and one hinged enough to not only provide the desired trim, but also to counter the aerodynamics of the flat portion.  In a big acft this is a significant difference.

Offline Frank N. O.

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Re: High or Low tail, what are the pros and cons?
« Reply #9 on: May 03, 2006, 01:17:22 PM »
Thank you very much for your posts, very interesting information there :)

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline fliboye

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Re: High or Low tail, what are the pros and cons?
« Reply #10 on: June 22, 2006, 01:03:59 AM »
t-tail is out of the prop wash will not fly until it wants too, and has a tendecy to quit flying in the flare so add 5kts to Vref. conversely the low tail flys well thanks to the propwash making smooth landings easier. supposedly :-\ ;)
I got into aviation because it was fun now I'm stuck cause I need the money ;-))))

Offline Frank N. O.

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Re: High or Low tail, what are the pros and cons?
« Reply #11 on: June 22, 2006, 01:45:26 AM »
Interesting info, thank you :)

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline fliboye

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Re: High or Low tail, what are the pros and cons?
« Reply #12 on: June 24, 2006, 01:08:21 AM »
sometimes experience is the best teacher books can usually leave part of the reality out  :o
I got into aviation because it was fun now I'm stuck cause I need the money ;-))))

Offline Frank N. O.

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Re: High or Low tail, what are the pros and cons?
« Reply #13 on: July 08, 2006, 01:34:46 PM »
True, but some experiences are best read instead of experienced, if you catch my drift :D

Btw, is that Bob Marley in your avatar?

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline fliboye

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Re: High or Low tail, what are the pros and cons?
« Reply #14 on: July 09, 2006, 09:19:20 AM »
no not really could not find how to put my own pic there but I did fly the bahamas for 4 years  ;D
I got into aviation because it was fun now I'm stuck cause I need the money ;-))))