Marjackson82 Posted November 19, 2009 Share Posted November 19, 2009 What are those numbers forward of the horizontal stabilizer in the B-52 for? Link to comment Share on other sites More sharing options...
Napoleon_Tanerite Posted November 19, 2009 Share Posted November 19, 2009 can't really make out in the pic, but taking a guess I'd say it is marking where the stab trim is set to. Link to comment Share on other sites More sharing options...
HiFlyer Posted November 19, 2009 Share Posted November 19, 2009 can't really make out in the pic, but taking a guess I'd say it is marking where the stab trim is set to. Yep. They're reference marks for the stab trim. You'll find them on most large aircraft that have a trimable horizontal stab, although the exact markings are different. The -135 has them, too, although if I recall there were only a center mark and two max deflection lines. Link to comment Share on other sites More sharing options...
Marjackson82 Posted November 19, 2009 Author Share Posted November 19, 2009 I was reading on Wikipedia that "In some aircraft models (mostly jets), the entire horizontal stabilizer rotates and functions as an elevator". Having flown nothing but C172s, I wasn't aware of that. So in larger aircraft there are no elevators per say, just the entire horizontal stabilizer acting as an elevator? Link to comment Share on other sites More sharing options...
afnav Posted November 19, 2009 Share Posted November 19, 2009 A pilot can tell you more, but the stabilizer trim on a BUFF is a really big deal, especially if the rudder-elevator hydraulics go out. We did a taxi-back in once with dual-system failure, and the AC said if we had gone airborne, we probably would have had to punch out. Link to comment Share on other sites More sharing options...
sentrymechanic Posted November 19, 2009 Share Posted November 19, 2009 Not really larger aircraft but most of your swing wing aircraft like B-1s and F-14s use the horizontal stabs as elevators and ailerons with the wings still retaining flaps and spoilers. And yes those are indeed travel markings for the horizontal stab on the pic of the BUFF. Link to comment Share on other sites More sharing options...
Schmity Posted November 19, 2009 Share Posted November 19, 2009 All aircraft (to my knowledge) have some type of elevator, be it a standard horizontally mounted elevator, an elevon or a ruddervator or whatever else some engineer has come up with. The h-stab is used to trim the aircraft so the pilot has full deflection of the elevator when trim is needed and is usually coupled to the autopilot system. Im sure there are more uses for it and possibly a better explanation, but I think that's the gist of it. Link to comment Share on other sites More sharing options...
Clayton Bigsby Posted November 19, 2009 Share Posted November 19, 2009 Does the BUFF have elevator tabs used to fly the stab into position like the KC-135 does, or does the H stab work "normally" where the elevators are elevators and the H stab surface is used for trim through a jackscrew? Link to comment Share on other sites More sharing options...
zrooster99 Posted November 19, 2009 Share Posted November 19, 2009 I was reading on Wikipedia that "In some aircraft models (mostly jets), the entire horizontal stabilizer rotates and functions as an elevator". Having flown nothing but C172s, I wasn't aware of that. So in larger aircraft there are no elevators per say, just the entire horizontal stabilizer acting as an elevator? You ever flown a Cherokee? The buff and the tanker have the marks. I'm pretty sure the 17 doesn't...you wouldn't be able to see them if it did. Many large jets have a trimable stab and an elevater. The 17 has stab trim, elevator trim and (obviously) elevators. Pitch changes are made via the elevators. Our stab trim is just that, trim. Link to comment Share on other sites More sharing options...
pawnman Posted November 19, 2009 Share Posted November 19, 2009 The B-1 has those markings too...and yes, the whole horizontal stab moves to function as an elevator. It's also a "rolling tail", meaning that the right and left side can move independently to roll the jet. Link to comment Share on other sites More sharing options...
skinny Posted November 19, 2009 Share Posted November 19, 2009 Does the BUFF have elevator tabs used to fly the stab into position like the KC-135 does, or does the H stab work "normally" where the elevators are elevators and the H stab surface is used for trim through a jackscrew? Fly the stab into position? Not really. The 135 has a horizontal stab, elevators, and what I think you're referring to known as elevator trim tabs. The H-Stab is electrically or manually driven and stays in place unless manipulated by the crew. The elevator still controls pitch and the elevator trim tabs assist the movement of the elevator at higher speed as the 135 is still a cable driven aircraft when it comes to flight controls (minus the rudder but that's a different story). Link to comment Share on other sites More sharing options...
theat6bisasham Posted November 19, 2009 Share Posted November 19, 2009 I fly the Buff.. Small elevator at the back of the stab. Yoke controls elevator. Trim controls the position of the stab - 9 units NoseDown to 4 units NoseUp - so marks are not equal both directions This means trim does not displace the yoke. High performance aircraft with huge margin between stall speed and top speed requires this design. But also this means your trim requirements are very imporant, because the elevator does not have nearly enough authority to control the aircraft if you are not trimed correctly. Link to comment Share on other sites More sharing options...
Steve Davies Posted November 19, 2009 Share Posted November 19, 2009 Trim controls the position of the stab - 9 units NoseDown to 4 units NoseUp - so marks are not equal both directions Does the DCC check the stab can travel to each trim limit following start? The lines are presumably there for *someone* to verify full and free travel to the extremes of deflection... Link to comment Share on other sites More sharing options...
ExBoneOSO Posted November 19, 2009 Share Posted November 19, 2009 The B-1 has those markings too...and yes, the whole horizontal stab moves to function as an elevator. It's also a "rolling tail", meaning that the right and left side can move independently to roll the jet. Primary roll control is with the stab, with additional roll augmentation from spoilers on the wing..it's always an eye opener for the uninitiated to watch a flight control check on the ground, and see the stab go full up, full down, then split with one side up and one side down. Does the DCC check the stab can travel to each trim limit following start? The lines are presumably there for *someone* to verify full and free travel to the extremes of deflection Yep, the ground crew confirms stab position during preflight. Sadly, the RAIDER 21 incident at Andersen showed how important stab trim position is on the BUFF. http://usaf.aib.law.af.mil/B-52H_Andersen_21Jul08.pdf Link to comment Share on other sites More sharing options...
Marjackson82 Posted November 19, 2009 Author Share Posted November 19, 2009 Very interesting. Thanks! Link to comment Share on other sites More sharing options...
Guest zos149 Posted November 19, 2009 Share Posted November 19, 2009 Any supersonic aircraft is going to have a fully movable horizontal stab. This is because of the shock wave that builds on the control surface near critical mach. (around Mach 1 for a horizontal stab) This makes a traditional moving elevator ineffective. Old Chuck discovered this in the X-1 when he lost all pitch authority near Mach 1. Link to comment Share on other sites More sharing options...
Napoleon_Tanerite Posted November 20, 2009 Share Posted November 20, 2009 Any supersonic aircraft is going to have a fully movable horizontal stab. This is because of the shock wave that builds on the control surface near critical mach. (around Mach 1 for a horizontal stab) This makes a traditional moving elevator ineffective. Old Chuck discovered this in the X-1 when he lost all pitch authority near Mach 1. it's not just supersonic aircraft-- it's pretty much all LARGE aircraft. AFIK, all airliners use the entire horizontal stab for trim, as do most private jets. It's a matter that it simply takes too much force to trim a big airplane using the elevator surface alone. Link to comment Share on other sites More sharing options...
zrooster99 Posted November 23, 2009 Share Posted November 23, 2009 it's not just supersonic aircraft-- it's pretty much all LARGE aircraft. AFIK, all airliners use the entire horizontal stab for trim, as do most private jets. It's a matter that it simply takes too much force to trim a big airplane using the elevator surface alone. I think zos is talking about a stabilator vs. stab trim which is what you're talking about. Link to comment Share on other sites More sharing options...
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