Power-On vs Power-Off Stall Speed

[Barrett]

Sidebar: early in the Super Hornet program, Pax River found that high AOA/low speed performance was not repeat not what was predicted. Turned out that computer modeling was flawed--don't know about wind tunnel tests or even if they were used. Anyway: the Pax bubbas fetched back a quantity of various grit sandpaper and affixed samples to the airframe until the desired burble/performance was achieved. Honest. Then the "slide rule" (yeahright) guys tweaked the data to finalize things.

 

[davparlr]

Davparlr,

I was in 89-12, 1988-1989 and experienced only the Tweet / Talon. The T-1 came well after my time as well as the other than white paint scheme on T-38A's. Currently the standard configuration is the T-38C, with full glass, GPS and HUD and is used in the Advanced pilot training as well as Introduction to Fighter Fundamentals (IFF).

They also got rid of the FAR / TTB rankings while I was there, but still tracked guys / gals under that philosophy.

The only A models left are hand me backs from Singapore that fly Red Air for the F-22 and F-35.

The USAF C models have had new wings installed at least twice, new seats with chute built in, and new intakes.

Cheers,
Biff

Yes, the T-38 wings have been replaced which is expected after 50+ years but I do not think there has been any upgrade to the basic airframe including tail section. I worked at Northrop for 29 years with about four years on the F-5 (basically a muscled-up T-38) and then about 20 years in B-2 Avionics Controls and Displays including being manager. If you have any comments from pilots on the B-2, specifically the Controls and Displays system, I would be grateful to hear about them.

I do have an interesting story about the F-5 that I think you would enjoy. During manufacturing, one station mated the tail section to the main section with bolts. Two men worked this station for many years with no problem. One day one of the men was on vacation and the other got sick. New men were brought in to mate the aircraft. They couldn't do it. The bolts holes did not align. The assembly line stopped. When the the sick man returned he was confronted. He said he knew that. They just took a larger drill bit and redrilled a bigger hole and pressed on. Northrop was in a uproar and spent emergency review of the stress guys to determine if that was a catastrophic modification. To everybodies relief, the results was no impact.

I'm not familiar with FAR/TTB. Could you explain?

 

[BiffF15]

Yes, the T-38 wings have been replaced which is expected after 50+ years but I do not think there has been any upgrade to the basic airframe including tail section. I worked at Northrop for 29 years with about four years on the F-5 (basically a muscled-up T-38) and then about 20 years in B-2 Avionics Controls and Displays including being manager. If you have any comments from pilots on the B-2, specifically the Controls and Displays system, I would be grateful to hear about them.

I do have an interesting story about the F-5 that I think you would enjoy. During manufacturing, one station mated the tail section to the main section with bolts. Two men worked this station for many years with no problem. One day one of the men was on vacation and the other got sick. New men were brought in to mate the aircraft. They couldn't do it. The bolts holes did not align. The assembly line stopped. When the the sick man returned he was confronted. He said he knew that. They just took a larger drill bit and redrilled a bigger hole and pressed on. Northrop was in a uproar and spent emergency review of the stress guys to determine if that was a catastrophic modification. To everybodies relief, the results was no impact.

I'm not familiar with FAR/TTB. Could you explain?

I haven't spoke with any B-2 guys so can offer no feedback.

I had not heard of the F-5 story but can believe it. They got the job done with a little ingenuity...

The 38 intakes were changed but not sure what the outcome was. Nice cockpit though.

FAR / TTB means two things: First it stands for Fighter Attack Recce / Tanker Transport Bomber qualified. The former did more contact, formation (4 ship) and low levels while the latter did more instruments and cross countries per the syllabus.

Those splits occurred after assignment night, with FAIPs doing the FAR track.

Cheers,
Biff

 

[special ed]

The bolts story reminds me of a piece in a book about Curtiss in WW2. It was the first flight of the wooden C-76 and workers and staff outside to watch. An engineer walked over to a shop foreman and commented " I hope four bolts in the stabilizer are enough". The foreman said, "what bolts? There are no bolts in the stabilizer". A hurried radio call brought the plane back.

 

[FSG43]

Recovery from a spin is power off, opposite rudder, nose down right?

Hello all,

I'd like to share a few thoughts about the subjects "de jour." Firstly, since I've used Zipper's post as an entryway to my ramblings, let me address spins in GA single-engine land (SEL)airplanes. Secondly, please excuse the ramblings... .

Spin practice is usually performed at altitudes of 3,000-ft. or more AGL. They're entered into with the power retarded to idle or just a tad above (depending upon the OAT and the need to keep the engine operating). As the pilot applies elevator back-pressure the airplane begins to pitch up; once the airplane's wing reaches its critical angle of attack (CAOA) it will stall. At the moment of the stall the pilot applies full rudder in the direction he/she wishes enjoy the rotational view. After one to two full rotations the pilot applies forward elevator pressure sufficient to unload the wing (eliminate the stall AOA often referred to as, "breaking the stall."); simultaneously the pilot applies full opposite rudder to stop the airplane's rotation. Once accomplished, and it's only a matter of a few seconds, the rotation stops, the pilot neutralizes the rudder and begins to apply elevator back-pressure to attain a flight attitude for a glide or climb, depending upon desire and "need." Power is usually applied during this phase.

Note: some of the newer airplanes have a limited up elevator which gives ya just enough pitch authority to make a good main gear touchdown but not place the wing into a stall... hence the mushing some folks talk about. Yes, mushing/no-stall can be because of loading too. That's why we used to lash-down a case of Aero-Shell oil in the baggage compartments of the Tri-Pacer and old Muskateers.

The wing has one AOA it will stall at- it's referred to as the "critical angle of attack (CAOA)." In all of the 50+ single-engine airplanes I've flown, this CAOA can be exceeded with a delayed stall when performing power off stalls when demonstrating take-off and departure stalls under T-O power or full power setting. This is due to the thrust and accelerated slipstream over the wing which generates additional lift to a point. At the time of the stall break, most of the airplanes pitched down a bit more briskly.

To the unskilled or unwary pilot this type stall can cause some to soil their drawers a bit. With a high AOA, under T-O or full power, the airplane will have some powerful yaw-producing forces being exerted upon it: p-factor and spiraling slipstream. These two are waiting to bite the uwary pilot. In U.S. certified and mfg. airplanes the propeller rotates clockwise from the cockpit view. Both of these yaw forces will lead to a fairly snappy roll to the left at the moment of the stall. This rolling event is coupled with a brisk pitch down, sometimes surprising the pilot. When this occurs, there are some pilots who go 'primal' and apply full elevator back-pressure, holding it there until colliding with the ground. They become a statisic along with any passengers accompanying them. I've investigated quite a few of these loss of control accidents. Very often, in airplanes equipped with them, you'd see the pilot's yoke horn (left side) bent back between 10 and 20-degrees. That's how hard the poor bugger was trying to get the "nose level."

In most of the SEL GA airplanes there's another force acting on the airplane. It's compensated for by the wing section opposite the propeller's rotation (engine's rotation too). This force is "torque;" a roll force. I've experienced this is larger SEL airplanes when playing about. What bites the pilot on occasion is the aerodynamic fix for torque effect on the airplane: wing incidence. On the U.S. airplanes it's the left wing which very often has a higher fixed angle of incidence than its kin on the right. At the time of the stall, the left wing tends to stall a bit sooner than the right side. This induces a roll... this too is a contributor to the rapid rolling experienced by some pilots during take-off and departure stalls. With age and Lord knows how many mechanics tweaking it, the angle of incidence can change. I was instructing in a brand new C-152 where the thing did a snapping roll to the left during a power-off, on heading, full stall. Returned to the FBO and had the mechanic look at it. Sure enough the left wing's angle of incidence was considerably greater than design/factory specs and production said it should have been. Two days later, the bird was a sweetheart... doing just what it was supposed to do.

As to spin training.... ALL of my pre-solo students were trained not just to recognize the incipient spin, but recover from it and a full, one-turn, spin. The spin requirement for US PPL was removed from the FAA's list of pilot competencies back in the early 60's.

Some of youse guys flying the Cessna 150/152 ans 172 series ought to try experience the adverse yaw spin. It demonstrates that overuse of the aileron during stall recovery, while applying full elevator back-pressure will spin the airplane nicely. This is a condition which can occur when the accident pilot mis-uses his/her controls trying to stop the rapid banking shortly after the stall occurs. I discovered this interesting maneuver during a flight with a CFI-A trainee.

Another interesting one is using rudder to keep the wings level during a deep stall exercise. In pre-1946 U.S. certificated airplanes the rudder was the main "wing" control during stall recoveries. After that it was co-ordinate use of the flight controls.
Anyway, with a different CFI-A trainee, after two pitch down-pitch up cycles, with the wing banking to te left, he was keeping the wing level with rudder because he was trained that way (wrong in modern certificated airplanes- coordinated control to maintain wings level). As the third cycle was beginning he applied right rudder without affect; over we went (Yahoo!); I took the opportunity to tell him to make sure he has full rudder applied and maintain full elevator back-pressure, just like some poor sot of a student pilot would shortly before colliding with the ground.

The airplane was in a rapidly descending stalling spiral to the left. I suggested he apply full right aileron and observe the results. Around we went. After that experience, he used coordinated controls during his stall recoveries.

Hope the above helps in some way.

Cheers,

F.

 

[XBe02Drvr]

Some of youse guys flying the Cessna 150/152 ans 172 series ought to try experience the adverse yaw spin.

I've been treated to that little delicacy by a number of hamfisted students over the years, mostly when I was phase-checking other instructors' students. Usually resulted in a consult with the instructor involved, especially if it transpired that the student hadn't had any spin training at all.
Students tended to be heavy on the ailerons with little to no rudder, and then noticing their error, boot in too much rudder. "Checkride-itis" also took its toll.
Cheers,
Wes

 

[FSG43]

Yup, the poor students that just reacted. When I encountered that type, regardless of certificate being sought, we'd go back to basic coordination exercises until there was demonstrated consistency.

Earlier in this lengthy exchange a couple of comments were made. I'd like to comment on them.

1. PA-38 Traumahawk- a dangerous airplane whose designers both stated it should have been de-certified and grounded. Even the then Chief Test Pilot for Piper told the then Company President the all PA-38's should be bought by Piper and scrapped. I'm not jesting gentlemen.

The basic problems were a weak wing (flexible) with a GAW-1 airfoil (hard break at the L/D Max). Make it a changeable section and you're in for some nasty aerodynamic surprises as many dead CFI's and their students attest.

It had poor roll authority at slow speeds and into the stall. It gained certification after stall strips were placed on the wings L.E. In front of the ailerons. That gave it the minimum required aileron authority for the stall portion of its certification.

2. Very often the poor thing would enter into either a flat spin or be unrecoverable from a normal spin (caused by airflow separation at the wing root). Dig up the NTSB report from around 1994, double fatal at Inman, KS.

The PA-38 was not designed with a "T-tail." and weak wing. Go look at the parts manual for the wing... count the ribs and rib-replacements. The elliptically shaped nose section aided in getting the thing into a flat spin. A former Piper test pilot made a video of him getting into a flat spin that was only
recoverable with a skin chute. He recommended the airplane be re-designed with this propensity as the design-out goal.

The Skipper was designed, in part, by one of the PA-38 designers. It's a different breed of cat- smoothed root area airfoil, stall strips, squarish nose section, RIGID wing structure.

3. The base leg turn to final approach has been the bane of many pilots. As many CFI's have observed during instructional flight and when administering stage checks or flight reviews, pilot coordination (physical and mental) are sorely lacking.

The lack of the realization about the need for coordination and actual lack of it very often leads to serious problems for pilots.

A directly related problem is situational awareness- where's the wind from? how to I compensate fir it in the pattern? when should I initiate the turn to base leg and final? This basic deficiency usually leads to an overshooting of the base leg turn initiation point as well as the turn to final.

To get the plane onto final when initiating the turn late, the pilot needs a faster rate of turn (again, because the turn was started late) but is hesitant to increase the bank angle close to the ground. Instead....

The pilot uses his rudder to increase the turn rate while applying opposite aileron to keep the bank "shallow." The errant pilot now is applying elevator back-pressure to control the pitch attitude and even slow the airplanes speed. Perfect mixture for the cross-controlled stall with incipient phase spin and subsequent collision with the ground. Most of the time the pilot applies and holds full back elevator pressure as they stare at the on-rushing ground.

One way to reduce these LOC events is thru better primary instruction in ground reference maneuvers, coordination exercises, minimum control airspeed exercises, stall training (partial and full) and the use of visual references when flying the traffic pattern (it is a ground reference maneuver).

The turn from base to final... a critical phase of flight that's often minimized in training.

Enjoy the evening folks,

FSG

 

[XBe02Drvr]

The lack of the realization about the need for coordination and actual lack of it very often leads to serious problems for pilots.

Occasionally a student would come along who just couldn't get the "hang" of coordination, and if he/she had the persistence and resources to stick with it, the younger instructors would send them to me. If they turned out to be a hard case, and were still game, I would send them over to the soaring center in the next valley. It's amazing what a yaw string right in front of your eyes can do. The original HUD. They generally came back to me much improved, but once in awhile one would get seduced by sailplanes and never be seen again, except when I instructed over there.
Cheers,
Wes

 

[fliger747]

In the days when nose draggers were not the overwhelming norm in flight instruction pilots did get a better understanding of the use of the rudder. Of course many of those planes had barn door ailerons and a great deal of adverse yaw. Landings, keeping the thing straight, avoiding ground loops, especially in X winds was a good teacher. My daughter after acquiring 200 hours went down to work on her instrument rating and the instructor perusing her log book was astounded that she had never flown a "nosedragger".

 

[XBe02Drvr]

the instructor perusing her log book was astounded that she had never flown a "nosedragger".

Lucky girl!

 

[XBe02Drvr]

PA-38 Traumahawk- a dangerous airplane whose designers both stated it should have been de-certified and grounded.

Dig up the NTSB report from around 1994, double fatal at Inman, KS.

CHI94FA097: Full Narrative.

Ouch!

 

[FSG43]

CHI94FA097: Full Narrative.

Ouch!

The cute little PA-38 had bug problems brought on by the desire to produce a "modern-looking" trainer (T-tail) cheaply (reducing wing ribs, etc.). It was supposed to compete with the C-150's. Due to its less than appropriate handling characteristics, it did not. The Piper design team gave the production design team a good product. The production design team diddled around and created a pretty dangerous airplane.

 

[gumbyk]

The cute little PA-38 had bug problems brought on by the desire to produce a "modern-looking" trainer (T-tail) cheaply (reducing wing ribs, etc.). It was supposed to compete with the C-150's. Due to its less than appropriate handling characteristics, it did not. The Piper design team gave the production design team a good product. The production design team diddled around and created a pretty dangerous airplane.

And yet the flying school I worked for flew with a fleet of up to 20 of them, and time-expired a number of airframes at 11k hours, without any stall/spin problems experienced. You trained for the aircraft you were using, and we were pretty hot on co-ordination.

I guess I should be dead...

 

[XBe02Drvr]

I admit to being an aeronautical bigot, and not having much use for the low end metal Pipers. From the hershey bar Cherokees right up through Apaches, Comanches, Sixes, Saratogas, Senecas, and of course, the infamous Traumahawk, I didn't like the way they handled, and felt they had too many unnecessary flaws built in. I used to see them apart in the shop for annuals and was conscious that with occasional exceptions (Comanches and long-wing Cherokees) they appeared to be built to the barest minimum structural strength. Our shop rebuilt quite a few damaged planes of all marques, and Pipers seemed to be the most fragile and Beeches the most robust. Aztecs, Navajos and on up didn't seem to be so bad, but we didn't see many of those.
In five or six thousand hours of instructing, I only had three or four hundred in Pipers, mostly instrument training and BFRs in privately owned aircraft.
Cheers,
Wes

 

[DerAdlerIstGelandet]

I never liked the Navajo, but the Cherokee is a great aircraft in my opinion.

 

[XBe02Drvr]

I never liked the Navajo, but the Cherokee is a great aircraft in my opinion.

I think we all tend to have a soft spot for what we grew up with. Despite being raised on strut braced high wings, I wound up a fan of Beechcrafts.

 

[DerAdlerIstGelandet]

I think we all tend to have a soft spot for what we grew up with. Despite being raised on strut braced high wings, I wound up a fan of Beechcrafts.

Beechcraft makes an amazing product. I love everything they put out. I worked at a Part 145 for 5 years that was a Beechcraft Service Center. 5 years of doing King Air phases and the occasional Bonanza or Baron annual. I love the Bonanza. My only turboprop Stick Time is is in King Airs.

 

[FSG43]

CHI94FA097: Full Narrative.

Ouch!

"Ouch" is right. There were numerous, well-written, articles on the PA-38's problems in Aviation Consumer after this accident.

 

[FSG43]

Beechcraft makes an amazing product. I love everything they put out. I worked at a Part 145 for 5 years that was a Beechcraft Service Center. 5 years of doing King Air phases and the occasional Bonanza or Baron annual. I love the Bonanza. My only turboprop Stick Time is is in King Airs.

King Airs were/are well made machines. The 200 series had a problem though- the aft upper cowl would separate in flight, often compromising the pressure vessel. In one instance it caused a nine fatal accident. When Beech was made aware of the problem and why it occurred, they fixed it.

 

[FSG43]

And yet the flying school I worked for flew with a fleet of up to 20 of them, and time-expired a number of airframes at 11k hours, without any stall/spin problems experienced. You trained for the aircraft you were using, and we were pretty hot on co-ordination.

I guess I should be dead...

Not really—- you were just fortunate. The 38' had a fatal accident rate that was, as I recall, six times that of the C-150 series; that's using the FAA's per 100,000 hours flown statistical model.