Tail Shake

[jrs14855]

There were at least two Velocitys that went all the way to the ground/water out of control. This is an issue that is pertinent only to canard aircraft. The t tail issue is different and is normally where the term deep stall is used. A prototype BAC111 crashed on a test flight in a deep stall.
The DC9 does not have direct control of the elevators. The yoke controls tabs which in turn move the elevators. To deal with the deep stall there is a hydraulic assist feature that moves the elevator directly in the elevator down position only, and only if there is a "disagreement between the yoke command and the elevator position. The low wing T tail aircraft have a problem with disturbed airflow from the wing affecting the tail. In low wing aircraft with a low horizontal tail, the horizontal is well below the disturbed airflow.

[miko38]

Hi Stu,
Do you happen to have any pictures of the strakes that you installed?
Thank you,
Mike

[strahler13]

Originally Posted by rocketman1988

You may find some interesting reading on deep stalls in the Velocity aircraft...

One guy road one all the way to the ground...and survived!

There are two documented incidences where deep stalls were encountered. Both of the experienced test pilots indicated that the airplanes stalled at an angle of attack of about 40 to 60 degrees, and "locked" in a non-rotating descent with an almost flat angle to the horizon. Despite efforts to push the nose down by the control stick, rocking the wings and even manually attempting to manipulate the center of gravity forward by shifting their body weight forward, neither pilot was able to recover from the stall. As both airplanes collided with terrain, both pilots remained unharmed due to the slow 1,000 foot per minute descent rate. In both cases, the airplane was within its normal weight and balance envelope.

[rvbuilder2002]

Originally Posted by crabandy

Not sure about the RV, but during my multi training I had several hours facing backwards (club seating) in a Baron and the tail shook a LOT during stalls.

As pointed out above, tail shake when an aircraft is held in a stall is not unusual. It occurs on a lot of certificated and experimental aircraft. It is prominent on the RV-10... probably because of the huge slotted flaps coupled with a specific relation ship of the elevation of the horizontal stab above the wing trailing edge. It occurs to some degree on most all of the RV models if you hold the airplane in a stall.
My point... it is nothing particularly unusual about the RV-10.

[jrs14855]

Post 23 is correct. Both airplanes survived relatively intact and both flew again relatively quickly. Both were based at Ft. Lauderdale Executive around 1989-90.
The blue airplane was purchased by a gentleman from Germany. He intended to ship it to Germany. I contracted with him to prepare the airplane for shipping. My recollection is that we found the airplane would not fit in a container and would have to go as deck cargo and would not be insurable. I then started building tanks to ferry the airplane but he decided to sell it in the US.
I flew the airplane several times. I would not take one as a gift, well maybe I would for the engine and junk the airframe. A horrid airplane.
I am not anti canard, I flew the Long Eze and liked it, however the Long does not meet my personal requirements for runway performance and baggage space.

[Stu McCurdy]

Originally Posted by Carl J. Niedermeyer

I'm not Stu, but thought this might help. My understanding is that the cause of the excessive tail shake at high AoA's on the RV-8s is the formation of two vortices; one from the wing root/fuselage junction, and the other from the landing gear/fuselage junction. These two vortices may coalesce into one larger, stronger vortex. The strake seems to capture and reduce the the strength of vortex or vortices.

Some folks have modified the wing root/fuselage fairing and the landing gear/fuselage fairing into one fairing that appears to eliminate the excessive buffet. I believe Randy Lervold's excellent RV-8 website discusses this.

My strake:

I am Stu (Falcon), and my strakes are essentially same as pictured. I got them in 2001 from Robertson in Arlington WA and reworked them to make them parallel to the wing. You can see the placement parallel to the wing root in a position to capture the dirty air coming off the landing gear upper fairings at high angle of attack and energizing the air so it flows smoothly back over the Horizontal Stab. It completely eliminates my previous Tail Shake.

[Caveman]

Originally Posted by strahler13

There are two documented incidences where deep stalls were encountered. Both of the experienced test pilots indicated that the airplanes stalled at an angle of attack of about 40 to 60 degrees, and "locked" in a non-rotating descent with an almost flat angle to the horizon. Despite efforts to push the nose down by the control stick, rocking the wings and even manually attempting to manipulate the center of gravity forward by shifting their body weight forward, neither pilot was able to recover from the stall. As both airplanes collided with terrain, both pilots remained unharmed due to the slow 1,000 foot per minute descent rate. In both cases, the airplane was within its normal weight and balance envelope.

I believe there were more than two of these accidents. I helped recover the aircraft involved in the following report. It was flown by a co-worker. He was definitely not an experienced test pilot. The descent rate was at least 2000 fpm, and if it hadn't been for some very large cottonwood trees sheering energy he likely would not have survived. He lost an eye from this accident. Long story short, the main wing stalled and the canard did not.

To see the report go to the link below and type in N57V for the registration it is the first report in the list:

http://www.ntsb.gov/aviationquery/index.aspx

Please bear in mind that this was a purchased aircraft that he did not build and it was a very early model. At least one of the above mentioned crashes, perhaps both, happened prior to this crash and the Velocity factory had incorporated wing changes, "Vortilons" IIRC, that had not been completed on my co-workers aircraft.

[Pat Stewart]

In this case we were at 4000 feet headed into a 16 knot headwind. I first did what I would call a mild slow flight flaps down stall and felt a little buffet in the stick at around 62 mph and stopped, probably short of the stall, my friend who is also a very high time pilot with a CFI then did a little more aggressive stall with a high AOA, the last time I looked at the airspeed it was dropping through 60 mph when I looked back at the tail. I would guess we were about 56 mph. The aircraft never dropped the nose or wing. We stopped the event after seeing the tail shake. I guess I was a little nervous about the cracks some of the other aircraft have had and did not want to push it any longer.

[dmaib]

Alex showed me this during my transition training back in 2008. I usually show it to my transition training customers. I have flown and stalled several -10's and they all do it. As I recall, SB 08-6-1, that Van's released in June of 2008 to add doublers to the F1010 bulkhead, was due to cracks on the bulkhead on Van's demonstrator aircraft. Presumably, that airplane has been stalled many, many times during flight test and years of demo flights.

Many years ago I had the opportunity to sit in a rear facing seat on a Citation II while it was being stalled. The amount of shaking and shuddering on the horizontal stab and elevators was very impressive!

[walkman]

Originally Posted by tadsargent

I am curious to know what is the difference between a Stall and a Deep Stall. I have never heard this reference before today.
Thanks

I think its the same as IFR vs hard IFR