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Snap Rolls

BrianP

Member
I’m sure this is a topic that has probably been actively debated in the past. I can’t seem to find past threads. My understanding is that Vans discourages snap rolls in the RV8. Some RV owners I’ve talked to say it’s no issue and that the tail construction is extremely strong. I heat bought an RV8 with inverted systems to do some aerobatics so am interested in the topic. Can someone point me to a thread where this has previously been covered?
 
Hammerhead is a low energy maneuver and can be done in RV's with sufficient pilot experience with no impact to airframe. A lot can go wrong with a hammerhead, however from an aircraft control standpoint.

Before you tail slide, take a look at the flight control attachments on a dedicated acro aircraft and then compare with the RV.

Personally, I do not snap RVs due to the monocoque fuselage construction. The stresses on the airframe substantially exceed that of a normal low-energy spin entry.
 
Vans discourages snap rolls in the RV8

Ain't RV-8 specific though... Vans discourages snaps in any RV.
Re tail slides, it is one of the figures thought of provoking cracks in the skins of the elevator and rudder...

I sure don't wanna sound condescending, but for anyone thinking of flying aeros, please take some tuition beforehand. There are flight instruction and courses, and that is IMHO, a major safety precaution. Those RVs (even the non -8...) accelerate pretty fast, and have light controls.

Maybe one also remembers that aluminum can only withstand a finite amount of repetitive fatigue cycles, making the material de facto not the best for this use. Witness current unlimited aircraft, none is made out of aluminum...
 
Snap roll or hammerhead or tail slide?

https://www.aopa.org/news-and-media...light-training-magazine/technique--snap-rolls

I've read some feel a bit uncomfortable with the hammerhead or tail slide, mainly due to the sounds coming out of the tail area, but I don't recall anyone saying that there is a problem with snap rolls.

It's in the service bulletin about the rv7 rudder change. Maybe elsewhere as well, but I know you can find it there.

"They were designed primarily as sport/cross country airplanes with sufficient performance and control authority to safely perform basic recreational aerobatics such as loops and rolls. We do not consider aerobatic maneuvers such as high speed multiple snap rolls and tail slides, which can impose high airframe loads to meet our definition of sport aerobatics."

The go on to suggest maneuvers that might be specifically prohibited in the Ops limits and lists both snap rolls and tail slides as examples.
 
So I did a lot of the acrobatic maneuvers during flight testing with a camera facing the tail.

- Hammerheads when flown properly are no issue at all.
- Tailslides I didn’t do after looking at the hinges
- SNAP rolls I did do but they were the only maneuvers in which the tail moved substantially. All other acro maneuvers the tail was rock solid.

After observing that I stopped doing SNAP rolls. Can you do them? Sure. Will they put a lot of fatigue on your tail? yes. In fact one guy who was doing lots of SNAPs in his RV had his horiz stab attachment bolts elongate requiring replacement at every other annual.

I think the RV is a great sportsman class acrobatic airplane and I had lots of fun competing with it.

In intermediate class where snap rolls are required your are really stretching it. Both in mission envelope and literally. People have done it but expect some additional maintenance.

Oliver
p.s. The only reason I can think of people recommending against hammerheads is that an unexperienced pilot might botch it and get into a tail slide or inverted spin. The first one is not good for your RV the second might confuse an unexperienced pilot with disastrous consequences.
 
One more comment on the legal side. During phase 1 flight testing every acrobatic maneuver that is allowed later must be demonstrated to be save and be part of the log book entry. So its up to the person doing the phase 1 testing if in your particular RV-8 snap rolls are legal. There are lots of RV-8s in which they are not.

So if snap rolls are listed and assuming the person signing the entry didn’t lie there was at least one snap roll flown in your RV.

Oliver
 
One more comment on the legal side. During phase 1 flight testing every acrobatic maneuver that is allowed later must be demonstrated to be save and be part of the log book entry. So its up to the person doing the phase 1 testing if in your particular RV-8 snap rolls are legal. There are lots of RV-8s in which they are not.
So if snap rolls are listed and assuming the person signing the entry didn’t lie there was at least one snap roll flown in your RV.
Oliver

Good to remember that this does not have to happen during the initial Phase I.

You may place the aircraft back into Phase I to do aerobatic maneuvers after you are more comfortable in the aircraft.
 
In general, the aerobatic RVs are not specifically designed for snap rolls, and certainly not for tail slides. But note that there are several very experienced and qualified pilots who snap roll their RVs successfully, including Van himself, and in competitions. But they are very careful and know what they are doing.

See the article "An Aerobatic Epistle", by Van himself:


Another article by Van himself on competition aerobatics, "IAC Aerobatics in RVs", with a good addendum on preparing your RV for aerobatics by Ron Schreck. Van again addresses snap rolls and tail slides in the article:


And note the "Aerobatics" section on Van's website:

 
acro

While probably not a significant risk, hammerheads do pose some risk of evolving into an inadvertent tailslide. Even when practicing a lot and doing intentional tailslides it is pretty rare for the airplane to slide backwards more than one airplane length. But if you actually slid backwards a long ways it could cause major damage in an RV or even structural failure. If the engine quit during or just before a hammerhead the airplane could tailslide enough to cause damage
Learn these maneuvers with an instructor in an airplane that is approved for tailslides. In any airplane have a plan to exit the maneuver in the event of engine failure or partial loss of power. For the hammerhead simply pitch the airplane nose down and keep apply neutral rudder.
 
Modern snap technique involves unloading. I've been following aerobatic discussions here for several years as my last plane likely will be an RV8 (after I get too old to fly Unlimited and Advanced sequences). I've never seen unloading mentioned. It allows a plane to snap well at an appreciably lower airspeed.

The idea of unloading is that after the snap breaks the downgoing wing acquires additional angle of attack from the downward motion so the fuselage can be pitched closer to the spin axis without unstalling it. Basically, as soon as the snap breaks you push the stick forward to appreciable resistance. The increase in roll rate is dramatic, and allows you to do a clean snap (no juddering or varying roll rate) with 10 - 20 less airspeed.

You may also add aileron at that point to increase the roll rate, as the aileron on the downgoing wing moves up into turbulent air and can't do much to unstall the wing. Finally, if you want to further reduce the stress on the airframe, in most planes you can neutralize the rudder because the extra drag of the stalled wing creates enough yaw to keep the autorotation going.

One thing to be aware of is that applying forward stick in a spin, which is called accelerating the spin, can make it difficult to stop until the stick is brought back. In my experience this is unnecessary in an unloaded snap - opposite rudder without bringing the stick back first is all that is needed to stop the snap - but there is the possibility that this might not apply to RVs.
 
Snaps

I unloaded the snaps, I call it accelerating the snap, for years in everything from the Pitts S1S to the Su26 and 29. I took it a step further in the Pitts by moving the stick slightly forward of neutral when upright and slightly aft when inverted. Five turns in the S1S, as many as you want in the Sukhoi.
Spins can be enhanced by going to full power as soon as the rotation starts with simultaneous forward stick. Stopping the spin is very consistent with only about 1/8 turn lead with aggressive full opposite rudder.
Back to the snaps my S1S would do five turns entering at 135 and finishing at 100 plus. If it is not properly accelerated the final turn will lose 100' and 10 m/h plus airspeed.
John Livingston may have been the initial source of accelerating the snap and spin. He had apparently mastered all that and much more starting around 1930. He was the inspiration for the book and movie Johnathan Livingston Seagull.
He had a heart attack while flying a Cassutt Racer, landed safely, taxied to the airport fire department. They took him to the hospital but he died on the way.
 
Are you proficient in acro?

I would not be new to acro and fly it in a RV.

Can a good pilot snap a RV? Sure.

Acceptable wear/tear and inspectability for damage? Sure.

Can you damage it from exceeding YOUR limits?

If yes, get proficient instruction in a purpose-built type.

Something above a Pitts or Suoer Decathalon- something clean that accellerates nose down, quite quickly.

You will then hopefully not want to do them in a RV.
 
Are you proficient in acro?

I would not be new to acro and fly it in a RV.

Can a good pilot snap a RV? Sure.

Acceptable wear/tear and inspectability for damage? Sure.

Can you damage it from exceeding YOUR limits?

If yes, get proficient instruction in a purpose-built type.

Something above a Pitts or Suoer Decathalon- something clean that accellerates nose down, quite quickly.

You will then hopefully not want to do them in a RV.

I actually bought the plane for my son to fly. He’s 13 and competed in the primaries this last summer. He’s had about 20h of Acro instruction in a Citabria. Probably will want him to have at least 200h of instruction in the RV8 before considering allowing him to do any acro solo.
 
Starting young- great! I was old in intermediate at 24 in a basic S1-S.

Why a RV with its reduced roll rate vs most anything but a Decathalon?

Will it be to get to and from a contest quickly, efficiently and possibly IFR/IMC? It certainly can do that, and legs to a contest and avoiding weathering out are nice options.

Does the roll rate vs lack of drag help centering rolls on a line segment?

Does the airfoil set help hold a vertical line accelerating and decelerating without hunting or anticipating the next pull or push? Most of the grading is centering rolls, proper headings, straight lines and symmetrical arcs under g at all speeds, whether slowing or accelerating.

Does it start and stop snap and spin segments reliably vs more traditional platforms? Folks have done lots of contests well with them, but they are not the standard to the majority.

Is that bad? No. An advantage or challenge? I don't know. Are 45 downline snaps with no speed loss or even while accellerating common?

As posted before, put on a gopro looking aft to and see what g and rotation presents.

That sounds like a step in the process towards the decision for each. 4g at 2x 1g stall speed snaps at 120 to 150 mph were bread and butter in a S-1. Intermediate was 5g to -2g unless fast- a RV is going to be going as fast, quicker and able to go too fast soon thereafter. Well flown, it could do intermediate with full inverted and a constant speed prop.

By my time we had the 4 IAC tech tips manuals, chock full of where to look for airframe and system issues- does the RV have that coverage for judged acro in a box wear and tear and ground proximity?

Please track down Jerry- RV-8 acro high time guru.
"RV8Squaz", here.
 
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In general, the aerobatic RVs are not specifically designed for snap rolls, and certainly not for tail slides. But note that there are several very experienced and qualified pilots who snap roll their RVs successfully, including Van himself, and in competitions. But they are very careful and know what they are doing.

See the article "An Aerobatic Epistle", by Van himself:


Another article by Van himself on competition aerobatics, "IAC Aerobatics in RVs", with a good addendum on preparing your RV for aerobatics by Ron Schreck. Van again addresses snap rolls and tail slides in the article:


And note the "Aerobatics" section on Van's website:



I encouraged Van to write the article on Aerobatics in RVs when I was on the IAC Board of Directors. The editor of the IAC magazine wanted the article but I insisted on putting the article in the EEA magazine which had over 250,000 subscribers verses the 4,000 subscribers to the IAC magazine. The IAC has never had many RV pilots in the membership and I wanted to introduce aerobatics to as many RV pilots as possible. Van submitted four or five drafts for my comments and we had many conversations centered around snap rolls. Van is understandably conservative when it comes to aerobatics. As the designer of the RV his reputation and exposure to liability suits cannot be overlooked so he is careful about what he puts in print. This is what he said about snap rolls in the article:

SNAP ROLL MANEUVERS
RVs are capable of performing snap rolls, but
these tend to be less crisp and of a lower roll
rate than many other aerobatic aircraft. Also,
I found that when trying to improve their
crispness by performing them at near
maneuvering speed limits, more than 4g was
experienced. Since this was a higher level
than I was comfortable with, I saw this as
one more deterrent to competition flying. I
did not include snaps in my air show rou-
tines other than when done at low speeds,
such as at the tops of loops. I feel safe saying
that regardless of pilot skills, RVs cannot
perform crisp snap rolls like those routinely
exhibited by new aerobatic designs. That
said, some competition aerobatic pilots have
shown that RVs can do snap rolls satisfacto-
rily for requirements of the Intermediate
class.


I was flying at the intermediate level in IAC competition at the time and had been doing snap rolls in my RV-8 for a few years. I always entered the maneuver well below maneuvering speed; the sweet spot was between 100 and 110 knots. I never saw more than 3 G's during the maneuver and found that unloading the aircraft once rotation began increased the rate of rotation and gave me a very nice snap. As with any aircraft, it took a lot of practice to perfect the snap. Of course I was concerned that asymmetric loads which were not measured on the G-meter might be subjecting the airframe to unsatisfactory loads so I carefully and frequently inspected the tail section. I never found any damage attributed to snaps.

The link to my aerobatic video in my signature block shows one of my Intermediate routines and there is a half snap on a 45 degree up line (1:12) in the routine. Check it out.
 
Of course I was concerned that asymmetric loads which were not measured on the G-meter might be subjecting the airframe to unsatisfactory loads so I carefully and frequently inspected the tail section. I never found any damage attributed to snaps.

Did you find damage attributed to other maneuvers, if so, what damage did you find?

Very nice video of your RV-8 routine.

-Marc
 
That's the way you do it

Beautiful aerobatic sequence in your signature line Ron. Maybe another concern is stress on the canopy. Three of us RV competitors at Intermediate have had cracked canopies.
Bill McLean
RV-4 slider
lower Alabama
Still competing at 81 y.o.:D
 
Did you find damage attributed to other maneuvers, if so, what damage did you find?

Very nice video of your RV-8 routine.

-Marc

As Bill McLean pointed out, cracked canopies may be attributed to aerobatic maneuvering. However, there have been many cracked canopies on RVs which do not participate in aerobatics. Personally, I think most of the canopy issues can be explained by stresses brought about due to the differential of contraction and expansion of plexiglass and the metal canopy frame when exposed to large temperature variations. After my canopy cracked I mounted the new canopy with Sikaflex. No problems since.

I never experienced any other airframe issues and I flew competition aerobatics and air shows for 10 years and 2250 hours.
 
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About canopy cracks...

I've been thinking about those cracked canopies and it reminded me of my friend Jon Thocker who heard his RV-8 canopy crack after he leveled off at 11,000 feet on a cold winter day. It cracked clear across right over his head and he said the crack was at least 3/8 in wide. Jon returned to his heated hangar where the crack closed up tight!

Right now I am replacing a portion of the plexi on a B-25 bomber upper turret. The old plexi showed several cracks around the screw holes. We are drilling oversized screw holes in the new plexi to allow for expansion and contraction of the part and we are being careful to set the screw loosely to allow the plexi to move. The same precautions should be taken when mounting an RV canopy to the metal frame with screws or rivets. If you are gluing the canopy to the frame be sure to let the canopy stand off from the frame so there is plenty of room for the glue to flex. About 1/8th of an inch should do it.
 
Canopy

I think the most common issue is the builders failure to polish the edges of the canopy to a perfect finish. Absolutely no tool marks remaining. Lightly chamfer to edges to the same standard. A very light chamfer on the screw holes. Absolutely no roughness in the hole chamfer.
The Pitts S2 canopies do not seem to have any issues. All Pitts failures that I know of are caused by the canopy departing on the ground or in flight. The reported rate of the latter is 2.5 canopies per airplane on average.
 
The link to my aerobatic video in my signature block shows one of my Intermediate routines and there is a half snap on a 45 degree up line (1:12) in the routine. Check it out.

My son had eyes like saucers and a grin from ear-to-ear when he watched that video.
 
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