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  #31  
Old 06-30-2020, 06:05 PM
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ronschreck ronschreck is offline
 
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Quote:
Originally Posted by dsowder View Post
I've flown RVs and think they're great, but I don't own one, so I hope you don't mind my comments. I've flown competition aerobatics for 27 years, have owned Pitts S-1, S-2B, and for last 15 years an Extra 300L. The S-1 was fixed pitch prop, the S-2B and Extra have counterweighted (i.e. "aerobatic") MT propellers.There's an important point to be made here: If you're planning aerobatics and any negative g time at all, I'd advise against a non-counterweighted (which is the usual) constant speed prop. These use oil pressure to force the blades to coarse pitch; if you lose oil pressure even briefly, the prop can go fine pitch and allow a massive engine overspeed at the speeds that an RV can fly.

I also fly a Lancair Legacy, which has a non-counterweighted prop and a Vne of 274 Knots. I don't even THINK about allowing the engine's oil pump to unport. This airplane is "just transportation".

Doug Sowder
IAC 14590 Lifetime
Hey Doug!

Welcome to the RV Forum. We can use a bit of aerobatic expertise here.
Hope to see you at Nationals this year.
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  #32  
Old 06-30-2020, 06:51 PM
Sparrowhwk Sparrowhwk is offline
 
Join Date: Mar 2019
Location: Prescott Az
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Default Do I need to rethink my inverted oil/fuel??

Dsowder posted:
"If you're planning aerobatics and any negative g time at all, I'd advise against a non-counterweighted (which is the usual) constant speed prop. These use oil pressure to force the blades to coarse pitch; if you lose oil pressure even briefly, the prop can go fine pitch and allow a massive engine overspeed at the speeds that an RV can fly. "

So if I hve a regular Hartzell, does that mean I shouldn't bother with fitting the inverted fuel & oil systems as I shouldn't be doing any negative G in the RV-8???
Or
Will the inverted oil system prevent the situation described by Dsowder from happening - is he referring to aircraft without the inverted oil system??

I had not heard this perspective before - and obviously installing a new prop as well as the inverted systems is a huge expense, which may not make sense for this aircraft.
Have many RV owners installed aerobatic props??? Ron???

Now I am wondering if I need to adjust my expectations for the RV8???
Thanks for any clarification etc
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  #33  
Old 07-01-2020, 04:16 AM
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ronschreck ronschreck is offline
 
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Quote:
Originally Posted by Sparrowhwk View Post
...
Have many RV owners installed aerobatic props??? Ron???

Now I am wondering if I need to adjust my expectations for the RV8???
Thanks for any clarification etc
As far as I know there are very few who have installed aerobatic CS props. I know that of all the pilots who flew on Team RV and Team Aerodynamix with me none had aerobatic props. In 10 years of competition aerobatics I have not come across a single RV competitor with one.

Your warning about over-speed is valid to a point. Yes, if oil pressure drops significantly you may get a rapid RPM increase. The engine noise will get your attention right away and even those flying formation next to you will hear it! It has happened to me on several occasions but I have always been able to snap the throttle back before things get out of hand. I have seen RPM jump to 3300 on occasion. Right now many of you are thinking ENGINE TEARDOWN! If you are a Pitts pilot you are thinking RIGHT ON! A momentary RPM surge is not a death sentence and many Pitts pilots keep the RPMs around 3300 all day long while flying aerobatics.

Having said this, I sure would have liked to have an aerobatic CS prop but I never figured the added expense was justified for the type of flying I did. It's a decision you will have to make on your own.
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  #34  
Old 07-08-2020, 04:08 PM
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skylor skylor is offline
 
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Location: Southern California
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Default Snap Rolls

Since much discussion in this thread has been about snap rolls, I thought I would share a bit of my own experiences.

1. The plane does roll faster doing a snap roll at 90 knots than an aileron roll at 175 knots.

2. I get some canopy skirt "slap" during snap rolls. I have also experienced skirt slap during other high angle of attack maneuvers (I should say, high angle of attack maneuvers when well above the level flight stall speed).

3. Here's a brief clip of my doing a snap roll. I do aerobatics just for fun, but obviously if I were to fly in competition I would need to work on my stopping point a bit!

Snap Roll

Skylor
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  #35  
Old 07-08-2020, 07:01 PM
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Gash Gash is offline
 
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Nice use of the 360 camera. I do the same thing to help me debrief my acro flights. I have a small suggestion that might help your snap roll. I see that you're simultaneously applying left rudder and aft elevator. Pause your video at 0:09 and look at the rudder and elevator deflection. Also note how your nose traveled up and left diagonally prior to any stall buffet. So what you're really getting here is a buried rudder roll (possibly even a coordinated aileron roll) with both wings stalled as you go around. It's not really a snap roll. Also, watching the rear cockpit stick movement, it's hard to be sure, but it looks like you're not getting the stick full forward. It looks to me like you're only going back to a neutral pitch position. Tail view video seems to confirm this. If you pause the video at 0:10 and then pan the camera to the rear, you'll see that the elevator is neutral.

You might get more of a "snap" if you go full aft stick first, getting the wings past the critical AOA, and then briskly put the stick full forward and very slightly left (like an upside down J) while simultaneously stomping in full left rudder. You have to hit the rudder stop. It all happens really fast...like 1/4 second fast. Get that stick back, break the airflow over the wings, and very quickly get the stick full forward and slightly left, with full rudder deflection at the same time. Use two hands on the stick.

If this sounds a little like a spin entry, that's because a snap roll has very similar characteristics to a spin (aggravated stall with pro-rotation rudder held until you're ready for the insanity to stop). So why the need for the quick forward stick movement? That actually helps you "snap" around the roll axis quicker, just like when figure skaters bring their arms close to the body.

A common error is to not get the stick fully forward fast enough, thus causing more of a buried shoulder roll than a snap roll. Another common error is to not be full throttle...I couldn't tell from the video, but it seems like you are.

Finally, a safety nit pick here that's worth noting. It would be a real bummer if that headset and yellow towel under the rear seat harnesses were to come out during aerobatics and get lodged somewhere you don't want it (under a rudder pedal, etc.) Many have made this mistake, myself included. I once did an inverted safety check prior to diving into the box for a practice flight and a half-full water bottle hit the canopy!
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Last edited by Gash : 07-08-2020 at 07:36 PM.
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  #36  
Old 07-08-2020, 08:16 PM
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skylor skylor is offline
 
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Location: Southern California
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Quote:
Originally Posted by Gash View Post
Nice use of the 360 camera. I do the same thing to help me debrief my acro flights. I have a small suggestion that might help your snap roll. I see that you're simultaneously applying left rudder and aft elevator. Pause your video at 0:09 and look at the rudder and elevator deflection. Also note how your nose traveled up and left diagonally prior to any stall buffet. So what you're really getting here is a buried rudder roll (possibly even a coordinated aileron roll) with both wings stalled as you go around. It's not really a snap roll. Also, watching the rear cockpit stick movement, it's hard to be sure, but it looks like you're not getting the stick full forward. It looks to me like you're only going back to a neutral pitch position. Tail view video seems to confirm this. If you pause the video at 0:10 and then pan the camera to the rear, you'll see that the elevator is neutral.

You might get more of a "snap" if you go full aft stick first, getting the wings past the critical AOA, and then briskly put the stick full forward and very slightly left (like an upside down J) while simultaneously stomping in full left rudder. You have to hit the rudder stop. It all happens really fast...like 1/4 second fast. Get that stick back, break the airflow over the wings, and very quickly get the stick full forward and slightly left, with full rudder deflection at the same time. Use two hands on the stick.

If this sounds a little like a spin entry, that's because a snap roll has very similar characteristics to a spin (aggravated stall with pro-rotation rudder held until you're ready for the insanity to stop). So why the need for the quick forward stick movement? That actually helps you "snap" around the roll axis quicker, just like when figure skaters bring their arms close to the body.

A common error is to not get the stick fully forward fast enough, thus causing more of a buried shoulder roll than a snap roll. Another common error is to not be full throttle...I couldn't tell from the video, but it seems like you are.

Finally, a safety nit pick here that's worth noting. It would be a real bummer if that headset and yellow towel under the rear seat harnesses were to come out during aerobatics and get lodged somewhere you don't want it (under a rudder pedal, etc.) Many have made this mistake, myself included. I once did an inverted safety check prior to diving into the box for a practice flight and a half-full water bottle hit the canopy!
Thanks for the input. It's definitely not a coordinated aileron roll because the ailerons remain neutral until I inadvertently apply "out-spin" aileron during the stop/recovery...but it may be a bit of a buried shoulder roll. I have done some other ones where I have managed to delay the rudder kick until after application of elevator. I haven't worked up the courage to get the stick more forward than about the neutral position during the snap...I am applying full throttle just prior to the elevator.

Good call on the headset and "seat protector" towel. They seem pretty secure under the belts but they probably could be jarred free. Next time I'll take them out.

Skylor
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  #37  
Old 07-08-2020, 09:44 PM
sandifer sandifer is offline
 
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Skylor, I might offer an alternative take on the snap roll. In your video, you definitely did a snap. You cannot mistake a snap for a shoulder roll since a shoulder roll is a very uncomfortable negative G roll with a much slower roll rate. A real snap is a smooth ride under nearly zero load in your seat. Producing a shoulder roll rather than a snap is caused by unloading the stick forward of neutral and applying in-spin aileron after failing to produce a snap break. This is usually caused by being too late on the rudder and unloading too early. If the snap breaks at all, it's not going to shoulder roll, even if you don't unload at all. In this case, you'll "bury" the snap and the rotation will be slow, but that's different from a negative G non-snap shoulder roll.

In your video, the main thing to tighten up is your stick movement. You should apply the aft stick MUCH more quickly. Keep in mind that your hand moves faster than your feet, so be careful to avoid being late on the rudder as you speed up your stick input. Consider the elevator and rudder movements as made simultaneously, and you'll naturally lead slightly with the elevator, which is proper technique. You did unload as the snap broke. I'll differ from Karl and suggest trying to AVOID using full deflection elevator inputs both in the initiation and the unload. I've never flown an airplane that required full aft elevator to do a good snap. The cleanest, fastest, lowest energy loss snaps are actually done with the LEAST amount of elevator input as your airplane will let you get away with. In most airplanes that snap half decent, you can do great snaps using less than half aft elevator deflection if your technique is good. RVs may need a little more than some more dedicated acro types, since RV wings really love to fly. Ron Schreck would be the man to advise you on RV-8 snaps in particular.

Regarding snap technique in general, you do NOT need to stall the airplane or necessarily even pull to the buffet on the snap entry. You only need sufficient AOA for the rudder input to THEN cause one wing to stall. If you unload the stick at just the right moment as this happens you'll get that nice clean explosion into the snap. It's a shocking difference the first time you happen to hit the inputs perfectly. The quality of the snap is amazingly sensitive to minuscule changes in the timing of all the inputs. Excessive elevator input just adds excess stress to the airplane, and causes higher drag and more energy loss through the snap. If you want to compete and get good snap scores, you'd need to be sure to show sufficient pitch change to the judges 2,000' below you, but that's another topic.

Regarding the unloading of the stick, most airplanes will do a great snap just by returning the stick to neutral. I've never flown an airplane that required full forward stick on the unload to do a good snap. Universal snap technique involves moving the elevator to a degree forward of neutral, but lots of airplanes have a point where any more forward elevator than necessary does not contribute further to the acceleration of the snap, and only adds excess drag.

Traditional snap technique also involves adding some in-snap aileron along with the unload of the elevator. Just be sure not to add any in-snap aileron until you start the elevator unload movement. The stick movement can be made like a "check" mark - pull straight aft, then in a diagonal line forward with the aileron. Get the aft elevator in and out as quickly as your airplane will let you get away with. You can experiment to see what effect varying amounts of elevator unload and in-spin aileron have on the snap rotation. But you should find that it's minor. The snap is mostly driven by the stalled wing and you can do quite nice snaps by unloading to neutral and adding no in-snap aileron. Some aileron and forward stick should accelerate the rotation a little though. The Pitts for example is generally quite insensitive to various amounts of forward stick and in-snap aileron, meaning you cannot turn a weak snap into a significantly better snap just with the aid of aileron....unlike what our carbon monoplane friends can get away with.

Also, read Alan Cassidy's book. Excellent coverage of the snap...and all the other maneuvers too. By far the best acro book out there.

And FWIW, a tail view of some snap inputs I shot in the Pitts years ago. About 2/3 elevator deflection both ways.

https://www.youtube.com/watch?v=TUH1lyerTio

Last edited by sandifer : 07-08-2020 at 10:09 PM.
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  #38  
Old 07-09-2020, 07:01 AM
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Saville Saville is offline
 
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Since we're talking aerobatic technique:

What entry speed and rudder-kick speeds do the aerobats here suggest for hammerheads in the RV-8?
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  #39  
Old 07-09-2020, 07:30 AM
sandifer sandifer is offline
 
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Originally Posted by Saville View Post
Since we're talking aerobatic technique:

What entry speed and rudder-kick speeds do the aerobats here suggest for hammerheads in the RV-8?
Entry speed is whatever allows you to get to vertical without stalling or falling out. You could do this from 100mph or from Vne, it doesn't matter. Entry speeds don't matter for the basic figures. Low cruise works for anything in an RV. Regarding when to kick, airspeed indication is not a good way to learn to do a good pivot, since airspeed will be dead by the time you need to pivot. If you're using airspeed as an indicator, you're going to be kicking early, and 'flying' over, meaning a large radius rather than the ideal minimal radius pivot.
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  #40  
Old 07-09-2020, 08:00 AM
flyinhood flyinhood is offline
 
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Acro guys practicing Hammers, do you guys have inverted oil?
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