Spinning the 8

Lately I've been stepping up my acro a little bit. I spend last Sunday spinning. I have noticed that first of all to get a good spin, it seems to be quite sensitive to technique. Without the proper entry technique I seem to get into a flight regime where it will mostly enter the spin, then vibrate a lot, fly out of it for about 1/4 turn, then do a 1/4 to 1/2 turn spin, and repeat.

It seems to do this more often going to the left, rather than the right.

My technique has been to get the airplane slow, say 70, then smoothly pull off all remaining power while smoothly raising the nose keeping wings level with rudder, stick centered laterally. At about 60 degrees pitch up the speed decays enough that the stall breaks at which time I put in full rudder in the direction I want to rotate, and haul the stick back into my lap if it isn't already there. Stick centered.

Seems to take about a 1/2 rotation to settle into the spin. I have to lead recovery by about 120 degrees. Loosing about 1,000' for two rotations plus recovery to a decent airspeed.

First, what should I alter in my technique?

Second, is this behavior normal/expected?

Thanks

Your technique sounds pretty good. Enter slow, as you mention. RVs aren't really good for high speed spin entry or snaps.

Individual specifics depend on your CG. But with mine, I have to be pretty deliberate to make it spin tightly. Up elevator, rudder into the maneuver. Hold neutral aileron until it begins rotating. Then feed in opposite aileron.

It will begin a "spin" in half a turn or so. After one turn (with opposite aileron) it'll wind up nicely.

Notice no extreme buffeting or vibration. There is the burbling air sucking on back of the canopy (slight whooshing) that you get with snap rolls or spins, and bumping the tail a bit. Guess I'm used to it.

Recovery is easy in 1 turn or less with neutralizing aileron and rudder (maybe a little opposite - been a while...), down elevator momentarily.

I'm sure that would be slightly different with someone in the backseat, but I don't do that - so that's all I know.

That sounds about right. I'll try feeding in the opposite aileron as you say.

The extreme buffeting is only when its doing the half in half out thing.

I'm trying to recover to about 165 to enter a loop

Stan Hodgkins did about 85 different spin configurations in the RV-8 as part of it's UK aerobatic approval.

The results are in 27 years of RVator and make interesting reading.

I've only done them a couple of times with a fairly forward CG, but found that centralising the controls stops the spin in about 1/2 a turn after 2 turns. Full anti spin controls P-A-R-E works almost immediately.

walkman said:

That sounds about right. I'll try feeding in the opposite aileron as you say.

The extreme buffeting is only when its doing the half in half out thing.

I'm trying to recover to about 165 to enter a loop

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Neat idea! Will give that a try.

Thanks for that RV-ator article, Mark. Missed that one. Busy building I guess...

Unless you're interested in getting into competition acro, you can enter a spin however you want. Lots of different ways. Although pitching up to 60 degrees is unnecessary. Each individual airplane (even among the same model) will have subtle differences in characteristics, so just learn what works best for you in your plane.

Spin entries to the right in many airplanes are smoother due to the gyroscopics pulling the nose down rather than up. In the Pitts with a metal prop, a left spin entry can tend to cause the nose to oscillate up and down a bit, and generally makes for a more wallowing entry compared to a right spin. But there are techniques to minimize this effect.

You can use a blip of power as the airplane stalls to help it break. Or you can enter it with power and pull it off as you apply rudder. As mentioned, aileron inputs have noticeable effects. So does unloading the elevator a bit around 1-turn.

In my experience helping folks clean up their competition spin entries, there seems to be one common mistake that will make for sloppy spin entries in various aicraft types - that's letting the airplane settle before applying spin inputs. I've seen a number of Decathlon pilots unable to get a spin at all by doing that.

When doing acro, place a spin after a figure that exits with very low energy - i.e. an Immelman or an upline that you cap off. Try flying a level power off line into the spin - no need to pitch the nose way up. Just keep the stick steadily coming back. Don't let the altimeter needle descend by a hair. Make it climb a hair. Hold a slight amount of rudder in the direction you want to spin as you near the stall. At the first stall/buffet indication, smoothly but quickly apply full rudder and full aft stick. After it breaks, if you sense a little bit of G build up and the airplane trying to fly out, try adding a quick out-spin aileron input, and then back to neutral. Outspin aileron increases the AoA on the down-going wing, causing it to stall more deeply. This increases the difference in AoA between the two wings. AoA differential is what drives the spin to begin with. Continuing to hold outspin aileron so that it stabilizes in that configuration will typically flatten the spin, making recovery slower.

Spinning during the 'incipient' phase is unstabilized because the airplane still has forward speed when it breaks. It takes a couple turns for the plane's trajectory to become vertical. You can minimize the duration of the incipient phase by getting as slow as possible before entering the spin...as in slower than you can fly with power off. Try flying a very steep upline (between 60 degrees and vertical) at full power and cap it off level at a speed indicating 15-20 mph BELOW your indicated power off stall speed. Pitch over so the nose is about 20 degrees above the horizon, and before the plane has a chance to settle, simultaneously apply spin inputs and pull power off. You'll drop it in with less forward speed, which can minimize the unsteadiness of the typical incipient phase associated with a faster power off entry speed. Sometimes in competition, we have no choice but to enter a spin in this manner. Also keeps things compact. Pretty boring to watch a plane float and float and float power off slowing down for a spin.

sandifer said:

Unless you're interested in getting into competition acro, you can enter a spin however you want. Lots of different ways. Although pitching up to 60 degrees is unnecessary. Each RV model will have subtle differences in characteristics, so just learn what works best for you in your plane.

Spin entries to the right in many airplanes are smoother due to the gyroscopics pulling the nose down rather than up. In the Pitts with a metal prop, a left spin entry can tend to cause the nose to oscillate up and down a bit, and generally makes for a more wallowing entry compared to a right spin. But there are techniques to minimize this effect.

You can use a blip of power as the airplane stalls to help it break. Or you can enter it with power and pull it off as you apply rudder. As mentioned, aileron inputs have noticeable effects. So does unloading the elevator a bit around 1-turn.

In my experience helping folks clean up their competition spin entries, there seems to be one common mistake that will make for sloppy spin entries in various aicraft types - that's letting the airplane settle before applying spin inputs. I've seen a number of Decathlon pilots unable to get a spin at all by doing that.

When doing acro, place a spin after a figure that exits with very low energy - i.e. an Immelman or an upline that you cap off. Try flying a level power off line into the spin - no need to pitch the nose way up. Just keep the stick steadily coming back. Don't let the altimeter needle descend by a hair. Make it climb a hair. Hold a slight amount of rudder in the direction you want to spin as you near the stall. At the first stall/buffet indication, smoothly but quickly apply full rudder and full aft stick. After it breaks, if you sense a little bit of G build up and the airplane trying to fly out, try adding a quick out-spin aileron input, and then back to neutral. Outspin aileron increases the AoA on the down-going wing, causing it to stall more deeply. This increases the difference in AoA between the two wings. AoA differential is what drives the spin to begin with. Continuing to hold outspin aileron so that it stabilizes in that configuration will typically flatten the spin, making recovery slower.

Spinning during the 'incipient' phase is unstabilized because the airplane still has forward speed when it breaks. It takes a couple turns for the plane's trajectory to become vertical. You can minimize the duration of the incipient phase by getting as slow as possible before entering the spin...as in slower than you can fly with power off. Try flying a very steep upline (between 60 degrees and vertical) at full power and cap it off level at a speed indicating 15-20 mph BELOW your indicated power off stall speed. Pitch over so the nose is about 20 degrees above the horizon, and before the plane has a chance to settle, simultaneously apply spin inputs and pull power off. You'll drop it in with less forward speed, which can minimize the unsteadiness of the typical incipient phase associated with a faster power off entry speed. Sometimes in competition, we have no choice but to enter a spin in this manner. Also keeps things compact. Pretty boring to watch a plane float and float and float power off slowing down for a spin.

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Fantastic!

To clarify, by "outspin" aileron, you mean against the rotation, correct?

ex. spinning to the left, full left rudder, add a dab of right aileron and then back out.

Eric, I really appreciate your detailed and well-written posts about aerobatic flight. Please keep up the good work.

walkman said:

Fantastic!

To clarify, by "outspin" aileron, you mean against the rotation, correct?

ex. spinning to the left, full left rudder, add a dab of right aileron and then back out.

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Yes, left rudder spin/right aileron and vice versa for upright spins. For quick jabs, use full aileron. This gets very aircraft specific, but this can help in the Pitts. The theory is universal, but each aicraft responds slightly differently.

DanH said:

Eric, I really appreciate your detailed and well-written posts about aerobatic flight. Please keep up the good work.

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Very generous Dan, thanks.

sandifer said:

....one common mistake that will make for sloppy spin entries in various aicraft types - that's letting the airplane settle before applying spin inputs. I've seen a number of Decathlon pilots unable to get a spin at all by doing that.

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I enter my spins (Decathlon) by slowing until I get within ~5 mph or so above the stall, then snap the stick all the way back with simultaneous rudder in the direction I want to spin. Aileron stays neutral. Works every time, either direction, but maybe I am not getting as vertical as I could, although when exiting after 1 turn I am generally pointing straight down. Maybe I should try waiting a little longer.

sandifer said:

Try flying a very steep upline (between 60 degrees and vertical) at full power and cap it off level at a speed indicating 15-20 mph BELOW your indicated power off stall speed. Pitch over so the nose is about 20 degrees above the horizon, and before the plane has a chance to settle, simultaneously apply spin inputs and pull power off.

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What does "cap it off level' mean? I first though it meant pitching over until level, but .........?

BTW, I echo Dan's comment and appreciate all you folks who so willingly share your expertise.

SMO said:

I enter my spins (Decathlon) by slowing until I get within ~5 mph or so above the stall, then snap the stick all the way back with simultaneous rudder in the direction I want to spin. Aileron stays neutral. Works every time, either direction,

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Like I said, outside of competition requirements, there are many ways to enter a spin, and this is definitely one of them. No such thing as a wrong way as long as you get the results you want.

But in competition, this technique would earn an automatic zero if the rules were applied properly. The airplane must be allowed to stall in unaccelerated flight before autorotation occurs. Snapping the stick back above stall speed will accelerate the pitch up, and is effectively a snap roll entry. Pilots must be careful to avoid displaying a snapped entry, which is why some pilots in Decathlons occasionally have trouble getting a clean spin entry, or one at all. Like every other figure that you wish to score well on, it takes a little technique and practice.

SMO said:

but maybe I am not getting as vertical as I could, although when exiting after 1 turn I am generally pointing straight down. Maybe I should try waiting a little longer.

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Do you mean you're trying to fly a perfect vertical downline after the spin? If so, you've probably already figured out that the recovery inputs vary, depending on how many turns you're doing. A 1-turn spin takes a significant pushover to establish a vertical attitude during or after recovery of the spin. A 1-1/4 spin requires a little less of a pushover, but also requires a yaw correction to establish a vertical attitude. A 1-1/2 turn spin automatically stops in a near vertical attitude - maybe even a few degrees negative.

SMO said:

What does "cap it off level' mean? I first though it meant pitching over until level, but .........?

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Just mean pushing over to a level flight attitude. Level flight attitude varies with speed, of course.

Great discussion!

I'm gonna head out into the box and apply what I just read regarding entry.

I might have missed it, for those reading this thread...if I dont "lock" the stick back to the stop throughout the spin she flies out of the spin to soon.

Thanks Eric

Regards,

Scott

sandifer said:

Just mean pushing over to a level flight attitude. Level flight attitude varies with speed, of course.

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Eric, I am a bit confused by this. Once the airplane is "capped off level", how do I then "pitch over so the nose is about 20 degrees above the horizon"? Did you mean to say "pitch up so the nose......."?

Would like to go out and give this maneuver a try, but want to be sure I understand what you are saying. Thanks.

So, I tried adding and removing the outspin aileron to correct the problem of spiraling out when doing spins to the left, didn't seem to help. Of course my technique could be way off.

Sandifer, where do you fly out of? Maybe we could meet up and you can show me what you are talking about?

Again last night, easy to spin to the right, spins to the left kept spiraling out. Controls on the stops, and I *thought* the aircraft was fully stalled when I put the rudder over, although in retrospect possibly I relaxed the full back stick a little at the top.

Regarding your comment about "capping off" an upline. I'm envisioning essentially a Humpty, but instead of going over all the way at the top, just pitching to a slightly nose high attitude then putting in the controls to induce a spin. Am I about right?

If so, what speed to pitch over?

Whats a good speed to kick the rudder for a hammerhead in the -8? I've been using high 60's but maybe that's a but too fast?

SMO said:

Eric, I am a bit confused by this. Once the airplane is "capped off level", how do I then "pitch over so the nose is about 20 degrees above the horizon"? Did you mean to say "pitch up so the nose......."?

Would like to go out and give this maneuver a try, but want to be sure I understand what you are saying. Thanks.

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Mark, sorry if I'm not clear. It's pretty simple - I just mean returning the airplane to level flight after flying an upline of some sort (45 deg, vertical, etc.). What I meant by the 20 degree nose up attitude, is that if you push over out of an upline back to level flight well below your power off stall speed, then it might take close to a 20 degree nose up attitude to fly at full power at this slow speed. The level fight attitude at very low speed with full power will be significantly nose-high.

For example, for a number of years, the IAC Primary sequence had a 45 upline followed by a 1-turn spin for the first two figures. On the 45 upline, you'll push over at a speed of your choosing to a level flight attitude (all competition figures start and end in a level flight path, ether upright or inverted). If you push over such that you're flying power on at around your power off stall speed, then the actual amount you pushover will be much less than 45 degrees - probably more like 25 degrees so that you're at the correct nose high level attitude for this slow speed before pulling power and spinning. In the Pitts, there's a figure in this year's Advanced Known sequence that involves a vertical up point roll, then pushing level for the line into a spin entry. By the time I push over, I'm indicating just over 40 mph due to the energy expended on the upline. Power off stall is 62 mph. I fly that slow line for a couple seconds, then pull power off and apply rudder and aft stick all at the same time. Instant spin entry.

walkman said:

So, I tried adding and removing the outspin aileron to correct the problem of spiraling out when doing spins to the left, didn't seem to help. Of course my technique could be way off.

Sandifer, where do you fly out of? Maybe we could meet up and you can show me what you are talking about?

Again last night, easy to spin to the right, spins to the left kept spiraling out. Controls on the stops, and I *thought* the aircraft was fully stalled when I put the rudder over, although in retrospect possibly I relaxed the full back stick a little at the top.

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This might just be the way your airplane behaves, given the CG at solo acro weights. Don't know. I only have experience flying spins in the RV-3 and RV-6/7, none of which had the issue of spiraling out. I can only suggest changes, but other experienced RV-8 drivers could better comment, since we're getting so aircraft specific. Even different RV-8's can have different characteristics, of course. What effect does a little power have on yours? I'm in the Raleigh, NC area (KTTA), but not sure I could help much on the issue of the airplane spiraling out of a spin, assuming you got the spin to start in the first place.

walkman said:

Regarding your comment about "capping off" an upline. I'm envisioning essentially a Humpty, but instead of going over all the way at the top, just pitching to a slightly nose high attitude then putting in the controls to induce a spin. Am I about right?

If so, what speed to pitch over?

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Yep, you got it. There's no magic airspeed - just find what works in your airplane without being so slow as to fall out, but not so fast that you must bleed speed slowing down for the spin. Too many factors to say a speed - depends on the steepness of your line, and how fast you pushover, among other things. The more you fly acro, the less it'll be about flying the "numbers". Most of it you have to do by feel.

walkman said:

Whats a good speed to kick the rudder for a hammerhead in the -8? I've been using high 60's but maybe that's a but too fast?

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This really isn't a good maneuver for flying by the numbers either. Do that and you will be kicking too early for a big flyover rather than a nice tight pivot. The RV has enough power that to do a good pivot, your ASI will pretty much have no indication. They just don't work well enough at low speed. I've heard some ASI's in certain Russian acro planes indicate well enough to use the ASI as an indicator for when to pivot. The best way to learn good pivot timing is with the help of a knowledgeable ground critiquer. If you're in the ATL area, hook up with IAC 3. But this subject was discussed a bit here:

http://www.vansairforce.com/community/showthread.php?p=848777#post848777

Walkman, I was taught by Rich Stowell that the hammerhead, properly done, gets to zero g's - essentially no airspeed, before kick over. In the Decathlon there is a little shudder that indicates this has been reached (not sure you would get anything similar in an -8), kick is immediate (don't want a tailslide!) followed by a two count and then opposite aileron. I am never looking at the gauges during this, too busy looking outside trying to keep vertical.

Thanks everyone. More excuses to go play.

walkman said:

Thanks everyone. More excuses to go play.

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Exactly...

Love these threads!

Thanks Sandifer

I join in thanking Sandifer for this great info. Very appreciated.