[Kevin Horton]

The first serious cold snap of the season hit last week. The overnight lows were in the -20 deg C (-4 deg F) range for several nights. Saturday my schedule allowed me to spend most of the day at the airport, so I plugged in the preheat at 10:30 AM, then went into Smiths Falls to do some final Christmas shopping. I started the engine just after 2 PM to go flying, dressed like a Michelin man, with all my cold weather flying gear.

Given that it was fairly cold, I decided to try some manoeuvres that probably wouldn't be possible in the summer. I experimented with loops from very slow speed. I found that I could get the aircraft around loops starting at 100 kt IAS. They were pretty ugly loops (quite egg shaped), as the airspeed was very slow going over the top, but they worked.

Next, I decided to try a manoeuvre that I used to enjoy in the Canadair CT-114 Tutor (Canadian military jet trainer) - if you've seen the Snowbirds aerobatic team, you've seen some Tutors. The Tutor had enough vertical penetration to do what we called a "Vertical 8". This was a half loop, followed by a roll to upright, then a loop, followed by a roll to upside down, then the second half of a loop. The manoeuvre would look like a figure eight - two balls, one on top of the other. In the Tutor, you started at 350 kt, pulled 5 g on the first half loop, and started the second one at about 200 kt. In the winter, when it was very cold, we could do what we called a "Snow Man", which was like a Vertical 8, but with a third ball on top. You started at VNE (412 kt), and pulled max allowed g (7.33 g) for the first one, and you were going very slow over the top of the third one, but it would make it around. Those were the days!

In the RV-8, I was quite impressed to find that I could start from 180 kt on the bottom of the first half loop, and have 100 - 110 kt at the start of the second loop. I pulled to idle coming down the back side of the loops, and there was no problem keeping the speed well below VNE (200 kt), as long as I got the g on early, and kept it on. Note that my three-blade MT prop has a huge amount of discing drag at idle, so someone with a different prop might find that airspeed control was a bigger issue.

I really didn't expect that this aircraft would have what it took to do a Vertical 8. Gotta love these cold temperatures

 

[WillyEyeBall]

Vertical 8

Kevin,
I saw Van do this maneuver in his "new" RV-4 in 1984 at Oskosh. That's one maneuver I haven't been able to do yet.

Bill McLean
RV-4 slider
Sky Dancing

 

[pierre smith]

What was your terminal speed after the split-ess..

....into the lower half loop?

Best,

 

[Kevin Horton]

What was your terminal speed after the split-ess into the lower half loop?

I was coming out the bottom of the second half loop at around 180 KIAS. I could have come out slower if I pulled a bit harder. I could have also easily busted VNE by a whole bunch if I was slow getting the g on.

 

[tinman]

Kevin,
Thanks for this post.
Do you have an inverted fuel/oil system? I have a fixed pitch with no inverted system and have found that I need a higher initial speed in order to pull a loop with any sort of "0" shape to it...my problem is probably pilot induced, but in order to round out the top of the loop, I must "push" a tiny bit on the top. Sometimes I burp a slug of oil, but never has the engine stumbled... I need a 3 g pullout to keep things slow...
Any tips? Should I expect an "egg" to be the best outcome?

 

[Kevin Horton]

Kevin,
Thanks for this post.
Do you have an inverted fuel/oil system? I have a fixed pitch with no inverted system and have found that I need a higher initial speed in order to pull a loop with any sort of "0" shape to it...my problem is probably pilot induced, but in order to round out the top of the loop, I must "push" a tiny bit on the top. Sometimes I burp a slug of oil, but never has the engine stumbled... I need a 3 g pullout to keep things slow...
Any tips? Should I expect an "egg" to be the best outcome?

I do have inverted fuel and oil systems, but I wasn't trying to do a nice, pretty, round loop, so I did not push going over the top. I was down around 40 kt going over the top, so it wasn't going to be pretty no matter what I did. But it sure was fun.

 

[jferraro17]

"...Those were the days."

Great post Kevin! I quoted this part because it brought a smile to my face, as a former T-37 IP. We could do a vertical 8 entering at Vne and g-locking the other guy

Sure motivates me to get this dang RV-8A done...and makes me wonder about those tiny bolts holding my tail on!

Merry Christmas!

Joe

 

[Danny King]

Vertical 8 from the top or Double split S

Kevin,
I had a Air Force student pilot (UPT) start a Split S at mil power, twenty thousand feet, and 200 knots. The aircraft was doing 500 knots when reaching level. Then he rolled inverted, and started a second Split S from 500 knots. I took the T-38 away from him, and recovered from the high speed dive before we broke windows less than ten thousand feet below us. Those truly were the days!

I going to try the vertical 8 in the Doll. Sounds like fun!

 

[zspivey]

Vertical 8

Have enjoyed all posts on the vertical 8.
Don't believe I will try it. I think I am a good pilot. The reason I think so is, I know my limitations. Believe this maneuver exceeds my limitations.
I do admire those of you who have the motor skills, knowlege and experience to fly this one. It must be great.

 

[rocketbob]

I do have inverted fuel and oil systems, but I wasn't trying to do a nice, pretty, round loop, so I did not push going over the top. I was down around 40 kt going over the top, so it wasn't going to be pretty no matter what I did. But it sure was fun.

Sounds like it! I'll have to give this a try. I like to do rolls on the top of loops, this will add a little bit to the fun. It doesn't matter how slow you are at the top if you unload, since the airplane can't stall at zero g.

 

[jferraro17]

...since the airplane can't stall at zero g.

Oh boy, here we go...





Joe

 

[KirkGrovesRV8]

no vert 8 here

But I did go out flying this AM, was 28 deg OAT and took off held 80mph and climbed out at 3050fpm passing thru 2500' I was still showing 2500fpm.
Gotta love clear cold air
And no bugs!

 

[rocketbob]

Oh boy, here we go...





Joe

I guess there's no such thing as an accelerated stall either.

 

[Paul K]

sounds interesting!

I have absolutely no idea what you guys are talking about although it is fun to read. I admire those of you who can do this.

My entire flying career has been in a spam-can Cessna and the most radical thing I ever did was a spin in a 177 and again in a PA12.

When I started building my 7 I promised myself I would seek some unusual attitude training and if that went well, some light acro training. Being a couple years from finishing, I have time to think about it some more and start looking for someone to train me. Not that I'm ready yet but any suggestions on how and who to start with?

 

[rvbuilder2002]

Kevin,
I saw Van do this maneuver in his "new" RV-4 in 1984 at Oskosh. That's one maneuver I haven't been able to do yet.

Bill McLean
RV-4 slider
Sky Dancing

The one that I have always considered Van's signature maneuver is the loop inside of a loop.

Very large first half of a loop with very tight/small inverted to inverted loop done at the top and then finish the big loop.
Likely made possible by precise energy management and an airplane with a great power to weight ratio (his RV-4 is pretty light).

 

[Kevin Horton]

Have enjoyed all posts on the vertical 8.
Don't believe I will try it. I think I am a good pilot. The reason I think so is, I know my limitations. Believe this maneuver exceeds my limitations.

I'm very happy to read this. I hesitated about making my original post for several days, out of fear it might lead some folks to try things they really shouldn't be trying. Just because one pilot in one aircraft at one altitude in one very cold temperature can do something doesn't guarantee that other pilots in other aircraft at other altitudes or other temperatures can do the same thing. Use good judgement.

For folks who want to experiment - break the manoeuvre down into pieces, and try the pieces first, establishing maximum and minimum airspeeds for critical points of the manoeuvre. Then, once you know all the pieces can be done individually, try linking them together into one manoeuvre, only moving on to the next part of the manoeuvre if you meet the minimum and maximum airspeeds at the gates.

E.g. - do a whole bunch of loops, with slower entry speeds on each one, and note the minimum airspeed at which you can make it all the way around. Then, do a bunch of Split-S's, starting from low speed, and a bit higher entry speed on each one, and determine the maximum speed at which you can start a Split-S. Then, wind that thing up to VNE, pull up into a loop, roll upright at the top and check the airspeed - if it is equal or higher than the minimum you already established, then pull up into the second half of the Vertical 8 - if the speed is too low - abort the manoeuvre. At the bottom of that loop, check the airspeed - if it is equal to or less than the maximum you established earlier, then continue with the last part of the Vertical 8. If the airspeed is too high - abort the manoeuvre.

 

[lucky]

kevin, can u post your W & B numbers, AC config for this partular acro flt?

kevin,
Have you found a sweet spot for your 8 when comes to Acro?
Can u post your W & B numbers, AC config for this partular acro flt?

 

[pierre smith]

An addendum...

...to Kevin's really detailed post.

This is where spin recovery training could really come in handy....you're on your back, at or below stall speed and the worst that can happen is that you fall out of the manoeuvre (British spelling). ....or is it? How 'bout, you fall out of the manoeuvre and spin? Any time you're in a nose high, low airspeed position, a spin can be a likely outcome.

Best,

 

[ao.frog]

Great idea!

Hi Kevin.

Thanks for the detailed post and the words of caution.

We did this in the F-16 when I was flying in the airforce, and to learn it, we did exactly like you wrote in your second post: broke up the maneuver into different parts.

In my -7, I've been experimenting with a roll on top of the loop before starting down on the second half of the loop.
Now, I'll try your idea too. With one person on board, low fuel and low temp, hopefully a -7 can do what a -8 can do....

Merry Christmas to you all from the coooooold Norway.....

 

[Kevin Horton]

kevin,
Have you found a sweet spot for your 8 when comes to Acro?
Can u post your W & B numbers, AC config for this partular acro flt?

If I plan to do acro, I remove all loose items from the aircraft, so I end up at a pretty forward CG. The stick forces would be lower if the CG was further aft, but I don't want the extra weight of something in the aft baggage compartment, nor do I want the risk of it coming loose.

The weight and CG during the vertical 8s would have been about 1525 lb and CG of 79.75" aft of the datum. I was starting at 4000 ft altitude. I didn't note the temperature at 4000 ft, but it should have been about -11 deg C (12 deg F), if I interpolate from temperatures at other altitudes. That gives a density altitude of about 1750 ft.

Note: I'm not suggesting than anyone should try this manoeuvre from 1750 ft - that would be a very bad idea, as it wouldn't leave much room to recover from a botched manoeuvre. I present the density altitude to make the point about how the ability of my aircraft to do a Vertical 8 on that day was certainly greatly helped by the cold temperature.

 

[drill_and_buck]

...to Kevin's really detailed post.

This is where spin recovery training could really come in handy....you're on your back, at or below stall speed and the worst that can happen is that you fall out of the manoeuvre (British spelling). ....or is it? How 'bout, you fall out of the manoeuvre and spin? Any time you're in a nose high, low airspeed position, a spin can be a likely outcome.

Best,

Pierre makes an excellent point.

When I wanted to learn acro I was fortunate to have access to a good aerobatic school and signed up for the basic class. We spent what I thought was an inordinate amount of time on spin recovery training including upright, inverted, multi-turn spins, accelerated spins, ...

I didn't realize how valuable the training was until I discovered how many ways you can fall into a spin, even from simple maneuvers. I was having some fun practicing hammerheads (stall turns), my vertical line wasn't great, got a little to slow and fell into an inverted spin during the turn. You wouldn't want this to be the first time you experience an inverted spin.

Anyone interested in flying aerobatic maneuvers in their RV should seek out basic aerobatic training. You'll have a great time and it is an investment with a strong ROI!

Wishing everyone a safe and happy New Year!

 

[jferraro17]

I just want to clear up a few comments here...at least as I am reading/understanding them, and with regard to what I was taught/have always understood...

There are 2 things required to spin an airplane...stall and yaw.

A stall ONLY happens when the critical Angle of Attack is exceeded... Has nothing to do with speed, attitude, g-load, or anyother peripheral measure at any given moment, they are only factors in exceeding the critical AoA. For example, it might take more g-load at a particular speed and bank angle to reach that critical AOA, but until you do, you don't have a stall. Without a stall, you can kick rudder all day but you won't spin.

The yaw portion is self-explainitory. But again, without the yaw, you could pull on a fully stalled stick all day, you won't spin.

How hard is it to NOT introduce these two things in some of the scenarios being discussed? Thats an indiviual pilot and airplane question.

May seem like semantics, but I want to make sure everything is clear...even if I'm the one who needs the clearing up. There are a lot of smart, experienced guys here, so don't heistate to tell me I'm wrong and explain.

Joe
Former Stan/Eval "Spin Pilot"

 

[AlexPeterson]

snip

The yaw portion is self-explanatory. But again, without the yaw, you could pull on a fully stalled stick all day, you won't spin.

Snip

Joe
Former Stan/Eval "Spin Pilot"

Well... maybe, but it would take constant rudder movements to stop any slight yaw disturbance. It is unstable at this point in yaw (it is like balancing a ball on top of another ball). Once a bug hits one of the wings (as an extreme and humorous example) and slightly slows it down, the rate of yaw will increase from zero, which in turn will drop that wing, which will yaw it more. Result of holding full aft stick will always be a spin, even with the rudder centered, won't it?

 

[Kevin Horton]

I just want to clear up a few comments here...at least as I am reading/understanding them, and with regard to what I was taught/have always understood...

There are 2 things required to spin an airplane...stall and yaw.

A stall ONLY happens when the critical Angle of Attack is exceeded... Has nothing to do with speed, attitude, g-load, or anyother peripheral measure at any given moment, they are only factors in exceeding the critical AoA. For example, it might take more g-load at a particular speed and bank angle to reach that critical AOA, but until you do, you don't have a stall. Without a stall, you can kick rudder all day but you won't spin.

The yaw portion is self-explainitory. But again, without the yaw, you could pull on a fully stalled stick all day, you won't spin.

How hard is it to NOT introduce these two things in some of the scenarios being discussed? Thats an indiviual pilot and airplane question.

I can't disagree with any of the above. Pierre's point is quite valid though - if the airspeed gets low enough you no longer have much aerodynamic control to use to control the yaw. Thus you could possibly end up in a spin if you run out of airspeed.

Having the engine at high power is a double-edged sword. The prop wash over the tail gives you quite a bit of yaw control, even if the airspeed is at zero. You can use this to your advantage by being active on the rudder to kill any yaw rate, which should keep you out of a spin.

The down side of being at high power at low speed is that the prop wash also creates a bit of sideslip if you don't use the rudder to counter it. The slower you get, the more the natural sideslip caused by the prop wash will be. If you don't keep on top of it with rudder input, this might help you get into a spin.

 

[jferraro17]

Result of holding full aft stick will always be a spin, even with the rudder centered, won't it?

I don't believe it's an absolute. You make a good, if not realistic--a bug, lol--arguement for SOME yaw being induced. But I also remember an exercise in the T-38 called a "falling leaf", where you did exactly that...full aft, centered stick with feet flat on the floor. The result was a kind of mushy stall and altitude loss basically staright ahead.

Now, I will agree that maintaining wings level is vey difficult, and the resulting difference in AoA on the 2 wings will cause one to drop off steeper than the other--hence a right breaking stall or left breaking stall. But THAT is not a spin.

Guys, keep in mind, all my spin training, and the vast majority of my flying was/is done in jets. Someday I hope to have the experise to discuss this all in terms of RVs/props.

Joe

 

[Snowflake]

I sent Kevin's story about the snowman to a former Moosejaw instructor and got this back:

"Yes, I used to love doing the Snowman. You could do it in the summer, too, if you were really clean and smooth. The Tutor had a vertical penetration of about 10,000 feet (which I have personally verified)."

So it sounds like Kevin has to work a bit more and get the summertime snowman done...

As for spin being inevitable with a centered rudder, I think you'd find that very few of our airplanes, as perfect as they may be to us, are perfectly straight. All it takes is for one wing to go first in the stall, and that puts some yaw in. I think it would start the spin on it's own if your feet were on the floor, but it may just spiral if you held rudder straight. I haven't explored stalls/spins in that level of detail yet. Something to add to the "to-do" list, I guess.

 

[L.Adamson]

I don't believe it's an absolute. You make a good, if not realistic--a bug, lol--arguement for SOME yaw being induced. But I also remember an exercise in the T-38 called a "falling leaf", where you did exactly that...full aft, centered stick with feet flat on the floor. The result was a kind of mushy stall and altitude loss basically staright ahead.

That's what my 6A did with just me in it & power to idle. It didn't spin, or drop a wing, and would probably just mush all the way to the ground.

L.Adamson

 

[N941WR]

I'm very happy to read this. I hesitated about making my original post for several days, out of fear it might lead some folks to try things they really shouldn't be trying...

Kevin,

You are so lucky I damaged my 135 hp O-290, otherwise I would just have to take my -9 out on a hot day and show you up with that snowman manoeuvre. But, now that I'm installing a 180 hp O-360 I guess I had better not do that.

Great story and writeup from you and the others. I sure wish my back and plane (in that order) would allow me to play with such manoeuvers.

Keep the detailed stories coming.

 

[Danny7]

The weight and CG during the vertical 8s would have been about 1525 lb and CG of 79.75" aft of the datum. I was starting at 4000 ft altitude.

Kevin, would you mind breaking down the weight into the airplane empty weight, fuel and pilot weights? 1525 sounds heavy, but i don't know what you weigh and your fuel load for the day was. I thought the 8's weighed in around 1100ish, so even if you are 200 pounds that would be 225 pounds of fuel. seems like a lot, but i know very little so maybe you could break it down for me

 

[Kevin Horton]

Kevin, would you mind breaking down the weight into the airplane empty weight, fuel and pilot weights? 1525 sounds heavy, but i don't know what you weigh and your fuel load for the day was. I thought the 8's weighed in around 1100ish, so even if you are 200 pounds that would be 225 pounds of fuel. seems like a lot, but i know very little so maybe you could break it down for me

Emtpy Weight: 1158 without wheel pants (removed because of snow on the taxiways and ramp).
Pilot Weight: 200 (full winter flying gear)
Fuel Weight: 28 USG for weight of 168 lb
Total: 1526, plus or minus a handfull of lb

The aircraft has an angle-valve IO-360-A1B6 with crankshaft counterweights, aerobatic three-bladed MT CS prop with counterweights, inverted oil system and full IFR panel. It's a bit heavier than I'd like, but it is what it is.