Micro VG's and Spins - Citabria

[lr60plt]

Hey all,

I really like the idea of Micro VG's and with the cost vs benefit being so good its something I would like to do in the future. However my airplane will be used for spin training as well. I've read that citabria's with vg's have a pretty hard time getting into and maintaining a spin when equipped with vg's.

Does anyone have any experience doing aerobatics or spins in a Citabria with VG's or know of one doing it? Id imagine that anything that was able to spin without them, would be able to with them...so im just looking for a little insight/opinion.

Thanks!

 

[dmccormack]

I have expereince with VGs on an A36 (Bonanza) and can tell you it made it basically un-stallable (the airplane would simply mush).

Never tried to spin it, but my guess would be it would take an accelerated zoom-stall and hard rudder kick.

 

[wsuffa]

I have expereince with VGs on an A36 (Bonanza) and can tell you it made it basically un-stallable (the airplane would simply mush).

Likewise my Commander. I took it to zero ground speed one day in the practice area in very slow flight (zero ground speed as noted by the ATC call asking what I was doing...). I stop trying power-on stalls once we hit a 30-degree deck angle.

Never tried to spin it, but my guess would be it would take an accelerated zoom-stall and hard rudder kick.

That would be my bet, too.

 

[Dan Thomas]

Read the fine print in the STC. It may make the aircraft illegal to spin or to do any other aerobatics, for that matter. Some of these add-ons aren't tested for spin recovery, and installing them removes that capability from the POH.

Dan

 

[David]

I have expereince with VGs on an A36 (Bonanza) and can tell you it made it basically un-stallable (the airplane would simply mush).

Never tried to spin it, but my guess would be it would take an accelerated zoom-stall and hard rudder kick.

My M35 Bonanza (same wing as the A36) had VG's and could be stalled just at a slower speed. The behavior at the stall with VG's is very abrupt and accompanied with a wing drop.

Here's some test reports on an F33 with VG's - worth reading.

http://www.nar-associates.com/technical-flying/vortex/Vgs_stall_wide_screen.pdf

http://www.nar-associates.com/technical-flying/vortex/Vgs_cruise_wide_screen.pdf

 

[dmccormack]

My M35 Bonanza (same wing as the A36) had VG's and could be stalled just at a slower speed. The behavior at the stall with VG's is very abrupt and accompanied with a wing drop.

I have about the same amount of time in a -35 (1947 E-185 model) and stalls were more pronounced. The A36 I flew had tip tanks, which may have changed the behavior, but there was no significant break or wing drop IF ball was basically centered.

 

[Henning]

Nice thing about the VGs on the Twin Cessnas is it reduces Vmc to below stall effectively eliminating it.

 

[CFI-Guy]

I've done spins in the High Country Explorer with VG's and can offer that likely because it stalls at such a slow airspeed it is quite hesitant to get into a spin to begin with. With the VG's creating a reduced stall speed there is less airflow over the control surfaces and if memory serves there wasnt a whole lot of flight control authority when the stall finally decided it was going to occur, thus getting the yaw required from the rudder was difficult. I think I found it easier to spin by forcing the stall at a higher airspeed (increase G's, increase stall speed) with a more abrupt pull up at a higher airspeed and then adding rudder. I dont recall it being hard to maintain the spin once you finally got into it however.

The guy to really ask about this might be Jerry at American Champion or Greg Koontz. Greg also might be on the acro exploder which would be another good source of info on the subject.

 

[lr60plt]

Thanks for all the input guys, I appreciate it. Good reading, and those links posted by David contained really good data.

I emailed the company and this was their reply:

Hello,
Thank you for the opportunity to answer your question. As you know, to spin, all control surfaces need to be stalled. You are correct, if you can spin it before, you can spin it after. The VGs lower the stall speed, but the aircraft still stalls, or it would not land. In flight test to obtain the STC, we are required to comply with the FAA regulations, including the spin requirement. Yes, the aircraft spins with VGs. It is less likely to unintentionally spin, and it more promptly recovers from a spin because the airflow reattaches at a slower airspeed. Vortex Generators improve the control response by creating higher velocity airflow (vortices) over the control surfaces. Micro VG STCs DO NOT change the airworthiness category, and therefore do not prohibit spins/aerobatics. We ship many kits directly to the American Champion factory, they are supportive of customers installing Micro VGs.

Thank you also for the link to the discussion. One additional comment that I would like to pass along regarding the wing roll in the stall (per David) on the Bonanza wing. The article referenced was evaluating another company’s VGs. The VG kit from Micro AeroDynamics on the Bonanza wing stalls straight ahead, with NO roll off.

In regard to a “more abrupt stall” with vortex generators installed – when the controls have reached the stop and you are no longer holding altitude – the aircraft is stalled even if you still have aileron authority. If the pilot does not recognize this stall and take corrective action, what the aircraft eventually does might be described as abrupt. On the other hand, it typically just mushes and the VGs give you controlability in this stalled condition.

Let me know if I can further assist.

Best Regards,
Flight Test Director
Micro AeroDynamics Inc.

 

[Henning]

Thanks for all the input guys, I appreciate i. Good reading, and those links posted by David contained really good data.

I emailed the company and this was their reply:

Hello,
Thank you for the opportunity to answer your question. As you know, to spin, all control surfaces need to be stalled. You are correct, if you can spin it before, you can spin it after. The VGs lower the stall speed, but the aircraft still stalls, or it would not land. In flight test to obtain the STC, we are required to comply with the FAA regulations, including the spin requirement. Yes, the aircraft spins with VGs. It is less likely to unintentionally spin, and it more promptly recovers from a spin because the airflow reattaches at a slower airspeed. Vortex Generators improve the control response by creating higher velocity airflow (vortices) over the control surfaces. Micro VG STCs DO NOT change the airworthiness category, and therefore do not prohibit spins/aerobatics. We ship many kits directly to the American Champion factory, they are supportive of customers installing Micro VGs.

Thank you also for the link to the discussion. One additional comment that I would like to pass along regarding the wing roll in the stall (per David) on the Bonanza wing. The article referenced was evaluating another company’s VGs. The VG kit from Micro AeroDynamics on the Bonanza wing stalls straight ahead, with NO roll off.

In regard to a “more abrupt stall” with vortex generators installed – when the controls have reached the stop and you are no longer holding altitude – the aircraft is stalled even if you still have aileron authority. If the pilot does not recognize this stall and take corrective action, what the aircraft eventually does might be described as abrupt. On the other hand, it typically just mushes and the VGs give you controlability in this stalled condition.

Let me know if I can further assist.

Best Regards,
Flight Test Director
Micro AeroDynamics Inc.

Like hit the ocean

 

[denverpilot]

The VGs lower the stall speed, but the aircraft still stalls, or it would not land.

ROFLMAO...

[Because it's wrong. Not because he's as funny as he thinks he is. You can land an un-stalled aircraft... of course.]

 

[Henning]

ROFLMAO...

[Because it's wrong. Not because he's as funny as he thinks he is. You can land an un-stalled aircraft... of course.]

However, how would you keep it on the ground once you got out?

 

[AcroBoy]

VG's probably make more sense on a twin, so Vmc becomes lower than Vso. On an aerobatic plane, where you'd like a sharp stall break, it makes no sense.

Regardless, they are bonded to the wing and tail, not sure if they'd end up sticking too long to fabric or if there was even an STC for a Cirabria.

No real advantage for any single other than a potential increase in gross weight.

 

[denverpilot]

However, how would you keep it on the ground once you got out?

Get out at high speed. Where it goes from there isn't your problem.

 

[Henning]

Get out at high speed. Where it goes from there isn't your problem.

I'd want a Decathalon and a skid suit but I'm game for a try. If I clip into a fuel cutout it may even be ok...

 

[ebetancourt]

VG's probably make more sense on a twin, so Vmc becomes lower than Vso. On an aerobatic plane, where you'd like a sharp stall break, it makes no sense.

Regardless, they are bonded to the wing and tail, not sure if they'd end up sticking too long to fabric or if there was even an STC for a Cirabria.

No real advantage for any single other than a potential increase in gross weight.

Reducing stall speed and landing distance not an advantage? I won't put them on my Citabria, but cost vs need is the reason. If I was bush oriented, wouldn't hesitate.

 

[lr60plt]

Regardless, they are bonded to the wing and tail, not sure if they'd end up sticking too long to fabric or if there was even an STC for a Cirabria.

No real advantage for any single other than a potential increase in gross weight.

The surface they are sticking to is the same type of paint as on most metal aircraft. And the list of compatible airplanes was in post #1....everything from a champ through decathlon.

There are a ton of advantages on a single...such as controllability at slower speeds (vgs under the tail as well), the already mentioned much slower stall speed... higher control surface effectiveness through a larger range of speed, etc. The "break" itself could still occur just as sharp, but you would probably just have to accelerate the stall a little bit.

And all for what...2lbs maybe? Seems like a good deal to me...

 

[lr60plt]

And in regards to the landing/stall comment....he probably meant it in a different context.

Ive flown a lot of airplanes that I wouldn't dare try to stall on landing.

 

[RoscoeT]

Reducing stall speed and landing distance not an advantage? I won't put them on my Citabria, but cost vs need is the reason. If I was bush oriented, wouldn't hesitate.

How would you use the reduced stall speed unless you modify your airplane with extended gear and/or tundra tires that cause the airplane to sit at a higher angle on the ground? If you touch down 3-point in the configuration you have now, it's going to occur at the same airspeed (AoA) with or without VGs. Landing distance will only be reduced if you touch down slower at a higher AoA. On a stock Citabria, this will put the mains way high in the air as the tail touches down. Not a pretty way to land.

VGs are controversial anyway. Many long time Super Cub bush pilots feel that a stock Cub without VGs can be operated just as short as one with VGs, and that you cannot "buy" short field performance...it must be earned through laboriously acquired skills.

 

[lr60plt]

I think the main advantage would be increased control surface effectiveness as those slower landing speeds.

 

[Henning]

How would you use the reduced stall speed unless you modify your airplane with extended gear and/or tundra tires that cause the airplane to sit at a higher angle on the ground? If you touch down 3-point in the configuration you have now, it's going to occur at the same airspeed (AoA) with or without VGs. Landing distance will only be reduced if you touch down slower at a higher AoA. On a stock Citabria, this will put the mains way high in the air as the tail touches down. Not a pretty way to land.

VGs are controversial anyway. Many long time Super Cub bush pilots feel that a stock Cub without VGs can be operated just as short as one with VGs, and that you cannot "buy" short field performance...it must be earned through laboriously acquired skills.

Really? Tagging tail first is routine on a three point for me. When I was first taught in a Citabria by an old Corsair pilot and the tail would tag and the mains would plant he'd call "Perfect, even a 10 knot gust won't pick you up now."

The key is the kinetic energy you can shed and stay under control going into a crash. That is the element about VGs that can save your life and makes them worth buying. They are the most value in crashworthiness you can buy right after a good shoulder harness set.

 

[lr60plt]

Really? Tagging tail first is routine on a three point for me.

I touch my tailwheel first every now and then too in the Citabria...seems to do fine. Many say they go for that as well in Pitt's.

 

[RoscoeT]

Really? Tagging tail first is routine on a three point for me. When I was first taught in a Citabria by an old Corsair pilot and the tail would tag and the mains would plant he'd call "Perfect, even a 10 knot gust won't pick you up now."

The key is the kinetic energy you can shed and stay under control going into a crash. That is the element about VGs that can save your life and makes them worth buying. They are the most value in crashworthiness you can buy right after a good shoulder harness set.

You both missed my point. In normal operations (not talking about crash), the only way to land slower is to fly at a higher AoA. Touching down at the normal 3-point attitude, even if it's a little tail-first as you describe will cause your landing speed to be the same whether you have VGs or not. You have to fly at a higher AoA than otherwise possible to take advantage of the speed reducing capability of VGs. To touchdown significantly more nose-high (higher AoA) and slower (with VGs) than is attainable without VGs will make for a pretty ugly landing, given how high the mains are when the tailwheel touches. I would imagine they could be a couple feet higher than the tailwheel if you're truly landing at the minimum speed attainable with VGs. That is why I made the comment about extended gear and/or large tundra tires. When you say you routintely touch down tailwheel first, you are talking about a few inches of difference, not feet. This is normal and fine. My point is you can't take much advantage of the reduced landing speed in normal operations (not crashes) of VGs unless you either extend the gear and/or add tundra tires, or accept the slam down of the mains as you touch down extremely nose high. I'm not saying there's anything wrong with generally touching down a little tailwheel first. I do it too.

 

[Capt. Geoffrey Thorpe]

This guy apparently likes vortex generators on his Cub.

http://youtu.be/QMpyZA1zQK0

(along with a lightweight starter, and a gell battery.)

Dunno what he has on the Taylorcraft he uses for soaring

http://youtu.be/E-u-MCDi7Gk

 

[denverpilot]

This guy apparently likes vortex generators on his Cub.

http://youtu.be/QMpyZA1zQK0

(along with a lightweight starter, and a gell battery.)

He's making soup!

 

[lr60plt]

You both missed my point. In normal operations (not talking about crash), the only way to land slower is to fly at a higher AoA. Touching down at the normal 3-point attitude, even if it's a little tail-first as you describe will cause your landing speed to be the same whether you have VGs or not. You have to fly at a higher AoA than otherwise possible to take advantage of the speed reducing capability of VGs. To touchdown significantly more nose-high (higher AoA) and slower (with VGs) than is attainable without VGs will make for a pretty ugly landing, given how high the mains are when the tailwheel touches. I would imagine they could be a couple feet higher than the tailwheel if you're truly landing at the minimum speed attainable with VGs. That is why I made the comment about extended gear and/or large tundra tires. When you say you routintely touch down tailwheel first, you are talking about a few inches of difference, not feet. This is normal and fine. My point is you can't take much advantage of the reduced landing speed in normal operations (not crashes) of VGs unless you either extend the gear and/or add tundra tires, or accept the slam down of the mains as you touch down extremely nose high. I'm not saying there's anything wrong with generally touching down a little tailwheel first. I do it too.

No, i understand what you are saying, as it is correct. I didn't say anything about shorter landing distances in my previous posts. I was only addressing the landing tailwheel first statement. I do a few inches often, and i think my worst (accidental) was when the mains were about a foot off the ground...and landing attitude that i would rather not see again. :wink2:

- That Taylorcraft vid is pretty cool.

 

[ebetancourt]

You both missed my point. In normal operations (not talking about crash), the only way to land slower is to fly at a higher AoA. Touching down at the normal 3-point attitude, even if it's a little tail-first as you describe will cause your landing speed to be the same whether you have VGs or not. You have to fly at a higher AoA than otherwise possible to take advantage of the speed reducing capability of VGs. To touchdown significantly more nose-high (higher AoA) and slower (with VGs) than is attainable without VGs will make for a pretty ugly landing, given how high the mains are when the tailwheel touches. I would imagine they could be a couple feet higher than the tailwheel if you're truly landing at the minimum speed attainable with VGs. That is why I made the comment about extended gear and/or large tundra tires. When you say you routintely touch down tailwheel first, you are talking about a few inches of difference, not feet. This is normal and fine. My point is you can't take much advantage of the reduced landing speed in normal operations (not crashes) of VGs unless you either extend the gear and/or add tundra tires, or accept the slam down of the mains as you touch down extremely nose high. I'm not saying there's anything wrong with generally touching down a little tailwheel first. I do it too.

I don't think I missed your point, but I don't accept your statement that a full stall equals a three-point landing or an almost three point landing. A three-point in my Waco is a tail low wheel landing. It is NOT stalled. In a full stall landing the tail wheel always touches, the mains plant themselves afterward. If it is really light it is certainly more than a few inches. If you take weight off the airplane by touching the tail wheel down, then you have lowered the stall speed and the mains really don't "crash" although it is a very firm arrival. Very light, the Citabria is the same. It is going to touch the tail first because the AOA in a full stall is pretty high. In a real short field with power the tail is even lower, but then you can ease the mains on by reducing power and probably are never fully stalled.

 

[RoscoeT]

but I don't accept your statement that a full stall equals a three-point landing or an almost three point landing.

Where did I say that? My whole point was that when you do a full-stall landing you are NOT 3-point. You are more nose high. And when you add VGs, you are making the full stall attitude even MORE nose high due to the fact that the VGs delay turbulent airflow, and delay the stall.

My point about a true 3-point landing (where all three tires touch simultaneously) is that whether you have VGs or not, the 3-point touchdown will occur at the same speed (above stall). VGs don't allow you do fly slower for a given AoA (as in 3-point attitude). So how can you ACTUALLY utilize VGs for landing slower without extending your gear and/or putting on big tires to raise the 3-point atittude?

And the majority of tailwheel airplanes are like you describe - not fully stalled in 3-point attitude. But since you can already touchdown with the nose higher (and slower) than in 3-point attitude (even without VG's), adding VGs will only cause the true full-stall attitude to be even more nose high.

You said that VGs will reduce your landing speed and distance. This assumes you can land in a more nose high attitude. I am asking you how you expect to utilize the slower stall speed (and supposed landing speed) of VGs without your mains being 2 ft. in the air when your tailwheel touches down. Most people are not going to be landing like that.

 

[ebetancourt]

Where did I say that?

When you said "a few inches." I would consider that a "near" 3 pt.

Most people are not going to be landing like that.

I guess I am not most people.

 

[RoscoeT]

I guess I am not most people.

You routinely land with the mains two feet in the air when the tailwheel touches? Ouch.

 

[AcroBoy]

If I understand the thread correctly, I think there is a distinction between a three point landing and a full stall landing. At least in my TD experience, around 400 in a Super Decathlon and around 500 in an Extra, the plane is not fully stalled at touchdown.

Fabric drumming would still raise concerns about VG's and their adhesion. They can and do break off of even metal planes.

For an acro plane, once the critical AOA is reached, a definite stall break is an advantage, as is the ability to keep a wing stalled, as in snaps and spin entry. I think VG's would inhibit this behaviour, and would be detrimental to an acro plane.

You probably need to decide whether the added expense will improve the already pretty good STOL abilities of a Citabria, or would worsen the already mediocre acro abilities.

 

[Diana]

You probably need to decide whether the added expense will improve the already pretty good STOL abilities of a Citabria, or would worsen the already mediocre acro abilities.

When I was considering putting them on my Citabria, that's what I came up with too, and decided to keep the airplane as is and not complicate things. I didn't add spades either.

 

[Henning]

You both missed my point. In normal operations (not talking about crash), the only way to land slower is to fly at a higher AoA. Touching down at the normal 3-point attitude, even if it's a little tail-first as you describe will cause your landing speed to be the same whether you have VGs or not. You have to fly at a higher AoA than otherwise possible to take advantage of the speed reducing capability of VGs. To touchdown significantly more nose-high (higher AoA) and slower (with VGs) than is attainable without VGs will make for a pretty ugly landing, given how high the mains are when the tailwheel touches.

I've never seen VGs increase the AOA that significantly. Most of what I notice from them is a smoother stall break and greater control effectiveness at low speed. You do pick up some AOA, but it's not like you're making out, it's not like a STOL cuff (which are also very effective at reducing landing speed and increase AOA on landing much more significantly than VGs). The landings will likely improve even with the extra AOA because when the wing finally does stall it'll drop down those last few inches more gently. Your theory on the subject does not hold up in practice.

 

[Capt. Geoffrey Thorpe]

If I understand the thread correctly, I think there is a distinction between a three point landing and a full stall landing. At least in my TD experience, around 400 in a Super Decathlon and around 500 in an Extra, the plane is not fully stalled at touchdown.

Not unusual, at least in my experience.

For an acro plane, once the critical AOA is reached, a definite stall break is an advantage, as is the ability to keep a wing stalled, as in snaps and spin entry. I think VG's would inhibit this behaviour, and would be detrimental to an acro plane.

VGs on the horizontal stabilizer can help with micro loops as I understand it.

 

[dmccormack]

If I understand the thread correctly, I think there is a distinction between a three point landing and a full stall landing. At least in my TD experience, around 400 in a Super Decathlon and around 500 in an Extra, the plane is not fully stalled at touchdown.

Pilots use "full stall" as shorthand for "the stall horn was blaring..."

Very few pilots are able to touch down at the precise moment lift gives out (and even that is a partial stall).

 

[Henning]

Pilots use "full stall" as shorthand for "the stall horn was blaring..."

Very few pilots are able to touch down at the precise moment lift gives out.

Actually by tagging the tail wheel first you effectively force the stall right there because you can no longer pitch up and you are adding a buttload of instant drag at the tail, then you instantly lose several more degrees AoA so you are immediately well below flying speed. That's why a perfect three point tagging tail wheel first will always be a 'full stall' because it can no longer fly without applying a buttload of power and accelerating. The added advantage is it moves your pivot point aft reducing your chances of ground looping in the touchdown transition and eliminates all that 'happy feet' happy horsecrap, hold the tail where it needs to be behind you and let it drag you down. Let nature do the work for you.

 

[ebetancourt]

So I went flying yesterday in the 7GCBC. This was an instructional ride for my 15 y/o granddaughter. She has been flying for about a year and has about 40 hours. (I can't wait for her birthday.) We had a new piece of equipment in the Citabria when we got to the airplane yesterday: a cover for the airspeed indicator. She did four three points, two without airspeed reference, then two with. All were tailwheel first with the mains about 6-8 inches above the ground, none were "full" stall. Since I no longer pay much attention to her flying I was able to really pay attention to the touchdowns with respect to this discussion.

First I said something stupid above, but the intent was sort of correct. If you touch down tailwheel first, the AOA reduces from the reduction in sink rate and the natural tendency for the airplane to change attitudes (front of the airplane comes down a little even if you try to hold it off) and the weight reduction does reduce the AOA required, so the airplane can fly a little longer. The return to pavement of the mains is not abrupt. On pavement the tail wheel friction is really not a factor (assuming straight with no drift).

We had other things to work on (I generally only get to fly with her once a week), but when we have more time, I will get her to do some 3 pt landings with no flaps. This should get the mains higher.

 

[ebetancourt]

That stuff below had a thread purpose; support the idea that slowing the stall speed would allow a shorter landing. Like Henning, I don't believe the change in AOA would be that great. Furthermore, landing tail wheel first does not have to result in slamming the main gear on.

I need to quit posting when I am in a hurry.

So I went flying yesterday in the 7GCBC. This was an instructional ride for my 15 y/o granddaughter. She has been flying for about a year and has about 40 hours. (I can't wait for her birthday.) We had a new piece of equipment in the Citabria when we got to the airplane yesterday: a cover for the airspeed indicator. She did four three points, two without airspeed reference, then two with. All were tailwheel first with the mains about 6-8 inches above the ground, none were "full" stall. Since I no longer pay much attention to her flying I was able to really pay attention to the touchdowns with respect to this discussion.

First I said something stupid above, but the intent was sort of correct. If you touch down tailwheel first, the AOA reduces from the reduction in sink rate and the natural tendency for the airplane to change attitudes (front of the airplane comes down a little even if you try to hold it off) and the weight reduction does reduce the AOA required, so the airplane can fly a little longer. The return to pavement of the mains is not abrupt. On pavement the tail wheel friction is really not a factor (assuming straight with no drift).

We had other things to work on (I generally only get to fly with her once a week), but when we have more time, I will get her to do some 3 pt landings with no flaps. This should get the mains higher.

 

[lr60plt]

That's one lucky granddaughter!

Next subject - INVERTED spins in 7ECA...with or without vg's!

 

[RoscoeT]

Next subject - INVERTED spins in 7ECA...with or without vg's!

I prefer inverted spins over upright...they recover more positively. Only in the 7ECA you'll just need to restart the engine afterwards...or not.