Steep Spirals

BoDEAN

New Member
Two CFI's where i fly, told me I should be at my Best Glide Speed. Is this correct? The posts above don't state this
 

pure_IMC

New Member
i would not do this at best glide. Im flying the arrow for my cfi and the best glide is 79. Now figure what your stall speed would be if you were doing a 60 degree bank.

You are pulling 2 g's in a 60 bank. Vs=60 in arrow

the square root of 2 x 60 = 85 knots

so you can see if you use best glide you would be s.o.l.

But of course this all depends what airplane you are using.

We typically use 90-100 knots in the arrow.

GOOD LUCK
 

BoDEAN

New Member
[ QUOTE ]
i would not do this at best glide. Im flying the arrow for my cfi and the best glide is 79. Now figure what your stall speed would be if you were doing a 60 degree bank.

You are pulling 2 g's in a 60 bank. Vs=60 in arrow

the square root of 2 x 60 = 85 knots

so you can see if you use best glide you would be s.o.l.

But of course this all depends what airplane you are using.

We typically use 90-100 knots in the arrow.

GOOD LUCK

[/ QUOTE ]

Using a Cessna 172RG
 

drumminpilot

Well-Known Member
Stall speed in a 172RG at 60 degrees of bank with a centered CG is 68 knots. Best glide is somewhere around 65 knots..... not good...... I've been doing my steep spirals in the RG at 80.
 

EDUC8-or

Well-Known Member
I keep seeing stall speed come up. It's not really an issue with this manuever. If you wanted to fly it at 50kts clean in the RG with 60 degrees of bank it can be done (that's max weight stall speed in that configuration)

Why? Because this is a power off, descending maneuver. Descending is the big word here. Let's say you were flying it at 50 kts clean. You could crank in 60 degrees of bank without stalling. All you would have to do is increase your rate of descent to compensate for the loss of the vertical component of lift. It's possible to do a 60 degree turn at 1G as long as you're descending.

Personally, I fly steep spirals in the RG at about 75-85kts.

I was up yesterday doing pattern work to prepare for my CFI ride. At 400' on the upwind leg, my CFI pulled the power. I was able to use 60 degrees of bank with no power at 65 kts to do a 180 and turn back to the airport and land. As long as you lower the nose, you can use lots of bank without stalling.
 

BoDEAN

New Member
When is your checkride?
You were doing a 180 degree power off approach? Those are fun.

You're right on the key word being descending. It isn't like a 60 degree bank in a steep turn, where you are maintaining altitude.
 

EDUC8-or

Well-Known Member
I'd like to get the ride done by the end of March. We have state testing for my 4th graders this week, so I've been spending more hours at work and very few hitting the books or at the airport.


Thanks for your great gouge on your oral. I'm sure your flight will go well!

By the way, we weren't doing to 180 approaches. My CFI pulled my power on the upwind leg at 400AGL. He wanted to see if I would panic or what I would do. It was REAL tight, but I was able to get it back around and land with the wind at my back. If the winds weren't blowing about 17kts I'm not sure if I would have made it. He was trying to prove a point to me that if I ever lost an engine at such a low altitude, I should already have a plan of action in my head, especially at familiar airports. Go to an airport that isn't busy (no one there or close to the pattern) and try it sometime. You'd be surprised with what you can do.
 

pure_IMC

New Member
sure this is a descending manuever, and sure you can turn 60 degrees at 50 knots. However you have to maintain your selected speed within 10 knots. If you go pulling 2 g's at 50 knts, you are going to have to apply some back pressure to maintain your airspeed, if you dont you are going to bolt right through pts. And hence, when you apply that back pressure, you stall.
 

EDUC8-or

Well-Known Member
I still think it can be done. Go up to about 2000' and simulate a traffic pattern. Pull your power on the base to final turn with your flaps out and try a 60-90 degree turn. As long as you keep your nose lowered it's possible to maintain your same airspeed and not stall the aircraft. Whenever you are taking out the vertical component of lift, stall speed is taken out of the picture.
 

bluelake

Well-Known Member
this thread is really confusing me. I dont understand how taking out the VCL takes stall speed out of the picture, as you suggest. I have been flying thse maneuvers at 90 KIAS in a C-172. Am I flying them too fast? Anyone that cites some references on this would be greatly appreciated...
 

EDUC8-or

Well-Known Member
90 knots is just fine to do it in a C172. Actually, it's probably better than best glide because this is an emergency descending manuever. You've already got your point where you want to land picked out, so you probably want to get down more quickly to take care of whatever problems you may have.

I'll try to give you an answer to your VCL question. What two things do you need to maintain altitude? Airspeed and angle of attack. What if your airspeed decreases? Then you must increase you AOA. In a level 60 degree turn, you have to pull back to maintain altitude. The back pressure will increase your AOA. If you are flying slowly and close to your critical AOA, you're going to stall.

If you make the same 60 degree turn without maintaining altitude, there is no increase in AOA, no increase in load on the wing, and no increase in stall speed.

Turns don't increase your load factor. Maintaining altitude during a turn due to the loss of VCL (by increasing your back pressure and AOA) does.

That's my stab in the dark. I hope I haven't cornfuzed you more.
 

aviator

New Member
I'm not sure thats correct....
Turns will always increase load factor, it doesn't matter if they are straight and level, climbing, or descending. The reason is centrifigal force. An object in motion has a tendency to remain in motion in the direction it is traveling, if you deflect that object (in this case an airplane in a turn) the intertia of that object resists the deflection and this is felt as a resulting force ie- centrifigul force. The addition of centrifugal force will add to the total load placed on the aircraft.
I think what may be missing here is that if you wanted to completely eliminate that positive force of 1g of lift you would have to be in free fall. Even though you are descending the wings are still producing lift.
Everything I have ever read states that load factor doubles at 60 degrees of bank with no reference to descent rates or airspeed.

Good topic of discussion I can see how your thinking it just doesn't seem right. Any ATP's or aerodynamic buffs please chime in!!!
 

EDUC8-or

Well-Known Member
I'm going to stick with my theory, here's why...

I'll agree that all turns can increase load factor. I don't agree that it doubles in a 60 degree turn unless you're in straight and level flight. If your airplane weighs 2000 pounds the wings must create 2000 pounds of lift in straight and level flight. In a 60 degree straight and level turn, the wings now must support the aircraft weight plus an additional 2000 pounds due to centrifugal force. The wings now must support 4000 pounds and load factor has doubled. If you take straight and level out of the equation, your wings don't have to support 4000 pounds, so load factor hasn't doubled. The load factor would be dependent on your rate of descent in a descending 60 degree banked turn.

I'll quote page 1-17 from the Pilot's Handbook of Aeronautical Knowledge. "A positive load occurs when back pressure is applied to the elevator, causing centifugal force to act in the same direction as the force of weight. A negative load occurs when forward pressure is applied to the elevator control, causing centrifufal force to act in a direction opposite to that of the force of weight. Curved flight producing a positive load is a result of increasing the angle of attack and consequently the lift. Increased lift always increases the positive load imposed upon the wings. However, the load is increased only at the time the angle of attack is increased. Once the angle of attack is established, the load remains constant."
 

bluelake

Well-Known Member
hmmm... but wait a minute, I thought I read in aerodynamics that in a descent, weight still equals lift. where'd that come from.. gotta go dig.

Well, at the end of the day, my concern is what the DE says (that I am gonna send Comm students to). He made the comment that this debate really isnt totally relevant cuz there's NO reason to fly at best glide speed (your not trying to glide the furthest distance - your already at your "landing point"), and that your not even trying to stay in the air the longest period of time (best endurance speed). RATHER, he said, ya wanna fly the airplane at the speed that makes it very controllable and responsive without bumping up against Va. Hence, he said that 90 KIAS in the C-172 was a wonderful speed to use.

I can sleep tonight, but this thread has been very useful fo rme
:) Thanks all.
 

EDUC8-or

Well-Known Member
I agree with bluelake that 90 knots is a good speed for this manuever. I wrote earlier in this thread about using a faster speed vs. best glide. This is basically an emergency descent and we want to get down ASAP in an emergency.
 

EatSleepFly

Well-Known Member
[ QUOTE ]
This is basically an emergency descent and we want to get down ASAP in an emergency.

[/ QUOTE ]

A steep spiral is basically an emergency descent? No way. Big difference. You're often way over Va durning an emergency descent. Emergency descent is if you've depressurized, or have a fire and need to get down NOW. Steep spiral is to get yourself down to a field that you want to land in but are too high (i.e. engine failure). Incidentally, best glide + 10 kts. works well for steep spirals.
 

BoDEAN

New Member
What altitude do most of you start the steep spirals at? 6500?

I started at 4000 the other day, and lost 1500 ft in one 360 turn, a no wind day
 

Raskal

New Member
Speed we're teaching in a 172RG=080 KIAS, works well. Start at 4500 AGL and roll out on specified heading at 1500 AGL (which is the requirement in the FAA Flying Handbook).

Regarding stalling, at 60deg of bank and using enough back pressure to maintain 80kts the horn is blaring and you're approaching an accelerated stall, but I have yet to see one of my students get into one, not very comfy but totally do-able.
 
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