Aerotow takeoff distance
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Aerotow takeoff distance
Ladies and Gents,
I have been trying to source exact performance figures for glider-aerotow.
Are there any exact numbers out there that someone could point me to? Ideally I want to know what the distance from beginning of the takeoff-roll until liftoff of the tug would be, utilising a PA150 tugging your average 2-seater, eg. Duo-Discus or ASK21. About 2000 AMSL, temp about ISA+20, level hard-dirt strip.
Any ideas, anyone?
Many thanks in advance!
Bug
I have been trying to source exact performance figures for glider-aerotow.
Are there any exact numbers out there that someone could point me to? Ideally I want to know what the distance from beginning of the takeoff-roll until liftoff of the tug would be, utilising a PA150 tugging your average 2-seater, eg. Duo-Discus or ASK21. About 2000 AMSL, temp about ISA+20, level hard-dirt strip.
Any ideas, anyone?
Many thanks in advance!
Bug
Bug,
Our club has 2 pawnees and a 150hp super cub. A month ago I was up at the club on my lunch break, and was recruited to do a tow. Seems our publicity director had lined up a ride for a journalist in one of our ASK21's. One pawnee was down for service. The other one had a dead battery, as some idiot (me) had left the master on the night before. So, out came the super cub. Our strip has 1100' of pavement, and another 400' of grass. Field elevation is 1709' ASL. If I remember right the temp was about 80 degrees F and the wind was calm. Both tanks were about 3/4 full. They had staged the ASK21 about 100' from the end, and our ropes are 200', so I had 800' of pavement and 400' of grass. I used most of it. After that 400' of grass the terrain drops off rapidly and suddenly there is about 800' of altitude. Initial 300' or so of the pavement was uphill slightly, then changing to downhill slightly for the rest of the run. That gives about 1200' of ground roll, it could have easily been another 1000' to make 50' above the field elevation.
In my old club we had a Grob103 and a 160 hp super cub. Field elevation of 700msl, length about 2600'. We used to tow the Grob on low DA days, or windy days. Eventually we banned towing the grob with the cub as the margin just wasn't there. At my new club the fact that we tow off the edge of a hill is what makes it safe. The pawnee still tows a lot better though.
We also have a duo discus, I'm not sure if the cub has towed that or not. Problem is they like to tow faster in the duo, but then in the cub you have no climb rate. In an ASK21 you can get away with going a little slower as it is a pretty forgiving ship.
-- IFMU
Our club has 2 pawnees and a 150hp super cub. A month ago I was up at the club on my lunch break, and was recruited to do a tow. Seems our publicity director had lined up a ride for a journalist in one of our ASK21's. One pawnee was down for service. The other one had a dead battery, as some idiot (me) had left the master on the night before. So, out came the super cub. Our strip has 1100' of pavement, and another 400' of grass. Field elevation is 1709' ASL. If I remember right the temp was about 80 degrees F and the wind was calm. Both tanks were about 3/4 full. They had staged the ASK21 about 100' from the end, and our ropes are 200', so I had 800' of pavement and 400' of grass. I used most of it. After that 400' of grass the terrain drops off rapidly and suddenly there is about 800' of altitude. Initial 300' or so of the pavement was uphill slightly, then changing to downhill slightly for the rest of the run. That gives about 1200' of ground roll, it could have easily been another 1000' to make 50' above the field elevation.
In my old club we had a Grob103 and a 160 hp super cub. Field elevation of 700msl, length about 2600'. We used to tow the Grob on low DA days, or windy days. Eventually we banned towing the grob with the cub as the margin just wasn't there. At my new club the fact that we tow off the edge of a hill is what makes it safe. The pawnee still tows a lot better though.
We also have a duo discus, I'm not sure if the cub has towed that or not. Problem is they like to tow faster in the duo, but then in the cub you have no climb rate. In an ASK21 you can get away with going a little slower as it is a pretty forgiving ship.
-- IFMU
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Hi IFMU!
Many thanks for your detailled answer, you've given me plenty to work with!
What you're saying ties in pretty much with numbers I've heard elsewhere, which is good news. Agreed, the 150hp Cub is not the friskiest, but then the 180hp versions are that much more expensive. (In our case we'd have approximately 2400ft to play with, but temperature is a concern)
Thanks again, and fly safe!
All the best
Bug
Many thanks for your detailled answer, you've given me plenty to work with!
What you're saying ties in pretty much with numbers I've heard elsewhere, which is good news. Agreed, the 150hp Cub is not the friskiest, but then the 180hp versions are that much more expensive. (In our case we'd have approximately 2400ft to play with, but temperature is a concern)
Thanks again, and fly safe!
All the best
Bug
Bug,
I have never towed with a 180 cub, but I bet it would rival a pawnee.
-- IFMU
I have never towed with a 180 cub, but I bet it would rival a pawnee.
-- IFMU
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There's so many variables that it simply isn't possible to quantify exact distances. That's why we keep it simple - if you don't think you're going to get safely airborne then don't take the tow. Contributors to take-off performance include:
Altitude/Air density
Air Temperature
Humidity
Runway condition (eg.. grass vs tarmac)
Wind - strength, direction, gusting
Glider performance (+ how dirty the wings are)
Tug performance (+ how dirty it is)
Glider wing loading (carrying water balance, max auw)
Tug weight (+ vs max auw - e.g full vs empty)
Glider & Tug pilot competency
That said, the US Air Force did some detailed research in order to develop a set of operating minima for their operation from high altitude sites.
Altitude/Air density
Air Temperature
Humidity
Runway condition (eg.. grass vs tarmac)
Wind - strength, direction, gusting
Glider performance (+ how dirty the wings are)
Tug performance (+ how dirty it is)
Glider wing loading (carrying water balance, max auw)
Tug weight (+ vs max auw - e.g full vs empty)
Glider & Tug pilot competency
That said, the US Air Force did some detailed research in order to develop a set of operating minima for their operation from high altitude sites.
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gpn01,
...prop typ, mixture-leaning procedure, runway gradient, obstacle considerations, etc. Yes, undoubtably there are many factors to take into consideration. What I am trying to do is to assume certain parameters and then apply them via any kind of researched figures, so as to see what kind of safety-margin would remain. Thanks for the input, safe tugging!
Bug
...prop typ, mixture-leaning procedure, runway gradient, obstacle considerations, etc. Yes, undoubtably there are many factors to take into consideration. What I am trying to do is to assume certain parameters and then apply them via any kind of researched figures, so as to see what kind of safety-margin would remain. Thanks for the input, safe tugging!
Bug
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IFMU
Never had the honour, limited time on the 18-150 only, but somebody I know did banner-towing with the 180hp version and he waxed lyrical about the thing! Do you guys have trouble finding spare bits for the Pawnees, by the way?
Bug
Never had the honour, limited time on the 18-150 only, but somebody I know did banner-towing with the 180hp version and he waxed lyrical about the thing! Do you guys have trouble finding spare bits for the Pawnees, by the way?
Bug
Bug,
In my old club we had a member that used to tow with a 180hp husky, he was mad about the airplane. Since I've moved onto another club, due to moving to another state, my old club has sold their cub and tows with a 180 hp husky. I haven't gotten back that way to fly it.
I don't know of any problem finding parts for the pawnees here in the states. They are trying to get me to be the maintenance coordinator for my club, though I'm not sure I want that job at the moment. Maybe when I retire, a good 20 years from now. But I've also not seen the pawnees in either club to have an appetite for parts. Engines wear out, we just had to replace magnetos in both our pawnees, but otherwise it seems mostly like consumables - brakes, tires, batteries, etc. The pawnee is a real workhorse. Dirt simple airplane.
-- IFMU
In my old club we had a member that used to tow with a 180hp husky, he was mad about the airplane. Since I've moved onto another club, due to moving to another state, my old club has sold their cub and tows with a 180 hp husky. I haven't gotten back that way to fly it.
I don't know of any problem finding parts for the pawnees here in the states. They are trying to get me to be the maintenance coordinator for my club, though I'm not sure I want that job at the moment. Maybe when I retire, a good 20 years from now. But I've also not seen the pawnees in either club to have an appetite for parts. Engines wear out, we just had to replace magnetos in both our pawnees, but otherwise it seems mostly like consumables - brakes, tires, batteries, etc. The pawnee is a real workhorse. Dirt simple airplane.
-- IFMU
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IFMU
Did some quick superficial checking: The Pawnees don't come cheap, certainly not over here in Yoorip. This is where you lads have it good, so much material to choose from, Stateside! (well, moot point for me and my mates anyhow, considering the costs
)
Bug
Did some quick superficial checking: The Pawnees don't come cheap, certainly not over here in Yoorip. This is where you lads have it good, so much material to choose from, Stateside! (well, moot point for me and my mates anyhow, considering the costs
)Bug
The Pawnees are great for towing. The first time I was behind one, it felt like a slingshot. Unless the crosswind is howling, you don't have to worry much about crabbing in air to correct for drift while towplane is still on ground as that's very few seconds.
Even better for clubs is that Pawnees come down like a brick after release without any worry about cracking cylinders
Going back to the original question, the big need is to work out distance to obstacles -- trees, houses, power lines, roads etc. Also need to know if terrain on takeoff path is flat, rising or descending.
IFMU and his buddies have it about as good as it gets as they're on the top of a ridge with an emergency strip 800' or so below [envy]
Even better for clubs is that Pawnees come down like a brick after release without any worry about cracking cylinders
Going back to the original question, the big need is to work out distance to obstacles -- trees, houses, power lines, roads etc. Also need to know if terrain on takeoff path is flat, rising or descending.
IFMU and his buddies have it about as good as it gets as they're on the top of a ridge with an emergency strip 800' or so below [envy]
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Going back to the original question regarding takeoff distances, etc. Here's a link to an interesting article:
http://www.eaa1000.av.org/technicl/takeoff/topaper.htm
For those who like to look at the theoretical minima it makes interesting reading!
http://www.eaa1000.av.org/technicl/takeoff/topaper.htm
For those who like to look at the theoretical minima it makes interesting reading!
Pawnee Pots
RBF,
Can you please expand on "Even better for clubs is that Pawnees come down like a brick after release without any worry about cracking cylinders" ?
This seems to be at odds with recieved wisdom.
Can you please expand on "Even better for clubs is that Pawnees come down like a brick after release without any worry about cracking cylinders" ?
This seems to be at odds with recieved wisdom.
K539, We have a Citabria and 2 Pawnees. The Citabria letdown is the more complicated.
SOSA Towing Procedures (Powerpoint Format)
SOSA Towing Procedures (Powerpoint Format)
Doodlebug,
Here's another data point for you.
180 HP Scout with fixed-pitch seaplane prop.
Grass strip, 3800' elevation, +25C, no wind.
Towing a Blanik near gross weight (1100 lb), I would typically get airborne, using one notch of flap, in about 1200' to 1500'
As RBF says, letdown procedures for Citabrias/Scouts are unusual but not difficult. I don't think there have been any cracked cylinders on the three Scouts I used to fly in Alberta.
I cannot read RBF's file - it won't open on my Mac, but here's the procedure I used (Schedule C):
http://www.soaring.ab.ca/towpilot.pdf
I42
Here's another data point for you.
180 HP Scout with fixed-pitch seaplane prop.
Grass strip, 3800' elevation, +25C, no wind.
Towing a Blanik near gross weight (1100 lb), I would typically get airborne, using one notch of flap, in about 1200' to 1500'
As RBF says, letdown procedures for Citabrias/Scouts are unusual but not difficult. I don't think there have been any cracked cylinders on the three Scouts I used to fly in Alberta.
I cannot read RBF's file - it won't open on my Mac, but here's the procedure I used (Schedule C):
http://www.soaring.ab.ca/towpilot.pdf
I42
Last edited by India Four Two; 22nd Oct 2007 at 17:10.
I42 and others unable to read ppt -- I converted last year's Towing Procedures to PDF with StarOffice and can send to those who PM me.
This year's can't be handled by my version of StarOffice
This year's can't be handled by my version of StarOffice
Interesting to see the difference in club ops. In both clubs I've been in, SOP has been to descend at high rpm and high speed. In the PA25, we run downhill at 120-140 mph ias. I've always heard there are two approaches, either slow (low cooling) and low power (low heating) or fast (high cooling) and high power (low heating). To my knowledge neither of my clubs has had problems with cracking cylinders either. We do the same thing in the super cub but at slower speeds.
We use 1.5 hours of tach time in the pawnee max between refills. If you fill it to the brim 1.5 hours will usually leave about 16 gallons in the tank. Some of our members who thought to use the gauge ended up in that emergency field 800' below.
Interesting to see that cleaning windshields is part of your SOP and spelled out in writing. In my club I swear they schedule me twice a month to tow because I think I'm the only one that actually cleans them!
We do no 1-minute cooldown before shutdown. Our first flight of the day is usually a tow, except for the new folks who might need a time or two around the patch to feel confident. My old club we always took it around the pattern once before we would tow.
One nice thing we have is tow reels. When I pull into the downwind I slow down under 100 and flip on the reel. Usually while on base or on final it is all reeled in. My old club didn't have that. When the reel fails, and we switch to a plain rope, I fly over the threshold of the ridge at no less than 300'. Even though the rope is only 200', I want extra margin in case of inattention or power failure. There is a scenic overlook with swings and people down there. Higher stakes than dragging a rope through the trees.
All the PA25's I've towed with (3 of them) have been 235 hp versions. They all have about a 10 mph IAS error with a glider on tow. You can't tow the glass guys too fast, usually 80-85 ias is good. I tow the Schweizers a lot slower, then we climb better, and they don't like to go too fast.
We burn nothing but autogas, except on the rare x-c retrieve where fuel is needed to get back safely. We have no CHT gauges.
I'm posting all this not to state that this is the way, but thought it might be interesting to compare.
I bet that 260 hp pawnee tows well!
-- IFMU
We use 1.5 hours of tach time in the pawnee max between refills. If you fill it to the brim 1.5 hours will usually leave about 16 gallons in the tank. Some of our members who thought to use the gauge ended up in that emergency field 800' below.
Interesting to see that cleaning windshields is part of your SOP and spelled out in writing. In my club I swear they schedule me twice a month to tow because I think I'm the only one that actually cleans them!
We do no 1-minute cooldown before shutdown. Our first flight of the day is usually a tow, except for the new folks who might need a time or two around the patch to feel confident. My old club we always took it around the pattern once before we would tow.
One nice thing we have is tow reels. When I pull into the downwind I slow down under 100 and flip on the reel. Usually while on base or on final it is all reeled in. My old club didn't have that. When the reel fails, and we switch to a plain rope, I fly over the threshold of the ridge at no less than 300'. Even though the rope is only 200', I want extra margin in case of inattention or power failure. There is a scenic overlook with swings and people down there. Higher stakes than dragging a rope through the trees.
All the PA25's I've towed with (3 of them) have been 235 hp versions. They all have about a 10 mph IAS error with a glider on tow. You can't tow the glass guys too fast, usually 80-85 ias is good. I tow the Schweizers a lot slower, then we climb better, and they don't like to go too fast.
We burn nothing but autogas, except on the rare x-c retrieve where fuel is needed to get back safely. We have no CHT gauges.
I'm posting all this not to state that this is the way, but thought it might be interesting to compare.
I bet that 260 hp pawnee tows well!
-- IFMU
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Hi
I've PDF'd the SOSA PPT file for those who can't open it.
SOSA Towing Procedures (PDF Format)
Steve
I've PDF'd the SOSA PPT file for those who can't open it.
SOSA Towing Procedures (PDF Format)
Steve
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Hi India Four Two,
Sorry, was out committing aviation.
Thanks for the input! Still a relatively short distance I see, in spite of the airfield elevation, runway-surface and weights (or masses, as the latest texts will have it
) which is encouraging.
Best regards,
Bug
Sorry, was out committing aviation.
Thanks for the input! Still a relatively short distance I see, in spite of the airfield elevation, runway-surface and weights (or masses, as the latest texts will have it
) which is encouraging.Best regards,
Bug
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Bug,
Sounds as if you are new to tugging - about to start?
Best advice is to talk carefully to those who have done it already, and are still in one piece, at the A/F proposed. And get checked out because it ain't like normal flying, at all.
The other advice I can offer is that if you get into tugging gliders you will get lots of 'unusual' experiences which require quick thinking and good airmanship. Constant lookout is vital as launching amongst a glider-infested environment can be challenging (modern gliders are very white).
If you get to the stage of being asked to go and aerotow retrieve a glider from a field landing ('aux vaches' as the French say, very aptly ), be very careful about the required distances for a successful retrieve. To illustrate, many moons ago (in the 70s), I landed my glider in a field during a competition. Very experienced tug pilot duly arrived in a Super Cub to tow me out. He insisted I push the glider (a 19m span Kestrel 19) to the edge of the field with the rudder almost in the hedge. We then paced the field and he did the calculations, and eyeballed the terrain, slope etc etc.
A volunteer wing man from the farm saw us off. We trundled down the slope but were not airborne by the time the ground started a gentle rise. A few seconds later, through the long nosed canopy I had this vision of the tug heading for the trees on the upwind (what wind?) end of the (what had seemed on walking it) very large field. All I remember was seeing the tug's flaps go more positive, the elevator go near vertical, following which he just got airborne and I followed suit with a bit more flap to leave terra firma. We cleared the trees by about a nat's whisker.
As we then slid gently over the trees of this mini forest my left leg was shaking on the rudder. The tuggie dropped me some 8 miles from the base airfield and I proceeded to complete a gentle glide home, thinking 'that was b***dy close'. On arrival at said base I went to the bar where the tuggie (a mature man with 000's of hours) had two glasses of whiskey, one in each hand. On the bar was a clean pair of underpants which he was about to change into. But he gave them to me instead.
'Nuff said.
Sounds as if you are new to tugging - about to start?
Best advice is to talk carefully to those who have done it already, and are still in one piece, at the A/F proposed. And get checked out because it ain't like normal flying, at all.
The other advice I can offer is that if you get into tugging gliders you will get lots of 'unusual' experiences which require quick thinking and good airmanship. Constant lookout is vital as launching amongst a glider-infested environment can be challenging (modern gliders are very white).
If you get to the stage of being asked to go and aerotow retrieve a glider from a field landing ('aux vaches' as the French say, very aptly ), be very careful about the required distances for a successful retrieve. To illustrate, many moons ago (in the 70s), I landed my glider in a field during a competition. Very experienced tug pilot duly arrived in a Super Cub to tow me out. He insisted I push the glider (a 19m span Kestrel 19) to the edge of the field with the rudder almost in the hedge. We then paced the field and he did the calculations, and eyeballed the terrain, slope etc etc.
A volunteer wing man from the farm saw us off. We trundled down the slope but were not airborne by the time the ground started a gentle rise. A few seconds later, through the long nosed canopy I had this vision of the tug heading for the trees on the upwind (what wind?) end of the (what had seemed on walking it) very large field. All I remember was seeing the tug's flaps go more positive, the elevator go near vertical, following which he just got airborne and I followed suit with a bit more flap to leave terra firma. We cleared the trees by about a nat's whisker.
As we then slid gently over the trees of this mini forest my left leg was shaking on the rudder. The tuggie dropped me some 8 miles from the base airfield and I proceeded to complete a gentle glide home, thinking 'that was b***dy close'. On arrival at said base I went to the bar where the tuggie (a mature man with 000's of hours) had two glasses of whiskey, one in each hand. On the bar was a clean pair of underpants which he was about to change into. But he gave them to me instead.
'Nuff said.