Goodday Mates,
Further to my restoration of my PA 18/95 C90 1000 Lb I wish to improve my skills for safe short take off andd landing. No flaps.
IAS at stall with engine idle, sea level 27 deg C, 1/2 fuel (2 tanks) and 2 pers is just below 50 mph, say 45.
Any suggestion or recommendation.
Thanks for your contributions.
Ciao, Gian
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Try several reduced power longer ground run takeoffs with the tail on the ground. If the airspeed pitot isn't bent and is as Piper intended with no tubing leaks, observe the AS when the plane lifts off. Duplicate that plus some reserve airspeed on future full power takeoffs and reduced power landings. It's as good as airspeed indication can be as an aid which isn't much.
Gary
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Take off tail low and accelerate in ground effect to 65-70mph which is Vy. Am not sure Vx in the flapless 90HP SC (55mph) gives any better gradient.
On landing it is all about using side slip, accurate speed in the side slip (50 mph IAS) and practising spot landings - many spot landings.
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add vortex generators for more stable slow flight.
I think by definition Vx gives a better gradient than Vy. It is about 50% better in my Stroker J-3. Lifting off above liftoff speed may be good for jets, but it doesn't help with Cubs.
Yes, I have heard about "zoom climbs" - but mathematically they don't work, because drag goes up as the square of airspeed.
Your stall speed is slower with power on. This will usually have the tailwheel a foot below the mains, and poor vis. The trick is to use the slip to help vis on approach, once into the flare wings level and release a bit of back pressure just before you think you will land. This should prevent a tail first landing ,takes practice to get it right. Tail high braking will give you good vis and traction, lift/hold the tail with the brakes.
DENNY
The physics are relatively straightforward - at gross does the power available curve give that much excess power over the power required curve at Vx in the 90HP SC.
The power required curve rises sharply on the back side of the drag curve, while conversely drops fast as you move to Vy.
Introduction to Flight can supply the calculus of the drag curve between Vx and Vy.
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Instead of spending money on gadgets - learn how to fly the plane. Minimum of 15 takeoffs and landings per week for a couple of months.Originally Posted by giangab
The above is great advice. Learn to fly the airplane and look outside.
In my opinion, right on; especially in a Cub-type plane. Flying by "The numbers" is easy to quickly sense and adjust from the view out the window. Not like a heavy, slippery airplane in that regard.
Last edited by Gordon Misch; 09-06-2019 at 12:44 AM.
Gordon
N4328M KTDO
Thanks for the time being. Flying, Training and experience are no sobstitutes. Good advice and tricks will surely help, as a good instructor.
My grass field is some 440 m long, well mainrained. Zero obstacles at 270 and trees and levve plus a wide river bed at 90. Some 50 ft say at 200 m. I will train on a 800 m grass field. So far I manage my field, but I need want to improve for safety and performance. Thanks again.
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Thanks L18C-95
so far I have much improvved my Cub flying.
mastering shortlandings is teasonably improoving, but short takoff with a reasonable climb 200-300 fpm) is still
an issue.
you sayd : Take off tail low and accelerate in ground effect to 65-70mph which is Vy. Am not sure Vx in the flapless 90HP SC (55mph) gives any better gradient.
my problem is, even trying your suggestion in TO, to
achieve 60-65 mph in ground effect (both alone or full
weight). I hardly get 55 mph.
my prop is a an alu macauley 72” dia end 48” pitch ( in etween standard 50” and short 46” pitch).
I will check the ASI calibration. I have a two tube combined pitot and static under the left wing as for 150 hp supercubs. I understand that calibration could be achieved by placing a small collar in front or back of the four static 1 mm holes: is there any advice on this regard?
mastering shortlandings is teasonably improoving, but short takoff with a reasonable climb 200-300 fpm) is still
an issue.
thanks to all of you for any imput.
blue skies with a 19/95
gian
Gian,
For better T/O performance, folks have know for years. Seaplane type props make a huge difference in all Cubs, but especially in lower powered ones. If you had a C-150 Seaplane prop
75/38 you could nearly half your T/O distance , to truely get the 95hp your engine can create you will need to see much bigger numbers static than you can get with your prop. My PA11/90 came with same prop you have 48 pitch. It was pretty lame at best......... I came up with a 38" prop and it then got off nearly as good, as the 160hp 18 I have now. The ROC was nearly double as well.
In today's world of composites the new Sensenich 76" G/A prop is the best choice you can make
For any 90/100 Cub. Legality is another subject all together.......... Best left up to the owners.
And as Denny told you in an early posting. Learning the art of the sideslip is THE secret in Cubs without flaps. Done correctly you will be able to land as short as the flaped cubs that out weigh you by 150/200 lbs.
Good luck and practice that sideslip till your not kicking it out until your in ground effect.
You have a wonderful Cub, it just has the wrong prop on it!
Cheers
E
Last edited by TurboBeaver; 07-24-2021 at 11:09 AM.
Something to check, most early PA-18s didn’t have a static system. The ASI, ALT, and VSI if installed were just vented behind the panel. As such, these instruments won’t provide a very accurate indication, and will change with the window or door open, air vent open, or heat on. Verify if you have a static system or not. If you don’t have a static system, forget about looking at the airspeed indicator, the greatest errors will be at low speed. Fly the airplane based on outside references, power settings, and feel. Remember - Power+Pitch=Performance.
Even with a static system, in a slip, the ASI will be inaccurate, so again fly by feel and visual cues on the outside.
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This is one of the most enjoyable things that I have learned in my relatively short time flying. Dropping out of the sky to flare and gently nail a precise point. Forgive my stupid question, I was 10 when you joined this forum, but...
Please correct me if I am wrong. My J-3 (sometimes S) has wheels and floats. Power is an A-65-8 spinning a 74 inch diameter 40 inch pitch prop. A-691 limits my choices to 74 max 72 min inches in diameter. I'm extrapolating from the graph on page 3 of my A-50, 65, 75, 80 operations manual. (I can't seem to find one for that Cont. A-56.) Lower pitch (climb) props spin faster at given load than standard props that spin faster than cruise props that produce fuel economy by reducing load and simultaneously burn.
(My mechanic says that nowadays, unless you have an untouched original one, the A-50, 65, 75, 80 are the same engine because the improved parts that allowed for higher sustained speeds replaced the original parts in production over a half a century ago. The engines just have different carb setups and stops due to different RPM limits. Looking at fuel consumption as an indicator of load it appears that as the top end speed increased with each succeeding model the propeller diameter was decreased reducing tip speed and load on the engine.)
Since "other" seaplane props seem to be larger in diameter than landplane props is this just a place where a good climb prop is the best a J-3 can do, or is there more to it. (Well, of course there is more to it.)
(I'm not planning on adding electrics, changing the prop, or "upgrading" the engine, I just like knowing why everything works the way it obviously does.)
I have a two tube combined pitot and static under the left wing as for 150 hp supercubs. I understand that calibration could be achieved by placing a small collar in front or back of the four static 1 mm holes: is there any advice on this regard?
A-50 is different from A-65 and A-75. Not sure off the top of my head, but there are differences. The A-65 can be converted to an A-75, and rumor has it that many later A-65s had all the A-75 parts when they left the factory. The A-80 is an oddball engine that you don’t want to use any parts from. There is a reason the TC states engines built after a certain date can’t be installed in certified aircraft.
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No need to use a collar, just learn the indications for your airplane. Recognize the there may be significant errors in your system, just learn what they are, and fly by pitch more than by airspeed.
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If you listen the cub will tell you if your too fast or too slow. The door is a good stall warning. If it’s floating you need to be paying attention
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What DGA and Tom said. Throw the airspeed indicator out. No need for it. Fly it by feel. If it’s an honest cub it will tell you when it’s uncomfortable. Pull off the bandaid and make yourself fly without it
Ideally you could throw the airspeed indicator out and do it by feel but for me, I like to have at least a rough reference as far as airspeed to what I'm feeling in the plane.
For takeoff I've tried a bunch of things but for my flapless J3 the best technique is to blow the tail up and accelerate down the runway tail high then aggressively rotate just short of hitting the tailwheel on the ground. This will "pop" the plane off and get you into ground effect then accelerate to 55 and start climbing. Takeoff is in 150-200 feet.
Go do a bunch of stalls. Figure out exactly where your plane stalls. Try and go just 5mph above that number through short final and into your landing flare. A lot of people don't know how to slow a plane down but it can be done safely as long as you know the stall speed, respect it, and don't do any crazy maneuvers when super slow. The forward slip is your friend when landing short with no flaps. High approach, don't drag it in, moderate to full slip then bring the slip out right before you begin flaring. You can modulate a slip to adjust approach angle and use pitch to maintain approach speed. Never push the nose over if you're high or you'll gain speed and blow your landing.
My approach speed is 45 with the plane going through 40 on short final to flare. Takeoff speed is 40 but could probably be lower. Your PA-18-95 should have similar numbers unless the rigging is just very poorly done. If you're stalling at 45 then something is very wrong. I would start with working on stalls and get that airspeed number nailed down.
Comparing your indicated airspeed numbers to most any other plane is not that helpful. Some are dead on and others are off by quite a bit. Use a GPS on a calm day and fly in several directions at several airspeeds, note airspeed and GPS speed, do some math. This will give you a better ideal of the speeds you are dealing with. If someone bumped your pitot tube it is very easy for it to be off by 5-10 mph. Adjust pitot tube so it is most correct at slow speeds. If it is off from the GPS speed that is fine, all you care about is when flying is an indicator of when the plane will stall. Getting advice on technique /equipment requires more accurate information and hence the use of GPS speeds (no wind or corrected for wind). Now as the others have it is better to learn to fly by feel, but until you have that skill fully developed a reference point on the airspeed is very helpful. From the numbers you have posted I suspect your ASI is off by quite a bit, hence any advice given is based on bad information and may or may not be helpful.
DENNY
Single ignition: "No aircraft of these models shall be eligible for original certification with single ignition engines after August 1, 1941. In addition, no aircraft of these models shall be eligible for recertification with single ignition engines unless such aircraft were either previously certificated with single ignition engines or were originally certificated prior to August 1, 1941." (A-696)
I have a Continental manual from 1948 that (on page 4) states "NOTE: Models A75 and A80 are no longer in production." They had moved on to the C85.
My A&P, a very experienced guy, is pretty unimpressed at the stated horsepower increases (for instance the lines on performance charts for the A75 and A80 lay right on top each other in the manual). A50, A65, and A75s engines consume the same fuel at the same horsepower. The latter two just have higher top ends.
The cases, -1, -8, -9 for instance, apparently have lots of differences. As time went by the case was modified so more items initially integral to the case became separate bolt on parts. (IE an -1 cases, for example, had only a single magneto mount. -8 has no provision for a starter. -9 cases do. But because of the mounting pad, the magneto mounts were separate parts and required gaskets and plugs and the change limited the type of mag that could be used.)
"(1.) General Description (a) All the engine models are identical in general construction with the differences in the power rating of the engine, maximum R.P.M., compression ratio, number of piston rings..." (page 4)
It goes through details of the improvements. It also says that where improvements were made the previous parts are now obsolete, no longer being produced, and details how the improved parts can be substituted. (IE: the older pistons had four rings, newer ones three. You can replace a set of flat pistons with the improved domed ones, etc.)
A65 to A75: Replacing the carburetor venturi and jets allows the engine to ingest more air and spin faster, that and putting a slightly smaller lighter propeller creates a practical A75, even if legally its still an A65.
Last edited by Ubiquitous; 07-24-2021 at 03:02 PM.
Some of the 65 to 75 upgrades were done by drilling the connecting rods for better oil distribution. This allowed higher rpm's for a longer period during takeoff and climbout with starving the engine for oil.
A65-a75 also changed pistons.
I think all engines prior to -8 (-1,-3, -5)are up exhaust engines- the exhaust port is on the top of the cylinder rather than below. -9 engines had provisions for a starter, Bendix E-160 as I recall, very heavy and hard to find.
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According to my manual most A65s and all A75s had the same pistons with three rings. The very earliest A65s had four rings (having two oil rings like the A50). The A50's piston had a flat head profile while the A65 and A75 shared the same shaped head (which also very slightly increased the compression ratio. The manual also says that all are interchangable as a set.
Looking at the manual I think they had to change the exhaust because Continental put the second spark plug up there. The -1, -3, -5 cases were different because they only had to accommodate a single magneto. The exhaust port is in the head, not the case.
In the O-145-B2 and B3, Lycoming just put the two spark plugs right next to one another. I guess that works for redundancy, the legal requirement. But I have to think the Continental layout produces a more complete burn. But maybe with such small cylinder displacement it didn't matter much.
I have zero interest in electrics. Hand propping is pretty easy once you get the hang of it. In my book, lighter is better, and simpler is better. No radios means fewer things to worry about. Fly by day, camp out by night: "Life is Good."
Last edited by Ubiquitous; 07-24-2021 at 07:13 PM.
The manual says both the con-rods and push rods had larger diameter oil passageways and that the improved con-rods had thicker bearings with the same original diameter at the crankshaft.
Reading between the lines, Piper recognized a limitation, designed an upgrade to improve the product, discontinued the production of the original in favor of the upgrade, but continued to sell the originals until their inventory ran out.
I guess that an across the board increase was not feasible because Piper had no way of knowing which engines received the upgraded parts. My A&P believes that 80 years later there are few original parts still in service.
Last edited by Ubiquitous; 07-24-2021 at 07:22 PM.
Re differences & similarities between the small continentals, this is a good resource:
www.bowersflybaby.com/tech/fenton.html
Cessna Skywagon-- accept no substitute!
Me personaly, when i take off i get the tail up as quick as i can then maintain a slightly tail low attitude, enough so your not plowing the wings through the air, not so tail high your driving all the weight down on the mains, and not so low its doing big hops tring to fly over every bump or mound.
Same here, start climbing at 45mph and work up to 60mph in about 20 seconds.
Glenn
"Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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