Reversible Propeller

[PPI Brian]

Hi Everyone,
I guess its about time to officially let the cat out of the bag regarding our next STC project since we will hopefully be having it at Oshkosh next week. We are still early in the paperwork process, but we have finally gotten our prototype Cub to function correctly with a new constant speed/reversible MT-Propeller. We are planning on using the same basic blades as we are currently using in our existing STC, and having it available for the O-320, or O-360 powered Super Cubs. Although it is quite effective in reducing landing distance on wheels, my main objective was to try to help the float and ski guys out a little. The propeller functions by moving a guarded toggle switch which commands the hydraulic governor to twist the blades through neutral into a fixed reverse pitch. You then control the amount of reverse by powering up the engine with the throttle. It also has a start lock feature which allows you to start the engine in neutral pitch, so it doesn't want to begin moving while on floats or ski's. As with any modification, I know its not for everyone, but I think it might come in handy for many applications. Please let me know your comments or concerns, as I still have time to address any new issues. Thanks for the input, and I hope to see you at Oshkosh!

Brian Sutton
Professional Pilots Inc.
12304 West 165th Ave.
Lowell, IN 46356
219-696-8726

 

[sj]

MEOW! Brian congrats on the progress! This is a very exciting modifcation for operations on floats (and maybe skis too?). I will be interested to hear how the activation works, how much power you can generate in reverse, and how it will help my short field landings... 8)

sj

 

[StewartB]

I have zero interest in beta on a Cub anyway, but after the crash of a Murphy Moose last year on final approach to Merrill that was reportedly caused by an uncommanded beta thrust event with an electric reversing MT prop, less than zero.

SB

 

[PPI Brian]

Steve,
We are still working on discovering the limitation of how much reverse thrust can be used, but I am pretty sure it will be higher than what you would probably want unless you are trying to take off backwards. The big advantage I have found on wheels is that it is nearly impossible to put it up on its nose with aggressive braking when the propeller is pushing you back on your tail. This is a significant advantage when loaded toward the forward end of your CG. I haven't been brave enough yet to get too crazy with it, but I'll let you know...

Stewart,
This is not an electrical MT-propeller, in fact, I have the only one of this kind in the world right now, but I would be interested in finding out the actual details of the accident. I'm not sure how you could get this one to go into reverse in flight since it has a mechanical centrifugal lock that prevents it from initial activation above about 1300 RPM in addition to the airspeed switch which works through your pitot static system. Please let me know if you have the actual details of the failure analysis. Thanks.

Brian

 

[StewartB]

Brian,

I'll be happy to connect you with some guys that know the details. I'll make a phone call and PM you.

Stewart

 

[SuperCub MD]

Glad the cat is finally out of the bag. I cannot wait to play with one of these....It may just redefine what a Super Cub can do on a short field.

 

[CRANMAN]

Too bad those of us with a solid crank can't take advantage of this. On floats I would gladly give up the weight penalty to have Beta.
Jon

 

[don d]

I suppost the reversable prop is for short landings. What good is it to land in a place you can't take-off from????? With my stock plane, above 6000 ft., I can land shorter than I can take-off from.

 

[aztecf]

How about us PA-12 guys?

Jeff

 

[Bill Rusk]

Sounds great. Landing short is always good. In an emergency I would rather take the wings off and trailer it out rather than RIP the wings off. Short just gives more options, not that you will use those options but nice to have. Congratulations.

Bill

 

[zane]

I suppost the reversable prop is for short landings. What good is it to land in a place you can't take-off from????? With my stock plane, above 6000 ft., I can land shorter than I can take-off from.

Skis or floats = no brakes.

 

[jgerard]

I have experienced a Pilatus Porter that was suffering from prop control issues related to the rigging and worn out prop control cable causing unpredictable lag time and response to the power lever. The lack of immediate and linear response to the power lever (as it normally would be) made using the beta range and reverse thrust to help control and adjust for a steep STOL decent, approach, and landing almost deadly. The aircraft would go from a stabilized condition to rapid accell or decell with just the slightest touch of the power lever and the lag between moving the power lever and the engine/prop responding was not predictable or consistent at all. Now when we got a few new parts installed and re-rigged the whole mess it was back to normal. Nice and smooth as butter. On a piston engine to make the prop work like it does on a turbine would require some fancy linkages. On a turbine when you go into the beta range the engine is at a low power setting and as you pull over and past the gate and into the reverse pitch area the farther back you pull the power lever the engine starts to make more power (increase in propeller RPM and fuel flow) and more rev-pitch. Fuel flow(power), and prop pitch are controlled by one lever on a turbine and operating in and out of beta is like a teeter-totter balancing act. Sea-Bee's had a reverse pitch capability and could back up. I don't know if it was ever able to be used while in flight though like a turbine set up is. On a piston engine with separate prop and throttle controls I am going to guess that the rev. pitch option is not available or recommended for use in flight since it would require 3 hands to properly operate the control stick, prop control (in and out of beta) and throttle. If this new MT system uses a toggle switch to set blade angle into a fixed Neg pitch I guess its so that after you make an normal landing you can hit the switch and then apply power to increase the rev-thrust. I think its a darn cool idea and hope that with the increase in the use of FADEC the possibility of a turbine style of beta and rev thrust control of the piston engine/prop combo will happen soon. Now you need 2 push button switches on the throttle knob. 1 for flap dump and a 2nd one for rev-thrust. Sounds like this new system won't let you select rev-pitch in flight which should prevent an untrained person from accidentally "goosing it" in rev-pitch instead of fwd-pitch when they are 50' over the nasty obstacles at the approach end of a short strip sending them right through the top of the pucker factor scale! Any way-good luck with the paperwork and see ya at OSH.

Jason
N3673T
N43643

 

[ground loop]

I can see a bigger advantage on skiis than on floats. On ice, stopping can be an issue. I can take off much, much shorter (on ice) than I can land on skiis. That is rarely the case on floats.
I was hoping that buying wheel skiis and using wheels and brakes would solve this problem.
On floats, reverse taxiing might be fun and helpful at times.
It seems, if this is a new thing, it is going to make the Husky the indisputable King on floats. It's major weakness has been landing it short, with ease, on floats. It scares me too think where an mvivion type float pilot would be able to get in and out of w/ a 200 hp Husky w/ a reversible prop on floats.

 

[cubflier]

I have no experience with reversible props but I'm having difficulty seeing any advantage to a cub on wheels. I lift the tail up sometimes to protect it from rough terrain/flying debris or provide me with visibility. It's nice to have the option of forward thrust to blow the tail down and would hate to be stuck in reverse pitch in this type of situation.

Also in the world of how much stuff can you do at time of landing, I usually don't bother dumping flaps on landing because the distraction provides no benefit in a shorter landing unless there is significant wind involved. Can you reverse the pitch instantaneously on landing? Seems like a lot of fast hand movements on landing.

Final issue would be the tendency to blow a nice pile of gravel through the prop.

I see the potential for backing up in a float plane and arresting a long skate across the ice on skis but this seems to be the practical limits of a reversible prop in a cub.

It's still an interesting mod and will certainly appeal to some.

Jerry

 

[StewartB]

If you used beta thrust on a Cub on slick ice....how hard would it be to keep it going straight and not swap ends? Hard, I'd guess. It will be interesting.

I'd also wondered about actuating beta to land short. What's your average short landing duration in time? Will you have enough time to actuate beta effectively?

How do turbine powered taildraggers use beta?

Stewart

 

[moneyburner]

I'd also wondered about actuating beta to land short. What's your average short landing duration in time? Will you have enough time to actuate beta effectively?

How do turbine powered taildraggers use beta?

Stewart

I'm going to guess that loosing the propwash on the tail surfaces at low speeds while in the air would be something to avoid. I've heard that the Pilatus guys would point it at the ground and go into beta while chasing skydivers, but that is entirely different. Think about being dirty, slow, nose in the air, and then have dead air on the tail all of the sudden.

You first!



I know that isn't what you're talking about, but wouldn't that suck? Reminds me of that video of the C-130 with the JATO bottles pointed forward that went off before they got on the ground - ouch!

 

[T.J.]

delete

 

[StewartB]

On Saturday I watched a Caravan land at Palmer. The pilot quickly used beta after touchdown. The nosegear squatted noticably. I wondered what would happen in a taildragger at that moment. In all the years I've watched tubine Otters, Beavers, and Porters at Hood, I can't recall any of them using beta thrust. That doesn't mean they don't. The question was genuine. How do turbine taildraggers use beta?

Stewart

 

[moneyburner]

On Saturday I watched a Caravan land at Palmer. The pilot quickly used beta after touchdown. The nosegear squatted noticably. I wondered what would happen in a taildragger at that moment. In all the years I've watched tubine Otters, Beavers, and Porters at Hood, I can't recall any of them using beta thrust. That doesn't mean they don't. The question was genuine. How do turbine taildraggers use beta?

Stewart

I remember reading something about Porters in Ernie's Alaska AV Memories, but don't know how to find it. I guess some of the guys he worked with were pretty good at using the tools at hand.
Speaking from a position of gross ignorance, it would seem that the Caravan's nosegear squatted because he was on the brakes - the prop shoving air forward wouldn't logically do that -at least it seems that way to me. I would think that directional control might be a problem if you were counting on the rudder.

I'm eager to hear what really happens - so now, I'll shut up and listen.

 

[StewartB]

I'd think deceleration would result in weight transfer regardless of the means of braking. We're talking about a lever and a fulcrum. The center of mass is ahead of the mains on a nosedragger. I may be wrong.

On the other hand, if the point of that decelerating force is at the extreme front of the moving body, there's more weight behind that point, and more leverage. The center of mass is behind the mains on a taildragger. Thus the earlier comment about slick ice and beta thrust. Who knows, I may be right.

Stewart

 

[Randyk]

I fly turbine Otters on wheelskis. Beta is good. Especially when stopping on downslope glaciers.... The POH says to have the tailwheel firmly planted on the ground first. That is also good.

I have heard that a bit of beta on short final will help if you're hot or high - but that procedure is discouraged in the POH....

 

[StewartB]

Randy,

Do you use beta when you return to Talkeetna? Even I can figure out why I don't see it on the gravel at Hood.

What's the anticipated consequence of using beta with the tail up?

Stewart

 

[moneyburner]

Okay, I'll shut up after this:

http://www.supercub.org/phpBB2/viewtopic.php?t=4936&highlight=pc6++porter

 

[Gordon Misch]

Stewart, if the line of thrust (imagine a line through the length of the crankshaft and extending aft through the airframe for a good approximation) from the prop is below the center of mass of the aircraft, the nose will pitch down with reverse thrust and up with forward thrust.

If the line of thrust is above the center of mass the reactions will be the opposite.

The pitch tendency from thrust would be in addition to any pitch tendency from braking with the wheels, so the net result would be the sum of the two influences.

 

[StewartB]

Gordon,

I appreciate the response. I remember talking to a Lake Buccaneer pilot that said the hardest thing to get used to was the nose down tendency when he added power, and the nose up when he reduced power, so I understand your concept.

I'm still curious about tail draggers using beta on a slick surface, and using beta in conjuction with brakes on a hard surface. I can't think of any beta-equipped airplanes that have tails as light as a Cub, or tails as eager to come over the top. Beta will be interesting, all right.

Stewart

 

[Randyk]

I use beta a lot. Not a lot of beta, but often. Even at LHD - but on gravel, I am careful, especially in crosswinds. You can pick up rocks if you come on with too much beta. The Otter prop is about 5' off the ground but it's as easy to nick it as a cub.

As for beta on the ground with the tail up, there is no air over the tail, so no directional control - not fun. You need the tail down to keep it straight....keep it straight...keep it straight...

I don't operate on bare ice much, and usually have the skis up if I do - there is a bit of braking and directional control available, but if the ice is wet, hold on to yer hat.....

We have electrically operated tailwheels, so we need to be slow to have effective tailwheel steering.

Anyway, I like beta, and it's very effective even in TW A/C. I am anxiously awaiting for those guys to get the turbine cub figured out.

RK

 

[StewartB]

Randy,

Thanks for elaborating.

Stewart

 

[mvivion]

Interesting discussion. I could see, as Randy points out, that reverse thrust on really slick ice could get pretty sporty.

I made the mistake of landing an amphib Beaver on a frozen lake surface once in Kodiak that was slick as deer guts on a doorknob. Good solid ice, previously drilled and measured by the guy to be picked up, but absolutely smooth, and temps right around freezing, so slick.

Landed gear down on tires. No particular sweat. Big lake. Parked and loaded.

Now time to go. Through no particular intelligent design on my part, just being some afraid of thin ice near the shore, I'd parked well out on the lake.

As I came up with power, the airplane went left. Not enough rudder to counteract, and brakes were useless for steering. Nosewheels, of course, don't steer.

Eventually, I just brought the power up to takeoff, the airplane did a couple gradually widening circles, and before the participants got dizzy, we got going fast enough to give the rudder some authority, and off we went.

I think on really slick stuff, yarding one into reverse could do some pretty interesting things. Maybe fun. Maybe not.

Floats offer a lot of benefits for reverse, or actually really only beta. Get in reverse, you can drive the heels under, steering is totally non existent to really unpredictable, but beta is VERY good on floats.

My question to you serious short field wheel guys is this:

In a Cub going in really short on wheels, is there really even TIME to cycle a prop from forward pitch to reverse, or even beta, during the average landing roll of a well flown Cub???? Seems to me a good driver would have it down and stopped before the blades even cycled, IF applied once on the ground. Or very nearly so. I guess part of the answer to that depends on how fast that prop cycles.

Maybe that last 50 feet might be shaved off, though.

Interesting concept.

MTV

 

[180Marty]

Turbine Air Tractor guys are always using reverse around here and I haven't seen a problem yet. A few years ago I helped the Covington mechanic replace a power section after the guy hit an electric wire with the prop which required mandatory replacement. When back together pilot backs out from between hangars and goes out to runway for takeoff I thought----- when going pretty fast on comes reverse for a stop. Anyway, I remember thinking that guy drives like he's mad with the machine.
Marty

 

[SuperCub MD]

The turbine DC3's come over to practice on the grass quite often. They always go to Beta with the tail still up, this pushes the tail down, which is counteracted by braking. Of cource they have differntial power to assist brakes for directional control which a Cub wouldn't have. They can stop those 3's in a very short distance doing this. You would have to keep a Cub straight with brakes alone, but you would be able to brake so hard the whole thing would probably be stopped before it ever had time to ground loop. True, the big advantage here is going to be floats and skis, but the limits of what it could do on wheels would be very interesting to explore. TJ's squat switch idea is very interesting.....