Official Skynetic Bison XT STOL Discussion Thread

[Warlox]

Today I flew at my local club. First with the slats still on then went home, removed them and headed back. I liked the slats to a point but slow flight felt unstable. Constantly tip stalling side to side. After I removed the slats the bison felt awesome. Shortly after that I crashed hard haha. Stalled into a full spin on the crosswind departure. Completely pilot error. I was able to glue everything back together in about an hour. I’m hoping my bison still flys alright after the repairs. It really felt great after removing the slats. More familiar and did everything I wanted it to do.

[SanExup]

I appreciate the discussion as well, thanks Starck Mad and Gilatrout

[ridgerunner]

... I truly hope this helps for some...

You helped me.
I don't own a Skynetics Bison XT, but as a life long pilot and engineer interested in all things fluid mechanics/aerodynamics, I am curious about this whole STOL tech thing - which is new to me. I've been following this thread for a while.

Thank you for your insights!

[Starck Mad]

I understand your sentiment. Motion RC is one of the very best in the business...I hold them in very high regard as I do other top companies I have made many purchases from. Horizon and Extreme Flight come to mind as well. While they are all so dang good at what they do, they are human and I've seen a miss or two from them all, but that is the exception not the rule thank goodness.

In the case of the Bison I think many make it sound worse than it is. Just my opinion. Yes, there have been some miss packed parts, and the slats/flap feature is a moving part feature that is unfortunately not correct. That said the miss packed parts is a China issue...they are a crap show right now, and MRC can't necessarily help that.

Other than that we have the light controller...I dunno...some get hot...some don't...mine is fine. The tires work fantastically, they are just simply a different kind of assembly RC pilots are not used to, again...mine are fine once I figured it out. And finally we have the flight performance. Mine flies great...does just what I want it to. For so many the issue is not that the plane flies bad...if it did I couldn't do it...it is that they don't know how to set it up correctly...nor do they know how to fly it correctly...yet the conclusion is it doesn't fly well. I'm not sure thats fair really.

MRC did what they do...they swing for the fences and go big, but I remind my self this is their first swing at a STOL plane...the very first. We get spoiled by EDF's and Warbirds that are divine...they've been doing that a while. Maybe they should have swung for a solid grounder for their first STOL plane, but if they did that they wouldn't be the awesome company they are. Usually...they hit everything out of the park...I wouldn't have them swing any other way...just my opinion.

[Gilatrout]

Thank you,. What you wrote is very important and many modelers would not know that.

I also understood that the design of the flaps was flawed for all the reasons you mention. This is why I spent hours with the linkages so that at full flaps the slats open as little as mechanically possible and still be connected to the flap mechanism as designed.

The P factor advice is also well received. I always fly with rudder and even so I forgot this important fact. I blame spending the last few years mostly flying jets and getting out of practice using the rudder to control roll at slow speeds.

I still cannot recommend the Bison. For the money, there are so many superior alternatives.

I probably end up fixing the slats like you did and getting the float kit at some point and keep it that way

Honestly, 90% of my disappointment is that I have never been disappointed or frustrated with a plane Motion made until now. Except for the Bison, almost every other plane is superior by far than others at similar price points. I expected better.

[Starck Mad]

Also...heck...may as well shed some light on everything right? The left wing dropping in slow flight. What causes this is P factor (torque). When at speed, flaps up...the plane is trimmed and going fast enough to make P factor a non issue. When you slow it down...assuming you have full flaps, slats in slat position...power is required to hold the plane in slow flight with the higher angle of attack caused by the slats, but now the forward speed has greatly decreased, but a decent amount of power is still prevalent, so P factor has much more affect (just like it does at the slower speed of take off). Some right rudder will be required to counter the effect of P factor in this position and keep the wings level...not as much as on take off because the power isn't that high, but it is there enough to require some right rudder. Aileron corrections...especially big corrections are not advised when slow, riding the slats as this can cause a off camber stall. If you're trying to correct with aileron and the wings are "rocking" you are close to an all out stall. Use the rudder instead.

All this stuff is a characteristic of this type/configuration of plane, and the Bison makes these characteristics stand out more than most models...doesn't mean its bad, just requires a different skill set than a Carbon Z Cub or Timber.

[Starck Mad]

I do. It was kinda the whole point so I was going to make it work. Spent hours adjusting linkages etc to get them to lay as flat as possible.

Literally the slats and stol were the only reason to get this plane so if disabling them is required just to get to fly right, then there is no point in owning it.

Well unfortunately that is an issue. The reason I have no problem slowing it down is my slats are fixed in the slat position. When the flaps are deployed if the slats are attached they deploy as spoilers at that point...which kills the airfoil and keeps the wing from making lift properly. That means you need lots of power and speed to keep it flying. When the slats are in the slat position (not deployed, in the same position as the leading edge of the wing) they absolutely do work. They will keep the boundary layer of laminar flow attached to the wing at a higher angle of attack...in other words...increasing your critical angle of attack, or slowing the stall speed down to a speed slower than the plane can achieve without them. Don't confuse the slats not moving with the flaps as not working.

It is unfortunate they were made this way. This is the big oversight in the instructions in my opinion because not many modelers have the aerodynamic knowledge to understand this isn't going to work well at all before hand so they do it, it won't slow down, and they think the plane is a pos. My experience with it was different because I knew before I ever got it I wouldn't do this. I saw the MRC development video of the slats "moving with the flaps" and knew that wasn't going to work, so my plan was always to keep the slats in the slat position so they can actually work the way they are supposed to. The second the trailing edge of the slats rotates up they become ineffective and the further they rotate up the more they become spoilers.

In a full scale Shock Cub the slats are articulating in the same way, BUT the pilot has independent control over the slats and flaps. If the slats had their own servos/channel on the Bison it would be perfect. The reason for this in full scale is it gives the pilot options. The Shock Cub (and Bison) have slotted flaps...which makes slowing the plane down with a lower deck angle (AOA) possible. This is good for landing in the back country so you can see over the nose of the plane and be aware of whats in front of you going into a new place. Using this technique the pilot will deploy the flaps and ever so slightly rotate the slats forward...barely enough to make them ineffective, but NOT spoilers. The landing speed is slow, but not as slow as possible. In a STOL contest the pilot will leave the slats in the slat position and deploy flaps...this raises the deck angle (AOA) and gets the plane as slow as possible, the pilot uses elevator and power to "ride" the slats in ground effect (very low...its called a drag in)...the pilot doesn't need to see over the nose in front of him because its a controlled environment. He only needs to see the landing line out the side of the aircraft. When he gets over the line he deploys the spoilers (rotates the slats all the way forward...killing lift) and chops the throttle...the plane falls in place right over the line at the slowest possible forward speed...thats the reason for the spoiler position, and why they rock bad to the bone shocks...this technique is called a "drop in" .

The big issue with the Bison is its an advanced plane that requires an understanding of aerodynamics a lot of modelers don't have (particularly how slats work and the difference in slats and spoilers)... and it requires skills to fly slow most are not used to. 3D pilots could adapt quickly because their Harrier skills are very similar, but sport pilots won't be used to this.

It doesn't help the instructions call for a step that keeps the slats from working for the sake of a "cool moving feature".

Sorry for the long response, but I've felt the need to write it here for a while...for everyone...after reading all the flying issues guys are having...My hope is this will provide some info and help anyone who reads it to understand what the Bison is, how it will work, and how and why it won't if you set it up the wrong way. Hopefully this will give people and understanding and realistic expectations of it. I concede...that part of the instructions are wrong, but I also can say its a great STOL plane if the slats are in the right position and its flown with proper technique. I'm not a magic pilot, the plane slows down fine for me because I knew what to expect and happen to be good at that particular way of flying.

I truly hope this helps for some...


Edit: To be clear what makes the slats "work" is not that they move...it is the way they divert airflow over the wing, keeping the laminar flow attached at a higher angle of attack. This can only happen if they are in the correct position. I think a lot of folks think unhooking them from the flaps in the case of the Bison means they are not working. This is incorrect. They do exactly what they are supposed to do if they are left in the correct position. Flaps down full, slats in slat position is how to get it slow, not flaps down full, spoilers deployed...which is your only option if you hook them together.

[Gilatrout]

Man I hate you're having a hard time with it. Do you have the slats hooked to the flaps?

I do. It was kinda the whole point so I was going to make it work. Spent hours adjusting linkages etc to get them to lay as flat as possible.

Literally the slats and stol were the only reason to get this plane so if disabling them is required just to get to fly right, then there is no point in owning it.

[Starck Mad]

Flew mine again today. I have to air one of the tires each flight...it's not leaking from the hub so the valve must be bad. Just need to remember a compressor. I'm going to replace these pia tires asap.

Flights were generally good. Uneventful takeoff. But I could not get it to slow down for landing. It would either drop like a stone or drop the left wing sometimes both. At speed, the plane is trimmed level hands off with all evolutions of flaps/slats. This behavior only happens when slow. Probably the left wing is stalling first because of the slats.


Short takeoff yes, short landing no way. I have to come with way more speed than this type should carry.


In the end, I cannot recommend this plane. The QC makes the build process a maddeningly frustrating exercise. What you have to do to get it flying right as designed far exceeds the skills of an entry pilot, and some of the fixes such as removing the slats negate the whole reason for experienced pilots to buy it. Touch and go's are the whole point in buying the Bison. With the slats, touch and go''s are just not fun. I want to like this plane, but I just can't.

Man I hate you're having a hard time with it. Do you have the slats hooked to the flaps?

[Gilatrout]

Flew mine again today. I have to air one of the tires each flight...it's not leaking from the hub so the valve must be bad. Just need to remember a compressor. I'm going to replace these pia tires asap.

Flights were generally good. Uneventful takeoff. But I could not get it to slow down for landing. It would either drop like a stone or drop the left wing sometimes both. At speed, the plane is trimmed level hands off with all evolutions of flaps/slats. This behavior only happens when slow. Probably the left wing is stalling first because of the slats.


Short takeoff yes, short landing no way. I have to come with way more speed than this type should carry.


In the end, I cannot recommend this plane. The QC makes the build process a maddeningly frustrating exercise. What you have to do to get it flying right as designed far exceeds the skills of an entry pilot, and some of the fixes such as removing the slats negate the whole reason for experienced pilots to buy it. Touch and go's are the whole point in buying the Bison. With the slats, touch and go''s are just not fun. I want to like this plane, but I just can't.

[Starck Mad]

Any good videos on the high aoa rudder flying you’re talking about?

Go to Model AV8R on Youtube. We have 2 on the Bison. 1st one has more STOL/slow flight, but there is some in both.

[Warlox]

Any good videos on the high aoa rudder flying you’re talking about?

[Starck Mad]

100% on the money! After your advice I flew a few batteries with primarily rudder input and it made all the difference on how it preformed in slow flight. In high alpha just before stall speed the ailerons are very infective and must have rudder input to maintain attitude just like you said in our previous exchange. I was never able to fully eliminate left pitch but in the end I removed the slats and now this Bison feels more familiar to my lazy flight technique. People who are not used to using the rudder on a regular basis during flight ( me being in this category) are going to have a difficult time with this plane in slow flight.

I'm really glad you took the steps to get it where you want it so you can enjoy it. Awesome that you tried the technique first before you gave up on it...you can put the slats back on or replace them with a new (maybe straighter?) set later on if you decide to mess with learning rudder more. Much respect for you for just stating what you want and admitting what you don't want to do...a lot of modelers have to find a issue with the airplane rather than just saying it may be more than they can or want to handle at this point. This is definitely an advanced airplane to set up and fly well.

[ebrahimijohn]

Steve I'll have to respectfully disagree. The low Reynolds number for a model does make the technique required for flying with slats different somewhat from a full scale plane, but they are not useless or a gimmick. You simply have to be willing to...and capable of...flying the model as required to take advantage of the slats. Our videos of the plane on Model AV8R prove it can be done and repeated easily by a pilot that fits that profile. You can clearly see the plane flying comfortably in higher alpha utilizing the slats. A model with slats isn't for everybody and that is fine...pilots may or may not be willing to learn the set up and flying skill set to have success with them. I'm a huge STOL plane fan and have trained and practiced these techniques for the last few years with other planes, and developed my rudder skills with 3D planes many years ago...so the Bison doesn't seem difficult to fly well with slats to me. I can see how it will feel uncomfortable for pilots not familiar with what to expect out of it or how to set it up, but just because someone can't do it...or doesn't want to learn how to...which is fine by the way, to each their own... doesn't make it a gimmick. The slats work for me...

100% on the money! After your advice I flew a few batteries with primarily rudder input and it made all the difference on how it preformed in slow flight. In high alpha just before stall speed the ailerons are very infective and must have rudder input to maintain attitude just like you said in our previous exchange. I was never able to fully eliminate left pitch but in the end I removed the slats and now this Bison feels more familiar to my lazy flight technique. People who are not used to using the rudder on a regular basis during flight ( me being in this category) are going to have a difficult time with this plane in slow flight.

[Starck Mad]

Leading edge slats work well on full scale aircraft but on scale models they are pretty much a useless gimick. They only produce more drag.


Air just doesn't scale well.

Steve

Steve I'll have to respectfully disagree. The low Reynolds number for a model does make the technique required for flying with slats different somewhat from a full scale plane, but they are not useless or a gimmick. You simply have to be willing to...and capable of...flying the model as required to take advantage of the slats. Our videos of the plane on Model AV8R prove it can be done and repeated easily by a pilot that fits that profile. You can clearly see the plane flying comfortably in higher alpha utilizing the slats. A model with slats isn't for everybody and that is fine...pilots may or may not be willing to learn the set up and flying skill set to have success with them. I'm a huge STOL plane fan and have trained and practiced these techniques for the last few years with other planes, and developed my rudder skills with 3D planes many years ago...so the Bison doesn't seem difficult to fly well with slats to me. I can see how it will feel uncomfortable for pilots not familiar with what to expect out of it or how to set it up, but just because someone can't do it...or doesn't want to learn how to...which is fine by the way, to each their own... doesn't make it a gimmick. The slats work for me...

[Warlox]

I got my bison out today with calm winds. Last week I cut out the windows and replaced with a clearer plexiglass. Much better visibility. I was able to trim out the left roll tendency and the bison flew pretty nice! Definitely turns with rudder and gets pretty tippy in slow flight with full flaps. Those that removed the slats entirely, is it still tippy in slow flight and did it get rid of the left roll tendencies?

[Starck Mad]

This was the absolute best thing I could have done! No matter what I did with the slats I could not make this plane fly comfortably. Once I removed them it was night and day! I really wanted to like this plane and now I do.

Glad you have it like you like it! Enjoy it bud!

[Sureshot]

Leading edge slats work well on full scale aircraft but on scale models they are pretty much a useless gimick. They only produce more drag.


Air just doesn't scale well.

Steve

[ebrahimijohn]

This was the absolute best thing I could have done! No matter what I did with the slats I could not make this plane fly comfortably. Once I removed them it was night and day! I really wanted to like this plane and now I do.

[Warlox]

Post pics please if you do remove the slats. I also get a heavy tip to my left wing. I’ve been playing with the slats to figure it out. I also have thought about removing them.