Official Skynetic Bison XT STOL Discussion Thread

[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.

[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]

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]

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]

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.

[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.

[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]

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.

[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!

[SanExup]

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

[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.

[ebrahimijohn]

I have put a dozen flights since removing the slats and this is what I have observed. #1. Lower speed take off and landings with dramatically improved handling. #2. No more left pitch at low speed. The amount of throttle needed to maintain flight at low speed is reduced therefore the torque of the motor no longer affects low speed flight. #3. Increased laminar flow reduces need for increased throttle in turns and at low speed flight which extends battery life giving me more flight time on same battery. One of the deciding factors for purchasing this plane was the slats, I had never had an RC with them and I thought they looked pretty bad ass on this plane. I could get the plane to fly decent with lots of rudder input and using the ailerons to counter pitch, but I could never get it to fly slow enough to be considered a STOL aircraft. A much more advanced pilot then myself may enjoy this type of flying, but for me it was not a fun plane to fly until I removed the slats. It is now one of my favorite planes to fly in almost any condition!

[Narly]

Have noticed in many of the posted videos lots of wing tip strikes in less than perfect landings; and since I do lotta that I came up with this mod:

Thought the exposed wing tips could be improved with drop tip "winglits" to protect the exposed wing tips and ailerons. Found carbon fiber sheet/plate 2mmx200x300 on ebay; made a template 1/2" larger than the airfoil top and bottom. Counter sink 6-32 blind nuts and epoxy into wing tips; but the trick is getting that done with no epoxy in the threads! Could also use screw in threaded inserts in 6-32 or small M sizes. Next I foam tacked on the stock black winglets in the recess. I cut the carbon fiber with a Jig saw with fine tooth metal cutting blade just outside the line and final sanded to shape with just sand paper on a block. Do use a good respirator since you don't want to breathe the fine carbon fiber dust. The cut out for the wing tip lights was with me old Dremel jigsaw with fine thread blade and a hand jigsaw. And the finished look:

Looks great and might even help knife edge flight (like I can even do dat). I haven't flown it yet 'cause it's 34* F outside and I don't have a suitable 6S batr'y because I spent all this months
budgit on a 48v. 17.5Ah Li-ion batr'y that is attached to a new e-bike !! 😎

[SEWERFLY]

That's a great mod

[SEWERFLY]

I have put a dozen flights since removing the slats and this is what I have observed. #1. Lower speed take off and landings with dramatically improved handling. #2. No more left pitch at low speed. The amount of throttle needed to maintain flight at low speed is reduced therefore the torque of the motor no longer affects low speed flight. #3. Increased laminar flow reduces need for increased throttle in turns and at low speed flight which extends battery life giving me more flight time on same battery. One of the deciding factors for purchasing this plane was the slats, I had never had an RC with them and I thought they looked pretty bad ass on this plane. I could get the plane to fly decent with lots of rudder input and using the ailerons to counter pitch, but I could never get it to fly slow enough to be considered a STOL aircraft. A much more advanced pilot then myself may enjoy this type of flying, but for me it was not a fun plane to fly until I removed the slats. It is now one of my favorite planes to fly in almost any condition!

Can you post a picture without your slats?

[ebrahimijohn]

I will take a better pic and upload to the forum.

[ebrahimijohn]

Have noticed in many of the posted videos lots of wing tip strikes in less than perfect landings; and since I do lotta that I came up with this mod:

Thought the exposed wing tips could be improved with drop tip "winglits" to protect the exposed wing tips and ailerons. Found carbon fiber sheet/plate 2mmx200x300 on ebay; made a template 1/2" larger than the airfoil top and bottom. Counter sink 6-32 blind nuts and epoxy into wing tips; but the trick is getting that done with no epoxy in the threads! Could also use screw in threaded inserts in 6-32 or small M sizes. Next I foam tacked on the stock black winglets in the recess. I cut the carbon fiber with a Jig saw with fine tooth metal cutting blade just outside the line and final sanded to shape with just sand paper on a block. Do use a good respirator since you don't want to breathe the fine carbon fiber dust. The cut out for the wing tip lights was with me old Dremel jigsaw with fine thread blade and a hand jigsaw. And the finished look:

Looks great and might even help knife edge flight (like I can even do dat). I haven't flown it yet 'cause it's 34* F outside and I don't have a suitable 6S batr'y because I spent all this months
budgit on a 48v. 17.5Ah Li-ion batr'y that is attached to a new e-bike !! 😎

This is a great mod, but I have a question regarding the pictures you uploaded. What happened to your other Crock?

[ebrahimijohn]

Can you post a picture without your slats?

[Narly]

@ebrahimijohn:

The 6 mo. old Cavalier KCS that I was doggie sitting f/ 3 days ate it, along w/ 1 hearing aid & the ear & nose pieces off my glasses ....... while I was concentrating on Bison mod 🙄
Xpensive lesson learned ..... 'bout 2 Bison's worth ......

[Nutz4flying]

Landing Gear Bracket Replacement

One of the features of the Skynetic Bison XT model is the unique metal articulating undercarriage. This design features breakaway parts that can be repaired or replaced while limiting risk of damage to internal parts of the model. Two of the breakaway parts are the brackets which attach the undercarriage to the bottom of the fuselage. The brackets that are supplied with the mLodel kit are made of molded metal, which when put under stress, will break at the attachment point to the bracket base or elsewhere. A replacement bracket from the model manufacturer is not available, except as one of the parts included in the undercarriage replacement package.


Big A Tools, an Ohio-based small business, has designed a replacement bracket specifically to fit the Bison XT. The replacement bracket will fit the fuselage’s recesses and the screw holes align with the fuselage attachment points as well as the undercarriage attachment points.


There is a quantity of 4 brackets shipped with each order. Keep two brackets in your field box for an on the spot repair if needed after your next hard landing. Use the original screws included with the kit.


Order the brackets directly from Big A Tools. https://www.etsy.com/listing/1110617...r-brackets-for