BLR VGs

[Cimarron]

I was flying a friends SC, 160 HP A model with the BLR VGs on it. Without any weight behind the pilot it seams the tail wants to stall before the wing when trying to put it down 3 point. This is the only one I have not been able to hit the tailwheel first power off.

CC says to put power in on landing to get the tail down, :crazyeyes: At this time I'm trying anything as it is a little scarry as the tail starts up before the wing stalls. Is there a fix for this? possibly VGs under the stab or something?

I have checked the weight and balance and am within the envelope.

[HydroCub]

Have you checked the elevator "up" limit..? It could be less the allowed. Pilots have been known to adjust this to the extreme allowed by certification. A few cranks of "up" trim will help too.

[Ruidoso Ron]

I have had the same problem with my 150 HP L-21B. I think that the problem really started to become most evident when I started putting large tires on. I now have 26" Goodyears and a Borer, and have to be very careful when solo. I make a point of throwing the tool bag and tiedowns in the extended baggage when I fly solo.

[Cimarron]

I have checked the elev travel and it is about 2 degrees past the limits. It seams that nose up trim may help a little but at the point it is about to land it still pitches down.

If the only fix is to throw weight in the back I may want to check out another VG system for him.

[54tw]

This is an old thread, but I'll add my similar experience.

Elevator cable had stretched or too long to begin with not allowing full up travel. Made up a new cable and it works great now.

[cubunltd]

Sounds to me like your airplane is nose heavy or at the extreme forward limit. It has nothing to do with the VG's. Check the empty weight C.G. I bet it's forward. Some PA18's are like that and you have to add a burst of power along with nose up trim on landing. You might also want to check your angle of incidence as this will also cause the same problem.

cubsunlimited@verizon.net


John

[Ruidoso Ron]

Cimarron, the zero thrust engine mount will solve that problem. It did for me!

[green horn]

Try shaving a foot or so off your round out, Also a touch of power when you start to run out of stick. Hope that helps.

[54tw]

Also a touch of power when you start to run out of stick.

That's been my experience too. It works.

[mghallen]

54tw,

Sorry to hijack this topic guys but, 54tw are you sellin N54TW?

Mike

[Jerry Burr]

Hi Cubunltd. I beg to partially differ with you on your statement regarding V.G.'s. I agree that it may not be the V.G.'s but it sure can be the V.G kit. With the delta fins on the BLR kit in front of the stabilizer pushing the tail up in the landing mode and made even more so by the addition of 31 inch tires it makes a very large difference. They are fighting the elevators every inch of the way. Wayne is in the process of cutting down on the area of his stabilizers so as to give the elevators more authority at high AOA's. That kit was designed and tested with 8.50's not 31's. Jerry. :-?

[cubunltd]

That's cool Jerry, but I have a supercub here with 3"extended gear and 26" tires that had the same problem. After the installation of the Strakes, it help the flair on landing. I guess each airplane is different in some way. There has been a lot of discussion on wing incidence lately and how far off a lot of them are. I have measured several that have gone through my shop and found they vary from .6 degrees to 1.8 degrees.
The thing to do would be to remove the strakes and see what happens without them.
John

[54tw]

Mike,

No, that's not me. 54tw is short for 1954 Tail Wheel. Just a "handle".

[mghallen]

Just a shot in the dark. There is a S2B for listed on the Barnstormers site with the registration N54TW.

[PA-18]

Hi I have the BLR vg's, the 31 inch bush wheels along with the 6 inch extended landing gear. I have no problem whatsoever with what you are experiencing. Try trimming your airplane for cruise flight, or leaving it in cruise trim, might be a better choice of words, slow the plane down enough that when you pull the first notch of flaps that will correct for the nose heavy controls and you need no trim input. Slow down further on the edge of stall for second notch of flaps and I think your problems will disappear. In other words, the trim tab in a supercub is only good for different load configurations, after that don't use it much like you would need to in a much heavier airplane. I have found this to be the best way to trim and fly a supercub over all its speed ranges. In short, trim for the load not the airspeed. Let speed and flap setting balance each other and you will find there is nothing wrong with your aircraft if it is rigged properly. Let me know how this works for you. :o

[Nastrovia]

That's cool Jerry, but I have a supercub here with 3"extended gear and 26" tires that had the same problem. After the installation of the Strakes, it help the flair on landing. I guess each airplane is different in some way. There has been a lot of discussion on wing incidence lately and how far off a lot of them are. I have measured several that have gone through my shop and found they vary from .6 degrees to 1.8 degrees.
The thing to do would be to remove the strakes and see what happens without them.
John

But something to think about before anyone randomly decides to remove either of the tail strakes from the BLR VG kit, you might want to read your STC cover sheet where it says:

?......modification consists of seventy-two (72) vortex generators mounted on the wings and two (2) tail strakes mounted on either side of the empennage. If more than six vortex generator are missing or damaged, or if a tail strake is missing or damaged, the aircraft is not airworthy and must be repaired before flight.......?

Just in case you wanted to know...
Vera

[cubunltd]

Nostrovia,
You are absolutely correct about removing the strake. I didn't mean to remove it forever, but only as a test to see if it solved the problem. You can get a temporary exp. cert. for research and developement for the test. After the test you put the strakes back on and get the Std. cert. back.
I really feel the problem is NOT with the strake anyway but either a forward C.G. configuration or a wing incidence issue.
I fly a lot of supercubs and some fly like PA-18 describes and some fly like Cimarron describes. They don't all fly the same. You have to fly them accordingly.

John

[kase]

I fly pretty much how PA18 describes, except when Im solo I give it 2 turns of nose up trim when on final to help get the tail down, and always land full flaps and carrying some power. My ewcg is 11.4. I was reading the other post about not being able to get the tail down and I just think you need to trim the nose up a some. My batt is under the front seat.

[Indabush]

An old cub pilot told me this, and works it works for me. He said he was hunting polar bears up in Kotzebue and an old eskimo showed him how to fly without messing with the trim once it was set up for cruise flight.
Hi I have the BLR vg's, the 31 inch bush wheels along with the 6 inch extended landing gear. I have no problem whatsoever with what you are experiencing. Try trimming your airplane for cruise flight, or leaving it in cruise trim, might be a better choice of words, slow the plane down enough that when you pull the first notch of flaps that will correct for the nose heavy controls and you need no trim input. Slow down further on the edge of stall for second notch of flaps and I think your problems will disappear. In other words, the trim tab in a supercub is only good for different load configurations, after that don't use it much like you would need to in a much heavier airplane. I have found this to be the best way to trim and fly a supercub over all its speed ranges. In short, trim for the load not the airspeed. Let speed and flap setting balance each other and you will find there is nothing wrong with your aircraft if it is rigged properly. Let me know how this works for you. :o

[mvivion]

One thing that hasn't been mentioned here is how current is the weight and balance on this aircraft? In other words, how ACCURATE is the weight and balance on this aircraft? LOTS of Cubs (and other aircraft) are operating on W/B that was done 20 or 30 years and thirty or forty modifications ago. You said that you calculated a weight and balance, but my point is: Did you calculate an accurate weight and balance, or is the data you're using so old as to be non applicable, though legal?

Point is, you could be substantially out of the forward limit and not know it.

MTV

[Dave Calkins]

...and substantially out of the forward limit means abysmal pitch "up" authority. Which is something that this VG kit limits by its' 'Strake'.

[907cub]

Dave, are you saying that the BLR kit limits the nose up pitch??

[bob turner]

I regularly fly a BLR equipped Cub (160 HP Borer 26" heavy landing gear Thrustline) and it flies pretty much like any other Cub. I can easily get the tailwheel down first and keep the mains off for a couple of seconds.

MTV raises a good point, but most Cubs do not get out of balance. The computations sure do, however, even after good Cub shops weigh them. If you weigh, use care to use the formula in the AFM. I have seen only one Cub with accurate weight and balance computations. About 3/4 of the problem is mixing datum lines - the rest is having the landing gear in the wrong spot, or, as above, using the wrong formula after weighing.

[Dave Calkins]

Dave, are you saying that the BLR kit limits the nose up pitch??

Read post number 11 above. Those strakes are an additional horizontal stabilizing force.

[907cub]

I've had BLR's on my cub for over twenty years, I think time gets away from me!! Never had any trouble with pitch up on landing. Some with nose down, but that is the product of putting a cub into c-180 duty. Not that I would fly over loaded or out of cg, that would be crazy!

[16-bravo]

Blr works great on my plane. Never had any issues whatsoever.