Trim Tabs vs. Jackscrew
- Thread starter Indabush
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mvivion
SPONSOR
Bozeman,MT
Because it works better 
Actually, it works a lot better. While the jackscrew has some limitations and liabilities of its own, it offers a very powerful trim system, while at the same time reducing drag which would be caused by a deflected control surface (in the case of a trim tab--which simply drives the elevator to trim the plane). So, you get the best of both worlds: Powerful trim at high AOA, and less drag in cruise.
MTV
Actually, it works a lot better. While the jackscrew has some limitations and liabilities of its own, it offers a very powerful trim system, while at the same time reducing drag which would be caused by a deflected control surface (in the case of a trim tab--which simply drives the elevator to trim the plane). So, you get the best of both worlds: Powerful trim at high AOA, and less drag in cruise.
MTV
Jim Miller
Registered User
Normandy TN
I would never dispute the advantages offered for the jack screw trim. I have also heard from people with trim tabs that they work reasonably well. I am going with a trim tab on my exp Cub/SuperCub just because it
is much simpilar to fabricate and install. It gets rid of a lot of pullies and the trim cable. For the kind of flying I will be doing I expect it to work ok for me.
is much simpilar to fabricate and install. It gets rid of a lot of pullies and the trim cable. For the kind of flying I will be doing I expect it to work ok for me.
Jim Miller said:
If you plan to operate your aircraft heavy and loaded to an aft CG, you might want to reconsider using the jackscrew. A moving stabilizer makes the aircraft much safer when aft loaded... you will have more pitch authority which is essential if you get into a deep stall.
If you go with a fixed stabilizer and trim the elevtor, you might want to increase the up/down limits of the elevators slightly. Running out of pitch control is a no-no, especially when struggling to maintain control of the aircraft.
.
Jim Miller
Registered User
Normandy TN
Hydrocub
My goal is to fit it into the 1320 gross wt LSA category. I will be flying solo 99% of the time with no more extra wt than a small bag. If I do carry passengers it will just be my wife and myself which together is about 270 total.
My goal is to fit it into the 1320 gross wt LSA category. I will be flying solo 99% of the time with no more extra wt than a small bag. If I do carry passengers it will just be my wife and myself which together is about 270 total.
Jim Miller said:
That won't be a problem and the trim tab setup should work fine then. If you aren't putting an extended baggage compartment in the fuselage, you should never have an aft CG problem. I would suggest you make the elevators balanced like the PA-18 has.
cubdriver2
FRIEND
upstate NY
Jim Miller said:
This makes no sence, some of the lightest certified 2 place aircraft ever built had jackscrews, E2 Cub, J2 Cub, J3 Cub, it gives you the ability to trim for ANY given speed and STILL have full elevator travel which gives you the safest and most comfortable range of tail authority.
Glenn
mvivion
SPONSOR
Bozeman,MT
I'm a bit confused as well about the relative complexity of the controls. Unless you're planning on using an electric trim drive on the trim tab, you still have to have cables, pulleys, etc.
Given a choice between the two, I'd definitely go for a trimmable stabilizer for all the reasons noted.
One of the distinct advantages the Super Cub has over the Husky is that the Cub uses a jackscrew trim system.
MTV
Given a choice between the two, I'd definitely go for a trimmable stabilizer for all the reasons noted.
One of the distinct advantages the Super Cub has over the Husky is that the Cub uses a jackscrew trim system.
MTV
On my 2+2 I have the trim tab. I have a trim lever above the seats on the x tube which activates one 144" teflon lined cable which ends in the last section of the fuse with metal belly. At that easily accesible area I connect to a 60" teflon lined cable which runs thru the elevator to the trim tab. Very simple set up. The trim tab on my J4 works fine. However the baggage area on the J4 is very small so hard to load heavy aft.
Also I have not flown my 2+2 or a supercub so could be my ignorace is showing. :-?
Also I have not flown my 2+2 or a supercub so could be my ignorace is showing. :-?
cubdriver2
FRIEND
upstate NY
Dan2+2, some of the J4s I have seen have a modified baggage area that goes to the floor, mine is still a sling but I think it's a little bigger then a stock one, one of the great things about a J4 is that the baggage capacity is 105 lbs and being a nose heavy plane it's almost impossible to get into a aft CG situation even with the rear tank filled as long as you empty it before the front tank, I love the J4 as is but when the time comes to rebuild it would be nice to switch it over to a adjustable stabilizer if it could be done, it's nice as is but I think it could be better with a adj stab.
Glenn
Glenn
skywagon8a
MEMBER
SE Mass MA6
I am in total agreement with MTV. The only thing a trim tab does is to reduce the force that the pilot has to apply to the stick. The movable stabilizer trims the airplane.
For example, I once had a 172 on floats. With the power off and trimmed nose up it felt as though it could have used more up elevator. If it was trimmed nose down in the same situation the trim tab was deflected up which increased the elevator effectiveness and pressure on the controls, sort of like an upside down flap on the elevator. Then even though the force was higher the elevator was more effective. This is also true of a Cessna 206. An opposite example is the Piper Cherokee. It has a stabilator, one moving surface with a trim tab for control pressure. It is small when compared to an elevator/stabilizer design, but very effective. With a trim tab system you will need more surface area than with a trimable stab for the same results.
If you insist on using a trim tab you will likely find that most of the time that the stab and elevator are not streamlined, thereby producing drag. Of course in a Cub perhaps this is not important.
For example, I once had a 172 on floats. With the power off and trimmed nose up it felt as though it could have used more up elevator. If it was trimmed nose down in the same situation the trim tab was deflected up which increased the elevator effectiveness and pressure on the controls, sort of like an upside down flap on the elevator. Then even though the force was higher the elevator was more effective. This is also true of a Cessna 206. An opposite example is the Piper Cherokee. It has a stabilator, one moving surface with a trim tab for control pressure. It is small when compared to an elevator/stabilizer design, but very effective. With a trim tab system you will need more surface area than with a trimable stab for the same results.
If you insist on using a trim tab you will likely find that most of the time that the stab and elevator are not streamlined, thereby producing drag. Of course in a Cub perhaps this is not important.
S
StewartB
How many of you have your trim set for neutral stick pressure on short final and at touch down? I'm not really interested in 5000' paved runway landings. Let's keep it to 1000' strips or shorter. Does the answer change with a shorter strip?
SB
SB
NimpoCub
Registered User
Nimpo Lake, BC . . . AKA "the Floatplane Capital o
I trim for cruise flight (only changes when load changes or I need to gradually increase/decrease altitude) and use the elevator to change pitch for takeoff/landing.
It's not hard work and seems completely natural.
Slow flight needs a bit of back pressure, but I need to be hanging on to the stick anyway.
To me, it's all part of being "@1" with the plane.
It's not hard work and seems completely natural.
Slow flight needs a bit of back pressure, but I need to be hanging on to the stick anyway.
To me, it's all part of being "@1" with the plane.
bob turner
Registered User
I am with Nimpo. We are probably the only two . . .
Jim Miller
Registered User
Normandy TN
cubdriver2 said:
mvivion
SPONSOR
Bozeman,MT
Jim,
The point is, a trim tab will NOT fly neutral with the elevator, except in one precise set of conditions of speed and loading.
Have you looked at the control system for a jackscrew trim system?? There really isn't all that much stuff involved, and you're not going to run one cable run all the way to that trim tab either....
But, if it winds your watch, I'd say go for it...that's why they call it homebuilding.
MTV
The point is, a trim tab will NOT fly neutral with the elevator, except in one precise set of conditions of speed and loading.
Have you looked at the control system for a jackscrew trim system?? There really isn't all that much stuff involved, and you're not going to run one cable run all the way to that trim tab either....
But, if it winds your watch, I'd say go for it...that's why they call it homebuilding.
MTV
behindpropellers
Registered User
NE Ohio
Jim Miller said:
WhiskeyMike
MEMBER
West Boxford MA
trim tab jack screw
I agree about the problems with the marine cable. I've had 2 Jodel 1050's which were the standard French trainer. A great plane built of all wood and fabric, but the trim was always a maintenance issue, and they creep out of place from the airstream hitting the trim tab. They are a lot of fun to fly, sort of like a low wing 100HP Cub with an accent.
A jackscrew tail is by far the most efficient. Oddly, I "like" the trim on the Husky, but only because of the fact that on planes used for towing, the tails shake a lot, all the time. It's a bit scary, and some have even been known to have broken the inner tube on the stabilizer. Not common. Apart from early strut issues, fixed by a SB, the Husky is well braced, but flies without the feel of the Cub. I'm now looking for someone who can get Charley Center's tail strut approved on my PA-12 -in the lower 48.
I agree about the problems with the marine cable. I've had 2 Jodel 1050's which were the standard French trainer. A great plane built of all wood and fabric, but the trim was always a maintenance issue, and they creep out of place from the airstream hitting the trim tab. They are a lot of fun to fly, sort of like a low wing 100HP Cub with an accent.
A jackscrew tail is by far the most efficient. Oddly, I "like" the trim on the Husky, but only because of the fact that on planes used for towing, the tails shake a lot, all the time. It's a bit scary, and some have even been known to have broken the inner tube on the stabilizer. Not common. Apart from early strut issues, fixed by a SB, the Husky is well braced, but flies without the feel of the Cub. I'm now looking for someone who can get Charley Center's tail strut approved on my PA-12 -in the lower 48.
Jim Miller
Registered User
Normandy TN
The marine cable idea was something I saw on this site. If a bad idea I will use something else. There are a lot of airplanes flying safely with trim tabs and I need to take a look at some of those. How are the cessna's, husky and other aircraft constructed trim tab wise. Are they a single cable push/pull or do they have a better set-up. Van's is another 200mph aircraft with trim tabs. Does anyone know how van's trim tabs are connected. My first post on this thread said that I in no way was disputing the superiority of the Piper jack screw tail system. I have flown my Colt for 15 years with the jack screw trim.
Cub junkie
Registered User
My Moms basement
On a Cub the jackscrew is king. A good cable system to emulate for a trim tab Cub would be the Aeronca Champ system. Two cables run all the way from the cockpit ceiling to the elevator.
behindpropellers
Registered User
NE Ohio
Jim Miller said:
Jim-
The problem is not the trim tab, or even the marine cable.. It is the fact you have one push/pull cable. If that cable breaks, the trim tab is free to flutter in the breeze. Once that lets go nasty things happen. A second cable will capture it for the short term.
Tim
Carey Gray
Registered User
Thun Field, Washington
This is kinda like the old days, where guys declared themselves experts and then gave advice on things they know nothing about. I miss the old days.
behindpropellers
Registered User
NE Ohio
Carey Gray said:This is kinda like the old days, where guys declared themselves experts and then gave advice on things they know nothing about. I miss the old days.
Carey-
Who are you talking to?
Jim Miller
Registered User
Normandy TN
I am too far along to reconsider the jack screw. Fuselage is welded, painted and modded to have a ground adjustable with washers/spacers horizontal tail. I am going to the best of my ability do a Van's aircraft manual cable trim system. He has about 10,000 such systems flying most in excess of 200 MPH. If we have any Van's experts on the site I would love to hear from them. I appreciate all advise that has been given and also know that a loose trim tab can lead to flutter and catastrophy.
