LG Position for Trainer

[Peter in Fairfax, VA]

So, when I look at model airplanes, I see the position of the main, conventional two wheel gear all over the place.  In early free flight models, the gear is nearly at the thrust washer.  Later stunters, about the CG.  That's a huge range!

So, what's best for a .19 sized IC trainer?  I am thinking the wheel axle would be roughly in line with the front of the tank, which is pretty far forward.  It would be flown over grass.  My thinking is that the forward position would make it less likely to flip over, a style point on landing that every pilot enjoys.  Pretty much, at NVCL, if you land the trainers without flipping them, it brings the house down.

Thoughts?

Thanks!

Peter

[Tim Wescott]

If you're flying off of dense grass 2" tall or taller, and you want no-flip landings, the best spot for the landing gear is in your flight kit.

Unless the grass is cut very short and the ground rolled, then a 19-sized model isn't going to be able to land without flipping.

I'd put the gear at about the leading edge of the wing, assuming a typical model, then I'd accept that on anything but perfect grass I'd get flips on landing.  Or I'd build an OT stunt model and use the stock gear position.

[Dave_Trible]

I think I'd agree with Tim.  I'm finishing a couple Sig Acromasters for my grandkids to fly with Enya .15s.  I decided to leave the gear off.  The wheels are too small to take off out of grass and a gear ensures a flip over on landing which can bust the rudder off.  Unless you fly by yourself with a stooge I think the gear is pointless.

Dave

[Tim Wescott]

...Unless you fly by yourself with a stooge I think the gear is pointless...

I can't resist mentioning it, but I can't really recommend it for an absolute newbie -- if it has a powerful enough engine, an Akromaster without wheels is a good candidate for a sleeve stooge.

You could just live with the thing flipping over on every landing.  That's basically what I did when I was learning the pattern off of grass.  I'd flown enough off of pavement that I know what a good landing is supposed to be, so I'd practice that, and not be surprised when the wheels touched down and the plane flipped.

I've only broken rudders on (ehem) powered landings.  So you could just not worry about it.  Or reinforce the rudder, or maybe make one that's longer and lower, with roughly the same area.  That way on those occasions when there is pavement to fly off of, you'll have wheels.

Or get an old refrigerator box and lay down a takeoff/landing strip.  With some applied cleverness you can make it fold up and go in your car, and if it's two refrigerator-heights long it should be plenty for any stunt trainer of any size.

[Mark wood]

The "rule of thumb" which kind of works is the front edge of the tire should be inline with the LE of the MAC. That's more or less a good place of reference depending on the amount of sweep and taper of the wing and the diameter of the tire. A better "ruler of thumb" is the contact point of the wheel should be on a line 15 degrees in front or behind the CG when the airplane is in a level attitude.

[Trostle]

 A better "ruler of thumb" is the contact point of the wheel should be on a line 15 degrees in front or behind the CG when the airplane is in a level attitude.

What do you mean "or behind"?

Keith

[Peter in Fairfax, VA]

For better or worse, we do like ROG takeoffs.  Though the field is primarily grass, we do have sets of three 4'x8' mats for takeoff runs at both circles. Though I've seen sleeve stooges used in various online videos, the "pin the tail before the ROG" style is the local custom.

[Mark wood]

What do you mean "or behind"?

Keith

On a tricycle gear airplane the contact point of the wheel should be 15 degrees behind the CG. For a conventional gear, tailwheel, airplane 15 degrees in front. As a "rule" the landing attitude of the airplane is about 15 degrees which places the CG directly over the wheel at ground contact. The result is that there is no resulting pitching moment generated by ground contact which results in reduced bounce or porpoising tendency. With wheels in front of this location a less than soft touchdown will result in a pitch up and the airplane likely becoming airborne again and begin a cycle.

[Tim Wescott]

... A better "ruler of thumb" is the contact point of the wheel should be on a line 15 degrees in front or behind the CG when the airplane is in a level attitude..

I was trying to keep things simple.  And I know some pretty darn good pilots who use the 15-degree rule on pavement, but have a second set of "grass gear" with the wheels further forward (for a taildragger, obviously).

When I was flying off of grass and consistently flipping Flight Streaks and Skyrays on landing, I built a Fancherized Twister with trike gear.  This never flipped on me, even in some really tall "plane killer" grass at the NW Regionals one year.  It was thick enough that I could barely take off -- but if I recall the landing it was, if not good, at least with the wheels pointing down when all came (rapidly) to rest.  Later, I found out that just flying a bigger plane on my usual field was enough to keep it from flipping.

Hmm -- a trike gear Akromaster.  That would be -- too much work.  And I suspect that it'd still flip if the grass were tall enough.

[Trostle]

On a tricycle gear airplane the contact point of the wheel should be 15 degrees behind the CG. For a conventional gear, tailwheel, airplane 15 degrees in front. As a "rule" the landing attitude of the airplane is about 15 degrees which places the CG directly over the wheel at ground contact. The result is that there is no resulting pitching moment generated by ground contact which results in reduced bounce or porpoising tendency. With wheels in front of this location a less than soft touchdown will result in a pitch up and the airplane likely becoming airborne again and begin a cycle.

I understand all of that.  You did not mention anything about a tricycle gear in your earlier post.  It was a bit confusing.  Your could correct it in your first post, then we could both remove these unnecessary and unneeded  posts.

Keith

[Tim Wescott]

... Don't over think it.

Oh, now where's the fun in that?

[Dennis Toth]

Peter,
You didn't say if you are building a kit, from plans or designing you own. If kit use what they recommend (usually straight down from leading edge is good), if from plans again go with what the designer suggests, if your own look at some recent ships that you like and use those numbers (moments and areas) fashioned to the lines you like. We fly off a soccer field and 1 3/4" wheels on Ringmaster size ships work fine, even when the grass is wet.

Landing on grass is not hard, just bring the ship in smooth and not too hot. Keep stepping back as you bring it around to keep line tension. Don't try to mush it in, fly it smoothly in.

Best,    DennisT

[Steve Helmick]

A good stout wire LG with big soft wheels somewhere from engine cylinder center to prop thrust washer is a good way to cushion power-on "landings" by beginners. Take a look at the Testor's Freshman series in the link below. The upright engine works way better for modern glow engines with mufflers.  Steve

https://www.worthpoint.com/worthopedia/vintage-freshman-29-testors-famous-41709147

[Peter in Fairfax, VA]

Thanks for the expertise; learned a lot.

Yes, those early free flight models had wheels forward for a reason.  That's what I went with, following motorman and Steve H, suggested.

Peter

[Peter in Fairfax, VA]

Result below.

Much appreciate that not only was my question addressed, but our whole training program was examined.

Yes, we know to use a small tank.  We advocate for that all the time with returning or new pilots.

Yes, we know that a Skyray 35 or a Phil Cartier trainer might fly better.

As far as the design, the attached one was built by an NVCL member, Dick Hauser.  It appears to borrow heavily from the genre:  Testor's Freshman, Guillows Trainer, Aldrich/Brodak Streak Trainer, Carl Goldberg Swordsman 18/Stuntman 23/Lil Wizard, Sig 1/2A Skyray, Sig Buster, numerous racers, etc.

Peter

[Peter in Fairfax, VA]

And thanks to Mark Wood for describing the pitching moment; sounds right.

[Dan McEntee]

Result below.

Much appreciate that not only was my question addressed, but our whole training program was examined.

Yes, we know to use a small tank.  We advocate for that all the time with returning or new pilots.

Yes, we know that a Skyray 35 or a Phil Cartier trainer might fly better.

As far as the design, the attached one was built by an NVCL member, Dick Hauser.  It appears to borrow heavily from the genre:  Testor's Freshman, Guillows Trainer, Aldrich/Brodak Streak Trainer, Carl Goldberg Swordsman 198/Stuntman 23/Lil Wizard, Sig 1/2A Skyray, Sig Buster, numerous racers, etc.

Peter

     What you have there looks fine to me. In this day and age, we have to distinguish between "Basic Trainer" and "Stunt Trainer". Anything that will stunt will  be too sensitive and too fragile for a raw beginner. It just has to fly, get up, go around and then come down. Sometimes it's easy to forget how difficult that was for us when we first attempted flight! That was out thought process when we worked up the TuffBaby for the Kidventure circles at Oshkosh.
  Type at you  later,
   Dan McEntee

[Ken Culbertson]

Result below.

I see you have taken care of the most important think you can do for a trainer - Cut off the Needle Valve stem! 

Ken

[phil c]

On a tricycle gear airplane the contact point of the wheel should be 15 degrees behind the CG. For a conventional gear, tailwheel, airplane 15 degrees in front. As a "rule" the landing attitude of the airplane is about 15 degrees which places the CG directly over the wheel at ground contact. The result is that there is no resulting pitching moment generated by ground contact which results in reduced bounce or porpoising tendency. With wheels in front of this location a less than soft touchdown will result in a pitch up and the airplane likely becoming airborne again and begin a cycle.

Another thing to consider-  the wheels, especially two wheel gear,  the axle should be set at least the height of the grass.  This can look gawky, so keeping the grass as low as possible, without killing it is best.
Really stiff gear will also keep one or both wheels twisting out of straight ahead when they touch down.  Carbon fiber gear is usually wide and stiff enough to track straight.  Doubling or tripling a music wire gear strut is heavy, but will be very stiff also.

[Scott Richlen]

   It just has to fly, get up, go around and then come down. 

Hey Peter!  I think he is talking about our "John Deere" trainer....

That Yellow and Red looks ready to go.  Good job!!