H5487

Howdy Guys,

I just received my (long desired) plans and short kit for a 78" Sailplane from Bob Holman. Woo Hoo!

Any suggestions for an engine? While it would be appropriate to put an ignition engine in it, I'll be building this famous old free-flighter for relaxing R/C-assist so I'd like to have a throttleable engine that's not too big (I'm not going to be doing stinkin' 3D!!!) but not too anemic either. (Note: I've been partial to Saitos in the past but I might be open to something new.)

Any other comments on building the Sailplane are appreciated.

Thanks!

Harvey

otrcman

My Sailplane was a SAM competition model, so I wanted all the power I could get. Initially I used an Anderson Spitfire 65, and later an Orwick 64. The Orwick had slightly more power and was a couple of ounces lighter.

Neither engine really over powered the model. That thick wing really holds the speed down. I could climb nearly vertical, but not at any great speed. On the other side of the coin, the Sailplane glides on just the slightest wisp of lift. So you could probably fly on any modern four stroke at just a crack above idle.

Any decent 45 to 52 four stroke would do nicely. Anything larger would be overkill.

Dick

H5487

Thanks Dick. I've got two Saitos that might work. The 'big' one is a .56 which might be more than I need and I'd end up carrying around some unnecessary weight. The other one is a .40 and is below your recommended range so it might be too small. However, it's the open-rockered version which would look very nice on this plane. Unfortunately, the open-rockered Saitos produced less power than the modern ones which means that ROG would probably be difficult?

I read Tandy Walker's Sailplane build thread and he used one of Woody Bartelt's McCoy .60 (ignition) replicas. However, I don't remember him saying if that motor was a good match for the plane.

Harvey

otrcman

Hi Harvy,

Having never owned an open rocker 40, I can't say whether it would be powerful enough. But they sure look neat !

I considered putting a McCoy 60 on my Sailplane to make it more competitive, but weight was a concern. The minimum SAM weight would have been 64 oz, but a Sailplane has so much wood in the structure that it's really hard to build to that weight. My total weight was 70 oz. in spite of some pretty aggressive lightening work.

Looking at Tandy's build thread, I'd guess that his model is pretty heavy. The McCoy would still pull it up smartly though, as that's a really powerful engine.

You mentioned ROG takeoffs. The Sailplane has a pretty strong nose down pitching moment. If you don't have enough elevator control, it can be difficult to pull off the ground if it builds too much speed before liftoff. In an effort to reduce overall weight, one of the things I did was to put an elevator on one side only. That was a mistake. If I let the plane build up too much speed on the ground, it wouldn't lift off even with full up elevator.

I guess I'm emphasizing the faults of the Sailplane here. Don't get me wrong, it's a magnificent design. It flies very well and there's nothing more beautiful in the air.

Dick

H5487

Dick, no need to apologize for giving me some frank advice. That's what I'm looking for and the reason for this thread.

However, I might have to take exception to your claim that there's nothing more beautiful in the air than a Sailplane. I think the whole civilized world has already designated the Lou Proctor Antic on floats to be the most beautiful thing in the air!

Harvey

ifr2lax

H5487,

Go to this URL for the SAM Chapter 15 website. This is the photographic build log by Tandy Walker for his Goldlberg SAILPLANE. Very impressive...and lots of help.

http://www.sam15.org/walkersailplaneproj.html

One thing to watch is that your plans are SYMMETRICAL from side to side;

Forget who did my Sailplane plans (these were NOT the Holman copy) but they were NOT symmetrical... A friend showed me how to fold them over, hold them against a plate glass door...the light shines through and it is obvious if there are any issues in left/right. Probably a good idea for any plans and the bigger the model the better.

I have the Bob Holman partial kit wood and it appears to be first class...

Pete

H5487

Thanks, Pete. The link that you included for Tandy's Sailplane Build thread was the same thread that I mentioned in post #3 above. It's a great wealth of info!

Harvey

otrcman

OK Harvey, I might have to concede that one to you. But don't count out the Sailplane until you see your's fly. Maybe I overstated my case with "most beautiful" but I'll stand my ground on "magnificent".

Dick

H5487

Dick,

I will agree with 'magnificent' as a fitting descriptor of an early airplane. After all, the word was used in the title of one of the greatest aviation movies of all time!

(Now I'm going to have that theme song stuck in my head for the rest of the evening! )

Harvey

H5487

Dick,

Did you install the horizontal stabilizer's "tip skids" when you built your Sailplane? I have my doubts that these little sub-stabilizer-looking things contribute much to yaw stability and suspect that they're included solely to protect the H-stab's tips from abrasion damage. (Their name might be a clue!) Since I'll be operating my model as an ROG, I'll install a tailwheel which will raise the stab a little higher when on the ground and possibly make the tip skids unnecessary. I see them as something to accidentally knock off.

Your opinion?

Harvey

otrcman

Yes, I did install the tip skids. As I recall, I made them of 1/16" birch plywood. I did break a skid one time out of hundreds of flights. Don't recall the circumstances, but I super glued it back in place at the field and never did any further repairs.

Whether the lack of skids would affect the stability, I can't say for sure. But the Sailplane is an excellent flyer both under power and in the glide, whereas the Zipper is a bearcat under power. I have always suspected that the tip skids were at least part of Goldberg's solution to the crazy power characteristics of the Zipper.

By the way, if you look at the photo in one of my earlier posts, you can see the position of the rudder hinge line. The rudder authority with that amount of movable surface was marginal. If the airplane zoomed nose up for any reason (like from a wind gust), the rudder wouldn't level the wings until the model picked up some speed. I had to be very careful not to bank too steeply when I was down low for fear of not being able to level the wings before I hit the ground. Contributing to this lack of authority were the small size of the rudder and also the limited travel available. The deflected rudder hit the deflected elevator at full throw. If I had it to do over again, I would have made dual elevators and canted the inner ends of the elevators so the rudder didn't couldn't hit them.

Dick

H5487

Thanks, Dick, that' good stuff to know. I had already bought the plans and short kit for a Zipper before I heard about its squirrelly characteristics when under power. I shelved my plans to build it when I found out that the Sailplane was a much-tamer design.

Tandy built his Sailplane with elevators on both sides and seemed to be happy with the results but was a little dissatisfied with the rudder authority. Therefore, I had already planned on building dual elevators and a slightly larger rudder. Anything else you would change if you built another Sailplane? What "earlier post" are you referring to?

Thanks for your help!

Harvey

otrcman

Post #2 in this thread should contain a picture of my Sailplane. You can see the rudder hinge line pretty clearly in the picture.

Dick

braddock VC

Just to have my $0.02 worth, my goldberg sailplane has an OS 40 Surpass with 12x5 graupner grey prop, a bit marginal for take off from the long grass on our strip but more than adequate airborne but not the 1500 feet per minute climb claimed for the prototype, iirc.
I have a spare OS 52 Surpass but really can't be bothered to change it until the 40 is properly run in to ascertain if things improve.