Zor

Hello everyone,

I have a question and do not know where I should ask.
I think I have done a fair amount of time looking for location or for an answer (about 3 hours).

I am building a Spectra electric powered sailplane.
It comes in the kit witha S600 goldfire brushed motor.and a supplied 8 x4 prop.

It is designed to land on grass on its belly (no landing gear).
I figure that the prop should be horizontal on landing.

The question is ___
Is there a way (method) of making this motor always stop so the prop would be horizontal.

The motor shaft DOES NOT have a flat on it so I want to make a flat so the setscrew has a proper place to be tightend on and little risk of the prop sliding off if the setscrew gets a bit loose (although well tightened initially).

I made some tests and that type of motor seem to stop in many orientations with the prop hitting the ground first.

Many thanks for any comments based on your experience.
I am new to electric propulsion.

Zor

TIA

Usually if you land on grass the blades of grass will move the prop blades out of the way while hitting them.

I always carry a few extra blades with me just incase. They do not break that often.

If you wanted to you could put a set of folders on it and never have to worry about it again.

I see no way to have the prop stop in one place everytime, although, at times I have looked at the prop while on approach and given a small blip once or twice while in the air just before landing to get the prop in a position that looked a little better than 12 and 6 o'clock.

Hope that helps.

Zor

Hello TIA

Thanks for that quick response.

Your last paragraph is the most helpfull.

I may consider installing a very light weight landing gear.

Thanks again for your nice reply.

Zor

da Rock

Consider that the manufacturer and the retailers of your model did not mention anything about the problem you think should be considered.

They aren't lax in that at all. They don't mention it because almost nobody has a problem. Twice a week, almost every week of the year, one of my flying fields has a bunch of retired guys who get together to fly. At least half those old boys fly electrics. All of them have at least one that lands on it's belly with an exposed prop. I frankly can't remember any prop breaking in the last year. (But then again, keep in mind my age.....

I flew a Siren for a year with either a folder or regular 2 blader. I swapped them often, trying to see if I could actually see any value in the folder. Truth is, I never considered that the 2 blader would give problems landing, especially after the first couple of landings. The brushless motors I've used in the last couple of years don't even stop the blade from windmilling in flight. They don't hold the blades anywhere close to rigid on landings. Never even skinned a blade. And since they usually came down slowly windmilling, they were almost guaranteed of a ground strike.

I believe you will discover there is nothing to worry about.

da Rock

You might also consider a "stand off" instead. Much lighter and much less drag.

They are easily made with a short piece of piano wire. One piece that projects down and slightly aft from the nose. That's it.

Or you could have two pieces projecting down and aft. They would be attached at the nose but separate out in an inverted "V". They would then also give some protection to the wingtips. All of them need only be long enough to maintain prop clearance on landing. In fact, they would work just as well if they only were half long enough for perfect clearance, as you will discover after using them awhile.

The model would still need to be hand launched of course.

BMatthews

This issue is why folding props are so popular on electric gliders. They not only reduce the drag in the air when folded but they also pretty much eliminate any worries at landing time provided you flare it so the nose doesn't dig in.

Brushed motors are officially passe'. Ditch that thing and buy a brushless outrunner package. A brushless of the same power as that kit motor is about a third to half the weight of the old can stuff. And these days you can get the budget motors, ESC's and lipo batteries for cheap. Places such as Hobby King will keep the added hit on your wallet to just a light bruise with no lasting scar. With the new motors and Lipo packs it is now possible to build electric gliders that are as light or sometimes even lighter than the old pure gliders. There's no longer a big weight penalty like there was back in the brushed motor days.

For a 2 meter such as the Spectra you'll want a motor with a max rated wattage of around 180 to 200. The model will likely come in at around 30 to 32 oz with the new brushless motor and related items. So you really won't need to run the motor at more than around 150 to 160 watts. The difference in what you prop the motor to draw and the max rating will just aid it in running a bit cooler and give it a longer life. The Kv value is sort of like the "gear ratio". It stands for thousands of rpm per volt. Hence the K (kilo) and v (volt). For a glider that benefits from using a bigger prop you want to get a motor with a lower Kv of around 900 to 1200 so it'll spin a prop of somewhere between 10 to 13 inches diameter and a pitch of 4 to 6 inches. The higher the Kv and the more cells in the Lipo pack the smaller the prop has to be in order to avoid forcing the motor to draw too much current and burn itself out. If you read the comments on most motors there is a list of props to use with 2S and 3S packs. The 3S packs require smaller props because of the extra voltage.

MaxAdventure

My Feedback: (7)

I fully agree with the wisdom that BMatthews posts, in addition;

Every decent brushless controller I've used has a brake option, and with the brake programmed there will be no windmilling.

The best props I've ever used have been Aeronaut and Graupner - they make some really efficient folding props and hardware. When I first changed to my Aeronaut, I saw a faster climb to altitude and less amp draw than the APC. It was well worth the cost.

*as a crazy side note, you can get a device to stop the motor with the prop horizontal. It's for ornithopters to hold the wings in glide mode. It's easier, cheaper, lighter to just go with a folding prop* ;-)

Zor

BMatthews, da Rock and TIA,

Thank you guys for your kind and very informative postings.

It is reassurance to read your valuable experience in this domain.

I wanted something to build and was fascinated by fellows at the flying field laying down on a lounging chair and flying their sailplane.

It was funny when a fellow laying on his chair in the shade was shaken up by a friend yelling "Hey wake up before your plane lands in the trees" .

This Spectra was the only electric sailplane at the LHS so I figure I could have fun by experimenting with it. I already was thinking of switching to an outrunner with rpm control and lipos. I will "fool around" with it first as it came and spend more money later.

I have an answer ready if someone asks me "What do you want for Xmas" __Hee ___ Hee !!!

I was going to buy a folding prop but the LHS does not carry them anymore. He is trying to get rid of all the kits he has left. Thus he gave me a good bargain I did not expect.

I am just about 60 to 70% done in the build and took quite a few pictures..

Building without rushing is so relaxing. I enjoy it a lot.

Thanks again fellows for the response. I really wondered where to make a posting with my question.

With the Santa Claus parade this comng Saturday and Sunday I think I am not too early to wish you an enjoyable Holiday Season.

Zor

MaxAdventure

My Feedback: (7)

Take a look at a great Canadian source for sailplanes and accessories: http://www.icare-rc.com/propellers_folding.htm
good choices of folding props

Zor

MaxAdventure,

Thanks for your posting also. We were typing at the same time I think.

I just read your posting as I was checking my last post.

I now feel much better about the risks of prop breakage. i already bought the only 8 x 4 prop the LHShad which is what came with the kit.

Best regards and thanks from . . .

Zor

BMatthews

An 8x4 on a brushed motor implies that it is a direct drive. Don't be surprised when the model barely "glides uphill". Those motors on direct drive did not have a lot going for them when it came to lifting a glider.

TIA

I think a Power 10 or 15 and a 3S lipo would be perfect for that plane.

Nor Cal Mikie

My Feedback: (3)

Rather than spend more $$ on a "brushless" motor and all the related gear mentioned, get yourself a folding prop. Folds back on landing and when the motor is turned off in flight. Get to know how the plane flys and handles before you really get hooked and want the "big stuff". Had more fun and air time with a Speed 600 and a folder on a Dynaflite modified Wanderer. You can always go bigger. And you will!

Zor

Hi Nor Cal Mikie,

That is basically what I wrote I would doin post #8.
I am certainly not expecting any kind of "super performance".

At this moment I have to build a new fin.
I got caught by a pint of Sig dope that is not tautening and the container and label is not labelled to show that.

Zor

Zor

Just wish to say thank you to all that helped.

Zor