Minimum airspeed
 

Minimum airspeed

What is the approximate minimum airspeed for a slope glider (100” span, 700sq in, and 5#)? I am attempting unsuccessfully to reach thermal height with power assist since slopes are not available. Achieved two ten-foot thuds today.

Bill

RE: Minimum airspeed
 

If you knew the number, what could you do with it?
There's no way for that number to be related to the airplane when you're not in the airplane reading a gauge.
The plane is telling you it's not happy with what you are doing.
Don't do that any more..
Find out what the plane needs... it sounds like more power.
The airspeed it will fly at will be whatever you can find that it will fly at.

RE: Minimum airspeed
 

And what engine are you using? For a 5 lb airplane (quite heavy so don't expect good light lift performance) I would suggest that you need a .15. Even there you need to learn to let the model come up to a good flying speed and then let it climb uphill without a lot of elevator persuasion.

RE: Minimum airspeed
 

Didn’t build the glider but guess that I am short on power with a 061. Unfortunately the pylon is rear mounted and little clearance exists for a prop larger than 6”.

1. Run faster.
2. Wait until the wind was blowing.
3. Throw it from a small knoll at the house/farm.
4. Find someone with a pick up truck for launch.

Sometimes the wind comes off the pond and up through the chute to the top of the knoll at a good clip. I am guessing the minimum airspeed to be 15 to 20 MPH similar to a glow setup. Will wait until the conditions are better and try again.

Bill

RE: Minimum airspeed
 

Good answers Bill. Gave me a bit of a chuckle.

Somehow you just need to loose about 2 lbs of weight or figure out how to put on a bigger engine. Powered gliders can do amazing things with lower power levels than "regular" models but 5 lbs (60 oz) for an 061 is just stacking the deck far too heavily against the poor engine.

Perhaps something like a 15 but with a cut down wider prop or even a 3 bladed one to get the blade area you need. A 15 generally works with a7 to 8 inch prop. No room even for those options? You would have to cut off the top of the engine pylon anyway to provide the new and larger mount. Build in an extra 1/2 to 3/4 inch of spacing.

RE: Minimum airspeed
 

Like Bruce says, that .061 is merely getting a hernia from trying to fly that thing.
A .15, or possibly a .25 would be more suited to the task.
I have a couple of glow powered 2 meter gliders with .15s.. but these barely get to 2 pounds AUW.
My glow powered 2M photoplanes are just about 4 pounds AUW, with modest performance.

RE: Minimum airspeed
 

I also thought the glider was very heavy. However it appears to be factory glassed with very little user construction. The wing is marked Aerofly. I have a 10 and a 15 engine but the engine goes behind the CG (rear pylon), which means more lead in the front.

Maybe in the next few days I can catch the wind coming up the chute at 10 to 12 MPH and get it to glide a few hundred feet. After seeing a few glides the changes might become clear. Sorry but not much is known about gliders at my end.

Thanks for the information.

Bill

RE: Minimum airspeed
 

Bill, is this the one?

http://www.hobby-lobby.com/images/hlan1329sm.jpg

I found that at the Hobby Lobby site but it's shown as no longer being available. If your example came out at 5 lbs then it's a small wonder.

If you wish to persue your motorized soaring I would suggest you cut your losses and get a better (as in lighter) model for your 061 that has a lower wing loading. I suspect it would be a lot less frustating.

A Spirit 2 meter with that engine on the nose would be great for example.

RE: Minimum airspeed
 

Hi-- I've been following your delema. Sorry but if I'm thinking right 5 pounds would be 80 ounces not 60. You can figure at 700 sq. in. divided by 144 sq. in. (1 sq. ft.) you have 4.8 sq. feet of wing area and if you divide 4.8 sq. ft. into 80 oz. you have a wing loading of 16.6 oz. per sq. ft. That is a lot of loading -- way to much for your engine. Have you thought about dropping the engine and using a wench or heavy duty hi-start? When you said you had a few thud landings (if they were flat thuds--not nose sticking in) that will tell you that you were not even close to the air speed it will need. I if it were me I would check the wing to stab incedence and the CG to make sure there right and make sure everything is square and straight. I would also take it out to a grassy field with about a 10 mph wind (no engine running) and throw it level at the horizon and find how hard I needed to throw it to get at least a 20 yard glide with a smooth landing. With a 10 mph wind, throwing straight into the wind, you will already have 10 mph air speed before you even throw it. Oh make sure the CG is a little nose heavy - you don't want to stall it that low. Well that's what I'd do before trying a hill or high up throw - there are usually turbulances coming up those places.
Good Luck - Hope this helped [8D]

RE: Minimum airspeed
 

Yes that’s the airplane.

You are correct about lighter but … I don’t build worth a hoot and it seriously limits my choices. Often and in this case airplanes are handed down knowing I will fret and redesign until successful.

Now that I have tackled the airplane it must fly. Compulsive or something … and I am too old for therapy.

You have helped understand the design requirements. Thanks a bunch.

Bill

RE: Minimum airspeed
 

Both were flat thuds. It was dead calm and I was not running very fast, throwing left-handed and the ground was flat. Didn’t know enough about slope gliders.

I like your suggestion. Up from the pond there is a 30 to 40 ft knoll and the lay of the land directs the wind up the chute at a reasonable speed when the direction is correct.

I removed the servo tray and epoxy on the servo rails is curing now. Tomorrow I will examine and run the engine, which did not seem to be turning very hard. Today it was learned that the engine was a Norvel. In haste the engine was not tacked.

Bill

RE: Minimum airspeed
 

You're right. My snap n' grab multiplication was way out.

At 80 oz and over 16oz/sq ft we have your basic non soaring glider here. Some of the big name hot shot pilots may be able to make it go up in a thermal but it's not going to be easy by any means.

Bill, even if you don't build at all there's far more thermal friendly RTF's out there. Almost anything in the 72 inch to 2 meter lineup intended for the smaller electric motors will adapt nicely to your 061.

For example if you were to get something like this Omega electric and put your 061 in the nose you would have a model that would probably climb at a 30 degree angle or more. Launching would entail a light push even in no wind conditions and this model would soar on a whisper. The engine on performance would be such that you could pull off a few fast passes, loops rolls and big smooth chandelles before using the last minute of the fuel to get up to a good thermal finding height.

This particular one I found is from Northeast Sailplanes. There's others there. This is just an example of what you could find that would fly so much better than that super heavy Aerofly.
http://www.nesail.com/detail.php?productID=130

http://www.nesail.com/pictures/omegae1.jpg

RE: Minimum airspeed
 

A more accurate weight is as follows:
1# 7.7oz both wings
2# 4.6oz Fuselage with servos and receiver
14.1oz battery and balance weight
------------
4# 10.4oz all up weight

Tacked the 061 engine and it will hold 11,500 RPM with a 7-4 prop cut to 6” diameter. Seems the engine should turn faster.

Wind was up and did a test glide and it sure is fast. Also hit the only tree available. Need a launch helper.

Bill

RE: Minimum airspeed
 

Too much prop. Try a 6X3, or even a 5X3 or 5X4. On 25% nitro with 1 head shim, you should be getting 18K or so at least.

RE: Minimum airspeed
 

Those add up to 29'ish ounces. If it truly is that light then the 061 should take it up in fine style.

RE: Minimum airspeed
 

Maybe I typed the information in an unclear way.

4# 10.4oz = 74.4oz or about 6oz shy of the original guess/estimate while laying parts on it while hanging in the balance cradle. The servo tray was removed and the weight was compacted to the front of the airplane. She is still a fat girl.

After this morning’s glide the minimum flight speed is guessed to be in excess of 15MPH.

Bill

RE: Minimum airspeed
 

Hi: Bill
Saw your last post and that is what I was afraid it might end up being. I was thinking 15 to 20 mph. I get the part about " I'll make it work ", I'm that way myself. But as time and planes have come and gone I have realized to say pass easier now. If you want to have fun thermaling and enjoy a good plane take the others advice and bight the bullet. If you want to get a idea of what your up aginst get in your car and drive down a road at 20 mph for 15 or 20 seconds and see how far you have gone. Now think of that plane trying to stay with a thermal for that time and distance. [X(] Flying sailplanes is really rewarding and you will probably find it relaxing as long as you don't have to fight a plane. Good Luck!

RE: Minimum airspeed
 

Well, if the whole model ready to fly weighs 74 oz then it's way too heavy for the 061. Those numbers you gave a couple of posts back don't make any sense at all then. WHere is the weight?

1# 7.7oz both wings
2# 4.6oz Fuselage with servos and receiver
14.1oz battery and balance weight

Ohhhhhh... now I see The 1# is one POUND 7.7 oz for the wings.

I haven't seen the # sign used to indicate pounds for years. My mistake.

I way burn that Aerofly as the abomination it is :D Nothing should be that heavy and expect to fly thermals. I don't know what it would fly like on the slope but at that weight I would think it would still be a mushy and heavy feeling performer. I hate to say bad things about any model but this one sounds like it's just way over the top.

RE: Minimum airspeed
 

May I get some advice and guidance on prop sizes for a 09 Enya? The LHS doesn’t stock pusher props making a normally simple issue more difficult.

Bench running the 09 with an 8-4 prop (tractor for testing) gives only 9500 RPM, which seems way too low. I found only two makes of pusher props, Graupner and Tornado and the selection was limited. Must be looking in the wrong place.

What prop size would you suggest? Where is a good source of supply for pusher props?

Thanks.

Bill

RE: Minimum airspeed
 

7x4 or 7x5. But in truth the Enya is not a very powerful engine. I used one with an old Topflite white nylon 8x4 and it worked well but those old props had a reputation for running flatter in pitch than the numbers said.

Pusher props are always a pain to get. But check the APC and Master websites for what they have.

Given the weight of the Aerofly and the fact that it doesn't use a high tech airfoil to let you at least take advantage of the speed that would normally come from such a heavy wing loading I can't help but think that you would be best off to move on to another model.

Or at least modify the Aerofly to a nose mounted engine so you can loose a heap of the nose ballast. Things may perk up enough to let you get some decent air time that way.

RE: Minimum airspeed
 

BMatthews,

Your advice has been good and it is appreciated. There is no illusion that the glider will ever thermal or even fly well. The objective is to simply put it in the air, to learn about small engines and gliders and have fun with the design modifications. Maybe along the way enough will be learned about gliders to decide on a project that might thermal.

An incremental approach is being taken pursuing the smallest/quickest issues first. A week ago I didn’t know what a Norvel engine was or how difficult pusher props were to find. I intend to get both engines running at a respectable RPM and then to attempt flight with the Norvel. I don’t expect to be successful. If unsuccessful the 09 engine will be substituted with another attempt at flight. If unsuccessful it will be decision time about a larger engine size or front mounting. If anything is learned and I have a good time the project will be considered a success.

Thanks again. Along the way more questions will come up.

Bill

RE: Minimum airspeed
 

Jim 2,

Almost no one understands why it is imperative to pursue all approaches until it works. It is both a blessing and a curse causing the successes to be great and the failures to be bad.

Probably the airplane was intended to be flown from the California cliffs bordering the Pacific Ocean. A Mac truck could be thrown off the cliff and thermaled back to the top.

Bill

RE: Minimum airspeed
 

Hi All,
My Bro bought me an Aerofly for Christmas. I sent it off to a pal to build and maiden for me and as I type it hasn't flown. It is now here in Calif with me. I found this thread by accident looking for a fast, strong sailplane after totaling my Omei. My Aerofly is brushless and about 5 lbs also. The testing by my pal always resulted in a tip stall. I'm a bit saddened by the news it doesn't fly well and have that same curse as Bill that I just want the barned thing to fly. I have a hellacious investment in it so far and would hate to just drop it off the side off a mountain and call it a day. I have some small repairs to make caused by shipping and then my usual chickening out of a maiden flight so it will be a while before she goes up but I will post here the results, good or bad.
Thanks for all the insight.
Oh. I added ailerons to the beast. Might help.

RE: Minimum airspeed
 

Lou, you may want to ensure you use lots of up aileron differential to help avoid tip stalls. And be sure to use minimal aileron if flying near stall and close to the ground.

Good luck to both of you. I understand Bill's efforts to learn as much as possible. Sometimes the journey is where the fun is.

RE: Minimum airspeed
 

Thanks Bruce. I'll be sure to do that. Fortunately I have a large farm to fly over. Reimburse the farmer for the sheared crops and all is well.
Lou