Aifoils for electric gliders

[davidleitch]

Um posting this in thermal forum because there are more glider flyers than electric glider flyers especially for 3 metre F3J, F3B and open thermal style planes.

Electric glider power systems for 3 metre gliders using lipo batteries can produce winch style power for a weight penalty of around 15-20 oz (430-580 g).

Moder F3J style gliders have unpowered, unballasted weights of around 65-70 oz (1850 -1990 g)

F3B unballasted gliders are at 76 oz.

So adding the power system increases all up weight by 25-30%

A quote from Mark Drela in these forums a couple of years ago stated:

You're not completely off. If you're talking about a specific airfoil, then yes, performance will start to suffer if you go too light and go well below the airfoil's intended Reynolds number. For example, the MH32 works best at around 100 oz weight (assuming typical 3m glider aspect ratio). As you reduce the weight and the Reynolds number, the tips will start to suffer first. Things are still sorta OK at 70 oz. But on my 48 oz Supra, using the MH32 on the narrow tips would be a disaster. Instead, it has DLG-type airfoils out there. The center airfoil is closer to an MH32. This lets the wing tolerate extremely low weights without excessive L/D loss.

So for an electric glider is MH 32 the best way to go, or one of the more modern airfoils such as the AG series or the HN series?

I already know that something like the AVA gives good thermal performance but my heart desires a moulded aileron plane that is capable of thermalling in light lift and yet is capable of hot dogging around the plance when the mood strikes.

[EricSoar]

I don't think that electric gliders need to be any heavier!

The reason is that pure gliders need a really strong fuselage and wing to handle wing launches. With electrics you take strength and weight out of fuselage and wing structure and add it back as an on board power system.

An open structure model like an Organic 2.5 metre (MH32), Pulsar 2.5E/Bingo 2.5 metre (RG15), or built up wing Graphite F3J 3 metre (MH32) meet these citeria. The wings are fast sections yet very light. If you fly in some wind (as I usually do), these models would be too light without the power system.

Take the Multipex Easy Glider (foamy) 2 metre. Where I live, the electric is a better thermal glider than the pure glider because the pure glider wing loading is too low and won't penetrate much breeze at all.

I think that a wing loading of 9 to 11 oz/sqft for a 2.5 to 3 metre electric glider, with a fastish section, will give you what you want. That kind of wing loading is not hard to achieve with Lipos.

Eric.

[Tuomo]

An open structure model like an Organic 2.5 metre (MH32), Pulsar 2.5E/Bingo 2.5 metre (RG15), or built up wing Graphite F3J 3 metre (MH32) meet these citeria. The wings are fast sections yet very light. If you in some wind (as I usually do), these models would be too light without the power system.


Originally MH32 was developed for pylon racing and it has done very well also in F3B and J. The problem with it is, however, that it needs plenty of ballast fo be fast. More modern (contemporary) F3B/J airfoils have wider flight enevelope from floating mode to speed with light wing loading.

For an example, unballasted D-box Graphithe glider is hopelessly slow for efficient thermalling. That is why it is not seen in F3J competitions.

Maybe the D-box approach is best in 2.5m electric glider.

However, in larger 3m+ size I would look for a reasonably light moldie. From the MH32 planes I have very good experience with Tragi 705. If flyes inherently well and its thermal performance is reasonable up to 3kg AUW.

My 705 E with 10xGP2200 weights around 2.6-2.7kg. It thermals beatifully and the added weight (compared to a glider) can only be felt in landings and weak thermals. (I also ballast the glider 705 to about 2.5kg in windy weather).

Now there is Super Light wing struture and a 3.5m wing available to 705 (that is 705 Plus). Both are very nice refinements a proven design. With a lipo setup one can thus have a 3.5m H32 below 2.5kg AUW. (I have 705 Plus wing on order.)

Looking at the specs (somawhat MH-32 like airfoil, plenty of wing area, light weight), Pike Perfect would also make a very good electric conversion??

Or how about electrified Mibo Shadow or Padzerka Aspire? Both are large moldies with rather spacious fuselages (for a glider). They have faster airfoils but perhaps the added span can compensate that?

[Wing-span]

The MH-32 section on the Tragi 705 is actually modified. The designers have thinned the section which effectively gives the airfoil a 'modern' twist. Fast when needed but when you apply camber changes with wide flaps the airfoil will behave very differently. The original full thickness section did'nt react like this.

[rdwoebke]

I agree with Eric. Electric sailplanes tend to have a bit easier landing task (due to the motor in the nose that could be damaged) and don't require as strong of a spar.

What about perhaps buying the fiberglass (lighter, right) Supra wing, then making your own special made fuselage? Perhaps using the Bubble Dancer boom (a bit lighter) and not using as heavy of a layup on the fuselage. I bet you could have it flying at say 70-80 ounces, where the molded Supra is flying now anyway.

Ryan

[Dbox]

http://www.sport-klemm.de/projekt01/index.php?idcatside=31
Here is the best of the best ,if You lucky to get one. MH-32 comes again.
Yuri.

[tknuutti]

For a floaty e-moldie I think Tuomo's suggestion of going with the latest larger span (3.5-3.7m) planes is a good one. Haven't flown a Shadow or Aspire, but a Perfect is still quite agile and can carry light ballast, 10oz/300gr, without hardly effecting thermal performance at all.

Rumours are Jaro is designing an e-fuse for the Espada RL? That should make a great electric, lightweight with a fast, thin foil.

Using an ESC with a high current BEC (Jazz 80), light motor and 3-4S lipos one could keep the weight increase quite minimal. Only around 250-300 gr of added weight after discarding the typical rx-pack and noseweight ~150-200gr.

[Blaster]

Ryan

Full carbon Supras are flying at 67 oz and lighter. Kyle loaded a Supra with 4 lbs and raced it in Viking races last fall.

We have a electric Supra under development .........more details soon....very soon


Barry

[rdwoebke]

Sounds good Barry. It will be out of my personal budget, but I'll oogle it none the less! :)

So there you go David, Barry and the gang will have a solution for you soon.

Ryan