Discussion Blade Questions

[Aerofreak]

Hi Guys,

I recently got some 70 mm chord Aerobalsa blades and have some questions on them:

- I read a few posts on the issues of (chordwise) blade balancing, what is the consequence if it not properly balanced?
- On the Aerobalsa site I could not find any hints or tips on making & installing the root plate (reinforment where the bolt sits) for the blades, any pointers?
- Anyone have some info on glassing the blades (pros, cons & maybe a procedure)


TIA

Jim

[Boneswamped]

Hello Jim,
- You could indeed glass the blades if you liked, and the process isn't terribly difficult if you can vacumn bag, but the benifit in my opinion is almost zero over a standard covered set. If the blades were all glass without a balsa core they may be lighter. Bill Friedlander did extensive testing of glass blades, and wind tunnel testing several years ago(you might try forum and internet searches to find the info). You can count on the need to replace a few sets of blades if you are learning to fly Autogyro's (forgive me, I'm not sure of your autogyro experience).
-Simply put without all the technobabble, if not properly chord balanced the blades will "Hunt" or try to pitch up or down differently because of improper c.g.

I'm with Jim on the AB blade finishing concerns. I've got two sets (small I bought to build a minimum, and larger for the RPG size) lying around I want to finish and try. Joe or Rich ; could you guys take a few photos of your blade process and set up for the AB blades? Particularly the setup that worked on the Profile. Is there a difference between the Profile, and RPG AB blade setup? I wouldn't think so I intend to test the larger AB blades on the Profile I just built.

Thanks in advance for any input guys,
-Mike

[SafeLandings]

Mike,
The Aerobalsa blades work well on my profile (2 3/8" wide ones)...the only thing I have found is that they do not like to be flown fast as it does strange things. For flying slow, hovering about they work excellent, you will find that you dont need to use as much power.

I have used the same 3 blades on my Kellet and my RPG ..youve seen the videos but here thay are again.

Kellet Profile tail hanging! (3 min 57 sec)

Rpg fitted with Aerobalsa blades (3 min 30 sec)

The 3 blades are just coated in balsloc, adding different amounts to suit the balancing process then covered in film. The Aerobalsa blades are very close if not perfectly balanced.
As for balancing here are a few photos of how I do them, it is the same for any of my blades. Try to get them to balance within 1/8" across the span. Cordwise balnce is only done to find the position of the mount hole, I like to have a bit of nose down attidude with mine.

You will find the Aerobalsa blades are very different to the stock blades, the gyro will become more sensitive to roll and pitch control.They just have to be set up to suit your needs at the field.
I wouldnt recommend using them for a begginer but Ive seen your flying Mike and you will be fine as you know how things feel with an autogyro.

Hope this helps


Regards Rich

[Aerofreak]

Hi guys,

Thanks for the answers.
Basically I have zero Gyro experience but want to try these blades for a VTOL model.

Rich, do you have more details such as material and build tips on the blade reinforcement pieces (extra material around the mount hole).

For now I will stick with simple covering but still have no idea on the mount hole pieces.

TIA,

Jim

[britinoz]

G Day JIm
In your question you ask specifically about mounting the blades and how to reinforce the area.
I have found that just bolting the assembly together only causes the blade to compress after a short time.
I hope this quickly taken pic may make sense to you.
I use a sharpened piece of K&S brass tube to remove a plug of Balse ,where the bolt will be fitted. I then cut a piece of hard wood dowel to the same thickness as the blade.The piece of dowel is then stuck in place in the blade between the two outer pieces of .4 mm ply When dry ,simply drill a hole the size of the bolt you will use. Works for me
Happy Landings
Chris

[Aerofreak]

Hi Chris,

Thanks for posting a solution.
I have read your post a number of times, the point about the dowel I understand.
But the last part was not really clear to me so I assumed you used two pieces of 0.4 mm ply which you glued on the blade?
I also assume because of the dowel installation the two harder pieces of ply are not able squeeze the balsa once the nut is tightened?

Jim

[Hephaistos]

Hello Jim.........

I just wrapped the roots of the blades with epoxy and a carbon-fiber-tape with a width of 50 mm. Three layers made about 0,6 mm of CF. Wet-pressing with spongy foam helps to get the useless epoxy out of the laminate. Its really strong, the blades may break, but never directly at the root-reinforcement........

Bye
Mike

[britinoz]

G Day JIM
Sorry I did not make my self clear on this matter.The dowel is sandwiched between the two outer skins of .4/.8mm ply on the hub.I lay it up in one operation using PVA.
I use squares of ply that are oversize ,well clamped overnight.and then trim to size the next day.Drill all the holes to the same position .The blade may break somewhere,but the hub will not fail.
Happy Landings
Chris...........

[Aerofreak]

Hi Guys,

It all clear to me now, I now have to something to work with.

Thanks!

Jim

[Boneswamped]

Here's the procedure that worked on my AB blades:

-I matched all the blades at each step of the building process to ensure they were identical in weight.

-I strengthened the trailing edges per Mike Smith's website

-The span balance is exact on all three

-The chord balance is at 25% M.A.C.

- I selected the mounting posistion a bit differently than what I understand Rich to have said above. Instead of placing the mounting hole at the chord balance point.....I place the mounting hole in the spot that will allow the blades to hang perpandicular to the floor when suspended vertically.

-All three blades are exactly 46 grams ready to mount(that is as accurate as my scale gets).

There is a very distinct improvement in lift with the AB blades, and as a result the settings used with other type blades will need to be adjusted slightly for success. i.e hang angle, trims and control throws since AB blades are much more responsive. I prefer very responsive aircraft, I don't use expo, or dual rates those functions are built into my thumbs.

I did note one issue with the AB blades, and that was at high speed there was a tendancy to flutter slightly resulting in uncommanded pitch/roll/and yaw excursions of about 5 to 6 deg depending on the speed, and severity of the manuever being attempted. I believe this can be resolved by stiffening the trailing edge with carbon fiber or other means. The easiest resolution is to reduce throttle. Just my opinion though.

There's absolutely nothing wrong with homebuilt blades, but for me personally, I'll be purchasing (incredibly reasonable priced) AB blades to save my free time for flying.

Regards,
-Mike