J&H Firefeather build

[TheAviator]

And it noses down sharply on a turn.

Sounds like you're trying to fly too slowly and doing a mild tip stall on turn entry. Don't be afraid to put the nose down a little.

I went back and saw that your glide mass is somewhere in the 140 grams range. That's definitely going to want to glide faster than you think.

From there I start to toss discus style - but just an arm sweep, not the spin and hop dance to put real energy into it. Again, if I tossed low, I could get a short, straight flat glide, but I haven't mastered the transition out of an arc at the top of an upward aimed throw. It would stall and dive, and full elevator wouldn't pull it out in the 20-30' of altitude it had. I didn't ever throw it into the ground, but 2, including the last, went a bit squirrely with a roll.

Yeah, the trick with a discus launch is that you want to push the nose over when you still have enough kinetic energy to maintain level flight. As scary as it seems, if you can't do that, you need to throw harder. Also, with a discus launch, you want to hold a momentary switch to pop the elevator up as you throw with the nose level. This rotates the plane nose up after release. When the nose gets to the attitude you want, you release the switch. If you're a right-handed thrower, it should be on the upper left corner of the Tx and vice versa. Last time I had a Spektrum transmitter I used the trainer button for this purpose.

I -really- wish that Joshua had a build version without the electric prop that calls out where the blasted thing is supposed to balance as a straight up DLG glider (not a DLG 'hotliner') and as a rocket boosted glider. With noseweight and a C3 in it, mine balances at the front of the aileron servo cutouts. That seems a little aft compared to the build video - and seems to be at about the 1/3 chord that people talk about. It seems reasonable - but I'm starting to think it's not right for this glider.

If it doesn't feel right, don't be afraid to move the CG forward. I fly farther forward CG than a lot of people that fly performance sailplanes and I do just fine. It's as much a matter of personal preference as anything else.

 

[Charles_McG]

Sounds like you're trying to fly too slowly and doing a mild tip stall on turn entry. Don't be afraid to put the nose down a little.

I went back and saw that your glide mass is somewhere in the 140 grams range. That's definitely going to want to glide faster than you think.



Yeah, the trick with a discus launch is that you want to push the nose over when you still have enough kinetic energy to maintain level flight. As scary as it seems, if you can't do that, you need to throw harder. Also, with a discus launch, you want to hold a momentary switch to pop the elevator up as you throw with the nose level. This rotates the plane nose up after release. When the nose gets to the attitude you want, you release the switch. If you're a right-handed thrower, it should be on the upper left corner of the Tx and vice versa. Last time I had a Spektrum transmitter I used the trainer button for this purpose.



If it doesn't feel right, don't be afraid to move the CG forward. I fly farther forward CG than a lot of people that fly performance sailplanes and I do just fine. It's as much a matter of personal preference as anything else.

Thanks for the tips.

 

[Paul Howard]

My 2 Centavos: As an RC Glider builder/flyer, if the air is clean and not too breezy, I like my CG little farther back for floatiness and quicker reactions to the stick to maximize catching and flying thermals, but if it's more turbulent out or breezier (usually the case) and I'm going to get daring and go "Tree Surfing" (sloping on the uplift over a row of trees at the edge), I'll add ballast at the CG point and weight in the nose to move the CG a little forward for less reactivity, more speed and resistance to turbulent air.

Carrying that over to a rocket boosted glider that I simply want to glide "nice" and not worried about maximizing gliding performance but more concerned with boosting well and under control, I agree with Charles about moving the CG forward a little, being used to a faster moving glide and keeping enough airflow over the wings and control surfaces.

Just curious, Did you build any "Washout" into your wing tips? I always "build it in" with improvised small jigs or wedges but you can induce it with heat before covering or even with heat after covering but then you have to keep checking it and re-heating and re-warping it into your wing tips. A little bit of washout really helps prevent tip-stalling in tighter or slower turns.

Cool little Glider you have there!!!

Hopefully that all makes sense -Paul

 

[Charles_McG]

Thanks for the thoughts.

For my next run in the neighborhood park, I've taken out the noseweight. I want to see how it handles as built. Well, kind of as built, since the Joshua never shows it in glider mode. I want to see how it handles like that. I'm still concerned that I couldn't pull the nose up. Then I'll work on speed.

And maybe I'll get something less fragile to practice with.

 

[Ez2cDave]

I went back and saw that your glide mass is somewhere in the 140 grams range. That's definitely going to want to glide faster than you think.

GLIDE SPEED FORMULA . . . ( No, I don't remember the source . . . It was sent to me about 30 years ago. )

GLIDE SPEED is in MPH ( miles per hour ).

 

[Ez2cDave]

I went back and saw that your glide mass is somewhere in the 140 grams range. That's definitely going to want to glide faster than you think.

Brian,

Knowing you and your line of work, here is something a little more "mathy" for you . . . LOL !

https://academicflight.com/articles/gliding-flight/straight-gliding-flight

Dave F.

 

[Charles_McG]

I’m putting this Firefeather on the shelf. It’s too fragile for my lack of skill. I can’t even toss it straight in the backyard like any non-RC glider I’ve built - and keep it one piece. All the repaired breaks rebroke - and the tail did this in a few gentle tosses landing on grass.

I loved building it. But I can’t fly it.

 

[Charles_McG]

Also, if I ever try another Firefeather, it will get Michigan Tech colors, since my boy didn’t last too long at UW Platteville.

 

[Crawf56]

I know the feeling...

I did a build thread on a Red Shift II rocket glider from J&H:
https://www.rocketryforum.com/threads/red-shift-ii-rg-from-arkansas-j-h-aerospace.158917/page-5

I really liked the design.......but I could not get it to fly right. The Red Shift is a similar animal to your Fire Feather.

And I have had other J&H designs that flew fantastic. But sometimes it just doesn't work out.

 

[burkefj]

GLIDE SPEED FORMULA . . . ( No, I don't remember the source . . . It was sent to me about 30 years ago. )

View attachment 576846

Glide speed in what units?

 

[kjohnson]

Glide speed in what units?

Well, grams/cm^2 of course.

 

[Charles_McG]

Well, grams/cm^2 of course.

I think you mean grams^1/2 / cm

 

[burkefj]

I think you mean grams^1/2 / cm

So furlongs per fortnight

 

[aerostadt]

Pretty simple formula. Doesn't say anything about lift coefficient (and/or camber) or drag coefficient. In any what is the units of the speed? The formula is worthless without it.

 

[Ez2cDave]

Glide speed in what units?

Sorry,

Glide Speed is in MPH.

 

[burkefj]

Interesting, all my RCRG's are in the 5 to maybe 10 oz per square foot range which is .15 to .3 g per square centimeter and have estimated glide speeds in the sub five to seven mile per hour range, which seems about right based on the visual landing speeds, with small 5-10 mph headwinds, zero ground speed...

 

[Ez2cDave]