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Apr 18, 2017, 07:25 PM
Registered User
Help!

Batman Plane


I saw a really neat batman plane at the electric fly-in in Akron (NEF) a few weeks ago (see attached BLACK picture). Can't remember the name of the guy who built it to give him credit for it, or to ask for help! If you read this, I'd sure appreciate your help!

Took a few camera shots of his plane, and tried to duplicate it (see attached WHITE picture). Failed miserably.

Very unstable in pitch. Upon hand launch, it just goes nose up, flips over, and flops.

Tried to reduce the slight reflex in the elevons a bit at a time. Could eventually get it to nose dive on launch, but not to fly! No happy medium between climbing and diving.

Wondering if the longitudinal axis is too short?

MY plane is 32 inch wingspan, and only 22 inches long from the carbon fiber bow in the front to the end of the tail. Don't have dimensions on the black plane.

I know people have built plenty of "roundish" planes over the years, but I'm not aware of an "oval" plane, especially one that flies w/ the short axis longitudinally.

My COG is at about 20% of the wingspan with the lipo right up against the back of the fire wall. Difficult to get it any farther forward w/o adding weights. Easy to move COG back, but I don't see a reason to right now.

Suggestions would be welcome....

Thanks!

Steve
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Apr 18, 2017, 09:10 PM
Registered User
There are other "bat" planes with a similar shape.

https://www.rcgroups.com/forums/show...n#post19701242

I blew up the picture of the black plane and do not see any hinge lines even though I can see the bottom of the control horns. Was it an elevon plane and not some weird wing-flex thing? Also. the original has a KFm type plate which might shift the weight forward somewhat. It also appears your plane has the electronics on top but the original looks like they are on the bottom (hard to be sure by the pictures). It is usually better to hang the weight (electronics) below the wing than to balance it on top: although that is rough on the electronics when landing.

I suspect the CG is very unforgiving in a plane like this and probably needs to be spot on. Maybe find a field of tall grass and try some glide tests to find the CG. Good luck.
Apr 19, 2017, 06:03 AM
Registered User
Snuffleupagus's Avatar
crispy1074 has 2 design variations of the batwing in several sizes on his website http://foamconceptjets.com one of which is the circular batman symbol design. He also has videos of builds and flights of those designs on his youtube channels (https://www.youtube.com/user/chrisallen1074 and https://www.youtube.com/channel/UCnC...41fa0TPTZPqxkQ). Perhaps you can watch some of the videos on his build to find answers to some of your questions. They are very detailed. Or contact him directly to see if he has any advice. Good luck.
Apr 19, 2017, 10:46 AM
I Look, Listen, and Learn
Timbo383's Avatar
From my phone it looks like his side wing verticle stabs, or whatever you call them(there is a name for them but it's beyond me) are more forward to the front then yours....even tho it doesnt make sense to me, maybe it flew better that way. Also, did you ask how well his flew?
Last edited by Timbo383; Apr 19, 2017 at 04:41 PM.
Apr 19, 2017, 02:54 PM
flyin' fool
goldguy's Avatar
Sounds like a CG issue.
Apr 19, 2017, 05:50 PM
I Look, Listen, and Learn
Timbo383's Avatar
You could get a cheap dtf or elmers foam board and leave the paper on for stiffness and make a 15 - 20 inch ws chuck glider version of this and play with the cg and/or design...I'm visualizing it with dual f-22 style verticals.... of the plane. Be better than to continue crashing this one.
Apr 20, 2017, 03:27 AM
Registered User
Have you done a power-off glide test?
If that doesn't go well there's almost no chance a powered flight will.
If you're not sure what I mean by "glide test", do a search on this site - there are probably at least a dozen threads that describe it.
Apr 20, 2017, 09:12 AM
Ft Lauderdale
Number_6's Avatar
Glide test good way for sure if you don't have/trust
published CG position from somebodies plans.

I used Foam Concept Jets pdf plans for F117 and
have the Bat Wing on the bench now....his F117 CG
location was good at maiden flight so will
go with his published CG for the Bat Wing.

I used Elmer's black foam board.

Apr 20, 2017, 10:34 AM
Registered User
Thanks for the advice.

Tried a glide test -- miserable. NEVER had something this bad! Just will not glide!

Next step is to put some weight forward in an attempt to get the CG even more forward.

The black version DOES have elevons, and seemed to fly well in the dome. The hinge line is just "invisible"in the photo. Here is a bottom view that shows it a bit better.

You are correct -- his electronics are on the BOTTOM whereas mine are on top (for protection).

Note also that his SERVO's are waaaay back -- more tail weight!

Appreciate the comments -- will keep trying!


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