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Author Topic: What to expect from a retractable landing gear?  (Read 2527 times)

Offline Peter Germann

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What to expect from a retractable landing gear?
« on: November 07, 2016, 06:17:42 AM »
Looking for symmetric behavior (turn rates) I have built "Symmetria", an in-line airplane with a fuselage installed two-leg retractable ldg. gear.

Basic specs are:
683 sq.in / 1'854 Grams (65.4 oz.)
Ample side area fwd. of wing, less behind it
Two gear servos weight: 54 Gr. (1.9 oz)
Hacker A 40 / APC 12 x 6 EP
Governed constant RPM: 9'300 (5.2 sec)
F2B flight (5'20 run time) consumption: 1'850 mAh (Gear up)
Extra consumption when flying F2B schedule with gear locked down: approx. 50 mAh
Flaps hingelines sealed
Motor thrust axis 0 up/down and 1.5 out
Stab incidence: 0
Leadouts 38 mm (1.5 in) behind c.g. (tangential when overhead)

While the airplane functions nicely so far, I'd be very interested to learn from comments on the "in-line / gear-up" concept of "Symmetria"

Thank you

Peter Germann


Offline Peter Germann

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Re: What to expect from a retractable landing gear?
« Reply #1 on: November 07, 2016, 08:22:33 AM »
Makes perfect sense to have retracts. Hats off to you Peter.

Thank you, Ty.

Weights are:
Two ea. e-flite EFLG 101 servos: 52 Gr. (driven from ESC 5 Volts BEC)
Two ea. 1/8" piano wire legs: 16 Gr.
Pair of 2" light wheels: 14 Gr.
Y-cable: 13 Gr.
Hubin FM-9 LG Timer: 4 Gr. heavier than std. FM-9

Total: 99 Gr. (3.5 oz)

No speed up in loops. AND it looks nice, too.
Peter Germann

Offline Robertc

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Re: What to expect from a retractable landing gear?
« Reply #2 on: November 08, 2016, 08:56:14 AM »
I've built three retract planes, all nitro, with two being twins.  Flown with gear down and up. 
To me, the difference was not huge - minor difference.  Gear up seemed a bit more consistent
between inside and outside, but with the gear down, still could fly about the same.
Wow factor was much more noticeable.
With electric, gear up = less drag = less battery usage.   Go back and look at Bob Hunt's twin
postings to get an idea.
Pics - Sheek's Mosquito w/retracts (2) Thunder Tiger 25s
        My own design twin w/ retracts (2) 28s

Offline phil c

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Re: What to expect from a retractable landing gear?
« Reply #3 on: November 09, 2016, 04:58:54 PM »
Retracts are more work, but with electric power it's simpler than glow power.  Just my opinion, but it only really adds a lot to the appearance in the air for WW-II semiscale planes.  They just look odd doing stunts with the gear down.
phil Cartier

Offline Peter Germann

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Re: What to expect from a retractable landing gear?
« Reply #4 on: November 10, 2016, 04:29:06 AM »
....They just look odd doing stunts with the gear down.

It is not so much the admittedly very nice look of "gear up and locked" but more so because, from what I have read here before, the asymmetric gear drag is supposed to be one of the reasons why many F2B designs are not of the in-line type. Consequently, my object was to eliminate suspected detrimental influence on flight characteristics caused by the drag of a fixed landing gear. Which is why I've built "Symmetria" with its retractable gear as in-line airplane. As I have recently flown it back-to-back, due to weather not too many times so far, both ways gear up or down without noticing dramatic differences, I'd be interested to read expert opinions on the theoretical value of having a retractable landing gear in a stunter.
Peter Germann

Offline Chuck_Smith

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Re: What to expect from a retractable landing gear?
« Reply #5 on: November 13, 2016, 05:58:31 AM »
... I'd be interested to read expert opinions on the theoretical value of having a retractable landing gear in a stunter.

I suspect it's more the "wow factor" than anything else. Let's face it - it looks freakin'  cool. Iff'n I thought about it too long I'd probably come to the conclusion that any reduction in drag would allow me to make a thicker wing all other things being equal. One thing to remember -  the drag coefficient of a well faired wheel is not much. I suspect very well designed wheel fairings give you more bang for the buck for a lot less weight.  I don't think our velocities just are high enough. If we were flying at 200+ things might be different.
AMA 76478

Offline FLOYD CARTER

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Re: What to expect from a retractable landing gear?
« Reply #6 on: November 13, 2016, 10:52:20 AM »
It is hard to see in this photo.  This P-51 built from the RSM Distribution kit.  OS46LA power.  Retracts are electric from Hobby King.  They retract and extend using my own design electronics, that monitors engine run.  (When engine quits, gear comes down.  Gear retracts 10 sec after launch).

I think the plane flies much better with gear retracted.  It seems faster, and turns seem smoother and tighter.  Could be just an illusion, but that "illusion" is really cool!

Floyd
"Growing old is easy.
 Staying old is hard"
AMA #796  SAM #188  LSF #020


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