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Old Feb 26, 2013, 01:42 AM
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Ashford. Kent. England
Joined Feb 2005
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Nice plane back at you Thomas..
I must admit to liking the propjet models, and you can go with a simpler profile job or a sorta scale, right up to full scale.. they all go well... and with KFm2 or 4 they are great..

Yesterday I scrapped an older tatty F22 and started building the bigger SU37 I recently drew up..
For size I reduced the wingspan to the width of my depron sheet.. 27.5".. 690mm
The main center layer was cut in one piece , going down from the nose to the aileron hinge line , the top outer layer which includes the nose goes back to the step line and was cut in two halves, cut down the center line.. all the vertical splines and fuzz parts are made from doubled up 6mm.. The lower step is a simple small layer which lines up with the leading edge and the step locations..(a swept back triangle)..
I put one CF spar in the wing lined up across the rear of the cutout for the motor..this was more to flatten my depron which was a bit curved on the sheet than for strength..
I started the build by fitting the spar..laminating the lower outer layer and fitting the lower fuzz parts. I went from there to laminating the top layer halves and fitting the fuzz top

still to do ..the ailerons , elevons , fins and rudders....then to fit the gear...
I am also deciding whether to fit the motor high enough so the prop can be kept inside the fuzz at the bottom, and at the same time fit some partialy hidden wheels at the front to make it capable for ground take offs... The Big F22 is setup like that and it works well..
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Old Feb 26, 2013, 02:30 AM
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Ashford. Kent. England
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On a summer day....here is that big F22 on the go... it uses an NTM35-36 1800kv motor which does make it go well... however the slot does make it noisy...
.
Big'n propjet on the go (5 min 13 sec)
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Old Feb 26, 2013, 12:05 PM
In Rc for a LONG TIME FFAA#1
laserman's Avatar
Canada, ON, Ottawa
Joined Jun 2004
1,375 Posts
the noise is losses, if you open up the opening for the slot in front of the prop with a arched shape on each side of the motor sound goes down and effective air flow increases also the same if you to this with the trailing area as well you will see a increase of performance

jim
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Old Feb 27, 2013, 03:21 AM
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Ashford. Kent. England
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Ive done that on different models and run sound measurements... it does work but I think personally the bigger hole spoils the looks ...In fact if you look at the big F22 you will see the slot is enlarged..and the sound was reduced considerably using this slot... you should have heard it before ....lol
sound levels are made worse because the enclosed depron build of the big F22 acts like a resonance chamber.. the lower fuz is fully covered, it wants opening up to let the noise disperse..
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Old Feb 27, 2013, 08:21 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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There has been some speculation in other threads and builds that using the "dog bone" shaped slot (sort of like a Lissajous pattern with wider rounded ends) contributes to abating the prop in a slot noise. But that might be just as unsightly too.

I don't fly where noise has to be limited but I don't really care for noisy airplanes either. My personal tolerance for noise would be something like a .049 motor without a muffler at the most.

Jack
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Old Feb 27, 2013, 10:18 AM
KlonWarz
Joined Dec 2012
454 Posts
:-)

lol

Stealthy Jack?
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Old Feb 27, 2013, 01:35 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by rusty case View Post
lol

Stealthy Jack?
It is too late for that I think. Almost everything in my life has an element of stealth to it if I am not wearing my hearing aids.

I gave about 40% of my hearing away while I was in the Navy. And that was while I was trying to compensate for and avoid things that caused hearing damage. So now I get my hearing aids from the VA. But they are good ones.

Makes me feel like Darth Vader when I am getting myself geared up and plugged in. The joke in the family is that I can set selective bandpass filters for specific voices and have one for "wife"...

Jack
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Old Feb 27, 2013, 02:45 PM
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Joined Dec 2006
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Memories of my Navy days

Jack...

Your post reminded me of going to a rifle range to shoot M-16s at Newport RI.
The year was 1951.

The noise was so LOUD you couldn't hear yourself think. I stuffed wads of tissue in my ears and am I glad I did that. We were subjected to lots of noise aboard the USS Yosemite AD-19, where I was stationed in Melville, RI.

Boy, did you drag up my old memories.

My greatest adventure was when, upon returning to my ship in Key West,
I was drunk and carrying two bottles of bleach in a paper bag back to the ship.
It was my turn to carry the bleach. Well, the bag broke right in front of the Presidential yacht, the Williamsburg! Harry Truman was in town that day. Fortunately for me, the Officer of the Deck had stepped away. Otherwise, I'd probably still be in the brig.

I crawled up the gang plank on my hands and knees and fell asleep in my bunk.
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Old Feb 27, 2013, 05:30 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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The good old days, for sure.

When I went to the range and we were shooting the .45 ACP, a lot of us would use a round of .45 ACP ammo in each ear to soften the noise. I had been wearing ear plugs when shooting for years but it was some time before they were automatically part of the deal at Navy ranges.

But I'll bet you were not shooting M-16's in 1951. I'll bet they were M-1 Garands. If they were they had an 8 shot en bloc clip that you shoved down into the receiver with your thumb. Does that sound familiar? There was a occupational disease associated with that rifle that was call the "M-1 Thumb". Those were acquired when you failed to get you thumb out of the way as the action closed.

The Garand was a .30-06, the M-14 was not in service until 1959 and used the 7.62mm NATO or .308 Winchester round. Then the M-16 came along in 1963 or so with it's wimply little 5.56 NATO cartridge. Navy armories always tended to be about one generation behind on small arms, especially so in our little and far from the front lines Naval Security Group commands. But that was always fine with me, I liked older the guns better.

Jack
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Old Feb 27, 2013, 07:33 PM
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Well, Jack, I'm sure that you are correct. For me, it was a lifetime ago.
Serving in the military can teach you a lot about people and life. I was also able to go to school on the G.I. Bill. All in all, a growing experience. I was just a hick from the sticks and didn't 't know much about the world.
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Old Feb 27, 2013, 08:54 PM
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NorCal
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When M16's first started showing up in jungle use a lot of guys were wishing they had a nice reliable but heavy M1 instead.
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Old Feb 28, 2013, 04:00 AM
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Ashford. Kent. England
Joined Feb 2005
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Yes Ive also tried the bow tie type of slot and again that does reduce noise levels...and I think it looks awfull.......
Volume is also related to the revs on the prop and the airframe design..and the materials we use for our model....even the balance of the prop makes a difference...
A while back we were using soft so called quiet motor mountings to reduce the noise transmitted through our airframes.. perhaps that method needs revisiting...I might try that with a layer of softer foam behind the mount..
My quietest models are my biplanes and my RC kites....the nosiest the high revving slot models..
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Old Feb 28, 2013, 10:02 AM
KlonWarz
Joined Dec 2012
454 Posts
When using a prop in a slot, i would guess knife edges are desirable... and some degree of dogbone might help since most thrust comes from the outer portion of a prop...

Question... has someone experimented with distance from the prop blade to the slot edges??? .. with relation to the prop radius and pitch?

Tnx
rc
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Old Feb 28, 2013, 10:21 AM
just Some Useless Geek
Chicagoland
Joined Oct 2008
2,538 Posts
You guys can look around this board and find all kinds of experimental results related to sound. Soft mounting the motor has little to do with the final noise level.

On my first XYZ prototype (more info to come) I had the pusher motor mounted to a plate across the open framework of crossed foam pieces. The whole airframe acted like a hollow guitar body, amplifying the noise and making the thing incredibly loud. When I was testing it out at Camera Park in Glendale Heights I used the space at the northwest corner. There was a cop at the southeast corner, as far away as you can get and still be in the park. He zipped over to where I was because he thought I was running a stinker. When he saw it was electric he relaxed, but still warned me not to run the thing at dinner time because he was sure the PD would get angry calls from the neighbors.

Good design and layout can mitigate a lot of noise issues. It's up to us to keep these inherently quiet electrics silent.
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Old Feb 28, 2013, 12:05 PM
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United States, CO, Colorado Springs
Joined Jan 2013
23 Posts
Edge 540.My first scratch build. new to the hobby but long time aviation enthusiast. The kfm airfoils intrigued me when i came across them and because they are so simple to construct with foam it makes sense to use them. I started with plans from 3dfoamy and added the kfm4 and tapered all the control surfaces with sand paper for lower drag. After i maidened it as a profile i decided it would be easy to put a skin on her and the tail had some flex in it i wanted to get rid of. bent some of the foam pieces to fit with hot water and a hairdryer. painted with acrylics and sealed with future. ended up putting packing tape over the foam and repainting to make it a little more slippery which added about 50 gm worth it i think. flies great and really fast. not quite 3D but close. it can climb strait up for hundreds of feet. finished weight 850 gm and 340 watt motor with at best 950 gm thrust. 6x4 prop, 1300mah batt 2200 kvm motor with kfm4 40 inch span with 7% thickness at 50% of chord. stall is very mild and i can fly this plane in super slow considering its weight. just had to share. thanks. next project is a kfm3 cub. waiting for parts.
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