RE: KMP F-7F Tigercat  
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RE: KMP F-7F Tigercat - 3/23/2008 8:31:14 PM   
flyscbs


 

Posts: 2
Joined: 7/24/2004
From: frankfort, IN, USA
Status: offline 		Col. Winter Sir, May I suggest the OS 120 AX. , I plan to use for my F-7F, the exhaust is an issue though, Bisson muffler's invert mount style, close fit on the cowls, may need the alter the size of the units, that means back to Bisson,
as for retract controls & doors, using an UP-3 brand valve unit www.up-1.com ( doors stay open on gear down ) and has varible speed on both circuits, from 3 to 10 seconds, and short throw cylenders for the doors with linkage setup as in a earilier forum, that were servo driven, very cool, but I will need more than a smaller pressure vessel. I want to use Robart F-7F units when available.
The 120 AX turn's 15x7 Master airscrew 3 blade at 8800 rpm. 16x8 3 blade at 7800 rpm. with the included muffler, that you can't use on the F-7F. OS has 9500rpm. as max recomended, with 3.1 HP. at 9000 rpm. ( my Saito 180 turns the 16x8 3 blade at 8000 rpm. with it's output in the 9000rpm. range at 2.9 HP.) As for my selection I wanted a scale sized & type props for the model with engines that con turn the props. With the number of servos needed on the F-7F, I will use a" Smart-fly" power expander pro, along with heaver gauge servo lead extentions for wing, with the only Y- harness for the flap servos( 3 drive outputs on the expander per Ch. and 4 flap servos ) Heavy gauge type switch & leads to battery, with Deans Ultra connectors , 6.0V at 4000mah or better. and a on board glow driver unit, McDaniel brand, twin engine type, servos and hardware are next on the list. I'll start assembly of the model when have all the parts, retracts & servos to go yet as the BIGGIES... I enjoy all that I read and see on this forum and has impressed and helped me. ps. I always thought the F-106 SEXY...

Thanks for reading, Craig Beaven

(in reply to CHARLES WINTER)
       Post #: 801

RE: KMP F-7F Tigercat - 3/24/2008 3:46:45 AM   
Keithfl


 

Posts: 14
Joined: 4/15/2005
From: , AUSTRALIA
Status: offline 		A question for VKerster and Anthony,

You've both suffered the misfortune of losing an F7F, but are in a position to give some insight into the strength of the wing centre section. This certainly worries me, and the same issue seems to have been raised by a few others.

Peering into the centre section from the outboard end, there is a full depth 1/8" plywood web with lightening holes between each of the ribs. I can't tell whether the ribs are continuous and the web in multiple pieces, or if the web is continous and the ribs in 2 pieces each. There also appears to be a small spar, possibly hardwood, of about 1/8" x 1/4", bonded to the plywood web, top & bottom. The wing joiner tube keys into the wing ribs, or plywood doublers added to the wing ribs, rather than directly to the web/spar structure.

Is that all there is? It really doesn't seem adequate for a 25-30 pound bird. I'm hoping those puny 1/8" x 1/4" spars are tapered, so they're much more substantial towards the centre. I realise that much of the model's weight is in the necelles, which means wing bending stresses are much less than for a single, but it still makes me nervous.

Given that you guys have been able to see the internal machinations, is there any real structure, other than what I've already seen?

Thanks,
Keith

< Message edited by Keithfl -- 3/24/2008 3:47:32 AM >

(in reply to flyscbs)
       Post #: 802

RE: KMP F-7F Tigercat - 3/24/2008 4:17:33 AM   
moki man


 

Posts: 39
Joined: 2/17/2008
From: Summerton, SC, USA
Status: offline 		Col. Sir, came home yesterday from the road, I'm an over-the-road car hauler and retired submariner and read my copy of FLY RC magazine. Boy did I get excited about this bird F-7F, so I've been sitting here for the last few hours soaking up info in this thread and just like I thought, that glowing review in the mags is just like 98% of most magazine reviews, you know, best plane every, flies as if on rails and the same old line... I must thank you and all the rest who have been posting here for all of the wonderful info. At this point the jury is still out for me at this time, I've read a lot of kit problems here and the only two that have actually flown crashed. Even the first review model for the mag crashed, not getting that warm fuzzy as of yet. I still like and maybe even want to try one so I'll be watching and reading every printed word on this subject. The better half in my household allows me about 3K a year for my r/c adventures/project and this baby will probaly wipe the 08 budjet and some of 09 as well so got make sure, well as sure as one can be in this hobby anyhow. Once again you all keep the info coming and good luck to all, especailly the gentelman who's on his second one, sorry for your loss.....Moki Man

(in reply to Keithfl)
       Post #: 803

RE: KMP F-7F Tigercat - 3/24/2008 8:04:03 PM   
Detlef Schmidt


 

Posts: 62
Joined: 2/22/2007
From: OSTERHOFEN BAVARIA, GERMANY
Status: offline 		Hi VKerster and Anthony.

did not realise until now that both of you broke the wing in pieces.

Now I really start to worry about my modifiction for the tank-layout.

Did you make measurements and/or pics of the broken wing structure?

Maybe its really weak - but than we need to open it and to reinforce it, because anyway the composite board can not do the job of well-sized stringers and ribs.

Cheers, Detlef

P.S.: Adjusted all RC and did run the 2 G26 engines todays without problems and with glorious synchro-sound.

As soon as our flying-field will be dry I would be ready for the maiden - but aslong as the centre-wing issue is pending I´ll keep the TC grounded !


_____________________________

...and always happy landings !

(in reply to moki man)
       Post #: 804

RE: KMP F-7F Tigercat - 3/25/2008 7:43:10 PM   
VKerster


 

Posts: 266
Joined: 12/14/2002
From: highland, MI, USA
Status: offline 		KEITHFL, YOU HAVE NOTHING TO WORRY ABOUT PERTAINING TO THE STRENGH OF THE CENTER SECTION. SEE MY PICS ON P.21, POST #512. MY BIRD WENT THRU AN OAK TREE, THEN HIT THE GROUND AT A 45 DEGREE ANGLE AND THE CENTER SCETION DIDN'T BREAK.


_____________________________

VKerster

(in reply to Keithfl)
       Post #: 805

RE: KMP F-7F Tigercat - 3/25/2008 11:36:20 PM   
Keithfl


 

Posts: 14
Joined: 4/15/2005
From: , AUSTRALIA
Status: offline 		Thanks VKerster,

I had examined your photos quite closely previously, and had noted that the centre section had broken, although with a tree strike, that probably doesn't say too much about structural strength! I'm sure that any wing, regardless of construction methods, could have broken in the same way. The break does seem to have occurred at the inboard end of the joiner tube, which would be a natural stress point. I guess the question is whether the wing would fail at the same point (or further inboard) under normal flying or landing stresses.

I was particularly interested in spar strength as my F7F is electric, with just under 5 pounds of batteries in the fuselage. Although overall airframe weight will probably be less than with gas power, wing bending stresses will be higher, due to having more of the mass located in the fuselage. Hence my concerns over spar stength.

Keith

(in reply to VKerster)
       Post #: 806

RE: KMP F-7F Tigercat - 3/26/2008 2:22:20 PM   
scale9planes


 

Posts: 9
Joined: 4/19/2006
From: canberraact, AUSTRALIA
Status: offline 		Hi Keith &Detlef

There is no spars through the wing only the 1/8 ply web which is one piece.
the wing broke because of the weight of the model when you have 28-30 pounds of model
something has to give when l rebuild it i will use nylon wing bolts this should help if i fall out of the sky again'.

Anthony


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(in reply to Detlef Schmidt)
       Post #: 807

RE: KMP F-7F Tigercat - 3/26/2008 7:45:20 PM   
CHARLES WINTER



Posts: 110
Joined: 1/29/2002
From: MERCED, CA, USA
Status: offline 		Hi T-Cat builders -- (Discussion about wing center section strength) This will be a LONG WINDED discussion and personal conclusion about the center section strength of our T-Cats. I was an Aeronautical Engineer working at Republic Aviation (Farmingdale Long Island, New York) in the early 1950s. I was working in the Hydraulic and Control section on F-84s-RF-84s and Very Secret F-105s. It is a well know fact that Republic Aviation aircraft were the most ruggedly built USAF fighter aircraft. The P-47 right up to the F-105 survived unbelieveable combat damage. I worked directly with the Airframe Section and it was a fact that the approach Republic Aviation designers and engineers took to STRENGTH and RUGGEDNESS was built into the extra strength in the aircraft skin covering. Now getting back to our T-Cats. When I first started to assemble my T-Cat, I was concerned about what I SAW and didn't SEE with reference to the strength of the wing center section. I would have liked to have seen a Metal or Carbon tube run through the center section into the wing area. I had to assume the designers and builders had built a VERY STRONG spar in the front and rear of the wing center section. This brings up the disussion of "Skin Strength". I was concerned enough to cut-away as little of the skin as possible for the exiting servo and air lines. I also added plywood rings epoxyied to the openings to strengthen and stop any cracking. The skin on my T-Cat is very thin and brittle. In CONCLUSION: Our T-Cats with fuel on board will be approximately 30 lbs. If you could compute the "G" forces coming out of a Loop with a little PANIC pull back on the elevator stick, you would be shocked at how high the "G" loads reach. These "G" pressures will migrate to the center section of our wings. I am still concerned about doing airobatics with this airplane. If I were to build another T-Cat, I would install a tube through the center section and as far as possible into the wing panels.

Col. Chuck Winter

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(in reply to scale9planes)
       Post #: 808

RE: KMP F-7F Tigercat - 3/27/2008 1:10:16 AM   
Keithfl


 

Posts: 14
Joined: 4/15/2005
From: , AUSTRALIA
Status: offline 		Anthony,

Thankyou for the photos, that really clarifies what structure is (and isn't!) in there. Not what I was hoping to see. There really does seem to be a stress point where the aluminium joiner tube ends, with no additional spar structure to take up the loads. Just the ply web and wing skins.

Charles,

I agree that high G loads may be an issue here. And while the skins will provide some strength, they are largely unsupported and will therefore be prone to buckling and failure before adding any real resistance to bending stresses. I may fill my centre section with an expanding 2-part foam, which would adhere to and support the skins, and allow them to become structural in the same way that a conventional foam core wing does. The skins would effectively act as a monocoque structure. Would certainly be a lot easier than opening up the wing and adding spar material.

Either way, I think I'll be moving as much of the hardware out of the fuselage & into the nacelles as I possibly can, just to minimise wing centre section loads.

Keith

(in reply to CHARLES WINTER)
       Post #: 809

RE: KMP F-7F Tigercat - 3/27/2008 3:45:41 AM   
duber3



Posts: 132
Joined: 10/6/2005
From: QC, QC, CANADA
Status: offline 		HI!

the wing center start making me very scary, they should make the aluminum tube pass all over the center,
I'm really disappointed about this plane, I had a problem whit the center, the trailing edge was crack all the way and
they replace it , anyway I know it's a little of topic but here my gears doors setup, I took the idea from Top Flite B25
it's very simple


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(in reply to Keithfl)
       Post #: 810

RE: KMP F-7F Tigercat - 3/27/2008 4:52:28 AM   
camdyson



Posts: 828
Joined: 7/20/2005
From: Bairnsdale, AUSTRALIA
Status: offline 		Regarding the expanding foam idea, some of these are pretty aggressive - be sure you're not going to bow the skins outward from the pressure of the foam.

Cam

(in reply to duber3)
       Post #: 811

RE: KMP F-7F Tigercat - 3/27/2008 5:31:44 AM   
Keithfl


 

Posts: 14
Joined: 4/15/2005
From: , AUSTRALIA
Status: offline 		Cam,

I've used some of the pressure-pack expanding foam, as well as 2-part expanding foam, and you're right - they can be pretty aggressive. I've found they can also keep expanding for quite some time after they appear to have gone off. I was going to experiment with epoxy - there's an additive than can be added to conventional resins that will cause it to foam on curing. I'm hoping its a more controlled expansion. I was also planning on building up the foam in multiple layers to help with this.

Keith

(in reply to camdyson)
       Post #: 812