Notices
Twin & Multi Engine RC Aircraft Discuss the ins & outs of building & flying multi engine rc aircraft here.

KMP F-7F Tigercat

Old 03-22-2008, 02:21 AM
  #801  
 
CHARLES WINTER's Avatar
 
Join Date: Jan 2002
Location: MERCED, CA
Posts: 367
Likes: 0
Received 3 Likes on 2 Posts
Default RE: KMP F-7F Tigercat

Hi Anthony, Did I read your post correctly? Did you damage your T-Cat or just land it straight ahead? I have concluded that I need engines that are 1.5 c.i. or larger plus new retracts that are Air Up and Air Down. If I put all my gear doors back on and particularly the large long nose door the spring down strength of the landing gear I have now may not be strong enough to lock the nose gear down with the air load during flight.

Col. Chuck Winter
Old 03-22-2008, 07:21 PM
  #802  
Member
 
Join Date: Feb 2007
Location: OSTERHOFEN BAVARIA, GERMANY
Posts: 84
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

Hi VKerster,

thanks for your ideas.

I planned that the stringers have to take all the forces appearing - and not the composite-board.

Maybe I have to redesign my centre-wing area, but the very week composite board does not look like taking too much forces especially when beeing compressed horizontally - and this is what happens on top of the wing when positive G-force will be apply.

I thought the only structure to withstand this forces caused by wing-load are the stringers in front and back of the wing and not the strucutre I have cutted away.

After your input I will have a look again and study my papers - or I will make a harware test: gross-weight: 30 lbs --> 10 G = 300 lbs

I will apply this load to the centre section of the wing next to my fuel tank while the wing is supported next to the nacelles.

If the test will be successfull I turst in my construction and open one bottle of beer - if not I will send you the beer !!!

... and order a new central wing section ;-))

Cheers, Detlef
Old 03-22-2008, 07:48 PM
  #803  
Junior Member
 
Join Date: Apr 2006
Location: canberraact, AUSTRALIA
Posts: 26
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

Hi Chuck
I broke the wing in half cracked the fuzz behind the wing & the nose cone i did not have the door covers on or retracts conected

Regards
Anthony
Old 03-23-2008, 02:31 PM
  #804  
Junior Member
My Feedback: (12)
 
Join Date: Jul 2004
Location: frankfort, IN
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Old 03-23-2008, 09:46 PM
  #805  
Member
 
Join Date: Apr 2005
Location: Sydney, AUSTRALIA
Posts: 55
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Old 03-23-2008, 10:17 PM
  #806  
Member
My Feedback: (12)
 
Join Date: Feb 2008
Location: Summerton, SC
Posts: 40
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Old 03-24-2008, 02:04 PM
  #807  
Member
 
Join Date: Feb 2007
Location: OSTERHOFEN BAVARIA, GERMANY
Posts: 84
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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 !
Old 03-25-2008, 01:43 PM
  #808  
Senior Member
 
Join Date: Dec 2002
Location: highland, MI
Posts: 275
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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.
Old 03-25-2008, 05:36 PM
  #809  
Member
 
Join Date: Apr 2005
Location: Sydney, AUSTRALIA
Posts: 55
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Old 03-26-2008, 08:22 AM
  #810  
Junior Member
 
Join Date: Apr 2006
Location: canberraact, AUSTRALIA
Posts: 26
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Attached Thumbnails Click image for larger version

Name:	Ay74429.jpg
Views:	81
Size:	29.5 KB
ID:	913922   Click image for larger version

Name:	Ql34176.jpg
Views:	66
Size:	26.1 KB
ID:	913923   Click image for larger version

Name:	Rx59899.jpg
Views:	65
Size:	24.8 KB
ID:	913924   Click image for larger version

Name:	Oh13786.jpg
Views:	76
Size:	26.0 KB
ID:	913925   Click image for larger version

Name:	Yj65502.jpg
Views:	66
Size:	28.3 KB
ID:	913926   Click image for larger version

Name:	Sq46964.jpg
Views:	61
Size:	29.5 KB
ID:	913927   Click image for larger version

Name:	Fb87640.jpg
Views:	60
Size:	26.1 KB
ID:	913928   Click image for larger version

Name:	Va72935.jpg
Views:	50
Size:	24.8 KB
ID:	913929  

Click image for larger version

Name:	Bv60209.jpg
Views:	49
Size:	26.0 KB
ID:	913930   Click image for larger version

Name:	Sd43831.jpg
Views:	55
Size:	28.3 KB
ID:	913931  
Old 03-26-2008, 01:45 PM
  #811  
 
CHARLES WINTER's Avatar
 
Join Date: Jan 2002
Location: MERCED, CA
Posts: 367
Likes: 0
Received 3 Likes on 2 Posts
Default RE: KMP F-7F Tigercat

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
Attached Thumbnails Click image for larger version

Name:	Bz78462.jpg
Views:	62
Size:	69.2 KB
ID:	914124   Click image for larger version

Name:	Fb88009.jpg
Views:	53
Size:	56.2 KB
ID:	914125  
Old 03-26-2008, 07:10 PM
  #812  
Member
 
Join Date: Apr 2005
Location: Sydney, AUSTRALIA
Posts: 55
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Old 03-26-2008, 09:45 PM
  #813  
Senior Member
 
duber3's Avatar
 
Join Date: Oct 2005
Location: QC, QC, CANADA
Posts: 179
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Attached Thumbnails Click image for larger version

Name:	Qo39688.jpg
Views:	63
Size:	68.7 KB
ID:	914473   Click image for larger version

Name:	Wr54317.jpg
Views:	72
Size:	59.5 KB
ID:	914474   Click image for larger version

Name:	Ye84330.jpg
Views:	60
Size:	53.6 KB
ID:	914475   Click image for larger version

Name:	Xr47289.jpg
Views:	77
Size:	49.2 KB
ID:	914476  
Old 03-26-2008, 10:52 PM
  #814  
 
camdyson's Avatar
 
Join Date: Jul 2005
Location: Bairnsdale, AUSTRALIA
Posts: 870
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Old 03-26-2008, 11:31 PM
  #815  
Member
 
Join Date: Apr 2005
Location: Sydney, AUSTRALIA
Posts: 55
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

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
Old 03-27-2008, 09:21 AM
  #816  
Member
 
Join Date: Feb 2007
Location: OSTERHOFEN BAVARIA, GERMANY
Posts: 84
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

Hi TC-builders,

as I have already opened the centre-wing area to install my fuel-tank I will do following:

Install two massive (about 6 - 8 mm plywood) stringers from the left to the right rib where the alu-tubes are ending in.

Additional I will apply carbon-rovings and carbon-fibre to build up 3 or 4 square-frames to guide the forces from the right to the left rib.

Cheers, Detlef

@VKerster: I would like to thank you personally , as you was the fellow who gave the input to me of insufficient stability of my centre-wing area. So in the end you are the guy who probably safed my plane !!! Thanks at all !
Old 03-27-2008, 01:03 PM
  #817  
Senior Member
 
Join Date: Jul 2006
Location: Hampshire, IL
Posts: 340
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

Can you post pictures when you do the mod.
Old 03-27-2008, 05:37 PM
  #818  
Member
 
Join Date: Feb 2007
Location: OSTERHOFEN BAVARIA, GERMANY
Posts: 84
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

Hi Mooney N9331V,

I will keep all of you updated.

Cheers, Detlef
Old 03-27-2008, 06:21 PM
  #819  
My Feedback: (14)
 
Join Date: Apr 2002
Location: Arizona
Posts: 870
Received 1 Like on 1 Post
Default RE: KMP F-7F Tigercat

Anthony

Real sorry to hear/see that your wing failed. For the loads and g's this plane will possibly
have to deal with and for the money, I thought that an I-beam spar that ran from the center
section to just pass the engine nacelles would have been used. I know that all foam sheeted
wing with this web design works well on sport and pattern planes but they don't weight 23+ lbs.
Just think how you would have felt if that was the all glass wing.

Ron
Old 03-27-2008, 07:08 PM
  #820  
Senior Member
 
Join Date: Dec 2002
Location: highland, MI
Posts: 275
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

DETLEF, YOU ARE WELCOME. ANTHONY'S WING LOOKS LIKE MY FIRST T-CAT, THIN BALSA SKIN WITH GLASS CLOTH ON THE INSIDE AND OUT. MY SECOND CAT IS SKINNED WITH A KEVLAR COMPOSITE (LOOKS LIKE PAINTED CARDBOARD) AND SEEMS MUCH STRONGER. T-CAT#1 WAS FROM THE 1ST BATCH AND T-CAT #2 WAS FROM THE SECOND BATCH. I'M CONCERNED WHY ANDREW KONDOR OF KMP IS SO QUIET ON THIS FORUM CONCERNING ANTHONY'S WING FAILURE.................[&:]
Old 03-27-2008, 07:46 PM
  #821  
Member
 
Join Date: Apr 2005
Location: Sydney, AUSTRALIA
Posts: 55
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

VKerster,

As I understand it, the damage to Anthony's F7F was not caused by wing failure, but by a stall on takeoff with insufficient airspeed. The wing was simply damaged in the arrival.


I've also had time to have a quiet think about the centre spar issue, and believe I've come up with a reasonably easy fix. As I see it, the main issue is that the joiner tubes end ubruptly with a butt-join against the inner ribs, and create a stress raiser at that point. Only the ply web and wing skins are left to carry wing bending stresses.

My solution: don't terminate the tubes at that point. Open up a hole in the root ribs to allow the tubes to extend into the innermost bay, and the 2 tubes will then meet at the centre. Make up a glass/carbon joiner tube at the appropriate dihedral angle, and glue the 2 tubes into it. The 2 tubes will now act as a single continuous spar, with no stress raiser points. A modest opening cut in the top or bottom skin at the centre would be sufficient to insert the angled joiner piece. The centre section would then have the ply web and continuous joiner tube to carry bending loads. The aluminium tubes supplied in the kit may be a little short to do this mod, but I'll probably be replacing them with carbon tubes anyway, so I'm not too concerned.

Keith
Old 03-27-2008, 08:29 PM
  #822  
 
CHARLES WINTER's Avatar
 
Join Date: Jan 2002
Location: MERCED, CA
Posts: 367
Likes: 0
Received 3 Likes on 2 Posts
Default RE: KMP F-7F Tigercat

Hi T-Cat builders, WOW --- WOW , Thank you Anthony for the pictures of your broken wing. I never imagined how poorly the wing center section was constructed. I feel (My Opinion) that most T-Cats would be lost sometime in their life from wing failure. Maybe VKerster lost his T-Cat from wing failure!!!! I immediately cut open the wing center section near the tube area to view what I was up-against in making a proper fix. I have some ideas, but just wanted to share these pictures with all of you. I personally would not fly my T-Cat again until I have a GOOD fix. The pictures show the location that I need to work on plus I ground away the plywood rib section to expose the opening to the fiberglass and aluminum tube.

Col. Chuck Winter
Attached Thumbnails Click image for larger version

Name:	Ge94079.jpg
Views:	79
Size:	76.1 KB
ID:	915271   Click image for larger version

Name:	Yw69041.jpg
Views:	78
Size:	60.2 KB
ID:	915272   Click image for larger version

Name:	Sq45610.jpg
Views:	73
Size:	50.1 KB
ID:	915273  
Old 03-27-2008, 08:54 PM
  #823  
Senior Member
 
Join Date: Jul 2006
Location: Hampshire, IL
Posts: 340
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

Hey guys


Has anyone lost a wing during the test flights or have they lost them due to engine failure etc.


Is the first batch ( wooden wing covered by glass ) suspect or is the second batch with the green fiber glassed hardboard also suspect.


I to am surprised Kondor has not had anything to say, this F7F is my second plane from KMP. My first ( KMP B 25 ) has wing issues I am now in the middle of dissecting and fixing.


Charles, cant wait to see your fix also. So far your mods have been very well thought out.
Old 03-27-2008, 09:02 PM
  #824  
Senior Member
 
Join Date: Jul 2006
Location: Hampshire, IL
Posts: 340
Likes: 0
Received 0 Likes on 0 Posts
Default RE: KMP F-7F Tigercat

Forgot one thing

Charles when you look from the inside towards the leading edge can you tell if it may have any type of forward spar in the leading edge or trailing edge area ???????????????????????????
Old 03-28-2008, 12:18 AM
  #825  
 
CHARLES WINTER's Avatar
 
Join Date: Jan 2002
Location: MERCED, CA
Posts: 367
Likes: 0
Received 3 Likes on 2 Posts
Default RE: KMP F-7F Tigercat

Hi T-Cat Builders, The start of my center section wing fix is: First goal is to join the 2 spars together in the center of the wing. I am using a 3/4 inch dia. aluminum tube #6016-T6 (Very Strong tubing) 10 inches long. With a little grinding and shaping I can insert this tube inside the 2 outer tubes. This new center tube protrudes inside the outer tubes approximately 2.5 inches each side. The next step will be epoxying the center tube inside the outer tubes. I will use slow cure epoxy (24 Hour) mixed with chopped carbon. I use this same type of mix in the manufacture of R/C racing props size 7 in. to 26 in. I will also develop a spar with this center tube fix. When I sign off from this post I'll start mixing some epoxy. I hope tomorrow I'll have the next step ready to discuss and show. I was asked a question "If I could see a spar in the leading or trailing edge of the wing", the answer is "I can't see any at all, just a solid hard balsa block in the leading edge that the wing hold down bolts go through".

Col. Chuck Winter
Attached Thumbnails Click image for larger version

Name:	Ki20232.jpg
Views:	86
Size:	59.2 KB
ID:	915471   Click image for larger version

Name:	Qo40699.jpg
Views:	86
Size:	62.0 KB
ID:	915472  

Thread Tools
Search this Thread

Contact Us - Manage Preferences Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.