Fuse and Crutch Updates new project

LAST EDITED ON Jul-26-04 AT 05:55 PM (CDT)
 
Here's a few shots of how I am saving weight. Note the drilled motormounts,they are also sanded to a taper. Balsa 3/16 doubler has been lightend for added clearance for the plastic tank. I will not be using a carbon fiber mat. I will use 1/64 plywood between doublers.

Ok ok.. There is more than one way to skin a cat. But after talking to Randy today I re-thought My plans and out comes the carbon fiber matt. I have built a new fuse ,crutch ect.. and will use the carbon fiber in it. Weigh both and see where I stand.

If you read in my posts I do not recommend any method of building as I build fast and have the luxury of experimentation.
I will post updates as it progresses

The voice of experience with this method speaks to you.USE CARBON FIBRE OR GLASS CLOTH IF you want more than 50 or so flights.

LAST EDITED ON Jul-25-04 AT 06:29 PM (CDT)
 
Ok I made a call and will take heed in your comment I will use 1/64 plywood between doublers.

LAST EDITED ON Jul-25-04 AT 10:53 PM (CDT)
 
Sparky,
Do you have the hardwood mounts glued directly to the balsa doublers or are the mounts glued to ply?? and then you are going to add the 1/64 ply between the balsa doubler and the fuse side? Just trying to get it straight in my head. Can't tell by looking at pictures. I am getting ready to do a crutch also.
Thanks

LAST EDITED ON Jul-26-04 AT 08:46 AM (CDT)
 
I have glued the plywood between the balsa doublers. But Be careful this is NOT a tried and true method. Unless your willing to experiment and can build fast I suggest you do it the tried and tested way. I can build a stunt ship in 1 1/2 months.

just out of curiosity, why did u not want to use carbon?

also which plane is this again??

You do very nice work, I'm sure it will be an excellent ship.

A few comments relevant to fuselage nose construction.

Randy Smith's SV series use balsa sheets with CF cloth in between, and they hold up extremely well. I believe it has less weight than similar areas of 1/64 ply wood.

At the same time, two sheets of balsa are involved to make the balsa-CF cloth-balsa lamination. I always wondered about the strength of the direct balsa doubler to engine mount glue joint, but I have never heard of a problem with it.

I personally prefer using 3/32" sheet for fuselage size, and 1/32" plywood doublers internally, running back past the flap line. While this seems like a lot of material, a large amount of it is removed when you cut out the wing holes, and you end up with a continuous smooth expanse of lamination.

[photo not recovered: 41048405020e77de.jpg]

Another way to add strength and save material is to mold nose curvature into the fuse sides. Again, the lamination holds it, and you end up having a strong continuous piece completely to the aft of the spinner, instead of a balsa block that either butts against the front of the fuse sides, or fuse sides that get sanded away a lot to shape the nose block.

I learned the molded curved nose technique from a video made by Bob Hunt. Although I used 1/32" ply material for the inner doubler lamination, Bob stated that he felt 1/64" would be adequate for many applications, particularly pipes with smaller, higher RPM (smooth running) motors.

[photo not recovered: 410484610290494d.jpg]

I also think the tapered aft engine mounts are a good idea and I do that in two planes. But I don't like drilling holes in the engine mounts, in my case they are reduced in cross section enough.

[photo not recovered: 410487840559c0ae.jpg]

Although the photo below is of a different ship (one with a pipe), the prefinished fuselage (with carved cowl and molded bottom block, ready to assemble and paint color) only weighted 6.8 ounces. That included covering with .56 oz fiberglass cloth, with medium silkspan over than (nitrate dope binder), and nitrate/talc filler. There were no cutouts on the fuselage aft sides.

[photo not recovered: 4104853d03a2a39a.jpg]

I understand your motivation for relieving the sides of the nose on the inside for a plastic fuel tank, but you're tossing away some strength with the trapezoidal cutout. Every sharply cut corner also creates a stress riser, which is where it will want to crack or fail. Using round or elliptical cutouts helps avoid these weak points.

In my case, to accommodate the wider plastic tank, I ended up simply widening the fuselage by 1/8". Very little weight is added that way.

A number of small improvements can eventually add up to some pretty nice weight savings.

Very best luck on your new ship!

[photo not recovered: 3e69bb3870f12ad5.jpg]

"The creative habit is like a drug. The particular obsession changes, but the excitement, the thrill of your creation lasts." -Henry Moore

LAST EDITED ON Jul-26-04 AT 08:02 AM (CDT)
 
Paul Walker wrote about glueing mounts to balsa and it didn't last. If I remember correctly the glue pulled away from the balsa doubler pulling balsa with it.
Some cross bracing left in that large cutout or even just some holes rather than removing all, would be beneficial with out any noticeable weight gain.

The amount of weight that will be saved by cutting out the balsa will not be noticable in the end. Take the two pieces and weigh them and see what you saved. But the amount of strength you have lost in the nose of your airplane will.

I have built a plane with 3/32 sides with 1/64 ply doublers and 1/16 molded top. The nose shook so bad it broke engine mounts inside of the first ten flights. The plane only lasted 3/4 of a season. At the Nats on my last official I noticed the motor ran out funny. When My brother picked up to carry it off of the circle the motor was haniging in the cowl. The PA 61 that is.

If you really want to save weight do it on the finish. Use whatever you fill with as you base color and add only a few stripes for effect and only four coats of dope clear. Save weight there it wont effect structure of your model.

Again I am not trying to tell you what to do. Just making suggestions.

LAST EDITED ON Jul-26-04 AT 11:33 PM (CDT)
 
Deleted

Bill

LAST EDITED ON Jul-27-04 AT 09:22 PM (CDT)
 
Thanks for all the construction hints guys!

>I have built a plane with 3/32 sides with 1/64 ply doublers
>and 1/16 molded top. The nose shook so bad it broke engine
>mounts inside of the first ten flights. The plane only
>lasted 3/4 of a season. At the Nats on my last official I
>noticed the motor ran out funny. When My brother picked up
>to carry it off of the circle the motor was haniging in the
>cowl. The PA 61 that is.

Really? Mine it 3/32 fuse sides with 1/64 ply, too, and the top block is probably less than 1/16 in most places. Seems to be holding up.

LAST EDITED ON Aug-02-04 AT 11:09 PM (CDT)
 
> Really? Mine it 3/32 fuse sides with 1/64 ply, too, and
>the top block is probably less than 1/16 in most places.
>Seems to be holding up.
>
> Brett

You have a Foam wing also. Think it helps some? I bet it does. Also when I built this plane it was only my third attempt at a built up. And my first at a scratch built. I am sure the lack of building skill played a large role in that plane's demise. That was in 97.

It was a good plane took 4th in my second Nats in Advanced.

I built another one exactly like it in 99 and it is still flying today with some stress cracks. It is pretty much an engine test bed and a contest plane when I am just feeling like flying and having fun and not really going for it. Oddly enough I can still win with it with almost zero practice. Kind of like an old shoe...

Incidentally both planes weighed 52-54oz at 675 sqrs.

>> Really? Mine it 3/32 fuse sides with 1/64 ply, too, and
>>the top block is probably less than 1/16 in most places.
>>Seems to be holding up.
>>
>> Brett
>
>You have a Foam wing also. Think it helps some? I bet it
>does. Also when I built this plane it was only my third
>attempt at a built up. And my first at a scratch built. I
>am sure the lack of building skill played a large role in
>that plane's demise. That was in 97.
>
>It was a good plane took 4th in my second Nats in Advanced.
>
>I built another one exactly like it in 99 and it is still
>flying today with some stress cracks. It is pretty much an
>engine test bed and a contest plane when I am just feeling
>like flying and having fun and not really going for it.
>Oddly enough I can still win with it with almost zero
>practice. Kind of like an old shoe...
>
>Incidentally both planes weighed 52-54oz at 675 sqrs.

Hi Doug, my Impact fuselage is built just as Brett described with 3/32 sides and 1/64 ply doublers with a built-up wing, with the finished airplane weighing 59 ounces. My engine mounts are maple with 1/4" dia. holes drilled close together in a staggered pattern horizontally from the rear (which go back to the main spar) all the way forward to the front firewall just behind the engine. The mounts are also cut out in the tank compartment area (in the top view) to 1/8" thick using radiused lead-ins to the thin area. The top block is definitely thinner than 1/16" for the most part (I subscribe to the Billy Werwage theory that if you don't break through once or twice when you are hollowing the block then you haven't removed enough balsa). I do not use fiberglass on the nose; I just cover the whole airplane with silkspan and dope. Wing root fillets are leather.

When I retired the ship it had over 1,400 flights on it and had no stress cracks at all. I was using one of Randy Smith's PA series piped engines in it.

I have a feeling (based on observation only as I have not run a 4-stroke for C/L PA) that the ship may not have fared as well with a 4-stroke engine. Just some observations.

>When I retired the ship it had over 1,400 flights on it and
>had no stress cracks at all. I was using one of Randy
>Smith's PA series piped engines in it.

A 40?

>
>>When I retired the ship it had over 1,400 flights on it and
>>had no stress cracks at all. I was using one of Randy
>>Smith's PA series piped engines in it.
>
>A 40?

Brad,

I did start flying it with a PA .40 but changed to a PA .61 for about the last 550 flights. Still no cracking problems.

Very nice work Larry. Glad you shared you photo's.

Winfred and Big Jim Greenaway always advised against drilling motor mounts....they report that "stress risers" will occur....I think that it's a poor way to remove weight and that it seriously weakens things.
I still pose the question: why not drill motor mounts from the back, creating, essentially, tubes. Tubes are stronger than solids. It would seem to me a good project to punish someone with.

See Ya

""Larry Wrote"""Randy Smith's SV series use balsa sheets with CF cloth in between, and they hold up extremely well. I believe it has less weight than similar areas of 1/64 ply wood.

At the same time, two sheets of balsa are involved to make the balsa-CF cloth-balsa lamination. I always wondered about the strength of the direct balsa doubler to engine mount glue joint, but I have never heard of a problem with it."""""

Hi Larry
I hope your doing well

I developed these techniques back in the 80s. They work very well if done the way I suggest.
The Cf mat\balsa front end is very robust, lighter than ply, absorbs vibration and dampens it rather than transmitting it to an area that will fail.
It will not fail , again if done properly. The motor mounts will not pull loose , split or fail, if it is epoxied properly to the various pieces. my plans show the detail on how to do this.

Caution NEVER use CA for the frontend of any ship using anyones techniques. CAs are brittle and can fail due to this.

There has been thousands of ships built using these techniques that are still flying.
I have ships that are over 10 years old with this way of building with zero problems, There have been ST60s in these planes, PA 40-65s, and other engines up to 77 in them again with no problems. I even had one with a counter rotating prop system that shook very hard , again with zero problem.
There was a flyer who put an SV-11 in under full power at a SIG contest straight in on the nose, He clean it up put a new prop on it and flew the next round.
As we all know people can make most anything fail, but you can be assured that this system will work. I have yet (knock on wood) to have a problem with any of the CF techniques I developed for any part of the planes .

I have 3 planes here that have over 1000 flights on them with balsa\cf front ends, they all have ZERO problems

There are other factors but most of the front end splits I have seen were due to misalignment of the motor and wood mounts that forced the split or poor glueing techniques , or not using a crutch insert on top of the mounts.

I will try to post a picture of an example

Regards

Also, CAs are also NOT FUEL PROOF.. In general, they are a poor choice for lamination gluing. My own exception to this is making laminated wing spar strips, with a 1/32" plywood center sheet.

Now, I've heard of people successfully using white glue for lamination. But it doesn't seem reasonable to me, since tight laminations can seal against airflow. I've heard horror stories of a crashed ship's broken nose revealing STILL WET white glue on an internal lamination!

A medium to slow epoxy glue seems the best choice for nose construction.

[photo not recovered: 3e69bb3870f12ad5.jpg]

"I have learned throughout my life as a composer chiefly through my mistakes and pursuits of false assumptions, not by my exposure to founts of wisdom and knowledge." -Igor Stravinsky

I am interested in seeing the new crutch and where the carbon fibre is layed up or attached etc.

What about the polyurethane stuff? I wonder how well that holds up.

Swell?

Sparky,
How's the new crutch coming along???

>Also, CAs are also NOT FUEL PROOF.. In general, they are a
>poor choice for lamination gluing. My own exception to this
>is making laminated wing spar strips, with a 1/32" plywood
>center sheet.

I guess I'm lucky, but all of my airplanes's engine mounts are glued together with CA, including the crutch and laminating the doublers.

>Now, I've heard of people successfully using white glue for
>lamination. But it doesn't seem reasonable to me, since
>tight laminations can seal against airflow. I've heard
>horror stories of a crashed ship's broken nose revealing
>STILL WET white glue on an internal lamination!

Yep, seen it several times. I don't know that Ambroid is any better - in fact, it might be worse in this respect.

>>Also, CAs are also NOT FUEL PROOF.. In general, they are a
>>poor choice for lamination gluing. My own exception to this
>>is making laminated wing spar strips, with a 1/32" plywood
>>center sheet.
>
> I guess I'm lucky, but all of my airplanes's engine mounts
>are glued together with CA, including the crutch and
>laminating the doublers.
>
>>Now, I've heard of people successfully using white glue for
>>lamination. But it doesn't seem reasonable to me, since
>>tight laminations can seal against airflow. I've heard
>>horror stories of a crashed ship's broken nose revealing
>>STILL WET white glue on an internal lamination!
>
> Yep, seen it several times. I don't know that Ambroid is
>any better - in fact, it might be worse in this respect.
>
> Brett

The salient point being, the lamination did not fail...used to see this on early foam combat wings joined with Elmer's. Only the outer edges of joints ever cured, which produces anxiety when you discover it, yet none of the joints failed (the foam would break first). Yes, it is a little disconcerting; no, I don't worry about it any more.
--Ray