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HELP! Engine Mounting Problem!

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Old 10-26-2006, 07:04 AM
  #1  
tasesq
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Default HELP! Engine Mounting Problem!

Hi All,

I am building a Kadet Senior - the manual states to make the spinner backplate 4-1/8" from the firewall face. As you can see in the photos below, I am able to JUST squeeze the needle valve onto the back of the engine, but I cannot fit the mount bolts!!!

1. Does the needle valve have to be level with the fuel tank and also the carby? or can I place it somewhere else in the aircraft?

2. Do I really have to have the engine 4-1/8" from the firewall? As you can see the engine mount bolts heads are 0.15" - can I simply move the engine forward by this much? Will it effect the pitch moment of the aircraft? I figure that the Seniors are generally tail heavy anyway, so moving the prop further away from the CoG will help this?

I appreciate any input - I hope this is not a silly question. This is my first aircraft, and I don't want to screw up a critical decision at this point and have to buy different mounts later.

Are these mount screws suitable for this purpose? Do i just use a bit of Locktite to ensure they do not come out of the blind nuts?

BTW: This is a OS 46AX on the mounts from the Kit (Engine just CA'd on at this point).

Photo 1: Spinner backplate 4-1/8" from firewall
Photo 2: Needle Valve from the left
Photo 3: Needle Valve from the Top
Photo 4: Needle Valve from the back (mounted vertically)
Photo 5&6: Head of mount bolts are approx 0.15 (including a small gap)
Photo 7: Kadet Manual Instructions

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Old 10-26-2006, 07:51 AM
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flapper
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Default RE: HELP! Engine Mounting Problem!

Hi,
You have raised a few good questions. One of the guys at our club has a 100" version of this plane. He uses it as a glider launcher from a frame on top of the wing.

It will be fine to move the engine forward of the suggested distance. It may actually be better anyway as it will assist with the CG balance. What I suggest you do is temporarily set up the engine and have all hardware in plane (servos, battery etc) and with wing on. Check CG. I wouldn't be surprised if you need to get more weight up front anyway. If you do, just move the engine forward about 1cm and see how you go. You can then resort to moving around battery and receiver to get correct CG. Saves adding any dead weight.

In regard to the engine secring bolts, just use the nylon insert lock nuts without locktite. You can also use metal self tapper screws. They won't vibrate loose in a hurry.

Check your CG and Lateral balance (side to side). Balance as necessary. If needed, try moving the engine even further forward. It won't create any major drama by ding this.

The gereral rule for the tank is to have the centre just under the level line of the carby. I havn't had any probs with tanks syphoning to the carby and I have a few engines set up where the carby is 1 to 2 inches lower than the centre line of the tank (P47 for example with an inverted 1.20FS).

Look at buying a CG machine or make your own. Use two dowls with pencil rubbers on the end. Set up in a block of wood or on your work bench. Works fine.

By spending a bit of time setting up and getting your balances right, you will enjoy your flying more and the inevitable will be delayed. Don't be too concerned about the changes with the engine position. Again, try and avoid adding dead weight.

Regards
Mark
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Old 10-26-2006, 07:55 AM
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Default RE: HELP! Engine Mounting Problem!

Realised you were referring to the mount to firewall bolts. Use ones that will sit fully in the threaded section of the blind nut or protruding a couple of millimetres. Just use some spring washers on top of a normal washer. You won't have any problems with these loosening up. Just check by holding engine and twist slightly. If loose, tighten.

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Old 10-26-2006, 08:00 AM
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Default RE: HELP! Engine Mounting Problem!

Hi,

Thanks for the reply.

I followed the manual with regard to the engine bolts - that is I mounted some metal blind nuts (that came with the kit) at the back of the firewall on doubler strips and epoxied them in place and the mounts screw into the blind nuts. Is this ok, or should i try to remove the blind nuts and use bolts and nylocks instead?

Also, the manual suggest to punch and drill holes in the mounts now (before the firewall is mounted onto the fuse) - is it better to wait as you have suggested? I can always (assuming I can get to the back of the firewall) remove the mounts and punch and drill the mounts later, although this would be a little harder than doing them now.

Is it easier to just move the engine an arbritary 1cm forward and hope that no dead weight in the tail is required? As i understand, the kadet senior is generally tail heavy anyway - and I am adding a tailwheel back there too.
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Old 10-26-2006, 08:09 AM
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Default RE: HELP! Engine Mounting Problem!

Oh - ok thanks.

The bolts supplied are not long enough

I'll go get some more steel bolts with a hex head and spring washers for the mounts. Thanks.
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Old 10-26-2006, 08:13 AM
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Default RE: HELP! Engine Mounting Problem!

Hi,
The blind nuts are fine. I take it you are building a kit? Usually the locations are pre punched. Just drill the holes and then epoxy in the blind nuts before glueing in firewall. Make sure you use epoxy for the firewall and some triangular stick on the sides for added securing.

I think I misread your original post re the bolts. I meant to use the nylock nuts for securing the engine to the mount. The blind nuts are the norm for securing the mount to the firewall.

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Old 10-26-2006, 08:20 AM
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Default RE: HELP! Engine Mounting Problem!

I followed the manual with regard to the engine bolts - that is I mounted some metal blind nuts (that came with the kit) at the back of the firewall on doubler strips and epoxied them in place and the mounts screw into the blind nuts. Is this ok, or should i try to remove the blind nuts and use bolts and nylocks instead?
The blind nuts are perfect for that application. They hold bolts that are tightened securely but you can also use lockwashers for extra peace of mind or you can use thread locker for even more security. What do you ment "...on doubler strips"???? If you added wood strips, they need to be fuelproofed or they may compress easily when fuel/oil hits them.

Also, the manual suggest to punch and drill holes in the mounts now (before the firewall is mounted onto the fuse) - is it better to wait as you have suggested? I can always (assuming I can get to the back of the firewall) remove the mounts and punch and drill the mounts later, although this would be a little harder than doing them now.
It's perfectly ok to wait to position the engine on the motor mounts until you absolutely must. It is much more accurate to drill the holes in the mounts with them off the airplane. Use a drill press and it's lots easier to get very accurate placement. Experienced modelers often wait until the very last to drill the mounts for the engine. It's a smart thing to do, especially if your model is not a scale model and you're wanting every scale measurement to be exactly like the original. Slight changes of prop location won't result in any real difference in flight characteristics. If you use blind nuts, it's easy to remove the mounts so it matters little if you do it now or later.


Is it easier to just move the engine an arbritary 1cm forward and hope that no dead weight in the tail is required? As i understand, the kadet senior is generally tail heavy anyway - and I am adding a tailwheel back there too.
It's actually not easier to do it either way. It's the same effort now or later. As for adding a tailwheel being a consideration, removing the nose wheel is actually more of a change. Both together will change the expected design distribution of weight. But you won't know if that matters with the parts and stuff of your particular airplane until it's almost done. And then if you've not drilled the motor hold down holes, you'll be better able to deal with what worked out with your part weights.
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Old 10-26-2006, 08:32 AM
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Default RE: HELP! Engine Mounting Problem!

Ok - Fantastic. Thanks everyone for the advice.

I'll use the blind nuts i've already epoxied in, but i'll use some spring washers under them for added security.

I'll wait to drill the engine mount holes, and when I do i'll use a bolt with a spring washer, and a nylock nut on the other end. I'll just CA the engine on while i am building, and then remove the mounts and drill the holes on the drill press at work once i have the wing on, and some idea of balance.

Also, when drilling the holes in the mounts, do i just use an everyday punch that you use in metal work to make a little dint, then drill the holes on the drill press? I have never worked with 'glass filled' mounts before!

As for needle valve placement, I assume I just make sure it protrudes somewhere outside the balsa cowl for adjustments - it doesn't matter if it is horizontal or vertical?

Thanks everyone!

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Old 10-26-2006, 08:34 AM
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Default RE: HELP! Engine Mounting Problem!

The Kadet Sr has a molded cowl right? And the design suggest upright engine mounting right. Is the cowl already open for the engine to stick up?

About the only problem you might encounter if you place the engine forward on the mounts would be the cowl interfering with the engine's carburetor. And removing the little area of the cowl to clear the carb would do little to the integrity of the cowl. And you might not need to remove anything if there is sufficient overall length to the cowl. If you move the cowl forward, the limit it can be moved and still look right is simple to see. Just move it forward and look to see if there is any overlap at all of cowl to fuselage. The only real consideration is that you have enough overlap so that the screws through the cowl have about 1/2" of cowl to hold the screws. If you don't have that much, but do have some overlap, then simply epoxy some blocks to the firewall to take the screws.

Matter of fact, it's often sensible to place a couple of blocks for that purpose simply to place screws farther forward for better leverage and to insure that you have a couple of good strong supports for at least a couple of screws.
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Old 10-26-2006, 08:40 AM
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Default RE: HELP! Engine Mounting Problem!

Actually, the Senior has a built up balsa cowl that is shaped as desired to fit the engine in - so moving the entire cowl forward a little if needed, or shaving some extra away for the carb is no problem.

I am thinking of having a red hot go at making a fibreglass cowl - but i will sheet and glass the wings and fuse and see how i go first. I can use the balsa cowl as a plug later if it seems not too hard.

Thankyou for your help.
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Old 10-26-2006, 08:45 AM
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Default RE: HELP! Engine Mounting Problem!

I'll just CA the engine on while i am building, and then remove the mounts and drill the holes on the drill press at work once i have the wing on, and some idea of balance.
You really don't need the engine on the mounts for anything until it's time to mount the cowl. It's heavy and makes handling the fuse somewhat more of a problem. When you need to drill for the motor control rod, simply hold the engine in place and eyeball the location. Works good for me. I've always liked to keep the engine away from all the dust and glue drips etc....

Also, when drilling the holes in the mounts, do i just use an everyday punch that you use in metal work to make a little dint, then drill the holes on the drill press? I have never worked with 'glass filled' mounts before!
A punch works. I've found that it can be offcenter. Any marking tool that has some bulk will be hard to hold square. The engine gets in the way more on one side than the other. I've used pencil leads and have a very slim pencil I use now. It's easy to mark the entire area of the mount down in the holes in the engine flanges. And the drill press accuracy is up to you anyway. BTW, it's really good to use a press vice to hold the work. I'm betting you already do.

As for needle valve placement, I assume I just make sure it protrudes somewhere outside the balsa cowl for adjustments - it doesn't matter if it is horizontal or vertical?
It makes not one whit of a difference. And the needle body on that engine can be fitted a couple of directions with no problems. It can also be moved off the engine, but it's not worth the effort.
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Old 10-26-2006, 08:49 AM
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Default RE: HELP! Engine Mounting Problem!

kewl..........

I am thinking of having a red hot go at making a fibreglass cowl - but i will sheet and glass the wings and fuse and see how i go first. I can use the balsa cowl as a plug later if it seems not too hard
It really isn't very hard to do. But is not exactly any great advantage. From the looks of your work, I'd suggest you shouldn't have any problems doing it. But like I said, it ain't no real deal to have.
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Old 10-26-2006, 08:50 AM
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Default RE: HELP! Engine Mounting Problem!

Ok - Thanks for all the advice.

This is my first rc aircraft, and my first build and i'm having a ball.

I've built the wing halves including adding ailerons, and have built the fuse. I'll mount the firewall next, and then the fuel tank and finish the nose section. Then comes joining the wing halves, and sheeting everything.

thanks for everyone's help.
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Old 10-26-2006, 08:55 AM
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Default RE: HELP! Engine Mounting Problem!

Hey mate, time to go fly. Temps in the middle 50s farenheit with little or no wind (so the temp matters little) and 6/10 clouds!!!

BTW, good chance I'll be buddyboxing a guy with his Senior today. Looking forward to it.

Enjoyed talking with ya'.
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Old 10-26-2006, 08:57 AM
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Default RE: HELP! Engine Mounting Problem!

Hey, get crackin' on that airplane mate..... Springs just around your corner ain't it!!!
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Old 10-26-2006, 08:57 AM
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Default RE: HELP! Engine Mounting Problem!

Cheers,

I'll post a photo when i'm done!
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