So many questions...

[Old and rusty]

Hey everybody,
noobie from WA state with so many questions
Ive recently laid out and put together a sort of a semi scale foam board Thomas Morse scout. with a 40" span. It weighed 650 grams with battery, motor, and radio. The motor is a 3D foamy combo from Grayson hobbies...I believe 1100kv. When it came time to get the CG right, of course and even though id kept the battery and radio as far forward as I could, it was still pretty tail heavy with the scout having such a short nose protruding past the upper wing. To get the CG forward it took 114 grams of lead in the cowling.
How much is too much for a model this size?

 

[Shurik-1960]

Your model is not a copy. Leave all the lead for fishing. Simply cut off part of the fuselage muzzle and by attaching bamboo skewers to both parts of the fuselage, determine the size of the insert to obtain the ideal center of gravity. Cut out the new parts and paste them in, but I usually cut out the new nose part entirely and put the motor with the regulator there : this way there are fewer joints-1, not 2.Before launching, it is necessary to throw it on the tall grass for planning. Reduce the roll of the model and, having received excellent planning, simply throw the model down the slope and smoothly add gas until the model begins to smoothly gain altitude.

 

[Old and rusty]

Your model is not a copy. Leave all the lead for fishing. Simply cut off part of the fuselage muzzle and by attaching bamboo skewers to both parts of the fuselage, determine the size of the insert to obtain the ideal center of gravity. Cut out the new parts and paste them in, but I usually cut out the new nose part entirely and put the motor with the regulator there : this way there are fewer joints-1, not 2.Before launching, it is necessary to throw it on the tall grass for planning. Reduce the roll of the model and, having received excellent planning, simply throw the model down the slope and smoothly add gas until the model begins to smoothly gain altitude.

Thanks for the reply shurik 1960...
lengthening the nose, guess that had never occurred to me. Will start on that tomorrow.
So before all the lead it had weighed in at 650 grams even. Is that in the ballpark of where a plane of that size should be?
Also a little puzzled over the physical size of these motors.The Grayson motor has no size marked on it, but looks exactly like a 2180 I have from another company, yet when looking it up on their site it says it's an 1100kv. Is that possible? I know a little about BL rc car motors, but these airplane motors have me a bit baffled...
is the 2180 a kv number?
...sorry to come right back with more questions....appreciate you taking the time to field my questions.

 

[luvmy40]

2180 is the size, height/diameter in mm. the kv rating is based on the windings. any size motor can be wound for different kv ratings.

 

[quorneng]

Picking a suitable motor for a particular plane is a complex process involving a number of variables.
Until you have the appropriate experience by the most reliable is to use a recommended motor, prop, speed controller and battery combination that is known to work for that plane.
It is worth noting that the motor, prop, speed controller and battery together are likely to cost quite a bit more than the plane itself so getting it wrong by much can damage one or all the components so it can prove to be expensive.

 

[Old and rusty]

Picking a suitable motor for a particular plane is a complex process involving a number of variables.
Until you have the appropriate experience by the most reliable is to use a recommended motor, prop, speed controller and battery combination that is known to work for that plane.
It is worth noting that the motor, prop, speed controller and battery together are likely to cost quite a bit more than the plane itself so getting it wrong by much can damage one or all the components so it can prove to be expensive.

Once again I appreciate the responses. Since taking a whack at this have been trying to gather as much info as I can on different foam board building techniques and whatever technical information people are willing to share in hopes of becoming a competent designer/ builder/ pilot.
The two flight systems I have both came as package combos each with 18 amp ESC's, saying they would handle 3s, and both came with 8/4 props. I'd also read that they could swing a 9/5 prop if desired.And I believe they're both 1100kv's Is this any more helpful in determining overall take off weights I should be shooting for?
Thanks again, I'll slow my roll on the questions now...

 

[Shurik-1960]

Depending on the brand of the engine, it is now very easy to set its maximum thrust. I usually make a model and, after weighing it together with the battery (which I want to use), determine which engine I will buy and which regulator is needed for it. If there is no wattmeter, then the recommended screw size should be put on the engine.With a wattmeter, it is easy to determine which screw will have a reasonable battery consumption.

 

[quorneng]

Please keep asking as many questions as you like. Remember the only stupid questions are the ones you don't ask!

If a motor has a recommended prop and battery type then I suggest you use them. It is unlikely to damage any of the electrical components.
The weight of the plane is a critical factor in the power required to fly.
The battery tends to be heavy enough as it is so it pays to worry less about making the plane "crash proof" (it never really is) but concentrate on making the airframe as light as possible but keeping it just strong and rigid enough. It is difficult to know where the limits are in model airframe design so it is best to initially follow an existing design and work from there.
Foam board is relatively cheap and is not too hard to repair so once you have built and flown something a degree of experimentation (and failure) is not too expensive.

My first foam RC plane was a simple ready to fly (RTF) job. I assembled it according to the instructions and flew it many times however it was not long before I felt bits could be improved. A process I kept up for over two years as I learned from web sites what was available and how best to use them. Eventually I had a plane that achieved a performance and duration quite beyond the original yet it was only 70% of the original's weight.
By that time only the bare fuselage "shell" remained everything else was new however its wing span remained the same.
That was 13 years ago and I now have many of "own design" foam planes in a range of sizes. They all fly but some are better than others!
Designing a successful plane from scratch is not an "overnight" process.

 

[Merv]

...Is this any more helpful in determining overall take off weights I should be shooting for?...

The 650g (22 oz) all up weight, AUW, you mentioned sounds reasonable to me for a plane with a 40 inch wing span.

FYI Some useful rules of thumb.

In that 40-50 inch wing span, shoot for a wing loading of 10-15 oz per square foot of wing area. Small planes (20") want a much lighter wing loading (1-2 oz) bigger planes (80") a heavyer wing loading. A motor about 100 watts per pound is a good starting place. 200 watts per pound if you are wanting unlimited vertical.

Here is some more detailed information

Motor Help

Need help selecting a motor. I want something that will work well for a Swappable Tutor but could also pull an old warbird through the air. Suggestions? Power packs are out of the picture, a Motor and props are the only supplies I still need.

forum.flitetest.com

 

[Tench745]

Tommy builders unite!

Mine is a 53" span, and was big enough with a light enough tail that I could push the batteries forward enough to get it to balance. Barely.
Rather than lengthening the nose, you could also shift the wings aft, cut away some material in the aft fuselage, or do some combination of all three.
Any pictures of your Tommy? We love to gawk at airplanes here.

 

[Shurik-1960]

By shifting the wing to the stabilizer, the aerodynamic balance is disrupted, which will lead to a loss of stability in flight: the aircraft will become excessively maneuverable and unstable.Tested on many models.The example of the Cessna 150 : the elongation of the muzzle gives excellent results in planning and flight, the shortening of the rear fuselage turned the model into an unstable one.You can try to do both options and come to your decision obtained in practice.

 

[Old and rusty]

Really do appreciate you guys fielding all these questions. It's funny, have been doing various types of hand launched gliders out of balsa or foam for me, my kids, and now grandkids for years, and it's always been pretty easy to get a good enough glide to keep the kids happy. But I'm finding out it's a whole different can of worms once you start adding power to it....not quite so easy, with lots of other things to consider.
Somewhere along the way id forgotten about consciously trying to keep the tail light. Of the foam board models I've done id doubled up the sheets for the rudder and stab. to help them hold up. (something I'd started when making gliders for my grandson with autism, who loves planes but can be a bit hard on them)lol. For the most part does everyone always use the single sheet for the tail surfaces? Another thing I may need to rethink is using acrylic paints. While I like how they look, I know they're probably not the lightest as far as finishes go. Likewise my idea of just building with the notion that a "little" nose weight after the fact would make everything right again....didn't exactly work out.
With my Tommy to try and get things in order lengthened the nose 2", (which hadn't occurred to me) and pared down the rear fuselage a bit, and was able to cut the weight in the cowl from 114-64 grams to get it to balance out. Just decided to try it without any more surgery, and if it flies, great...if not the foam board is cheap and I'll start another, this time being a little more mindful of what to avoid.
Thanks again guys.

 

[Tench745]

Really do appreciate you guys fielding all these questions. It's funny, have been doing various types of hand launched gliders out of balsa or foam for me, my kids, and now grandkids for years, and it's always been pretty easy to get a good enough glide to keep the kids happy. But I'm finding out it's a whole different can of worms once you start adding power to it....not quite so easy, with lots of other things to consider.
Somewhere along the way id forgotten about consciously trying to keep the tail light. Of the foam board models I've done id doubled up the sheets for the rudder and stab. to help them hold up. (something I'd started when making gliders for my grandson with autism, who loves planes but can be a bit hard on them)lol. For the most part does everyone always use the single sheet for the tail surfaces? Another thing I may need to rethink is using acrylic paints. While I like how they look, I know they're probably not the lightest as far as finishes go. Likewise my idea of just building with the notion that a "little" nose weight after the fact would make everything right again....didn't exactly work out.
With my Tommy to try and get things in order lengthened the nose 2", (which hadn't occurred to me) and pared down the rear fuselage a bit, and was able to cut the weight in the cowl from 114-64 grams to get it to balance out. Just decided to try it without any more surgery, and if it flies, great...if not the foam board is cheap and I'll start another, this time being a little more mindful of what to avoid.
Thanks again guys.

Sometimes I will double up foam on big and/or fast models. My Cafe Racer, my 53" Tommy, and my 92" Spirit of St Louis all have double-thickness tail surfaces. On those models I removed all the paper from the foam to save a little weight then glued on some balsa to mount hinges into and add some rigidity back into the tail surfaces.

In general, when I'm laminating foam together, I remove the paper from the sides I'm gluing together since it adds very little stiffness to the part and I don't need the extra weight.

 

[Shurik-1960]

For light aerobatic aircraft with a flight span of up to 1 m, I always make the elevator and rudder from 2 layers of foam 3 mm thick with carbon reinforcement. Then I evenly stack the glued product between 3 mm thick glasses and treat both surfaces with sandpaper. The result is durable and lightweight parts with a thickness of 3 mm. I glue both parts together using a lightweight glue analog of UHU POR. I put 2-sided adhesive tape or masking tape inside along the turn line. At the end, I cut through carefully .

 

[Old and rusty]

Happy to hear I'm not the only one doubling up tail surfaces. Didn't want to be doing something considered ridiculous. I do the same with mine, removing the paper on the two sides being glued, with a hard balsa strip set into one side so that it's flush at the surface. Have never tried carbon fiber, but am curious about it...how thick are the strips? Once glued I'll also sand the edges and normally use a thin masking tape to help protect the edges. Is the UHU POR something from a hardware store? Of all the stuff that works for foam, is hot glue somewhat heavy?I'm relatively new at welding a hot glue gun so suspect my glue joints and fillets get a bit heavy handed, so I know that doesn't help.
(all you video guys just make it look so easy)lol
Frequently I hear of using minwax, is that for foam without paper covering on it?

PS hadn't got the tommy out to test yet, but took my 40" span Dakota bipe over to the test " hopping spot" where it took off , got about 20 yards downrange, then flared up into a stall, then dove into a fence. Wind was a little gusty, but was also still messing with down trim. Think it's balanced out fairly well, so not quite sure what to think. If the upper wing had too much incidence could that cause it to act this way? Had my daughter trying to catch it (unsuccessfully) on camera. But will get a better angle on it for the next flight.
As always, I thank you guys for all the cosmic knowledge.

 

[luvmy40]

https://www.amazon.com/dp/B000KSQU1K/?tag=lstir-20

UHU Por is a foam safe cement. It's lighter than hot glue but takes 24 hours to cure. Pretty sure it stays flexible when cured. The Minwax (OIL BASED) is for "water proofing" the DTFB with the paper on. It also protects the foam core from spray can propellants.

 

[Old and rusty]

Wow, 24 hrs on the dry time sounds like forever. I might start using the gorilla glue that expands as it cures again. spritz it with a little water it will cure in about 4 hours. (Or attempt to be less heavy handed with the hot glue)
Will have to look into the minwax. Is this the same stuff you would apply to woodwork with a rag, or some kind of spray finish?
I appreciate everybody's patience with all the questions... thanks luvmy40

 

[Mr NCT]

I like the matte finish for painting over. To treat dtfb go in sections. Brush on, watch for it to penetrate paper, wipe off excess with paper towel, let dry 24 hours.

 

[Piotrsko]

Ummm gorilla glue doesn't get to full strength until it's waaay past being not sticky to the touch. Rtfi. Many instances, thats strong enough. If you absolutely cant wait overnight, there are some adhesives that fully cure in lots shorter times. Even Elmers white glue baked in a 125 degree oven, assuming your oven actually runs 125.

Some epoxies and silicone 2part get to "cured" in as low as 5 minutes, but they aren't easy to assemble with.

 

[Merv]

...Or attempt to be less heavy handed with the hot glue...

That is the key to using hot glue, just use less. My goal is one full size glue stick per plane.

BTW, I also double layer my rudder & elevator. It makes them far more durable. I have the hinge in the center & make the bevels before gluing them together.