Peanut P-51 for RFFS-100?

[rkissin]

Having successfully built the Pixel, I'm wanting to fly faster.

Scaling down Dave's Micro Mustang to Peanut Scale = 13" WS and about 30 square inches of wing area.

Assuming the same setup as the Pixel and AUW of 24 - 25 grams, will it fly?

[gjohnson]

Roy,
I don't know if it will fly. Dave will know that. But, keep in mind that a faster flying plane like this will require the actuators to push harder against the airflow. That could be a problem as these don't have that much excess power.

Gordon

[Dave Robelen]

Hello Roy, Gordon,
I do believe that would be too small Roy. Basically, the batteries required to get a motor putting out the required thrust would hardly fit in it, and the wing loading would be "outa sight". Why not shoot for about 45-50 sq. in. and run an N20 on 4 cells.
Gordon, airloads should not be much of an issue if the surface is aerodynamically balanced. My first RFFS-100 was a micro delta with 13" span and full length elevons. I flew it with 3 cells cranking a KP-00 and it zipped right along. Control was smooth and powerful. I used the same hinge setup that I showed on the Pixel. Like Roy, I have the "hots" for more zip, but the only way I see to get down in size at present is with the biplane format. Compact with adequate area.
Cheers, Dave

[rkissin]

Thanks Dave. A 15" WS should give about 45 squares. That's still 17% smaller than the Micro Mustang, and as we all know, smaller planes have higher moral value.

[Dave Robelen]

Hi Roy,
At that small size I would expect a sheet balsa wing ALA Skeeter to work out a little better. Meanwhile, you could always cheat a little more area in without adding span. Certainly the Micro Mustang is already pretty far from true scale so a little more would do little harm.
Long live the micro's Dave

[Dave Robelen]

Hi Roy,
A PS. If you are going with rudder control be sure and increase the dihedral as the original is inadequte for rudder turns. Something along the lines of that foam Cox bird look alike.
Dave

[rkissin]

Roger that on the rudder.

Or we could try something really innovative: Aileron mixing with dual actuators. The only problem is that the Rx only handles two servos.

[Dave Robelen]

Hi Roy,
I thought that Clarence said the RFS-100 could handle two actuators in one slot. Cetainly the BIRD style from Cloud 9 could be doubled up, they are a higher resistance. Just install so they drive in opposite ways.
A thought, Dave

[pease1]

Clarance did indeed say you could drive a pair of ailerons on one channel of the RFFS-100, just reverse the coils on one of the ailerons (or is that reverse the magnet?)

I agree with Dave. At this scale, forget the covered wings and go for a single surface 1/32" balsa wing. At this small of a scale, I prefer the inherent stability of the R/E system over the A/E system, but I know ailerons are more scale for a Mustang. The second reason R/E is better, is those actuators are really going to mess up your wing airfoil, effectively reducing your wing area.

What about a small version of the DJ Aerotech 'Roadkill' style of profile mustang? That should work nicely.

Al

[Aeronutz]

We have some experience of WW2, low wing, 25g models
See our web site and some vidoe clips too
Matts Spitfire is the most up to date machine at about 22g and 14" span, but is has a profile fuslage which makes it fly better as drag seems to be a problem at these sizes.
If you are using R.C. then check out the voltage required?

We are just trying Lithium Polymer cells at about 6g and 220mA/hr, these will run at about 3.5v under load, so our voltage boosters will not have to work so hard. Carbon props. and mucle wire actuators will help things along too .....
Seems likes its a good time to start micro plane flying

Mark
Aeronutz

http://www.aeronutz.flyer.co.uk/

[gjohnson]

Mark,
Are you using any of the 135mAh LiPoly cells that Matt Keenon has recently used? Also, what are you doing to make sure you don't draw them down below 3v in flight and ruin the cell? Do you just land early?

Gordon

[Aeronutz]

We are nwo up to date, so I can't tell you from experience like have done in the past
No, our cell is LP220 which I assume is 220mA/Hrs and about 6g.
Seems like we can have 3.5v with about 700mA load on it.
I am told we can go down to "about 2.5v" and I think it woudl be easy enough to use a didode like devise to cut off the motor somehow.
We are trying to sort out how much load the cells can take, I like the idea of a mulit engine machine about 20" span and 8 channels using muscle wire actuators for the 220 cell. If we can get the smaller one then thats great too, maybe a F14 ?
3.5v will make a KP00 rev liek hell and draw a whooping current so maybe use a Kenway style motor direct drive?
Charge, launch, observe.
Mark

[Dave Robelen]

Hello Aeronutz,
I have been doing some discharge tests on a 16 gram 450 mah Li-Ion cell, with currents ranging from .75A to 1.5A. During most of the discharge the voltage will range between 3.3 and 3.2 volts. Perhaps the cell you have is a somewhat different chemistry. This one is used onthe KP-00 with a large ratio and large dia. prop. We are still at the front of this new technology, with much to learn. Thanks for sharing your experiences.
Regards, Dave

[Aeronutz]

Hello Dave,
I have no idea!! It is a lithium Polymer cell, is yours a polymer?
Anyway, when I get my charger I will do some tests on the Kenway motors direct drive with little props and also see how our dc/dc boosters like producing 100mA and 5v from 2.5v minium

Our man Ray flew a two motor B29 with outboard free wheeling props at our last fun fly, used three 50mA cells I think. Flew well but it was a little fast for us, it was originally a rubber power plane!! He used two Kenway style motors direct drive and infra red control. I think his ducted fans woudl go well with these polymers too

Bernard tried the orange GWS 65mm prop and said it was ok on his 13g F/F direct drive KP00 Depron foam plane with two 70mA NiMH cells.

So if I can use two Kenway's and direct drive I was thinking of doing a B17 in silver colour with yellow fin or maybe a B25 in pink? Rudder, elevator, motors, undercarriage, move one of two turrets, lights eh? we have 8 channels, what else?
Should be about 28" span for a B17
Mark
Like the Pixel by the way, nice garden flyer size plane

[Dave Robelen]

Hello Mark,
Thanks for the kind remarks. At present I am limited to outdoor flying, so it is RF for me. Somehow I wonder about the efficiency of runnung direct drive on these small motors. I designed a model called the Turbo Sport (published in Model Aviation) which used the airship control system that sold for $25.00 complete. The design contest that I entered required that the system be used in an airplane with no more mods than removing the plastic shell.
My solution was wing mounted twin N20 motors spinning direct drive props. Control over the motors was the only flight control. The system running on 3.6V delivered about 2.5V to the motors under load. After messing with prop design a good bit, and building a glider like model, I had a very presentable situation. I believe this was the birth of the control arrangement where the only flight control was motor thrust.
I said all that to mention that when the contest was ended, I fitted the model with gear drives and larger props with a substantial boost in performance. Long live innovation!
Regards, Dave

[gjohnson]

Mark,
My 135mAh LiPoly cells and charger should arrive late this week or early next week. I'll test and post what I learn. Mine will be simpler than Dave's. I'll just charge and hook one up to a geared M20-LV and record what happens. Matt Keennon cautions not to draw the cells below 3v (but he has heard some say as low as 2.7v) or it may destroy the cells -- i.e., they lose half their amp-hours. The cell he used in his Scout was a Kokam Eng. (Korea) cell, which I believe is what mine will be. I intend to not draw them below 3v till we know more. We need some method to keep from going below that limit. Do you have any ideas? I'm not an EE, but I'm sure I could build something from Radio Shack parts if someone told me what to get.

Gordon

[phuffstatler]

This the P51 I stuck my RFFS into last night... Picked up a Hobbico all-foamie model at my local Hobby Town. $9.99. Could have bought a lot of 1/32 for that I'll bet...

Trimmed a 1/2 cowl out of the nose, installed a 1/8 balsa firewall, sliced up the tail feathers to mount the actuators, took out a 1/4 ounce nose weight, put it back in cause it needed it :(, made the wing removable and one piece (held in place by a small T-pin) and mounted the pc board inside with double sticky tape. ran the antennae (sp?) wire right out the top and over the back....

Using 3 50mah cells on it.

Looks great, very filling...

It weighs right at 2 ounces... oh no...

Gonna try it anyway... maybe I'll get a good long turning glide out of it.... :)
If I can get a camera to work, I'll post some photos of the mods... if it all works.

phil in austin

[Dave Robelen]

Hi Gordon & co.,
The literature that came with the cell I am working with is strong about not drawing it down below 3V. Skyhooks & Rigging is preparing a special hybrid rec/esc (narrow band) for this application. It has the 3V cutdown feature and is intended to work on a single Li-Ion cell. The club in Ontario is actively flying these in models that use either a KP-00 or LV M20 geared fairly high (5-1 to 8-1) and with wing loadings around .4 grams/sq. in.
The wing areas range from 150-300 sq.in. I saw some of these models at the Toledo fly-in, They were true indoor machines with very light structure and coverings such as RA Microlite. Two controls seemed typical, (rudder, throttle), and they were definitely slow gentle flyers.
Gordon, all I am doing to evaluate the cell is connecting it to several different resistances that will provide representative current levels, and then plotting voltage vs. time.
Regards, Dave

[gjohnson]

Dave,
I intend to do the same thing versus time. But, the question I (we) want to answer is how do these stack up versus what I've already got. So, I'll take a single motor/gear/prop combination that I'm interested in and run it on a single LiPoly cell, then 120x2 and 120x3 NiMh and if I get time maybe some 50mAh NiCd's too. This won't answer what the cells are capable of delivering. But, it will show what they will do versus existing batteries on an application appropriate for a large number of indoor flyers.

I'm thinking we should start a new thread, as this one has drifted. I'll do that when I have my results.

Gordon

[Dave Robelen]

Hello Gordon,
There seem to be as many flavors of these Li-Ion cells as there are minnows in my pond. The one that I am woking with at present weighs 16 grams, and appears to be a bit current limited.
I can get the full capacity at a rate of .6A, but at 1.0A the capacity and voltage plunge to about .25AH, and 3.2V under load.
The normal application is in "floaters" which can fly on 1-2 watts.
I will be looking forward to your results driving a motor typical of the RFFS-100 setup.
Regards, Dave

[dhurd]

Phil,
Is there anyway you can remove the weight and use the batteries to adjust the CG? Seems to me if you took out the weight it would be at a more reasonable weight for the rffs-100.

REgards,
Dan

[phuffstatler]

I had the battery right up in the nose. I guess I could go an extra cell.... it's just a heavy little model. it has an 18" span, so hopefully it won't fall too fast....


phil in Austin

[Jason Nowell]

Phil,

Go for it, I did a Hobbico p-40 with an 18" span and it flew great, even in a gym. DD GWS motor and 6 - 120mAh NimH cells. It felt heavy, but it flew great.

Jason

[phuffstatler]

Hey Jason, it's done now... Worked really well, better than expected...

http://home.austin.rr.com/huffstatler/phil_p51.jpg

is the really big picture of it (and me)....


http://home.austin.rr.com/huffstatler/page4.html

is my Aviation page with a smaller photo of it...

be good,
phil in austin