• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

FTFC'18 WWII Blohm and Voss P.170 designed by Willsonman and Mid7night

willsonman

Builder Extraordinare
Mentor
#1
Ok, Project announcements are always fun. I seem to be under the radar for a few folks on these pages so here goes.

Ben and I will work together to make a Blohm and Voss P.170. These are the views we will work from.

bvp170-1.jpg

The aerodynamics are currently under evaluation and we will bring something to the table that not only looks great, but will fly great as well.

More details to come.
 

willsonman

Builder Extraordinare
Mentor
#2
I've had this airplane in my build list for awhile now. I've seen it attempted a few times as-is with poor success and one time with a vertical on the tail... cheating.

The idea is that Blohm and Voss nearly always approached aerodynamic design with an open mind. They typically used proprietary airfoils on their aircraft. This is apparent from their single entry in the database that uses a foil I've never seen. So, in the spirit of their open mind and given the limited drawing and never a mockup ever made... let's define some assumptions.

This was intended to be a fighter-bomber and a fast one at that. There were no defensive guns incorporated as it's speed in excess of 400MPH was to be its main defense. With a bomb load of 2200 pounds this was indeed a true raw-power aircraft.

Airfoil
Being proposed in 1942, it can be assumed that the Germans were then privy to the work that the NACA was doing in airfoil analysis and collaborative German work would have lent itself to airfoils that incorporate laminar flow as a means of drag reduction. The P-51 Mustang incorporates this method and was prototyped in 1940. Further still, the B-24, incorporating the Davis airfoil, was revealed to have the same laminar flow properties along with a high amount of lift for heavy bombing runs. Given these historical facts we will be incorporating a Davis airfoil for this model.

Stabilization
A general rule of thumb for model aviation states that for trainer-style aircraft the H-stab should be around 15-20% of the main wing area and the V-stab should be roughly 33% of the H-stab area. Measuring out the profiles of the 3-views available it gives me an H-stab area of ~11% and V-stab is at 25% of the H-stab. Since this is not a conventional trainer style we will be lenient in these figures. For a fighter, the 11% is a fairly good number comparing to other heavy fighters of the era such as the P-47. The vertical area is completely insufficient in respect to a safe margin for yaw stability. Further still, the yaw moment is so close to the neutral point that any rudder deflection will not yield much control. These are clear observations when you look at the math. It will never fly as-drawn. Therefore I'm sure Dr. Voght would have realized this and increased the surface area to stabilize yaw. I will increase the area however, Rudders are not likely to be incorporated as they would still serve no purpose. Yaw control will be under the authority of thrust differential.

The picture below is a model that I never completed of this project for RealFlight. You can clearly see the deviation on the vertical stabilizers. The drawings also do not indicate where the flap/aileron separation was intended to be, therefore they will just be split in the middle.
RF P170.png

Also of note is the idea of a bomber. This could be a simple attack bomber but with such a bomb capacity, it could also serve as a dive bomber, thus having better precision for key targets. The last of the dive bombers fr the US was the SB2C Helldiver, which had a bomb capacity of 2000 pounds, or about the same intended load for the P.170. Tail buffeting in dives was a major problem for this style of attack and both German and US solutions were to utilize split-flaps to be deployed during high-angle attack runs. It makes sense as a means of creating drag to control speed and help the airplane track straighter through differing densities of air as it dives. I will attempt to incorporate split flaps in my design as well.

Ben has graciously offered to help me with developing plans. I could do it but it would take me far longer than his skills.
 

rockyboy

Skill Collector
Mentor
#3
Looking forward to seeing this one develop! She's got a beauty of a figure! Lots of curves that resemble the Golden Age racers too. :D
 

SlingShot

Maneuvering With Purpose
#4
Airfoil
Being proposed in 1942, it can be assumed that the Germans were then privy to the work that the NACA was doing in airfoil analysis and collaborative German work would have lent itself to airfoils that incorporate laminar flow as a means of drag reduction. The P-51 Mustang incorporates this method and was prototyped in 1940. Further still, the B-24, incorporating the Davis airfoil, was revealed to have the same laminar flow properties along with a high amount of lift for heavy bombing runs. Given these historical facts we will be incorporating a Davis airfoil for this model.

Stabilization
A general rule of thumb for model aviation states that for trainer-style aircraft the H-stab should be around 15-20% of the main wing area and the V-stab should be roughly 33% of the H-stab area. Measuring out the profiles of the 3-views available it gives me an H-stab area of ~11% and V-stab is at 25% of the H-stab. Since this is not a conventional trainer style we will be lenient in these figures. For a fighter, the 11% is a fairly good number comparing to other heavy fighters of the era such as the P-47. The vertical area is completely insufficient in respect to a safe margin for yaw stability. Further still, the yaw moment is so close to the neutral point that any rudder deflection will not yield much control. These are clear observations when you look at the math. It will never fly as-drawn. Therefore I'm sure Dr. Voght would have realized this and increased the surface area to stabilize yaw. I will increase the area however, Rudders are not likely to be incorporated as they would still serve no purpose. Yaw control will be under the authority of thrust differential.
Thank you for this basic info! Using this guideline, it looks like most of the heavy bombers lend themselves to decent flyers when scaled down. Would that be accurate?
 
#5
Oh boy, you and Ben are going to make the rest of us in the FTFC'18 Challenge look like amateurs. Looks great, I can't wait to see how it flies.
 

wilmracer

I build things that fly (sometimes)
Mentor
#6
Interesting! I'll definitely be watching.

  • What span/scale are you thinking?
  • Any thought about drag rudders on a gyro for yaw and keep the "scale" outline?
  • I seem to remember that other modelers who attempted this aircraft had issues with the wings/booms twisting. I assume you're going to need some solid structure in there to address that.
 

willsonman

Builder Extraordinare
Mentor
#7
SlingShot: It depends. Bigger always does fly better but when you get into surface area ratios it can be tricky as the lift does not scale. Then if you try to incorporate an airfoil into the H-stab you can get all sorts of issues too as the tail will produce more lift than is required. It really is a happy balance.

Erospace: mmm, probably not. Given that my intention is much like the Gotha, the looks of this aircraft will likely be very attune to the FT-style. The Bugatti was a one-off and the intent is to have something another person could build. I will say that I will likely keep to my usual hotwire cut wings as it will be quite simple to do. Depending on the chord of the wing, 2" foam is my go-to for that. Size will likely depend on that factor.
 

willsonman

Builder Extraordinare
Mentor
#8
Carl: There is also a possibility of using the split flaps as drag flaps to regulate yaw. It is something to still look into. Wing twist will come from a robust wing spar. Torsional loads will be great with a motor and battery along with wiring and retracts. The weight will be the main factor in this but proper ply location will be key. Size is still TBD but I would like to see it fairly big.
 

PsyBorg

Wake up! Time to fly!
#9
I had contemplated this as a choice as well early when the contest was announced. After reading your analysis I am glad I have not got into this. Seems a lot of factors in play I had no idea about yet. Can we assume that since you have teamed with Ben there will be official wind tunnel testing for this? :p

I think it is awesome that this years competition has so many people teaming up to work on the projects. That is what FT is all about and with guys like you and Ben detailing as much about your builds as you do I am sure there will be a lot of learning going on as well for all.

Oh yeah.. I forgot. I HAVE seen a few versions in different scales on you tube and they seem to fly nicely. I think I only saw one with cheater clear vertical stabs to keep it under control. The rest are as you stated differential steering. I did not realize that they were intended for "Heavy Bomber" duty though as with the agility I saw in the videos I assumed a "Fighter / Escort " role with the speed. I guess reading really IS fundamental.
 
Last edited:

willsonman

Builder Extraordinare
Mentor
#10
I think you misread :p This is not a heavy bomber but a fighter/bomber. If you recall, the P-47 was in this role and the bomb load was limited to 2500 pounds. However, it was designated as ground attack fighter/ bomber. As the P.170 was not specified, I'm taking liberty to allow it to be more flexible in it's mission tactics by adding the dive bomber attribute.
 

PsyBorg

Wake up! Time to fly!
#11
Again.. I am failing at that whole "Reading is fundamental" think of late.. Maybe my brain is lacking oxygen with these allergies / cold I am battling atm.
 

Mid7night

Jetman
Mentor
#12
Just want to jump in and say I'm super excited to work with Joshua on this! He sent me his starter model ...which means now I've got to actually DO something with it! :p

I've actually never collaborated like this with another (very competent) builder, so I'm excited to see what my 3D models and drawings turn into. :D
 

PsyBorg

Wake up! Time to fly!
#13
We ALL are mate. The teams that are forming are actually scary as several are the caliber of professional level design and building that could easily form a company if they wanted and be successful. You guys would be one of them.
 

willsonman

Builder Extraordinare
Mentor
#14
Awe shucks. :rolleyes:

Ben is making progress so I'll let him post what he has. I've been giving thought around weights, power plants, retracts, etc. A lot of it will be dependent on the AUW, which I am very bad a guessing of foam board builds.

So far we are looking at roughly a 74" wing span. This may decrease as it is maxing out the thickness of the wing at 2". Sometimes, for hot wire cutting, the foam is not entirely flat and having 1/8 of an inch on the top and bottom to account for that can make life easier. Overall, it is my usual preferred size for aircraft. It should break down nicely for transport and have good presence in the air.
 

Mid7night

Jetman
Mentor
#15
Here's that progress!

P170_progress.jpg

As you can see, we're modifying the tails on the side-pods. I'm retaining the lower profile, and adding to the top in a similar way to how Joshua did on his sim model.

The three 'fuse' bodies are relatively simple, except for the rear-center. But even that part shouldn't be too hard to actually build - it was tedious to model without breaking it into too many small patches, but as it is now it should unwrap fairly nicely.

Next I just need to extrude a wing section, and start populating the innards so Joshua knows where to put the hardpoints! :p
 

Mid7night

Jetman
Mentor
#18
We have WINGS! And a tail too. Per Joshua's specification, the wing will have (designed) 2° of washout at the tip, and the dihedral matches the drawing; it's only like 1.5° of dihedral (measured at the tip) anyway.

BV P-170 wings.jpg
 

willsonman

Builder Extraordinare
Mentor
#19
Looks good! I'm thinking that the H-stab can just be a double lamination of foam board. I'm not sure a hotwire cut stab will be something folks will want to deal with. The wing can easily be cut as separate pieces but they are just squares. I'm also thinking that the Ailerons and Flaps can be made from foam board so a clean trailing edge on the wing cuts can be avoided. It can be tricky. The wings can be done in two panels at around 18-19" wide. Much easier cut with a more manageable size and the bow does not have to be huge either.
 

willsonman

Builder Extraordinare
Mentor
#20
Doing some further digging around... I think I would like to use this motor. Using a 9x9 prop, I should get around 700W per motor... That should get me into the 2KW club. :cool: Keeping to 60A ESCs should be fine and keep the cost down. I'm pretty sure Ben can work with the stated dimensions to incorporate a motor mount inside the longer cowl. This should prove useful for battery placement as well.